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   11956篇
  免费   1177篇
  国内免费   3篇
  13136篇
  2023年   49篇
  2022年   117篇
  2021年   235篇
  2020年   100篇
  2019年   161篇
  2018年   193篇
  2017年   175篇
  2016年   321篇
  2015年   499篇
  2014年   542篇
  2013年   636篇
  2012年   914篇
  2011年   904篇
  2010年   584篇
  2009年   534篇
  2008年   749篇
  2007年   720篇
  2006年   651篇
  2005年   668篇
  2004年   673篇
  2003年   602篇
  2002年   607篇
  2001年   153篇
  2000年   116篇
  1999年   137篇
  1998年   155篇
  1997年   108篇
  1996年   105篇
  1995年   92篇
  1994年   89篇
  1993年   96篇
  1992年   75篇
  1991年   72篇
  1990年   86篇
  1989年   96篇
  1988年   79篇
  1987年   59篇
  1986年   63篇
  1985年   58篇
  1984年   67篇
  1983年   74篇
  1982年   67篇
  1981年   60篇
  1980年   58篇
  1979年   39篇
  1978年   47篇
  1977年   44篇
  1975年   33篇
  1973年   34篇
  1971年   34篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The nicotinic acid hydroxylase from Clostridium barkeri is a selenoenzyme, as evidenced by the copurification of selenium with enzyme activity. This conclusion is supported by data showing a 23-fold increase in nicotinic acid hydroxylase activity when C. barkeri was cultured in media supplemented with selenium. A labile, selenium-containing compound was released from the native protein by treatment with either chaotropic agents and heat or by heating alone. A stable selenium compound was formed when the enzyme was alkylated prior to denaturation. This compound had the same chromatographic properties as dialykyl selenide in a number of systems. The formation of dialkyl selenide upon alkylation is not consistent with the selenium moiety being selenocysteine. Thus, nicotinic acid hydroxylase represents a new type of selenoenzyme.  相似文献   
3.
4.
5.
6.
7.
Red blood cell (RBC) adhesion to vessel wall endothelium is a potent catalyst of vascular occlusion and occurs in oxidative stress states such as hemoglobinopathies and cardiovascular conditions. These are often treated with vitamin E (VitE), a “classic” antioxidant. In this study, we examined the effects of VitE on RBC adhesion to vascular endothelial cells (EC), and on translocation of phosphatidylserine (PS) to RBC surface, known as a potent mediator of RBC/EC adhesion, facilitating thrombus formation. Treatment of RBC with VitE strongly induces (up to sevenfold) PS externalization and enhances (up to 20-fold) their adherence to EC. The VitE hydrophilic analogue—Trolox—does not incorporate into cell membranes. Trolox did not exhibit any of these effects, implying that the VitE effect is due to its known ability to incorporate into cell membranes. The membrane-incorporated VitE significantly reduced the level of reactive oxygen species in H2O2-treated RBC, demonstrating that VitE elevates RBC/EC adhesion despite acting as an anti-oxidant. This study demonstrates for the first time that contrary to the common view of VitE as a beneficial supplement, VitE may introduce a circulatory risk by inducing flow-disturbing RBC adherence to blood vessel wall and the pro-thrombotic PS exposure.  相似文献   
8.
Two acrasid cellular slime molds. Guttulinopsis vulgaris and G. nivea, are compared at the ultrastructural level. The amoebae of the two species are indistinguishable except for the presence of intranuclear fibers in G. vulgaris. Both species share some unusual features, including: plate-like cristae in the mitochondria, production of microbody-like organelles in the perinuclear space, spores with thin bilaminar walls, and stalks containing microfilaments bound in striated bundles. These and other observations are discussed with regard to the development of the sorocarps and the relationship of the genus to other members of the Acrasida.  相似文献   
9.
A Monte Carlo simulation of clone growth is discussed from the point of view of clonal volume. It is shown that clone volume is a good representation of the number of cells per clone for a wide range of single cell growth equations. However, the rate at which the coefficient of variation in clonal volume approaches that of cell number per clone is strongly dependent upon the particular growth equation.  相似文献   
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