全文获取类型
收费全文 | 8537篇 |
免费 | 530篇 |
国内免费 | 25篇 |
专业分类
耳鼻咽喉 | 127篇 |
儿科学 | 267篇 |
妇产科学 | 266篇 |
基础医学 | 884篇 |
口腔科学 | 140篇 |
临床医学 | 776篇 |
内科学 | 2236篇 |
皮肤病学 | 80篇 |
神经病学 | 838篇 |
特种医学 | 329篇 |
外科学 | 947篇 |
综合类 | 93篇 |
一般理论 | 6篇 |
预防医学 | 974篇 |
眼科学 | 157篇 |
药学 | 556篇 |
中国医学 | 2篇 |
肿瘤学 | 414篇 |
出版年
2023年 | 32篇 |
2022年 | 19篇 |
2021年 | 173篇 |
2020年 | 84篇 |
2019年 | 169篇 |
2018年 | 191篇 |
2017年 | 160篇 |
2016年 | 145篇 |
2015年 | 173篇 |
2014年 | 282篇 |
2013年 | 389篇 |
2012年 | 630篇 |
2011年 | 692篇 |
2010年 | 377篇 |
2009年 | 373篇 |
2008年 | 567篇 |
2007年 | 690篇 |
2006年 | 640篇 |
2005年 | 614篇 |
2004年 | 581篇 |
2003年 | 533篇 |
2002年 | 466篇 |
2001年 | 102篇 |
2000年 | 73篇 |
1999年 | 82篇 |
1998年 | 104篇 |
1997年 | 77篇 |
1996年 | 59篇 |
1995年 | 69篇 |
1994年 | 47篇 |
1993年 | 45篇 |
1992年 | 47篇 |
1991年 | 28篇 |
1990年 | 34篇 |
1989年 | 62篇 |
1988年 | 37篇 |
1987年 | 23篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 31篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1973年 | 6篇 |
1971年 | 6篇 |
排序方式: 共有9092条查询结果,搜索用时 578 毫秒
991.
Petar Bezinovi? Darko Rovi? Nena Ron?evi? Lovorka Bilajac 《Croatian medical journal》2015,56(3):297-305
Aim
To examine associations between different forms of internet use and a number of psychological variables related to mental health in adolescents.Methods
A cross-sectional survey was carried out on a representative sample of students (N = 1539) from all high schools in the region of Istria in Croatia (14-19 years). The associations between four factors of internet use and nine mental health indicators were analyzed using canonical correlation analysis.Results
The four canonical functions suggested a significant association between different types of internet use and specific indicators of mental health (P < 0.001). Problematic internet use, more typical among boys, was associated with general aggressive behavior and substance abuse (P < 0.001). Experiences of harassment, more typical among girls, were associated with health complaints, symptoms of depression, loneliness, and fear of negative evaluation (P < 0.001). Using the internet for communication and entertainment was associated with better relationships with peers (P < 0.001), while use of the internet for academic purposes was associated with conscientiousness (P < 0.001).Conclusion
The results suggest that different patterns of internet use are significantly associated with specific sets of positive and negative mental health indicators. The data support the assumption that internet use can have both positive and adverse effects on the mental health of youth.New technologies, and especially the use of computers and the internet, are part of the everyday lives of young people and have a significant impact on their psychological development. Indeed, this mass use of new media technologies presents parents and society with a challenge to protect and support the positive development of children and youth. To date, a number of studies have examined the positive and negative aspects of using internet technologies.Literature points to several positive aspects of internet use (1,2): for information acquiring, communication, and social networking, entertainment, and online shopping. More specifically, adolescents use the internet as a useful source of information about school assignments, daily events, interests and hobbies, or health and sexuality concerns. In these instances, online activities aimed at connecting with peers have a significant place. Visiting social networking sites and using communication tools such as email, chat, forums, and discussion groups enables the creation of friendships and social groups and contributes to the development of personal identity (3). The use of computers and the internet (cyberspace) has also been argued to provide opportunities for new and faster learning, exercising one''s self-control, considering different opinions, expressing one''s attitudes and tolerance, and developing skills in critical thinking and decision-making (4). Best et al (5) found that use of online communication technologies contributed to increased self-confidence, better perception of social support, greater social capital, positive experimenting with one’s own identity, and greater opportunities for open self-disclosure. Conversely, adolescents who do not use the internet might trail behind in the development of such positive attitudes and traits and risk being rejected by their peers (6). Finally, Livingstone et al (7) found that a certain amount of risk exposure was useful in building resilience.In contrast to these positive influences of internet use, harmful effects of internet abuse range from exposure to inappropriate sexual content, pornography, and violence (2,7) to humiliation and cyber-bullying (6,8-10) and internet addiction (11,12). Research has confirmed the link between internet abuse and social isolation, depression and, anxiety (1,5,13,14), alcohol and drug abuse and gambling (15), and problems with physical health (16). Ybarra and Mitchell (17) found a connection between experiences of threats or humiliation in the virtual world and absences from school, lower school achievement, substance use disorders, delinquency and depression. Fekkes et al (18) point to the association between victimizing experiences and a number of physical, emotional, and behavioral problems, such as headaches, tension, fatigue, loss of appetite, enuresis, and sleeping problems. Slonje and Smith (19) define such experiences as a product of cyber-bullying and argue that this can be viewed as another form of aggressive behavior. Gender has emerged as a significant predictor of the manner in which the internet is used. Specifically, girls tend to experience victimizing experiences, while boys more frequently demonstrate antisocial behavior (20,21).Although many studies have identified both positive and negative correlates of internet use, there have been only a few studies using complex multivariate analyses to identify broader patterns of internet use and adolescent mental health (22,23). Less is known about how adolescents exhibiting different personalities and different emotional and behavioral patterns engage in internet use and what might be the consequences of this engagement. The aim of this study was to determine the specific patterns of internet use and mental health among adolescents. The following hypotheses were tested:H1: Problematic internet use is associated with externalized symptoms and other negative indicators of mental health. Exposure to victimizing and disturbing content on the internet is associated with internalized symptoms and negative indicators of mental health.H2: Prosocial internet use (aimed at connecting with peers and entertainment) and internet use for school purposes are associated with positive aspects of mental health.H3: Problematic internet use is present more often in young men, while exposure to disturbing content on the internet is more frequently experienced by young women. 相似文献992.
Dagan R Givon-Lavi N Zamir O Sikuler-Cohen M Guy L Janco J Yagupsky P Fraser D 《The Journal of infectious diseases》2002,185(7):927-936
A double-blind, randomized study involving 264 toddlers attending day care centers was conducted to document the effect of a 9-valent pneumococcal conjugate vaccine on the carriage rate of pneumococci. Of 3750 cultures done on nasopharyngeal samples obtained from subjects during a 2-year follow-up period after vaccination, 65% were positive for Streptococcus pneumoniae. In all age windows, the rate of carriage of vaccine-type pneumococci was lower among subjects who received the pneumococcal vaccine than among control subjects, because the acquisition rate was lower in the former group. The effect was most pronounced among subjects aged < or =36 months. The sample size enabled us to study protection against carriage of S. pneumoniae serotypes 6B, 9V, 14, 19F, and 23F; significant protection against all serotypes except 19F was seen in the pneumococcal-vaccine group. The rate of carriage of serotype 6A (not included in the vaccine) was also reduced significantly, but the rate of carriage of serotype 19A (not included in the vaccine) was not. The rate of carriage of non-vaccine-type pneumococci (excluding serotype 6A) was higher in the pneumococcal-vaccine group than in the control group. 相似文献
993.
Overall survival of relapsed and refractory multiple myeloma patients after adjusting for crossover in the MM‐003 trial for pomalidomide plus low‐dose dexamethasone 下载免费PDF全文
Gareth Morgan Antonio Palumbo Sujith Dhanasiri Dawn Lee Katja Weisel Thierry Facon Michel Delforge Albert Oriol Mohamed Zaki Xin Yu Lars Sternas Christian Jacques Ron Akehurst Fritz Offner Meletios A. Dimopoulos 《British journal of haematology》2015,168(6):820-823
In the phase III MM‐003 trial, pomalidomide plus low‐dose dexamethasone (POM+LoDEX) improved overall survival (OS) versus high‐dose dexamethasone (HiDEX) in 455 patients with relapsed and refractory multiple myeloma (RRMM) after treatment with bortezomib and lenalidomide. Here, a two‐stage Weibull method was used to adjust for the crossover of patients in the HiDEX arm to pomalidomide‐based therapy. The adjusted difference in median OS between patients in the POM+LoDEX and HiDEX arms was 7·0 months (12·7 vs. 5·7 months, respectively). These findings provide important evidence for understanding the clinical efficacy of pomalidomide on OS benefits seen in RRMM patients. 相似文献
994.
Arturo Abdelnour Adriano Arguedas Ron Dagan Carolina Soley Nurith Porat Maria Mercedes Castrejon Eduardo Ortega-Barria Romulo Colindres Jean-Yves Pir?on Rodrigo DeAntonio Melissa K. Van Dyke 《Medicine》2015,94(2)
Acute otitis media (AOM) microbiology was evaluated in children after 7-valent pneumococcal conjugate vaccine (PCV7) introduction in Costa Rica (private sector, 2004; National Immunization Program, 2009).This was a combined prospective and retrospective study conducted in a routine clinical setting in San José, Costa Rica. In the prospective part of the study, which was conducted post-PCV7 introduction (2010–2012), standard bacteriological procedures were used to evaluate the etiology and serotype distribution of middle ear fluid samples collected by tympanocentesis or otorrhea from children aged 3–59 months diagnosed with AOM. E-tests were used to evaluate antimicrobial susceptibility in culture-positive samples. Retrospective data recorded between 1999 and 2004 were used for comparison of bacterial etiology and serotype distribution before and after PCV7 introduction. Statistical significance was evaluated in bivariate analyses at the P-value < 0.05 level (without multiplicity correction).Post-PCV7 introduction, Haemophilus influenzae was detected in 118/456 and Streptococcus pneumoniae in 87/456 AOM episodes. Most H. influenzae isolates (113/118) were non-typeable. H. influenzae was more (27.4% vs 20.8%) and S. pneumoniae less (17.1% vs 25.5%) frequently observed in vaccinated (≥2 PCV7 doses or ≥1 PCV7 dose at >1 year of age) versus unvaccinated children. S. pneumoniae non-susceptibility rates were 1.1%, 34.5%, 31.7%, and 50.6% for penicillin, erythromycin, azithromycin, and trimethoprim/sulfamethoxazole (TMP-SMX), respectively. H. influenzae non-susceptibility rate was 66.9% for TMP-SMX. Between pre- and post-PCV7 introduction, H. influenzae became more (20.5% vs 25.9%; P-value < 0.001) and S. pneumoniae less (27.7% vs 19.1%; P-value = 0.002) prevalent, and PCV7 serotype proportions decreased among pneumococcal isolates (65.8% vs 43.7%; P-value = 0.0005). Frequently identified pneumococcal serotypes were 19F (34.2%), 3 (9.7%), 6B (9.7%), and 14 (9.7%) pre-PCV7 introduction, and 19F (27.6%), 14 (8.0%), and 35B (8.0%) post-PCV7 introduction.Following PCV7 introduction, a change in the distribution of AOM episodes caused by H. influenzae and pneumococcal serotypes included in PCV7 was observed in Costa Rican children. Pneumococcal vaccines impact should be further evaluated following broader vaccination coverage. 相似文献
995.
Harrie C M van den Bosch Jos J M Westenberg Wikke Setz-Pels John Wondergem Ron Wolterbeek Lucien E M Duijm Joep A W Teijink Albert de Roos 《Journal of cardiovascular magnetic resonance》2015,17(1)
Background
Vascular disease expression in one location may not be representative for disease severity in other vascular territories, however, strong correlation between disease expression and severity within the same vascular segment may be expected. Therefore, we hypothesized that aortic stiffening is more strongly associated with disease expression in a vascular territory directly linked to that aortic segment rather than in a more remote segment. We prospectively compared the association between aortic wall stiffness, expressed by pulse wave velocity (PWV), sampled in the distal aorta, with the severity of peripheral arterial occlusive disease (PAOD) as compared to atherosclerotic markers sampled in remote vascular territories such as PWV in the proximal aorta and the normalized wall index (NWI), representing the vessel wall thickness, of the left common carotid artery.Methods
Forty-two patients (23 men; mean age 64±10 years) underwent velocity-encoded cardiovascular magnetic resonance (CMR) in the proximal and distal aorta, whole-body contrast-enhanced MR angiography (CE-MRA) and carotid vessel wall imaging with black-blood CMR in the work-up for PAOD. Strength of associations between aortic stiffness, carotid NWI and peripheral vascular stenosis grade were assessed and evaluated with multiple linear regression.Results
Stenosis severity correlated well with PWV in the distal aorta (Pearson rP=0.64, p<0.001, Spearman rS=0.65, p<0.001) but to a lesser extent with PWV in the proximal aorta (rP=0.48, p=0.002, rS=0.22, p=0.18). Carotid NWI was not associated with peripheral stenosis severity (rP=0.17, p=0.28, rS=0.14, p=0.37) nor with PWV in the proximal aorta (rP=0.22, p=0.17) nor in the distal aorta (rP=0.21, p=0.18). Correlation between stenosis severity and distal aortic PWV remained statistically significant after correction for age and gender.Conclusions
Distal aortic wall stiffness is more directly related to peripheral arterial stenosis severity than markers from more remote vascular territories such as proximal aortic wall stiffness or carotid arterial wall thickness. Site-specific evaluation of vascular disease may be required for full vascular risk estimation. 相似文献996.
997.
Wolfram R Cheneau E Mintz GS Pichard AD Satler LF Kent KM Suddath WO Pinnow EE Waksman R 《The American journal of cardiology》2004,94(12):1551-1554
This study aimed to compare the outcomes of patients with late total occlusion (LTO) versus patients with recurrence in the absence of LTO after intracoronary radiation therapy for in-stent restenosis. LTO, especially in the context of acute myocardial infarction, after intracoronary radiation therapy for in-stent restenosis, is associated with negative clinical outcomes after 6 and 12 months compared with in-stent restenosis without LTO. 相似文献
998.
Caños DA Mintz GS Berzingi CO Apple S Kotani J Pichard AD Satler LF Suddath WO Waksman R Lindsay J Weissman NJ 《Journal of the American College of Cardiology》2004,44(1):53-56
OBJECTIVES: We sought to examine saphenous vein graft (SVG) lesions that fail within the first year after operation. BACKGROUND: Saphenous vein grafts remain patent for approximately 10 years; however, up to 15% to 20% of SVGs become occluded within the first year. METHODS: We studied 100 patients who underwent percutaneous coronary intervention (PCI) for early (<1 year post-implantation) SVG failure lesions and compared them with a diabetes- and hypercholesterolemia-matched cohort of late SVG failures (>1 year). Coronary angiography and intravascular ultrasound images were analyzed. RESULTS: The majority of patients in both groups were males who presented with unstable angina; 36% were diabetic. Graft ages were 6.0 +/- 2.9 months and 105.4 +/- 50.8 months, respectively. The early SVG failure lesion location was more often ostial or proximal (62% vs. 42%, respectively). Early SVG failures were angiographically smaller than late failures (reference: 2.47 +/- 0.86 mm vs. 3.26 +/- 0.83 mm, p < 0.001) but had similar lesion lengths. Intravascular ultrasound showed that early failure lesions had smaller proximal and distal reference lumen areas (7.3 +/- 6.8 mm2 vs. 10.6 +/- 3.8 mm2, p = 0.026) and greater reference plaque burden than late failures (52.3% vs. 36.1%, p < 0.001). After PCI, 20.6% of early and 30.6% of late failure lesions had creatine kinase-myocardial band (CK-MB) greater than twice normal. CONCLUSIONS: Early SVG failure is mostly proximal or ostial, lesions appear focal, and early SVGs appear smaller than late SVGs. Intravascular ultrasound shows significant reference segment plaque burden, suggesting more severe, diffuse SVG disease. 相似文献
999.
1000.
Michael P. Schwartz Zhonggang Hou Nicholas E. Propson Jue Zhang Collin J. Engstrom Vitor Santos Costa Peng Jiang Bao Kim Nguyen Jennifer M. Bolin William Daly Yu Wang Ron Stewart C. David Page William L. Murphy James A. Thomson 《Proceedings of the National Academy of Sciences of the United States of America》2015,112(40):12516-12521
Human pluripotent stem cell-based in vitro models that reflect human physiology have the potential to reduce the number of drug failures in clinical trials and offer a cost-effective approach for assessing chemical safety. Here, human embryonic stem (ES) cell-derived neural progenitor cells, endothelial cells, mesenchymal stem cells, and microglia/macrophage precursors were combined on chemically defined polyethylene glycol hydrogels and cultured in serum-free medium to model cellular interactions within the developing brain. The precursors self-assembled into 3D neural constructs with diverse neuronal and glial populations, interconnected vascular networks, and ramified microglia. Replicate constructs were reproducible by RNA sequencing (RNA-Seq) and expressed neurogenesis, vasculature development, and microglia genes. Linear support vector machines were used to construct a predictive model from RNA-Seq data for 240 neural constructs treated with 34 toxic and 26 nontoxic chemicals. The predictive model was evaluated using two standard hold-out testing methods: a nearly unbiased leave-one-out cross-validation for the 60 training compounds and an unbiased blinded trial using a single hold-out set of 10 additional chemicals. The linear support vector produced an estimate for future data of 0.91 in the cross-validation experiment and correctly classified 9 of 10 chemicals in the blinded trial.There is a pressing need for improved methods to assess the safety of drugs and other compounds (1–5). Success rates for drug approval are declining despite higher research and development spending (6), and clinical trials often fail due to toxicities that were not identified through animal testing (7). In addition, most of the chemicals in commerce have not been rigorously assessed for safety despite growing concerns over the potential impact of industrial and environmental exposures on human health (2–5). Animal models are costly, time consuming, and fail to recapitulate many aspects of human physiology, which has motivated agencies such as the National Institutes of Health (NIH) and the US Environmental Protection Agency (EPA) to initiate programs that emphasize human cellular approaches for assessing the safety of drugs (1) and environmental chemicals (2, 3). In vitro cellular models that accurately reflect human physiology have the potential to improve the prediction of drug toxicity early in the development pipeline (1) and would provide a cost-effective approach for testing other sources of chemical exposure, including food additives, cosmetics, pesticides, and industrial chemicals (2–5).The human brain is particularly sensitive to toxic insults during development and early childhood (8), and there is growing concern that exposure to environmental chemicals may be linked to the rising incidence of neurodevelopmental disorders worldwide (4). Human brain development is mediated by highly coordinated cellular interactions between functionally distinct cell types that include neurons, glia, blood vessels, and microglia (9–15), each of which may be involved in neurotoxicity mechanisms (16–18). The cellular diversity of the developing brain complicates efforts to assess developmental neurotoxicity in vitro, because toxins might target numerous distinct cell types or cellular interactions and the underlying toxicity mechanisms are often unknown (3–5). Neurotoxicity has been evaluated using brain-derived cells in aggregate culture or coculture, neural stem cells, and other in vitro platforms, and these studies suggest that complex neurotoxic effects can be mimicked by incorporating cellular diversity into the model system (16, 18–20). However, many of these studies rely on animal cells that poorly reflect human physiology or primary human cells that are not scalable and introduce batch variability.Although in vitro human cellular models have historically been hampered by inadequate access to cellular components of the human brain, human embryonic stem (ES) cells (21) and induced pluripotent stem (iPS) cells (22, 23) now offer a scalable source for tissue-specific cell types. Here, reproducible 3D neural constructs that incorporated vascular and microglial components were fabricated for developmental neurotoxicity screening by culturing precursor cells derived from the H1 human ES cell line on synthetic hydrogels under defined conditions. Machine learning was used to build a predictive model from RNA sequencing (RNA-Seq) data for neural constructs exposed to a training set of 60 toxic and nontoxic chemicals and then to make predictions in a blinded trial using a set of 10 additional compounds. 相似文献