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   202275篇
  免费   50876篇
  国内免费   8188篇
耳鼻咽喉   2673篇
儿科学   5848篇
妇产科学   2993篇
基础医学   29484篇
口腔科学   7379篇
临床医学   28534篇
内科学   41511篇
皮肤病学   8582篇
神经病学   19214篇
特种医学   6517篇
外国民族医学   48篇
外科学   26744篇
综合类   21291篇
现状与发展   26篇
一般理论   44篇
预防医学   12377篇
眼科学   4479篇
药学   19009篇
  78篇
中国医学   7456篇
肿瘤学   17052篇
  2024年   367篇
  2023年   1823篇
  2022年   4598篇
  2021年   7159篇
  2020年   9163篇
  2019年   14263篇
  2018年   13876篇
  2017年   14709篇
  2016年   15176篇
  2015年   16809篇
  2014年   18236篇
  2013年   18179篇
  2012年   13150篇
  2011年   13856篇
  2010年   15012篇
  2009年   10132篇
  2008年   8530篇
  2007年   7813篇
  2006年   7663篇
  2005年   7400篇
  2004年   5838篇
  2003年   5763篇
  2002年   5346篇
  2001年   4515篇
  2000年   4051篇
  1999年   3318篇
  1998年   1778篇
  1997年   1685篇
  1996年   1433篇
  1995年   1290篇
  1994年   1097篇
  1993年   701篇
  1992年   1076篇
  1991年   867篇
  1990年   751篇
  1989年   632篇
  1988年   625篇
  1987年   557篇
  1986年   458篇
  1985年   350篇
  1984年   219篇
  1983年   171篇
  1982年   91篇
  1981年   103篇
  1980年   84篇
  1979年   120篇
  1978年   56篇
  1977年   61篇
  1976年   51篇
  1975年   46篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Measurements of the fetal eyeball and its pattern of growth   总被引:1,自引:0,他引:1  
  相似文献   
22.
Transient transfection of pLB2CAT constructs bearing short synthetic oligonucleotides derived either from the tyrosine hydroxylase (TH) promoter or other sources was used to examine functional cAMP regulatory element (CRE) activity in a variety of cell lines. The region containing only the putative TH CRE was found to be as or more effective in conferring cAMP responsiveness onto pLB2CAT (which employs the TK promoter) than the immediate 272 bp region of the TH promoter. Increases in CAT activity of 10- to 20-fold were observed in JEG-3 cells with a single insert of the TH CRE region (-31 to -54) in pLB2CAT, and the presence of a second insert generated only a modest further increase. This construct also responded to cAMP in 4 other cell lines tested but the degree of increase was less dramatic. Inserts containing the consensus 8 bp CRE motif embedded in other natural or artificial contexts served generally as weak functional CREs in all cell lines tested. In vitro analysis revealed that a specific protein-DNA complex apparently containing a single protein with a MW of 45-50 kDa was formed equally well with JEG-3 cell nuclear extract and CRE-bearing-TH and other fragments which produced dramatically different cAMP effects in vivo. These results suggest specificity in the effects of cAMP on different CREs which are dictated by contextual differences.  相似文献   
23.
24.
Dry skin (xerosis) is a common dermatosis affecting people of varying skin types and ages and various areas of the body. It is associated with both skin thickening and skin thinning and is triggered by both exogenous (e.g. climate, environment, lifestyle) and endogenous (e.g. medication, hormone fluctuations, organ diseases) factors. Skin requires a water content of 10–15% to remain supple and intact. This water is either ‘static’ (i.e. bound) or ‘dynamic’. The predominance of hydrophobic substances in intercellular constituents is a means of regulating the humidity of the skin. Emollients, highly effective treatment adjuncts in the management of all dry skin disorders, help to restore damaged intercorneocyte lipid structures and increase the water content of the skin, helping to reduce scaling and improving its barrier function.  相似文献   
25.
OBJECTIVES: To explore the morphological and functional findings of transvaginal sonography (TVS) in the diagnosis and management of distal ureteral calculi. METHODS: We retrospectively reviewed the imaging studies in seven cases of distal ureteral calculi (study group) and 20 cases of female volunteers without urinary tract infection (control group). All 27 patients had undergone TVS for assessment of the lower urinary tract. The variables measured on ultrasound included the presence or absence of distal ureteral calculi, the size and location of a calculus if present, the presence or absence of the ureter jet phenomenon, morphological changes of the ureteral papilla and adjoining tissue, and the height of the ureteral papilla, as well as vascular changes seen on Doppler imaging. RESULTS: In the controls, 80% of the ureteral papillae were triangular and 20% trapezoidal. The average (+/-SD) height of the ureteral papillae was 3.5 +/- 0.7 mm on the right and 3.6 +/- 0.9 mm on the left. There was no statistically significant difference between the heights of the right and left papillae (P = 0.619). In the study group, echogenic stones were identified in all seven patients and a hypoechogenic tubular structure connected to the involved papilla was identified in 6/7 patients. The average height of the involved papilla was 6.7 +/- 1.6 mm. Ureteric jets were visible in all patients in both the study and control groups. CONCLUSION: In patients with distal ureteral calculi, TVS provides a rapid, non-invasive and repeatable means of assessing the morphology and function of the distal ureter.  相似文献   
26.
27.
28.
29.
Ganoderma sinensis has been used widely in Oriental countries for the prevention and treatment of various diseases including cancer. Previous studies have shown that the lipid extract from Ganoderma exhibits direct cytotoxicity against tumor cells. Here, it is reported that the lipid extract from germinating G. sinensis spores, at lower concentrations that have no direct tumoricidal activity, induce potent antitumor immune responses in human monocytes/macrophages. Upon stimulation with the lipid extract, monocytes/macrophages exhibited markedly increased production of proinflammatory cytokines and surface expression of costimulatory molecules. Conditioned medium from stimulated cells effectively suppressed the growth of tumor cells. Apparently, the lipid extract triggered macrophage activation via a mechanism different from that associated with LPS. Moreover, it was observed that the lipid extract could partially re‐establish the antitumor activity of the immunosuppressive tumor‐associated macrophages. These results indicated that in addition to its direct tumoricidal activity, the lipid extract from G. sinensis spores could exert antitumor activity by stimulating the activation of human monocytes/macrophages. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
30.
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