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   2284篇
  免费   129篇
  国内免费   195篇
林业   239篇
农学   242篇
基础科学   323篇
  343篇
综合类   1009篇
农作物   37篇
水产渔业   111篇
畜牧兽医   185篇
园艺   23篇
植物保护   96篇
  2024年   11篇
  2023年   39篇
  2022年   67篇
  2021年   52篇
  2020年   75篇
  2019年   86篇
  2018年   44篇
  2017年   89篇
  2016年   96篇
  2015年   60篇
  2014年   107篇
  2013年   118篇
  2012年   146篇
  2011年   184篇
  2010年   134篇
  2009年   110篇
  2008年   113篇
  2007年   122篇
  2006年   112篇
  2005年   94篇
  2004年   96篇
  2003年   60篇
  2002年   62篇
  2001年   57篇
  2000年   39篇
  1999年   39篇
  1998年   42篇
  1997年   35篇
  1996年   37篇
  1995年   37篇
  1994年   35篇
  1993年   29篇
  1992年   35篇
  1991年   30篇
  1990年   41篇
  1989年   24篇
  1988年   25篇
  1987年   17篇
  1986年   5篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
排序方式: 共有2608条查询结果,搜索用时 15 毫秒
21.
本文根据灌溉配水渠系的运行特点,提出在一定轮期和来水流量限制条件下实现下级配水渠最优组合及其配水时间最优排序的一种0-1规划模型,实例运算表明,这种方法可有效减少无效弃水和闸门调节次数,同时对渠道横断面的设计有参考意义。  相似文献   
22.
The paper researches on the degradation of LAS (Linear Alkyl benzene Sulphonate) by combining AS1.860 immobilized with low intensity ultrasonic irradiation. The paper also discusses the influence of pH, rotary velocity, LAS concentration and the condition of low intensity ultrasonic irradiation on the degradation of LAS, the degradation rate of LAS is the main index of our experiment, the results of orthogonal test shows that low ultrasonic irradiation can increase the metabolizing of microorganism cells and facilitate the biodegradation of immobilized cells to LAS, here we research the degradation condition of 50mg/L LAS simulation wastewater with low ultrasonic irradiation, and the results show that the influence is obvious, the optimization degradation rate is about 83%, nine point five percent higher than that of the immobilized cells without ultrasonic irradiation.  相似文献   
23.
The rank one updating formula and the parallel eliminating algorithm for linear recurrence systems ane combined fo form a MTMD parallel algorithm fo solve tridiagonal Toeplitz Cinear equations. This algorithm has a simple strictire and requires onlty a few storages as well as in-terprocessor communications. There is no special demand on the number of processors in the parallel system. The speedup can come dose to p12 comparing with the LU decomposition method (p is the number of processors). It is worth pointing out that it is proposed algcmthn that considels and organizes the parallel arithmetic in the first order linear ricurrence systems with constant coefficients.  相似文献   
24.
Based on the maximum flow principle about networks, a network flow approach to reliability evaluation in large scale netwerks ty mixing inereasing flow with decreasing flow is proposed in this paper.This approach gets the initial flow of each branch in a r.etwork associated with a state of the retwork by decreasing flows of some branches correlative to another state of the network.As a result, the number of flow compute required can be reduced enormously.The numerical example shows that the approach is powerful. The comparison of this approach with the minimal cutset one is also given in this paper.  相似文献   
25.
The research theme of this paper is about how third-party logistics provider design a kind of effective incentive mechanism which can not only avoid the moral hazard behavior of the subcontractor , but also promote subcontractor to raise the serving performance constantly, until obtaining the best TPL performance .Through building bilevel programming model where constructing the Nash equilibrium model this paper, the anthors assume subcontract decision variable as endogenetic variable first, and then analyze the optimal solution with the restraint of Nash equilibrium at the time of decision variable as exogenous variable, push the subcontract relationship research at the principal-agent level into the lay that principal-agent combining with whole contract performance optimal decision.  相似文献   
26.
Some properties of feasible direction in the convx case are generalized to, the corresponding properties in generalized covex case and their applications for multiobjective mathematical programming are discussed in this paper.  相似文献   
27.
In this paper, a kind of grey linear programming with grey interval coefficients is discussed,the definitions of the first and second whitenized linear programmlngs and the grey dual linear programmings are presented, the relationships between the solutions of the above three kinds of programming and the solution of the primal programming are explored, and some new conclusions are obtained.  相似文献   
28.
This paper discusses the problem of long-range generation expansion planning. A dynamic model for long-range expansion planning is set up and an algorithm-a two-step programming is presented, which is used here in a case.  相似文献   
29.
A fast dual algorithm is presented for the piecewise linear programming with successively increasing slopes. The concept of the pointer is used to derive the optimality and the feasibility conditions based on the dual simplex principle, which avoids enlarging the scale of the problem due to introducing piecewise variables so that storage and calculating requirements are reduced. Finally,the example is given to demonstrate the effectiveness of the presented algorithm.  相似文献   
30.
Based on the analysis and study on some existed models for two-dimensional Guillotine Cutting-Stock problem, it is pointed out that some kinds of the models may miss some good cutting patterns,and some may result in inadequate solutions because of only considering the patterns with the smallest waste. A kind of revised two-dimensional cutting-stock models are developed,which transform the two-dimensional problem into the one-dimensional one using the dimension-decreasing heuristic method and whose initial patterns are considered comprehensively. In this kind of models, not only the least waste,but also the other constraints,such as the demands and the relative area of the order plates are considered.  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