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   468509篇
  免费   3733篇
  国内免费   972篇
化学   232901篇
晶体学   6831篇
力学   23603篇
综合类   15篇
数学   64964篇
物理学   144900篇
  2019年   3245篇
  2018年   11638篇
  2017年   12328篇
  2016年   9922篇
  2015年   4604篇
  2014年   6341篇
  2013年   16060篇
  2012年   15619篇
  2011年   25094篇
  2010年   16429篇
  2009年   16349篇
  2008年   22544篇
  2007年   25653篇
  2006年   13329篇
  2005年   17372篇
  2004年   13564篇
  2003年   12600篇
  2002年   10870篇
  2001年   10749篇
  2000年   8535篇
  1999年   6424篇
  1998年   5612篇
  1997年   5551篇
  1996年   5313篇
  1995年   4895篇
  1994年   5010篇
  1993年   4595篇
  1992年   5271篇
  1991年   5351篇
  1990年   5133篇
  1989年   5041篇
  1988年   5068篇
  1987年   4895篇
  1986年   4649篇
  1985年   6117篇
  1984年   6485篇
  1983年   5417篇
  1982年   5713篇
  1981年   5546篇
  1980年   5457篇
  1979年   5550篇
  1978年   5984篇
  1977年   5738篇
  1976年   5861篇
  1975年   5465篇
  1974年   5560篇
  1973年   5719篇
  1972年   3957篇
  1971年   3390篇
  1970年   3093篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
181.
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   
182.
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   
183.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content in contrast those of L-lysine and L-histidine esters.  相似文献   
184.
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   
185.
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   
186.
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   
187.
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   
188.
189.
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   
190.
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