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   249篇
  免费   21篇
  国内免费   17篇
  2023年   4篇
  2022年   7篇
  2021年   14篇
  2020年   5篇
  2018年   7篇
  2017年   5篇
  2016年   5篇
  2015年   6篇
  2014年   8篇
  2013年   10篇
  2012年   15篇
  2011年   15篇
  2010年   13篇
  2009年   14篇
  2008年   11篇
  2007年   21篇
  2006年   12篇
  2005年   13篇
  2004年   9篇
  2003年   8篇
  2002年   6篇
  2001年   9篇
  2000年   9篇
  1999年   5篇
  1998年   8篇
  1997年   3篇
  1996年   3篇
  1993年   2篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   3篇
  1987年   3篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   5篇
  1977年   4篇
  1976年   2篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1966年   1篇
  1965年   1篇
排序方式: 共有287条查询结果,搜索用时 15 毫秒
11.
Standard esophageal ballon with silver electrodes implanted in it is suggested for simultaneous registration of the hysteresis loop and electromyogram of the diaphragm. The method provides qualitatively new information on the work of the respiratory muscles.  相似文献   
12.
13.
This study combined morphological and morphometric information on egg clutches, egg capsules and paralarvae of two sympatric coastal octopuses from New Zealand waters, Octopus huttoni and Pinnoctopus cordiformis, to provide species-specific traits to identify their early life stages obtained from field surveys. Eggs of O. huttoni (2.5 mm length; 1 mm width) were entwined with one another forming strings that ranged from 11 to 25.8 mm in length. Eggs of P. cordiformis (6.4 mm length; 1.5 mm width) were significantly bigger than those of O. huttoni and were grouped in small clusters of about seven eggs. Paralarvae O. huttoni and P. cordiformis differed in hatching size (1.4 mm versus 3.1 mm mantle length), number of suckers per arm (four versus eight), number of lamellae per outer demibranch (five versus ten) and arrangements of chromatophores in the body surface (29 to 59 versus 91 to 179), respectively. The morphological traits described in hatchlings from the laboratory allowed comparisons with field-collected paralarvae, suggesting that such characters were reliable species-specific patterns to enable a consistent differentiation between the early life stages of these two sympatric species, even in the absence of the brooding female.  相似文献   
14.
Rotavirus is a major cause of pediatric diarrheal illness worldwide. To explore the role of organized intestinal lymphoid tissues in infection by and immunity to rotavirus, lymphotoxin alpha-deficient (LTα−/−) mice that lack Peyer''s patches and mesenteric lymph nodes were orally infected with murine rotavirus. Systemic rotavirus was cleared within 10 days in both LTα−/− and wild-type mice, and both strains developed early and sustained serum antirotavirus antibody responses. However, unlike wild-type mice, which resolved the intestinal infection within 10 days, LTα−/− mice shed fecal virus for approximately 50 days after inoculation. The resolution of fecal virus shedding occurred concurrently with induction of intestinal rotavirus-specific IgA in both mouse strains. Induction of intestinal rotavirus-specific IgA in LTα−/− mice correlated with the (late) appearance of IgA-producing plasma cells in the small intestine. This, together with the absence of rotavirus-specific serum IgA, implies that secretory rotavirus-specific IgA was produced locally. These findings indicate that serum IgG responses are insufficient and imply that local intestinal IgA responses are important for the clearance of rotavirus from intestinal tissues. Furthermore, they show that while LTα-dependent lymphoid tissues are important for the generation of IgA-producing B cells in the intestine, they are not absolutely required in the setting of rotavirus infection. Moreover, the induction of local IgA-producing B cell responses can occur late after infection and in an LTα-independent manner.  相似文献   
15.
Endothelial progenitor cells (EPC) participate in revascularization and angiogenesis. EPC can be cultured in vitro from mononuclear cells of peripheral blood, umbilical cord blood or bone marrow; they also can be transdifferentiated from mesenchymal stem cells (MSC). We isolated EPCs from Wharton's jelly (WJ) using two methods. The first method was by obtaining MSC from WJ and characterizing them by flow cytometry and their adipogenic and osteogenic differentiation, then applying endothelial growth differentiating media. The second method was by direct culture of cells derived from WJ into endothelial differentiating media. EPCs were characterized by morphology, Dil-LDL uptake/UEA-1 immunostaining and testing the expression of endothelial markers by flow cytometry and RT-PCR. We found that MSC derived from WJ differentiated into endothelial-like cells using simple culture conditions with endothelium induction agents in the medium.  相似文献   
16.

Recent field surveys performed in the newly-discovered Taurida Cave (Crimea, Russia, Late Villafranchian, 1.8–1.5 Ma) enabled us to unearth dentognathic remains of the dirk-toothed cat Megantereon. Here we describe in detail the recovered remains further comparing it anatomically and biometrically with coeval Eurasian and African sites. The performed analysis suggests the inclusion of the Taurida remains in the hypodigm of the Villafranchain European species Megantereon adroveri, a medium-sized saber-toothed cat poorly known in Europe as a consequence of the scarcity and fragmentary nature of the known remains. Our results and the putative transitional characters displayed by the Taurida specimen support the idea put forward by previous authors of a continuous European lineage of dirk-toothed cats.

  相似文献   
17.
为了合理利用羌活和宽叶羌活的药用植物资源,同时保护其物种多样性,该研究利用SSR分子标记技术对羌活与宽叶羌活邻域及异域分布的23个自然种群,共计227个个体进行多样性和种间分化研究.结果显示:(1)两个物种具有中等水平的遗传多样性;羌活的平均等位基因数(Na)、有效等位基因数(Ne)和期望杂合度(He)分别为2.603...  相似文献   
18.
19.
20.
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