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   338708篇
  免费   3614篇
  国内免费   1428篇
电工技术   5962篇
综合类   562篇
化学工业   49378篇
金属工艺   13833篇
机械仪表   10494篇
建筑科学   7764篇
矿业工程   1969篇
能源动力   8512篇
轻工业   27843篇
水利工程   3736篇
石油天然气   7514篇
武器工业   49篇
无线电   39198篇
一般工业技术   69430篇
冶金工业   61224篇
原子能技术   8962篇
自动化技术   27320篇
  2021年   2874篇
  2020年   2171篇
  2019年   2668篇
  2018年   4808篇
  2017年   4898篇
  2016年   5276篇
  2015年   3245篇
  2014年   5578篇
  2013年   14905篇
  2012年   8920篇
  2011年   11944篇
  2010年   9419篇
  2009年   10859篇
  2008年   11190篇
  2007年   11187篇
  2006年   9586篇
  2005年   8797篇
  2004年   8637篇
  2003年   8372篇
  2002年   8077篇
  2001年   8162篇
  2000年   7814篇
  1999年   8036篇
  1998年   19306篇
  1997年   13734篇
  1996年   10528篇
  1995年   8109篇
  1994年   7091篇
  1993年   7083篇
  1992年   5173篇
  1991年   4957篇
  1990年   4901篇
  1989年   4878篇
  1988年   4489篇
  1987年   4032篇
  1986年   4023篇
  1985年   4487篇
  1984年   4083篇
  1983年   3824篇
  1982年   3565篇
  1981年   3596篇
  1980年   3580篇
  1979年   3360篇
  1978年   3360篇
  1977年   3782篇
  1976年   4877篇
  1975年   2906篇
  1974年   2825篇
  1973年   2834篇
  1972年   2420篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Occupational airway diseases are now receiving attention in industry, although study is hampered by a lack of readily-available data. The interpretation of the data that is available, and also of the root problems themselves, is itself a difficult problem. This paper has been written as a literature review which it is hoped that other researchers can take either as a starting point or as a refresher.  相似文献   
102.
103.
104.
105.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating  相似文献   
106.
The precautionary principle (PP), according to one of its definitions, says that lack of certainty, given the current scientific and technological knowledge, shall not delay effective and proportionate actions to prevent hazards, taking into account cost-benefit considerations. Rather than being a single principle, a variety of statements of the PP are found in international treaties and other documents. Apart from any specific legal force of the documents, countries (e.g., France) have used these statements as a starting point for their own guidance documents and regulations for addressing specific environmental and health issues, for example regulation of genetically modified organisms. Thus, any discussion of the precautionary principle must address a complex legal and regulatory situation. We briefly review different statements of the PP and important commentary, largely from the European Union. We provide references to the original source documents (many of which are found in English on the World Wide Web).  相似文献   
107.
108.
The article presents the results of experimental investigations of critical (limit) heat fluxes upon evaporation on porous coatings, and it substantiates the physical model of the process.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 4, pp. 607–614, October, 1985.  相似文献   
109.
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers.  相似文献   
110.
The purpose and current construction status, at the Institute of Theoretical and Experimental Physics, of an experimental electronuclear setup, combining a pulsed proton linear accelerator (36 MeV, 0.5 mA) and a subcritical blanket thermal-power assembly 100 kW, are discussed. The main equipment is already available or is being built in industry. The setup can be used to investigate the dynamics of the interaction of a linac–driver and a subcritical reactor and problems concerning the accelerator–driver and the target–blanket assembly. The proton beams and neutron fluxes will be used for applied purposes. In the future it will be possible to increase substantially the current and energy of the proton beam.  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