全文获取类型
收费全文 | 50141篇 |
免费 | 3877篇 |
国内免费 | 3861篇 |
专业分类
57879篇 |
出版年
2024年 | 137篇 |
2023年 | 633篇 |
2022年 | 1505篇 |
2021年 | 2415篇 |
2020年 | 1636篇 |
2019年 | 2078篇 |
2018年 | 2179篇 |
2017年 | 1754篇 |
2016年 | 2287篇 |
2015年 | 2668篇 |
2014年 | 3400篇 |
2013年 | 3673篇 |
2012年 | 4182篇 |
2011年 | 3866篇 |
2010年 | 2731篇 |
2009年 | 2387篇 |
2008年 | 2719篇 |
2007年 | 2410篇 |
2006年 | 2111篇 |
2005年 | 1750篇 |
2004年 | 1636篇 |
2003年 | 1546篇 |
2002年 | 1261篇 |
2001年 | 1033篇 |
2000年 | 851篇 |
1999年 | 626篇 |
1998年 | 393篇 |
1997年 | 322篇 |
1996年 | 312篇 |
1995年 | 326篇 |
1994年 | 293篇 |
1993年 | 230篇 |
1992年 | 293篇 |
1991年 | 263篇 |
1990年 | 210篇 |
1989年 | 193篇 |
1988年 | 129篇 |
1987年 | 176篇 |
1986年 | 145篇 |
1985年 | 131篇 |
1984年 | 103篇 |
1983年 | 95篇 |
1982年 | 82篇 |
1981年 | 79篇 |
1980年 | 52篇 |
1979年 | 62篇 |
1978年 | 66篇 |
1976年 | 51篇 |
1973年 | 63篇 |
1972年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Natural heparin complexes proved to activate the anticoagulation system. The obtained experimental data convincingly confirm that glutamic acid alone, and particularly in a complex with heparin, has a considerable preventive potential and efficiently protects experimental animals with induced diabetes mellitus. 相似文献
42.
43.
N. E. Belyaeva V. Z. Pashchenko G. Renger G. Yu. Riznichenko A. B. Rubin 《Biophysics》2006,51(6):860-872
A mathematical model of photosystem II (PSII) events was used to analyze chlorophyll fluorescence transients in the time domain from 100 ns to 10 s after excitation with a saturating 10-ns flash, applied as a part of specialized illumination protocol, using preparations of a thermophilic strain of the unicellular green alga, Chlorella pyrenoidosa Chick (using both intact and diuron-treated cells). Analysis of simulation results has proven that particular attention should be given to flash-induced recombination processes, including nonradiative recombination in PSII, while subsequent charge transfer along the electron transport chain of thylakoid membrane can be adequately described by a single reaction of quinone reoxidation. The PSII model was extended by taking inhibition by diuron of the electron transport in the acceptor side of PSII into account, which allowed simulation of fluorescence induction curves observed in the presence of this inhibitor. The model parameters were determined (stromal pH, rate constants of nonradiative recombination, and the initial reduction state of the quinone pool) which provided adequate simulation of experimentally observed ratios of the maximal and initial fluorescence levels (F m/F 0). 相似文献
44.
Experimental evaluation of the mass of food withdrawn by larvae of the Siberian moth during their development on larch, cedar pine, fir, spruce, and common pine was carried out. The obtained dependences between the masses of larvae and food withdrawn by them can be directly used to determine the withdrawn food rate of Siberian moth on each of the Siberian conifer species. 相似文献
45.
To investigate the mechanism of inclusion body formation and the effect of a hydrophobic sequence on the in vivo polypeptide folding, the aggregation caused by recombinant fusion beta-galactosidase in Escherichia coli was examined. Two plasmids were constructed: pTBG(H-) carried only the preS2 sequence of the hepatitis B virus surface antigen (HBsAg) in front of the beta-galactosidase gene (lacZ) while pTBG(H+) carried an additional sequence encoding the amino-terminal hydrophobic sequence of the S region of HBsAg between preS2 and lacZ. Unlike cells expressing the fusion protein not containing the hydrophobic sequence, E. coli JM109/pTBG(H+) exhibited temperature-sensitive production of beta-galactosidase. As the culture temperature increased the activity decreased dramatically. This decrease in activity was not due to a decrease in fusion polypeptide production, but rather the fusion polypeptides containing the hydrophobic sequence aggregated within the cells at high temperature. However once the fusion polypeptides folded into proper conformation at low temperature, they maintained the activity even at high temperature. The results indicate that aggregation is a consequence of incorrect folding and assembly of the polypeptides, and is not derived from the native structure. The aggregates of the pTBG(H+)-encoded fusion polypeptides did not revert to active form when the culture temperature was lowered. 相似文献
46.
An analysis is made of the general expression for the density of a nonlinear charge induced in a magnetized plasma in the interaction between two arbitrary waves. Asymptotic expressions for the nonlinear induced charge density are derived for the first time in the case where both of the interacting waves are short-scale. 相似文献
47.
48.
49.
R. K. Chailakhyan Yu. V. Gerasimov A. I. Kuralesova N. V. Latsinik E. N. Genkina M. R. Chailakhyan 《Biology Bulletin》2001,28(6):575-584
We present the results of a study on the proliferative and differentiation potential of individual clones of stromal fibroblasts growing in monolayer cultures of bone marrow cells. Each precursor cell yielding a large colony in primary culture is capable of up to 34 doublings in vitro. The transplantation of clones or monoclonal strains of stromal fibroblasts into the open system results in the formation of microenvironment consisting of the bone and reticular tissue and is suitable for the differentiation of all three lines of hemopoiesis. Evidence has been obtained that, in a closed system, individual clones are capable of differentiation into the bone, cartilaginous, and reticular tissues. In other words, the adult organism has a common cell precursor for these tissues. 相似文献
50.
A. Yu. Korolyuk A. V. Egorova I. E. Smelansky N. V. Filippova 《Contemporary Problems of Ecology》2008,1(1):49-58
The phytocenotic diversity of the Altai steppe piedmont is described. Plant communities were ordinated along the moisture gradient. The results were used to analyze the structure of vegetation of steppe hill massifs. Distribution of steppe vegetation over an ideal hill was simulated, and the main patterns of distribution were typified. 相似文献