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   694681篇
  免费   77302篇
  国内免费   524篇
  772507篇
  2018年   5689篇
  2016年   7635篇
  2015年   10494篇
  2014年   12252篇
  2013年   17869篇
  2012年   20726篇
  2011年   21145篇
  2010年   13778篇
  2009年   12428篇
  2008年   18637篇
  2007年   19505篇
  2006年   18333篇
  2005年   17509篇
  2004年   17092篇
  2003年   16324篇
  2002年   16354篇
  2001年   31865篇
  2000年   32625篇
  1999年   25462篇
  1998年   8555篇
  1997年   8926篇
  1996年   8465篇
  1995年   8050篇
  1994年   7919篇
  1993年   7787篇
  1992年   20915篇
  1991年   20336篇
  1990年   19584篇
  1989年   18968篇
  1988年   17825篇
  1987年   16959篇
  1986年   15855篇
  1985年   15953篇
  1984年   13194篇
  1983年   11355篇
  1982年   8905篇
  1981年   8099篇
  1980年   7466篇
  1979年   12773篇
  1978年   10034篇
  1977年   9176篇
  1976年   8597篇
  1975年   9760篇
  1974年   10454篇
  1973年   10332篇
  1972年   9562篇
  1971年   8448篇
  1970年   7468篇
  1969年   7211篇
  1968年   6550篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked.  相似文献   
82.
83.
84.
The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments.  相似文献   
85.
86.
The precipitation of tobacco mosaic virus by sodium chondroitin sulfate in an aqueous solution was investigated kinetically by means of turbidimetry. The virus solution became turbid after the addition of chondroitin sulfate. A threshold concentration of chondroitin, 1.33 mg/ml, was required for virus precipitation, irrespective of the virus concentration. The precipitation resulted from a mutual spatial exclusion phenomenon, leading to the separation of the virus as a crystalline phase. The dimension of chondroitin sulfate calculated at the threshold concentration agreed well with that obtained by other methods. The initial slopes and the aggregation half-times of the virus aggregates depended on both chondroitin and virus concentrations and the former increased with the increase in concentration of each. Above the threshold concentration of chondroitin sulfate, tobacco mosaic virus aggregation was a rapid-aggregation process and ended within 100 sec.  相似文献   
87.
88.
89.
The linkage of the Phi, Pgd, Po2, S, H and halothane sensitivity loci was followed in a Belgian Landrace family, heterozygous for these systems over 6 generations. Recombination next to the S locus occurred mainly in pigs belonging to this particular family. From this investigation the position of the S locus is proved to be outwith the Phi-Pgd region, next to Phi . Therefore the gene sequence S - Phi - Hal -H- Po2 -Pgd is proposed. Higher recombination rates were observed in the female parental line of the multiheterozygous family when compared to the male parental line. Additional data from animals, unrelated to this strain, confirm the evidence of close linkage of the S system to the nearest marker loci.  相似文献   
90.
Fumaria capreolata was taken into cell suspension culture. The culture yielded a biomass of about 12 g dry weight per liter of medium; the dried cells contained ca. 0.1% of alkaloids. Besides choline, the following ten known isoquinoline alkaloids were isolated from the cell extract in crystalline form: coptisine, dehydrocheilanthifoline; (+)-isoboldine; magnoflorine; N-methylcoclaurine; (+)-reticuline; (–)-pallidine; protopine; sanguinarine; (–)-scoulerine. This is the most diverse isoquinoline alkaloid spectrum thus far published for a cell suspension culture.  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