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   616110篇
  免费   61860篇
  国内免费   447篇
  678417篇
  2018年   5570篇
  2016年   7252篇
  2015年   8990篇
  2014年   10834篇
  2013年   16016篇
  2012年   17390篇
  2011年   18330篇
  2010年   12464篇
  2009年   11359篇
  2008年   16192篇
  2007年   16984篇
  2006年   16005篇
  2005年   15340篇
  2004年   15229篇
  2003年   14840篇
  2002年   14632篇
  2001年   26671篇
  2000年   26778篇
  1999年   21156篇
  1998年   7136篇
  1997年   7497篇
  1996年   7167篇
  1995年   6720篇
  1994年   6629篇
  1993年   6513篇
  1992年   17881篇
  1991年   17539篇
  1990年   17578篇
  1989年   17170篇
  1988年   16132篇
  1987年   15290篇
  1986年   14025篇
  1985年   14662篇
  1984年   11943篇
  1983年   10319篇
  1982年   7768篇
  1981年   7016篇
  1980年   6546篇
  1979年   11416篇
  1978年   8831篇
  1977年   8312篇
  1976年   7948篇
  1975年   8809篇
  1974年   9557篇
  1973年   9437篇
  1972年   8580篇
  1971年   7884篇
  1970年   6908篇
  1969年   6687篇
  1968年   6267篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production.  相似文献   
222.
The authors studies the effects of blood serum and IgG fraction from dogs immunized with brain and blood sera from patients with multiple sclerosis and schizophrenia on lipid peroxidation in rat brain homogenates. Measured the content of diene conjugates (DC) and malonic dialdehyde (MDA) in the rat brain after administering the IgG fraction. It was established that antioxidant activity of blood sera and IgG fraction from control animals and donors was significantly higher as compared to experimental. Administration of the IgG fraction brought about an increase in the content of DC and MDA in the brain of experimental animals. It is concluded that complement-dependent brain antibodies present in the blood serum of patients with schizophrenia and multiple sclerosis potentiate lipid peroxidation in the cerebral tissue and that the unsophisticated and informative method for antibody determination may be used in clinical practice.  相似文献   
223.
224.
225.
226.
227.
228.
We isolated and sequenced 26 microsatellites from two genomic libraries of peach cultivar 'Redhaven', enriched for AC/GT and AG/CT repeats, respectively. For 17 of these microsatellites, it was possible to demonstrate Mendelian inheritance. Microsatellite polymorphism was assayed in 50 peach and nectarine cultivars. Of the 1300 PCRs carried out, all but two produced amplified products of the expected size. All microsatellites were polymorphic, showing 2-8 alleles per locus. Heterozygosity ranged from 0.04-0.74 (mean 0.47); the discrimination power (PD) ranged from 0.04-0.84 (mean 0.60). Cultivar heterozygosity varied greatly, with one cultivar ('Independence') being homozygous at all loci. The set of microsatellites discriminated all cultivars investigated, except several sport mutations, i.e., 'Dixitime' vs. 'Springcrest', 'Compact Redhaven' vs. 'Redhaven', and two pairs of cultivars, 'Venus' vs. 'Orion' and 'Elegant Lady' vs. 'Rome Star', whose pedigrees are controversial. We were able to analyze the paternity of several cultivars. In most cases, the parenthood was confirmed. The comparison of three long-living 'Redhaven' accessions supplied by different repositories did not provide any evidence of somatic instability of microsatellites. Hence, microsatellites, ranked according to their information content, are recommended as markers of choice for peach fingerprinting and suggestions are provided for interpreting band profiles and the correct sizing of alleles.  相似文献   
229.
Irradiation conditions in which laboratory animals were kept in experimental laboratories of Chernobyl and Kiev after the accident at the Chernobyl A.P.S. are described. The data are presented on the spectral structural and activity of radionuclides in the diet as well as in the organs and tissues of the animals. The radiation loads have been estimated with regard to an external gamma component and the internal one contributed by the incorporated radionuclides. It has been shown that radiation doses received by the animals during their lifetime due to these contributions do not exceed units of cGy.  相似文献   
230.
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