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   260篇
  免费   22篇
林业   7篇
农学   11篇
基础科学   3篇
  27篇
综合类   31篇
农作物   8篇
水产渔业   49篇
畜牧兽医   109篇
园艺   11篇
植物保护   26篇
  2022年   4篇
  2021年   6篇
  2020年   10篇
  2019年   4篇
  2018年   11篇
  2017年   4篇
  2016年   5篇
  2015年   2篇
  2014年   4篇
  2013年   15篇
  2012年   10篇
  2011年   12篇
  2010年   9篇
  2009年   7篇
  2008年   10篇
  2007年   5篇
  2006年   7篇
  2005年   8篇
  2004年   11篇
  2003年   13篇
  2002年   13篇
  2000年   6篇
  1999年   6篇
  1998年   7篇
  1996年   4篇
  1995年   4篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   4篇
  1989年   4篇
  1988年   4篇
  1986年   3篇
  1983年   2篇
  1982年   7篇
  1981年   3篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1976年   6篇
  1975年   4篇
  1974年   3篇
  1973年   5篇
  1970年   2篇
  1942年   1篇
  1941年   1篇
  1939年   1篇
  1933年   1篇
  1916年   1篇
  1893年   1篇
排序方式: 共有282条查询结果,搜索用时 359 毫秒
71.
Canine transmissible venereal tumor (CTVT) is an infectious cell line circulating in many feral dog populations. It originated once, about 10,000 years ago. Phylogenetic analyses of mitochondrial sequences from dogs, wolves, and a geographically diverse collection of CTVT samples indicate that the cancer has periodically acquired mitochondria from its host. We suggest that this may be because the cancer's own mitochondria have a tendency to degenerate, due to high mutation rates and relaxed selection, resulting in host mitochondria being more fit.  相似文献   
72.
73.
74.
75.
76.
Statistical algorithms for detecting safety signals are beginning to be applied to Animal Health Pharmacovigilance (PV) databases. How these signal detection algorithms (SDAs) perform in an animal health PV database is the subject of this report. Statistical methods and SDAs were assessed against a set of known signals in order to identify which SDAs were most appropriate for signal detection using the Elanco Animal Health PV database. A reference set of adverse events that should signal was created for 31 products across four species. Nine SDAs based on five disproportionality statistical methods were evaluated against the reference set. The performance metrics were sensitivity, precision, specificity, accuracy, and F score. For bovine and porcine products, the Observed‐to‐Expected (O/E) SDA was the closest in terms of geometric distance to 100% sensitivity and 100% precision. For canine and feline products, the Information Component (IC) SDA was geometrically closest to 100% sensitivity and 100% precision. Principal Component Analysis confirmed that the O/E and IC SDAs were unique performers with respect to one another and other SDAs. The performance of the SDAs was dependent on the choice of the statistical method with differences seen between animal species.  相似文献   
77.
78.
79.
80.
Summary Crossability within Ipomoea section Batatas is complex because of genetic, cytogenetic and physiological interactions. This complexity is responsible for the fact that knowledge about phylogenetic relationships within this section remains preliminary. Between 1988 and 1991, studies of planting, pollination and evaluation of progenies were carried out at the facilities of CIP in La Molina and San Ramon, Peru. Self-compatibility was found in nine diploid species. Self-incompatibility was found in diploid I. trifida, tetraploid I. tiliacea and both tetraploid and hexaploid I. batatas. Sexual compatibility is though to be related to a multiallelic sporophytic incompatibility system which is expressed in the stigmatic papillae. Altogether, 4,162 cross pollinations were made between 11 species and 76 interspecific combinations of 110 possible combinations in a diallel 11×11 design. From these 76 interspecific combinations only 38 survived, and in these crossability (= proportion between number of fruits harvested/pollinations made) ranged from 0.01 to 1.00 at La Molina. At San Ramon, 11 out of 17 cross combinations were successful, and in these crossability ranged from 0.01 to 0.71. Crossability appeared to be influenced by latitude which is related to flowering synchrony. The early death of seedlings is hypothesized to be related to a genomic imbalance between embryo and endosperm. Maternal effects were found in crosses between diploids and tetraploids which produced triploid and diploid offspring, and in crosses between hexaploids and diploids which gave rise to hexaploid offspring. This study shows that I. trifida and I. x leucantha may act as bridge species for gene flow from wild Ipomoea species to the genepool of the sweetpotato.  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