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   420162篇
  免费   43680篇
  国内免费   196篇
  464038篇
  2016年   4526篇
  2015年   5966篇
  2014年   7071篇
  2013年   10635篇
  2012年   11508篇
  2011年   11987篇
  2010年   8150篇
  2009年   7487篇
  2008年   10689篇
  2007年   11346篇
  2006年   10679篇
  2005年   10158篇
  2004年   10250篇
  2003年   10014篇
  2002年   9818篇
  2001年   17346篇
  2000年   17391篇
  1999年   14051篇
  1998年   4977篇
  1997年   5286篇
  1996年   5011篇
  1995年   4728篇
  1994年   4632篇
  1993年   4629篇
  1992年   12266篇
  1991年   12072篇
  1990年   12083篇
  1989年   11856篇
  1988年   11165篇
  1987年   10500篇
  1986年   9819篇
  1985年   10238篇
  1984年   8439篇
  1983年   7275篇
  1982年   5613篇
  1981年   5020篇
  1980年   4694篇
  1979年   8082篇
  1978年   6300篇
  1977年   5940篇
  1976年   5672篇
  1975年   6130篇
  1974年   6697篇
  1973年   6568篇
  1972年   6122篇
  1971年   5535篇
  1970年   4767篇
  1969年   4782篇
  1968年   4453篇
  1967年   3808篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
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   
172.
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   
173.
174.
175.
176.
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   
177.
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   
178.
The infection of Planorbarius banaticus with sporocysts of Cotylurus cornutus is accompanied by an increase in aldolase activity of molluscs' haemolymph of 1.2 fold. In solutions of nitroammofoska (0.1, 1 and 10 mg/1) the activity of this ferment in infected individuals increases much higher than in non-infected ones. This results in fast carbohydrate expenditures by molluscs, intermediate hosts of trematodes, and their death from exhaustion.  相似文献   
179.
The effects of corticotropin-releasing hormone (CRH) injected into the dorsal neostriatum on the open-field and shuttle-box behavior were studied in rats with high (Koltushi high avoidance, KHA) and low (Koltushi low avoidance, KLA) capability for avoidance learning. The effects of this hormone on the behavior of these rat strains were different. In KLA rats with passive strategy of behavior the CRH injection led to a rapid locomotor activation in the open field, while the rats with active behavioral strategy (KHA) reacted to the injection by a significant decrease in locomotion and change for the passive mode of behavior. The same CRH effects on locomotion were obtained in the shuttle-box experiments. Moreover, in the KLA rats the neurohormone injection resulted in an improvement of avoidance learning in contrast to the KHA rats, in which CRH substantially impaired avoidance learning. The obtained evidence is discussed in terms of the important role of striatal CRH in the choice of behavioral strategy in stress.  相似文献   
180.
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