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   164005篇
  免费   8484篇
  国内免费   144篇
林业   6948篇
农学   4643篇
基础科学   1088篇
  18300篇
综合类   32591篇
农作物   6501篇
水产渔业   7253篇
畜牧兽医   83948篇
园艺   1894篇
植物保护   9467篇
  2018年   1994篇
  2017年   2234篇
  2016年   2059篇
  2015年   1765篇
  2014年   2186篇
  2013年   5880篇
  2012年   4145篇
  2011年   5097篇
  2010年   3308篇
  2009年   3369篇
  2008年   5120篇
  2007年   4736篇
  2006年   4530篇
  2005年   4251篇
  2004年   4279篇
  2003年   4287篇
  2002年   4052篇
  2001年   4974篇
  2000年   4971篇
  1999年   3754篇
  1998年   1592篇
  1997年   1598篇
  1995年   1853篇
  1994年   1664篇
  1993年   1682篇
  1992年   3383篇
  1991年   3730篇
  1990年   3625篇
  1989年   3615篇
  1988年   3275篇
  1987年   3395篇
  1986年   3567篇
  1985年   3476篇
  1984年   2746篇
  1983年   2509篇
  1982年   1673篇
  1981年   1632篇
  1979年   2584篇
  1978年   2047篇
  1977年   1712篇
  1976年   1619篇
  1975年   1733篇
  1974年   2277篇
  1973年   2326篇
  1972年   2303篇
  1971年   2212篇
  1970年   2103篇
  1969年   1931篇
  1968年   1605篇
  1967年   1720篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Based upon a survey of the pathophysiology of haemostasis, the causes of epistaxis in the dog are discussed, and guidelines for a diagnostic and therapeutic approach are given.  相似文献   
122.
123.
The use of saline solutions was tested to determine their efficacy as replacements for ovarian fluid as sperm activators and to eliminate variability encountered with the use of Ovarian fluid. We tested fertilization rate of semen from eight males on Atlantic salmon Salmo salar eggs after five sperm-activating solutions and a non-activating saline were substituted for ovarian fluid. We used solutions shown acceptable for use with other salmonid species. The six solutions tested were a non sperm-activating phosphate-buffered saline (PBS, 7.2 g/L NaCl, 1.48 g/L Na2HPO4, 0.43 g/L K H2PO4), a Tris buffer (6.99 g/L NaCl, 3.63 g/L Tris and 2.42 g/L glycine), a Borax buffer (12.2 g boric acid/L in solution 1, 76 g disodium tetraborate/L combined 100:118, then 1 L combined with 3.7 L water and 18 g NaCl), and three solutions of 9.25 g/L (125 mM) NaCl buffered to pH 6.0, 7.5, and 8.9. The latter five solutions activated sperm immediately on contact, while PBS required additional water to activate sperm. The PBS solution was the least effective (mean percent eyed eggs 37.6%) for egg fertilization. The mean percent eyed eggs for the other five saline solutions (range 78% to 86%) were not significantly different. Sperm from one male provided significantly lower egg fertilization (39.6%) when compared with the other seven males (67.2–87.4% egg fertilization). Percent egg fertilization was not related to number of live sperm cells per egg. Our results show that osmotically-balanced sperm-activation solutions, even those with a pH range from 6.0 to 8.9 provide adequate media for fertilization of Atlantic salmon eggs. Fertilization in a deactivation saline and water reactivation of sperm resulted in low egg fertilization.  相似文献   
124.
The accumulation of soluble carbohydrates in vegetative parts of sweet sorghum ( Sorghum bicolor (L.) Moench.) represents an intermediate reserve pool for grain filling as well as an irreversible storage up to maturity. In order to study the effect of Sterility on soluble sugar accumulation in vegetative parts, two cytoplasmic male sterile (CMS) lines of sweet sorghum were compared with their corresponding fertile mamtainers for non-structural carbohydrate concentrations in shoots. Plants were harvested at four different physiological stages. The lines showed significant differences in the yield of non-structural carbohydrates. At maturity, the yields of soluble carbohydrates from vegetative parts of the two sterile lines were 93 % and 43 % higher than the yield of the two corresponding fertile lines. At that stage, sucrose represented about 80 % of total soluble carbohydrates and the higher yield of soluble carbohydrates of sterile lines was mainly due to the higher yield of sucrose. This indicates that the yield of extractable carbohydrates, especially sucrose, in vegetative parts of sweet sorghum could be considerably improved by using sterile lines which are utilized in hybrid production.  相似文献   
125.
126.
127.
128.
129.
SDI Goals     
  相似文献   
130.
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