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   208499篇
  免费   9975篇
  国内免费   932篇
  219406篇
  2021年   1244篇
  2019年   984篇
  2018年   13272篇
  2017年   11942篇
  2016年   9341篇
  2015年   3125篇
  2014年   3168篇
  2013年   4372篇
  2012年   8799篇
  2011年   17293篇
  2010年   15151篇
  2009年   10940篇
  2008年   13754篇
  2007年   15252篇
  2006年   4124篇
  2005年   4248篇
  2004年   4645篇
  2003年   4514篇
  2002年   4104篇
  2001年   4854篇
  2000年   4453篇
  1999年   3493篇
  1998年   1310篇
  1997年   1227篇
  1996年   1085篇
  1995年   987篇
  1993年   1021篇
  1992年   2614篇
  1991年   2632篇
  1990年   2591篇
  1989年   2364篇
  1988年   2232篇
  1987年   2114篇
  1986年   1943篇
  1985年   1961篇
  1984年   1644篇
  1983年   1449篇
  1982年   1115篇
  1981年   1060篇
  1979年   1546篇
  1978年   1261篇
  1977年   1116篇
  1976年   1077篇
  1975年   1249篇
  1974年   1349篇
  1973年   1421篇
  1972年   1496篇
  1971年   1376篇
  1970年   984篇
  1969年   1009篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
124.
125.
The combination of alpha interferon and vinblastine has been reported to yield a response rate of 30-40% in previously untreated patients with metastatic renal cell carcinoma. This combination was given to nine patients with advanced metastatic renal carcinoma after they failed or relapsed on alpha-interferon alone, to attempt to evaluate the role of vinblastine in this combination. Neither complete nor partial response was observed. Two patients had disease stabilization for two and seven months. Our preliminary results suggest that vinblastine did not add to the efficacy of interferon in this group of patients.  相似文献   
126.
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   
127.
Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature, particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case – Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population, but it is not (always) impossible.  相似文献   
128.
129.
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   
130.
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   
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