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   3040919篇
  免费   243596篇
  国内免费   6156篇
耳鼻咽喉   43501篇
儿科学   96916篇
妇产科学   82676篇
基础医学   431745篇
口腔科学   88369篇
临床医学   278863篇
内科学   589059篇
皮肤病学   64558篇
神经病学   253533篇
特种医学   120756篇
外国民族医学   1131篇
外科学   457699篇
综合类   72525篇
现状与发展   1篇
一般理论   1310篇
预防医学   246392篇
眼科学   71834篇
药学   225430篇
  7篇
中国医学   5752篇
肿瘤学   158614篇
  2018年   31937篇
  2017年   24663篇
  2016年   27604篇
  2015年   30742篇
  2014年   43735篇
  2013年   67285篇
  2012年   89944篇
  2011年   95227篇
  2010年   56269篇
  2009年   53229篇
  2008年   90168篇
  2007年   95946篇
  2006年   96699篇
  2005年   93945篇
  2004年   90919篇
  2003年   87764篇
  2002年   85934篇
  2001年   138868篇
  2000年   143977篇
  1999年   121064篇
  1998年   35308篇
  1997年   31998篇
  1996年   31566篇
  1995年   30587篇
  1994年   28739篇
  1993年   26684篇
  1992年   97422篇
  1991年   94410篇
  1990年   91484篇
  1989年   88238篇
  1988年   81505篇
  1987年   80662篇
  1986年   76256篇
  1985年   73121篇
  1984年   55512篇
  1983年   47344篇
  1982年   28943篇
  1981年   25794篇
  1979年   52134篇
  1978年   36837篇
  1977年   31186篇
  1976年   29394篇
  1975年   30873篇
  1974年   38000篇
  1973年   36177篇
  1972年   33715篇
  1971年   31299篇
  1970年   29261篇
  1969年   27279篇
  1968年   24942篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Bipolar disorder (BD) is a common psychiatric mood disorder affecting more than 1-2% of the general population of different European countries. Unfortunately, there is no objective laboratory-based test to aid BD diagnosis or monitor its progression, and little is known about the molecular basis of BD. Here, we performed a comparative proteomic study to identify differentially expressed plasma proteins in various BD mood states (depressed BD, manic BD, and euthymic BD) relative to healthy controls. A total of 10 euthymic BD, 20 depressed BD, 15 manic BD, and 20 demographically matched healthy control subjects were recruited. Seven high-abundance proteins were immunodepleted in plasma samples from the 4 experimental groups, which were then subjected to proteome-wide expression profiling by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight tandem mass spectrometry. Proteomic results were validated by immunoblotting and bioinformatically analyzed using MetaCore. From a total of 32 proteins identified with 1.5-fold changes in expression compared with healthy controls, 16 proteins were perturbed in BD independent of mood state, while 16 proteins were specifically associated with particular BD mood states. Two mood-independent differential proteins, apolipoprotein (Apo) A1 and Apo L1, suggest that BD pathophysiology may be associated with early perturbations in lipid metabolism. Moreover, down-regulation of one mood-dependent protein, carbonic anhydrase 1 (CA-1), suggests it may be involved in the pathophysiology of depressive episodes in BD. Thus, BD pathophysiology may be associated with early perturbations in lipid metabolism that are independent of mood state, while CA-1 may be involved in the pathophysiology of depressive episodes.  相似文献   
72.
Hepatic NADPH-cytochrome P450 oxidoreductase null (HRN?) mice exhibit normal hepatic and extrahepatic biotransformation enzyme activities when compared to wild-type (WT) mice, but express no functional hepatic cytochrome P450 activities. When incubated in vitro with [14C]-diclofenac, liver microsomes from WT mice exhibited extensive biotransformation to oxidative and glucuronide metabolites and covalent binding to proteins was also observed. In contrast, whereas glucuronide conjugates and a quinone-imine metabolite were formed when [14C]-diclofenac was incubated with HRN? mouse liver, only small quantities of P450-derived oxidative metabolites were produced in these samples and covalent binding to proteins was not observed. Livers from vehicle-treated HRN? mice exhibited enhanced lipid accumulation, bile duct proliferation, hepatocellular degeneration and necrosis and inflammatory cell infiltration, which were not present in livers from WT mice. Elevated liver-derived alanine aminotransferase, glutamate dehydrogenase and alkaline phosphatase activities were also observed in plasma from HRN? mice. When treated orally with diclofenac for 7 days, at 30 mg/kg/day, the severities of the abnormal liver histopathology and plasma liver enzyme findings in HRN? mice were reduced markedly. Oral diclofenac administration did not alter the liver histopathology or elevate plasma enzyme activities of WT mice. These findings indicate that HRN? mice are valuable for exploration of the role played by hepatic P450s in drug biotransformation, but poorly suited to investigations of drug-induced liver toxicity. Nevertheless, studies in HRN? mice could provide novel insights into the role played by inflammation in liver injury and may aid the evaluation of new strategies for its treatment.  相似文献   
73.
74.
75.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
76.
77.
78.
79.
Nidogen 1 (NID1) is a glycoprotein found in basement membranes involved in cross-linking collagen IV and laminin. The role of NID in breast cancer has only been evaluated in a small number of studies and the findings of these studies have been inconsistent. Our previous work revealed that highly tumorigenic murine mammary tumor cells express high levels of Nid1 while weakly tumorigenic mammary tumor cells express low levels of Nid1. To investigate Nid1, two stable knockdown lines were created, and Nid1 knockdown was confirmed at both the mRNA and protein level. Nid1 knockdown significantly reduced cell proliferation and migration/invasion and these reductions in proliferation and migration/invasion could be rescued by conditioned media containing NID1 protein. The reduced migration/invasion observed in the Nid1 knockdown cells was not associated with significant alterations in the epithelial gene Cdh1 or the mesenchymal genes Snai1, Snai2, Twist1, Twist2, Zeb1 and Zeb2. Therefore, suppression of Nid1 expression reduces proliferation and migration/invasion in claudin-low murine mammary tumor cells.  相似文献   
80.
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