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   1336166篇
  免费   117464篇
  国内免费   1422篇
  2021年   17949篇
  2020年   12683篇
  2019年   16245篇
  2018年   17723篇
  2017年   16527篇
  2016年   28231篇
  2015年   42758篇
  2014年   50779篇
  2013年   77219篇
  2012年   37876篇
  2011年   26335篇
  2010年   44057篇
  2009年   45248篇
  2008年   25002篇
  2007年   23248篇
  2006年   28521篇
  2005年   29359篇
  2004年   28891篇
  2003年   26412篇
  2002年   24517篇
  2001年   31452篇
  2000年   28614篇
  1999年   29534篇
  1998年   25320篇
  1997年   25041篇
  1996年   24689篇
  1995年   22829篇
  1994年   22660篇
  1993年   21719篇
  1992年   26050篇
  1991年   24264篇
  1990年   22931篇
  1989年   23814篇
  1988年   21864篇
  1987年   20770篇
  1986年   19649篇
  1985年   21628篇
  1984年   21797篇
  1983年   19348篇
  1982年   20258篇
  1981年   19483篇
  1980年   18234篇
  1979年   18172篇
  1978年   17107篇
  1977年   16620篇
  1976年   15732篇
  1975年   15049篇
  1974年   15468篇
  1973年   15951篇
  1972年   13522篇
排序方式: 共有10000条查询结果,搜索用时 935 毫秒
991.
992.
993.
In recent years, Staphylococcus epidermidis has become a major nosocomial pathogen and the most common cause of intravascular catheter-related bacteremia, which can increase morbidity and mortality and significantly affect patient recovery. We report a draft genome sequence of Staphylococcus epidermidis AU12-03, isolated from an intravascular catheter tip.  相似文献   
994.
This Perspective addresses one of the major puzzles of adipogenesis in adipose tissue, namely its resistance to cellular stress. It introduces a concept of “density” of integrin binding sites in extracellular matrix, proposes a cellular signaling explanation for the observed effects of matrix elasticity and of cell shape on mesenchymal stem cell differentiation, and discusses how specialized integrin binding sites in collagen IV-containing matrices guard two pivotal physiological and evolutionary processes: stress-resistant adipogenesis in adipose tissues and preservation of pluripotency of mesenchymal stem-like cells in their storage niches. Finally, it proposes strategies to suppress adipogenesis in adipose tissues.  相似文献   
995.
996.
The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately.  相似文献   
997.
998.
999.
B.H. Vickery  G.I. McRae 《Life sciences》1980,27(15):1409-1413
Fourteen regularly cycling female rhesus monkeys were observed daily for menstruation and bled from the saphenous vein at regular intervals throughout the study. Plasma samples were assayed by RIA for progesterone levels. The animals were divided into 3 subgroups. The first (n=5) received daily subcutaneous injections of 1000 IU hCG from the 18th to 36th day following onset of menstruation. The second (n=7) received the same hCG treatment and was also implanted subcutaneously from the 18th to 40th days with 1.2 mg [Des-gly10, DTrp6, ProNHEt9] LHRH contained in cholesterol matrix pellets. The third (n=2) was untreated. Intermenstrual interval was significantly extended by hCG treatment. The extension was partially overcome by the LHRH agonist. The hCG-induced elevation in plasma progesterone to peak values over 17ng/ml was blocked by the LHRH agonist to give mean values not significantly different from control luteal phase levels. Plasma estradiol levels were unaffected by hCG or LHRH agonist.  相似文献   
1000.
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