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   213篇
  免费   25篇
林业   14篇
农学   1篇
  4篇
综合类   74篇
农作物   5篇
水产渔业   9篇
畜牧兽医   117篇
园艺   2篇
植物保护   12篇
  2020年   4篇
  2019年   5篇
  2018年   3篇
  2017年   9篇
  2016年   11篇
  2015年   6篇
  2014年   7篇
  2013年   38篇
  2012年   9篇
  2011年   6篇
  2010年   7篇
  2009年   6篇
  2008年   8篇
  2007年   6篇
  2006年   3篇
  2005年   2篇
  2004年   2篇
  2003年   7篇
  2002年   2篇
  2001年   3篇
  2000年   2篇
  1999年   3篇
  1998年   7篇
  1997年   6篇
  1996年   7篇
  1995年   3篇
  1994年   2篇
  1992年   2篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   5篇
  1986年   4篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1979年   2篇
  1978年   2篇
  1973年   5篇
  1972年   2篇
  1970年   5篇
  1969年   1篇
  1968年   2篇
  1967年   2篇
  1966年   1篇
  1960年   1篇
  1943年   2篇
  1941年   1篇
  1937年   1篇
排序方式: 共有238条查询结果,搜索用时 0 毫秒
231.
Evidence from Luna 9 does not preclude the possibility that the moon may have a surface made up largely of very fine rock particles. The degree to which they attach to each other and the resulting firmness of the ground cannot yet be closely estimated.  相似文献   
232.
233.
Large [moment magnitude (M(w)) ≥ 7] continental earthquakes often generate complex, multifault ruptures linked by enigmatic zones of distributed deformation. Here, we report the collection and results of a high-resolution (≥nine returns per square meter) airborne light detection and ranging (LIDAR) topographic survey of the 2010 M(w) 7.2 El Mayor-Cucapah earthquake that produced a 120-kilometer-long multifault rupture through northernmost Baja California, Mexico. This differential LIDAR survey completely captures an earthquake surface rupture in a sparsely vegetated region with pre-earthquake lower-resolution (5-meter-pixel) LIDAR data. The postevent survey reveals numerous surface ruptures, including previously undocumented blind faults within thick sediments of the Colorado River delta. Differential elevation changes show distributed, kilometer-scale bending strains as large as ~10(3) microstrains in response to slip along discontinuous faults cutting crystalline bedrock of the Sierra Cucapah.  相似文献   
234.
A mature female alpaca was evaluated for weight loss and a 10-day history of anorexia, diarrhea, abdominal distension, and ventral edema. Ultrasonography revealed a hepatic mass, culture of which identified Corynebacterium pseudotuberculosis. This is the first reported case of an internal caseous lymphadenitis lesion resulting in clinical disease in a camelid.  相似文献   
235.

We combined two protein-marking enzyme-linked immunosorbent assays (ELISA) with a predator gut content ELISA to monitor the movement and feeding activity of commercially-purchased Hippodamia convergens Guèrin-Mèneville (Coleoptera: Coccinellidae) under realistic field conditions during two field seasons in central Arizona. The protein-marking ELISAs were used to differentiate released H. convergens from the native beetles. Commercially purchased beetles marked with rabbit immunoglobulin G (IgG) were released into cotton fields and chicken IgG marked beetles were released into adjacent cantaloupe fields. Results showed that the total native beetle abundance in each crop was about the same size. The recovery rates after 15 days for the released beetles were less than 1.0% over all the releases, indicating that they dispersed readily from the release site. Of the recaptured beetles containing rabbit IgG (cotton), 82.2% were recovered in cotton and 11.8% moved to cantaloupe. Of those containing chicken IgG (cantaloupe), 66.5% were recovered in cantaloupe and 33.5% moved to cotton. A predator gut content ELISA was used to determine if there were differences in the frequency of predation of released versus indigenous H. convergens on the silverleaf whitefly, Bemisia argentifolii Bellows &; Perring (Homoptera: Aleyrodidae). The proportion of beetles containing whitefly antigens was always higher for the released beetles than for their native counterparts. Our results demonstrate an approach to combine protein marking and predator gut content ELISAs that allows the simultaneous comparison of feeding and intercrop movement of native and commercially-obtained biological control agents.  相似文献   
236.
Cutaneous trombidiosis caused by larvae of trombiculid mites (Vercammenia gloriosa and V. zweifelorum) in the skin of a wild tree frog, Litoria wilcoxii, in northern Queensland, Australia manifested as small, domed vesicular lesions on the dorsal and lateral surfaces posterior to the eyes. The lesions contained small, orange trombiculid mites, with a surrounding minimal inflammatory reaction. The general health and behaviour of the frog appeared unaffected. Provisional diagnosis of cutaneous trombidiosis can be made from its distinctive clinical appearance and confirmed by biopsy with direct microscopic examination of mites. This case report represents a new host record.  相似文献   
237.
238.
Reflectivity and polarization laws for the powder sample and its spectrum are close to the mean for the lunar maria. Solid samples show a marked absorption feature at 1 micron. The low albedo appears to be due to a surface coating on dust grains rather than to volume absorption. The high-frequency electrical properties resemble those of a fine powder made from typical dense terrestrial rocks and are consistent with previous estimates from ground-based radar observations. The differential mass spectrum is almost constant from 100 micron particles down to 0.1 micron particles; most particles are smaller than 0.3 micron. Their shapes disclose a variety of processes of generation.  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