全文获取类型
收费全文 | 109560篇 |
免费 | 1384篇 |
国内免费 | 901篇 |
专业分类
111845篇 |
出版年
2023年 | 214篇 |
2022年 | 308篇 |
2021年 | 548篇 |
2020年 | 379篇 |
2019年 | 432篇 |
2018年 | 12281篇 |
2017年 | 11036篇 |
2016年 | 8100篇 |
2015年 | 1483篇 |
2014年 | 1312篇 |
2013年 | 1646篇 |
2012年 | 5464篇 |
2011年 | 13961篇 |
2010年 | 12713篇 |
2009年 | 8869篇 |
2008年 | 10563篇 |
2007年 | 12123篇 |
2006年 | 1051篇 |
2005年 | 1176篇 |
2004年 | 1586篇 |
2003年 | 1576篇 |
2002年 | 1227篇 |
2001年 | 575篇 |
2000年 | 457篇 |
1999年 | 272篇 |
1998年 | 120篇 |
1997年 | 109篇 |
1996年 | 88篇 |
1995年 | 75篇 |
1994年 | 71篇 |
1993年 | 85篇 |
1992年 | 131篇 |
1991年 | 144篇 |
1990年 | 96篇 |
1989年 | 80篇 |
1988年 | 95篇 |
1987年 | 79篇 |
1986年 | 61篇 |
1985年 | 57篇 |
1984年 | 63篇 |
1983年 | 60篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 30篇 |
1979年 | 42篇 |
1978年 | 30篇 |
1975年 | 39篇 |
1972年 | 258篇 |
1971年 | 294篇 |
1962年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
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
83.
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
84.
An evaluation of four methods for measuring cholesterol absorption by the intestine in man 总被引:11,自引:0,他引:11
Critical comparisons have been made in 12 patients of four methods for measuring cholesterol absorption from the intestine. Methods I-III depend on the use of labeled cholesterol (intravenously or continuous labeling orally) in conjunction with sterol balance measurements; Method IV can be carried out with only a single test dose containing labeled cholesterol plus labeled beta-sitosterol. In the latter technique absorption is calculated as the loss of cholesterol relative to beta-sitosterol during intestinal transit. Method III (isotopic steady-state method) proved to be undependable because of uncertainties in determining the existence of an isotopic steady state. However, Method IV gave good agreement with Methods I and II, and it appears to have certain practical as well as theoretical advantages. Although Method IV requires collections of stools for up to 8 days, it is nevertheless the most rapid and the simplest of all the methods for estimating absorption. It can also be used in certain situations, such as in fur-licking animals, when Methods I and II are inadequate. Therefore, this method would seem to be a valuable addition to other isotopic techniques for estimating cholesterol absorption in man. 相似文献
85.
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
86.
87.
Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis> 总被引:6,自引:0,他引:6
Sokawa et al. suggest that rel- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited. 相似文献
88.
AVRAM HERSHKO PIERRE MAMONT ROBERT SHIELDS GORDON M. TOMKINS 《Nature: New biology》1971,232(33):206-211
A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells. 相似文献
89.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore. 相似文献
90.
ALINA TAYLOR 《Nature: New biology》1971,234(48):144-145
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein. 相似文献