全文获取类型
收费全文 | 12430篇 |
免费 | 1347篇 |
国内免费 | 1294篇 |
专业分类
化学 | 3049篇 |
晶体学 | 70篇 |
力学 | 1082篇 |
综合类 | 207篇 |
数学 | 7018篇 |
物理学 | 3645篇 |
出版年
2024年 | 16篇 |
2023年 | 121篇 |
2022年 | 175篇 |
2021年 | 206篇 |
2020年 | 302篇 |
2019年 | 275篇 |
2018年 | 307篇 |
2017年 | 392篇 |
2016年 | 432篇 |
2015年 | 274篇 |
2014年 | 558篇 |
2013年 | 902篇 |
2012年 | 650篇 |
2011年 | 658篇 |
2010年 | 519篇 |
2009年 | 733篇 |
2008年 | 789篇 |
2007年 | 824篇 |
2006年 | 737篇 |
2005年 | 690篇 |
2004年 | 573篇 |
2003年 | 585篇 |
2002年 | 539篇 |
2001年 | 491篇 |
2000年 | 422篇 |
1999年 | 405篇 |
1998年 | 341篇 |
1997年 | 310篇 |
1996年 | 278篇 |
1995年 | 226篇 |
1994年 | 176篇 |
1993年 | 109篇 |
1992年 | 150篇 |
1991年 | 135篇 |
1990年 | 105篇 |
1989年 | 76篇 |
1988年 | 69篇 |
1987年 | 71篇 |
1986年 | 61篇 |
1985年 | 67篇 |
1984年 | 50篇 |
1983年 | 30篇 |
1982年 | 37篇 |
1981年 | 37篇 |
1980年 | 33篇 |
1979年 | 35篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
31.
Lihong Wang 《Annals of the Institute of Statistical Mathematics》2004,56(2):251-264
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L
2-estimates) and the least absolute deviation estimates (L
1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which
has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies
of the above estimators. 相似文献
32.
33.
Halszka TutajGasiska 《Mathematische Nachrichten》2003,257(1):108-116
34.
给出引理解决了方程非振动解与其各阶导数的符号关系,并由此得到了若干判别准则,用于判别三阶线性脉冲微分方程解的振动性与渐近性,举例说明了准则的有效性。本文推广了相关文献的结果。 相似文献
35.
风力发电机组变速恒频控制系统研究 总被引:2,自引:0,他引:2
全面介绍了一种最新应用于风力发电中的新型电机—无刷双馈电机,并分析了这种新型电机作变速恒频运行的原理并对这种电机进行了动态特性仿真研究,给出了形式简洁的控制方程和易于实现的控制方案。 相似文献
36.
Oracle inequality is a relatively new statistical tool for the analysis of nonparametric adaptive estimates. Oracle is a good pseudo-estimate that is based on both data and an underlying estimated curve. An oracle inequality shows how well an adaptive estimator mimics the oracle for a particular underlying curve. The most advanced oracle inequalities have been recently obtained by Cavalier and Tsybakov (2001) for Stein type blockwise estimates used in filtering a signal from a stationary white Gaussian process. The authors also conjecture that a similar result can be obtained for Efromovich–Pinsker (EP) type blockwise estimators where their approach, based on Stein's formula for risk calculation, does not work. This article proves the conjecture and extends it upon more general models which include not stationary and dependent processes. Other possible extensions, a discussion of practical implications and a numerical study are also presented. 相似文献
37.
Most of the methods used in the ARCH literature for selecting the appropriate model are based on evaluating the ability of the models to describe the data. An alternative model selection approach is examined based on the evaluation of the predictability of the models in terms of standardized prediction errors. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
38.
We obtain exponential upper bounds for tails of distributions of generalized L-statistics based on a sample from an exponential distribution. We prove the asymptotic normality of generalized L-statistics based on a sample from the uniform distribution on [0,1] and of L-statistics with decomposed kernels (without any restrictions on the sample distribution type). 相似文献
39.
Yousef Bisabr 《International Journal of Theoretical Physics》2004,43(10):2137-2148
We investigate a conformal invariant gravitational model which is taken to hold at early universe. The conformal invariance allows us to make a dynamical distinction between the two unit systems (or conformal frames) usually used in cosmology and elementary particle physics. In this model we argue that when the universe suffers phase transition, the resulting mass scale introduced by particle physics should have a variable contribution to vacuum energy density. This variation is controlled by the conformal factor which is taken as a dynamical field. We then deal with the cosmological consequences of this model. In particular, we shall show that there is an inationary phase at early times. At late times, on the other hand, it provides a mechanism which makes a large effective cosmological constant relax to a sufficiently small value. Moreover, we shall show that the conformal factor acts as a quintessence field that leads the universe to accelerate at late times. 相似文献
40.
The effect of viscous dissipation on the development of the boundary layer flow from a cold vertical surface embedded in a Darcian porous medium is investigated. It is found that the flow evolves gradually from the classical Cheng–Minkowycz form to the recently discovered asymptotic dissipation profile which is a parallel flow. 相似文献