全文获取类型
收费全文 | 12442篇 |
免费 | 1410篇 |
国内免费 | 586篇 |
专业分类
化学 | 7138篇 |
晶体学 | 565篇 |
力学 | 272篇 |
综合类 | 73篇 |
数学 | 640篇 |
物理学 | 5750篇 |
出版年
2024年 | 6篇 |
2023年 | 78篇 |
2022年 | 156篇 |
2021年 | 190篇 |
2020年 | 233篇 |
2019年 | 233篇 |
2018年 | 228篇 |
2017年 | 248篇 |
2016年 | 430篇 |
2015年 | 408篇 |
2014年 | 529篇 |
2013年 | 976篇 |
2012年 | 622篇 |
2011年 | 826篇 |
2010年 | 720篇 |
2009年 | 818篇 |
2008年 | 812篇 |
2007年 | 959篇 |
2006年 | 877篇 |
2005年 | 675篇 |
2004年 | 671篇 |
2003年 | 578篇 |
2002年 | 509篇 |
2001年 | 376篇 |
2000年 | 329篇 |
1999年 | 280篇 |
1998年 | 294篇 |
1997年 | 196篇 |
1996年 | 158篇 |
1995年 | 157篇 |
1994年 | 159篇 |
1993年 | 107篇 |
1992年 | 103篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 58篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 36篇 |
1983年 | 14篇 |
1982年 | 33篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 39篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
本文提出等效远场的可变孔径方法,由测量光纤远场累积分布求得模场半径。并且利用Petermann关于模场半径的新定义,推出了一种对非高斯模场分布也适用的求模场半径的方法。实验表明,这种测量方法简便可靠,在不同的制备端面下,重复测量的标准误差小于0.04μm。 相似文献
62.
We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO3 by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films. 相似文献
63.
Cao H. P. Chen G. Grechkoseeva M. A. Mazurov V. D. Shi W. J. Vasil'ev A. V. 《Siberian Mathematical Journal》2004,45(6):1031-1035
The spectrum of a finite group is the set of its element orders. A finite group G is said to be recognizable by spectrum, if every finite group with the same spectrum as G is isomorphic to G. The purpose of the paper is to prove that for every natural m the finite simple Chevalley group F
4(2
m
) is recognizable by spectrum. 相似文献
64.
CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states
Fabrizio Evangelista A. RuoccoValdis Corradini M.P. DonzelloCarlo Mariani Maria Grazia Betti 《Surface science》2003,531(2):123-130
We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage. 相似文献
65.
Makoto Sakata Takafumi Itsubo Yutakata Moritomo Yasuo Ohishi 《Journal of Physics and Chemistry of Solids》2004,65(12):1973-1976
The experimental and analytical method of the high-pressure powder experiment at BL10XU, SPring-8, is described. There is no doubt that BL10XU must be one of the most appropriate beam lines for high pressure X-ray diffraction experiment taking advantage of third generation synchrotron source. As an example of the advanced charge density study under high pressure, the structural change of Cs2Au2Br6 by applying pressure is studied by Rietveld/MEM analysis. It reveals that the structural change of Cs2Au2Br6 by applying pressure occurs basically at electron level, such as valence state change and chemical bonding, which may be called the electronic phase transition. 相似文献
66.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
67.
68.
69.
E. García-Matres N. Stüßer M. Hofmann M. Reehuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):35-42
The magnetic structures of Mn1-xFexWO4 with x
= 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase
diagram could be completed in the coexistence range of different magnetic structures up to x
= 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector
= (±1/4, 1/2, 1/2) was found for x
⩽ 0.22 while the magnetic spins order with
= (1/2, 0, 0) for x
≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with
= (- 0.214, 1/2, 0.457) occur in the diffraction pattern up to x
= 0.29 indicating the occurence of a reentrant phase. For 0.12 ⩽
x
⩽ 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed
to a spin arrangement with
= (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed
Mn2+- and Fe2+-ions in the coexistence range 0.12 ⩽
x
⩽ 0.29 of different magnetic structures related to those of pure MnWO4 and FeWO4.
Received 9 October 2002 Published online 14 March 2003 相似文献
70.
Nikolaos S. PAPAGEORGIOU Nikolaos YANNAKAKIS 《数学学报(英文版)》2005,21(5):977-996
This is the first part of a work on second order nonlinear, nonmonotone evolution inclusions defined in the framework of an evolution triple of spaces and with a multivalued nonlinearity depending on both x(t) and x(t). In this first part we prove existence and relaxation theorems. We consider the case of an usc, convex valued nonlinearity and we show that for this problem the solution set is nonempty and compact in C^1 (T, H). Also we examine the Isc, nonconvex case and again we prove the existence of solutions. In addition we establish the existence of extremal solutions and by strengthening our hypotheses, we show that the extremal solutions are dense in C^1 (T, H) to the solutions of the original convex problem (strong relaxation). An example of a nonlinear hyperbolic optimal control problem is also discussed. 相似文献