全文获取类型
收费全文 | 29747篇 |
免费 | 5183篇 |
国内免费 | 4567篇 |
专业分类
化学 | 22234篇 |
晶体学 | 613篇 |
力学 | 1507篇 |
综合类 | 404篇 |
数学 | 3241篇 |
物理学 | 11498篇 |
出版年
2024年 | 87篇 |
2023年 | 460篇 |
2022年 | 848篇 |
2021年 | 977篇 |
2020年 | 1076篇 |
2019年 | 1269篇 |
2018年 | 961篇 |
2017年 | 975篇 |
2016年 | 1341篇 |
2015年 | 1488篇 |
2014年 | 1726篇 |
2013年 | 2232篇 |
2012年 | 2807篇 |
2011年 | 2720篇 |
2010年 | 2180篇 |
2009年 | 2144篇 |
2008年 | 2370篇 |
2007年 | 2022篇 |
2006年 | 1958篇 |
2005年 | 1695篇 |
2004年 | 1392篇 |
2003年 | 1075篇 |
2002年 | 1105篇 |
2001年 | 868篇 |
2000年 | 686篇 |
1999年 | 570篇 |
1998年 | 375篇 |
1997年 | 289篇 |
1996年 | 288篇 |
1995年 | 254篇 |
1994年 | 243篇 |
1993年 | 196篇 |
1992年 | 136篇 |
1991年 | 139篇 |
1990年 | 98篇 |
1989年 | 67篇 |
1988年 | 77篇 |
1987年 | 40篇 |
1986年 | 48篇 |
1985年 | 58篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1957年 | 5篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Ag/InP Schottky结是制作TE场助光电阴极的关键,本文利用Auger分析技术,详细地研究了热处理对Ag/InPSchottky结界面特性的影响。实验结果表明高温长时间热处理会导致严重界面相互扩散,同时使Schottky结的势垒高度降低,理想因子增大,泡利负电性理论很好地解释了扩散效应。势垒高度的降低及理想因子的增大也是由界面互扩散造成的,这种扩散导致界面特性由Schotthy特性向欧姆性质转化。为防止界面互扩散及Schottky结特性的退化,可选用负电性小的金属制作Schottky结,并在工艺上尽量减少热处理的温度和时间。 相似文献
112.
Jun Nakagawa Richard F. Wormsbecher David O. Harris 《Journal of Molecular Spectroscopy》1983,97(1):37-64
Single-mode cw dye laser excitation spectra of the (0, 00, 0)-(0, 00, 0), (1, 00, 0)-(1, 00, 0), (0, 11, 0)-(0, 11, 0) bands of the 611- to 607-nm system of SrOH and SrOD were observed and assigned. The spectrum is consistent with a 2Σ-2Σ system where the molecule is linear in both electronic states. The rotational analysis is obtained by measuring P-R separations in the excitation spectrum. A technique which greatly aided in the spectral assignment that utilizes a monochromator as a bandpass filter in obtaining excitation spectra is described. A new spin-rotation constant, γ(+) - γ(?), was found necessary to fit the l-type doubling of the (0, 11, 0) mode in B2Σ+ of SrOH. This new constant is assumed to arise from two vibronic states, split by Renner-Teller interaction, of the (0, 11, 0) mode of A2Π. From a perturbation treatment of this electronic interaction, ?ω2 of the (0, 11, 0) mode of A2Π was found to be 14 cm?1. The linear structure of SrOH and SrOD in both electronic states is consistent with the model, in the one-electron approximation, in that the transition involves the promotion of the unpaired 5s to the 5p orbital localized on the strontium. 相似文献
113.
The uncertainty principle lies at the heart of quantum physics, and is widely thought of as a fundamental limit of the measurement precision of incompatible observables. Here it is shown that the traditional uncertainty relation in fact belongs to the leading order approximation of a generalized uncertainty relation. That is, the leading order linear dependence of observables gives the Heisenberg type of uncertainty relations, while higher order nonlinear dependence may reveal more different and interesting correlation properties. Applications of the generalized uncertainty relation and the high order nonlinear dependence between observables in quantum information science are also discussed. 相似文献
114.
LiuYanyan WuJun 《分析论及其应用》2003,19(4):342-354
A set is called regular if its Hausdorff dimension and upper box-counting dimension coincide. In this paper, we prove that the random self-con formal set is regular almost surely. Also we determine the dimen-sions for a class of random self-con formal sets. 相似文献
115.
We prove that there exists a maximal ideal of a BCI-algebra X in which each subalgebra is an ideal.AMS Subject Classification (1991): 06F35, 03G25.The second author was supported by the LG Yonam Foundation (1995). 相似文献
116.
Sparse approximate inverse (SAI) techniques have recently emerged as a new class of parallel preconditioning techniques for
solving large sparse linear systems on high performance computers. The choice of the sparsity pattern of the SAI matrix is
probably the most important step in constructing an SAI preconditioner. Both dynamic and static sparsity pattern selection
approaches have been proposed by researchers. Through a few numerical experiments, we conduct a comparable study on the properties
and performance of the SAI preconditioners using the different sparsity patterns for solving some sparse linear systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
117.
An incomplete factorization method for preconditioning symmetric positive definite matrices is introduced to solve normal equations. The normal equations are form to solve linear least squares problems. The procedure is based on a block incomplete Cholesky factorization and a multilevel recursive strategy with an approximate Schur complement matrix formed implicitly. A diagonal perturbation strategy is implemented to enhance factorization robustness. The factors obtained are used as a preconditioner for the conjugate gradient method. Numerical experiments are used to show the robustness and efficiency of this preconditioning technique, and to compare it with two other preconditioners. 相似文献
118.
Affective property of image and fractal dimension 总被引:3,自引:0,他引:3
Affective information processing is an advanced research direction in the AI world. Affective Information of image was taken as the objective of research in this paper. The influence of color vision properties’ histograms of image on human emotions was analyzed. Then based on fractal theory, the fractal aspect of different kinds of images was analyzed in keeping with the space domain. After that, psychological testing method of semantic difference was applied to verify the uniformity of the objective and subjective evaluations. At last, a conclusion was drawn that image having different affective properties could be classified by their fractal dimensions. 相似文献
119.
本文研究了具有鉴相特性g()=((1+k)sin())/(1+kcos())的三阶锁相环路方程奇点的拓扑结构. 相似文献
120.
A new real time formalism, based on the closed-time-path Green's function theory (CTPGF),is employed to obtain Ward-llfrkahashi identities of QED at finite temperature. It is shown that WT identity in coordinate space is of the same covariant form aa that in vacuum field theory. A perturbative check is provided to #how that in momentum spze, Takahashi's iden tities hold only in a weak sense. 相似文献