全文获取类型
收费全文 | 22478篇 |
免费 | 1966篇 |
国内免费 | 1113篇 |
专业分类
化学 | 2497篇 |
晶体学 | 81篇 |
力学 | 2877篇 |
综合类 | 138篇 |
数学 | 14789篇 |
物理学 | 5175篇 |
出版年
2024年 | 44篇 |
2023年 | 235篇 |
2022年 | 206篇 |
2021年 | 380篇 |
2020年 | 643篇 |
2019年 | 620篇 |
2018年 | 589篇 |
2017年 | 598篇 |
2016年 | 615篇 |
2015年 | 539篇 |
2014年 | 918篇 |
2013年 | 2383篇 |
2012年 | 894篇 |
2011年 | 1256篇 |
2010年 | 1001篇 |
2009年 | 1373篇 |
2008年 | 1378篇 |
2007年 | 1349篇 |
2006年 | 1215篇 |
2005年 | 985篇 |
2004年 | 937篇 |
2003年 | 878篇 |
2002年 | 825篇 |
2001年 | 699篇 |
2000年 | 688篇 |
1999年 | 622篇 |
1998年 | 512篇 |
1997年 | 510篇 |
1996年 | 356篇 |
1995年 | 276篇 |
1994年 | 263篇 |
1993年 | 212篇 |
1992年 | 165篇 |
1991年 | 167篇 |
1990年 | 114篇 |
1989年 | 84篇 |
1988年 | 75篇 |
1987年 | 85篇 |
1986年 | 66篇 |
1985年 | 100篇 |
1984年 | 126篇 |
1983年 | 74篇 |
1982年 | 89篇 |
1981年 | 80篇 |
1980年 | 71篇 |
1979年 | 68篇 |
1978年 | 61篇 |
1977年 | 42篇 |
1976年 | 30篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
51.
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
52.
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
53.
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
54.
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
55.
Johan Helsing 《BIT Numerical Mathematics》2006,46(2):307-323
A sparse mesh-neighbour based approximate inverse preconditioner is proposed for a type of dense matrices whose entries come
from the evaluation of a slowly decaying free space Green’s function at randomly placed points in a unit cell. By approximating
distant potential fields originating at closely spaced sources in a certain way, the preconditioner is given properties similar
to, or better than, those of a standard least squares approximate inverse preconditioner while its setup cost is only that
of a diagonal block approximate inverse preconditioner. Numerical experiments on iterative solutions of linear systems with
up to four million unknowns illustrate how the new preconditioner drastically outperforms standard approximate inverse preconditioners
of otherwise similar construction, and especially so when the preconditioners are very sparse.
AMS subject classification (2000) 65F10, 65R20, 65F35, 78A30 相似文献
56.
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
57.
本文主要解决奇异非光滑方程组的解法。应用一种新的次微分的外逆,我们提出了牛顿法和不精确牛顿法,它们的收敛性同时也得到了证明。这种方法能更容易在一引起实际应用中实现。这种方法可以看作是已存在的解非光滑方程组的方法的延伸。 相似文献
58.
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
59.
We consider Markov processes built from pasting together pieces of strong Markov processes which are killed at a position
dependent rate and connected via a transition kernel. We give necessary and sufficient conditions for local absolute continuity
of probability laws for such processes on a suitable path space and derive an explicit formula for the corresponding likelihood
ratio process. The main tool is the consideration of the process between successive jumps – what we call ‘elementary experiments’
– and criteria for absolute continuity of laws of the process there. We apply our results to systems of branching diffusions
with interactions and immigrations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
60.
We investigate an operator renormalization group method to extract and describe the relevant degrees of freedom in the evolution of partial differential equations. The proposed renormalization group approach is formulated as an analytical method providing the fundamental concepts of a numerical algorithm applicable to various dynamical systems. We examine dynamical scaling characteristics in the short-time and the long-time evolution regime providing only a reduced number of degrees of freedom to the evolution process. 相似文献