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   739篇
  免费   13篇
  国内免费   2篇
化学   399篇
晶体学   9篇
力学   71篇
数学   113篇
物理学   162篇
  2022年   7篇
  2021年   8篇
  2020年   7篇
  2018年   10篇
  2017年   6篇
  2016年   11篇
  2015年   9篇
  2014年   13篇
  2013年   64篇
  2012年   24篇
  2011年   33篇
  2010年   15篇
  2009年   19篇
  2008年   22篇
  2007年   33篇
  2006年   24篇
  2005年   21篇
  2004年   21篇
  2003年   9篇
  2002年   23篇
  2001年   10篇
  2000年   11篇
  1999年   18篇
  1998年   9篇
  1997年   5篇
  1996年   15篇
  1995年   10篇
  1994年   10篇
  1993年   11篇
  1992年   13篇
  1991年   8篇
  1990年   10篇
  1989年   11篇
  1988年   8篇
  1987年   10篇
  1986年   10篇
  1985年   15篇
  1984年   15篇
  1983年   15篇
  1982年   10篇
  1981年   9篇
  1980年   9篇
  1979年   11篇
  1977年   8篇
  1976年   18篇
  1975年   15篇
  1974年   13篇
  1973年   11篇
  1972年   5篇
  1971年   10篇
排序方式: 共有754条查询结果,搜索用时 15 毫秒
41.
The catenary form of loss function is considered in the framework of Bayesian decision theory. The mathematical tractability of this form seems to be unrecognized; it contains quadratic loss as a limiting case. For various probability distributions expressions are given for posterior analysis, and limiting properties are investigated.  相似文献   
42.
A bi-matrix threat game is defined as a triple (A,B,S) whereA andB arem×n payoff matrices, andS is a closed convex subset of the plane, with (a ij,B ij) εS for eachi,j. Given (threat) mixed strategiesx andy,Nash's model suggests that the eventual outcome will be that point (u, v) εS which maximizes the product (u ?xAy t) (v ?xBy t) subject touxAy t,vxBy t. Optimality of the threat strategies is then defined in the obvious way. A constructive proof of existence of optimal threat strategies is given; in particular, it is shown that they are optimal strategies for the matrix gameA-kB, wherek is to be determined. In this paper,k is approximated by aNewton-Raphson technique. Two examples are solved in detail.  相似文献   
43.
The infrared absorption spectra of two related compounds, butyronitrile (CH3CH2-CH2CN) and methylthioacetonitrile (CH3SCH2CN) have been examined in the liquid and solid phases. Vapour phase spectra of butyronitrile have also been recorded. Evidence is given for the existence of two rotational isomers trans and gauche, for both compounds. In both cases the energy difference between the two rotamers appears to be small with the gauche form identified as the low energy conformer for butyronitrile. For methylthioacetonitrile it was not possible to determine the more stable rotational isomer.  相似文献   
44.
We present a theory for the transport of molecules adsorbed in slit and cylindrical nanopores at low density, considering the axial momentum gain of molecules oscillating between diffuse wall reflections. Good agreement with molecular dynamics simulations is obtained over a wide range of pore sizes, including the regime of single-file diffusion where fluid-fluid interactions are shown to have a negligible effect on the collective transport coefficient. We show that dispersive fluid-wall interactions considerably attenuate transport compared to classical hard sphere theory.  相似文献   
45.
Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.  相似文献   
46.
An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations.  相似文献   
47.
A series of highly sulfonated, ether‐containing polybenzimidazoles (SOPBI) with controlled sulfonation degrees were synthesized from various stoichiometric ratio mixtures of sodium 6,6'‐oxybis(3‐carboxybenzenesulfonate) (SODBA), 4,4'‐oxydibenzoic acid (ODBA), and 3,3'‐diaminobenzidine (DAB) by solution copolycondensation in poly(phosphoric acid). The resulting sulfonated polymers were further sulfonated by grafting of pendant sulfonic acid chains via a reaction of 1,3‐propane sultone with lithiated‐N of the imidazole rings in the polymer backbone, yielding materials with high, absolute IEC values (3.42–4.15 meq g?1). Due to self‐neutralization, the solid state polymers possessed “free” acid content of 1.40 to 2.15 meq g?1, were soluble in organic solvents yet insoluble in aqueous solution, while displaying proton conductivites (11–47 mS cm?1) at elevated temperatures (80 °C, 95% RH). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3654–3666  相似文献   
48.
49.
50.
The preparation, isolation and characterisation of 1,3-bis(diphenylphosphino)indene (1) from indene and chlorodiphenylphosphine is described. The reaction of 1 with selenium gives the diselenide adduct 1,3-bis(diphenylselenophosphino)indene (2) which was characterised crystallographically. Deprotonation of 1 and treatment with ferrous chloride gives the unstable tetraphosphine complex bis(1,3-bis(diphenylphosphino)indenyl)iron(II) (3). Complex 3 decomposes to the diphosphine complex bis(1-diphenylphosphinoindenyl)iron(II) (4) via replacement of one diphenylphosphine substituent per indenyl ligand by a hydrogen atom. Complex 4 was also prepared by treatment of two equivalents of 1-diphenylphosphinoindenide with ferrous chloride. The heterobimetallic complex tetracarbonyl(bis(1-diphenylphosphinoindenyl)iron(II))molybdenum(0) (5) was also prepared and crystal structures of both the meso (5a) and C2-symmetric racemic (5b) isomers are reported.  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