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   157443篇
  免费   1446篇
  国内免费   493篇
电工技术   2581篇
综合类   2350篇
化学工业   20610篇
金属工艺   10855篇
机械仪表   9101篇
建筑科学   3347篇
矿业工程   1409篇
能源动力   2379篇
轻工业   5039篇
水利工程   2255篇
石油天然气   2449篇
无线电   16313篇
一般工业技术   35820篇
冶金工业   9639篇
原子能技术   1744篇
自动化技术   33491篇
  2023年   176篇
  2022年   455篇
  2021年   555篇
  2020年   444篇
  2019年   457篇
  2018年   20989篇
  2017年   20668篇
  2016年   13476篇
  2015年   1360篇
  2014年   818篇
  2013年   1220篇
  2012年   5656篇
  2011年   16659篇
  2010年   15178篇
  2009年   12008篇
  2008年   12486篇
  2007年   15158篇
  2006年   594篇
  2005年   5025篇
  2004年   3191篇
  2003年   2875篇
  2002年   1334篇
  2001年   370篇
  2000年   494篇
  1999年   257篇
  1998年   461篇
  1997年   305篇
  1996年   324篇
  1995年   283篇
  1994年   242篇
  1993年   244篇
  1992年   228篇
  1991年   265篇
  1990年   159篇
  1989年   176篇
  1988年   224篇
  1987年   183篇
  1986年   154篇
  1985年   176篇
  1984年   156篇
  1983年   168篇
  1982年   162篇
  1981年   155篇
  1968年   194篇
  1967年   169篇
  1966年   200篇
  1965年   174篇
  1957年   150篇
  1955年   153篇
  1954年   165篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
The paper firstly defined the remote sensing information quantification, analyzed the necessity of developing remote sensing quantification, figured out the application guidelines requirement, and pointed out the importance of quantification research. Then taking the remote sensing application research of CBERS-02 data quantification as the example, the paper described the whole quantification system of “remotely sensed digital signal-radiation information-field parameter inversion”. Finally the paper gave the prospect for the development trend of the quantitative remote sensing.  相似文献   
992.
993.
The removal of a mixture of painting solvents from waste air using a biofiltration process was evaluated in this project. The pollutants removed included hydrophobic (aromatic hydrocarbons) and hydrophilic (water soluble ketones and esters) compounds. A trickle bed reactor with a defined immobilized mixed culture on polyethylene Pall rings was utilized in this biodegradation study. The removal efficiencies (RE) of the individual groups of pollutants during loading experiments were determined. An increase of the aromatic hydrocarbons loading resulted in a drop of their REAROM with no effect on the RE value of ketones. The overloading of ketones caused a rapid drop in REAROM and a small drop in REKET. To achieve a restoration of the biocatalyst degradation properties after the increase in loading, an addition of phosphate to the aqueous medium was implemented which successfully restored the removal efficiency.  相似文献   
994.
We have studied the effect of illumination on the current-voltage characteristics and the temperature dependence of conductivity of MnGaInS4 single crystals. Under illumination, the current in a sample was 104–105 times the dark value. It is established that the light-induced current buildup is due to the carrier release from the traps filled under illumination. The energy positions of levels are determined.  相似文献   
995.
This article attempts to determine the mechanisms governing the grain growth process that occurs during lamination annealing of a cold-rolled, motor-lamination (CRML) steel. A new simulation approach linking a Monte Carlo model with electron backscatter diffraction (EBSD) scans used as input has been employed to incorporate the effects of crystallographic texture on the simulated grain growth process. The results from the texture analysis and the computer simulation of the grain growth process indicate that both stored energy driven grain growth and anisotropic grain boundary growth influence the overall grain growth occurring during lamination annealing.  相似文献   
996.
A framework has been developed for extracting reliable twin statistics from a deformed microstructure using crystallographic twin identification techniques with spatially correlated electron backscatter diffraction (EBSD) data. The key features of this analysis are the use of the mathematical definition of twin relationships, the inclination of the common K 1 plane at a twin boundary, and the correct identification of the parent orientation in a parent/twin pair. Methods for identifying the parent in a parent/twin pair will be briefly discussed and compared. Twin area fractions are then categorized by operative twin systems, number of active twin variants in each system, and corrected twin widths. These statistics are reported here for α-zirconium samples deformed in quasi-static four-point bend beams and in a 100 m/s Taylor cylinder impact test. Analysis of the statistics also begins to reveal the roles that deformation rate and relative orientation of the boundary conditions to the material’s symmetry axes play in determining the twinning activity that accommodates the imposed boundary conditions. These improved twin statistics can help quantify the deformation processes in materials that deform by twinning as well as serve to provide better validation of proposed models of the deformation processes.  相似文献   
997.
Twenty-five years of natural coordinates   总被引:3,自引:0,他引:3  
In the early eighties, the author and co-workers created and further developed the natural coordinates to describe the motion of 2-D and 3-D multibody systems. Natural coordinates do not need angles or angular parameters to define orientation, leading to constant inertia matrices and to the simplest form of the constraint equations. Natural coordinates are composed by the Cartesian coordinates of some points and the Cartesian components of some unit vectors distributed on the different bodies of the system. The points and vectors can be located in the joints, being shared by contiguous bodies, decreasing or even eliminating the need to set joint constraints and reducing the total number of variables. However, other authors prefer not to share variables in order to get even simpler equations and to keep a bigger decoupling of equations, which is preferable in some cases. In this paper the history of natural coordinates is reviewed, as well as the main contributions coming from other research groups. In the second part of the paper some application areas in which natural coordinates can be particularly advantageous are examined. Commemorative Contribution.  相似文献   
998.
Passivity Analysis of Dynamic Neural Networks with Different Time-scales   总被引:1,自引:0,他引:1  
Dynamic neural networks with different time-scales include the aspects of fast and slow phenomenons. Some applications require that the equilibrium points of the designed networks are stable. In this paper, the passivity-based approach is used to derive stability conditions for dynamic neural networks with different time-scales. Several stability properties, such as passivity, asymptotic stability, input-to-state stability and bounded input bounded output stability, are guaranteed in certain senses. A numerical example is also given to demonstrate the effectiveness of the theoretical results.  相似文献   
999.
Detection of isomorphism among kinematic chains is essential in mechanical design, but difficult and computationally expensive. It has been shown that both traditional methods and previously presented neural networks still have a lot to be desired in aspects such as simplifying procedure of identification and adapting automatic computation. Therefore, a new algorithm based on a competitive Hopfield network is developed for automatic computation in the kinematic chain isomorphism problem. The neural approach provides directly interpretable solutions and does not demand tuning of parameters. We have tested the algorithm by solving problems reported in the recent mechanical literature. Simulation results show the effectiveness of the network that rapidly identifies isomorphic kinematic chains.  相似文献   
1000.
Motion picture films are susceptible to local degradations such as dust spots. Other deteriorations are global such as intensity and spatial jitter. It is obvious that motion needs to be compensated for before the detection/correction of such local and dynamic defects. Therefore, we propose a hierarchical motion estimation method ideally suited for high resolution film sequences. This recursive block-based motion estimator relies on an adaptive search strategy and Radon projections to improve processing speed. The localization of dust particles then becomes straightforward. Thus, it is achieved by simple inter-frame differences between the current image and motion compensated successive and preceding frames. However, the detection of spatial and intensity jitter requires a specific process taking advantage of the high temporal correlation in the image sequence. In this paper, we present our motion compensation-based algorithms for removing dust spots, spatial and intensity jitter in degraded motion pictures. Experimental results are presented showing the usefulness of our motion estimator for film restoration at reasonable computational costs. Received: 9 July 2000 / Accepted: 13 January 2002 Correspondence to:S. Boukir  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