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   185017篇
  免费   9958篇
  国内免费   121篇
林业   7307篇
农学   5384篇
基础科学   1282篇
  20826篇
综合类   35696篇
农作物   6947篇
水产渔业   8741篇
畜牧兽医   94282篇
园艺   2213篇
植物保护   12418篇
  2018年   2104篇
  2017年   2310篇
  2016年   2196篇
  2015年   1892篇
  2014年   2310篇
  2013年   6551篇
  2012年   4489篇
  2011年   5611篇
  2010年   3508篇
  2009年   3522篇
  2008年   5506篇
  2007年   5259篇
  2006年   5173篇
  2005年   4816篇
  2004年   4718篇
  2003年   4775篇
  2002年   4667篇
  2001年   5461篇
  2000年   5267篇
  1999年   4345篇
  1998年   1786篇
  1997年   1824篇
  1995年   2086篇
  1994年   1925篇
  1993年   1839篇
  1992年   3889篇
  1991年   4039篇
  1990年   4154篇
  1989年   4151篇
  1988年   3859篇
  1987年   3914篇
  1986年   3998篇
  1985年   3857篇
  1984年   3280篇
  1983年   2924篇
  1982年   2006篇
  1981年   1887篇
  1980年   1831篇
  1979年   2992篇
  1978年   2496篇
  1977年   2186篇
  1976年   1973篇
  1975年   2127篇
  1974年   2789篇
  1973年   2775篇
  1972年   2788篇
  1971年   2550篇
  1970年   2419篇
  1969年   2170篇
  1967年   1906篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
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   

993.
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   

994.
The Colorado beetle is protected against predators by the secretions of defensive glands located on the pronotum and the elytra. The single major compound of the secretion was identified as gamma-L-glutamyl-L-2-amino-3(Z),5-hexadienoic acid by spectroscopic and chemical methods. This compound, which contains a nonprotein beta,gamma- unsaturated amino acid, is toxic to ants (Myrmica rubra) at a concentration 10(-2) molar, which is less than its estimated concentration in the secretion (1.8 x 10(-1) molar).  相似文献   
995.
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   
996.
997.
998.
999.
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