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   2960篇
  免费   296篇
  国内免费   125篇
林业   611篇
农学   235篇
基础科学   66篇
  279篇
综合类   1068篇
农作物   108篇
水产渔业   109篇
畜牧兽医   635篇
园艺   75篇
植物保护   195篇
  2024年   18篇
  2023年   56篇
  2022年   65篇
  2021年   75篇
  2020年   87篇
  2019年   113篇
  2018年   61篇
  2017年   105篇
  2016年   111篇
  2015年   111篇
  2014年   247篇
  2013年   201篇
  2012年   258篇
  2011年   168篇
  2010年   203篇
  2009年   204篇
  2008年   152篇
  2007年   120篇
  2006年   138篇
  2005年   190篇
  2004年   121篇
  2003年   109篇
  2002年   40篇
  2001年   39篇
  2000年   39篇
  1999年   26篇
  1998年   21篇
  1997年   13篇
  1996年   138篇
  1995年   9篇
  1994年   19篇
  1993年   10篇
  1992年   15篇
  1991年   20篇
  1990年   10篇
  1989年   6篇
  1988年   7篇
  1987年   5篇
  1986年   2篇
  1985年   7篇
  1984年   3篇
  1983年   5篇
  1982年   3篇
  1981年   8篇
  1980年   3篇
  1979年   9篇
  1978年   4篇
  1976年   3篇
  1975年   3篇
  1955年   1篇
排序方式: 共有3381条查询结果,搜索用时 31 毫秒
21.
根据国家石漠化综合治理草地畜牧业工程的需要,应用营养学、饲料学等学科理论,本文对贵州喀斯特石漠化地区白酒糟资源的利用价值进行了综合评价,包括其营养价值、饲用价值、生态价值和经济价值。同时针对白酒糟饲料化开发利用过程中存在的加工技术滞后、理论研究不足、地域条件限制等问题进行了分析,提出了运用青贮法和微生物发酵等关键技术、强化基础理论研究、构建饲料加工中心等相应解决对策,并指出大力发展以白酒糟为原料的非常规饲料加工业是喀斯特石漠化地区发展生态畜牧业的重要举措,也是巩固石漠化治理成果的有效办法。  相似文献   
22.
23.
Comparison of sampling sites and detection methods for Haemophilus parasuis   总被引:3,自引:0,他引:3  
Objective To improve the isolation rate and identification procedures for Haemophilus parasuis from pig tissues. Design Thirteen sampling sites and up to three methods were used to confirm the presence of H. parasuis in pigs after experimental challenge. Procedure Colostrum‐deprived, naturally farrowed pigs were challenged intratracheally with H parasuis serovar 12 or 4. Samples taken during necropsy were either inoculated onto culture plates, processed directly for PCR or enriched prior to being processed for PCR. The recovery of H parasuis from different sampling sites and using different sampling methods was compared for each serovar. Results H parasuis was recovered from several sample sites for all serovar 12 challenged pigs, while the trachea was the only positive site for all pigs following serovar 4 challenge. The method of solid medium culture of swabs, and confirmation of the identity of cultured bacteria by PCR, resulted in 38% and 14% more positive results on a site basis for serovars 12 and 4, retrospectively, than direct PCR on the swabs. This difference was significant in the serovar 12 challenge. Conclusion Conventional culture proved to be more effective in detecting H parasuis than direct PCR or PCR on enrichment broths. For subacute (serovar 4) infections, the most successful sites for culture or direct PCR were pleural fluid, peritoneal fibrin and fluid, lung and pericardial fluid. For acute (serovar 12) infections, the best sites were lung, heart blood, affected joints and brain. The methodologies and key sampling sites identified in this study will enable improved isolation of H parasuis and aid the diagnosis of Glässer's disease.  相似文献   
24.
25.
26.
Brans of 23 traditional and 12 improved (both red and white) rice varieties in Sri Lanka were screened for anti-amylase and anti-glycation activities in vitro. Varieties which showed the highest inhibitory activities at screening were further investigated for anti-glucosidase and glycation reversing as anti-diabetic properties. The same varieties were studied for selected antioxidant properties. Significantly high anti-amylase and anti-glycation activities were observed for bran extracts of red varieties compared to white varieties at screening. Traditional red rice varieties, Masuran, Sudu Heeneti, Dik Wee and Goda Heeneti, exhibited significant and dose dependent anti-amylase, anti-glycation and glycation reversing activities. These varieties also showed marked antioxidant properties. It is concluded that brans of Sri Lankan traditional red rice varieties Masuran, Sudu Heeneti, Dik Wee and Goda Heeneti may be potential food supplements for diabetes.  相似文献   
27.
28.
29.
Some new concepts of coneD_s convexity,coneD-s quasiconvexity,cone D-s pseudoconvexity,s right derivative of vector value mapping are proposed;and their related properties are discussed;the optimality necessary conditions and sufficient conditions for constrained extremum problem(VP)involving in cone D-s convex mapping are extablished;the relation between local optimal solution and global optimal solution;as well as the relation between weakly efficient solution and efficient solution for (VP) are derived;the corresponding results generalize the related results of classic convex programming.  相似文献   
30.
The FCBP(Fuzzy calculating BP) algorithm which is proposed by this paper hasovercome the sensitivity for samples,reduced the number of input layer's samples,lightened the burden of input layer.it is suitable to fuzzy inference and pattern recognition.  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