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   401437篇
  免费   3621篇
  国内免费   949篇
电工技术   6881篇
综合类   192篇
化学工业   64283篇
金属工艺   21643篇
机械仪表   14305篇
建筑科学   8252篇
矿业工程   4226篇
能源动力   8198篇
轻工业   24849篇
水利工程   5364篇
石油天然气   14769篇
武器工业   30篇
无线电   37957篇
一般工业技术   90509篇
冶金工业   61425篇
原子能技术   13842篇
自动化技术   29282篇
  2021年   3853篇
  2019年   3749篇
  2018年   7070篇
  2017年   7335篇
  2016年   7730篇
  2015年   4381篇
  2014年   7546篇
  2013年   17066篇
  2012年   11169篇
  2011年   14468篇
  2010年   11621篇
  2009年   13189篇
  2008年   13274篇
  2007年   12923篇
  2006年   10738篇
  2005年   9664篇
  2004年   9390篇
  2003年   8916篇
  2002年   8753篇
  2001年   8613篇
  2000年   8383篇
  1999年   7891篇
  1998年   16680篇
  1997年   12591篇
  1996年   9624篇
  1995年   7550篇
  1994年   6752篇
  1993年   6859篇
  1992年   5532篇
  1991年   5557篇
  1990年   5582篇
  1989年   5460篇
  1988年   5305篇
  1987年   5045篇
  1986年   4898篇
  1985年   5345篇
  1984年   5120篇
  1983年   4823篇
  1982年   4550篇
  1981年   4693篇
  1980年   4557篇
  1979年   4706篇
  1978年   4887篇
  1977年   5188篇
  1976年   6181篇
  1975年   4398篇
  1974年   4433篇
  1973年   4540篇
  1972年   3985篇
  1971年   3672篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Intensive use of the benchmark simulation model No. 1 (BSM1), a protocol for objective comparison of the effectiveness of control strategies in biological nitrogen removal activated sludge plants, has also revealed a number of limitations. Preliminary definitions of the long-term benchmark simulation model No. 1 (BSM1_LT) and the benchmark simulation model No. 2 (BSM2) have been made to extend BSM1 for evaluation of process monitoring methods and plant-wide control strategies, respectively. Influent-related disturbances for BSM1_LT/BSM2 are to be generated with a model, and this paper provides a general overview of the modelling methods used. Typical influent dynamic phenomena generated with the BSM1_LT/BSM2 influent disturbance model, including diurnal, weekend, seasonal and holiday effects, as well as rainfall, are illustrated with simulation results. As a result of the work described in this paper, a proposed influent model/file has been released to the benchmark developers for evaluation purposes. Pending this evaluation, a final BSM1_LT/BSM2 influent disturbance model definition is foreseen. Preliminary simulations with dynamic influent data generated by the influent disturbance model indicate that default BSM1 activated sludge plant control strategies will need extensions for BSM1_LT/BSM2 to efficiently handle 1 year of influent dynamics.  相似文献   
12.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction.  相似文献   
13.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient, the duration of the degassing operation, and the vacuum used in the treatment. __________ Translated from Metallurg, No. 7, pp. 68–69, July, 2006.  相似文献   
14.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended.  相似文献   
15.
Using Java-based tools in multimedia collaborative environments accessed over the Internet can increase an application's client base. Most operating systems support Java, and its "compile once-run everywhere" architecture is easy to maintain and update. The Java-based tools presented here let users share Internet resources, including resources originally designed for single use.  相似文献   
16.
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal.  相似文献   
17.
V. G. Deibuk 《Semiconductors》2003,37(10):1151-1155
The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data.  相似文献   
18.
At some point in their careers, clinicians who work or consult in forensic and correctional settings will almost certainly encounter individuals who exhibit psychopathic personality features. Because of the widespread use of this disorder to inform legal and clinical decision making, psychologists should be exceedingly familiar with the relevant research literature on this topic before venturing into these settings. This article reviews the empirical bases of several clinically relevant claims and assertions regarding psychopathy and concludes that many areas of research are decidedly more equivocal in their findings than is commonly perceived. Although there is much to be gained by assessing psychopathy in various contexts, clinicians need to be cautious about drawing overzealous and empirically questionable conclusions about an important disorder that also has great potential for abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
19.
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa.  相似文献   
20.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.  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