全文获取类型
收费全文 | 104614篇 |
免费 | 7646篇 |
国内免费 | 210篇 |
出版年
2021年 | 1145篇 |
2020年 | 1032篇 |
2019年 | 1014篇 |
2018年 | 2425篇 |
2017年 | 2269篇 |
2016年 | 2972篇 |
2015年 | 3783篇 |
2014年 | 3931篇 |
2013年 | 5133篇 |
2012年 | 6297篇 |
2011年 | 5826篇 |
2010年 | 3589篇 |
2009年 | 2929篇 |
2008年 | 4761篇 |
2007年 | 4586篇 |
2006年 | 4373篇 |
2005年 | 3753篇 |
2004年 | 3620篇 |
2003年 | 3310篇 |
2002年 | 3089篇 |
2001年 | 4265篇 |
2000年 | 4003篇 |
1999年 | 2913篇 |
1998年 | 1043篇 |
1997年 | 841篇 |
1996年 | 788篇 |
1995年 | 705篇 |
1994年 | 626篇 |
1993年 | 558篇 |
1992年 | 1787篇 |
1991年 | 1599篇 |
1990年 | 1477篇 |
1989年 | 1425篇 |
1988年 | 1307篇 |
1987年 | 1262篇 |
1986年 | 1121篇 |
1985年 | 1117篇 |
1984年 | 892篇 |
1983年 | 735篇 |
1982年 | 565篇 |
1979年 | 828篇 |
1978年 | 639篇 |
1975年 | 675篇 |
1974年 | 780篇 |
1973年 | 756篇 |
1972年 | 745篇 |
1971年 | 690篇 |
1970年 | 677篇 |
1969年 | 684篇 |
1968年 | 578篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
191.
T P Chernobel' T I Randmaa Z Ia Maksimova A A Shinkorenko V N Migunov 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1987,(11):88-90
A total of 218 batches of blood preparations produced from different raw materials have been studied by means of enzyme immunoassay kits (Abbott Laboratories, USA). The assays have revealed that the preparations under study are nonstandard with respect to the content and isolation rate of HBsAg, the marker of hepatitis B virus. These data necessitate search for the ways of improving the quality of blood preparations. 相似文献
192.
Kh S Khamitov E I Bogdanov F A Khabirov V Z Khamidullina 《Biulleten' eksperimental'no? biologii i meditsiny》1983,96(11):24-26
Experiments with 22 rats have shown that the anterior tibial muscle in the stage of incomplete reinnervation is marked by decreased force and retardation of the semi-relaxation of an isometric contraction. In completely reinnervated muscles, the changes in the contractility are determined by the degree of nerve damage. The group of animals with the sciatic nerve injury demonstrated the contractility characteristic of a slower muscle, in contrast to the group with the fibular nerve damage. 相似文献
193.
194.
195.
196.
Gene frequencies and microdifferentiation among the Makiritare Indians. I. Eleven blood group systems and the ABH-Le secretor traits: a note on Rh gene frequency determinations. 总被引:11,自引:8,他引:3
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
H Gershowitz M Layrisse Z Layrisse J V Neel C Brewer N Chagnon M Ayres 《American journal of human genetics》1970,22(5):515-525
197.
198.
199.
200.
The role of carboxylic amino acids Asp-9 and Glu-36 in the activity of CPL1 lysozyme was investigated by site-directed mutagenesis. The enzymatic activity of the single mutants D9E, D9N, D9H, D9K, D9A, E36D, E36Q, E36K, and E36A and of the double mutant D9A-E36A was analyzed using a highly sensitive radioactive assay. All mutants but D6K showed detectable activities. Interestingly, the mutants E36D and E36Q retained 67% and 37% activity, respectively. Amino acid replacements at position 9 turned out to be more critical for activity than at position 36. In analogy to the mechanism described for hen egg-white lysozyme, where the proton donor play a central role, we propose that, in the CPL1 lysozyme, Asp-9 might act as the proton donor for activation of the substrate, and Glu-36 could help in the stabilization of the intermediate oxocarbocation. The residual activity of lysozyme mutants lacking one or two of the acidic amino acids may be explained by the participation of a water molecule as proton donor and/or to electrostatic contributions in the active center stabilizing the transition state of the reaction. Our results are in agreement with the hypothesis that enzymes have been optimized during evolution from an ancestral protein able to bind more tightly the transition state of the substrate than the substrate itself, by the acquisition of amino acids serving a function in catalysis. 相似文献