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   318649篇
  免费   33781篇
  国内免费   257篇
  2018年   3128篇
  2017年   3065篇
  2016年   4074篇
  2015年   5212篇
  2014年   5893篇
  2013年   9218篇
  2012年   10962篇
  2011年   11588篇
  2010年   7183篇
  2009年   6165篇
  2008年   10180篇
  2007年   10390篇
  2006年   9832篇
  2005年   9240篇
  2004年   9047篇
  2003年   8703篇
  2002年   8501篇
  2001年   13013篇
  2000年   13270篇
  1999年   10127篇
  1998年   3778篇
  1997年   3940篇
  1996年   3895篇
  1995年   3452篇
  1994年   3457篇
  1993年   3420篇
  1992年   8207篇
  1991年   8130篇
  1990年   7756篇
  1989年   7713篇
  1988年   7077篇
  1987年   6824篇
  1986年   6205篇
  1985年   6480篇
  1984年   5487篇
  1983年   4640篇
  1982年   3663篇
  1981年   3411篇
  1980年   3188篇
  1979年   5183篇
  1978年   4051篇
  1977年   3940篇
  1976年   3664篇
  1975年   4056篇
  1974年   4375篇
  1973年   4274篇
  1972年   3777篇
  1971年   3559篇
  1970年   3184篇
  1969年   3093篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
91.
92.
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   
93.
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   
94.
95.
96.
97.
98.
A new fern-like fossil plant is described from the lower Upper Devonian of southern Ellesmere Island, Canadian Arctic Archipelago. The plant occurs in an Archaeopteris-dominated flora preserved in the Nordstrand Point Formation (Mid-Late Frasnian) near Bird Fiord. The plant has a pinnate vegetative system with three branch orders and laminate sphenopteroid pinnules. Primary pinnae usually diverge from the main axis in distichous pairs (quadriseriate), but can depart singly (biseriate). Each primary pinna bears a basal catadromic aphlebia. Anatomically, the plant exhibits a mesarch, bipolar protostele that is ribbon- to clepsydropsoid-shaped in the main axis. Primary pinna traces are also initially bipolar and crescent-shaped, but may become four-ribbed before dividing into a pair of bipolar traces. The morphology and anatomy of this plant are nongymnospermous and are most similar to Zygopteridales (particularly Rhacophytaceae and Zygopteridaceae). The Frasnian age of Ellesmeris shows that laminated foliage had evolved in some zygopterid ferns much earlier than previously recognized. The Sphenopteris-like pinnules of Ellesmeris indicate the need for caution when attributing such a convergent foliar design to other plant groups, such as the Devonian gymnosperms.  相似文献   
99.
A method is described which allows a clear demonstration of capillaries and muscle fibers in the heart and skeletal muscle of experimental animals. The fluorescent dyes fluorescein isothiocyanate (FITC) and lissamine rhodamine B 200 (RB 200) were conjugated with a protein of high (gamma-globulin) and low (myoglobin) molecular weight, respectively, and were intravitally injected into the vascular system of rats. FITC globulin distributes itself in the intravasal space and RB 200 myoglobin in the extracellular. In histological sections the capillary lumina and the borderlines of the muscular fibers can be clearly identified and quantitatively evaluated because of the selective fluorescence in the respective structures.  相似文献   
100.
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