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   2123篇
  免费   203篇
  国内免费   6篇
耳鼻咽喉   30篇
儿科学   67篇
妇产科学   64篇
基础医学   255篇
口腔科学   13篇
临床医学   267篇
内科学   395篇
皮肤病学   49篇
神经病学   239篇
特种医学   52篇
外科学   244篇
综合类   16篇
一般理论   5篇
预防医学   356篇
眼科学   9篇
药学   134篇
  1篇
肿瘤学   136篇
  2024年   5篇
  2023年   68篇
  2022年   81篇
  2021年   192篇
  2020年   105篇
  2019年   144篇
  2018年   171篇
  2017年   115篇
  2016年   86篇
  2015年   88篇
  2014年   111篇
  2013年   133篇
  2012年   184篇
  2011年   159篇
  2010年   58篇
  2009年   65篇
  2008年   70篇
  2007年   72篇
  2006年   58篇
  2005年   43篇
  2004年   46篇
  2003年   36篇
  2002年   28篇
  2001年   16篇
  2000年   18篇
  1999年   14篇
  1998年   5篇
  1996年   4篇
  1995年   7篇
  1993年   4篇
  1992年   10篇
  1991年   8篇
  1990年   9篇
  1989年   6篇
  1988年   10篇
  1987年   14篇
  1986年   7篇
  1985年   7篇
  1984年   5篇
  1983年   9篇
  1982年   7篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1978年   7篇
  1977年   4篇
  1976年   6篇
  1975年   4篇
  1974年   3篇
  1971年   3篇
排序方式: 共有2332条查询结果,搜索用时 15 毫秒
1.
2.
DNA methylation at CpG dinucleotides is an important epigenetic regulator common to virtually all mammalian cell types, but recent evidence indicates that during early postnatal development neuronal genomes also accumulate uniquely high levels of two alternative forms of methylation, non-CpG methylation and hydroxymethylation. Here we discuss the distinct landscape of DNA methylation in neurons, how it is established, and how it might affect the binding and function of protein readers of DNA methylation. We review studies of one critical reader of DNA methylation in the brain, the Rett syndrome protein methyl CpG-binding protein 2 (MeCP2), and discuss how differential binding affinity of MeCP2 for non-CpG and hydroxymethylation may affect the function of this methyl-binding protein in the nervous system.  相似文献   
3.
4.
5.
6.
This study investigated the social-psychological predictors of self-reported actual and intended physical activity in a university workforce sample. Based on the 'Theory of Planned Behaviour', but with additional variables of benefits, barriers and self-efficacy, it was found that both intended and actual activity could be predicted but only when strenuous activity was considered. In addition, the predictors were different for men and women. Specifically, the best predictors of intention to exercise were attitude, perceived control, benefits and self-efficacy for women, but only attitude for men. Predicting self-reported strenuous activity for women were intention and self-efficacy, and for men intention and attitude. Theoretical and practical implications for attitude research and exercise promotion are discussed.  相似文献   
7.
Extended-spectrum beta-lactamases (ESBLs) are enzymes found in gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. In 1999, the National Committee for Clinical Laboratory Standards (NCCLS) published methods for screening and confirming the presence of ESBLs in Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli. To evaluate the confirmation protocol, we tested 139 isolates of K. pneumoniae that were sent to Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) from 19 hospitals in 11 U.S. states. Each isolate met the NCCLS screening criteria for potential ESBL producers (ceftazidime [CAZ] or cefotaxime [CTX] MICs were > or =2 microg/ml for all isolates). Initially, 117 (84%) isolates demonstrated a clavulanic acid (CA) effect by disk diffusion (i.e., an increase in CAZ or CTX zone diameters of > or =5 mm in the presence of CA), and 114 (82%) demonstrated a CA effect by broth microdilution (reduction of CAZ or CTX MICs by > or =3 dilutions). For five isolates, a CA effect could not be determined initially by broth microdilution because of off-scale CAZ results. However, a CA effect was observed in two of these isolates by testing cefepime and cefepime plus CA. The cefoxitin MICs for 23 isolates that failed to show a CA effect by broth microdilution were > or =32 microg/ml, suggesting either the presence of an AmpC-type beta-lactamase or porin changes that could mask a CA effect. By isoelectric focusing (IEF), 7 of the 23 isolates contained a beta-lactamase with a pI of > or =8.3 suggestive of an AmpC-type beta-lactamase; 6 of the 7 isolates were shown by PCR to contain both ampC-type and bla(OXA) genes. The IEF profiles of the remaining 16 isolates showed a variety of beta-lactamase bands, all of which had pIs of < or =7.5. All 16 isolates were negative by PCR with multiple primer sets for ampC-type, bla(OXA), and bla(CTX-M) genes. In summary, 83.5% of the K. pneumoniae isolates that were identified initially as presumptive ESBL producers were positive for a CA effect, while 5.0% contained beta-lactamases that likely masked the CA effect. The remaining 11.5% of the isolates studied contained beta-lactamases that did not demonstrate a CA effect. An algorithm based on phenotypic analyses is suggested for evaluation of such isolates.  相似文献   
8.
A total of 40 Neisseria gonorrhoeae isolates, representing 19 penicillin-resistant isolates (from 8 heterosexual patients and 11 homosexual patients) and 21 penicillin-susceptible isolates (from 15 heterosexual patients and 6 homosexual patients) and obtained from the same geographic area, were examined. Lectin agglutination patterns were based on the reactivity of the isolates with the following 14 lectins: concanavalin A, Lens culinaris, Trichosanthes kinlowii, Griffonia simplicifolia I, Arachis hypogeae (peanut agglutinin), Glycine max (soybean agglutinin), Dolichos bifloris, Griffonia simplicifolia II, Solanum tuberosum (potato starch agglutinin), Triticum vulgaris (wheat germ agglutinin), Limax flavus, Phaseolus vulgaris, Ulex europaeus I, and Lotus tetragonolobus. All isolates were serotyped with monoclonal antibodies specific for gonococcal outer membrane protein I and auxotyped, and the plasmid content was determined. Resistant patient isolates were selected for their decreased penicillin susceptibility, and control isolates were selected for their penicillin susceptibility. Even though the patient isolates demonstrated resistance to penicillin, no phenotypic differences in lectin-grouping patterns were demonstrated between the two study groups; i.e., two predominant lectin groups were observed. No resistance-associated plasmids were detected. All patient isolates were serogroup IB (serovars IB-1, IB-2, and IB-4), whereas 12 of 21 control isolates were serogroup IA (P less than 0.05). Isolates obtained from different anatomical sites in the same patient (cervical and rectal) agreed with regard to lectin patterns and serovars but not auxotypes.  相似文献   
9.
BACKGROUND: Young adults, especially men, are among those least likely to consult healthcare professionals when mentally distressed or suicidal. AIMS: To investigate the help-seeking behaviours of mentally distressed young adults. Design of study: Cross-sectional survey. SETTING: Bristol and surrounding areas, including inner-city, suburban and urban locations. METHOD: A questionnaire was sent to a sample of 3004 young adults aged 16-24 years. This assessed probable mental disorder (using the 12-item general health questionnaire [GHQ-12]), suicidal thoughts (GHQ-28 suicide subscale), and help-seeking behaviours. RESULTS: Most responders who were assessed as having probable mental disorders (GHQ "cases") had not sought help. Help seeking was more common in female GHQ cases than male cases (34.8% and 21.8%,respectively; P = 0.003) and women with suicidal thoughts more commonly sought help than men with suicidal thoughts (41.6% and 30.9%, respectively; P = 0.15). Small proportions of male and female GHQ cases (7.5% and 8.9%, respectively; P = 0.6), and less than one in five responders with suicidal thoughts, had consulted a general practitioner. In more female than male cases, help was sought from family and friends (30.7% and 18.4%, respectively; P = 0.004). GHQ score was the strongest predictor of help seeking. Men had a higher threshold of severity at which they would seek help than women. Recent experience of suicidal thoughts appeared to be a stronger predictor of formal help seeking in mentally distressed women than mentally distressed men. CONCLUSION: Distressed young adults are reluctant to seek help. Men are particularly unlikely to do so unless severely distressed and tend not to seek lay support. Sex differences in help seeking may be important in understanding the high suicide rate for men.  相似文献   
10.
We evaluated nucleic acid amplification testing (NAAT) for Zika virus on whole-blood specimens compared with NAAT on serum and urine specimens among asymptomatic pregnant women during the 2015–2016 Puerto Rico Zika outbreak. Using NAAT, more infections were detected in serum and urine than in whole blood specimens.  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