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   251768篇
  免费   1582篇
  国内免费   402篇
化学   115326篇
晶体学   3410篇
力学   13580篇
综合类   7篇
数学   39714篇
物理学   81715篇
  2019年   1171篇
  2018年   10432篇
  2017年   11288篇
  2016年   6590篇
  2015年   2422篇
  2014年   2540篇
  2013年   6435篇
  2012年   9315篇
  2011年   18802篇
  2010年   11514篇
  2009年   11635篇
  2008年   16450篇
  2007年   20080篇
  2006年   5605篇
  2005年   11978篇
  2004年   7910篇
  2003年   7316篇
  2002年   5318篇
  2001年   4488篇
  2000年   3629篇
  1999年   2613篇
  1998年   2285篇
  1997年   2203篇
  1996年   2156篇
  1995年   2001篇
  1994年   1974篇
  1993年   1804篇
  1992年   2065篇
  1991年   2197篇
  1990年   1994篇
  1989年   2003篇
  1988年   1949篇
  1987年   1848篇
  1986年   1773篇
  1985年   2284篇
  1984年   2430篇
  1983年   1992篇
  1982年   2168篇
  1981年   2056篇
  1980年   1979篇
  1979年   2136篇
  1978年   2314篇
  1977年   2081篇
  1976年   2160篇
  1975年   2057篇
  1974年   2107篇
  1973年   2139篇
  1972年   1379篇
  1971年   1222篇
  1968年   1177篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
83.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
84.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange.  相似文献   
85.
Kinetic, sorption and selectivity properties of commercial adsorbents are improved by adding petroleum residues (tar asphaltene concentrates) 13% of whole mass. Obtained adsorbents can be used for selective extraction of nobel metals from multicomponent polymetallic solutions of heavy metals and fro sewages purification for removing arsenic.  相似文献   
86.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron...  相似文献   
87.
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual polytope.  相似文献   
88.
89.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity. PACS 47.80.Jk, 47.40.Ki, 47.60.+i  相似文献   
90.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased.  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