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   9479篇
  免费   724篇
  国内免费   728篇
林业   1107篇
农学   660篇
基础科学   369篇
  896篇
综合类   3721篇
农作物   416篇
水产渔业   516篇
畜牧兽医   1241篇
园艺   264篇
植物保护   1741篇
  2024年   46篇
  2023年   203篇
  2022年   382篇
  2021年   371篇
  2020年   372篇
  2019年   414篇
  2018年   294篇
  2017年   386篇
  2016年   396篇
  2015年   363篇
  2014年   566篇
  2013年   472篇
  2012年   713篇
  2011年   651篇
  2010年   496篇
  2009年   570篇
  2008年   476篇
  2007年   562篇
  2006年   483篇
  2005年   384篇
  2004年   349篇
  2003年   291篇
  2002年   243篇
  2001年   201篇
  2000年   194篇
  1999年   149篇
  1998年   126篇
  1997年   108篇
  1996年   110篇
  1995年   93篇
  1994年   73篇
  1993年   80篇
  1992年   73篇
  1991年   64篇
  1990年   55篇
  1989年   42篇
  1988年   37篇
  1987年   17篇
  1986年   7篇
  1985年   6篇
  1984年   2篇
  1983年   2篇
  1980年   2篇
  1979年   2篇
  1973年   1篇
  1956年   1篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The biological effects of ELFMES including proliferation and apoptosis of cells as well as the damage of DNA are initially evaluated with the treatment of plant cells and human pulmonary fibroblasts in low frequency magnetic fields with certain intensity and different time intervals in vitro. Cell culture, counting in vitro, fluorescent dyeing analysis and single cell gel electrophoresis are adopted. The results demonstrate that the electromagnetic field with the intensity of 3mT can affect the proliferation and apoptosis of cells significantly.  相似文献   
82.
83.
In this paper, by use of the pseudo-gradient vector field, the three critical points theorem in [2] is extended to the C1 function in the Ba-nach space, and therefore the three critical, points theorem in [5] is strengthened and the existence of the saddle point of the C2 function is discussed.  相似文献   
84.
Crossover operator and mutation operator are basic operators of genetic algorithm , which play important roles in improving the quality of the solution populations. We propose the improved crossover operator , mutation operator and rotation operator on the basis of good point set with the traveling salesman problem , the experimental result shows these operators are very efficient.  相似文献   
85.
With the rapid increase of the Internet user and widely application of Web,the current network technology is facing great challenge. More and more multimedia operations occupy plenty of bandwidth,and result in the network congestion. Therefore,people begin to use QoS to utilize the bandwidth effectively,and ensure the transport of the emergent operation data. The paper introduces the protocols and basic components of QoS,then expatiates the conception and the basic principles of policy control QoS, moreover,emphasizes the structure model of policy control QoS and how it runs. At last,it introduces the transport process of data packets under the control of policies in a policy control QoS system,and how to make the policies in the real world.  相似文献   
86.
A new globally convergent algorithm was presented for a continuous differen-tiable nonlinear programming by defining a measure function deviating from the Kuhn-Tucker point. With this algorithm which can be used to get the optimum solution of the problem,the optimal lagrangian multiplier corresponding the optimal solution of the problem was also obtained. A new iterative algorithm for quadratic programming is obtained when applying the general algorithm to quadratic programming. Finally,a numerical example was given.  相似文献   
87.
This paper ainalyses the size effect of the fracture energy of concrete tested bythree point bending. It is shown that positive errors of test results of fracture energy increase,ornegative errors decrease with increasing of the specimen ize. The phenomenon is one of main causesresulting in the size effect of fracture energy.  相似文献   
88.
89.
This paper analyses the thermal moist characteristics of the hull layer beside an air layer at lower temperature in an envelope for a cold storage and presents a new method of waterproof by air layer. With test data from engineering practice, the theory on the barrier of self moisture proof at the surface sublayer of the hull layer in an attic on a cold storage is proven. The dried zone about three phase point is confirmed. It is a new knowledge for thermophysics on thermal design of a cold storage with an optimum thermal performance.  相似文献   
90.
In this paper,by the use of Farkas lemma and its inve-rse proposition,the generalized Kuhu-Tuoker conditions for the existanceof strong minimum point in differential multiobjective programming inBanach spaces and the existance of sufficient condition of weak Paretominimum Foint are derived.  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