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   526259篇
  免费   7107篇
  国内免费   1473篇
电工技术   9606篇
综合类   526篇
化学工业   78868篇
金属工艺   19978篇
机械仪表   15207篇
建筑科学   12679篇
矿业工程   2269篇
能源动力   14545篇
轻工业   47105篇
水利工程   5222篇
石油天然气   9336篇
武器工业   37篇
无线电   60032篇
一般工业技术   101936篇
冶金工业   103686篇
原子能技术   10588篇
自动化技术   43219篇
  2022年   3164篇
  2021年   4909篇
  2020年   3485篇
  2019年   4568篇
  2018年   7820篇
  2017年   7620篇
  2016年   7950篇
  2015年   5563篇
  2014年   9260篇
  2013年   24110篇
  2012年   14643篇
  2011年   20183篇
  2010年   15834篇
  2009年   17733篇
  2008年   18131篇
  2007年   17807篇
  2006年   15540篇
  2005年   14249篇
  2004年   13628篇
  2003年   13415篇
  2002年   12654篇
  2001年   12851篇
  2000年   11890篇
  1999年   12610篇
  1998年   32871篇
  1997年   22934篇
  1996年   17476篇
  1995年   13053篇
  1994年   11297篇
  1993年   10991篇
  1992年   7930篇
  1991年   7436篇
  1990年   7279篇
  1989年   7019篇
  1988年   6484篇
  1987年   5773篇
  1986年   5671篇
  1985年   6283篇
  1984年   5907篇
  1983年   5177篇
  1982年   4905篇
  1981年   4972篇
  1980年   4714篇
  1979年   4616篇
  1978年   4419篇
  1977年   5345篇
  1976年   6983篇
  1975年   3796篇
  1974年   3554篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.  相似文献   
83.
84.
Abstract This article presents a study of a large scale incorporation of one data acquisitionsystem into physics teaching in Israel. By 1994 about 30% of the schools throughout the country used the V-scope, a 3-D multibody motion tracing system, in their lab programme. The views and reactions of post-training teachers, experienced teachers and students on various aspects of using the system are described, analysed and compared.  相似文献   
85.
Gilbenclamide, a widely used potent hypoglycaemic agent was solubllized using β -Cyclodextrin and β -Cyclodextrin derivatives. Complexes were prepared by kneading method in a molar ratio of 1:1 of the drug and the cyclodextrlns respectively. The Glibenclamide β -Cyelocextrin complex was characterized and evaluated by I.R. studies, Differential Scanning Calorimotry 6 X-ray diffractometry. The in-vitro dissolution rates of drug from inclusion complexes of β Cyclodextrins and its derivatives were compared. A significant Improvement In dissolution lor, rates of Gllbenclamide was observed with Inclusion complexes of all the Cyclodextrins. However, the solubilizing effect was more in case of β-Cyclodextrin derivatives.  相似文献   
86.
87.
The paper presents the results of research in the convection drying of unidirectional glass fibre bobbins on the basis of which the relations are suggested required to calculate the process of drying in the design of drying equipment.  相似文献   
88.
No generally accepted principles and guidelines currently exist to help engineers design local interaction mechanisms that result in a desired global behavior. However, several communities have developed ways of approaching this problem in the context of niched application areas. Because the ideas underlying these approaches are often obscured or underemphasized in technical papers, the authors review the role of self-organization in their work. They provide a better picture of the status of the emerging field of self-organizing systems or autonomic computing.  相似文献   
89.
An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal  相似文献   
90.
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures  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