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   177263篇
  免费   9417篇
  国内免费   120篇
林业   8698篇
农学   6272篇
基础科学   1149篇
  23700篇
综合类   26405篇
农作物   7137篇
水产渔业   9170篇
畜牧兽医   89624篇
园艺   2815篇
植物保护   11830篇
  2019年   1692篇
  2018年   3320篇
  2017年   3687篇
  2016年   3049篇
  2015年   2312篇
  2014年   2844篇
  2013年   6858篇
  2012年   5439篇
  2011年   7111篇
  2010年   4947篇
  2009年   4821篇
  2008年   6726篇
  2007年   6569篇
  2006年   5586篇
  2005年   5282篇
  2004年   4942篇
  2003年   5095篇
  2002年   4575篇
  2001年   5594篇
  2000年   5645篇
  1999年   4487篇
  1998年   1919篇
  1997年   1817篇
  1996年   1714篇
  1995年   1999篇
  1994年   1776篇
  1993年   1653篇
  1992年   3468篇
  1991年   3650篇
  1990年   3602篇
  1989年   3530篇
  1988年   3235篇
  1987年   3219篇
  1986年   3226篇
  1985年   3123篇
  1984年   2565篇
  1983年   2217篇
  1982年   1528篇
  1979年   2332篇
  1978年   1870篇
  1977年   1516篇
  1976年   1591篇
  1975年   1652篇
  1974年   1986篇
  1973年   1977篇
  1972年   1872篇
  1971年   1774篇
  1970年   1689篇
  1969年   1696篇
  1967年   1529篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
A transitional cell carcinoma of the urinary bladder was found in a beluga whale stranded in the St. Lawrence middle estuary. Various organs of this animal were submitted to high resolution gas chromatography coupled with mass spectrometry analysis. High frequency of urinary bladder cancer in the human population of the same area and the presence of carcinogenic compounds in the marine environment of this animal are discussed.

Concurrent isolation of Edwardsiella tarda from various organs of this whale is also reported.

  相似文献   
992.
Caprine β-mannosidosis, a fatal inherited deficiency of the lysosomal enzyme β-mannosidase, was diagnosed in neonatal female Nubian crossbred twin kids from a small herd near Guelph, Ontario. The kids had been tetraplegic since birth, with whole body tremors, abnormal nystagmus and an intention tremor of the head.  相似文献   
993.
Periodic seismic (shaking) stress influenced the growth of sexual and asexual reproductive structures of three cultivated species. It delayed anthesis of Lycopersicon esculentum Mill. 'Patio' but not of Tagetes erecta L. 'Jubilee' or Solanum tuberosum L. 'Kennebec'. Shaken 'Jubilee' marigold plants produced the same number of flowers as undisturbed plants, but flowers of shaken plants were smaller. In contrast, seismic-stressed 'Patio' tomato produced fewer buds and flowers, but fruit set was enhanced relative to that of controls. Seismic stress also reduced tuber weight of 'Kennebec' potato, whereas tuber number was unaffected. The overall effect of seismic stress was to reduce the growth of reproductive structures and, in some cases, the number of reproductive structures that developed.  相似文献   
994.
995.
996.
997.
As a result of the radioactive decay of rhenium-187 (4.6 x 10(10) years) the osmium-187/osmium-186 ratio changes in planetary systems as a function of time and the rhenium-187/osmium-186 ratio. For a value of the rhenium-187/osmium-186 ratio of about 3.2, typical of meteorites and the earth's mantle, the present-day osmium-187/osmium-186 ratio is about 1. The earth's continental crust has an estimated rhenium-187/osmium-186 ratio of about 400, so that for a mean age of the continent of 2 x 10(9) years, a present-day osmium-187/osmium-186 ratio of about 10 is expected. Marine manganese nodules show values (6 to 8.4) compatible with this expectation if allowance for a 25 percent mantle osmium supply to the oceans is allowed. The Cretaceous-Tertiary boundary iridium-rich layer in the marine section at Stevns Klint, Denmark, yields an osmium-187/osmium-186 ratio of 1.65, and the one in a continental section in the Raton Basin, Colorado, is 1.29. The simplest explanation is that these represent osmium imprints of predominantly meteoritic origin.  相似文献   
998.
999.
Performance of enzymes and whole cells in commercial applications can often be dramatically improved by immobilization of the biocatalysts, for instance, by their covalent attachment to or adsorption on solid supports, entrapment in polymeric gels, encapsulation, and cross-linking. The effect of immobilization on enzymatic properties and stability of biocatalysts is considered. Applications of immobilized enzymes and cells in the chemical, pharmaceutical, and food industries, in clinical and chemical analyses, and in medicine, as well as probable future trends in enzyme technology are discussed.  相似文献   
1000.
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