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   2163篇
  免费   147篇
  国内免费   207篇
林业   228篇
农学   175篇
基础科学   279篇
  320篇
综合类   1008篇
农作物   48篇
水产渔业   107篇
畜牧兽医   182篇
园艺   52篇
植物保护   118篇
  2024年   13篇
  2023年   45篇
  2022年   77篇
  2021年   82篇
  2020年   68篇
  2019年   85篇
  2018年   64篇
  2017年   86篇
  2016年   111篇
  2015年   74篇
  2014年   133篇
  2013年   91篇
  2012年   177篇
  2011年   159篇
  2010年   99篇
  2009年   139篇
  2008年   94篇
  2007年   158篇
  2006年   98篇
  2005年   93篇
  2004年   81篇
  2003年   80篇
  2002年   48篇
  2001年   40篇
  2000年   46篇
  1999年   38篇
  1998年   23篇
  1997年   36篇
  1996年   24篇
  1995年   21篇
  1994年   24篇
  1993年   25篇
  1992年   22篇
  1991年   19篇
  1990年   17篇
  1989年   14篇
  1988年   9篇
  1987年   2篇
  1986年   1篇
  1978年   1篇
排序方式: 共有2517条查询结果,搜索用时 15 毫秒
21.
Su Su 《保鲜与加工》1993,(4):125-129
This paper points out the shortcoming of the existing project break-even analysis method. A new improved method-the dynamic project break-even analysis method has been put forward.  相似文献   
22.
A three critical point theorem is proved. As its applications, Dirichlet problem for a class of quasilinear elliptic equations cf second order is considered.  相似文献   
23.
24.
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   
25.
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   
26.
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   
27.
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   
28.
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   
29.
30.
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   
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