全文获取类型
收费全文 | 6792篇 |
免费 | 721篇 |
国内免费 | 2篇 |
专业分类
7515篇 |
出版年
2021年 | 65篇 |
2019年 | 60篇 |
2018年 | 73篇 |
2017年 | 65篇 |
2016年 | 116篇 |
2015年 | 180篇 |
2014年 | 230篇 |
2013年 | 291篇 |
2012年 | 362篇 |
2011年 | 379篇 |
2010年 | 242篇 |
2009年 | 219篇 |
2008年 | 344篇 |
2007年 | 412篇 |
2006年 | 342篇 |
2005年 | 377篇 |
2004年 | 356篇 |
2003年 | 358篇 |
2002年 | 314篇 |
2001年 | 100篇 |
2000年 | 88篇 |
1999年 | 99篇 |
1998年 | 102篇 |
1997年 | 76篇 |
1996年 | 80篇 |
1995年 | 76篇 |
1994年 | 67篇 |
1993年 | 67篇 |
1992年 | 87篇 |
1991年 | 70篇 |
1990年 | 64篇 |
1989年 | 61篇 |
1988年 | 66篇 |
1987年 | 57篇 |
1986年 | 52篇 |
1985年 | 72篇 |
1984年 | 88篇 |
1983年 | 65篇 |
1982年 | 78篇 |
1981年 | 100篇 |
1980年 | 85篇 |
1979年 | 55篇 |
1978年 | 73篇 |
1977年 | 78篇 |
1976年 | 63篇 |
1975年 | 60篇 |
1974年 | 67篇 |
1973年 | 46篇 |
1969年 | 46篇 |
1967年 | 50篇 |
排序方式: 共有7515条查询结果,搜索用时 15 毫秒
101.
102.
Dictyostelium RasG Is Required for Normal Motility and Cytokinesis, But Not Growth 总被引:1,自引:0,他引:1 下载免费PDF全文
Richard I. Tuxworth Janet L. Cheetham Laura M. Machesky George B. Spiegelmann Gerald Weeks Robert H. Insall 《The Journal of cell biology》1997,138(3):605-614
RasG is the most abundant Ras protein in growing Dictyostelium cells and the closest relative of mammalian Ras proteins. We have generated null mutants in which expression of RasG is completely abolished. Unexpectedly, RasG− cells are able to grow at nearly wild-type rates. However, they exhibit defective cell movement and a wide range of defects in the control of the actin cytoskeleton, including a loss of cell polarity, absence of normal lamellipodia, formation of unusual small, punctate polymerized actin structures, and a large number of abnormally long filopodia. Despite their lack of polarity and abnormal cytoskeleton, mutant cells perform normal chemotaxis. However, rasG− cells are unable to perform normal cytokinesis, becoming multinucleate when grown in suspension culture. Taken together, these data suggest a principal role for RasG in coordination of cell movement and control of the cytoskeleton. 相似文献
103.
Brief overview of control of genetic expression by antisense oligonucleotides and in vivo applications 总被引:7,自引:0,他引:7
Gerald Zon 《Molecular neurobiology》1995,10(2-3):219-229
Over the past several years, the use of synthetic oligonucleotides and functional analogs thereof as a possibly general means
of controlling genetic expression has received widespread attention. Following a brief overview of some of the basic principles
and strategies for this approach, attention is focused here on summarizing some recent reports of in vitro and, in particular,
in vivo investigations in various animal models using phosphorothioate analogs of 2′-deoxyoligo-nucleotides. In view of these
findings, which include studies related to neurobiology, this field should find significant utility in applications of the
antisense method for controlling genetic expression. 相似文献
104.
105.
Michael J. Barber Andrew S. Zektzer Gerald M. Rosen Helen A. Demos Elmer J. Rauckman 《生物化学与生物物理学报:生物膜》1984,776(1):159-168
Hepatic microsomal membranes, prepared under various conditions that yield either ‘intact’ or ‘disrupted’ microsomal vesicles, have been labeled via the sulfhydryl groups of intrinsic membrane proteins using nitroxide analogs of . Electron paramagnetic resonance spectra revealed the presence of two dominant classes of bound label corresponding to differing degrees of immobilization, the ratio of which were quantitated using a parameter designated the ‘’ ratio. For latent microsomes, the value of this parameter was determined to be and was influenced by factors such as label/protein ratio, incubation period, nitroxide structure, temperature and pH. The ratio was also sensitive to the degree of membrane integrity as revealed by the latency of mannose 6-phosphate activity of glucose-6-phosphohydrolase. In addition, membrane disruption resulted in a corresponding decrease in the order parameter for nitroxide-labeled fatty acids intercalated within the lipid bilayer. The ratio was observed to be dependent upon the method of microsome preparation yielding values of for ‘hypertonically disrupted’ vesicles and for ‘mechanically disrupted’ vesicles. Microsomal marker enzymes such as cytochrome and FAD-containing monooxygenase retained significant levels of functionally following nitroxide incorporation. 相似文献
106.
James C. Willey Clementh E. Moser Jr. Curtis C. Harris 《Cell biology and toxicology》1984,1(1):145-154
The effects of aplysiatoxin and debromoaplysiatoxin on the clonal growth rate, cross-linked envelope formation and plasminogen activator secretion of normal human bronchial epithelial cells were studied. Neither compound was mitogenic over a wide range of concentrations (10–13 to 10–7M). Both aplysiatoxin and debromoaplysiatoxin inhibited clonal growth rate with 50% inhibitory concentrations of 3 × 10–11M and 10–10M, respectively. Both compounds induced the formation of cross-linked envelopes and increased plasminogen activator secretion with equal potency. These data are similar to those previously obtained with 12-0-tetradecanoylphorbol-13-acetate and teleocidin B and suggest that aplysiatoxin and debromoaplysiatoxin induce terminal squamous differentiation in normal human bronchial epithelial cells.Abbreviations TPA
12-0-tetradecanoylphorbol-13-acetate
- NHBE
Normal Human bronchial epithelial
- ID50
50% inhibitory concentration (dose)
- PA
Plasminogen activator
- CLE
Cross-linked envelope
- LHC
Laboratory of Human Carcinogenesis 相似文献
107.
108.
The effects of mannitol were investigated by comparing some metabolic features in colonial derivatives, I-110 and L1-110,
ofRhizobium japonicum strain 3IIb110, grown either on glucose alone (G-cells) or in glucose media supplemented with mannitol (GM-cells). The polyol
stimulated the synthesis of not only mannitol dehydrogenase, which is active in derivative L1-110, but also the nicotinamide
adenine dinucleotide (NAD)-linked 6-phosphogluconate (6-PG) dehydrogenase (EC 1.1.1.43). As revealed by radiorespirometry,
when GM-cells were allowed to metabolize glucose, they produced relatively more CO2 from the first and sixth carbons of the sugar than G-cells did. This finding is evidence that NAD-linked 6-PG dehydrogenase
might initiate an unknown pathway different from the hexose cycle and the pentose phosphate (PP) pathway. Mannitol exerted
no allosteric control on the oxygen consumption and the glucose transport systems. Active uptake of the polyol was correlated
with the presence of mannitol dehydrogenase (EC 1.1.1.67); it did not hinder the transport of glucose even though both systems
derive their energy for active transport from a common source presumptively characterized as the energized membrane state.
Mannitol, however, suppressed by two- or threefold the glucose uptake system. Addition of the polyol to the cell suspensions
of both colonial types ofR. japonicum metabolizing glucose caused an immediate 40–50% drop of adenosine triphosphate (ATP) concentrations, owing in part to the
mannitol kinase reaction. Type I-110 failed to overcome this reduction of ATP levels, and low growth rates could results.
In contrast, type L1-110 offsets the reduction of ATP concentration by oxidizing mannitol as an additional source of energy
through mannitol dehydrogenase, fructokinase, and a sequence of glycolytic reactions. The polyol also induced type L1-110
to produce extracellular slimy materials that, apparently, harbor amounts of ATP and proteins. 相似文献
109.
When LETS protein positive and negative cells were co-cultured, the positive cells remained as positive and the negative cells remained as negative. Apparently the transformed cells do not secrete factors which are sufficient to influence the distribution of surface LETS protein on normal cells. 相似文献
110.
C.Walter Ogston Gerald J. Jonak Charles E. Rogler Susan M. Astrin Jesse Summers 《Cell》1982,29(2):385-394
Woodchuck hepatitis virus (WHV), like the related hepatitis B virus, induces in its natural host hepatocellular carcinomas that contain integrated viral sequences. As a first step in determining whether and how the integrated sequences contribute to formation of the tumors in which they are found, we have cloned two such integrations of WHV and have determined their structure by restriction mapping and heteroduplex electron microscopy. The identity of the cloned sequences was confirmed by comparison of restriction sites in the clones with those located by Southern blot analysis of tumor DNA. Viral sequences in both integrations are extensively rearranged, and in neither were all parts of the viral genome represented. In this respect, the behavior of WHV in vivo is similar to that of other DNA tumor viruses that have been studied in vitro. We discuss the implications of these results in relation to possible mechanisms for tumor induction by WHV. 相似文献