全文获取类型
收费全文 | 22080篇 |
免费 | 2450篇 |
国内免费 | 2347篇 |
专业分类
化学 | 2311篇 |
晶体学 | 33篇 |
力学 | 1868篇 |
综合类 | 585篇 |
数学 | 16070篇 |
物理学 | 6010篇 |
出版年
2024年 | 27篇 |
2023年 | 177篇 |
2022年 | 285篇 |
2021年 | 372篇 |
2020年 | 441篇 |
2019年 | 478篇 |
2018年 | 486篇 |
2017年 | 643篇 |
2016年 | 743篇 |
2015年 | 540篇 |
2014年 | 1110篇 |
2013年 | 1452篇 |
2012年 | 1165篇 |
2011年 | 1389篇 |
2010年 | 1270篇 |
2009年 | 1525篇 |
2008年 | 1534篇 |
2007年 | 1628篇 |
2006年 | 1435篇 |
2005年 | 1364篇 |
2004年 | 1105篇 |
2003年 | 1025篇 |
2002年 | 854篇 |
2001年 | 787篇 |
2000年 | 727篇 |
1999年 | 625篇 |
1998年 | 553篇 |
1997年 | 530篇 |
1996年 | 389篇 |
1995年 | 309篇 |
1994年 | 260篇 |
1993年 | 195篇 |
1992年 | 172篇 |
1991年 | 147篇 |
1990年 | 147篇 |
1989年 | 99篇 |
1988年 | 92篇 |
1987年 | 85篇 |
1986年 | 72篇 |
1985年 | 95篇 |
1984年 | 74篇 |
1983年 | 54篇 |
1982年 | 77篇 |
1981年 | 69篇 |
1980年 | 50篇 |
1979年 | 43篇 |
1978年 | 35篇 |
1977年 | 30篇 |
1976年 | 31篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zbigniew J. Jurek 《Journal of multivariate analysis》1983,13(4):578-604
Let
= {Ut: t > 0} be a strongly continuous one-parameter group of operators on a Banach space X and Q be any subset of a set
(X) of all probability measures on X. By
(Q;
) we denote the class of all limit measures of {Utn(μ1 * μ2*…*μn)*δxn}, where {μn}Q, {xn}X and measures Utnμj (j=1, 2,…, n; N=1, 2,…) form an infinitesimal triangular array. We define classes Lm(
) as follows: L0(
)=
(
(X);
), Lm(
)=
(Lm−1(
);
) for m=1, 2,… and L∞(
)=m=0∞Lm(
). These classes are analogous to those defined earlier by Urbanik on the real line. Probability distributions from Lm(
), m=0, 1, 2,…, ∞, are described in terms of their characteristic functionals and their generalized Poisson exponents and Gaussian covariance operators. 相似文献
992.
993.
994.
995.
996.
Onno de Vegt Herman Vromans Fried Faassen Kees van der Voort Maarschalk 《Particle & Particle Systems Characterization》2005,22(4):261-267
The particle size distribution of fine chemicals in the solid state, like active pharmaceutical ingredients, is often a critical parameter. To achieve the desired particle size distribution, milling of such materials is usually the method of choice. Since these chemicals are often scarcely available, experimental optimization of milling is not possible. Therefore, a model to predict the milling conditions has been developed. The model estimates the rate of breakage function, and needs mechanical properties like hardness and yield strength as input to calculate the rate of breakage function. This paper attempts to check the validity of the model by a series of experiments. A comparison of the experimental results with the outcomes of the model using five different model compounds has been performed. It appears that the rate of breakage function can be estimated by: The model is able to rank the compounds by degree of fracture as an effect of milling. It was also possible to perform a quantitative prediction of the impact of milling pressure on the milling behavior. Finally, it appeared that the prediction of the large particles in the distribution was significantly better than small ones. Because the oversized material is usually the most critical parameter, the conclusion is that the model has acceptable practical applicability. 相似文献
997.
Ya-Jun Gao 《General Relativity and Gravitation》2005,37(1):1-17
A so-called extended elliptical-complex (EEC) function method is proposed and used to further study the Einstein–Maxwell-dilaton-axion theory with p vector fields (EMDA-p theory, for brevity) for
. An Ernst-like
matrix EEC potential is introduced and the motion equations of the stationary axisymmetric EMDA-p theory are written as a so-called Hauser–Ernst-like self-dual relation for the EEC matrix potential. In particular, for the EMDA-2 theory, two Hauser–Ernst-type EEC linear systems are established and based on their solutions some new parametrized symmetry transformations are explicitly constructed. These hidden symmetries are verified to constitute an infinite-dimensional Lie algebra, which is the semidirect product of the Kac–Moody algebra
and Virasoro algebra (without centre charges). These results show that the studied EMDA-p theories possess very rich symmetry structures and the EEC function method is necessary and effective. 相似文献
998.
J.?H.?Asad R.?S.?Hijjawi A.?Sakaj J.?M.?KhalifehEmail author 《International Journal of Theoretical Physics》2005,44(4):471-483
The resistance between arbitrary sites of infinite square network of identical resistors is studied when the network is perturbed by removing two bonds from the perfect lattice. A connection is made between the resistance and the lattice Green’s function of the perturbed network. By solving Dyson’s equation the Green’s function and the resistance of the perturbed lattice are expressed in terms of those of the perfect lattice. Some numerical results are presented for an infinite square lattice. 相似文献
999.
Quantum systems with quadratic Hamiltonians are considered. Some results about the time evolution of homogeneous polynomials and of quantum correlation functions are given. The image of arbitrary orbit of Weyl–Heisenberg group under this time evolution is shown to be again an orbit of this group. For quantum free particle it is shown that its time evolution intersects arbitrary such orbit at most once. A result about existence of more orbits having the same dispersion of some quantum position is presented.PACS: 02.20.Qs, 02.30.Sa 相似文献
1000.
Todd B. Sauke Joseph F. Becker 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,91(4):453-484
The instrument response function (IRF) of a spectrometer limits the accuracy of measured spectroscopic parameters by broadening recorded spectral lines/features. We describe methods to model the effects of the IRF on spectral data, to minimize the IRF widths, and to measure the resulting width of the spectrometer IRF. We have modeled the IRF of our Tunable Diode Laser Spectrometer as a Voigt function. A real-time method of eliminating the effects of low-frequency spectrometer drift has been implemented and has resulted in a substantial reduction in the width of the IRF, its residual Gaussian component reduced from about to about . An accurate measurement of the IRF Gaussian width utilizes a computationally simple method making use of the spectral dependence of the RMS noise of each signal-averaged data point. Various noise sources affecting the spectrometer (preamp/detector noise, laser AM noise, and laser FM noise) are identified and separately quantified by use of the same method. The IRF Gaussian-width measurement can be automatically applied to each measured spectrum of an experimental data set. A related method is discussed which allows accurate determination of the spectral dependence of statistical noise appropriate for use in quantitative Chi-square fitting of absorption spectra. We explore simple, efficient numerical processes which can dramatically enhance the quality and usefulness of acquired spectral data, improving the ability to apply TDL spectroscopy to high-precision, quantitative measurements and the determination of detailed spectroscopic lineshape parameters. This paper provides a guide for interested readers to implement these developments in their own spectrometers. 相似文献