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   110826篇
  免费   6762篇
  国内免费   9959篇
林业   9241篇
农学   7535篇
基础科学   5437篇
  11746篇
综合类   51558篇
农作物   8215篇
水产渔业   5118篇
畜牧兽医   16113篇
园艺   7645篇
植物保护   4939篇
  2024年   693篇
  2023年   2021篇
  2022年   4572篇
  2021年   4931篇
  2020年   4505篇
  2019年   4554篇
  2018年   3177篇
  2017年   5205篇
  2016年   3497篇
  2015年   5202篇
  2014年   5560篇
  2013年   6722篇
  2012年   9200篇
  2011年   9228篇
  2010年   8695篇
  2009年   7801篇
  2008年   7839篇
  2007年   7415篇
  2006年   6073篇
  2005年   4992篇
  2004年   2977篇
  2003年   2047篇
  2002年   2408篇
  2001年   2096篇
  2000年   1893篇
  1999年   1007篇
  1998年   441篇
  1997年   406篇
  1996年   321篇
  1995年   309篇
  1994年   311篇
  1993年   224篇
  1992年   240篇
  1991年   217篇
  1990年   142篇
  1989年   138篇
  1988年   103篇
  1987年   73篇
  1986年   43篇
  1985年   16篇
  1984年   27篇
  1983年   17篇
  1982年   15篇
  1981年   19篇
  1980年   10篇
  1979年   13篇
  1962年   18篇
  1957年   12篇
  1956年   36篇
  1955年   21篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
921.
The high-speed access for medical digital image sequences was restricted to special device and complicated system in the past. The authors present a new method of high-speed access for medical digital image sequences which can be performed on general computer by means of the combination of Serial ATA(SATA) and Redundant Array of Independent Disk(RAID).Then they introduce the scheme of system configuration and software program. Lastly the testing result is given and the speediness,cheapness and conveniency of this method are elucidated.  相似文献   
922.
The influence of the structure and location of dam and weir on fluid flow state in a two-strand tundish is studied, and a set of optimal structure, combining with the average residence time calculated from RTD curve, is obtained. The result indicates that the fluid flow state can be changed and the path of the fluid flow can be prolonged as well as the average residence time is improved after using dam and weir. But there are some dead zones after fluid passed through the dam and weir. Combination scheme of No. one dam and weir is better than the others. Its average residence time is 299 s and the volume fraction of dead zone is 31.0%. After the optimization of flowing control parameters in tundish, the best case is that the distance between dam and weir is 290 mm and the distance between weir and the long nozzle is 383 mm. The longest average residence time is 351 s and the minimum volume fraction of dead zone is 19.0% under the above situation. Compared with that of no dam and weir, the average residence time increases by 65 s and the dead zone volume fraction decreases by 15.0%. Based on Newton formula, the calculated results show that the inclusions with diameter larger than 17.5 μm can float up within 351 s under this optimization situation.  相似文献   
923.
The design of multi-controller and multi-mode control law is presented for the three-link Acrobot on horizontal bar by employing Human simulated intelligent control method based on sensory-motor Schema.Imitated the characteristics of gymnast's swing-up and handstand movement,the control process of robot is divided by six sequence phase.Then the sensory cell and motor cell and the group of sensory-motor schema is designed based on the analysis of quality-quantity combination.The simulation results show that the controller ensures the gesture and the energy to the desired goal,farther more the motion control of giant swing backword is realized in the simulation.  相似文献   
924.
925.
Aiming at ensuring that product family improvement is based on customer needs while taking full advantage of enterprise history database, firstly, customer needs in the product family improvement are expressed. Then a method of realizing the mapping of customer needs to functional requirements is presented, which is based on quality function development and association rule mining. Finally, an example illustrates the good application of the method.  相似文献   
926.
The 2D motif method is a surface characterization method promising to separate roughness and waviness from a profile and is adopted by ISO,so is meaningful to extend this method to 3D.Vincent's watershed algorithm is employed for the generation of 3D-motif.A smallest area selecting criteria is proposed for the use of clearing the small motifs which are concerned as noise.As there are no manipulating factors as 2D-method,a multi-scale analysis is employed based on area and depth criteria,the use of depth criteria is to prevent the combination of two adjacent motifs if there is a significant peak on the border of them.Finally the surface of C(100) are analyzed by the presented method,the texture of this surface has been characterized.  相似文献   
927.
928.
With the progress of science and technology, the astronautics has obtained great development and researched in many countries, the problem on rocket safety control is important during the rocket launching proceeding, and is also the focus of every space country. At first, the importance of rocket safety control is introduced and the characteristics of the existing system for the safety of rockets are analyzed. After indicating its disadvantages, the design idea, system framework and method for realization of the knowledge-based intelligent decision-making system are proposed to improve certainty and authenticity of safety decision, containing correspond knowledge and adopting the technology of intelligent decision and reasoning on AI.  相似文献   
929.
An equivalent model for hollowing-center grounding device is proposed, the hollowing-center grounding device resistance is calculated with the surface charge simulation method and the computer programme is programmed based on this model. The accuracy of the model and method is validated by experimentation.  相似文献   
930.
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