全文获取类型
收费全文 | 1623832篇 |
免费 | 152965篇 |
国内免费 | 1747篇 |
专业分类
1778544篇 |
出版年
2021年 | 18262篇 |
2019年 | 16279篇 |
2018年 | 19149篇 |
2017年 | 17990篇 |
2016年 | 29239篇 |
2015年 | 43249篇 |
2014年 | 51365篇 |
2013年 | 77579篇 |
2012年 | 46932篇 |
2011年 | 37913篇 |
2010年 | 47036篇 |
2009年 | 47267篇 |
2008年 | 34791篇 |
2007年 | 33465篇 |
2006年 | 36710篇 |
2005年 | 37790篇 |
2004年 | 36915篇 |
2003年 | 34185篇 |
2002年 | 32061篇 |
2001年 | 51787篇 |
2000年 | 49631篇 |
1999年 | 44897篇 |
1998年 | 27566篇 |
1997年 | 27386篇 |
1996年 | 26540篇 |
1995年 | 24710篇 |
1994年 | 24326篇 |
1993年 | 23553篇 |
1992年 | 37814篇 |
1991年 | 35885篇 |
1990年 | 34491篇 |
1989年 | 34937篇 |
1988年 | 32181篇 |
1987年 | 30216篇 |
1986年 | 28584篇 |
1985年 | 29991篇 |
1984年 | 28128篇 |
1983年 | 24348篇 |
1982年 | 23110篇 |
1981年 | 21968篇 |
1980年 | 20473篇 |
1979年 | 23756篇 |
1978年 | 21263篇 |
1977年 | 20117篇 |
1976年 | 18845篇 |
1975年 | 18921篇 |
1974年 | 19689篇 |
1973年 | 19964篇 |
1972年 | 17124篇 |
1971年 | 15635篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Wendy A. Douglass Robert H. Hyland Christopher D. Buckley Aymen Al-Shamkhani Jacqueline M. Shaw Sarah L. Scarth David L. Simmons S.K.Alex Law 《FEBS letters》1998,440(3):125
The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR. 相似文献
132.
133.
134.
The ability to metabolically label proteins with 35S-methionine is critical for the analysis of protein synthesis and turnover. Despite the importance of this approach, however, efficient labeling of proteins in vivo is often limited by a low number of available methionine residues, or by deleterious side-effects associated with protein overexpression. To overcome these limitations, we have created a methionine-rich variant of the widely used HA tag, called HAM, for use with ectopically expressed proteins. Here we describe the development of a series of vectors, and corresponding antisera, for the expression and detection of HAM-tagged proteins in mammalian cells. We show that the HAM tag dramatically improves the sensitivity of 35S-methionine labeling, and permits the analysis of Myc oncoprotein turnover even when HAM-tagged Myc is expressed at levels comparable to that of the endogenous protein. Because of the improved sensitivity provided by the HAM tag, the vectors and antisera described here should be useful for the analysis of protein synthesis and destruction at physiological levels of protein expression. 相似文献
135.
A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans 下载免费PDF全文
Norio Suzuki Matthew Buechner Kiyoji Nishiwaki David H. Hall Hiroyuki Nakanishi Yoshimi Takai Naoki Hisamoto Kunihiro Matsumoto 《EMBO reports》2001,2(6):530-535
The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities. 相似文献
136.
I. N. Semenchuk L. A. Taranova A. A. Kalenyuk P. V. Il’yasov A. N. Reshetilov 《Applied Biochemistry and Microbiology》2000,36(1):69-72
The operating and storage stability of a receptor element of an amperometric biosensor based on thePseudomonas rathonis strain T capable of degrading surfactants was tested. Microbial cells were immobilized by incorporation in gels (agar, agarose,
and calcium-alginate), polyvinyl alcohol membrane, adhesion to Chromatographic paper GF/A, or by cross-linking induced by
glutaric aldehyde. Incorporation of microbial cells in agar gel provides long-standing conservation of their activity and
viability during measurements of high concentrations of surfactants and allows the receptor element of the biosensor to be
rapidly recovered after measurements. 相似文献
137.
138.
139.
An algorithm is proposed that allows one to identify the MHD mode structure in toroidal plasmas by processing signals from Mirnov probes measuring plasma MHD activity. The algorithm differs fundamentally from the diagnostic methods presently used in tokamaks, being simpler and more efficient. The algorithm is based on constructing an analytic signal using the Hilbert transformation of the Mirnov signals at a given instant. The phase and amplitude dependences obtained take into account the toroidal effects and allow one to determine the number and amplitude of the excited MHD mode. The algorithm was approbated with both test signals and actual signals from MHD diagnostics in the T-10 tokamak. It is demonstrated that the algorithm can be used to analyze single-mode MHD instabilities in toroidal plasmas. 相似文献
140.