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   75080篇
  免费   711篇
  国内免费   689篇
电工技术   1438篇
综合类   47篇
化学工业   11230篇
金属工艺   3451篇
机械仪表   2643篇
建筑科学   1645篇
矿业工程   503篇
能源动力   1859篇
轻工业   6389篇
水利工程   849篇
石油天然气   2303篇
武器工业   41篇
无线电   7226篇
一般工业技术   16508篇
冶金工业   12448篇
原子能技术   2629篇
自动化技术   5271篇
  2022年   590篇
  2021年   912篇
  2020年   698篇
  2019年   782篇
  2018年   1556篇
  2017年   1568篇
  2016年   1772篇
  2015年   951篇
  2014年   1566篇
  2013年   3582篇
  2012年   2376篇
  2011年   2838篇
  2010年   2376篇
  2009年   2649篇
  2008年   2632篇
  2007年   2563篇
  2006年   2199篇
  2005年   1927篇
  2004年   1840篇
  2003年   1797篇
  2002年   1706篇
  2001年   1684篇
  2000年   1683篇
  1999年   1566篇
  1998年   3678篇
  1997年   2603篇
  1996年   1943篇
  1995年   1528篇
  1994年   1330篇
  1993年   1351篇
  1992年   996篇
  1991年   1053篇
  1990年   1073篇
  1989年   1055篇
  1988年   941篇
  1987年   874篇
  1986年   878篇
  1985年   935篇
  1984年   778篇
  1983年   766篇
  1982年   676篇
  1981年   689篇
  1980年   662篇
  1979年   646篇
  1978年   621篇
  1977年   774篇
  1976年   933篇
  1975年   580篇
  1974年   551篇
  1973年   543篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
71.
A unified approach to decision making with extremal many-criteria models, expert estimates, and voting is developed on the basis of reference and distance concepts and taxonomy methods. It involves the solution of many-criteria problems with the Pareto optimum. Examples demonstrating the effectiveness and universality of the approach are given.  相似文献   
72.
We demonstrate, for the first time to our knowledge, that a fast coherent collision between two Kerr spatial solitons can give rise to a significant phase shift for both interacting beams. The maximal collision-induced phase shift ≈π rad takes place when the amplitudes of the solitons are equal (η12) and the length of the interaction zone is comparable with a soliton phase period. Depending on the ratio η21, and the collision angle between the solitons, the magnitude of the phase shift can be varied within a reasonable range, for example from 180° to 40°. The analysis of the effect performed by the finite-difference beam-propagation method has shown that it is insensitive to the initial phase difference between the incident beams (δi), even in the case when η 1≠η2. It has been demonstrated that the phenomenon can be used for all-optical three-soliton logic elements, which are capable of providing more than 3-dB signal amplification and possess bi -independent output characteristics  相似文献   
73.
A new sensitive method for imaging of the spatial distribution of microwave intensity is proposed. The method is based on the imaging of the 6P-recombination continuum of cesium, emitted from a nonequilibrium plasma of the positive column of gas discharge in a cesium vapor-xenon mixture. It is demonstrated that the spatial distribution of intensity of 35-GHz microwave radiation measured by this method in a focal plane of a lens well coincides with the pattern obtained with the aid of a movable microwave detector. The time resolution of the proposed microwave imaging system reaches 1 ms.  相似文献   
74.
We describe main models and methods for the calculation of contact rigidity and wear resistance of friction couples using thin-walled structural elements such as beams, plates, or shells. We analyze certain specific features of their contact interaction on the basis of theories describing stress-strain state. We also consider mathematical models of the wear of junctions that take into account the frictional heating of contacting surfaces and anisotropy of their properties. A series of theoretical calculations is corroborated experimentally.  相似文献   
75.
This study investigates the phenotype of turbulent (Re = 5,200) and laminar (Re = 2,000) flow-generated Pseudomonas fluorescens biofilms. Three P. fluorescens strains, the type strain ATCC 13525 and two strains isolated from an industrial processing plant, D3-348 and D3-350, were used throughout this study. The isolated strains were used to form single and binary biofilms. The biofilm physiology (metabolic activity, cellular density, mass, extracellular polymeric substances, structural characteristics and outer membrane proteins [OMP] expression) was compared. The results indicate that, for every situation, turbulent flow-generated biofilms were more active (p < 0.05), had more mass per cm(2) (p < 0.05), a higher cellular density (p < 0.05), distinct morphology, similar matrix proteins (p > 0.1) and identical (isolated strains -single and binary biofilms) and higher (type strain) matrix polysaccharides contents (p < 0.05) than laminar flow-generated biofilms. Flow-generated biofilms formed by the type strain revealed a considerably higher cellular density and amount of matrix polysaccharides than single and binary biofilms formed by the isolated strains (p < 0.05). Similar OMP expression was detected for the several single strains and for the binary situation, not dependent on the hydrodynamic conditions. Binary biofilms revealed an equal coexistence of the isolated strains with apparent neutral interactions. In summary, the biofilms formed by the type strain represent, apparently, the worst situation in a context of control. The results obtained clearly illustrate the importance of considering strain variation and hydrodynamics in biofilm development, and complement previous studies which have focused on physical aspects of structural and density differences.  相似文献   
76.
Translated from Atomnaya Énergiya, Vol. 67, No. 5, pp. 358–359, November, 1989.  相似文献   
77.
The photoelectric properties of cotton fibers treated with iodine were studied in the fundamental absorption range. The samples exhibit a sublinear illumination-current characteristic and a long-term relaxation of photoconductivity (PC) after UV irradiation (=5 eV) of the iodine-doped fibers. A PC mechanism is proposed which explains both the nonlinear variation of photocurrent with illumination intensity and the PC decay according to a bimolecular recombination law after UV irradiation of the iodine-doped fiber in the fundamental absorption range.  相似文献   
78.
The results of investigation of initial stage of the tantalum borating as well as the effect of oxygen and hydrogen on it are presented. The scheme of the initial stage of tantalum boron saturation is proposed.  相似文献   
79.
Introduction of the BER? KOMPAKS® automated system at the Vyksa Metallurgical Plant to safely and efficiently manage the operation of the plant’s equipment has allowed the facility to begin operating that equipment based on real-time evaluations of its actual physical condition. Introduction of the new system has also allowed better coordination of repair-scheduling with ongoing production operations, significantly improved the reliability and readiness of the equipment for operation at 100% capacity, completely eliminated the human factor from the process of monitoring the condition of equipment, and made it possible to check the quality and timeliness of equipment maintenance and repair work so as to ensure safe, efficient operation of the entire production complex.  相似文献   
80.
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