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   243313篇
  免费   2886篇
  国内免费   427篇
电工技术   4338篇
综合类   262篇
化学工业   39767篇
金属工艺   9416篇
机械仪表   7422篇
建筑科学   5514篇
矿业工程   1393篇
能源动力   5189篇
轻工业   24933篇
水利工程   2498篇
石油天然气   5101篇
武器工业   32篇
无线电   25319篇
一般工业技术   45126篇
冶金工业   45994篇
原子能技术   5981篇
自动化技术   18341篇
  2021年   2137篇
  2019年   2036篇
  2018年   3506篇
  2017年   3447篇
  2016年   3719篇
  2015年   2258篇
  2014年   3929篇
  2013年   10251篇
  2012年   6217篇
  2011年   8362篇
  2010年   6599篇
  2009年   7296篇
  2008年   7691篇
  2007年   7787篇
  2006年   6959篇
  2005年   6100篇
  2004年   5873篇
  2003年   5650篇
  2002年   5742篇
  2001年   5603篇
  2000年   5421篇
  1999年   5367篇
  1998年   12745篇
  1997年   9027篇
  1996年   6969篇
  1995年   5379篇
  1994年   4800篇
  1993年   4681篇
  1992年   3697篇
  1991年   3415篇
  1990年   3622篇
  1989年   3492篇
  1988年   3343篇
  1987年   2923篇
  1986年   2955篇
  1985年   3402篇
  1984年   3236篇
  1983年   2909篇
  1982年   2762篇
  1981年   2840篇
  1980年   2736篇
  1979年   2637篇
  1978年   2706篇
  1977年   2978篇
  1976年   3850篇
  1975年   2390篇
  1974年   2248篇
  1973年   2386篇
  1972年   1984篇
  1971年   1869篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The Raman spectrum of water adsorbed on a metallic silver surface reveals an anomalously large shift of the vibrational frequency as compared to that in the bulk. The results are compared to data reported by other researchers, and possible interpretations of the observed phenomenon are discussed.  相似文献   
53.
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the...  相似文献   
54.
Journal of Communications Technology and Electronics - A new method is proposed to represent electromagnetic field in inhomogeneous 2D periodic medium (PM) as a discrete set of amplitude vectors...  相似文献   
55.
Biological information is stored in DNA, RNA and protein sequences, which can be understood as genotypes that are translated into phenotypes. The properties of genotype–phenotype (GP) maps have been studied in great detail for RNA secondary structure. These include a highly biased distribution of genotypes per phenotype, negative correlation of genotypic robustness and evolvability, positive correlation of phenotypic robustness and evolvability, shape-space covering, and a roughly logarithmic scaling of phenotypic robustness with phenotypic frequency. More recently similar properties have been discovered in other GP maps, suggesting that they may be fundamental to biological GP maps, in general, rather than specific to the RNA secondary structure map. Here we propose that the above properties arise from the fundamental organization of biological information into ‘constrained'' and ‘unconstrained'' sequences, in the broadest possible sense. As ‘constrained'' we describe sequences that affect the phenotype more immediately, and are therefore more sensitive to mutations, such as, e.g. protein-coding DNA or the stems in RNA secondary structure. ‘Unconstrained'' sequences, on the other hand, can mutate more freely without affecting the phenotype, such as, e.g. intronic or intergenic DNA or the loops in RNA secondary structure. To test our hypothesis we consider a highly simplified GP map that has genotypes with ‘coding'' and ‘non-coding'' parts. We term this the Fibonacci GP map, as it is equivalent to the Fibonacci code in information theory. Despite its simplicity the Fibonacci GP map exhibits all the above properties of much more complex and biologically realistic GP maps. These properties are therefore likely to be fundamental to many biological GP maps.  相似文献   
56.
57.
Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings.  相似文献   
58.
59.
60.
In optimization of transient problems, a robust, stable, and efficient numerical scheme for time integration is of much importance. Recently, the mixed Lag  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