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   963666篇
  免费   104669篇
  国内免费   477篇
  1068812篇
  2018年   8525篇
  2016年   11619篇
  2015年   15515篇
  2014年   18569篇
  2013年   26010篇
  2012年   29845篇
  2011年   30389篇
  2010年   20915篇
  2009年   19318篇
  2008年   27642篇
  2007年   28564篇
  2006年   26931篇
  2005年   25749篇
  2004年   25737篇
  2003年   24811篇
  2002年   24238篇
  2001年   40821篇
  2000年   41081篇
  1999年   32851篇
  1998年   12236篇
  1997年   12689篇
  1996年   12105篇
  1995年   11432篇
  1994年   11235篇
  1993年   11051篇
  1992年   27668篇
  1991年   27203篇
  1990年   26897篇
  1989年   26191篇
  1988年   24231篇
  1987年   23569篇
  1986年   21656篇
  1985年   21961篇
  1984年   18092篇
  1983年   15656篇
  1982年   12094篇
  1981年   10759篇
  1980年   10298篇
  1979年   17260篇
  1978年   13754篇
  1977年   12482篇
  1976年   11890篇
  1975年   13149篇
  1974年   14279篇
  1973年   14050篇
  1972年   12532篇
  1971年   11687篇
  1970年   10003篇
  1969年   9482篇
  1968年   8573篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
Antigenic change on the surface of immature oocytes of Ascaris occurred during passage through the oviduct. Using immunodiffusion and immunoelectrophoretic techniques we examined the possible relationship between the antigenic change of immature oocytes and the junctional fluid (JF) which is present in the fertilization chamber. From the immunodiffusion it was found that the anti-immature oocyte serum (A-I serum) had more immunoprecipitation arcs than did the anti-mature oocyte serum (A-M serum) when reacted against the junctional fluid. This indicated that A-I serum contained more immunoglobulins that reacted with junctional fluid than did the A-M serum. This result was substantiated by using immunoelectrophoretic analysis and two dimension crossed immunoelectrophoresis. Our results suggest that during the migration toward the oviduct-uterine junction the immature oocytes might shed surface proteins into the luminal fluid. Alternatively, the membrane surface of mature oocytes may be altered by the interaction with the substances present in the junctional fluid.  相似文献   
996.
997.
998.
The ergosterol and lecithin absorption IR-spectra were studied in a nonpolar anhydrous medium. The thermodynamical and spectral characteristics of dimeric associates and the enthalpy value for trimeric associates of this sterol are determined. Thermodynamical and spectral parameters of ergosterol intermolecular associates with lecithin in a nonpolar anhydrous medium are found. It is established that the intermolecular interaction of lecithin with ergosterol occurs according to the mechanism of hydrogen bond. A conclusion is drawn that the presence of binary bonds and methyl groups in the cyclic and aliphatic parts of the sterol molecule affects greatly the structure of the model membrane and its strength. It is shown that under conditions of the experiment the oxygen of the phosphate group contributes to formation of the molecular associates of lecithin with sterols and not that of the carbonyl group. The obtained experimental data may be at use when studying structural disturbances of native membranes in norm and with different pathologies.  相似文献   
999.
1000.
A total of 764 breeding soundness examinations was conducted on beef bulls utilizing the method of examination and criteria for classifying bulls of the Society for Theriogenology. In addition to this examination each bull was subjected to scrotal circumference measurement and to weighing. Classification of the bulls according to breeding soundness potentials was as follows: 88% of the bulls were satisfactory potential breeders, 8% of the bulls were questionable potential breeders and 4% of the bulls were unsatisfactory potential breeders. The proportions of bulls in each classification; satisfactory, questionable, or unsatisfactory; were not different among the four breeds evaluated. The majority of bulls evaluated in this study were between 14 and 36 months of age and weighed between 900 and 1500 pounds. For the ages and weights evaluated, scrotal circumference measurement variances were not closely related to age and weight differences. There was a tendency shown for “Questionable” and “Unsatisfactory Potential Breeders” to have smaller scrotal circumference measurements. The study indicates that Angus, Charolais, Horned Hereford and Polled Hereford bulls of breeding ages and weights should have scrotal circumference measurements of at least 32 centimeters in order to be classified as “Satisfactory Potential Breeders”.  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