全文获取类型
收费全文 | 93483篇 |
免费 | 760篇 |
国内免费 | 507篇 |
专业分类
化学 | 35004篇 |
晶体学 | 912篇 |
力学 | 7187篇 |
数学 | 34254篇 |
物理学 | 17393篇 |
出版年
2021年 | 151篇 |
2020年 | 218篇 |
2019年 | 200篇 |
2018年 | 10559篇 |
2017年 | 10355篇 |
2016年 | 6321篇 |
2015年 | 1098篇 |
2014年 | 589篇 |
2013年 | 1071篇 |
2012年 | 4491篇 |
2011年 | 11439篇 |
2010年 | 6065篇 |
2009年 | 6426篇 |
2008年 | 7374篇 |
2007年 | 9549篇 |
2006年 | 1125篇 |
2005年 | 2133篇 |
2004年 | 2285篇 |
2003年 | 2658篇 |
2002年 | 1670篇 |
2001年 | 465篇 |
2000年 | 480篇 |
1999年 | 307篇 |
1998年 | 378篇 |
1997年 | 340篇 |
1996年 | 425篇 |
1995年 | 289篇 |
1994年 | 257篇 |
1993年 | 238篇 |
1992年 | 202篇 |
1991年 | 218篇 |
1990年 | 180篇 |
1989年 | 170篇 |
1988年 | 204篇 |
1987年 | 198篇 |
1986年 | 164篇 |
1985年 | 257篇 |
1984年 | 274篇 |
1983年 | 205篇 |
1982年 | 282篇 |
1981年 | 257篇 |
1980年 | 270篇 |
1979年 | 248篇 |
1978年 | 231篇 |
1977年 | 199篇 |
1976年 | 198篇 |
1975年 | 168篇 |
1974年 | 173篇 |
1973年 | 180篇 |
1972年 | 93篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
61.
Noboru Nakatani 《Optical Review》2003,10(4):206-210
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow. 相似文献
62.
James Murdock 《Journal of Differential Equations》2004,205(2):424-465
Hypernormal forms (unique normal forms, simplest normal forms) are investigated both from the standpoint of foundational theory and algorithms suitable for use with computer algebra. The Baider theory of the Campbell-Hausdorff group is refined, by a study of its subgroups, to determine the smallest substages into which the hypernormalization process can be divided. This leads to a linear algebra algorithm to compute the generators needed for each substage with the least amount of work. A concrete interpretation of Jan Sanders’ spectral sequence for hypernormal forms is presented. Examples are given, and a proof is given for a little-known theorem of Belitskii expressing the hypernormal form space (in the inner product style) as the kernel of a higher-order differential operator. 相似文献
63.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive
projections in Dedekind complete vector lattices and f-algebras.
AMS Classification: 47B65, 46A40, 06F25 相似文献
64.
Valery V. Kiselev 《Central European Journal of Physics》2004,2(3):523-534
We calculate the leptonic constant for the pseudoscalar ground state of the B
c
meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy
quark current in nonrelativistic QCD as matched with full QCD. 相似文献
65.
Gaston Casanova 《Advances in Applied Clifford Algebras》2004,14(2):249-252
We define analytic functions within Clifford Algebras CL, and study their trigonometric properties. We write the addition formulas when their arguments, A and B in CL, commute, this generalizes ordinary trigonometry. We examine in particular the case A2 = 1.
相似文献
66.
M. Lashkarizadeh Bami 《Semigroup Forum》2004,69(2):219-229
In the present paper it is shown that if S1 and S2 are two
Clifford topological semigroups satisfying certain conditions
and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T
maps S1 topologically isomorphically onto S2. Furthermore, T
maps M
l
n(S1) (M(S1), respectively) isometrically
isomorphically onto M
l
n(S2) (M(S2), respectively). Indeed,
we have obtained a generalization of a well-known result of
Ghahramani, Lau and Losert for locally compact groups to a more
general setting of Clifford topological semigroups. 相似文献
67.
Andrew Barton 《The Journal of the Operational Research Society》1987,38(10):965-974
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area. 相似文献
68.
Sven Walter 《Acta Analytica》2005,20(3):32-47
Frank Jackson and Philip Pettit have defended a non-reductive account of causal relevance known as the ‘program explanation
account’. Allegedly, irreducible mental properties can be causally relevant in virtue of figuring in non-redundant program explanations which convey information not conveyed by explanations in terms of the physical properties that actually do the ‘causal work’.
I argue that none of the possible ways to spell out the intuitively plausible idea of a program explanation serves its purpose,
viz., defends non-reductive physicalism against Jaegwon Kim’s Causal Exclusion Argument according to which non-reductive physicalism is committed to epiphenomenalism because irreducible mental properties are ‘screened
off’ from causal relevance by their physical realizers. Jackson and Pettit’s most promising explication of a program explanation
appeals to the idea of invariance of effect under variation of realization, but I show that invariance of effect under variation of realization is neither necessary nor sufficient for causal relevance. 相似文献
69.
70.
Experimental analysis, modeling, and theoretical design of McMaster pore-filled nanofiltration membranes 总被引:1,自引:0,他引:1
A side-by-side comparison of the performance of McMaster pore-filled (MacPF) and commercial nanofiltration (NF) membranes is presented here. The single-salt and multi-component performance of these membranes is studied using experimental data and using a mathematical model. The pseudo two-dimensional model is based on the extended Nernst–Planck equation, a modified Poisson–Boltzmann equation, and hydrodynamic calculations. The model includes four structural properties of the membrane: pore radius, pure water permeability, surface charge density and the ratio of effective membrane thickness to water content. The analysis demonstrates that the rejection and transport mechanisms are the same in the commercial and MacPF membranes with different contributions from each type of mechanism (convection, diffusion and electromigration). Solute rejection in NF membranes is determined primarily by a combination of steric and electrostatic effects. The selectivity of MacPF membranes is primarily determined by electrostatic effects with a significantly smaller contribution of steric effects compared to commercial membranes. Hence, these membranes have the ability to reject ions while remaining highly permeable to low molecular weight organics. Additionally, a new theoretical membrane design approach is presented. This design procedure potentially offers the optimization of NF membrane performance by tailoring the membrane structure and operating variables to the specific process, simultaneously. The procedure is validated at the laboratory scale. 相似文献