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   4114篇
  免费   228篇
  国内免费   167篇
林业   381篇
农学   388篇
基础科学   71篇
  337篇
综合类   1644篇
农作物   160篇
水产渔业   95篇
畜牧兽医   904篇
园艺   376篇
植物保护   153篇
  2024年   20篇
  2023年   77篇
  2022年   143篇
  2021年   224篇
  2020年   213篇
  2019年   216篇
  2018年   93篇
  2017年   146篇
  2016年   219篇
  2015年   210篇
  2014年   268篇
  2013年   273篇
  2012年   650篇
  2011年   237篇
  2010年   223篇
  2009年   181篇
  2008年   122篇
  2007年   96篇
  2006年   92篇
  2005年   96篇
  2004年   75篇
  2003年   77篇
  2002年   59篇
  2001年   45篇
  2000年   38篇
  1999年   33篇
  1998年   24篇
  1997年   20篇
  1996年   145篇
  1995年   13篇
  1994年   27篇
  1993年   17篇
  1992年   26篇
  1991年   24篇
  1990年   16篇
  1989年   10篇
  1988年   7篇
  1987年   5篇
  1986年   4篇
  1985年   10篇
  1984年   3篇
  1983年   6篇
  1982年   1篇
  1981年   7篇
  1980年   2篇
  1979年   8篇
  1978年   2篇
  1976年   3篇
  1975年   3篇
排序方式: 共有4509条查询结果,搜索用时 15 毫秒
41.
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   
42.
43.
44.
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   
45.
46.
47.
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   
48.
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   
49.
The wavelet analysis are used in the detection of edges within the cross sectionfrom projections of parallel beams. This method can be applied in computerized tomography (CT) inorder to reduce the noise and the number of projections.  相似文献   
50.
This paper generalizes all known results on Rabinowitz's minimal periodic solution conjecture under the assumption that Hamiltonian function is C2 strictly convex.  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