全文获取类型
收费全文 | 10626篇 |
免费 | 1046篇 |
国内免费 | 847篇 |
专业分类
化学 | 2812篇 |
晶体学 | 96篇 |
力学 | 532篇 |
综合类 | 165篇 |
数学 | 5459篇 |
物理学 | 3455篇 |
出版年
2023年 | 76篇 |
2022年 | 207篇 |
2021年 | 256篇 |
2020年 | 310篇 |
2019年 | 276篇 |
2018年 | 281篇 |
2017年 | 287篇 |
2016年 | 372篇 |
2015年 | 285篇 |
2014年 | 534篇 |
2013年 | 841篇 |
2012年 | 473篇 |
2011年 | 570篇 |
2010年 | 480篇 |
2009年 | 598篇 |
2008年 | 685篇 |
2007年 | 731篇 |
2006年 | 584篇 |
2005年 | 505篇 |
2004年 | 467篇 |
2003年 | 480篇 |
2002年 | 394篇 |
2001年 | 349篇 |
2000年 | 311篇 |
1999年 | 286篇 |
1998年 | 262篇 |
1997年 | 206篇 |
1996年 | 208篇 |
1995年 | 153篇 |
1994年 | 144篇 |
1993年 | 99篇 |
1992年 | 86篇 |
1991年 | 74篇 |
1990年 | 61篇 |
1989年 | 56篇 |
1988年 | 63篇 |
1987年 | 51篇 |
1986年 | 40篇 |
1985年 | 53篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 44篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 40篇 |
1978年 | 27篇 |
1977年 | 29篇 |
1976年 | 25篇 |
1975年 | 10篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time. 相似文献
82.
We establish some liminf theorems on the increments of a (N,d)-Gaussian process with the usual Euclidean norm, via estimating upper bounds of large deviation probabilities on the suprema
of the (N,d)-Gaussian process.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
83.
YunFei Liu ShengCai Shi ShengLin Yu 《International Journal of Infrared and Millimeter Waves》2003,24(12):2069-2077
When electromagnetic waves propagate through a wire grid, there will be some evanescent space harmonics generated around the wire grid. In this paper, we mainly investigate their effects on the transmission characteristics of a Gaussian beam by cylindrical wire grids. The results are compared with those without taking account of evanescent space-harmonics. 相似文献
84.
We have used the periodic quantum-mechanical method with density functional theory at the B3LYP level in order to study TiO2/Sn doped (1 1 0) surfaces and have investigated the structural, electronic and energy band properties of these oxides. Our calculated relaxation directions for TiO2 is the experimental one and is also in agreement with other theoretical results. We also observe for the doped systems relaxation of lattice positions of the atoms. Modification of Sn, O and Ti charges depend on the planes and positions of the substituted atoms. Doping can modify the Fermi levels, energy gaps as well as the localization and composition of both valence and conduction band main components. Doping can also modify the chemical, electronic and optical properties of these oxides surfaces increasing their suitability for use as gas sensors and optoelectronic devices. 相似文献
85.
G. Mastroianni 《Numerical Algorithms》1995,10(1):113-126
The author gives some upper and lower bounds for the generalized Christoffel functions related to a Ditzian-Totik generalized weight. As an application, an error estimate of Gauss quadrature formula inL
1-weighted norm is derived.Dedicated to Prof. Luigi Gatteschi on the occasion of his 70th birthdayWork sponsored by MURST 40%. 相似文献
86.
The potential of the internal rotation of the methyl group was determined for o-, m-, and p-fluorotoluene cations by pulsed field ionization spectroscopy. The potential of the internal rotational motion was also surveyed for other toluene derivative cations. It was found that the barrier height generally increases by ionization. The increase in the barrier height has been discussed in connection with the reduction of the internal rotational constant B by ionization. The geometrical distortion of the methyl group during the internal rotation has been suggested. 相似文献
87.
A transient molecular network model is built to describe the nonlinear viscoelasticity of polymers by considering the effect
of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories.
The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used
to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully
the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes.
Thus the micromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity
may be disclosed.
The project supported by the National Natural Science Foundation of China and Doctorial Fund 相似文献
88.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
89.
本文研究了包括二阶离化过程的强激光场下的双光子自电离。导出了光电子谱的解析表达式,并对一些特殊情况下的光电子谱进行了分析。 相似文献
90.