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   4246篇
  免费   399篇
  2021年   51篇
  2020年   28篇
  2019年   25篇
  2018年   49篇
  2017年   43篇
  2016年   81篇
  2015年   138篇
  2014年   140篇
  2013年   191篇
  2012年   247篇
  2011年   225篇
  2010年   143篇
  2009年   135篇
  2008年   182篇
  2007年   205篇
  2006年   195篇
  2005年   208篇
  2004年   204篇
  2003年   183篇
  2002年   188篇
  2001年   60篇
  2000年   40篇
  1999年   53篇
  1998年   63篇
  1997年   42篇
  1996年   45篇
  1995年   55篇
  1994年   58篇
  1993年   49篇
  1992年   45篇
  1991年   31篇
  1990年   38篇
  1989年   27篇
  1987年   37篇
  1986年   27篇
  1985年   29篇
  1984年   37篇
  1983年   37篇
  1982年   50篇
  1981年   44篇
  1980年   41篇
  1979年   26篇
  1978年   40篇
  1977年   28篇
  1976年   32篇
  1975年   29篇
  1974年   37篇
  1973年   38篇
  1972年   26篇
  1967年   23篇
排序方式: 共有4645条查询结果,搜索用时 31 毫秒
971.
972.
In this article I have the following principle aims: first to demonstrate the intertextuality of the film roles of Humphrey Bogart during the decades of the 1930s to the 1950s; second, to show how the transformation of persona in film roles relates to changes in the social and cultural environment of that period; and finally, as an outcome of this examination, I consider the dialectic of contrast and continuity in terms of how it provides an understanding of “otherness.”  相似文献   
973.
We provide histological details of the development of oocytes in the cyprinodontid flagfish, Jordanella floridae. There are six stages of oogenesis: Oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis [PG]), secondary growth (vitellogenesis), oocyte maturation and ovulation. The ovarian lamellae are lined by a germinal epithelium composed of epithelial cells and scattered oogonia. During primary growth, the development of cortical alveoli and oil droplets, are initiated simultaneously. During secondary growth, yolk globules coalesce into a fluid mass. The full‐grown oocyte contains a large globule of fluid yolk. The germinal vesicle is at the animal pole, and the cortical alveoli and oil droplets are located at the periphery. The disposition of oil droplets at the vegetal pole of the germinal vesicle during late secondary growth stage is a unique characteristic. The follicular cell layer is composed initially of a single layer of squamous cells during early PG which become columnar during early vitellogenesis. During primary and secondary growth stages, filaments develop among the follicular cells and also around the micropyle. The filaments are seen extending from the zona pellucida after ovulation. During ovulation, a space is evident between the oocyte and the zona pellucida. Asynchronous spawning activity is confirmed by the observation that, after ovulation, the ovarian lamellae contain follicles in both primary and secondary growth stages; in contrast, when the seasonal activity of oogenesis and spawning ends, after ovulation, the ovarian lamellae contain only follicles in the primary growth stage. J. Morphol. 277:1339–1354, 2016. © 2016 Wiley Periodicals, Inc.  相似文献   
974.
975.
The design, synthesis and assessment of β-carboline core-based compounds as potential multifunctional agents against several processes that are believed to play a significant role in Alzheimer’s disease (AD) pathology, are described. The activity of the compounds was determined in Aβ self-assembly (fibril and oligomer formation) and cholinesterase (AChE, BuChE) activity inhibition, and their antioxidant properties were also assessed. To obtain insight into the mode of action of the compounds, HR-MS studies were carried out on the inhibitor-Aβ complex formation and molecular docking was performed on inhibitor-BuChE interactions. While several compounds exhibited strong activities in individual assays, compound 14 emerged as a promising multi-target lead for the further structure-activity relationship studies.  相似文献   
976.
977.
978.
979.
xynB is one of at least four genes from the cellulolytic rumen anaerobe Ruminococcus flavefaciens 17 that encode xylanase activity. The xynB gene is predicted to encode a 781-amino acid product starting with a signal peptide, followed by an amino-terminal xylanase domain which is identical at 89% and 78% of residues, respectively, to the amino-terminal xylanase domains of the bifunctional XynD and XynA enzymes from the same organism. Two separate regions within the carboxy-terminal 537 amino acids of XynB also show close similarities with domain B of XynD. These regions show no significant homology with cellulose- or xylan-binding domains from other species, or with any other sequences, and their functions are unknown. In addition a 30 to 32-residue threonine-rich region is present in both XynD and XynB. Codon usage shows a consistent pattern of bias in the three xylanase genes from R. flavefaciens that have been sequenced.  相似文献   
980.
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