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   6643篇
  免费   375篇
  国内免费   670篇
林业   510篇
农学   498篇
基础科学   1366篇
  1054篇
综合类   3366篇
农作物   122篇
水产渔业   168篇
畜牧兽医   427篇
园艺   44篇
植物保护   133篇
  2024年   42篇
  2023年   191篇
  2022年   281篇
  2021年   314篇
  2020年   264篇
  2019年   289篇
  2018年   150篇
  2017年   224篇
  2016年   261篇
  2015年   241篇
  2014年   353篇
  2013年   317篇
  2012年   491篇
  2011年   563篇
  2010年   501篇
  2009年   434篇
  2008年   393篇
  2007年   417篇
  2006年   379篇
  2005年   363篇
  2004年   294篇
  2003年   175篇
  2002年   147篇
  2001年   115篇
  2000年   91篇
  1999年   72篇
  1998年   63篇
  1997年   57篇
  1996年   35篇
  1995年   31篇
  1994年   19篇
  1993年   22篇
  1992年   23篇
  1991年   21篇
  1990年   14篇
  1989年   14篇
  1988年   14篇
  1987年   4篇
  1986年   3篇
  1983年   1篇
  1982年   1篇
  1980年   2篇
  1956年   2篇
排序方式: 共有7688条查询结果,搜索用时 89 毫秒
91.
This paper uses the method of mixed-type series to derive the analyticsolution of cylindrical shell roof,being simply supported transversely,arbitra-rily restrained longitudinally and subjected to gereral transverse local loads.This paper also presents the analytic expressions of the solutions for somekinds of local load.Some examples of this kind of shell roof subjected to ainlined single force near the middle of it with free lorgitudinal edges aregiven.The computation shows that the convergence of the solution is woll  相似文献   
92.
As the important method and instrument of agile manufacture,the technology of distributed collaborative design and manufacturing has become the hotspot of manufacturing. The basic concept and key technologies of IP_VPN are introduced in this paper,and a collaborative design network model based on IP_VPN is presented. Distributed collaborative design is a multi_user,multitask involved system, which is consisted of lots of collaborative processs,so the network security is the key of distributed collaborative design. We research on the security of collaborative design network based on IP_VPN, hence get a conclusion:we can construct an economical?practical and secure collaborative design network system by the application of data encryption,user authentication and access control based on the role,etc.  相似文献   
93.
This article presents an implement of component using COM technology for collecting environmental monitoring data in environment monitoring system. The component makes the separation of data collection and data analysis available.Simultaneously by using the interface of connectable object in COM,itmakes the cooperation of the environment monitoring software with other parts of fault management software available,and also the seamless connection.It improves the system's performance by adding extensibility and potential cooperatibility.  相似文献   
94.
Distribution Network Structure planning is a complex combinatorial optimization problem,which is difficult to solve properly by using traditional optimization methods.In order to solve this problem,Improved Immune Genetic Algorithm is introduced to the distribution network optimal planning. Improved Immune Genetic Algorithm draws into the immune diversity and antibody's density mechanism to maintain the individual's diversity and remains evolution algorithm's global stochastic searching ability,so it can promote diversity and the whole optimal-searching ability of genetic algorithm.The optimal module takes the minimum annual cost as its object,and the capacity and voltage drop of feeder and the radiation of distribution network as its restrictions.According to the require of radiation of distribution network,the spanning tree of the alternative network is taken as the initial solution to speed up the calculation.And the branch-exchange method is used in designing crossover operator and mutation operator to avoid the radiation checking and enhance the optimizing ability.This algorithm has been illustrated effectively by examples,at the same time,the calculation example demonstrates that,the algorithm has higher calculation speed than the traditional immune genetic algorithm.  相似文献   
95.
The exact three di me nsional temperatu re distribution and thermal analysiS to inte-grated circuit substrates have been presen ted by means of numerical method of a fin ite difference.Thismethed.which will overcome the di fficuItv of mathematical deduction mav be consltieredas an analytical way aided by com puters for thermal design of electron ic compon ents.  相似文献   
96.
Some thoroughly research on the basic method for load state detection in MIN is introduced. Load sources of SCP and SSP in MIN are analyzed in detail after investigating the relationship between inter resource and load state in the system. And load detection parameters and model are presented. Moreover, a novel strategy to detect system load state based on fusion of multi detection data is presented. By some test, the theory and method are proved most feasible. Our research show that load state of MIN can be recognized by detecting utility of internal resource utilizing of single node in MIN, and multi redundant detecting data fusion is effective approach to improve the reliability and trust degree of the result.  相似文献   
97.
While design the fuzzy controller, it is very important to determine the membership function of fuzzy variables.The data can be broadly classified as fuzzy sets by using the classification property of the BP neural network. The author selects a BP neural network with one hide layer and uses S function to the input and hide layer, and linear function to the output layer.Advanced BP algorithm isused to train the BP neural network in the environment of MATLAB . The nearer to the target values is the better the last output is.With the trained BP network , the membership values of the inputs can be got ten. This method has high rate and low error.  相似文献   
98.
99.
WDM technology is the basis of optical network implementation. Due to eliminating SONET/SDH and ATM elements, and allowing direct connection with IP routers, IP over WDM can reduce network cost and simplify network expansion . In this thesis, the structure and protocol layers of IP over WDM are firstly explained. Then the procedures of this network are described briefly. At last, the problems and future of IP over WDM are analyzed  相似文献   
100.
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