全文获取类型
收费全文 | 131034篇 |
免费 | 17249篇 |
国内免费 | 12069篇 |
专业分类
化学 | 82266篇 |
晶体学 | 1372篇 |
力学 | 7237篇 |
综合类 | 679篇 |
数学 | 21409篇 |
物理学 | 47389篇 |
出版年
2024年 | 350篇 |
2023年 | 2070篇 |
2022年 | 3674篇 |
2021年 | 3745篇 |
2020年 | 4194篇 |
2019年 | 3973篇 |
2018年 | 4825篇 |
2017年 | 4700篇 |
2016年 | 5667篇 |
2015年 | 5444篇 |
2014年 | 6492篇 |
2013年 | 8381篇 |
2012年 | 12333篇 |
2011年 | 11711篇 |
2010年 | 8387篇 |
2009年 | 7855篇 |
2008年 | 7187篇 |
2007年 | 6534篇 |
2006年 | 6146篇 |
2005年 | 8937篇 |
2004年 | 7444篇 |
2003年 | 5138篇 |
2002年 | 3109篇 |
2001年 | 2513篇 |
2000年 | 2037篇 |
1999年 | 2220篇 |
1998年 | 1845篇 |
1997年 | 1628篇 |
1996年 | 1599篇 |
1995年 | 1408篇 |
1994年 | 1281篇 |
1993年 | 1023篇 |
1992年 | 1068篇 |
1991年 | 929篇 |
1990年 | 785篇 |
1989年 | 610篇 |
1988年 | 475篇 |
1987年 | 394篇 |
1986年 | 375篇 |
1985年 | 298篇 |
1984年 | 216篇 |
1983年 | 180篇 |
1982年 | 143篇 |
1981年 | 96篇 |
1980年 | 71篇 |
1979年 | 53篇 |
1976年 | 101篇 |
1975年 | 59篇 |
1974年 | 48篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
221.
Nonlocal vertex algebras generated by formal vertex operators 总被引:2,自引:0,他引:2
Haisheng Li 《Selecta Mathematica, New Series》2005,11(3-4):349-397
This is the first paper in a series to study vertex algebra-like objects arising from infinite-dimensional quantum groups
(quantum affine algebras and Yangians). In this paper we lay the foundations for this study. For any vector space W, we study what we call quasi compatible subsets of Hom (W,W((x))) and we prove that any maximal quasi compatible subspace has a natural nonlocal (namely noncommutative) vertex algebra
structure with W as a natural faithful quasi module in a certain sense, and that any quasi compatible subset generates a nonlocal vertex algebra
with W as a quasi module. In particular, taking W to be a highest weight module for a quantum affine algebra we obtain a nonlocal vertex algebra with W as a quasi module. We also formulate and study a notion of quantum vertex algebra and we give general constructions of nonlocal
vertex algebras, quantum vertex algebras and their modules. 相似文献
222.
Neodymium doped bismuth layer structure ferroelectrics (BLSFs) ceramics CaBi4−xNdxTi4O15 (x=0, 0.25, 0.50, 0.75) were prepared by solid-state reaction method. X-ray diffraction pattern showed that single phase was formed when x=0-0.75. The refined lattice parameters showed that a (b) axes decrease at x=0.25 and increase with more Nd3+ dopant. The effects of Nd3+ doping on the dielectric and ferroelectric properties of CaBi4Ti4O15 ceramics are studied. Nd3+ dopant decreased the Curie temperature linearly, and the dielectric loss, tan δ, as well. The remnant polarization of Nd3+ doped CaBi4Ti4O15 ceramics was increased by 80% at x=0.25, while more Nd3+ dopant decreased the remnant polarization. CaBi3.75Nd0.25Ti4O15 ceramics had the largest piezoelectric constant d33. The structure and properties of CaBi4−xNdxTi4O15 ceramics showed that Nd3+ may occupy different crystal locations when Nd3+ content x is less than 0.25 and more than 0.50. 相似文献
223.
224.
Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature 下载免费PDF全文
Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm. 相似文献
225.
Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H2O)2 (C4H5O5)2] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound CuII. The electronic structure of the compound is consistent with its crystal structure. 相似文献
226.
We investigate the origin of ultraviolet (UV) emission from Mg0.12 Zn0.88 O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region. 相似文献
227.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
228.
On Best Approximations from RS-sets in Complex Banach Spaces 总被引:2,自引:0,他引:2
ChongLI 《数学学报(英文版)》2005,21(1):31-38
The concept of an RS-set in a complex Banach space is introduced and the problem of best approximation from an RS-set in a complex space is investigated. Results consisting of characterizations, uniqueness and strong uniqueness are established, 相似文献
229.
本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类,证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群. 相似文献
230.