全文获取类型
收费全文 | 16811篇 |
免费 | 348篇 |
国内免费 | 52篇 |
专业分类
化学 | 9714篇 |
晶体学 | 139篇 |
力学 | 572篇 |
数学 | 2586篇 |
物理学 | 4200篇 |
出版年
2021年 | 176篇 |
2020年 | 208篇 |
2019年 | 200篇 |
2018年 | 172篇 |
2017年 | 154篇 |
2016年 | 330篇 |
2015年 | 300篇 |
2014年 | 301篇 |
2013年 | 814篇 |
2012年 | 644篇 |
2011年 | 806篇 |
2010年 | 518篇 |
2009年 | 438篇 |
2008年 | 700篇 |
2007年 | 636篇 |
2006年 | 665篇 |
2005年 | 580篇 |
2004年 | 582篇 |
2003年 | 465篇 |
2002年 | 476篇 |
2001年 | 354篇 |
2000年 | 312篇 |
1999年 | 236篇 |
1998年 | 207篇 |
1997年 | 210篇 |
1996年 | 259篇 |
1995年 | 228篇 |
1994年 | 219篇 |
1993年 | 260篇 |
1992年 | 275篇 |
1991年 | 256篇 |
1990年 | 212篇 |
1989年 | 184篇 |
1988年 | 217篇 |
1987年 | 251篇 |
1986年 | 218篇 |
1985年 | 274篇 |
1984年 | 263篇 |
1983年 | 223篇 |
1982年 | 243篇 |
1981年 | 246篇 |
1980年 | 233篇 |
1979年 | 240篇 |
1978年 | 232篇 |
1977年 | 230篇 |
1976年 | 213篇 |
1975年 | 209篇 |
1974年 | 178篇 |
1973年 | 177篇 |
1972年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
31.
We discuss the approximation of performance measures in multi-class M/M/k queues with preemptive priorities for large problem instances (many classes and servers) using class aggregation and server reduction. We compared our approximations to exact and simulation results and found that our approach yields small-to-moderate approximation errors. 相似文献
32.
Mari Grobbelaar‐Van Dalsen 《Mathematical Methods in the Applied Sciences》2004,27(11):1301-1315
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
33.
34.
35.
A.M. van der Kraan 《Hyperfine Interactions》1998,111(1-4):23-34
In modern society the application of catalysts, and hence, research in the field of catalysis, is becoming more and more important. In the strongly increasing chemical industry most reaction processes are performed with the aid of catalysts. Knowledge about the structure of the active sites present at the surface of catalysts will facilitate the design of new catalysts with better performances. Such knowledge can be obtained by Mössbauer spectroscopy, which is an excellent in-situ characterization technique due to the high penetrating power of the γ-radiation used and the sensitivity of the spectral parameters for the chemical state and local environment of the Mössbauer atoms. 相似文献
36.
We consider an optimal growth (multi-sector) model with nonconvex technology. Using the Clarke results on generalized gradients, we prove that the value function has left and right derivatives with respect to the initial capital stock, without requiring supermodularity assumptions. 相似文献
37.
38.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
39.
W. von der Linden 《Applied Physics A: Materials Science & Processing》1995,60(2):155-165
The reconstruction of physical quantities from (computer-) experimental data is very often hampered by the presence of noise, insufficient information and above all by the ill-posed nature of the underlying inversion problem. It will be demonstrated that the maximum entropy concepts is particularly suited for this type of data-analysis problems. It is based on Bayesian statistics and provides a consistent probabilistic theory to obtain unbiased results, independent of any model assumptions. This is particularly desirable if there is no additional information to justify these hypotheses. If, on the other hand, additional prior knowledge is available, it can be effectively incorporated into the computation, leading to more stringent confidence intervals. 相似文献
40.
We present a pole expansion for the propagators in the framework of normalized quantum electrodynamics and compare it with the more canonical results from S-matrix theory. 相似文献