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   145829篇
  免费   8298篇
  国内免费   83篇
林业   5384篇
农学   4360篇
基础科学   1030篇
  16861篇
综合类   25490篇
农作物   5401篇
水产渔业   7324篇
畜牧兽医   76239篇
园艺   1782篇
植物保护   10339篇
  2018年   1792篇
  2017年   1981篇
  2016年   1861篇
  2015年   1627篇
  2014年   1988篇
  2013年   5421篇
  2012年   3817篇
  2011年   4784篇
  2010年   2965篇
  2009年   2998篇
  2008年   4716篇
  2007年   4498篇
  2006年   4365篇
  2005年   4059篇
  2004年   3971篇
  2003年   3968篇
  2002年   3905篇
  2001年   4704篇
  2000年   4552篇
  1999年   3701篇
  1998年   1469篇
  1997年   1488篇
  1996年   1401篇
  1995年   1748篇
  1994年   1581篇
  1993年   1508篇
  1992年   3158篇
  1991年   3286篇
  1990年   3332篇
  1989年   3326篇
  1988年   3054篇
  1987年   3141篇
  1986年   3223篇
  1985年   3089篇
  1984年   2608篇
  1983年   2310篇
  1982年   1579篇
  1981年   1474篇
  1980年   1427篇
  1979年   2317篇
  1978年   1909篇
  1977年   1626篇
  1976年   1443篇
  1975年   1540篇
  1974年   2076篇
  1973年   2086篇
  1972年   2058篇
  1971年   1825篇
  1970年   1716篇
  1969年   1572篇
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
871.
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   
872.
Advances in immunoparasitology   总被引:1,自引:0,他引:1  
A selective review of the advances in immunoparasitology is presented. It is selective simply because it is not feasible to embrace the whole field of parasitology within the compass of a single review paper, for if it were attempted, it would suffer undue abbreviation. Emphasis is placed on the advances in helminthology and especially the gastro-intestinal parasites of ruminants, an obvious selection because of the interests of the author. Reviews are always somewhat retrospective in outlook; to write a review at the present time is especially foolhardy since developments in biology are such that totally new concepts can arise almost overnight, as it were. This is a particularly healthy state, and the discipline of parasitology is caught up in the application and interpretation of molecular biological considerations. "Parasitism" is a field of increasing importance and challenge.  相似文献   
873.
874.
875.
876.
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   
877.
On April 14, 1983, federal district court judge Gerhard Gesell overturned, as "arbitrary and capricious," a Department of Health and Human Services regulation that required hospitals to post notices concerning the illegality of denying life-saving care to handicapped infants and encouraged anyone with knowledge of such a case to report it to HHS via a telephone hotline. This article reviews the evolution and implementation of the HHS regulation, the legal challenge to it, and the judge's ruling.  相似文献   
878.
879.
880.
Cellulose from plants having crassulacean acid metabolism was enriched in deuterium but not in oxygen-18 in relation to cellulose from C(3) and C(4) plants growing in the same area, indicating that the deuterium enrichment is due to isotopic fractionation during biochemical reactions rather than during evapotranspiration. Hydrogen and oxygen stable isotope ratios of cellulose from the plants in this restricted area showed more variability than that observed in samples collected across an entire continent. Biological factors appear to be as important as environmental factors in determining the isotope ratios of plant cellulose.  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