首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   181377篇
  免费   14342篇
  国内免费   49篇
  2018年   1808篇
  2017年   1757篇
  2016年   2249篇
  2015年   2139篇
  2014年   2936篇
  2013年   4190篇
  2012年   4805篇
  2011年   5313篇
  2010年   3718篇
  2009年   3355篇
  2008年   4861篇
  2007年   5130篇
  2006年   4831篇
  2005年   4543篇
  2004年   4690篇
  2003年   4596篇
  2002年   4572篇
  2001年   8385篇
  2000年   8579篇
  1999年   6314篇
  1998年   1989篇
  1997年   2037篇
  1996年   1803篇
  1995年   1674篇
  1992年   5198篇
  1991年   5363篇
  1990年   5141篇
  1989年   5116篇
  1988年   4732篇
  1987年   4485篇
  1986年   4076篇
  1985年   4234篇
  1984年   3408篇
  1983年   2911篇
  1982年   1929篇
  1981年   1728篇
  1980年   1718篇
  1979年   3214篇
  1978年   2550篇
  1977年   2280篇
  1976年   2081篇
  1975年   2547篇
  1974年   2884篇
  1973年   2802篇
  1972年   2651篇
  1971年   2415篇
  1970年   2118篇
  1969年   2022篇
  1968年   1906篇
  1967年   1743篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The action of solar light transformed by special screens has been studied on CD-1 male mice. In the active control group, mice were irradiated through screens absorbing the UV-component. In the experimental group, screens transforming the UV-component into the orange-red light were used. In the active control, changes in the swimming activity, as compared to the same parameter before irradiation, were manifested much less than in animals of the experimental group. A morphological analysis showed changes in the structure of all cardiomyocyte organelles studied: the relative area of mitochondria in the experimental mice increased by more than 20% compared to intact animals (p < 0.05). A significant increase in the area of the sarcoplasmic reticulum, by 23.4% (p < 0.05), and in the volume of the myofibrillar apparatus, by 19.4% (p < 0.05), was detected. The results of our experiment show that the irradiation with using an additional orangered component improves the physical endurance 1.5 times and initiates morphogenetic processes in cardiac muscle cells.  相似文献   
993.
DNA- and RNA-binding proteins of chromatin from Escherichia coli   总被引:3,自引:0,他引:3  
The different proteins present in chromatin of Escherichia coli have been analyzed by a variety of techniques. The chromatin was isolated using a previously published procedure (Sj?stad, K., Fadnes, P., Krüger, P.G. Lossius, I. and Kleppe, K. (1982) J. Gen. Microbiol. 128, 3037) and solubilized by the action of micrococcal nuclease or DNAase I. The DNA-protein and RNA-protein complexes thus obtained were purified by sucrose gradient centrifugation and isopycnic gradient centrifugation in metrizamide in low ionic strength. The protein: DNA ratio of the DNA-protein complexes was estimated from the latter method and found to be approx. 1.75. The protein components were analyzed further by one- and two-dimensional gel electrophoresis. Approx. 15 major polypeptides were detected in the DNA-protein complex, whereas 10 were present in the RNA-protein complex. The majority of the polypeptides in both complexes had acidic isoelectric pH. The polypeptides in the two complexes differed markedly and only two polypeptides, having molecular weights of 57,000 and 37,000, respectively, were found to be common in both complexes. In agreement with earlier studies, the basic protein HU was not present in the DNA-protein complex. Affinity studies of the proteins from chromatin using DNA- and RNA-Sepharose columns in general confirmed the above conclusions. The two-dimensional gel electrophoretic patterns of the proteins in the different complexes were compared with those of proteins in the inner and outer membranes. Only one of the major polypeptides present in the inner membrane, having a molecular weight of 57,000, was enriched in the DNA-protein complex.  相似文献   
994.
A fermentation system with a plug scheme unit has been developed, offering a variety of solutions to measurement, control, and operational problems. By means of the program unit, e.g., automatic pH control assigned to the dynamic of batch cultures and the feed of different ingredients controlled by a time program or a given variable have been solved. The continuous culture volume was controlled by a level controlled by a level controller equipped with a photosensor. A method was developed for variable control that provide information on the activity of the culture, and allows direct measurement of the different rate values, e.g., generation time or specific product formation rate. Applicability of the direct measurement of generation time is presented in the qualification of molasses and in a static off-line optimization process.  相似文献   
995.
996.
A total of 1 968 persons aged 18-20 years belonging to organized groups were immunized with different doses of polysaccharide meningococcal divaccine, groups A and C, by means of syringes and jet injectors under the conditions of a controlled epidemiological trial. Systemic reactions to the injection of the preparation were found to be absent. Local reactions manifested by inflammation, swelling and tenderness at the site of injection were faintly pronounced and disappeared in 48 hours, which is indicative of low reactogenicity of the preparation under study.  相似文献   
997.
The influence of immunization with P. aeruginosa vaccine on the immune status of volunteer donors has been studied. Immunization with P. aeruginosa vaccine in doses of 0.5-0.5-1.0 ml at intervals of 7 days has been found to lead to the 13-fold increase of the titer of specific antibodies, lasting for 3-4 months, which ensures the possibility of obtaining anti-P. aeruginosa hyperimmune plasma with standard titers. The injection of P. aeruginosa vaccine to donors leads to the activation of humoral immunity simultaneously with the increase of the absolute and relative number of rosette-forming B-lymphocytes without essential changes in the amount of rosette-forming T-lymphocytes.  相似文献   
998.
The method of intravenous administration of UV-irradiated donor plasma to patients with jaundice of different genesis has been tested in the experiments on rats and used clinically in 20 patients. Biochemical and morphological studies have shown that such treatment causes stable improvement in the liver functional state.  相似文献   
999.
Heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro (ACTH4-10 analog) at a dose of 0.015 mg/kg failed to alter open field behaviour of rats in the first test series. The peptide abolished amphetamine-induced stimulation of the exploratory and grooming behaviour. Extinction of the rats' exploratory behaviour during second test series in the open field (7 days later) was disturbed when haloperidol or apomorphine were injected before the first test series. When the peptide was administered with haloperidol or apomorphine, the extinction tended to become normal. Heptapeptide failed to change noradrenaline, dopamine or 5-hydroxytryptamine content in the rat forebrain. However, this peptide at a concentration of 10(-4) M moderately diminished tyrosine hydroxylation velocity in the rat striatal or hypothalamic synaptosomes, the effect depending on tyrosine concentration. These data suggest the involvement of catecholaminergic component into the heptapeptide action on the behaviour of rats.  相似文献   
1000.
A mutant of Escherichia coli which is more resistant to shortwave UV light than its wild-type parent strain and which can synthesise DNA polymerase I constitutively has been further analysed. It carries two mutational alleles which are located about 1.5 min apart and cotransducible by P1 with the argH locus. The two mutational alleles have been segregated and their analysis shows that one of them is responsible for UV hyper-resistance whereas the other mutation confers UV sensitivity. Recombinant plasmids carrying various sections of the polA regulatory region, linked to a galK gene, were introduced into the mutant strains. Analysis of galactokinase shows that the enzyme activity in the UV hyper-resistant mutant is increased. The results suggest that the synthesis of DNA polymerase I in E. coli is inducible.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号