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   508863篇
  免费   6790篇
  国内免费   1629篇
电工技术   9449篇
综合类   739篇
化学工业   75938篇
金属工艺   16869篇
机械仪表   14490篇
建筑科学   13442篇
矿业工程   1315篇
能源动力   14437篇
轻工业   52363篇
水利工程   4182篇
石油天然气   5306篇
武器工业   13篇
无线电   65210篇
一般工业技术   94166篇
冶金工业   95412篇
原子能技术   7844篇
自动化技术   46107篇
  2021年   3682篇
  2020年   2762篇
  2019年   3452篇
  2018年   5614篇
  2017年   5493篇
  2016年   5900篇
  2015年   4309篇
  2014年   7357篇
  2013年   23979篇
  2012年   12673篇
  2011年   17892篇
  2010年   13921篇
  2009年   15898篇
  2008年   16733篇
  2007年   16733篇
  2006年   15095篇
  2005年   13808篇
  2004年   13450篇
  2003年   13132篇
  2002年   12543篇
  2001年   13014篇
  2000年   12111篇
  1999年   13004篇
  1998年   31015篇
  1997年   21973篇
  1996年   16956篇
  1995年   13073篇
  1994年   11643篇
  1993年   11343篇
  1992年   8299篇
  1991年   7915篇
  1990年   7616篇
  1989年   7365篇
  1988年   7127篇
  1987年   5905篇
  1986年   5917篇
  1985年   7108篇
  1984年   6407篇
  1983年   5956篇
  1982年   5409篇
  1981年   5589篇
  1980年   5167篇
  1979年   4966篇
  1978年   4616篇
  1977年   5506篇
  1976年   7032篇
  1975年   3961篇
  1974年   3748篇
  1973年   3815篇
  1972年   3044篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Nguyen  C. 《Electronics letters》1994,30(25):2149-2150
A new miniature bandpass filter, comprising three-conductor short-circuited spurline resonators of approximately a quarter-wavelength long, with a very wide bandwidth approaching multioctaves is reported for the first time. The chain matrix of the filter resonator is derived. The new filter has been developed using microstrip line with less than 1 dB insertion loss over a passband from 2 to 8 GHz. Reasonably good agreement between the measured and calculated results is observed  相似文献   
993.
The purpose of this work is to evaluate the effects of post-deposition heat treatments on high and low crystallinity hydroxyapatite coatings on Ti6Al4V alloy. HA layers were produced by the vacuum plasma spray (VPS) technique, and the desired degrees of crystallinity were obtained by changing the deposition parameters. An analysis of the mechanical properties of the coatings and their adhesion to the substrate has been done by shear strength test. X-ray diffraction analysis was used to detect the structure and the chemical components in which HA dissociates during the deposition process and heat treatments. The data obtained indicates that heat treatments can increase the crystallinity of HA, but they also introduce a mechanical degradation of the coatings. After heat treatments, it was also observed that a large amount of tetracalcium phosphate was formed.  相似文献   
994.
The T1208 inventory in a HTR fuel element is transmuted from Th232. By measuring the T1208 gamma radiation in a suitable scan configuration it is possible to distinguish fuel elements with and without Thorium contents non-destructively even after a long cooling time.  相似文献   
995.
Some of the most outstanding experimental evidences for unconventional superconductivity in heavy-electron materials are rewiewed and discussed.  相似文献   
996.
A specially designed tube viscometer was used to measure apparent viscosity during flow of Bologna type sausage emulsions moving through a pipe. Emulsions varied in fat content (from 21.8 to 44.3%) and in moisture/protein ratio (from 3.7 to 5.6), and the effects of added sodium chloride, sodium diphosphate, starch and blood plasma were investigated in a 36% fat, 3.7 moisture/protein emulsion.
The shear stresses determined as a function of shear rate were fitted by a power law. Yield stress of the emulsions was negligible relative to the applied stress. However, inspection of the flow profiles indicated that considerable slip of the sausage emulsion occurred at the pipe wall. Both emulsion flow and slip contribute to overall flow behaviour, so a kind of effective viscosity is determined. Intrinsic rheological properties and wall slip will both be affected by the composition of the sausage emulsion.  相似文献   
997.
Sorge  R. 《Electronics letters》1994,30(23):1986-1988
A technique for evaluating the generation rare profile of MOS structures based on the measurement of gate current transients at two different gate voltage waveforms in non-equilibrium nonsteady-state is presented. The method allows the evaluation of the generation rate profile in the bulk of inhomogeneously doped MOS structures without requiring knowledge of the doping profile and provides, in contrast to high frequency methods, reliable results in such cases where MOS structures with high series resistances are to be investigated  相似文献   
998.
Qin  Y.M. Ciric  I.R. 《Electronics letters》1994,30(24):2028-2029
The Tikhonov regularisation technique is widely used in the solution of inverse scattering problems. One of the difficulties in applying this technique is the proper selection of the associated regularisation parameter. Based on a stochastic model of the reconstruction process, a simple method is presented for selecting this parameter for an efficient implementation of various microwave imaging methods  相似文献   
999.
1000.
The problem of fracture of the adhesive joint between two elastic bodies, due to crack propagation along the joint, acted upon by heat and active agent flux through the crack surfaces is considered. Temperature and concentration of the agent inside the crack are assumed to be constant, which implies comparatively low flux conductivity of adjacent materials. The effect of an additional flux resistance concentrated at the crack surfaces is considered. This resistance is due to the adhesive layer remnants, and causes the temperature and concentration in materials at the crack edge to be dependent on the crack speed. The effect of the applied loads on deforming the materials is supposed to be sufficiently large to neglect influence of temperature and concentration on deformations. The reverse influence, as well as cross-influence of heat and concentration transfer on each other, are also neglected. The only mechanical role played by temperature and concentration of the agent under such circumstances is their influence on fracture of the adhesive joint.  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