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   198488篇
  免费   22349篇
  国内免费   2456篇
耳鼻咽喉   5630篇
儿科学   6700篇
妇产科学   3295篇
基础医学   7585篇
口腔科学   1910篇
临床医学   32786篇
内科学   53623篇
皮肤病学   7774篇
神经病学   18484篇
特种医学   7076篇
外国民族医学   1篇
外科学   44033篇
综合类   589篇
现状与发展   72篇
一般理论   49篇
预防医学   12325篇
眼科学   3721篇
药学   3216篇
  1篇
中国医学   50篇
肿瘤学   14373篇
  2024年   849篇
  2023年   5372篇
  2022年   1876篇
  2021年   3914篇
  2020年   6574篇
  2019年   3090篇
  2018年   8398篇
  2017年   8038篇
  2016年   9140篇
  2015年   9193篇
  2014年   16623篇
  2013年   17490篇
  2012年   8287篇
  2011年   8490篇
  2010年   11878篇
  2009年   15597篇
  2008年   8402篇
  2007年   6646篇
  2006年   9043篇
  2005年   6301篇
  2004年   5364篇
  2003年   4076篇
  2002年   4077篇
  2001年   3981篇
  2000年   3158篇
  1999年   3432篇
  1998年   4029篇
  1997年   3756篇
  1996年   3585篇
  1995年   3388篇
  1994年   2139篇
  1993年   1755篇
  1992年   1491篇
  1991年   1506篇
  1990年   1134篇
  1989年   1263篇
  1988年   1094篇
  1987年   924篇
  1986年   959篇
  1985年   789篇
  1984年   638篇
  1983年   591篇
  1982年   600篇
  1981年   496篇
  1980年   428篇
  1979年   347篇
  1978年   359篇
  1977年   434篇
  1975年   300篇
  1972年   315篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.

Objective

To compare perioperative and long-term outcomes in patients undergoing hemiarch and aggressive arch replacement for acute type A aortic dissection (ATAAD).

Methods

From 1996 to 2017, we compared outcomes of hemiarch (n = 322) versus aggressive arch replacements (zones 2 and 3 arch replacement with implantation of 2-4 arch branches, n = 150) in ATAAD. Indications for aggressive arch were arch aneurysm >4 cm or intimal tear in the aortic arch that was not resectable by hemiarch replacement, or dissection of arch branches with malperfusion.

Results

Patients in the aggressive arch group were significantly younger (mean age: 57 vs 61 years old) and had significantly longer hypothermic circulatory arrest, cardiopulmonary bypass, and aortic crossclamp times. There were no significant differences in perioperative outcomes between hemiarch and aggressive arch groups, including 30-day mortality (5.3% vs 7.3%, P = .38) and postoperative stroke rate (7% vs 7%, P = .96). Over 15 years, Kaplan–Meier survival was similar between hemiarch and aggressive arch groups (log-rank P = .55, 10-year survival 70% vs 72%). Given death as a competing factor, incidence rates of reoperation over 15 years (2.1% vs 2.0% per year, P = 1) and 10-year cumulative incidence of reoperation (14% vs 12%, P = .89) for arch and distal aorta pathology were similar between the 2 groups.

Conclusions

Both hemiarch and aggressive arch replacement are appropriate approaches for select patients with ATAAD. Aggressive arch replacement should be considered for an arch aneurysm >4 cm or an intimal tear at the arch unable to be resected by hemiarch replacement, or dissection of the arch branches with malperfusion.  相似文献   
3.

Background

The International Agency for Research on Cancer (IARC) has recently classified glyphosate as a Group 2A ‘probably carcinogenic to humans’. Due to this carcinogenic classification and resulting international debate, there is an increased demand for studies evaluating human health effects from glyphosate exposures. There is currently limited information on human exposures to glyphosate and a paucity of data regarding glyphosate's biological half-life in humans.

Objective

This study aims to estimate the human half-life of glyphosate from human urine samples collected from amenity horticulture workers using glyphosate based pesticide products.

Methods

Full void urine spot samples were collected over a period of approximately 24?h for eight work tasks involving seven workers. The elimination time and estimation of the half-life of glyphosate using three different measurement metrics: the unadjusted glyphosate concentrations, creatinine corrected concentrations and by using Urinary Excretion Rates (UER) (μg L?1, μmol/mol creatinine and UER μg L?1) was calculated by summary and linear interpolation using regression analysis.

Results

This study estimates the human biological half-life of glyphosate as approximately 5 ½, 10 and 7 ¼ hours for unadjusted samples, creatinine corrected concentrations and by using UER (μg L?1, μmol/mol creatinine, UER μg L?1), respectively. The approximated glyphosate half-life calculations seem to have less variability when using the UER compared to the other measuring metrics.

Conclusion

This study provides new information on the elimination rate of glyphosate and an approximate biological half-life range for humans. This information can help optimise the design of sampling strategies, as well as assisting in the interpretation of results for human biomonitoring studies involving this active ingredient. The data could also contribute to the development or refinement of Physiologically Based PharmacoKinetic (PBPK) models for glyphosate.  相似文献   
4.
Purpose: Numerous studies have reported a robust relationship between early phonological awareness (PA) and subsequent reading achievement, in addition to the critical role of the alphabetic principle in predicting and supporting later reading and spelling development. Given this association, there has been an increasing push to teach these skills to young children prior to word level reading and spelling instruction. This study evaluated the effectiveness of the Cracking the Code (CtC) program with students aged 3;8–5;4. CtC is a teacher-implemented program, designed to explicitly target PA skills and alphabet knowledge.

Method: A pre-test post-test group design was used to evaluate the effectiveness of the program. Four schools in metropolitan Western Australia were randomly assigned to either the control or experimental condition within a parallel groups design. The control group participated in an alternative program matched for duration and frequency, targeting semantics and grammar.

Result: The children in the experimental condition improved significantly more in PA, alphabet knowledge and non-word reading, and spelling after intervention than the control group.

Conclusion: These findings demonstrate that classroom-based, teacher-delivered PA and alphabet knowledge instruction can be effective for 3;8–5;4 year-olds.  相似文献   

5.
6.

Background

Few U.S. studies have explored how children experience a parent's mobility disability and its effects on their daily lives.

Objective

We aimed to engage youth ages 13–17 who had at least one parent with mobility disability in describing their perceptions of their parent's disability and its consequences for their daily and family life.

Methods

Participants videoed and photographed their experiences following general guidelines from the researchers about topics of interest. Participants made their own choices about what they submitted. We used conventional content analysis to identify broad themes.

Results

The mean (standard deviation) age of the 10 participants was 15.2 (1.9) years; 5 were male; 9 participants were white. All 5 girls submitted multiple self-focused (selfie) videos made in their bedrooms; the 5 boys submitted more diverse data files. Several broad themes or topics emerged including: the effects of timing and trajectory of the parent's disability; perceptions of early maturity and responsibility; fears and frustrations relating to the parent's disability; support and emerging resilience; and sense of social justice. Participants generally felt their parents' disability made them become – compared to their peers – more mature, responsible, capable of performing household tasks, and aware of disability civil rights.

Conclusions

Participants raised many issues that health care providers should be aware of when youth have parents with mobility disability. A parent's mobility disability may be associated with resilience but also may pose challenges for youth. More research is needed to understand better adolescents' experiences and how clinicians might best assist these youth.  相似文献   
7.
While colorectal cancer (CRC) screening rates have been increasing in the general population, rates are considerably lower in Federally Qualified Health Centers (FQHCs), which serve a large proportion of uninsured and medically vulnerable patients. Efforts to screen eligible patients must be accelerated if we are to reach the national screening goal of 80% by 2018 and beyond. To inform this work, we conducted a survey of key informants at FQHCs in eight states to determine which evidence-based interventions (EBIs) to promote CRC screening are currently being used, and which implementation strategies are being employed to ensure that the interventions are executed as intended. One hundred and forty-eight FQHCs were invited to participate in the study, and 56 completed surveys were received for a response rate of 38%. Results demonstrated that provider reminder and recall systems were the most commonly used EBIs (44.6%) while the most commonly used implementation strategy was the identification of barriers (84.0%). The mean number of EBIs that were fully implemented at the centers was 2.4 (range 0–7) out of seven. Almost one-quarter of respondents indicated that their FQHCs were not using any EBIs to increase CRC screening. Full implementation of EBIs was correlated with higher CRC screening rates. These findings identify gaps as well as the preferences and needs of FQHCs in selecting and implementing EBIs for CRC screening.  相似文献   
8.
Bridging immunoassays commonly used to detect and characterize immunogenicity during biologic development do not provide direct information on the presence or development of a memory anti-drug antibody (ADA) response. In this study, a B cell ELISPOT assay method was used to evaluate pre-existing ADA for anti-TNFR1 domain antibody, GSK1995057, an experimental biologic in treatment naive subjects. This assay utilized a 7-day activation of PBMCs by a combination of GSK1995057 (antigen) and polyclonal stimulator followed by GSK1995057-specific ELISPOT for the enumeration of memory B cells that have differentiated into antibody secreting cells (ASC) in vitro. We demonstrated that GSK1995057-specific ASC were detectable in treatment-naïve subjects with pre-existing ADA; the frequency of drug-specific ASC was low and ranged from 1 to 10 spot forming units (SFU) per million cells. Interestingly, the frequency of drug-specific ASC correlated with the ADA level measured using an in vitro ADA assay. We further confirmed that the ASC originated from CD27+ memory B cells, not from CD27?-naïve B cells. Our data demonstrated the utility of the B cell ELISPOT method in therapeutic protein immunogenicity evaluation, providing a novel way to confirm and characterize the cell population producing pre-existing ADA. This novel application of a B cell ELISPOT assay informs and characterizes immune memory activity regarding incidence and magnitude associated with a pre-existing ADA response.  相似文献   
9.
10.
Inhalation of ash can be of great concern for affected communities, during and after volcanic eruptions. Governmental and humanitarian agencies recommend and distribute a variety of respiratory protection (RP), most commonly surgical masks. However, there is currently no evidence on how effective such masks are in protecting wearers from volcanic ash. In Part I of this study (Mueller et al., 2018), we assessed the filtration efficiency (FE) of 17 materials from different forms of RP against volcanic ash and a surrogate, low-toxicity dust, Aloxite. Based on those results, we now present the findings from a volunteer simulation study to test the effect of facial fit through assessment of Total Inward Leakage (TIL).Four different disposable RP types that demonstrated very high median FE (≥96% for Aloxite; ≥89% for volcanic ash) were tested without provision of training on fit. These were an industry-certified mask (N95-equiv.); a surgical mask from Japan designed to filter PM2.5; a flat-fold basic mask from Indonesia; and a standard surgical mask from Mexico, which was also tested with an added medical bandage on top, as an additional intervention to improve fit.Ten volunteers (6 female, 4 male) were recruited. Each RP type was worn by volunteers under two different conditions simulating cleaning-up activities during/after volcanic ashfall. Each activity lasted 10?min and two repeats were completed for each RP type per activity. Dust (as PM2.5) concentration inside and outside the mask was measured with two TSI SidePak aerosol monitors (Models AM510 and AM520, TSI, Minnesota, USA) to calculate TIL. A questionnaire was administered after each test to collect perceptions of fit, comfort, protection and breathability.The best-performing RP type, across both activities, was the industry-certified N95-equiv. mask with 9% mean TIL. The standard surgical mask and the basic flat-fold mask both performed worst (35% TIL). With the additional bandage intervention, the surgical mask mean TIL improved to 24%. The PM2.5 surgical mask performed similarly, with 22% TIL. The N95-equiv. mask was perceived to provide the best protection, but was also perceived as being uncomfortable and more difficult to breathe through.This study provides a first objective evidence base for the effectiveness of a selection of RP types typically worn around the world during volcanic crises. The findings will help agencies to make informed decisions on the procurement and distribution of RP in future eruptions.  相似文献   
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