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   99152篇
  免费   7697篇
  国内免费   32篇
  2021年   849篇
  2018年   1320篇
  2017年   1248篇
  2016年   1650篇
  2015年   1739篇
  2014年   2103篇
  2013年   2992篇
  2012年   3265篇
  2011年   3395篇
  2010年   2508篇
  2009年   2120篇
  2008年   3089篇
  2007年   3039篇
  2006年   2865篇
  2005年   2703篇
  2004年   2706篇
  2003年   2602篇
  2002年   2415篇
  2001年   4452篇
  2000年   4199篇
  1999年   3255篇
  1998年   1044篇
  1997年   1035篇
  1996年   917篇
  1995年   838篇
  1992年   2506篇
  1991年   2526篇
  1990年   2544篇
  1989年   2297篇
  1988年   2123篇
  1987年   2045篇
  1986年   1872篇
  1985年   1875篇
  1984年   1542篇
  1983年   1336篇
  1982年   939篇
  1981年   896篇
  1979年   1474篇
  1978年   1158篇
  1977年   1041篇
  1976年   1004篇
  1975年   1199篇
  1974年   1304篇
  1973年   1385篇
  1972年   1226篇
  1971年   1076篇
  1970年   960篇
  1969年   990篇
  1968年   871篇
  1967年   851篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
New material ofTrischizolagus dumitrescuae from Moldova and Ukraine is described. The variation of p3 inTrischizolagus shows the gradual shift of morphotype frequencies from the ‘Hypolagus’ pattern in Turolian through the mixture of three patterns (including ‘Nekrolagus’ morphotype) in Early Ruscinian to the dominant ‘Alilepus’ pattern in the Late Ruscinian samples. These transformations took place parallel to that of the North AmericanNekrolagus. Probably North AmericanSylvilagus, Brachylagus, andRomerolagus had an North American origin fromNekrolagus, whereas Eurasiatic and AfricanOryctolagus, Caprolagus, Nesolagus, andPoelagus could have originated in the Old World fromTrischizolagus.  相似文献   
142.
143.
Bacillus thuringiensis serotype H-14 spores and crystals, produced in 51 fermenters, were centrifuged and resuspended in emulsified palm olein to give 3.2 x 10(11) colony forming units (cfu)/ml. The suspension was mixed with a cassava-molasses-palm olein-charcoal (CMPC-2) mixture which served as the carrier, adhesive, dispersant and protectant. The final concentration of the formulation was 3.2 x 10(9) cfu/ml. The lethal concentrations capable of killing 50% of the test population (LC50) of CMPC-2 during 0, 1 and 2 years of storage at 32 +/- 4 degrees C were 0.056, 0.058 and 0.058 mg/ml respectively as against 0.054, 0.051 and 0.054 mg/ml for the Institut Pasteur Standard-1978 (IPS-78) during the corresponding period. The chi 2 tests showed that the results were homogeneous at P = 0.05. The relative potencies of the preparations were 964.3, 879.3 and 931 International toxic units (ITU) Aedes aegypti as compared with the 1000 ITU assigned to IPS-78. At 95% confidence limits there was no significant difference between the potencies of CMPC-2 and IPS-78. Field tests showed that CMPC-2 provided between 87.5 and 100% control of natural populations of Aedes spp. and Cutex spp. Sedimentation tests showed that CMPC-2 settled markedly during storage. This, therefore, required that the product be thoroughly shaken before use.  相似文献   
144.
The experiments on rats have shown that total hepatic ischemia reduces the content of microsomal cytochromes P-450 and b5 and causes amidopyrine and aniline disturbances over a 2-3-week post-ischemic period. The analysis of hepatocyte ultrastructure has revealed the interdependence of structural and functional changes in endoplasmic reticulum during recovery period. The damage of monooxygenase inducibility correlated with stable decline in the number of fixed ribosomes in post-ischemic period.  相似文献   
145.
We used Chelex 100 chelating resin to prepare DNA for the polymerase chain reaction (PCR) from two species of Hymenopteran parasitoids, Trioxys pallidus and Diglyphus begini. Chelex 100 produces consistent DNA yields for both species, as measured with Hoescht dye fluorometry. Approximately twice as much DNA was obtained from individual D. begini wasps than from T. pallidus wasps, but there were no differences in yield between sexes. We used this DNA to perform random amplified polymorphic DNA (RAPD) analysis, a PCR technique that amplifies various regions of the genome using arbitrarily chosen 10-base primers. Of the 120 primers tested using T. pallidus, 92 produced a total of 342 scorable bands, 118 of which exhibited presence/absence polymorphism. Of the 25 primers tested using D. begini, 18 produced a total of 53 scorable bands, 30 of which exhibited presence/absence polymorphism. The level of genetic variation detected using this technique was greater than any found in Hymenoptera using allozymes. Scorable bands segregated as dominant Mendelian traits. Potential uses of RAPD-PCR in genetic analyses on parasitic Hymenoptera are discussed.  相似文献   
146.
147.
148.
149.
Reactivity of neurones in orbitofrontal cortex of the cat to the action of light or sound was studied in consecutive stages of alimentary behaviour conditioned by the smell and then the sight of food. Changes were found of the character of neuronal reactions to the light and sound stimuli at the change of smell to the sight of food. A conclusion is drown, that polysensory properties of the neurones of the orbitofrontal cortex provide integral organization of brain sensory function at separate stages of alimentary behaviour.  相似文献   
150.
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