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   179660篇
  免费   874篇
  国内免费   262篇
化学   89713篇
晶体学   2636篇
力学   9380篇
综合类   7篇
数学   20912篇
物理学   58148篇
  2020年   1849篇
  2019年   2291篇
  2018年   3398篇
  2017年   3523篇
  2016年   4157篇
  2015年   1852篇
  2014年   3587篇
  2013年   7055篇
  2012年   5533篇
  2011年   6589篇
  2010年   5512篇
  2009年   5636篇
  2008年   6360篇
  2007年   6328篇
  2006年   5622篇
  2005年   4984篇
  2004年   4823篇
  2003年   4366篇
  2002年   4522篇
  2001年   5001篇
  2000年   3690篇
  1999年   2823篇
  1998年   2603篇
  1997年   2457篇
  1996年   2253篇
  1995年   2048篇
  1994年   2005篇
  1993年   2038篇
  1992年   2075篇
  1991年   2380篇
  1990年   2317篇
  1989年   2386篇
  1988年   2270篇
  1987年   2294篇
  1986年   2128篇
  1985年   2657篇
  1984年   2674篇
  1983年   2317篇
  1982年   2371篇
  1981年   2276篇
  1980年   2076篇
  1979年   2393篇
  1978年   2548篇
  1977年   2643篇
  1976年   2732篇
  1975年   2539篇
  1974年   2468篇
  1973年   2634篇
  1972年   2153篇
  1971年   1974篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
We investigate the properties of maximum likelihood estimators in observation schemes of random variables that arrive at random time moments on a Poisson trajectory defined on some ergodic process.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 59, pp. 98–105, 1986.  相似文献   
972.
973.
974.
The present paper establishes sufficient conditions for the uniformly bounded of any solution of (1.1) and which tend to zero as t → ∞.  相似文献   
975.
The nonlocal initial problem for nonlinear nonautonomous evolution equati-ons in a Banach space is considered. It is assumed that the nonlinearities havethe local Lipschitz properties. The existence and uniqueness of mild solutionsare proved. Applications to integro-differential equations are discussed.The main tool in the paper is the normalizing mapping (the generalizednorm).  相似文献   
976.
977.
The complex formation between chromogenic capped calix 4 arene derivatives comprising indophenol indicator group(s), and aliphatic amines has been studied by UV/Vis spectroscopy. The equilibrium constants have been determined in ethanol, and—for one ligand—also in dimethylsulfoxide. The results have been interpreted in terms of various types of host–guest interactions and of steric effects.  相似文献   
978.
Stoichiometry and kinetics of reactions of 2,6-diphenyl-4-chloropyrylium, 4-chloroflavylium, 4-bromoflavylium, and 4-iodoflavylium perchlorates with nucleophiles N,N-dimethylaniline and n-phenylenediamine are studied using cyclic voltammetry and spectroscopy. Nucleophilic substitution in these compounds proceeds via the formation of a charge-transfer complex, which converts into a radical ion pair as a result of the electron transfer. Heterolytic clevage of the C–Hal bond occurs at the stage of pyranyl (flavanyl) radical.  相似文献   
979.
The coalescence of branches in the Y junctions of single-wall carbon nanotubes (10 nm long) is predicted to occur when the branches approach each other under the action of a load (~10 nN) applied to their ends. A transition to the new state with parallel branches bound by molecular interactions was simulated and the energy characteristics were calculated by the molecular dynamics method. The Y junctions with parallel branches are stable at temperatures up to 2000 K. It is established that there is a threshold distance between the branch ends, below which the branches exhibit spontaneous sticking under the action of molecular attraction forces. If the branches are unloaded before this threshold distance is reached, they oscillate (acting as a nanodimensional “tuning fork”) at a frequency of ~100 GHz.  相似文献   
980.
The pseudopotential augmented-plane-wave method was used to study the surface structure of thin copper films with monolayers of Co, Ni, and Cs. Local densities of electron states, distributions of charge densities in the layers, and electron energy spectra are analyzed. The effect of adsorbates on the electronic properties of the Cu(001) surface and work function are discussed. Satisfactory agreement with available experimental data has been obtained.  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