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   197901篇
  免费   2133篇
  国内免费   632篇
电工技术   4064篇
综合类   123篇
化学工业   26711篇
金属工艺   7507篇
机械仪表   5461篇
建筑科学   4039篇
矿业工程   747篇
能源动力   4659篇
轻工业   14406篇
水利工程   1707篇
石油天然气   2843篇
武器工业   7篇
无线电   27302篇
一般工业技术   37393篇
冶金工业   45423篇
原子能技术   3564篇
自动化技术   14710篇
  2021年   1247篇
  2019年   1282篇
  2018年   2125篇
  2017年   2108篇
  2016年   2171篇
  2015年   1498篇
  2014年   2623篇
  2013年   7954篇
  2012年   4464篇
  2011年   6111篇
  2010年   4934篇
  2009年   5773篇
  2008年   6148篇
  2007年   6199篇
  2006年   5637篇
  2005年   5304篇
  2004年   5250篇
  2003年   5091篇
  2002年   4899篇
  2001年   5305篇
  2000年   4917篇
  1999年   5436篇
  1998年   15634篇
  1997年   10315篇
  1996年   7933篇
  1995年   5788篇
  1994年   5015篇
  1993年   5024篇
  1992年   3390篇
  1991年   3261篇
  1990年   3215篇
  1989年   3039篇
  1988年   2788篇
  1987年   2238篇
  1986年   2302篇
  1985年   2608篇
  1984年   2314篇
  1983年   2064篇
  1982年   1903篇
  1981年   2044篇
  1980年   1791篇
  1979年   1659篇
  1978年   1658篇
  1977年   2022篇
  1976年   2702篇
  1975年   1422篇
  1974年   1369篇
  1973年   1316篇
  1972年   1124篇
  1971年   957篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
54.
55.
The optical properties of bismuth telluride crystals doped with donor-and acceptor-type impurities are studied. The fact that energy corresponding to the resonance frequency of plasma oscillations of free charge carriers (plasmons) approaches the band-gap energy is detected in the infrared spectral region, where the main elementary excitations in the electronic system of these materials are observed. The mentioned approach of energies varies the intensity of electron-plasmon interaction, which affects the recombination processes in the materials widely used for the fabrication of thermoelectric energy converters.  相似文献   
56.
We propose a model that enables software developers to systematically evaluate and compare all possible alternative reuse scenarios. The model supports the clear identification of the basic operations involved and associates a cost component with each basic operation in a focused and precise way. The model is a practical tool that assists developers to weigh and evaluate different reuse scenarios, based on accumulated organizational data, and then to decide which option to select in a given situation. The model is currently being used at six different companies for cost-benefit analysis of alternative reuse scenarios; we give a case study that illustrates how it has been used in practice.  相似文献   
57.
Notches were machined in specimens of INCONEL 718 by a broaching process, where differing broaching runs led to differing extents of subsurface deformation and surface roughness. Fatigue tests were carried out at 600 °C with a trapezoidal loading waveform at 0.25 Hz. The broaching process that led to the more severe subsurface deformation (but lower surface roughness) showed the worst fatigue performance. Analysis of total strain amplitude in the notch root with the aid of an elastoplastic finite-element (FE) model showed that the work hardening related to the subsurface deformation caused by the different broaching can account for the difference in fatigue lives. Differences in initiation and growth behavior were seen for the two broached finishes as well as for broached and subsequently polished samples. These differences are discussed in terms of a change in crack growth initiation and growth mechanisms due to the presence of the work-hardened layer.  相似文献   
58.
Thermal Transformations of an Aluminoborophosphate Binder   总被引:1,自引:0,他引:1  
Thermal transformations of a commercial aluminoborophosphate binder are studied in a broad temperature range by optical microscopy, x-ray diffraction, IR spectroscopy, and thermal analysis. The introduction of B2O3 reduces the temperature of phosphate polycondensation, enhances the stability of cyclometaphosphates in a broad temperature range (180–1100°C), and reduces the stability of hydrogen phosphates.  相似文献   
59.
60.
A method is developed, based on word-searching, which provides a rapid test for the statistical significance of DNA sequence similarities for use in databank searching. The method makes allowance for the lengths and dinucleotide compositions of the sequences being compared. A way is also described to calculate the power of the test, i.e. the probability of detecting a given similarity as being statistically significant. The effects on the power of the test of the scoring method, word length, sequence length, and sequence composition are examined. A novel scoring method is shown to be superior to the method currently used in most word-searching algorithms.  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