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   27854篇
  免费   1048篇
  国内免费   45篇
电工技术   357篇
综合类   40篇
化学工业   6289篇
金属工艺   450篇
机械仪表   561篇
建筑科学   1447篇
矿业工程   112篇
能源动力   744篇
轻工业   2158篇
水利工程   264篇
石油天然气   77篇
无线电   2023篇
一般工业技术   5135篇
冶金工业   5147篇
原子能技术   221篇
自动化技术   3922篇
  2023年   262篇
  2022年   439篇
  2021年   665篇
  2020年   440篇
  2019年   533篇
  2018年   631篇
  2017年   554篇
  2016年   722篇
  2015年   626篇
  2014年   847篇
  2013年   1594篇
  2012年   1304篇
  2011年   1708篇
  2010年   1215篇
  2009年   1156篇
  2008年   1324篇
  2007年   1230篇
  2006年   1046篇
  2005年   858篇
  2004年   818篇
  2003年   727篇
  2002年   605篇
  2001年   474篇
  2000年   408篇
  1999年   456篇
  1998年   800篇
  1997年   596篇
  1996年   492篇
  1995年   452篇
  1994年   405篇
  1993年   381篇
  1992年   295篇
  1991年   209篇
  1990年   294篇
  1989年   283篇
  1988年   231篇
  1987年   245篇
  1986年   248篇
  1985年   292篇
  1984年   239篇
  1983年   241篇
  1982年   228篇
  1981年   217篇
  1980年   195篇
  1979年   209篇
  1978年   188篇
  1977年   204篇
  1976年   251篇
  1975年   176篇
  1974年   135篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Performance on computer-simulated, everyday memory tasks was found to deteriorate with age in 434 Belgian (aged 14–88 yrs) and 434 American Ss matched on gender and age. This age-related memory decline was reasonably consistent across samples. Difficulties in cross-cultural research and the advantages of ecologically valid measurement instruments are discussed. Instruments included a grocery list selective reminding test, the Wechsler Memory Scale, the Benton Visual Retention Test, and the Wechsler Adult Intelligence Scale (WAIS). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
32.
The gas flow sputter technique was invented a few years ago particularly for the inexpensive fabrication of sophisticated ceramic layers. Meanwhile, it has matured and become increasingly powerful. Today it is on the verge of being applied in industrial fabrication processes. The present article gives an overview over the method, its characteristics and the numerous applications.  相似文献   
33.
34.
Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees.  相似文献   
35.
The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
36.
This paper highlights the role of the faculty member in recruiting students currently enrolled in B.S. programs in engineering and the sciences into full-time pursuit of a graduate-level engineering degree. The faculty member is demonstrated to be in a unique position to influence such students, providing strong counterforces to a confluence of attitudes and pressures experienced during the B.S. experience which effectively create a barrier to full-time engineering graduate study. We analyze this barrier via the method of force field analysis, and demonstrate that effective recruitment into full-time graduate study must be based on a four-fold strategy of education, expectations, improved B.S. experience and better control of the B.S. environment. Approaches to implement these strategies are discussed.  相似文献   
37.
A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5---TiO2 catalysts with different V/Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V/Ti ratio.

These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V/Ti ratio would have large V2O5 crystals acting as support of a V/TiO2 solid solution. In contrast, those samples with a low V/Ti ratio, would have the solid solution supporting vanadium pentoxide crystals.  相似文献   

38.
39.
The effect of salt addition, in the form of a fluxing agent containing equivalent amounts of NaCl and KCl, on the microstructure and mechanical properties of 359/SiC/10p composite has been investigated. Both microstructure and properties are affected, with the removal of magnesium and strontium and the introduction of sodium and potassium being responsible for the degradation in properties. Thermodynamic calculations have been carried out to account for the effect of salt addition in terms of the surface adsorption of sodium and potassium impurities and the consequent changes in the surface-interface tension of their binary alloys. Mechanisms for the degradation of properties have been discussed.  相似文献   
40.
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