全文获取类型
收费全文 | 22590篇 |
免费 | 4683篇 |
国内免费 | 1851篇 |
专业分类
化学 | 4745篇 |
晶体学 | 273篇 |
力学 | 5647篇 |
综合类 | 272篇 |
数学 | 3750篇 |
物理学 | 14437篇 |
出版年
2024年 | 62篇 |
2023年 | 238篇 |
2022年 | 576篇 |
2021年 | 612篇 |
2020年 | 689篇 |
2019年 | 617篇 |
2018年 | 625篇 |
2017年 | 776篇 |
2016年 | 925篇 |
2015年 | 798篇 |
2014年 | 1280篇 |
2013年 | 1772篇 |
2012年 | 1411篇 |
2011年 | 1651篇 |
2010年 | 1390篇 |
2009年 | 1427篇 |
2008年 | 1525篇 |
2007年 | 1559篇 |
2006年 | 1435篇 |
2005年 | 1316篇 |
2004年 | 1146篇 |
2003年 | 1082篇 |
2002年 | 877篇 |
2001年 | 796篇 |
2000年 | 702篇 |
1999年 | 581篇 |
1998年 | 589篇 |
1997年 | 409篇 |
1996年 | 336篇 |
1995年 | 295篇 |
1994年 | 257篇 |
1993年 | 239篇 |
1992年 | 183篇 |
1991年 | 181篇 |
1990年 | 132篇 |
1989年 | 117篇 |
1988年 | 101篇 |
1987年 | 85篇 |
1986年 | 56篇 |
1985年 | 67篇 |
1984年 | 42篇 |
1983年 | 22篇 |
1982年 | 40篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1976年 | 8篇 |
1971年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
Blow Up of Solutions to Semilinear Wave Equations with Critical Exponent in High Dimensions 总被引:5,自引:2,他引:3 下载免费PDF全文
Yi ZHOU 《数学年刊B辑(英文版)》2007,28(2):205-212
In this paper, the author considers the Cauchy problem for semilinear wave equations with critical exponent in n≥4 space dimensions. Under some positivity conditions on the initial data, it is proved that there can be no global solutions no matter how small the initial data are. 相似文献
92.
The mechanism of X-ray waveguide-resonance propagation or the radiation superstream model, which can become the ground of X-ray nanophotonics, is discussed briefly. Some attention is devoted to features consideration of the simplest devices characterized by the waveguide-resonance transportation of X-ray beams. The experimental data showing the user possibilities of a simplest waveguide-resonators application for diffractometry are presented. We discuss the main reasons to improve the metrological characteristics for total reflection X-ray fluorescence (TXRF) analytical method in case when the target exciting beam is formed by a waveguide-resonator. Some problems appearing during the waveguide-resonator application are formulated. 相似文献
93.
S. Juneja 《Queueing Systems》2007,57(2-3):115-127
Efficient estimation of tail probabilities involving heavy tailed random variables is amongst the most challenging problems
in Monte-Carlo simulation. In the last few years, applied probabilists have achieved considerable success in developing efficient
algorithms for some such simple but fundamental tail probabilities. Usually, unbiased importance sampling estimators of such
tail probabilities are developed and it is proved that these estimators are asymptotically efficient or even possess the desirable
bounded relative error property. In this paper, as an illustration, we consider a simple tail probability involving geometric
sums of heavy tailed random variables. This is useful in estimating the probability of large delays in M/G/1 queues. In this setting we develop an unbiased estimator whose relative error decreases to zero asymptotically. The key
idea is to decompose the probability of interest into a known dominant component and an unknown small component. Simulation
then focuses on estimating the latter ‘residual’ probability. Here we show that the existing conditioning methods or importance
sampling methods are not effective in estimating the residual probability while an appropriate combination of the two estimates
it with bounded relative error. As a further illustration of the proposed ideas, we apply them to develop an estimator for
the probability of large delays in stochastic activity networks that has an asymptotically zero relative error.
相似文献
94.
In the present paper, we consider the problem of the optimal reconstruction of the solution of the wave equation from the approximate values of the Fourier coefficients of the function specifying the initial form of the string. For an operator defined on the weight space of vectors from l 2, we present the solution of the more general problem of reconstruction from the approximate values of the coordinates of these vectors. 相似文献
95.
In hardware design, it is necessary to simulate the anticipated behavior of the integrated circuit before it is actually cast in silicon. As simulation procedures are long due to the great number of tests to be performed, optimization of the simulation code is of prime importance. This paper describes two mathematical models for the minimization of the memory access times for a cycle-based simulator.An integrated circuit being viewed as a directed acyclic graph, the problem consists in building a graph order on the vertices, compatible with the relation order induced by the graph, in order to minimize a cost function that represents the memory access time. For both proposed cost functions, we show that the corresponding problems are NP-complete. However, we show that the special cases where the graphs are in-trees or out-trees can be solved in polynomial time. 相似文献
96.
J.E. Lorenzo H. Requardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):185-186
Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K0.3MoO3 and (TaSe4)2I. We have shown that the anomaly in the C
P
/
T
3
data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds.
Received 21 February 2002 Published online 19 July 2002 相似文献
97.
98.
99.
100.