全文获取类型
收费全文 | 3182篇 |
免费 | 339篇 |
出版年
2021年 | 38篇 |
2018年 | 26篇 |
2016年 | 44篇 |
2015年 | 82篇 |
2014年 | 88篇 |
2013年 | 106篇 |
2012年 | 167篇 |
2011年 | 148篇 |
2010年 | 71篇 |
2009年 | 74篇 |
2008年 | 119篇 |
2007年 | 112篇 |
2006年 | 114篇 |
2005年 | 116篇 |
2004年 | 109篇 |
2003年 | 98篇 |
2002年 | 97篇 |
2001年 | 91篇 |
2000年 | 105篇 |
1999年 | 83篇 |
1998年 | 36篇 |
1997年 | 22篇 |
1996年 | 28篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 36篇 |
1992年 | 77篇 |
1991年 | 73篇 |
1990年 | 70篇 |
1989年 | 48篇 |
1988年 | 63篇 |
1987年 | 65篇 |
1986年 | 59篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 42篇 |
1982年 | 36篇 |
1981年 | 40篇 |
1980年 | 24篇 |
1979年 | 65篇 |
1978年 | 62篇 |
1977年 | 44篇 |
1976年 | 53篇 |
1975年 | 36篇 |
1974年 | 38篇 |
1973年 | 30篇 |
1972年 | 37篇 |
1971年 | 27篇 |
1968年 | 26篇 |
1966年 | 22篇 |
排序方式: 共有3521条查询结果,搜索用时 15 毫秒
91.
The larval–pupal transformation of Manduca sexta is accompanied by the loss of the abdominal prolegs. The proleg muscles degenerate, the dendritic arbors of proleg motoneurons regress, and a subset of the proleg motoneurons dies. The regression and death of proleg motoneurons are triggered by the prepupal peak of ecdysteroids in the hemolymph. To investigate the possible involvement of protein synthesis in these events, we gave insects repeated injections of the protein synthesis inhibitor, cycloheximide (CHX), during the prepupal peak. Examination of insects 3–5 days following CHX treatment showed that CHX inhibited the death of proleg motoneurons and the production of pupal cuticle in a dose-dependent fashion. When insects were allowed to survive for 10 days after the final CHX injection, motoneuron death and pupal cuticle production sometimes occurred belatedly, apparently in response to the ecdysteroid rise that normally triggers adult development. CHX treatments that inhibited motoneuron death were less effective in inhibiting dendritic regression in the same neurons. In another set of experiments, abdomens were isolated from the ecdysteroid-secreting glands prior to the prepupal peak, and infused with 20-hydroxyecdysone (20-HE). Single injections of CHX delivered just prior to the start of the 20-HE infusion inhibited motoneuron death and pupal cuticle production, but in the range of doses tested, did not prevent dendritic regression. Our findings suggest that protein synthesis is a required step in the steroid-mediated death of proleg motoneurons, and that dendritic regression is less susceptible to inhibition by CHX than is motoneuron death. © 1993 John Wiley & Sons, Inc. 相似文献
92.
93.
Phosphoinositide 3-kinases and membrane traffic 总被引:8,自引:0,他引:8
Phosphoinositide 3-kinases (PI 3-kinases) and their 3-phosphoinositide products were identified initially as components of intracellular signalling pathways emanating from cell surface receptors. A new role for 3-phosphoinositides in the constitutive movement o f proteins from one intracellular compartment to another was proposed with the discovery of homology between the product of a yeast gene important for vacuolar sorting, Vps34p, and a mammalian PI 3-kinase. Recent studies have implicated PI 3-kinase as an essential component in membrane traffic at specific steps o f the trans-Golgi-network-endosomal pre-lysosomal system. Evidence largely emerging from the insulin-stimulated glucose transport system suggests that PI 3-kinase may also mediate the effects o f growth factors on membrane traffic events. These studies suggest a possible link between growth-factor-stimulated and constitutive membrane traffic in the endosomal system. 相似文献
94.
95.
Crystallization and preliminary crystallographic analysis of recombinant human P38 MAP kinase.
下载免费PDF全文
![点击此处可从《Protein science : a publication of the Protein Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S. Pav D. M. White S. Rogers K. M. Crane C. L. Cywin W. Davidson J. Hopkins M. L. Brown C. A. Pargellis L. Tong 《Protein science : a publication of the Protein Society》1997,6(1):242-245
The recombinant human p38 MAP kinase has been expressed and purified from both Escherichia coli and SF9 cells, and has been crystallized in two forms by the hanging drop vapor diffusion method using PEG as precipitant. Both crystal forms belong to space group P2(1)2(1)2(1). The cell parameters for crystal form 1 are a = 65.2 A, b = 74.6 A and c = 78.1 A. Those for crystal form 2 are a = 58.3 A, b = 68.3 A and c = 87.9 A. Diffraction data to 2.0 A resolution have been collected on both forms. 相似文献
96.
Mutation of a single MalK subunit severely impairs maltose transport activity in Escherichia coli.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The maltose transport system of Escherichia coli, a member of the ABC transport superfamily of proteins, consists of a periplasmic maltose binding protein and a membrane-associated translocation complex that contains two copies of the ATP-binding protein MalK. To examine the need for two nucleotide-binding domains in this transport complex, one of the two MalK subunits was inactivated by site-directed mutagenesis. Complexes with mutations in a single subunit were obtained by attaching a polyhistidine tag to the mutagenized version of MalK and by coexpressing both wild-type MalK and mutant (His)6MalK in the same cell. Hybrid complexes containing one mutant (His)6MalK subunit and one wild-type MalK subunit were separated from those containing two mutant (His)6MalK proteins based on differential affinities for a metal chelate column. Purified transport complexes were reconstituted into proteoliposome vesicles and assayed for maltose transport and ATPase activities. When a conserved lysine residue at position 42 that is involved in ATP binding was replaced with asparagine in both MalK subunits, maltose transport and ATPase activities were reduced to 1% of those of the wild type. When the mutation was present in only one of the two subunits, the complex had 6% of the wild-type activities. Replacement of a conserved histidine residue at position 192 in MalK with arginine generated similar results. It is clear from these results that two functional MalK proteins are required for transport activity and that the two nucleotide-binding domains do not function independently to catalyze transport. 相似文献
97.
Spontaneous deletion mutants of the Lactococcus lactis temperate bacteriophage BK5-T and localization of the BK5-T attP site. 总被引:3,自引:3,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Spontaneous deletion mutants of the temperate lactococcal bacteriophage BK5-T were obtained when the phage was grown vegetatively on the indicator strain Lactococcus lactis subsp. cremoris H2. One deletion mutant was unable to form stable lysogens, and analysis of this mutant led to the identification of the BK5-T attP site and the integrase gene (int). The core sequences of the BK5-T attP and host attB regions are conserved in a number of lactococcal phages and L. lactis strains. 相似文献
98.
99.
R B Shireman L Mace S Davidson 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1984,175(4):420-423
The effects of dichloroacetate, a known hypocholesterolemic agent, were studied in cultured growing and confluent human fibroblast cells. Microscopic examination showed no visible adverse effects of dichloroacetate on confluent cells during exposure to concentrations as high as 5 mM for 96 hr. Higher concentrations resulted in cell death after varying periods of incubation. There were no viable cells after 24 hr of exposure to 100 mM dichloroacetate. In contrast, much lower concentrations proved lethal to growing cells; cell growth, as determined by cell numbers at specified times after splitting, was suppressed by 1 mM dichloroacetate and 5 mM concentrations resulted in cell death. Similar effects were noted with glyoxylate. The hypocholesterolemic effect of dichloroacetate is probably not due to any effect on the low density lipoprotein pathway, since concentrations of up to 1 mM dichloroacetate did not affect the cellular binding and uptake of 125I-labeled low density lipoprotein. It is concluded that growing and rapidly metabolizing cells are much more sensitive to the toxic effects of dichloroacetate and glyoxylate than confluent cells. 相似文献
100.