全文获取类型
收费全文 | 150594篇 |
免费 | 4047篇 |
国内免费 | 845篇 |
出版年
2018年 | 14505篇 |
2017年 | 13608篇 |
2016年 | 9340篇 |
2015年 | 1063篇 |
2014年 | 754篇 |
2013年 | 1036篇 |
2012年 | 6126篇 |
2011年 | 16775篇 |
2010年 | 15505篇 |
2009年 | 11541篇 |
2008年 | 13258篇 |
2007年 | 15672篇 |
2006年 | 971篇 |
2005年 | 2282篇 |
2004年 | 2027篇 |
2003年 | 2312篇 |
2002年 | 2019篇 |
2001年 | 2189篇 |
2000年 | 2120篇 |
1999年 | 1472篇 |
1998年 | 484篇 |
1997年 | 498篇 |
1996年 | 506篇 |
1995年 | 425篇 |
1994年 | 433篇 |
1993年 | 456篇 |
1992年 | 1098篇 |
1991年 | 1144篇 |
1990年 | 1075篇 |
1989年 | 1046篇 |
1988年 | 979篇 |
1987年 | 919篇 |
1986年 | 770篇 |
1985年 | 746篇 |
1984年 | 599篇 |
1983年 | 535篇 |
1982年 | 382篇 |
1981年 | 342篇 |
1980年 | 332篇 |
1979年 | 564篇 |
1978年 | 449篇 |
1977年 | 412篇 |
1976年 | 338篇 |
1975年 | 467篇 |
1974年 | 469篇 |
1973年 | 414篇 |
1972年 | 1100篇 |
1971年 | 975篇 |
1970年 | 266篇 |
1969年 | 240篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
71.
Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than
between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites
and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial
isolation of the population and gene drift. 相似文献
72.
With the help of a suction manometric device, the relation between the deformation of Xenonus laevis embryo at the gastrula and neurula stages and the value of the applied force has been studied. Stiffness modules of embryonic
tissues were in the order of several dozens of Pascal and they were inversely proportional during deformation from 40 to 20%.
At the gastrula stage, a uniform or an increasing rate of expansion of the embryo body in the suction capillary with the diameter
of approximately half that of the embryo was observed for 30 min after the action of the suction forces. The length of the
stretched portion of the embryo correlates with the value of its deformation at the first minute. As a result of the expansion,
the total body surface area of the deformed embryo increases more than twice compared to intact embryos. After expelling the
embryo from the capillary, its surface reduced and the deformation became smoothened within 5 min, which indicates the existence
of tensional force in the expanded embryo. These data confirm that, at the embryo gastrula stage, external mechanical forces
do not only passively deform the embryo but also initiate the active expansion of the embryo which takes place at zero external
force and overcomes the tensional resistance of tissues. The mechanism of active expansion and its link with the processes
of normal morphogenesis are discussed. 相似文献
73.
N. G. Morozova M. A. Maslov V. V. Myagchenkov G. A. Serebrennikova 《Russian Journal of Bioorganic Chemistry》2010,36(5):657-662
An approach to the synthesis of cationic carbohydrate surfactants with potential antimicrobial and transfecting activities
is proposed. 相似文献
74.
A. A. Serov 《Plasma Physics Reports》2009,35(7):572-582
Electron beam relaxation in plasma under conditions typical of laboratory plasma devices based on a steady-state beam-plasma discharge was investigated. It is shown that the measured dependences of the beam loss factor in a discharge operating at a moderately low gas pressure disagree with theoretical dependences calculated for a longitudinally uniform plasma. Analytic dependences obtained in the framework of quasilinear theory with allowance for longitudinal plasma inhomogeneity agree with experimental data. Some effects caused by the influence of the main discharge parameters on electron beam relaxation are analyzed. 相似文献
75.
76.
Cyclic GMP directly regulates a cation conductance in membranes of bovine rods by a cooperative mechanism 总被引:18,自引:0,他引:18
Cyclic GMP causes the release of endogenous Ca2+ from rod outer segments, whose plasma membrane has been made permeable, or from isolated discs. Approximately 11,000 Ca2+ ions are released per disc at saturating concentrations of cyclic GMP. The velocity and the amplitude of the release of Ca2+ are dependent on the concentration of cyclic GMP. The maximal rate of the Ca2+ efflux is approximately 7 X 10(4) Ca2+ ions s-1 rod-1. The Ca2+ release by cyclic GMP is independent of light. The activation of the efflux occurred within a narrow range of the cyclic GMP concentration (30-80 microM) and does not obey a simple Michaelis-Menten scheme. Instead, the kinetic analysis of the Ca2+ efflux suggests that a minimum number of 2 molecules of cyclic GMP activates the ion conductance in a cooperative fashion. The release of Ca2+ by cyclic GMP requires a gradient of Ca2+ ions across the disc membrane. If the endogenous Ca2+ gradient is dissipated by means of the ionophore A23187, the release of Ca2+ by cyclic GMP is abolished. Ca2+ is released by analogues of cyclic GMP which are either modified at the 8-carbon position of the imidazole ring or by the deaza-analogue of cyclic GMP. Congeners of cyclic GMP which are modified at the ribose, phosphodiester, or pyrimidine portion of the molecule are ineffective. The hydrolysis of cyclic GMP by the light-regulated phosphodiesterase of rod outer segments is not a necessary condition for the Ca2+ release because 8-bromo-cyclic GMP, a congener resistant to hydrolysis, is a more powerful activator of the release than cyclic GMP itself. Ca2+ release by cyclic GMP is inhibited by organic and inorganic blockers of Ca2+ channels. The l-stereoisomer of cis-diltiazem blocks the release of Ca2+ at micromolar concentrations, whereas the d-form is much less effective. These results suggest that disc membranes contain a cationic conductance which is permeable to Ca2+ ions and which is regulated through the cooperative binding of at least 2 molecules of cyclic GMP to regulatory sites of the transport protein. By this mechanism, subtle changes in the concentration of cyclic GMP could promote large changes in the flux of Ca2+ ions across the disc membrane. 相似文献
77.
78.
79.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
80.
Recent studies have revealed an unexpected synergism between two seemingly unrelated protein families: CCN matricellular proteins
and the tumor necrosis factor (TNF) family of cytokines. CCN proteins are dynamically expressed at sites of injury repair
and inflammation, where TNF cytokines are also expressed. Although TNFα is an apoptotic inducer in some cancer cells, it activates
NFκB to promote survival and proliferation in normal cells, and its cytotoxicity requires inhibition of de novo protein synthesis
or NFκB signaling. The presence of CCN1, CCN2, or CCN3 overrides this requirement and unmasks the apoptotic potential of TNFα,
thus converting TNFα from a proliferation-promoting protein into an apoptotic inducer. These CCN proteins also enhance the
cytotoxicity of other TNF cytokines, including LTα, FasL, and TRAIL. Mechanistically, CCNs function through integrin α6β1 and the heparan sulfate proteoglycan (HSPG) syndecan-4 to induce reactive oxygen species (ROS) accumulation, which is essential
for apoptotic synergism. Mutant CCN1 proteins defective for binding α6β1-HSPGs are unable to induce ROS or apoptotic synergism with TNF cytokines. Further, knockin mice that express an α6β1-HSPG-binding defective CCN1 are blunted in TNFα- and Fas-mediated apoptosis, indicating that CCN1 is a physiologic regulator
of these processes. These findings implicate CCN proteins as contextual regulators of the inflammatory response by dictating
or enhancing the cytotoxicity of TNFα and related cytokines. 相似文献