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   231770篇
  免费   14273篇
  国内免费   649篇
林业   23190篇
农学   13889篇
基础科学   2933篇
  41423篇
综合类   17475篇
农作物   17000篇
水产渔业   16208篇
畜牧兽医   85305篇
园艺   6239篇
植物保护   23030篇
  2021年   2404篇
  2020年   2819篇
  2019年   3612篇
  2018年   3832篇
  2017年   4185篇
  2016年   4657篇
  2015年   4231篇
  2014年   5576篇
  2013年   16135篇
  2012年   5566篇
  2011年   7324篇
  2010年   7071篇
  2009年   7699篇
  2008年   6761篇
  2007年   5764篇
  2006年   6467篇
  2005年   5695篇
  2004年   5617篇
  2003年   5372篇
  2002年   4689篇
  2001年   5414篇
  2000年   5191篇
  1999年   4956篇
  1998年   4072篇
  1997年   4122篇
  1996年   3862篇
  1995年   4410篇
  1994年   3783篇
  1993年   3473篇
  1992年   3910篇
  1991年   4107篇
  1990年   3774篇
  1989年   3677篇
  1988年   3276篇
  1987年   3377篇
  1986年   3189篇
  1985年   3559篇
  1984年   3387篇
  1983年   3221篇
  1982年   2705篇
  1981年   2642篇
  1980年   2619篇
  1979年   2809篇
  1978年   2594篇
  1977年   2435篇
  1976年   2283篇
  1975年   2084篇
  1974年   2167篇
  1973年   2118篇
  1972年   1851篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
1. It has been shown that both the variety of wheat and the environment under which growth took place influenced the quantities of starch and cell wall carbohydrate contents of wheat.

2. The different varieties of wheat investigated contained different proportions of water‐soluble to water‐insoluble hemicelluloses.

3. By comparison of the arabinose to xylose ratios it was concluded that water‐soluble and insoluble arabinoxylans of wheat were branched to the same degree.

4. Starch from six wheat varieties grown in the U.K. was very well digested by adult cockerels and true metabolisable energy values of the wheats were high.

5. Small amounts of cell wall carbohydrates were digested by adult cockerels.  相似文献   

962.
1. Conditions affecting the keeping quality of traditional farm‐fresh turkeys were investigated.

2. Storage of uneviscerated Wrolstad turkeys at 4 °C for 10 days caused no statistically significant changes in meat flavour or texture.

3. During further storage at —2 °C, however, there was a slight but significant change in flavour, which became more marked with time in birds which had been eviscerated after the initial period at 4 °C.

4. Both eviscerated and uneviscerated birds became slightly tougher during storage.

5. Initial holding at 4 °C increased the numbers of psychrotrophic bacteria on the skin by about 103 but subsequent changes at — 2 °C were slight for uneviscerated birds.

6. Eviscerated carcases had higher counts than uneviscerated birds after storage at — 2 °C and, although ‘off’ odours were not detected, spoilage appeared to be imminent at the end of the 20‐d period.  相似文献   

963.
Book reviews     
Birds Their Structure and Function, By A. S. King and J. McLelland, 1984. 2nd ed. 334 pp. illustrated. London, Baillière Tindall. £9.50. ISBN 0 7020 0872 9.

Proceedings of the 2nd European Symposium on Poultry Welfare, 1985. 360 pp. illustrated. German Branch of the World's Poultry Science Association, Celle, Institut für Kleintierzucht.  相似文献   

964.
The earliest fossil record of African anthropoid primates (monkeys and apes) comes from the Jebel Qatrani Formation in the Fayum depression of Egypt. Reevaluation of both geologic and faunal evidence indicates that this formation was deposited in the early part of the Oligocene Epoch, more than 31 million years ago, earlier than previous estimates. The great antiquity of the fossil higher primates from Egypt accords well with their primitive morphology compared with later Old World higher primates. Thus, the anthropoid primates and hystricomorph rodents from Fayum are also considerably older than the earliest higher primates and rodents from South America.  相似文献   
965.
966.
967.
968.
Two field trials were conducted to evaluate the efficacy of a Moraxella bovis bacterin in the control of infectious bovine keratoconjunctivitis. The bacterin did not affect the incidence of infectious bovine keratoconjunctivitis in either trial but did appear to reduce the severity of lesions, treatments required and withdrawals from pasture required in one trial. Possible reasons for the apparently contradictory results are offered. It is suggested that the bacterin may be of some value when used in conjunction with other preventive measures.  相似文献   
969.
Colloidal aggregation and other random growth processes produce structures that behave differently from ordinary bulk matter. Much of this behavior can be described in terms of the invariance of the aggregates under changes of spatial length scale: they appear to be fractals. There are two types of basic mechanisms for producing fractal aggregates. Those in which aggregation proceeds cluster by cluster can be understood qualitatively in terms of a solvable schematic model. The diffusion-limited aggregation or deposition of individual particles to make a large cluster is not as well understood. It is closely related to several irreversible processes in other areas of physics, such as two-fluid displacement in porous materials and the dielectric breakdown of insulators. More generally, disorderly growth mechanisms provide structures having unique properties, many of which can be understood by using simple statistical principles.  相似文献   
970.
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