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   14975篇
  免费   1458篇
  国内免费   945篇
化学   12018篇
晶体学   41篇
力学   756篇
综合类   66篇
数学   826篇
物理学   3671篇
  2024年   13篇
  2023年   231篇
  2022年   374篇
  2021年   371篇
  2020年   573篇
  2019年   527篇
  2018年   510篇
  2017年   610篇
  2016年   729篇
  2015年   687篇
  2014年   750篇
  2013年   1013篇
  2012年   1034篇
  2011年   1023篇
  2010年   789篇
  2009年   915篇
  2008年   866篇
  2007年   912篇
  2006年   789篇
  2005年   707篇
  2004年   640篇
  2003年   571篇
  2002年   439篇
  2001年   319篇
  2000年   274篇
  1999年   235篇
  1998年   234篇
  1997年   154篇
  1996年   162篇
  1995年   166篇
  1994年   144篇
  1993年   95篇
  1992年   91篇
  1991年   79篇
  1990年   54篇
  1989年   47篇
  1988年   45篇
  1987年   33篇
  1986年   26篇
  1985年   25篇
  1984年   28篇
  1983年   19篇
  1982年   26篇
  1981年   19篇
  1980年   8篇
  1979年   6篇
  1978年   6篇
  1976年   3篇
  1973年   2篇
  1959年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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   
992.
Plasma Chemistry and Plasma Processing - A new integral mean diffusivity is proposed for the calculation of the mass transfer rate around a small particle immersed in a thermal plasma gas....  相似文献   
993.
N Barik 《Pramana》1981,16(5):403-408
An empirical mass formula is tested for the basic fermion sequences of charged quarks and leptons. This relation is a generalization of Barut’s mass formula for the lepton sequence (e, μ, τ......). It is found that successful mass extrapolation to the third and possibly to other higher generations (N>2) can be obtained with the first and second generation masses as inputs, which predicts the top quark massm t to be around 20 GeV. This also leads to the mass ratios between members of two different sequences (i) and (i′) corresponding to the same higher generations (N>2).  相似文献   
994.
This paper builds on the work of Mett and Hyde [J. Magn. Reson. 165 (2003) 137]. Various aqueous flat-cell geometries in the perpendicular orientation have been studied using Ansoft High Frequency Structure Simulator (version 9.0, Pittsburgh, PA) and Computer Simulation Technology Microwave Studio (version 5.0, Wellesley Hills, MA). The analytic theory of Mett and Hyde has been refined to predict optimum dimensions of multiple sample cell structures including the effect of the sample holder dielectric properties and the interaction of the cells with each other on EPR signal strength. From these calculations and simulations we propose a practical multiple cell sample structure for use in commercial rectangular TE102 cavities that yields 2.0-2.3 times higher sensitivity relative to a single flat-cell in the nodal orientation. We also describe a modified TE102 resonator design with square rather than cylindrical sample-access stacks that is predicted to give a factor of 2.2-2.7 enhancement in EPR signal strength of a single flat-cell in the nodal orientation. These signal enhancements are predicted with sample holders fabricated from polytetrafluoroethylene. Additional improvement in EPR signal of up to 75% can be achieved by using sample holder materials with lower dielectric constants.  相似文献   
995.
Fritzsch type of mass matrices for the 2×2 case and appropriate Lagrangians enable the choice of Yukawa constants of the Lagrangians in terms of the gauge constants. The mass matrices for the four quarks are shown to be proportional to VL. The Cabibbo angle is computed to be 1336′.  相似文献   
996.
The mass spectral fragmentation of five dinuclear Cu(II) complexes of the general formula [Cu2(Rdtc)tpmc] (ClO4)3, where tpmc and Rdtc refer to N, N, N, N-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc), or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, has been investigated. The results were shown to be of mechanistic significance, clarifying the major products of their fragmentation. A possible mechanism entails a multi-step decomposition process that can be separated into individual steps depending on their molecular structures. Every step is determined to some extent by the nature of the intermediates.__________Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 38–42, January–February, 2005.  相似文献   
997.
Pyrochlore with mixed-valence Ce was synthesized by firing and annealing Ce(NO3)4, TiO2, and Ca(OH)2 with a stoichiometry of CaCeTi2O7 at 1300 °C. The product contains Ce-pyrochlore, Ce-rich perovskite, CeO2 (cerianite), and minor CaO. Electron energy-loss spectroscopy (EELS) revealed both Ce4+ and Ce3+ in the Ce-pyrochlore with a Ce4+ to total Ce (Ce4+/ΣCe) of 0.80 giving . Cerium in the perovskite and cerianite is dominated by Ce3+ and Ce4+, respectively. High-resolution transmission electron microscope (HRTEM) images show that the boundary between Ce-pyrochlore and Ce-rich perovskite is semi-coherently bonded. The orientational relationship between the neighboring Ce-pyrochlore and Ce-rich perovskite is not random. Ce-pyrochlore (CaCeTi2O7) is a chemical analogue for CaPuTi2O7, which is a proposed ceramic waste form for deposition of excess weapons-usable Pu in geological repositories. It is postulated, based on the presence of Ce3+ in the Ce-pyrochlore, that neutron poisons such as Gd can be incorporated into the CaPuTi2O7 phase.  相似文献   
998.
Based on the numeric solution of a system of coupled channels for vector mesons (S-and D-waves mixing)and for tensor mesons (P- and F- waves mixing) mass spectrum and wave functions of a family of vector mesons q in triplet states a e obtained. The calculations are performed using a well-known Cornell potential with a mixed Lorentz- structure of the confinement term. The spin-dependent part of the potential is taken from the Breit-Fermi approach.The effect of irregular terms of the potential is considered within the framework of the perturbation theory and/or of the configuration interaction approach, modified for a system of coupled equations. It is shown that even a small integral contribution of the D-wave to the total wave function of q system is very impotant for the calculation of certain characteristics of the meson states.  相似文献   
999.
1000.
Four amino acids and four different hair samples were studied in order to get information about the decomposition of human hair, using combined (TG-MS) and DSC techniques. The thermal stability of the investigated amino acid samples was different. Since they contain identical functional groups (-NH2, -COOH) some common mass/charge units were identified. However, due to their different chemical composition remarkable differences have also been obtained. The results of the investigation of the amino acids were helpful to study the thermal fragmentation of the hair samples. In our experiments, the effect of the heating rates was also studied. This revised version was published online in July 2006 with corrections to the Cover Date.  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