全文获取类型
收费全文 | 41171篇 |
免费 | 2401篇 |
国内免费 | 1950篇 |
专业分类
化学 | 22657篇 |
晶体学 | 233篇 |
力学 | 4064篇 |
综合类 | 551篇 |
数学 | 8248篇 |
物理学 | 9769篇 |
出版年
2024年 | 73篇 |
2023年 | 399篇 |
2022年 | 1114篇 |
2021年 | 1122篇 |
2020年 | 1069篇 |
2019年 | 1013篇 |
2018年 | 906篇 |
2017年 | 1154篇 |
2016年 | 1541篇 |
2015年 | 1164篇 |
2014年 | 1651篇 |
2013年 | 2838篇 |
2012年 | 2332篇 |
2011年 | 2151篇 |
2010年 | 1825篇 |
2009年 | 2325篇 |
2008年 | 2294篇 |
2007年 | 2625篇 |
2006年 | 2146篇 |
2005年 | 1937篇 |
2004年 | 1872篇 |
2003年 | 1557篇 |
2002年 | 1203篇 |
2001年 | 987篇 |
2000年 | 964篇 |
1999年 | 861篇 |
1998年 | 828篇 |
1997年 | 719篇 |
1996年 | 661篇 |
1995年 | 630篇 |
1994年 | 552篇 |
1993年 | 461篇 |
1992年 | 425篇 |
1991年 | 364篇 |
1990年 | 334篇 |
1989年 | 223篇 |
1988年 | 222篇 |
1987年 | 145篇 |
1986年 | 120篇 |
1985年 | 148篇 |
1984年 | 116篇 |
1983年 | 58篇 |
1982年 | 95篇 |
1981年 | 54篇 |
1980年 | 45篇 |
1979年 | 77篇 |
1978年 | 33篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
R. Grosseuvres A. Comandini A. Bentaib N. Chaumeix 《Proceedings of the Combustion Institute》2019,37(2):1537-1546
The present work reports new experimental and numerical results of the combustion properties of hydrogen based mixtures diluted by nitrogen and steam. Spherical expanding flames have been studied in a spherical bomb over a large domain of equivalence ratios, initial temperatures and dilutions at an initial pressure of 100 kPa (Tini = 296, 363, 413 K; N2/O2 = 3.76, 5.67, 9; %Steam = 0, 20, 30). From these experiments, the laminar flame speed , the Markstein length L’, the activation energy Ea and the Zel'dovich β number have been determined. These parameters were also simulated using COSILAB® in order to verify the validity of the Mével et al. [1] detailed kinetic mechanism. Other parameters as the laminar flame thickness δ and the effective Lewis number Leeff were also simulated. These new results aim at providing an extended database that will be very useful in the hydrogen combustion hazard assessment for nuclear reactor power plant new design. 相似文献
2.
文[1]提出了两个DEA的逆问题,并用搜索法来解.而本文根据所证的定理,对每个问题一般只要解二、三个线性规划问题就能得到答案. 相似文献
3.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
4.
5.
固体力学有限元体系的结构拓扑变化理论 总被引:2,自引:1,他引:1
本文是文[1]的继续.文[1]提出了杆件系统的结构拓扑变化理论和拓扑变化法本文将这一理论和方法推进到连续体有限元体系;且在此基础上揭示出有限元体系的一个新性质,称为基本位移之梯度的正交性定理,从而给出一套设计敏度的显式表达式,可直接用于计算. 相似文献
6.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
7.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
8.
M. Gorkunov M. Lapine E. Shamonina K.H. Ringhofer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):263-269
Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements
are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice
ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size
and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency
range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials
with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour
in an external magnetic field.
Received 19 April 2002 Published online 31 July 2002 相似文献
9.
Robert S. Strichartz 《Proceedings of the American Mathematical Society》2002,130(3):805-817
Harmonic mappings from the Sierpinski gasket to the circle are described explicitly in terms of boundary values and topological data. In particular, all such mappings minimize energy within a given homotopy class. Explicit formulas are also given for the energy of the mapping and its normal derivatives at boundary points.
10.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献