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   8147篇
  免费   421篇
  国内免费   4篇
  2022年   92篇
  2021年   171篇
  2020年   114篇
  2019年   116篇
  2018年   171篇
  2017年   145篇
  2016年   227篇
  2015年   296篇
  2014年   367篇
  2013年   487篇
  2012年   539篇
  2011年   469篇
  2010年   327篇
  2009年   239篇
  2008年   338篇
  2007年   343篇
  2006年   275篇
  2005年   302篇
  2004年   245篇
  2003年   248篇
  2002年   220篇
  2001年   202篇
  2000年   169篇
  1999年   156篇
  1998年   77篇
  1997年   64篇
  1996年   56篇
  1995年   57篇
  1994年   51篇
  1992年   122篇
  1991年   92篇
  1990年   134篇
  1989年   101篇
  1988年   108篇
  1987年   96篇
  1986年   84篇
  1985年   95篇
  1984年   91篇
  1983年   65篇
  1982年   70篇
  1981年   92篇
  1980年   66篇
  1979年   99篇
  1978年   67篇
  1977年   69篇
  1976年   50篇
  1975年   60篇
  1974年   58篇
  1973年   49篇
  1972年   48篇
排序方式: 共有8572条查询结果,搜索用时 890 毫秒
91.
92.
93.
A technique is described for determination of rubella hemagglutination-inhibiting antibody in only 50 to 100 muliters of whole blood.  相似文献   
94.
95.
The increased sensitivity and improved agglutination and settling patterns of formalinized sheep erythrocytes in a new buffer, HEPES (N-2-hydroxyethylpiperazine N'-2'-ethanesulfonic acid), make this system more suitable for use in the rubella hemagglutination-inhibition test.  相似文献   
96.
Some biochemical properties ofTrigonella foenum-groecum infected withPeronospora trifoliorum have been investigated. Qualitative changes were observed in lipids, coumarins, amino acids and indole compounds only. A quantitative study of the phosphate content was also carried out. Neutral lipids did not show any significant changes. In addition to the fourteen phospholipid bands, the infected leaves contained a new band corresponding in Rf to phosphatidic acid or polyglycerophosphate. Seven coumarins were present in both the extracts. In addition 3-hydroxy coumarin, 5-hydroxy-4-methylcoumarin and 7-hydroxy-4-methyl-coumarin were detected in infected leaves. Higher levels of indole acetic acid and three of its derivatives were observed due to infection. Infection altered the free amino acid content. Tryptophan appeared and the total phosphate content increased. Increase in phenols and indoles suggest a higher respiratory rate whereas a higher content of inorganic phosphate suggests uncoupling of phosphorylation from respiration.  相似文献   
97.
98.
Summary Five rates of limestone and 4 rates of fertilizers were used in a split-plot design to study their effects under field conditions on Mo, Cu, B, Mn, and Zn levels in mixed forage tissue and soil, and on the forage yield. An increase in soil pH resulted in an increase in Mo and Cu content of plant tissue while B, Mn, and Zn decreased. The micro-nutrient content of the tissue increased as the harvesting season progressed. Increasing rates of applied fertilizer did not affect the micro-nutrient content of the forage tissue or soil. Liming to a pH of 5.6 and above reduced the availability of Mn and Zn in the soil. In general, the available B was low at pH values greater than 6.1. Lime did not affect the quantities of Mo and Cu in the soil. Manganese is supplied in large quantities by limestone and is not apt to be deficient in limed soil. However, addition of B and Zn may be required on the high pH soils of Eastern Canada in future. Molybdenum was adequate where the soil was limed to a pH of 6.1 or greater. The dry-matter yield of forage increased significantly with successive increases in lime up to pH 6.6 and with each increment of fertilization. Contribution No.226, Research Branch, Research Station, P.O. Box 1210, Charlottetown, P.E.I. and No.166, Experimental Farm, Nappan, N.S.  相似文献   
99.
Summary Experiments were conducted to determine the influence of N, P, and K and of the NP and NK interactions on root yields and tissue concentrations of N, P, and K of rutabagas grown on a sandy loam soil under greenhouse conditions. Root yields were increased by applications of N and K but not by added P. The yield response to N was dependent on K supply. The highest dry matter content in roots was associated with the lowest rates of N and K and the lowest root yields. The N content of tissue at the early vegetative stage increased with increasing rates of N and decreased with increasing rates of P and K. The N content of root tissue at harvest increased at the highest rates of N but was unaffected by rates of P and K. The P and K content of root tissue increased with increasing rates of P and K, respectively. The levels of nutrients in early vegetative tissue associated with optimum yields were about 2.6, 0.24, and 2.0% for N, P, and K, respectively. The corresponding values in the leaf tissue at harvest were about 1.2, 0.12, and 1.5% N, P, and K, respectively. Contribution No.222.  相似文献   
100.
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