全文获取类型
收费全文 | 12925篇 |
免费 | 1373篇 |
国内免费 | 960篇 |
专业分类
化学 | 3124篇 |
晶体学 | 147篇 |
力学 | 1194篇 |
综合类 | 159篇 |
数学 | 6872篇 |
物理学 | 3762篇 |
出版年
2024年 | 14篇 |
2023年 | 133篇 |
2022年 | 172篇 |
2021年 | 248篇 |
2020年 | 364篇 |
2019年 | 395篇 |
2018年 | 347篇 |
2017年 | 387篇 |
2016年 | 449篇 |
2015年 | 363篇 |
2014年 | 580篇 |
2013年 | 1214篇 |
2012年 | 578篇 |
2011年 | 716篇 |
2010年 | 588篇 |
2009年 | 707篇 |
2008年 | 773篇 |
2007年 | 800篇 |
2006年 | 679篇 |
2005年 | 632篇 |
2004年 | 592篇 |
2003年 | 532篇 |
2002年 | 521篇 |
2001年 | 478篇 |
2000年 | 454篇 |
1999年 | 404篇 |
1998年 | 325篇 |
1997年 | 330篇 |
1996年 | 211篇 |
1995年 | 171篇 |
1994年 | 157篇 |
1993年 | 116篇 |
1992年 | 97篇 |
1991年 | 110篇 |
1990年 | 55篇 |
1989年 | 53篇 |
1988年 | 55篇 |
1987年 | 54篇 |
1986年 | 42篇 |
1985年 | 65篇 |
1984年 | 55篇 |
1983年 | 34篇 |
1982年 | 43篇 |
1981年 | 30篇 |
1980年 | 28篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
21.
22.
23.
P. E. Cladis 《Journal of statistical physics》1991,62(5-6):899-925
We first discuss nonlinear aspects of phase transition theory applied to a particular liquid crystal phase transition. A simple derivation is given to show how two coupled Goldstone modes (one appearing as gauge fluctuations of the ordered phase) can force a phase transition, against all expectations, to take place discontinuously (theory of Halperin, Lubensky, and Ma)-but the discontinuity may be immeasurably small. Then, we describe a new dynamical test of phase transition order, developed by Cladiset al., that turns out to be more sensitive than x-ray diffraction and adiabatic calorimetry. Quantitative data found by this new method are in excellent agreement with the measurements of adiabatic calorimetry and x-ray diffraction as well as expectations implicit in the predictions of HLM.This is the text of an after-banquet talk given at the CNLS Workshop on the Dynamics of Concentrated Systems. 相似文献
24.
Harel and Puri (1989, J. Multivariate Anal. 29) studied the asymptotic behavior of the U-statistic and the one-sample rank order statistic for nonstationary absolutely regular processes. In this note, we present some applications of these results for Markov processes as well as ARMA processes. 相似文献
25.
It is long known that the Fokker-Planck equation with prescribed constant coefficients of diffusion and linear friction describes
the ensemble average of the stochastic evolutions in velocity space of a Brownian test particle immersed in a heat bath of
fixed temperature. Apparently, it is not so well known that the same partial differential equation, but now with constant
coefficients which are functionals of the solution itself rather than being prescribed, describes the kinetic evolution (in
the N→∞ limit) of an
isolated
N-particle system with certain stochastic interactions. Here we discuss in detail this recently discovered interpretation.
An erratum to this article can be found at 相似文献
26.
本文给出Riccati方程及另外一类具有代表性微分方程的亚纯解(n,1)级的上界估计,在一定条件下确立了文[2]中的猜测的正确性。 相似文献
27.
Cosmic dust and our origins 总被引:1,自引:0,他引:1
J Mayo Greenberg 《Surface science》2002,500(1-3):793-822
The small solid particles in the space between the stars provide the surfaces for the production of many simple and complex molecules. Processes involving the effects of ultraviolet irradiation of the thin (hundredth micron) mantles are shown to produce a wide range of molecules and ions also seen in comets. Some of the more complex ones inferred from laboratory experiments are expected to play an important role in the origin of life. An outline of the chemical evolution of interstellar dust as observed and as studied in the laboratory is presented. Observations of comets are shown to provide substantial evidence for their being fluffy aggregates of interstellar dust as it was in the protosolar nebula, i.e. the interstellar cloud which collapsed to form the solar system. The theory that comets may have brought the progenitors of life to the earth is summarized. 相似文献
28.
针对刚性约束层、柔性约束层以及液体约束层,从激光诱导冲击波阵面状态、汽化物(包括气体和等离子体)扩散以及冲击波的反射进行分析,发现对于脉宽小于冲击波通过汽化物层的时间间隔的短脉冲激光,约束层并不能直接提高冲击波的冲量,而对于脉宽大于冲击波通过汽化层时间间隔的激光,其增强冲击效果是通过约束汽化物的扩散,提高压力幅值和由于冲击波在约束层与工件表面的多次反射而延长对工件的作用时间来实现的.刚性约束层能最大地增加冲击冲量,而柔性约束层和液体约束层的主要优点是其形状可与非平面形工件表面符合.
关键词:
激光
约束层
扩散
反射波 相似文献
29.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
30.
We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility. 相似文献