全文获取类型
收费全文 | 214217篇 |
免费 | 8081篇 |
国内免费 | 919篇 |
专业分类
223217篇 |
出版年
2021年 | 881篇 |
2018年 | 15059篇 |
2017年 | 14042篇 |
2016年 | 10364篇 |
2015年 | 2489篇 |
2014年 | 2461篇 |
2013年 | 3334篇 |
2012年 | 8454篇 |
2011年 | 18835篇 |
2010年 | 16935篇 |
2009年 | 12782篇 |
2008年 | 15260篇 |
2007年 | 17519篇 |
2006年 | 3206篇 |
2005年 | 4187篇 |
2004年 | 4065篇 |
2003年 | 4212篇 |
2002年 | 3729篇 |
2001年 | 4727篇 |
2000年 | 4447篇 |
1999年 | 3256篇 |
1998年 | 1059篇 |
1997年 | 1057篇 |
1996年 | 944篇 |
1995年 | 842篇 |
1994年 | 841篇 |
1993年 | 867篇 |
1992年 | 2469篇 |
1991年 | 2512篇 |
1990年 | 2467篇 |
1989年 | 2223篇 |
1988年 | 2082篇 |
1987年 | 1999篇 |
1986年 | 1827篇 |
1985年 | 1823篇 |
1984年 | 1509篇 |
1983年 | 1323篇 |
1982年 | 946篇 |
1981年 | 873篇 |
1979年 | 1436篇 |
1978年 | 1128篇 |
1977年 | 1016篇 |
1976年 | 973篇 |
1975年 | 1169篇 |
1974年 | 1257篇 |
1973年 | 1339篇 |
1972年 | 1875篇 |
1971年 | 1692篇 |
1970年 | 932篇 |
1969年 | 955篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
101.
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
102.
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
103.
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
104.
The capillaries of the cardiac muscle were investigated in the goat by means of light microscopy, transmission electron microscopy and scanning electron microscopy, and the following results were obtained. The capillaries of the working cardiac muscles were numerous, arranged mainly parallel to the long axis of muscle cells and formed dense elongated networks. On the contrary, those of the terminal Purkinje fibers were relatively few in number, oriented in various directions and formed loose and circularly meshed networks surrounding the fibers. Such findings were discussed in correlation with the physiology and functional morphology of various types of the cardiac muscle cells. 相似文献
105.
106.
A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto new production and regenerated production.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom. 相似文献
107.
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
108.
109.
V. S. Oganov O. L. Vinogradova N. S. Dudov V. S. Baranov A. S. Minenkov A. V. Bakulin V. E. Novikov O. E. Kabitskaya M. V. Moskalenko A. S. Glotov O. S. Glotov D. V. Popov 《Human physiology》2008,34(2):182-190
The association of the polymorphism of the VDR, Col1a1, and CALCR genes with a form of osteoporosis frequently occurring as a consequence of intense physical exercise in athletes was studied. Biochemical parameters of bone remodeling and its neuroendocrine regulation, as well as the bone masses, of 22 amateur athletes were determined immediately before a strenuous nine-week training cycle (TC) and eight months later. The possible association of these factors with the polymorphism of the genes coding for bone tissue proteins was studied. Long-term intense physical training was found to be associated with a significant activation of bone tissue resorption accompanied by continued rapid synthesis. Nevertheless, and in spite of the strong activation of resorption caused by the TC, the athletes exhibited no osteoporosis (even eight months after the discontinuation of the TC); some of them, however, displayed an individual tendency to osteopenia. According to the results of genetic analysis, this was associated with the polymorphism of predisposition genes (genotype TT of the VDR gene and the functionally weakened s allele of the Col1a1 gene). 相似文献
110.