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   116083篇
  免费   7043篇
  国内免费   10504篇
林业   7861篇
农学   5785篇
基础科学   5763篇
  11231篇
综合类   57029篇
农作物   7981篇
水产渔业   5415篇
畜牧兽医   18670篇
园艺   8714篇
植物保护   5181篇
  2024年   953篇
  2023年   2493篇
  2022年   5438篇
  2021年   5200篇
  2020年   4983篇
  2019年   4925篇
  2018年   3412篇
  2017年   5681篇
  2016年   3716篇
  2015年   5650篇
  2014年   5989篇
  2013年   7234篇
  2012年   9932篇
  2011年   10221篇
  2010年   9909篇
  2009年   8778篇
  2008年   8763篇
  2007年   7750篇
  2006年   6318篇
  2005年   5005篇
  2004年   3111篇
  2003年   1844篇
  2002年   1982篇
  2001年   1762篇
  2000年   1608篇
  1999年   566篇
  1998年   53篇
  1997年   34篇
  1996年   15篇
  1995年   25篇
  1994年   25篇
  1993年   22篇
  1992年   32篇
  1991年   19篇
  1990年   6篇
  1989年   4篇
  1988年   4篇
  1987年   23篇
  1986年   20篇
  1985年   3篇
  1981年   16篇
  1976年   3篇
  1966年   3篇
  1965年   3篇
  1964年   5篇
  1963年   2篇
  1962年   31篇
  1957年   3篇
  1956年   35篇
  1955年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
This paper provides a conception of brightness and puts stress upon application of brightness to science of illuminating engineering and actual illuminating engineering.  相似文献   
972.
Two dimensional Optimum Cutting Stock is a NP complicated problem. Each of optimum software gets the cutting results by using proximate and heuristic methods. But different optimum methods and their optimum software may not realize perfect effect according to certain data framework. Furthermore, enterprises can not buy lots of optimum software to choose the most optimized plan. Because of such problems, this paper provides a two dimensional optimum cutting stock method based on Internet and offers the real implementing technique of such method. The experiments, show that this method promotes the general optimum effect of two dimensional optimum cutting stock greatly.  相似文献   
973.
In this paper,notions on appropriate technology for the Steel Construction Congregated Apartments are proposed in order to deal with the technical impediment that arises from applying steel structural techniques to the congregated apartments.The appropriate technology for the steel construction congregated apartments is defined as systematic technologies that are in harmony with the status quo of Chinese productive force level,social culture and building technology,and as the strategies of choosing or balancing technology according to sustainable development principle.The principal design and constructing strategies of appropriate technology are as follows:(1) organization of residential space combined with steel construction techniques,(2) suitable structural system,(3) a new idea of fire resistance,and(4) kit building technique etc.A technological concept analysis about an ideal model of a steel construction system congregated apartment combined with the appropriate technology is also presented.  相似文献   
974.
Pushover analysis is a tool to study the inelastic behavior of structures under strong seismic action. The 3D-pushover analysis was performed to analyze the inelastic lateral-torsional coupled response of multistory asymmetric structures. The symmetric frame and frame-wall systems were studied in this paper, and the capability curve of the top displacement and base shear,the story drift and the position of rotation center were compared with reference to corresponding symmetric structures. The characters of inelastic response of multistory asymmetric structures were found. The conclusion provides reference for performance-based seismic design of asymmetric structures.  相似文献   
975.
976.
Valuation based on the bill of quantifies will change the existing valuation mode of tender and bidding. For the standardized management of tender and bidding for power projects and the inteUigentized information management of power enterprises, it is an inevitable trend of reform to apply the valuation mode based on the bill of quantifies. According to the characteristics of power projects, this paper expounds the working process of the valuation mode based on the bill of quantities and analyzes the goal and function need of the tender and bidding management system. Considering the calculation procedure of the valuation and the quote strategy of quantities bill, the composition of fees for the valuation is settled and the calculation method is designed. To establish the management system of tender and bidding with a valuation based on the bill of quantities is beneficial for the costing reform of power projects and the perfection of the tender and bidding market. Therefore it is of great significance to spread the new management mode of project costing with a valuation based on the bill of quantities.  相似文献   
977.
Voltage fluctuation and flicker is one of the main causation that imperils reliability of power supply. Steelmaking EAF with large load of distribution network produces large impact and interference on the public electric network in operation. So it is very important to control reactive power for voltage fluctuation and flicker mitigation. STATCOM possessing high response speed is an effective measure to mitigate voltage fluctuation and flicker of distribution network. Here, comparing to static var compensation, many advantages of STATCOM are analyzed. Operation principles COM mitigating voltage fluctuation and flicker, general control strategies and control method are introduced cussed. The researching pivot and trend in the future are also discussed. of STAT- and discussed. The researching pivot and trend in the future are also discussed.  相似文献   
978.
Analysis and Control on Roof Stability of Rock-salt Cavity   总被引:1,自引:0,他引:1  
Analysis and control on roof stability of rock-salt cavity are very important to ensure safety and benefit in production, build and use of repertorv of rock salt cavity. Dynamic balance process and instability process of rock-salt carity roof are studied, and instability mechanism of rock-salt cavity roof is studied with catastrophe theory, and the influencing factor are analyzed, which will be theoretical basis of rock-salt cavity stability control.  相似文献   
979.
A digital detecting system of the dielectric loss in the capacitive equipment is introduced based on virtual instruments.This system can real-time collect,analyze,process and storage electrical signals with National Instruments' program LabVIEW and ADLINK,s DAQ board.Through the simulation test in lab and the real test in electric substation,it is shown that this system has high accuracy on testing the dielectric loss in the capacitive equipment,the real test data is stable and the relative error of real dielectric loss is less than 5%.It is to say that this system can meet the requirement of the real on-line monitoring.  相似文献   
980.
为了研究水润滑橡胶合金轴承结构参数对其低速重载工况下摩擦噪声的影响,使用复模态分析方法建立了水润滑橡胶合金轴承系统仿真模型,采用专业仿真软件分析了不同摩擦系数及结构参数条件下摩擦噪声产生的概率,进而研究结构参数对摩擦噪声的影响,进行了平板型和圆弧型结构的水润滑橡胶合金轴承摩擦噪声的对比实验。研究结果表明,水润滑橡胶合金轴承的水槽半径大小、摩擦面形状以及摩擦副的摩擦系数对水润滑橡胶合金轴承的摩擦噪声有较大影响,而水槽的形状对轴承摩擦噪声的影响不大。对一定结构尺寸的水润滑橡胶合金轴承,水槽半径为4 mm、平面型摩擦面的结构可以大大减少轴承出现摩擦噪声的可能性,相关实验结果与计算结果是吻合的。  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