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   186238篇
  免费   10228篇
  国内免费   174篇
林业   8811篇
农学   6028篇
基础科学   1219篇
  23769篇
综合类   30563篇
农作物   7303篇
水产渔业   9248篇
畜牧兽医   94505篇
园艺   2593篇
植物保护   12601篇
  2019年   1751篇
  2018年   2703篇
  2017年   3019篇
  2016年   2809篇
  2015年   2400篇
  2014年   2944篇
  2013年   7370篇
  2012年   5465篇
  2011年   6651篇
  2010年   4345篇
  2009年   4420篇
  2008年   6512篇
  2007年   6218篇
  2006年   5763篇
  2005年   5415篇
  2004年   5152篇
  2003年   5322篇
  2002年   4826篇
  2001年   5613篇
  2000年   5609篇
  1999年   4494篇
  1998年   1974篇
  1997年   1911篇
  1996年   1766篇
  1995年   2128篇
  1994年   1850篇
  1993年   1756篇
  1992年   3582篇
  1991年   3842篇
  1990年   3741篇
  1989年   3785篇
  1988年   3466篇
  1987年   3389篇
  1986年   3529篇
  1985年   3382篇
  1984年   2828篇
  1983年   2482篇
  1982年   1723篇
  1979年   2630篇
  1978年   2071篇
  1977年   1807篇
  1976年   1826篇
  1975年   1939篇
  1974年   2306篇
  1973年   2367篇
  1972年   2215篇
  1971年   2094篇
  1970年   2028篇
  1969年   2004篇
  1967年   1802篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
941.
942.
From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled.  相似文献   
943.
944.
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   

945.
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   

946.
In the series of experiments with labelled urea three colostomized laying hybrids were butchered after a six-day application of 1% urea with 96.06 atom-% 15N excess (15N') in the ration and another 2 days with a supplement of 1% unlabelled urea. Out of the individual samples from crop, gizzard, small intestine, caecum and rectum, the content of the small intestine and the caecum showed the highest labelling with greater than 1 atom-% 15N'. The TCA soluble fraction of the content of the gizzard was more highly and that of the intestines less labelled than the total nitrogen. The tissue of the gizzard is distinctly less labelled than the "omasum system" and the small intestine. The atom-% 15N' of the oesophagus with crop and glandular stomach largely showed agreement in the individual hens with that of intestinal tissue and ranged between 0.71 and 0.89 atom-%. 2% of the 15N' supplemented with the urea could be recovered in the content and the tissue of the gastro-intestinal tract.  相似文献   
947.
948.
949.
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   
950.
Recent optical experiments have demonstrated cases in which mirror symmetry in stable atoms is broken during absorption of light. These results, which are in contradiction with quantum electrodynamics, support the theory of unification of the electromagnetic and weak forces. The interpretation of these experimental results is based on exchanges of weak neutral Z(0) bosons between the electrons and the nucleus of the atom. The information obtained from low-energy experiments is different from, but complementary to, the results of high-energy experiments. Sensitive measurements in a simple, reliably computable atom are in quantitative agreement with the standard electroweak theory and put stringent constraints on alternative models. Attaining sufficient accuracy in the experiments and the computations for the electroweak radiative corrections to manifest themselves is now the challenge for experimenters and theorists.  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