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   531849篇
  免费   59285篇
  国内免费   326篇
  2018年   5237篇
  2017年   5098篇
  2016年   6962篇
  2015年   8789篇
  2014年   10510篇
  2013年   15308篇
  2012年   16999篇
  2011年   17377篇
  2010年   11720篇
  2009年   10769篇
  2008年   15189篇
  2007年   15760篇
  2006年   14701篇
  2005年   14093篇
  2004年   13956篇
  2003年   13332篇
  2002年   12846篇
  2001年   28355篇
  2000年   28226篇
  1999年   21872篇
  1998年   6547篇
  1997年   7149篇
  1996年   6544篇
  1995年   6230篇
  1994年   5988篇
  1993年   5969篇
  1992年   17061篇
  1991年   16306篇
  1990年   15714篇
  1989年   15219篇
  1988年   13938篇
  1987年   12955篇
  1986年   12055篇
  1985年   11818篇
  1984年   9666篇
  1983年   8098篇
  1982年   6001篇
  1981年   5387篇
  1980年   5104篇
  1979年   8946篇
  1978年   6817篇
  1977年   6273篇
  1976年   5652篇
  1975年   6238篇
  1974年   6760篇
  1973年   6541篇
  1972年   5978篇
  1971年   5433篇
  1970年   4683篇
  1969年   4401篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Characteristics of morphology and number of melanomacrophage centers (MMCs) in the liver and spleen of the roach Rutilus rutilus and the amount of pigments in MMCs during the Haff disease outbreak and the death of fish in Lake Kotokel in relation to these parameters in the roach from Lake Baikal are described. Pathological changes in the microvasculature and parenchyma in the liver of the roach from Lake Kotokel were found. The area of melanomacrophage centers in the liver of the roach from this lake was significantly smaller, whereas the number and size of these centers in the spleen was significantly larger than in the roaches from Lake Baikal. Among the pigments studied, the strongest response to the content of this toxin in the water body was shown by hemosiderin. An increase in its amount in the spleen MMCs testifies to an enhanced degradation of erythrocytes and iron release, which may be caused by the damage of cells of the erythrocyte lineage by the toxin.  相似文献   
2.
3.
Developmental axon branching dramatically increases synaptic capacity and neuronal surface area. Netrin-1 promotes branching and synaptogenesis, but the mechanism by which Netrin-1 stimulates plasma membrane expansion is unknown. We demonstrate that SNARE-mediated exocytosis is a prerequisite for axon branching and identify the E3 ubiquitin ligase TRIM9 as a critical catalytic link between Netrin-1 and exocytic SNARE machinery in murine cortical neurons. TRIM9 ligase activity promotes SNARE-mediated vesicle fusion and axon branching in a Netrin-dependent manner. We identified a direct interaction between TRIM9 and the Netrin-1 receptor DCC as well as a Netrin-1–sensitive interaction between TRIM9 and the SNARE component SNAP25. The interaction with SNAP25 negatively regulates SNARE-mediated exocytosis and axon branching in the absence of Netrin-1. Deletion of TRIM9 elevated exocytosis in vitro and increased axon branching in vitro and in vivo. Our data provide a novel model for the spatial regulation of axon branching by Netrin-1, in which localized plasma membrane expansion occurs via TRIM9-dependent regulation of SNARE-mediated vesicle fusion.  相似文献   
4.
5.
6.
The kidneys are exposed to hypoxic conditions during development. Hypoxia-inducible factor (HIF), an important mediator of the response to hypoxia, is believed to have an important role in development. However, the relationship between HIF and branching morphogenesis has not been elucidated clearly.  相似文献   
7.
The present work aimed to study the effect of palm pollen extract (PPE) as an anticoccidial and anti-apoptotic modulator during the course of murine intestinal Eimeria papillata infection. The fact that PPE has an anticoccidial efficacy against intestinal E. papillata infection in mice has been clarified by the reduction of faecal output of oocysts on day five post infection from 49.5 × 103 to 34 × 103 oocyst/g. Moreover, the number of intracellular eimerian stages of zygots and developing oocysts decreased by about 89% and that of schizonts and gamonts to 42% and 72%, respectively. E. papillata infection also induced an increase in the number of apoptotic cells from 17.5 to 122.8 apoptotic nuclei/10 villous crypt units (VCU). In addition, it caused a state of systemic inflammatory response as revealed by an elevation in levels of the pro-inflammatory biomarkers, inducible nitric oxide synthase (iNOs) and tumor necrosis factor alpha (TNF-α) from 5.3 and 78.3 to 33 pmol ml?1 and 96.3 pg ml?1 in blood, respectively, with concurrent duplication in the total leucocytic number. Upon treatment of infected mice with the aqueous PPE, the activity of iNOs was reduced by 55% and the level of TNF-α was decreased by 30%. Moreover, the total leucocytic count was significantly reduced from 9.05 × 103 to 7.8 × 103 cells/mm3. Based on our results, PPE showed both anti-coccidial, anti-inflammatory and anti-apoptotic activities. So it can be used in developing new herbal medicine against animal coccidiosis and may be suitable agent for treating eimeriosis associated inflammatory response.  相似文献   
8.
9.
10.
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