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   71792篇
  免费   4456篇
  国内免费   6482篇
林业   5121篇
农学   3839篇
基础科学   3258篇
  7079篇
综合类   35430篇
农作物   5225篇
水产渔业   2911篇
畜牧兽医   11416篇
园艺   5142篇
植物保护   3309篇
  2024年   618篇
  2023年   1522篇
  2022年   3552篇
  2021年   3219篇
  2020年   3147篇
  2019年   3191篇
  2018年   2151篇
  2017年   3589篇
  2016年   2318篇
  2015年   3552篇
  2014年   3657篇
  2013年   4457篇
  2012年   6133篇
  2011年   6337篇
  2010年   5945篇
  2009年   5044篇
  2008年   5155篇
  2007年   4843篇
  2006年   3922篇
  2005年   3104篇
  2004年   1953篇
  2003年   1250篇
  2002年   1232篇
  2001年   1159篇
  2000年   1022篇
  1999年   378篇
  1998年   39篇
  1997年   17篇
  1996年   15篇
  1995年   20篇
  1994年   17篇
  1993年   18篇
  1992年   20篇
  1991年   15篇
  1990年   12篇
  1989年   4篇
  1988年   2篇
  1987年   8篇
  1986年   13篇
  1985年   2篇
  1981年   7篇
  1966年   2篇
  1965年   2篇
  1962年   12篇
  1959年   1篇
  1958年   1篇
  1957年   3篇
  1956年   34篇
  1955年   12篇
  1953年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The green is as a symbol of no pollution,no public harm and environmental protection. The green automobile is the inevitable results that the automobile technique continuously developes. A new style vehicle--the green automobile is the urgent solicit of environmental protection is developed. The automobile industry can develop continuously. This article mainly discusses the importance of the green auto_mobile's research and development,the development status in quo and prospect of the green auto_mobile technique in the world,and states the relationship between the green automobile technique and environmental protection from green technical system theoretically clarify the study of green automobile,including its design and the system,the manufacture and its technology,the energy,the rebuild engineering and a series of subjects. How to evaluate the cycle and the evaluable mark of the green automobile,the prospect of green automobile are pointed out.  相似文献   
992.
In TT&C system,unified spread spectrum framework and adaptive antenna digital beamforming technologies are used to track, telemetry and command objects. Constant modulus array (CMA) and adaptive signal canceller estimate the direction of arrival (DOA) of every signal and use the optimum weighted vector to form the beams. The phase weighted vectors estimated from DOA improve the processing gain as well as being utilized in the transmitting of tele command signal to form the beam of specified object. Its processing performance is researched and simulated in this paper.  相似文献   
993.
The design of Bio-clean operating room in modern hospital is quite different from that of traditional operating room. This paper discusses three aspects of Bio-clean operating room design: air clean standard and air purification, interior equipment system and interior finish. It is hoped that this discussion will conduce to later designs.  相似文献   
994.
995.
The analysis of vibration response of structure with TMD is carried out under earthquake ,considering the ground-structure interaction. The varying rule of square difference of displacement of structure with the TMD on or off by changing the first inherent frequency is also presented .It has been proved by comparing and analyzing that a TMDstructure with optimum parameters can efficiently reduce the vibration of structure under strong wind and earthquake,when the main frequency of the ground motion is within the range of TMD vibration reducing frequency.  相似文献   
996.
Swindle exists commonly in any securities markets, where swindle has led to serious influences on regulations and the normal development of our securities market. The paper attempts to develop a game model of supervision on swindle in the securities market so as to investigate the relationship between supervisor and supervisee from the microcosmic aspect, and analyze the microcosmic mechanism resulting to swindle in the securities market, and enlighten our securities supervision as to swindle in the securities market.  相似文献   
997.
Intrusion detection system is an essential component of network security protection mechanisms. Most intrusion detection system can not adapt the variation of network environment. Aiming at this problem, an adaptive strategy that composed of condition space and strategy space is proposed. The condition space describes the network environment and the strategy space describes the strategy. There is an exclusive strategy corresponds to a certain environment state in condition space. On the base of the adaptive strategy, an adaptive intrusion detection system based on agent and data mining is designed. The simulation experiments indicate that the adaptive strategy is effective.  相似文献   
998.
A new type of inorganic anchoring material is developed as a substitution for anchoring adhesive to overcome some imperfections in the process of planting reinforcing steel bar.The mix proportion of the anchoring material is determined by experiments.The compressive strength,adhesive force to concrete,volume stability and anchoring force with steel bar are studied.The early strength of the anchoring inorganic material is quite high: for 1d up to 38.5MPa and 3d up to 60MPa.It is a good adhesive to concrete and the adhesive strength of 28d is about 2MPa.The anchoring material will have tiny volume expansion with the age,which is beneficial to enhancing the anchoring force.The essential component of the inorganic anchoring material is cement-based material,so some defects of the organic macromolecular material can be avoided,such as poor stability and requirement for vigorous construction conditions.Its characteristics in early strength,adhesive force to concrete and volume expansion can satisfy the requirement of the construction to the planting reinforcing steel bar and the loading force,thus it can be used as a substituting material for anchoring adhesive.  相似文献   
999.
With the development of circulating fluidized bed boiler(CFB),the study field of external heat exchanger(EHE) is greater in extent and degree.In order to research the working process of EHE,the model which deals with flow and heat transfer of EHE for 300MW CFB of Dong Fang Boiler Grou PCo.Ltd.is presented.Based on the cell modeling theory,the EHE is divided into several chamber by heating surfaces.The mass and energy conservation equations of each cell have been developed according to some reasonable assumption.The complete mathematical model has been compiled by Fortran and solved by classical Algorithm of Runge-Kutta.The static test and perturbation experiment of simulating model has been performed.The simulation results show that the model has been reached the steady state rapidly,the dynamic responses are reasonable and the modeling presented in the paper is reliable and appropriate.  相似文献   
1000.
The colored patterns on arbitrary cut plane is an important method in 3D data-field visualization of finite element.By using the technology of the Object-Oriented Programming and the method of scan-line,the colored patterns on arbitrary cut plane are given.The example by the OPENGL of Visual C++ R6 can support the theory satisfactorily.  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