首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   52967篇
  免费   3695篇
  国内免费   178篇
耳鼻咽喉   607篇
儿科学   1067篇
妇产科学   799篇
基础医学   6789篇
口腔科学   704篇
临床医学   4878篇
内科学   12807篇
皮肤病学   543篇
神经病学   5187篇
特种医学   2105篇
外科学   8499篇
综合类   586篇
一般理论   65篇
预防医学   3646篇
眼科学   925篇
药学   3183篇
中国医学   49篇
肿瘤学   4401篇
  2023年   257篇
  2022年   430篇
  2021年   1437篇
  2020年   901篇
  2019年   1298篇
  2018年   1643篇
  2017年   1122篇
  2016年   1205篇
  2015年   1443篇
  2014年   2167篇
  2013年   2513篇
  2012年   4330篇
  2011年   4301篇
  2010年   2409篇
  2009年   2154篇
  2008年   3758篇
  2007年   3870篇
  2006年   3757篇
  2005年   3691篇
  2004年   3297篇
  2003年   3039篇
  2002年   2739篇
  2001年   326篇
  2000年   228篇
  1999年   335篇
  1998年   488篇
  1997年   441篇
  1996年   356篇
  1995年   325篇
  1994年   251篇
  1993年   236篇
  1992年   151篇
  1991年   132篇
  1990年   118篇
  1989年   100篇
  1988年   89篇
  1987年   74篇
  1986年   78篇
  1985年   105篇
  1984年   126篇
  1983年   108篇
  1982年   137篇
  1981年   111篇
  1980年   97篇
  1979年   45篇
  1978年   64篇
  1977年   58篇
  1976年   50篇
  1975年   42篇
  1974年   42篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
ObjectiveTo evaluate the effect of a smoking ban in high schools on smoking behaviour among Chilean students.MethodsWe conducted an interrupted time-series analysis, using repeated cross-sectional data from Chile’s school population survey (2000–2011) for high-school students aged 12–18 years and a control group of persons aged 19–24 years. Poisson regression models were used to assess trends in smoking behaviour before and after the policy changes. The outcome measures were self-reported smoking prevalence (any smoking in the past month) and high frequency of smoking (smoking 15 days or more per month).FindingsFrom 2005 to 2011, the prevalence of smoking declined among high-school students by 6.8% per year compared with 3.6% decline per year in the control group. The decline in the target group was 2.9% (95% confidence interval, CI: 0.18 to 5.00) greater. We estimated that 5–6 years after enforcing the law, smoking prevalence among high-school students was 13.7% lower as a result of the ban. The impact of the smoking ban was primarily driven by declines in smoking prevalence among students in grades 8 to 10. The smoking ban did not significantly alter the frequency of smoking.ConclusionThe 2005 school smoking ban reduced smoking prevalence among younger high-school students in Chile. Further interventions targeting older individuals and frequent smokers may be needed.  相似文献   
992.

Objective

To propose two new indicators for monitoring access to antiretroviral treatment (ART) for human immunodeficiency virus (HIV); (i) the time from HIV seroconversion to ART initiation, and (ii) the time from ART eligibility to initiation, referred to as delay in ART initiation. To estimate values of these indicators in Cameroon.

Methods

We used linear regression to model the natural decline in CD4+ T-lymphocyte (CD4+ cell) numbers in HIV-infected individuals over time. The model was fitted using data from a cohort of 351 people in Côte d’Ivoire. We used the model to estimate the time from seroconversion to ART initiation and the delay in ART initiation in a representative sample of 4154 HIV-infected people who started ART in Cameroon between 2007 and 2010.

Findings

In Cameroon, the median CD4+ cell counts at ART initiation increased from 140 cells/μl (interquartile range, IQR: 66 to 210) in 2007–2009 to 163 cells/μl (IQR: 73 to 260) in 2010. The estimated average time from seroconversion to ART initiation decreased from 10.4 years (95% confidence interval, CI: 10.3 to 10.5) to 9.8 years (95% CI: 9.6 to 10.0). Delay in ART initiation increased from 3.4 years (95% CI: 3.1 to 3.7) to 5.8 years (95% CI: 5.6 to 6.2).

Conclusion

The estimated time to initiate ART and the delay in ART initiation indicate that progress in Cameroon is insufficient. These indicators should help monitor whether public health interventions to accelerate ART initiation are successful.  相似文献   
993.
Archives of Sexual Behavior - Online partner seeking is associated with sexual risk behavior among young adults (specifically men who have sex with men), but this association has yet to be explored...  相似文献   
994.
ObjectivesPatient-physician language concordance among limited English proficient (LEP) patients is associated with better outcomes for specific clinical conditions. Whether or not language concordance contributes to use of specific preventive care services is unclear.MethodsWe pooled data from the 2007 and 2009 California Health Interview Surveys to examine mammography, colorectal cancer (CRC) screening, and influenza vaccination use among self-identified LEP Latino and Asian (i.e., Chinese, Korean, and Vietnamese) immigrants. We defined language concordance by respondents reporting that their physician spoke their non-English language. Analyses were completed in 2013–2014.ResultsLanguage concordance did not appear to facilitate mammography use among Latinas (adjusted odds ratio [AOR] = 1.02, 95% confidence interval [CI] 0.72, 1.45). Among Asian women, we could not definitively exclude a negative association of language concordance with mammography (AOR=0.55, 95% CI 0.27, 1.09). Patient-physician language concordance was associated with lower odds of CRC screening among Asians but not Latinos (Asian AOR=0.50, 95% CI 0.29, 0.86; Latino AOR=0.85, 95% CI 0.56, 1.28). Influenza vaccination did not differ by physician language use among either Latinos or Asians.ConclusionsPatient-physician language concordance was not associated with higher use of mammography, CRC screening, or influenza vaccination. Language concordance was negatively associated with CRC screening among Asians for reasons that require further research. Future research should isolate the impact of language concordance on the use of preventive care services from health system factors.Language barriers in health care may reduce the quality of care received by limited English proficient (LEP) patients, serve as a hurdle to the receipt of preventive care services, and contribute to health disparities.13 Patient-physician communication is enhanced by language concordance (i.e., when the physician is fluent in the patient''s non-English language). Language concordant care is associated with patient trust in physicians and greater satisfaction,4,5 increased medication adherence,6 and higher rates of glycemic control among diabetic patients.7 In contrast, language barriers are not associated with other conditions, such as mortality or length of stay in patients with myocardial infarction.8Latinos and Asians are the fastest-growing racial/ethnic minority groups in the United States.9 Preventive care services use, such as mammography for breast cancer screening, colorectal cancer (CRC) screening, and influenza vaccination, are suboptimal in both populations.1016 Studies of the association between patient-physician language concordance and completion of preventive care practices report inconsistent findings. Prior work, while limited in scope, suggests that language concordance may be negatively associated with receipt of CRC screening and positively associated in some groups with mammography and influenza vaccination.1720 However, this work has been limited by sampling selection and by significant variation in key definitions such as LEP or language concordance itself.1820The California Health Interview Survey (CHIS) includes representative samples of major racial/ethnic minority groups and is conducted in multiple languages including English, Spanish, Mandarin, Cantonese, Korean, and Vietnamese. We used CHIS to examine the associations between patient report of patient-physician language concordance and patient report of use of mammography, CRC screening, and influenza vaccination among LEP Latino and Asian Americans in California.  相似文献   
995.
Objectives. We examined correlations between gender, race, sexual identity, and technology use, and patterns of cyberbullying experiences and behaviors among middle-school students.Methods. We collected a probability sample of 1285 students alongside the 2012 Youth Risk Behavior Survey in Los Angeles Unified School District middle schools. We used logistic regressions to assess the correlates of being a cyberbully perpetrator, victim, and perpetrator–victim (i.e., bidirectional cyberbullying behavior).Results. In this sample, 6.6% reported being a cyberbully victim, 5.0% reported being a perpetrator, and 4.3% reported being a perpetrator–victim. Cyberbullying behavior frequently occurred on Facebook or via text messaging. Cyberbully perpetrators, victims, and perpetrators–victims all were more likely to report using the Internet for at least 3 hours per day. Sexual-minority students and students who texted at least 50 times per day were more likely to report cyberbullying victimization. Girls were more likely to report being perpetrators–victims.Conclusions. Cyberbullying interventions should account for gender and sexual identity, as well as the possible benefits of educational interventions for intensive Internet users and frequent texters.Cyberbullying is the “willful and repeated harm inflicted [on another] through the use of computers, cell phones, or other electronic devices.”1(p5) Among 6th- through 10th-grade students nationally, 4% reported being cyberbullying perpetrators, 5% reported being a victim of cyberbullying, and 5% reported being perpetrators–victims (meaning that they have both perpetrated and been victimized by cyberbullying) during the previous 2 months.2 Among middle-school students in the southeastern and northwestern United States, a nonprobability sample of 3767 students by Kowalski and Limber3 found that 11% reported being a victim of cyberbullying, 4% were cyberbullying perpetrators, and 7% were perpetrators–victims during the previous 2 months. Cyberbullying may be more insidious than traditional bullying, because cyberbullying can quickly reach wide audiences (e.g., e-mails sent to an entire school), can be perpetrated anonymously, and is not bound to in-person interactions.4,5 Although cyberbullying has garnered widespread media attention, to our knowledge, no previous study has explored correlates of cyberbullying with a representative probability sample in an urban middle-school sample.Cyberbullying is associated with a host of health and behavioral health consequences. Research has suggested that cyberbullying may have a greater effect on depression and suicidal ideation than traditional offline bullying.6 Both perpetration and victimization are associated with mental health consequences, including lower self-esteem,7 recent depressive symptoms,5,8,9 and suicidal ideation.5,8,10 Cyberbullying perpetrators are more likely to have problems with their behavior, peer relationships, and emotions, and are less likely to be prosocial than their peers who are neither cyberbullying perpetrators nor victims of cyberbullying.11 Specifically, female cyberbullying perpetrators express greater anxiety and depression than their female peers who are not cyberbullying perpetrators.12 Cyberbullying victimization is also strongly associated with substance use, violent behavior, and risky sexual behavior among high-school students.10Cyberbullying disproportionately affects youths who are already vulnerable to mental health and behavioral health disparities, including members of sexual minorities (i.e., gay, lesbian, bisexual), girls, and racial and ethnic minorities. More than half of sexual-minority middle- and high-school students nationally report being a cyberbully victim during the previous year, with almost one fifth reporting often or frequent victimization.13 Female students are significantly more likely to be cyberbully perpetrators–victims than their male peers.9,14 Studies have reported that male students are significantly more likely to be cyberbullying perpetrators2,15 and significantly less likely to be cyberbully victims.2,6,9 Middle-school boys are more likely to cyberbully others because of their race, sexual identity, or both.16 African American students are more likely to be cyberbully perpetrators and Hispanic students are more likely to be cyberbully perpetrators–victims than their White peers.2Cyberbullying may occur across a variety of technology platforms, and the specific qualities of each platform may affect how cyberbullying is perpetrated and experienced. Earlier studies suggested that instant messaging, chat rooms, and message boards were the most common mediums for middle-school students who experienced cyberbullying.3,17 More recently, youths have migrated to social media platforms such as Facebook,18–20 necessitating an examination of cyberbullying across more contemporary and emerging platforms for youth interaction.More frequent use of technology has also been associated with cyberbullying. Students who use the Internet for at least 3 hours per day and those who use instant messaging and Web cams are significantly more likely to have been cyberbully victims at least 7 times during the previous year.17 Frequent Internet users are significantly more likely to be cyberbully perpetrators, victims, and perpetrators–victims.14Research has shown that even though cyberbullying takes place in a virtual space, most cyberbullying perpetrators know their victims and vice versa. Moreover, 73% of victims reported being “pretty sure” or “totally sure” about the identity of their cyberbully, with 51% of cyberbullying perpetrators identified as a classmate, 43% as someone who they only knew online, and 20% as an in-person, nonclassmate relation.17 Cyberbullying perpetrators of middle-school victims were most often a classmate or a stranger; cyberbullying perpetrators most often reported that they cyberbullied classmates, friends, and strangers.3This study expanded previous work with high-school samples2 and nonprobability samples of middle-school students3,17 to explore the role of sexual identity, gender, race, and technology use patterns in a random sample of urban middle-school students in Los Angeles County, California. The study focused on demographic characteristics including sexual identity, patterns of technology use (i.e., frequency of Internet use, texting, parental rules regarding Internet use), and platforms on which middle-school students experience cyberbullying (i.e., Facebook, Twitter, e-mail, text messaging) to inform interventions to disrupt this maladaptive behavior and help protect early adolescents from the consequences of cyberbullying.  相似文献   
996.

Background

Lead (Pb) exposure and obesity are co-occurring risk factors for decreased bone mass in the young, particularly in low socioeconomic communities.

Objectives

The goal of this study was to determine whether the comorbidities of Pb exposure and high-fat diet–induced obesity amplify skeletal deficits independently associated with each of these risk factors, and to explore associated mechanisms of the observed deficiencies.

Methods

Five-week-old male C57BL/6J mice were placed on low-fat (10% kcal, LFD) or high-fat (60% kcal, HFD) diets for 12 weeks. Mice were exposed to lifetime Pb (50 ppm) through drinking water.

Results

HFD was associated with increased body mass and glucose intolerance. Both HFD and Pb increased fasting glucose and serum leptin levels. Pb and HFD each reduced trabecular bone quality and together had a further detrimental effect on these bone parameters. Mechanical bone properties of strength were depressed in Pb-exposed bones, but HFD had no significant effect. Both Pb and HFD altered progenitor cell differentiation, promoting osteoclastogenesis and increasing adipogenesis while suppressing osteoblastogenesis. In support of this lineage shift being mediated through altered Wnt signaling, Pb and non-esterified fatty acids in MC3T3 cells increased in vitro PPAR-γ activity and inhibited β-catenin activity. Combining Pb and non-esterified fatty acids enhanced these effects.

Conclusions

Pb and HFD produced selective deficits in bone accrual that were associated with alterations in progenitor cell activity that may involve reduced Wnt signaling. This study emphasizes the need to assess toxicants together with other risk factors relevant to human health and disease.

Citation

Beier EE, Inzana JA, Sheu TJ, Shu L, Puzas JE, Mooney RA. 2015. Effects of combined exposure to lead and high-fat diet on bone quality in juvenile male mice. Environ Health Perspect 123:935–943; http://dx.doi.org/10.1289/ehp.1408581  相似文献   
997.
998.
A growing number of community-based organizations and community–academic partnerships are implementing processes to determine whether and how health research is conducted in their communities. These community-based research review processes (CRPs) can provide individual and community-level ethics protections, enhance the cultural relevance of study designs and competence of researchers, build community and academic research capacity, and shape research agendas that benefit diverse communities.To better understand how they are organized and function, representatives of 9 CRPs from across the United States convened in 2012 for a working meeting.In this article, we articulated and analyzed the models presented, offered guidance to communities that seek to establish a CRP, and made recommendations for future research, practice, and policy.A growing number of community-based organizations and community–academic partnerships are implementing processes to determine whether and how health research is conducted in their communities.1–12 These community-based research review processes (CRPs) can provide individual- and community-level ethics protections, enhance the cultural relevance of study designs and competence of researchers, build community and academic research capacity, and help to set research agendas that benefit diverse communities. In 2009, with funding from the Greenwall Foundation, Community-Campus Partnerships for Health (CCPH) completed the first national study of CRPs in the United States.2,13The study identified 109 CRPs that mainly function through community–academic partnerships, community-based organizations, community health centers, and tribes, with 30 more in development. These CRPs were primarily formed to ensure that the involved communities are engaged in and directly benefit from research and are protected from its harms. Some are federally recognized institutional review boards (IRBs) that approve, monitor, and review research involving human participants. Others are advisory bodies. They all routinely examine issues that institution-based IRBs typically do not, such as community risks and benefits of the research and cultural appropriateness of the study design.2,13To better understand how CRPs are organized and function, CCPH, The Bronx Health Link, and the Albert Einstein College of Medicine convened representatives of 3 community IRBs, 5 community-based research review committees, and 1 university-based community research review committee in the United States for a working meeting in 2012 (see the box on page 1295). The meeting goals were to celebrate successes, identify promising practices, address challenges, and plan collaborations. The 9 participating CRPs were purposefully invited to reflect diversity in terms of geography, community served, organizational structure, and experience. Meeting proceedings described the CRPs in attendance and highlighted the emerging themes.1 In this article, we articulated and analyzed their diverse models, offered guidance to communities that seek to establish or strengthen a CRP, and outlined an agenda for future research, practice, funding, and policy.

Community-Based Research Review Processes Discussed in This Article

Name and LocationAcronymYear EstablishedReview Structure
Bronx Community Research Review Board, Bronx, NYBxCRRB2010Research review and advisory board
Center for Community Health Education Research and Service, Inc., Boston, MACCHERS2004Research review committee
Community Ethical Review Board, WE ACT for Environmental Justice, Inc., Harlem, NYCERBIn developmentEmerging research review committee
Community Research Advisory Board, University of Pittsburgh, Pittsburgh, PACRAB2001University-based research review committee
Galveston Island Community Research Advisory Committee, Galveston Island, TXGICRAC2005Grassroots research advisory committee
Hispanic Health Council, Hartford, CTHHC2000IRB
North Carolina American Indian Health Board, Winston-Salem, NCNCAIHB2009State-wide research review committee
Papa Ola Lokahi, Honolulu, HIPOL-IRB1999IRB
Special Service for Groups, Los Angeles CASSG2004IRB
Open in a separate windowNote. IRB = institutional review board.  相似文献   
999.
Bioinformatics approaches to examine gene‐gene models provide a means to discover interactions between multiple genes that underlie complex disease. Extensive computational demands and adjusting for multiple testing make uncovering genetic interactions a challenge. Here, we address these issues using our knowledge‐driven filtering method, Biofilter, to identify putative single nucleotide polymorphism (SNP) interaction models for cataract susceptibility, thereby reducing the number of models for analysis. Models were evaluated in 3,377 European Americans (1,185 controls, 2,192 cases) from the Marshfield Clinic, a study site of the Electronic Medical Records and Genomics (eMERGE) Network, using logistic regression. All statistically significant models from the Marshfield Clinic were then evaluated in an independent dataset of 4,311 individuals (742 controls, 3,569 cases), using independent samples from additional study sites in the eMERGE Network: Mayo Clinic, Group Health/University of Washington, Vanderbilt University Medical Center, and Geisinger Health System. Eighty‐three SNP‐SNP models replicated in the independent dataset at likelihood ratio test P < 0.05. Among the most significant replicating models was rs12597188 (intron of CDH1)–rs11564445 (intron of CTNNB1). These genes are known to be involved in processes that include: cell‐to‐cell adhesion signaling, cell‐cell junction organization, and cell‐cell communication. Further Biofilter analysis of all replicating models revealed a number of common functions among the genes harboring the 83 replicating SNP‐SNP models, which included signal transduction and PI3K‐Akt signaling pathway. These findings demonstrate the utility of Biofilter as a biology‐driven method, applicable for any genome‐wide association study dataset.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号