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   217篇
  免费   34篇
  2022年   4篇
  2021年   2篇
  2018年   2篇
  2017年   2篇
  2015年   7篇
  2014年   6篇
  2013年   6篇
  2012年   6篇
  2011年   5篇
  2010年   2篇
  2009年   5篇
  2008年   9篇
  2007年   3篇
  2006年   9篇
  2005年   8篇
  2004年   3篇
  2003年   6篇
  2002年   4篇
  2001年   4篇
  1999年   6篇
  1998年   12篇
  1997年   4篇
  1996年   12篇
  1995年   5篇
  1994年   9篇
  1993年   9篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1989年   7篇
  1988年   7篇
  1987年   5篇
  1986年   6篇
  1985年   3篇
  1984年   9篇
  1983年   5篇
  1981年   2篇
  1977年   3篇
  1976年   5篇
  1975年   5篇
  1973年   3篇
  1955年   2篇
  1954年   3篇
  1946年   1篇
  1944年   1篇
  1943年   1篇
  1941年   1篇
  1940年   1篇
  1934年   1篇
  1920年   1篇
排序方式: 共有251条查询结果,搜索用时 20 毫秒
51.
正出版:高等教育出版社出版时间:2018年7月ISBN:978-7-04-049873-8定价:180元内容简介本书原版是国际上最具声誉的微生物学教科书之一,2017年最新版次为第10版。本书秉承《Prescott微生物学》一直以来博大精深、新颖、系统的特点,几乎涵盖了微生物学领域的所有概念,具有一定的深度和广度。全书共9篇43章,既包含学习微生物学的目的、微生物学的化学原理、研究微生物的技术方法、微生物的特  相似文献   
52.
Transgenic mice bearing a murine retroviral envelope transgene (Fv4) have Fv4 gp70env (SU) in their serum in amounts sufficient to block infection by ecotropic virus in vitro. Fv4 Env in serum is derived largely but not exclusively from hematopoietic cells. Tail cells from Fv4 mice and cell lines transduced with the Fv4 env transgene synthesize both components of the envelope protein (gp70 SU and p15E TM) but secrete the gp70 moiety, in the absence of retroviral particles. Blocking of the ecotropic viral receptor by secreted gp70 SU may contribute to resistance to retroviral infection in these mice.  相似文献   
53.
54.
Cytochrome c oxidase subunit II (COII), encoded by the mitochondrial genome, exhibits one of the most heterogeneous rates of amino acid replacement among placental mammals. Moreover, it has been demonstrated that cytochrome c oxidase has undergone a structural change in higher primates which has altered its physical interaction with cytochrome c. We collected a large data set of COII sequences from several orders of mammals with emphasis on primates, rodents, and artiodactyls. Using phylogenetic hypotheses based on data independent of the COII gene, we demonstrated that an increased number of amino acid replacements are concentrated among higher primates. Incorporating approximate divergence dates derived from the fossil record, we find that most of the change occurred independently along the New World monkey lineage and in a rapid burst before apes and Old World monkeys diverged. There is some evidence that Old World monkeys have undergone a faster rate of nonsynonymous substitution than have apes. Rates of substitution at four-fold degenerate sites in primates are relatively homogeneous, indicating that the rate heterogeneity is restricted to nondegenerate sites. Excluding the rate acceleration mentioned above, primates, rodents, and artiodactyls have remarkably similar nonsynonymous replacement rates. A different pattern is observed for transversions at four-fold degenerate sites, for which rodents exhibit a higher rate of replacement than do primates and artiodactyls. Finally, we hypothesize specific amino acid replacements which may account for much of the structural difference in cytochrome c oxidase between higher primates and other mammals.   相似文献   
55.
56.
Considerable interest has been focused on the role of myosin light chain LC(2) in the contraction of vertebrate striated muscle. A study was undertaken to further our investigations (Moss, R.L., G.G. Giulian, and M.L. Greaser, 1981, J. Biol. Chem., 257:8588-8591) of the effects of LC(2) removal upon contraction in skinned fibers from rabbit psoas muscles. Isometric tension and maximum velocity of shortening, V(max), were measured in fiber segments prior to LC(2) removal. The segments were then bathed at 30 degrees C for up to 240 min in a buffer solution containing 20 mM EDTA in order to extract up to 60 percent of the LC(2). Troponin C (TnC) was also partially removed by this procedure. Mechanical measurements were done following the EDTA extraction and the readditions of first TnC and then LC(2) to the segments. The protein subunit compositions of the same fiber segments were determined following each of these procedures by SDS PAGE of small pieces of the fiber. V(max) was found to decrease as the LC(2) content of the fiber segments was reduced by increasing the duration of extraction. EDTA treatment also resulted in substantial reductions in tension due mainly to the loss of TnC, though smaller reductions due to the extraction of LC(2) were also observed. Reversal of the order of recombination of LC(2) and TnC indicated that the reduction in V(max) following EDTA treatment was a specific effect of LC(2) removal. These results strongly suggest that LC(2) may have roles in determining the kinetics and extent of interaction between myosin and actin.  相似文献   
57.
We constructed an infectious molecular clone of acquired immunodeficiency syndrome-associated retrovirus. Upon transfection, this clone directed the production of infectious virus particles in a wide variety of cells in addition to human T4 cells. The progeny, infectious virions, were synthesized in mouse, mink, monkey, and several human non-T cell lines, indicating the absence of any intracellular obstacle to viral RNA or protein production or assembly. During the course of these studies, a human colon carcinoma cell line, exquisitely sensitive to DNA transfection, was identified.  相似文献   
58.
59.
Bombesin and the C-terminal portion of gastrin-releasing peptide (GRP14-27) each increase clonal growth rate and colony-forming efficiency of normal human bronchial epithelial cells. These effects occur in the presence or absence of an optimal concentration (5 ng/ml) of epidermal growth factor (EGF). In contrast to EGF bombesin and GRP14-27 do not stimulate cell migration. Thus, bombesin and the C-terminal fragment of gastrin-releasing peptide represent a new class of peptides mitogenic for normal human epithelial cells.  相似文献   
60.
Ribosomal RNAs have secondary structures that are maintained by internal Watson-Crick pairing. Through analysis of chordate, arthropod, and plant 5S ribosomal RNA sequences, we show that Darwinian selection operates on these nucleotide sequences to maintain functionally important secondary structure. Insect phylogenies based on nucleotide positions involved in pairing and the production of secondary structure are incongruent with those constructed on the basis of positions that are not. Furthermore, phylogeny reconstruction using these nonpairing bases is concordant with other, morphological data.   相似文献   
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