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   288276篇
  免费   3146篇
  国内免费   970篇
电工技术   4266篇
综合类   2454篇
化学工业   42952篇
金属工艺   14944篇
机械仪表   9994篇
建筑科学   6133篇
矿业工程   2715篇
能源动力   5758篇
轻工业   16382篇
水利工程   4155篇
石油天然气   8053篇
武器工业   22篇
无线电   30600篇
一般工业技术   60948篇
冶金工业   36923篇
原子能技术   6865篇
自动化技术   39228篇
  2021年   2070篇
  2019年   2018篇
  2018年   17884篇
  2017年   16835篇
  2016年   13810篇
  2015年   2827篇
  2014年   4006篇
  2013年   8946篇
  2012年   8760篇
  2011年   16425篇
  2010年   13977篇
  2009年   11930篇
  2008年   13264篇
  2007年   14109篇
  2006年   5685篇
  2005年   6287篇
  2004年   5722篇
  2003年   5690篇
  2002年   4895篇
  2001年   4565篇
  2000年   4355篇
  1999年   4252篇
  1998年   10237篇
  1997年   7207篇
  1996年   5539篇
  1995年   4141篇
  1994年   3610篇
  1993年   3848篇
  1992年   2995篇
  1991年   3018篇
  1990年   2890篇
  1989年   2853篇
  1988年   2874篇
  1987年   2510篇
  1986年   2568篇
  1985年   2854篇
  1984年   2688篇
  1983年   2555篇
  1982年   2300篇
  1981年   2269篇
  1980年   2347篇
  1979年   2360篇
  1978年   2382篇
  1977年   2487篇
  1976年   2876篇
  1975年   2188篇
  1974年   2068篇
  1973年   2166篇
  1972年   1940篇
  1971年   1755篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
81.
82.
The effect of the composition of sensitizing–activating solutions on the activation efficiency and the chemical coppering of diamond powders is studied. The results demonstrate that stabilizing additives improve the stability of the solutions, influence the average coppering rate, and play a key role in determining the morphology and quality of the resultant coatings. The most effective stabilizing additive is synthamid-10, which ensures the deposition of high-quality copper coatings.  相似文献   
83.
The structure and mechanical properties of nanocrystalline aluminum alloy 1570 obtained by means of severe plastic deformation have been studied. Being tested in a temperature range from 300 to 400°C, the alloy exhibits high-strain-rate superplasticity. At 400°C, the superplasticity is manifested in a very broad range of strain rates, extending from 5 × 10?3 to 1 s?1.  相似文献   
84.
85.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  相似文献   
86.
A combination of concept (the product portfolio and the product life cycle) and empirical research (the PIMS study) can aid in clarifying the key issues involved in the selection of a firm's core strategies. Strategy control is multistage: periodic re-evaluation of strategy alternatives by use of the marketing audit; an analytical framework for control of chosen strategies by breaking down components and reporting their performance variances; and 'marketing segment' analysis for control of the detailed marketing plan.?  相似文献   
87.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals.  相似文献   
88.
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   
89.
The photoelectric parameters of silicon solar cells degraded under the action of 60Co gamma-radiation can be partly restored using an ultrasonic treatment (UST). The growth of the maximum output power of solar cells after the UST is related to a redistribution of the radiation defects and an increase in the homogeneity of a semiconductor crystal structure.  相似文献   
90.
The dispersion of potassium niobate (KNbO3) ceramics is analysed using the multiple-arc approach. This has revealed a high frequency arc that is unattainable by the Cole-Cole single arc analysis. The temperature dependence of the new arc is derived through the spread parameter of the relaxation distribution and interpreted in terms of the ferroelectric property of the KNbO3 ceramics. It is shown that the overall dispersion behaviour of the ceramics is mainly due to the existence of two distinctly different polarisation mechanisms. The arc approach has also provided an effective tool for network simulation of dispersion whereby the ceramics are modelled by nine parallel R-C branches over the frequency range 102-105 Hz used  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