全文获取类型
收费全文 | 1670篇 |
免费 | 94篇 |
国内免费 | 82篇 |
专业分类
化学 | 129篇 |
晶体学 | 6篇 |
力学 | 46篇 |
综合类 | 12篇 |
数学 | 1223篇 |
物理学 | 430篇 |
出版年
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 35篇 |
2019年 | 39篇 |
2018年 | 35篇 |
2017年 | 29篇 |
2016年 | 40篇 |
2015年 | 25篇 |
2014年 | 46篇 |
2013年 | 108篇 |
2012年 | 44篇 |
2011年 | 83篇 |
2010年 | 66篇 |
2009年 | 90篇 |
2008年 | 94篇 |
2007年 | 91篇 |
2006年 | 74篇 |
2005年 | 72篇 |
2004年 | 49篇 |
2003年 | 60篇 |
2002年 | 61篇 |
2001年 | 40篇 |
2000年 | 52篇 |
1999年 | 66篇 |
1998年 | 53篇 |
1997年 | 47篇 |
1996年 | 32篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有1846条查询结果,搜索用时 16 毫秒
21.
22.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献
23.
Nadjib Bouzar 《Annals of the Institute of Statistical Mathematics》2004,56(3):497-510
The purpose of this paper is to introduce and study the concepts of discrete semi-stability and geometric semi-stability for
distributions with support inZ
+. We offer several properties, including characterizations, of discrete semi-stable distributions. We establish that these
distributions posses the property of infinite divisibility and that their probability generating functions admit canonical
representations that are analogous to those of their continuous counterparts. Properties of discrete geometric semi-stable
distributions are deduced from the results obtained for discrete semi-stability. Several limit theorems are established and
some examples are constructed. 相似文献
24.
Alexander Koldobsky 《Advances in Applied Mathematics》2004,33(4):728-732
The Busemann–Petty problem asks whether origin-symmetric convex bodies in Rn with smaller areas of all central hyperplane sections necessarily have smaller n-dimensional volume. The solution was completed in the end of the 1990s, and the answer is affirmative if n4 and negative if n5. Since the answer is negative in most dimensions, it is natural to ask what information about the volumes of central sections of two bodies does allow to compare the n-dimensional volumes of these bodies in all dimensions. In this article we give an answer to this question in terms of certain powers of the Laplace operator applied to the section function of the body. 相似文献
25.
In this paper, some new uniform frames with block size four and index one or three are obtained. The known existence results for (4,1)‐frames and (4,3)‐frames are both improved to the extent that only a finite number of possible exceptions remain. © 2003 Wiley Periodicals, Inc. 相似文献
26.
Michael A. Zazanis 《Queueing Systems》1992,11(4):419-428
We examine level crossings of sample paths of queueing processes and investigate the conditions under which the limiting empirical distribution for the workload process exists and is absolutely continuous. The connection between the density of the workload distribution and the rate of downcrossings is established as a sample path result that does not depend on any stochastic assumptions. As a corollary, we obtain the sample path version of the Takács formula connecting the time and customer stationary distributions in a queue. Defective limiting empirical distributions are considered and an expression for the mass at infinity is derived.This research has been supported in part by NSF Grants ECS-8811003 and DDM-8905638. 相似文献
27.
The subject of spectral distribution methods where one derives and applies the locally smoothed forms of observables in nuclei
is briefly reviewed. It is well understood that the local forms (with respect to energy) of the level density function, expectation
values and strength densities are Gaussian, linear (or ratio of Gaussians) and a bivariate Gaussian respectively. To accomodate
symmetries in the above forms, one has to deal with multivariate distributions in general; for example the angular-momentum
(J) decomposition leads to a bivariate Gaussian form for the level density. These results extend to indefinitely large spaces
by method of partitioning and they generate convolution forms. The origin of these remarkable spectral properties is discussed
and shell model examples are given to substantiate their applicability to nuclear systems. Spectral distribution theory is
a practical, usable theory because the smoothed forms are defined in terms of traces of low particle-rank operators, and the
trace information propagates. Finally we discuss the application of the spectral methods for a wide range of nuclear problems;
these include binding energies, orbit occupancies, electromagnetic andβ-decay sum rule quantities, analysis of operators, symmetry breaking, numerical level densities, and determination of bounds
on time-reversal non-invariant part of nucleon-nucleon interaction. 相似文献
28.
Sergio Albeverio Yeneng Sun Jiang-Lun Wu 《Transactions of the American Mathematical Society》2007,359(2):517-527
It is shown that for a large collection of independent martingales, the martingale property is preserved on the empirical processes. Under the assumptions of independence and identical finite-dimensional distributions, it is proved that a large collection of stochastic processes are martingales essentially if and only if the empirical processes are also martingales. These two results have implications on the testability of the martingale property in scientific modeling. Extensions to submartingales and supermartingales are given.
29.
Optimization of plate buckling resistance is very complicated, because the in-plane stress resultants in the prebuckled state of a plate are functions of thickness distribution. This paper discusses the problem of finding the optimum thickness distribution of isotropic plate structures, with a given volume and layout, that would maximise the buckling load. A simple numerical method using the finite-element analysis is presented to obtain the optimum thickness distribution. Optimum designs of compression-loaded rectangular plates with different boundary conditions and plate aspect ratios are obtained by using the proposed method. Optimum designs from earlier studies and the methods of buckling analysis used to attain these results are discussed and compared with the designs from the proposed method. This paper also examines the reliability of the optimality criterion generally used for plate buckling optimization, which is based on the uniform strain energy density. 相似文献
30.
K. R. Muraleedharan Nair N. Unnikrishnan Nair 《Annals of the Institute of Statistical Mathematics》1988,40(2):267-271
In this note, a characterization of the Gumbel's bivariate exponential distribution based on the properities of the conditional moments is discussed. The result forms a sort of bivariate analogue of the characterization of the univariate exponential distribution given by Sahobov and Geshev (1974) (cited in Lau and Rao ((1982), Sankhy Ser. A, 44, 87)). A discrete version of the property provides a similar conclusion relating to a bivariate geometric distribution. 相似文献