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   103577篇
  免费   5530篇
  国内免费   10220篇
林业   8826篇
农学   10008篇
基础科学   4570篇
  13113篇
综合类   45047篇
农作物   7289篇
水产渔业   6934篇
畜牧兽医   12846篇
园艺   4189篇
植物保护   6505篇
  2024年   572篇
  2023年   1625篇
  2022年   3073篇
  2021年   3394篇
  2020年   3478篇
  2019年   4139篇
  2018年   2938篇
  2017年   4361篇
  2016年   5346篇
  2015年   5154篇
  2014年   5471篇
  2013年   6193篇
  2012年   8314篇
  2011年   8040篇
  2010年   6344篇
  2009年   5910篇
  2008年   5672篇
  2007年   6496篇
  2006年   5775篇
  2005年   4522篇
  2004年   3473篇
  2003年   2585篇
  2002年   2101篇
  2001年   1808篇
  2000年   1711篇
  1999年   1461篇
  1998年   1241篇
  1997年   1097篇
  1996年   976篇
  1995年   982篇
  1994年   807篇
  1993年   793篇
  1992年   742篇
  1991年   620篇
  1990年   603篇
  1989年   441篇
  1988年   339篇
  1987年   218篇
  1986年   175篇
  1985年   77篇
  1984年   40篇
  1983年   25篇
  1982年   22篇
  1981年   39篇
  1980年   20篇
  1979年   20篇
  1978年   15篇
  1962年   14篇
  1956年   10篇
  1955年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Operational Deflection Shapes of large scale electromechanical system can be ex-tracted directly from multipoints response of the operating system by using of the modal shape analy-sis method. Thev can be used for engineers evaluating the practical dynamic beavior of the largescale elecltromechanical system,checking the existence of local reso,iance of the Stibsystem. and in-dentifying the wcakened positions of the rigidity of structure, In this paper the method of measuringand extracting the operational deflection shal1e of the electromecha nical system is given and theavailability of operational deflection shape is proved by analyzing the actual vibration of a large ex-haust fan system as an example.  相似文献   
952.
According to the character of PD in GIS, the authors design four kinds of GIS defection models. The GIS gray intensity images are constructed based on mass specimens gathered by the ultra - high frequency and high speeds systems, Aiming at the PD characteristics and its defections, A PCA-FDA method is put forward based on PD images. The principal component analysis is employed to condense the dimension of PD images, then the optimal sets of statistically uncorrelated discriminant vectors are extracted, and the minimum distance classifier is constructed as classifier. The identified results show that this method can effectively elevated the discrimination of the four kinds of defects in GIS PD.  相似文献   
953.
954.
The study in molecular morphology is given with a highresolution Atomic Force Microscope AFM.IPC-208B.By taking TiN thim film prepared by magnerton sputtering method and polymide(PI) fibre for examples,the preferenthal growing plme of TiN thin film,the atomic arranges of TiN thin film on the preferential growing plme and the surficial micro-structure can be ascertained form the three-dimensional images obtamed by AFM.IPC-208B.These experiments not only identify small structures of the materials,but also affirm that AFM.IPC-208B holds the precision of atomic level and potential application in micro-structure field,at the same time it establishs the groundwork for the application in micro-process kingdom.  相似文献   
955.
EEG spot-recording for clinical patients in the bed is always advocated due to easing patients and making them comfortable. But EEG signals recorded in the ward exposed to various noisesand interference is less effective in the EEG analysis. Atemporal-spatial filter is designed for noise removing of clinical EEG signals, the first filtering is temporal filtering using band-pass filter, and the second filtering is spatial filtering with ICA-based spatial filter. Experimental results indicate that various noises and interferences, such as power interference, blinking, eyes movements, muscle moments, ECG artifacts, etc., are removed effectively, individually or simultaneously.  相似文献   
956.
汽车是人机协同控制的复杂系统,基于NI PXIe8108实时控制器、PXI7842R数据采集卡、模拟驾驶输入设备及相关软硬件搭建了驾驶模拟仿真系统;用LabVIEW编程语言建立了车辆动力学模型;用虚拟引擎Unity3D软件开发了视景系统;并通过数据库技术使仿真过程与视景系统相结合,实现仿真过程与三维动画实时视景系统的数据交互。结果表明:通过人在环路模拟驾驶仿真实验,使仿真过程中引入了驾驶模拟操纵,实现了人在环路的人机交互式仿真,得到汽车相关性能仿真结果,为驾驶过程中人和汽车协同控制仿真和极端工况下的仿真,提供了一种安全、可靠的人车协同控制仿真环境。  相似文献   
957.
A video Monitor &Control system of tunnel based on DSP/BIOS is proposed,which is different from traditional video Monitor & Control system.It uses DSP to process image,and uses enhanced video input processor to qcquire image.This system satisfies all requirements of video supervision,and is a low cost system.It has a good application foreground.The system has been confirmed as a good veracity and practicability system through testing in the Zhongliang Mountain tunnel of Chongqing.  相似文献   
958.
959.
The monitoring and assessment scheme of the Caiyuanba Yangtze Bridge is present by sensitivity analysis. The mechanics character of the six ties is studied by numerical simulation, and then the sensor location and selection are discussed considering the technique of sensor and construction situation. The trend of the displacement at the sensor location is analyzed according to different damage level of ties, the pattern associating with several displacements which are sensitive to damage at ties is bring forward to improve assessment reliability. The result can assist implement of structural health monitoring system to the same type as this bridge.  相似文献   
960.
The subject matter of this paper is to analyze the stability of excavated high slope. On the base of typical engineering case in Wulong, Chongqing, the geological conditions and potential failure pattern of the high slope are discussed. Then, the limit equilibrium method and the stereographic projection method are used to synthetically analyze the stability of excavated high slope. As a result, it indicates that the stability of the high slope in insufficient and some retaining structures ought to be adopted for the high slope as soon as possible.  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