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   379521篇
  免费   43864篇
  国内免费   219篇
  2018年   3479篇
  2016年   4946篇
  2015年   6985篇
  2014年   8061篇
  2013年   11247篇
  2012年   14052篇
  2011年   14231篇
  2010年   9027篇
  2009年   7972篇
  2008年   12402篇
  2007年   12719篇
  2006年   12075篇
  2005年   11615篇
  2004年   11247篇
  2003年   11041篇
  2002年   10694篇
  2001年   13025篇
  2000年   13199篇
  1999年   10618篇
  1998年   4657篇
  1997年   4547篇
  1996年   4535篇
  1995年   4180篇
  1994年   4213篇
  1993年   4140篇
  1992年   8994篇
  1991年   8633篇
  1990年   8386篇
  1989年   8305篇
  1988年   7820篇
  1987年   7726篇
  1986年   7174篇
  1985年   7374篇
  1984年   6397篇
  1983年   5743篇
  1982年   4719篇
  1981年   4521篇
  1980年   4135篇
  1979年   6395篇
  1978年   5103篇
  1977年   4839篇
  1976年   4653篇
  1975年   4959篇
  1974年   5423篇
  1973年   5283篇
  1972年   4828篇
  1971年   4396篇
  1970年   3870篇
  1969年   3880篇
  1968年   3451篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Establishment of pregnancy in cattle has been proposed to depend on production of a conceptus protein, bovine trophoblast protein-1 (bTP-1), which has a high degree of sequence homology with bovine interferon-alpha (bIFN-alpha), especially the alpha II subfamily. A preparation of bovine conceptus secretory proteins enriched for bTP-1 has antiviral and physico-chemical properties similar to other bIFN-alpha. Antiviral activity is initially detectable in uterine flushings on Day 14 of pregnancy, when the conceptus measures 4-5 mm in length, and increases as the conceptus elongates through Day 18. Day 17 conceptuses produce more than 10(6) U antiviral activity during 24 h of culture. All IFNs induce the enzyme 2',5'-oligoadenylate synthetase, which catalyzes production of 2',5'-oligo(A), which in turn is involved in antiviral and growth inhibitory effects of IFNs. This enzyme activity is induced in Madin-Darby bovine kidney cells by the partially purified bTP-1 preparation similarly to IFN-alpha, -beta, and -gamma. Likewise, the partially purified bTP-1 and bIFN-alpha 1 induce 2',5'-oligo(A) synthetase activity in monolayers of endometrial epithelial and stromal cells. Compared to epithelial cells, stromal cells have higher baseline activity of 2'-5'-oligo(A) synthetase activity (p less than 0.01) and show a greater degree of induction in the presence of either the partially purified bTP-1 or bIFN-alpha 1 (p less than 0.01). Also, 2',5'-oligo(A) synthetase of endometrial stromal cells is induced to a greater degree by our enriched bTP-1 preparation than by bIFN-alpha 1 (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
112.
113.
114.
115.
Georg Söderbom 《Ethnos》2013,78(1-2):95-100
Current debates over the concept of culture are examined, especially with regard to the relationship of culture to bounded collectivities, human nature, and individuality; present‐day views are seen against the background of back‐and‐forth swings in the history of anthropological thought. Recent theorizing about cultural acquisition is also considered.  相似文献   
116.
Selective diapedesis of Th1 cells induced by endothelial cell RANTES.   总被引:16,自引:0,他引:16  
Differentiated CD4 T cells can be divided into Th1 and Th2 types based on the cytokines they produce. Differential expression of chemokine receptors on either the Th1-type or the Th2-type cell suggests that Th1-type and Th2-type cells differ not only in cytokine production but also in their migratory capacity. Stimulation of endothelial cells with IFN-gamma selectively enhanced transmigration of Th1-type cells, but not Th2-type cells, in a transendothelial migration assay. Enhanced transmigration of Th1-type cells was dependent on the chemokine RANTES produced by endothelial cells, as indicated by the findings that Ab neutralizing RANTES, or Ab to its receptor CCR5, inhibited transmigration. Neutralizing Ab to chemokines macrophage-inflammatory protein-1alpha or monocyte chemotactic protein-1 did not inhibit Th1 selective migration. Whereas anti-CD18 and anti-CD54 blocked basal levels of Th1-type cell adherence to endothelial cells and also inhibited transmigration, anti-RANTES blocked only transmigration, indicating that RANTES appeared to induce transmigration of adherent T cells. RANTES seemed to promote diapedesis of adherent Th1-type cells by augmenting pseudopod formation in conjunction with actin rearrangement by a pathway that was sensitive to the phosphoinositol 3-kinase inhibitor wortmannin and to the Rho GTP-binding protein inhibitor, epidermal cell differentiation inhibitor. Thus, enhancement of Th1-type selective migration appeared to be responsible for the diapedesis induced by interaction between CCR5 on Th1-type cells and RANTES produced by endothelial cells. Further evidence that CCR5 and RANTES play a modulatory role in Th1-type selective migration derives from the abrogation of this migration by anti-RANTES and anti-CCR5 Abs.  相似文献   
117.
Variability of pseudocholinesterase   总被引:1,自引:0,他引:1  
  相似文献   
118.
119.
120.
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