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   7656篇
  免费   363篇
  国内免费   625篇
林业   883篇
农学   798篇
基础科学   690篇
  976篇
综合类   3468篇
农作物   255篇
水产渔业   205篇
畜牧兽医   911篇
园艺   189篇
植物保护   269篇
  2024年   54篇
  2023年   153篇
  2022年   275篇
  2021年   295篇
  2020年   278篇
  2019年   362篇
  2018年   168篇
  2017年   318篇
  2016年   368篇
  2015年   371篇
  2014年   423篇
  2013年   449篇
  2012年   696篇
  2011年   664篇
  2010年   447篇
  2009年   436篇
  2008年   365篇
  2007年   406篇
  2006年   363篇
  2005年   298篇
  2004年   242篇
  2003年   209篇
  2002年   132篇
  2001年   146篇
  2000年   93篇
  1999年   104篇
  1998年   87篇
  1997年   60篇
  1996年   72篇
  1995年   52篇
  1994年   60篇
  1993年   42篇
  1992年   41篇
  1991年   31篇
  1990年   31篇
  1989年   20篇
  1988年   14篇
  1987年   11篇
  1986年   6篇
  1985年   1篇
  1955年   1篇
排序方式: 共有8644条查询结果,搜索用时 15 毫秒
71.
Aiming at the oneness of acid to deliquesce stratum-jam applied in scene at the present time,which is incapable of deliquescing complex dirty simultaneously,this article confects a new multifunctional O/W acid.This acid is an emulsified mixture containing 15% hydrochloric acid as its extro-posture,high dissolved oil as its internal state under the function of some proper exterior active reagent.It is composed of 0.5%OP-10,0.5%Span80,0.2%Tween80,0.06%imidazole and 0.01%twelve-alcohol,and the content of oil is equal to the acid content.It can be indicated that this acid has good ability of resolving mineral(CaCO_3,MgCO_3) and organic compound(mainly colloidal bitumen) when it was poured into the stratum,so that it can deliquesce oleic stratum-jam,resume and improve the penetrability of stratum,boost the ability of liquid flowing up.  相似文献   
72.
By analyzing the process of enterprise information engineering construction and intra relationship among information system requirement, business process modeling, application system constructing and project management, one of 4 meta model composed of requirement engineering, process engineering, application system engineering and support engineering is proposed for enterprise information engineering. The developments and applications of the business processes and its application systems are integrated into the same development space and application space. Basing on this, a prototype system composed of requirement modeling environment, business process modeling environment, application system modeling environment, and support engineering environment has been designed and built, which is used for supporting enterprise information engineering constructing. It is valued for the enterprise information engineering construction in our country.  相似文献   
73.
In this paper the test results of mixed mode fracture of three kinds of brittle rock under two kinds of stress paths are reported. The fracture mechanism and failure patterns of brittle lock under different stress paths are discussed. Theory analysis and test results show that the Compression- Shear fracture criterion of brittle rock can be expressed:  相似文献   
74.
Bomsster is a key load-bearing part of railway lorry bogie.Because of its inherent defects casting-steel bomsster could not meet the demands of the heavy load,acceleration and security for lorry.So forging process is proposed to form it.The forming performance of forging-steel bomsster is analyzed.A forging technology is presented which realizes two forging-steel bomsster parts formed in one die.With the plastic forming simulation software DEFORM-3D,the simulation and optimization of the forming process of forging bomsster has been taken based on 3D rigid visco-plastic FEM theory.Optimized scheme has been used to direct the pilot product.The results of product's testing and application suggest that the new forging technology is feasible and the performance of the product is credibility and stabilization.The factory has realized large scale production of a series of forging-steel bomsster.Remarkable benefits of both economy and society have been achieved.  相似文献   
75.
In view of the complication of compreliensive evaluation to development projectplanning alternatives,an AHP model for comprehensive evaluation to the alternatives is advanced,the way of determinating the weight of each index affecting the aIternatives' quality is expounded,and the general methods of evaluating the alternatives with the indexes are given.  相似文献   
76.
Based on the experimental study of the compound rock's behavior at rock salt's over-layer under single compression and tri-axial compression condition, the basic mechanical properties of the rock have been obtained. It could serve as reference to research work and production.  相似文献   
77.
Based on the analysis of the status of building construction in China, the development of Assembled Structure System (ASS) can solve not only the problems in construction, but also is the key for realization of building industrialization. On the basis of technique innovations, a study on the structural performance, construction method and precast production of ASS should be carried out to inherit the old one and overcome its demerits. The process reengineering should be done in the construction enterprise to promote the development of building industrialization.  相似文献   
78.
Condition assessment on power transformer is an important approach to improve reliability of transformer and provide proper decision-making for condition-based maintenance. For long, static assessment method used in the past has already not adapted to the development of modem electricity transmission and distribution technology. So based on the deficiency of fuzzy synthetic assessment method, matter-element synthetic assessment method is introduced. The method can evaluate transformer condition not only in quality but also in quantity. Because each index weight can be given fairly and fast through improved analytic hierarchy process, which need not carry on consistency chec accuracy of assessment can be improved. Examples analysis has proved that assessment method of power transformer condition based on matter-element theory is rational and effective.  相似文献   
79.
This paper takes "how to estimate the complex security of Large Convention and Exhibition Centre effectively" as the research goal.Based on analyzing the difficulties,target system,technical constitution,probing into the architecture,safety science,and using for reference the mathematics,operational research,statistics and modern system theory and method,trying to explore establishing an evaluation methodological system,which is provided with integrated characters on subject.Based on these ways,it exerts "quality to quantity" fuzzy analytical hierarchy process(FAHP) and aims at discussing the safety grade assessment of the Chongqing International Conference Exhibition Center focusing on designing theories.The aim is to enhance the integration of design practice and safe consciousness,strengthen the building safety management,and perfect city public security system.In practice,it is also an efficient tool for favoring values of architectural environmental safety.  相似文献   
80.
This paper applies the Gear-4 algorithm to constitute the companion models lor the circuit elements and electromagnetic relays commonly used in relay protective devices. The interface computation, which describes the node equation of companion model and differential equation of mechanical moving part for the electromagnetic Jelay, is also presented. For the reason mentioned above, it makes possible* to solve more accurately the transient process of relay protective devices including electromagnetic relay using the companion model method. The simplicity and effectiveness of interface computation have been proved by the example calcultaion.  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