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   226篇
  免费   40篇
林业   9篇
农学   7篇
基础科学   1篇
  21篇
综合类   42篇
农作物   4篇
水产渔业   12篇
畜牧兽医   166篇
植物保护   4篇
  2023年   3篇
  2021年   5篇
  2020年   3篇
  2018年   3篇
  2017年   4篇
  2016年   6篇
  2015年   4篇
  2014年   6篇
  2013年   11篇
  2012年   12篇
  2011年   6篇
  2010年   7篇
  2009年   7篇
  2008年   3篇
  2007年   6篇
  2006年   6篇
  2005年   8篇
  2004年   5篇
  2002年   8篇
  2001年   7篇
  2000年   4篇
  1999年   5篇
  1998年   3篇
  1997年   6篇
  1996年   3篇
  1995年   4篇
  1991年   4篇
  1990年   3篇
  1989年   8篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1985年   4篇
  1984年   4篇
  1983年   5篇
  1982年   3篇
  1980年   5篇
  1979年   7篇
  1978年   3篇
  1975年   3篇
  1974年   5篇
  1973年   7篇
  1972年   3篇
  1971年   2篇
  1970年   3篇
  1969年   5篇
  1967年   2篇
  1965年   3篇
  1964年   2篇
  1960年   3篇
排序方式: 共有266条查询结果,搜索用时 421 毫秒
261.
Horizontal borders were deleted progressively from square and circular dot patterns containing disparate forms. Stereoscopic depth and anomalous contour occur in the absence of horizontal borders and the form in depth does not always assume the shape of the dot patterns. The stereoscopic effects depend on a laterally disparate form in the stereogram.  相似文献   
262.
Lower Cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves. Strontium data from an interval spanning 7 million years in the Berriasian-Valanginian imply that global sea level fluctuated about 50 meters over time scales of 200,000 to 500,000 years, which is in agreement with the Exxon sea level curve. Oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes. If glaciation caused all the rapid sea level changes in the Cretaceous that are indicated by the Exxon curve, then an Antarctic ice sheet may have existed despite overall climatic warmth.  相似文献   
263.
Sebum from the ventral scent marking gland of the male Mongolian gerbil was fractionated and tested for its ability to elicit behavioral response in a conditioning task and in a stimulus preference situation. The active fraction was identified as phenylacetic acid; both it and a synthetic sample elicited the same behavioral response. Phenylacetic acid appears to be a major pheromone of the male Mongolian gerbil.  相似文献   
264.
Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees latitude is terrain rich in hydrogen, probably H2O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H2O and/or OH.  相似文献   
265.
We present a draft sequence of the genome of Aedes aegypti, the primary vector for yellow fever and dengue fever, which at approximately 1376 million base pairs is about 5 times the size of the genome of the malaria vector Anopheles gambiae. Nearly 50% of the Ae. aegypti genome consists of transposable elements. These contribute to a factor of approximately 4 to 6 increase in average gene length and in sizes of intergenic regions relative to An. gambiae and Drosophila melanogaster. Nonetheless, chromosomal synteny is generally maintained among all three insects, although conservation of orthologous gene order is higher (by a factor of approximately 2) between the mosquito species than between either of them and the fruit fly. An increase in genes encoding odorant binding, cytochrome P450, and cuticle domains relative to An. gambiae suggests that members of these protein families underpin some of the biological differences between the two mosquito species.  相似文献   
266.
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