全文获取类型
收费全文 | 22919篇 |
免费 | 3095篇 |
国内免费 | 2210篇 |
专业分类
化学 | 8325篇 |
晶体学 | 102篇 |
力学 | 1401篇 |
综合类 | 372篇 |
数学 | 10492篇 |
物理学 | 7532篇 |
出版年
2024年 | 45篇 |
2023年 | 264篇 |
2022年 | 479篇 |
2021年 | 546篇 |
2020年 | 683篇 |
2019年 | 692篇 |
2018年 | 593篇 |
2017年 | 638篇 |
2016年 | 882篇 |
2015年 | 753篇 |
2014年 | 1158篇 |
2013年 | 1822篇 |
2012年 | 1110篇 |
2011年 | 1354篇 |
2010年 | 1146篇 |
2009年 | 1480篇 |
2008年 | 1574篇 |
2007年 | 1661篇 |
2006年 | 1418篇 |
2005年 | 1194篇 |
2004年 | 1075篇 |
2003年 | 1066篇 |
2002年 | 871篇 |
2001年 | 737篇 |
2000年 | 780篇 |
1999年 | 683篇 |
1998年 | 676篇 |
1997年 | 485篇 |
1996年 | 400篇 |
1995年 | 259篇 |
1994年 | 280篇 |
1993年 | 191篇 |
1992年 | 168篇 |
1991年 | 135篇 |
1990年 | 101篇 |
1989年 | 97篇 |
1988年 | 96篇 |
1987年 | 62篇 |
1986年 | 60篇 |
1985年 | 66篇 |
1984年 | 79篇 |
1983年 | 32篇 |
1982年 | 63篇 |
1981年 | 39篇 |
1980年 | 42篇 |
1979年 | 47篇 |
1978年 | 29篇 |
1977年 | 22篇 |
1976年 | 24篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In the present paper, some new almost fixed point theorems and fixed point theorems for lower semicontinuous type multivalued mappings are obtained in metrizable H-spaces. 相似文献
52.
3-Hydroxy-4-hydroxymethyl pyrrolidin-2-ones, easily prepared from the Baylis–Hillman adduct 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate, are useful intermediates in the synthesis of bioactive compounds. In order to understand the mechanism involved in this reaction, vibrational and Montecarlo molecular mechanics conformational analysis on 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate were carried out, confirming the existence of a low energy intramolecular H-bonded five-member ring. 相似文献
53.
54.
The Raman shifts of nanocrystalline GaSb excited by an Ar^ ion laser at wavelengths 514.5, 496.5, 488.0, 476.5,and 457.9nm are studied by an SPEX-1403 laser Raman spectrometer respectively, and they are explained by phonon confinement, tensile stress, resonant Raman scattering and quantum size effects. The Stokes and anti-Stokes Raman spectra of GaSb nanocrystals strongly support the Raman feature of GaSb nanocrystals. The calculated optical spectra compare well with experimental data on Raman scattering GaSb nanocrystals. 相似文献
55.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
56.
SUN Qiyu 《数学年刊B辑(英文版)》2003,24(3):367-386
In this paper, the author at first develops a method to study convergence of the cascade algorithm in a Banach space without stable assumption on the initial (see Theorem 2.1), and then applies the previous result on the convergence to characterizing compactly supported refinable distributions in fractional Sobolev spaces and Holder continuous spaces (see Theorems 3.1, 3.3, and 3.4). Finally the author applies the above characterization to choosing appropriate initial to guarantee the convergence of the cascade algorithm (see Theorem 4.2). 相似文献
57.
G. C. Psarras 《Journal of Polymer Science.Polymer Physics》2007,45(18):2535-2545
The charge transport properties of polymer matrix–carbon black composites are investigated in this study. Direct current conductivity is examined with varying parameters: the temperature and the conductive filler content. Conductivity data are analyzed by means of percolation theory, and both percolation threshold and critical exponent are determined at each of the examined temperatures. The temperature dependence of conductivity and the agreement of experimental results with the variable range hopping model reveal hopping conduction as the predominant transport mechanism, below and in the vicinity of the critical concentration of carbon black particles. At higher concentrations, the contribution of hopping transport to the overall conductivity is reduced and a balance between hopping and conduction via geometrical contact occurs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2535–2545, 2007 相似文献
58.
O. Castaños 《Journal of Molecular Spectroscopy》2007,241(1):51-60
A simple algebraic approach to calculate general Franck-Condon overlaps is extended to evaluate non-Condon factors for two one-dimensional harmonic oscillators. The method is based on the use of eigenstates of the harmonic oscillator annihilation operator which allows to obtain in terms of a multi-dimensional Hermite polynomial the overlap of harmonic oscillator functions associated with different Born-Oppenheimer potentials. The presented approach is self-contained, only basic concepts of quantum mechanics associated with the harmonic oscillator system are needed. The obtained expression for the Franck-Condon overlaps is similar to the Ansbacher’s formula and equivalent to the one calculated by Malkin and Man’ko. However our final expression has the advantages that only real numbers are involved and it is straightforward to get the limit case of equal frequencies. Concerning the non-Condon factors two approaches leading to different formulas are considered, both of which reduce to triple sums of products of three Hermite polynomials. 相似文献
59.
60.
A locally convex space is said to be a Gateaux differentiability space (GDS)provided every continuous convex function defined on a nonempty convex open subset D of the space is densely Gateaux differentiable in D.This paper shows that the product of a GDS and a family of separable Frechet spaces is a GDS,and that the product of a GDS and an arbitrary locally convex space endowed with the weak topology is a GDS. 相似文献