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   89730篇
  免费   4720篇
  国内免费   9798篇
林业   9876篇
农学   12803篇
基础科学   7793篇
  13897篇
综合类   29705篇
农作物   5262篇
水产渔业   3421篇
畜牧兽医   12351篇
园艺   3524篇
植物保护   5616篇
  2024年   412篇
  2023年   1135篇
  2022年   2874篇
  2021年   3874篇
  2020年   3436篇
  2019年   3419篇
  2018年   2398篇
  2017年   3420篇
  2016年   3104篇
  2015年   4153篇
  2014年   3998篇
  2013年   4923篇
  2012年   5906篇
  2011年   6290篇
  2010年   5838篇
  2009年   5415篇
  2008年   5103篇
  2007年   4989篇
  2006年   4736篇
  2005年   4363篇
  2004年   2119篇
  2003年   1857篇
  2002年   1823篇
  2001年   1812篇
  2000年   1861篇
  1999年   2093篇
  1998年   1828篇
  1997年   1552篇
  1996年   1375篇
  1995年   1330篇
  1994年   1253篇
  1993年   1129篇
  1992年   995篇
  1991年   828篇
  1990年   693篇
  1989年   583篇
  1988年   419篇
  1987年   290篇
  1986年   149篇
  1985年   92篇
  1984年   75篇
  1983年   53篇
  1982年   54篇
  1981年   43篇
  1980年   35篇
  1979年   13篇
  1978年   12篇
  1965年   14篇
  1964年   10篇
  1963年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
The paper studies a drug deliversy system for protein and find the optimum preparation condition.Cross-linked alginate(Alg) microcapsule was used to prepare microcapsule for protein,using bovine serum album(BSA) as a model drug.Effect of different cations and content of protein on configuration,size and enveloped rate of microcapsule were investigated.It is shown that Ba-Alg microcapsule has steady configuration,homogeneous size and high-enveloped rate.Also electrophoresis of native BSA before microencapsulation and after microencapsulation is measured by(SDS-PAGE),it is found that no significant change is observed BSA integrity.Release of BSA from microcapsule in vitro presents sustained release in some extent,and initial burst effect is significantly obvious.Microenpsulation drug in alginate will be a wishful drug delivery system.  相似文献   
952.
The characteristics of pretreatment and cyclic control stream are analysed:the form of cyclic embedded hardware circuit,the idea for designing the pretreatment program.The chart model of the system is established preliminarily.  相似文献   
953.
A new type of three dimenstional inner microfin tube is devoloped. Under four different pressures and in the range of condensing mass velocities from 33 to 153 kg/m2 . s,and by the experimental study of the three kinds of tubes with different microfin parameters, the performances of the condensation heat transfer for R11 in the horizontal microfin tubes and obtained. The experiments show that the inner microfin tube is a hopeful and nighty effective condensing heat transfer enhancement tube.  相似文献   
954.
东方百合生殖器官诱导鳞茎的繁殖技术研究   总被引:3,自引:0,他引:3  
以东方百合的花托、花丝、花柱和子房为材料,直接诱导鳞茎和低温锻炼繁殖技术研究。结果表明,4种生殖器官均可直接诱导出鳞茎,分化能力依次为花托〉花丝〉花柱〉子房;鳞茎的中层鳞片分化能力最强;鳞茎分化和生根的最佳培养基是MS+KT0.05mg/L+NAA0.2mg/L+白糖5%+琼脂0.5%;试管鳞茎移栽的适宜方法是生根的试管鳞茎在2-5℃下,保持60d后栽培到泥炭土:珍珠岩=8:2的基质中,锻炼培养20d。  相似文献   
955.
In urban design, only by continuous and dynamic research work from design to finally putting it into practice, can we made good control on city appearance. This article analyzes nowadays defects in our urban design from two aspects as the result establishment and validated control, and tries to conceive a feasibility plan to solve the problem.  相似文献   
956.
957.
According to the requirements of communication power supply, such as high reliability, wide application and high availability, the authors raise a new remote control design for a multi-output power supply for communication equipment based on TCPIP protocol and embedded technology. Then the hardware design is given for the system is discussed based on Ethernet professional chip PRTL8019AS and related circuits. The firmware software design for the salve-computer based TCPIP technology, and the soft design of communieation and control for the master-computer are proposed based on Winsoek and MFC technology in detail A test machine is built to do the testing, the test results prove that the test machine works stably and well, satisfies the design rules and also provides a feasible method for the remote supervise in communication power supplier whose requirement includes remote supervise, no-people on duty and so on.  相似文献   
958.
It's recommended that the term coupled in temperature and strain is nonlinear and is significant in thermoelastic theory. Using the solution of linear coupled and uncoupled theory and selecting appropriate general coordinates, authers approach the nonlinear coupled problems with a variational method. A solution to the problem in half space, is given. It is shown that the difference between the nonlinear coupled theory and the linear coupled or uncoupled theory would be notable when the amplitute of temperature is much larger than that of the reference slate.  相似文献   
959.
In this paper the reimprovement for G. I. Taylor theory of plastic deformation in impact of cylindical projectiles is done. The impulse in the reimproved theory is G. I. Taylor' s 1/2, and 3/4 of G. I. Taylor' s improved theory. The analytical solution of the reimproved theory shows that it gives better agreement with exprimental results than those of the original Taylor' s theory and, the improved theory.  相似文献   
960.
In this paper, taking a D1201 spindle as an example, we discuss the dynamic analysis of spindle by using the theory of the complex model, we also analyse the factors which effect the dynamic characterics of spindle and give results which arc reference value to improving the structure of spindle,  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