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   23248篇
  免费   1441篇
  国内免费   2753篇
林业   2272篇
农学   1930篇
基础科学   3201篇
  5368篇
综合类   9943篇
农作物   782篇
水产渔业   888篇
畜牧兽医   1511篇
园艺   333篇
植物保护   1214篇
  2024年   210篇
  2023年   648篇
  2022年   949篇
  2021年   881篇
  2020年   947篇
  2019年   1049篇
  2018年   710篇
  2017年   1096篇
  2016年   1302篇
  2015年   1143篇
  2014年   1205篇
  2013年   1338篇
  2012年   1709篇
  2011年   1751篇
  2010年   1445篇
  2009年   1356篇
  2008年   1293篇
  2007年   1346篇
  2006年   1153篇
  2005年   962篇
  2004年   771篇
  2003年   609篇
  2002年   476篇
  2001年   365篇
  2000年   349篇
  1999年   318篇
  1998年   286篇
  1997年   285篇
  1996年   239篇
  1995年   238篇
  1994年   199篇
  1993年   172篇
  1992年   164篇
  1991年   147篇
  1990年   124篇
  1989年   92篇
  1988年   63篇
  1987年   22篇
  1986年   10篇
  1985年   3篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1963年   2篇
  1962年   2篇
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
201.
202.
To research the problem of plastic art design and emulation of products with the virtual reality technology can short the product development cycle and reduce the cost. This paper discusses the information based on the product feature ,solid model with parameters, the structure and function of this system. Combined the product properties with its solid model. Proposed a method with CAD to create the model of the product based on features in the product design. Expressed its feature parameter and shape of model fully .In the case for a deceleration box the feature model has solved the problem of physical information ,geometry information and the informative process in its production management system efficiently.  相似文献   
203.
Hydrodynamic models have been widely applied to river and coastal engineering projects. Understanding the hydrodynamic process is a prerequisite to modeling the pollution and sediment transport process. Hydrodynamic models of varying degrees of complexity should be selected appropriately according to the object of study, physical properties of the flow domain and hydrodynamic features. The essential procedure of hydrodynamic simulation is described in this paper. The main problems such as selection of model dimension in physical space, choice of variables, boundary conditions, initialization, design of computational grid, model resolution, parameterization of smaller scale fluctuations and sub-grid scale processes, model calibration and verification are investigated.  相似文献   
204.
The society-economy-environment appraisal for construction project can help our government to control macro-economy, make correlation policy and formulate laws and draw up city plan.It has great influence on the sustainable development of our society and it is the demand of the law for the environment evaluation in China.This paper introduced the basic structure of society-economy-environment appraisal system for construction project and the thought of elements transaction.Using the method of AHP, the model of project analyzing and optimizing selection is designed.For the more, the methods of the optimizing models on the selected schemes are put forward.Finally, the integrative analysis has been made on the system design and appliance of this appraisal system.  相似文献   
205.
This paper analyzes the structure and line current waveform of 3-phase AC voltage regulation circuit. As an application of 3-phase AC voltage regulation circuit, a high-frequency welding device's simulation model and harmonic analysis of line current are presented. Results of simulation are compared to field measurements. The two are in a good agreement, so this simulation model is correct. Two single-tuning filters and one second-order HPF are designed according to the device's harmonic condition. Simulation results of the circuit with filters indicate decrease of the harmonics in current of power supply, and the waveform is close to sinusoidal wave, which prove correctness of the solution to harmonics pollution.  相似文献   
206.
A developing method is given which based on object-oriented modeling techniques for management information systems.The modeling techniques,especially,from CDM to PDM conversion,make it possible that the method can be used for developing such management information systems which based on relational database.The result shows that it can raise the efficency of the system developing,improve the system tability,enhance the system maintenability.  相似文献   
207.
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   
208.
Characteristics of a tire are the foundation of vehicle dynamics studying, especially play a vital role in vehicle handling study. It is necessary to establish a tire model in the simulation for vehicle handling because the tire characteristics got by test can not be satisfied.The optimization of fitting to the tire test data curves by Magic Formula is discussed, included the digitalization of tire test data curves, designing objective functions and optimization processes,etc. Finally the parameters in Magic Formula tire model are obtained and they lay a foundation for the development of vehicle handling aftertime.  相似文献   
209.
Based on the model of Human Simulation Intelligent Controller (HSIC) presented briefly, a detailed algorithm was described for the servo system control by using the method of HSIC. Simulation results obtained proves the good performance of the control algorithm.  相似文献   
210.
Considering the character of slope resistant engineering invest benefit, in line with security and economy balmaced, combining initial investment and anticipated hazard loss, disaster resistant engineering should be satisfied with the criterion of minimum cost. Decision tree model is adopted as analyzing means, and risk decision-making of slope design is carried out. Project input-output radio adopting dynamic analysis can reflect project investment benefit more accurately. At last this paper analyzes some questions in process of slope resistant engineering with benefits enumerate.  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