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   13359篇
  免费   961篇
  国内免费   54篇
耳鼻咽喉   158篇
儿科学   367篇
妇产科学   192篇
基础医学   1625篇
口腔科学   285篇
临床医学   1548篇
内科学   2974篇
皮肤病学   258篇
神经病学   1264篇
特种医学   636篇
外科学   2106篇
综合类   131篇
一般理论   5篇
预防医学   950篇
眼科学   337篇
药学   756篇
中国医学   15篇
肿瘤学   767篇
  2023年   88篇
  2022年   172篇
  2021年   366篇
  2020年   206篇
  2019年   325篇
  2018年   393篇
  2017年   255篇
  2016年   327篇
  2015年   407篇
  2014年   481篇
  2013年   595篇
  2012年   1014篇
  2011年   982篇
  2010年   577篇
  2009年   472篇
  2008年   863篇
  2007年   847篇
  2006年   804篇
  2005年   743篇
  2004年   593篇
  2003年   578篇
  2002年   471篇
  2001年   183篇
  2000年   159篇
  1999年   207篇
  1998年   114篇
  1997年   113篇
  1996年   80篇
  1995年   70篇
  1994年   66篇
  1993年   49篇
  1992年   98篇
  1991年   107篇
  1990年   96篇
  1989年   105篇
  1988年   93篇
  1987年   89篇
  1986年   79篇
  1985年   101篇
  1984年   86篇
  1983年   56篇
  1982年   60篇
  1981年   48篇
  1980年   60篇
  1979年   76篇
  1978年   52篇
  1976年   41篇
  1975年   41篇
  1974年   41篇
  1973年   42篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
BACKGROUND: Previous studies have raised concerns regarding the safety of regular use of beta2-agonists for treating asthma. Few studies have explored the safety of at least 1 year of use of racemic albuterol, and none have examined long-term dosing of levalbuterol. OBJECTIVE: To examine the long-term safety of levalbuterol hydrofluoroalkane (HFA) vs racemic albuterol HFA administered via metered-dose inhaler (MDI) in patients with stable asthma. METHODS: Patients with mild to moderate asthma (mean forced expiratory volume in 1 second [FEVI], 68.3% of predicted) 12 years or older participated in a multicenter, parallel-group, open-label study. Patients were randomized to levalbuterol HFA MDI (90 microg; 2 actuations of 45 microg; n = 496) or racemic albuterol HFA MDI (180 microg; 2 actuations of 90 microg; n = 250) for 52 weeks of 4 times daily dosing. The primary end point was the incidence of postrandomization adverse events. Asthma exacerbations and pulmonary parameters were also assessed. RESULTS: The overall incidence of adverse events was similar for levalbuterol (72.0%) and racemic albuterol (76.8%). Rates of beta-mediated adverse events, serious adverse events, and discontinuations because of adverse events were low (<15%) and were comparable between groups. Rates of asthma adverse events for levalbuterol and racemic albuterol were 18.3% and 19.6%, respectively. Mean percentage of predicted FEV1 improved after dosing and was stable for both groups. CONCLUSION: In this trial, up to 52 weeks of regular use of levalbuterol HFA MDI or racemic albuterol HFA MDI was well tolerated, and no deterioration of lung function was detected during the study period.  相似文献   
82.
83.
Summary Study design: As part of a large screening study of perinatal depression, pregnant women were screened for demographic, depression and treatment variables in obstetrics clinics. Women taking antidepressant medication prior to conception were included in the sample as the study aimed to document rates of antidepressant medication use, and relationship to depressive symptomatology.Results: Among women who reported using antidepressant medications within 2 years prior to screening (n = 390, or 11% of all women), 22% reported current use of these medications. Women who reported using antidepressant medications (52%) and those who discontinued them (49%) evidenced elevated depressive symptoms during pregnancy.Conclusions: Both women who discontinue and some who continue antidepressants during pregnancy demonstrate depressive symptoms, suggesting sub-optimal management of both groups. Future studies should carefully assess the adequacy of treatments prescribed as well as the monitoring and adherence of recommended treatments. Full symptom remission should be the goal for antenatal and postnatal depression in order to minimize risk to mother and baby.  相似文献   
84.
Bone substitute materials can induce bone formation in combination with mesenchymal stem cells (MSC). The aim of the current study was to examine ectopic in vivo bone formation with and without MSC on a new resorbable ceramic, called calcium deficient hydroxyapatite (CDHA). Ceramic blocks characterized by a large surface (48 m2/g) were compared with beta-tricalcium phosphate (beta-TCP), hydroxyapatite (HA) ceramics (both ca. 0.5 m2/g surface) and demineralized bone matrix (DBM). Before implantation in the back of SCID mice carriers were freshly loaded with 2x10(5) expanded human MSC or loaded with cells and kept under osteogenic conditions for two weeks in vitro. Culture conditions were kept free of xenogenic supplements. Deposits of osteoid at the margins of ceramic pores occurred independent of osteogenic pre-induction, contained human cells, and appeared in 416 MSC/CDHA composites compared to 216 MSC/beta-TCP composites. ALP activity was significantly higher in samples with MSC versus empty controls (p<0.001). Furthermore, ALP was significantly (p<0.05) higher for all ceramics when compared to the DBM matrix. Compared to previous studies, overall bone formation appeared to be reduced possibly due to the strict human protocol. Ectopic bone formation in the novel biomaterial CDHA varied considerably with the cell pool and was at least equal to beta-TCP blocks.  相似文献   
85.
Summary The majority of women who quit smoking during pregnancy will resume smoking during the postpartum period. Little is known, however, about the predictors of postpartum relapses to smoking. Changes in mood and increases in concerns about weight are common during the postpartum period, and these factors may affect womens postpartum smoking behavior. In this paper, we present a model of the relationship among mood, weight concerns and postpartum smoking. Data from previous postpartum relapse prevention trials are reviewed and evidence of a connection between changes in mood and weight concerns to postpartum relapse is presented. Directions for future research on the prevention of smoking relapses during the postpartum period, and the roles of mood and weight concerns in smoking relapse are presented.  相似文献   
86.
87.
88.
89.
Human type 1 diabetes is thought to be mediated by autoreactive T cells specific for antigens expressed by pancreatic beta cells. However, it is unclear which autoantigens and determinants thereof are the targets of the autoimmune attack. Using comprehensive peptide libraries that cover the entire sequence of two major candidate autoantigens, GAD65 and proinsulin, we measured the in vivo frequencies of peptide-specific, IFN-gamma-producing memory T cells in 27 diabetic patients, 14 high risk individuals, and 15 partially HLA-matched healthy controls. Compared to the controls, both a higher number of determinants on the islet cell antigens were recognized and the frequencies of peptide specific cells were increased in patients and high risk individuals. Inclusion of signal enhancing anti-CD28 antibody further accentuated this difference. Considerable heterogeneity in peptide recognition was seen even in DRB1*04, DQB1*0302 matched individuals. Unlike its peptides, the GAD protein antigen did not recall a T cell memory response. The highly heterogeneous recognition of a multitude of peptide determinants on both autoantigens, occurring in the absence of protein recognition, and the low functional avidity of the memory cells involved jointly suggest that the autoimmune T cell repertoire in human type 1 diabetes primarily targets cryptic determinants engaged by determinant spreading.  相似文献   
90.
BAG1 over-expression in brain protects against stroke   总被引:3,自引:0,他引:3  
The co-chaperone BAG1 binds and regulates 70 kDa heat shock proteins (Hsp70/Hsc70) and exhibits cytoprotective activity in cell culture models. Recently, we observed that BAG1 expression is induced during neuronal differentiation in the developing brain. However, the in vivo effects of BAG1 during development and after maturation of the central nervous system have never been examined. We generated transgenic mice over-expressing BAG1 in neurons. While brain development was essentially normal, cultured cortical neurons from transgenic animals exhibited resistance to glutamate-induced, apoptotic neuronal death. Moreover, in an in vivo stroke model involving transient middle cerebral artery occlusion, BAG1 transgenic mice demonstrated decreased mortality and substantially reduced infarct volumes compared to wild-type littermates. Interestingly, brain tissue from BAG1 transgenic mice contained higher levels of neuroprotective Hsp70/Hsc70 protein but not mRNA, suggesting a potential mechanism whereby BAG1 exerts its anti-apoptotic effects. In summary, BAG1 displays potent neuroprotective activity in vivo against stroke, and therefore represents an interesting target for developing new therapeutic strategies including gene therapy and small-molecule drugs for reducing brain injury during cerebral ischemia and neurodegenerative diseases.  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