全文获取类型
收费全文 | 93264篇 |
免费 | 319篇 |
国内免费 | 884篇 |
专业分类
94467篇 |
出版年
2019年 | 6篇 |
2018年 | 11840篇 |
2017年 | 10670篇 |
2016年 | 7450篇 |
2015年 | 587篇 |
2014年 | 281篇 |
2013年 | 292篇 |
2012年 | 4206篇 |
2011年 | 12804篇 |
2010年 | 12000篇 |
2009年 | 8226篇 |
2008年 | 9782篇 |
2007年 | 11356篇 |
2006年 | 250篇 |
2005年 | 505篇 |
2004年 | 962篇 |
2003年 | 1024篇 |
2002年 | 785篇 |
2001年 | 263篇 |
2000年 | 167篇 |
1999年 | 27篇 |
1998年 | 13篇 |
1997年 | 26篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 48篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 23篇 |
1982年 | 10篇 |
1975年 | 8篇 |
1972年 | 247篇 |
1971年 | 277篇 |
1970年 | 7篇 |
1965年 | 13篇 |
1963年 | 5篇 |
1962年 | 24篇 |
1956年 | 6篇 |
1954年 | 6篇 |
1952年 | 6篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
Identification of the major tRNA(Phe) binding domain in the tetrameric structure of cytoplasmic phenylalanyl-tRNA synthetase from baker's yeast 总被引:1,自引:0,他引:1
Native cytoplasmic phenylalanyl-tRNA synthetase from baker's yeast is a tetramer of the alpha 2 beta 2 type. On mild tryptic cleavage it gives rise to a modified alpha 2 beta 2 form that has lost the tRNA(Phe) binding capacity but is still able to activate phenylalanine. In this paper are presented data concerning peptides released by this limited proteolytic conversion as well as those arising from exhaustive tryptic digestion of the truncated beta subunit. Each purified peptide was unambiguously assigned to a unique stretch of the beta subunit amino acid sequence that was recently determined via gene cloning and DNA sequencing. Together with earlier results from affinity labelling studies the present data show that the Lys 172-Ile 173 bond is the unique target of trypsin under mild conditions and that the N-terminal domain of each beta subunit (residues 1-172) contains the major tRNA(Phe) binding sites. 相似文献
144.
Purification and characterization of a toxin inhibiting protein synthesis from Croton mongue, a Madagascar Euphorbiaceae 总被引:1,自引:0,他引:1
Monguine, a thermostable toxic protein was extracted from the seeds of Croton mongue (Euphorbiaceae) and purified by ion-exchange chromatography on DEAE-cellulose and gel filtration on Sephadex G-25 and G-15. Polyacrylamide gel electrophoresis of purified monguine in the presence of sodium dodecyl sulfate and after treatment with 2-mercaptoethanol showed one band corresponding to a molecular weight of 9000. The same molecular weight was determined by analytical centrifugation. Amino acid analysis revealed a high content in both aspartic and glutamic acids (or the corresponding amides). The LD50 (24 h) is 12 mg/kg of mouse body weight. Monguine inhibits protein synthesis in hepatoma tissue culture cells and globin synthesis in a rabbit reticulocyte lysate. 相似文献
145.
The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K+, Ca2+ and Mg2+ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed. 相似文献
146.
N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus). 相似文献
147.
A method is described in which polypeptides can be separated, with a high band resolution, by electrophoresis through "pore gradient" acrylamide gel (15 cm in length) in a sodium dodecyl sulfate-urea dissociating system. The applicability of this technique to the analysis of virus structural components was examined with the adenovirus type 2 model system. 相似文献
148.
Role of Peroxidase when Hydroxyproline-rich Protein in Plant Cell Walls is increased by Ethylene 总被引:9,自引:0,他引:9
Ethylene may control the growth of plant cells by regulating hydroxylation of specific wall proteins. 相似文献
149.
Demonstration of an “Excitation-Contraction Recoupling” Mechanism in Mammalian Ventricular Myocardium 总被引:1,自引:0,他引:1
A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.1 recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch2 and Lab3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon. 相似文献
150.
The Structure of Calf Liver Cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>5</Subscript> at 2.8 Å Resolution 总被引:5,自引:0,他引:5
CYTOCHROME b5 is a haem-containing protein in the microsomes of liver tissue. It interacts specifically with a flavo-protein, cytochrome b5 reductase, which catalyses the transfer of electrons from NADH to the haem iron of the cytochrome1. The microsomal cytochrome b5 system has been implicated in fatty acid desaturation reactions2 and a similar system in erythrocytes may catalyse the reduction of methaemoglobin3. Calf liver cytochrome b5, solubilized by pancreatic lipase, has a molecular weight of 11,000 and consists of ninety-three amino-acids in the sequence shown in Fig. 1 (refs. 4 and 5). The haem group is non-covalently bound to the protein and can be removed reversibly by acid acetone treatment6. 相似文献