全文获取类型
收费全文 | 15473篇 |
免费 | 386篇 |
国内免费 | 94篇 |
专业分类
化学 | 9933篇 |
晶体学 | 157篇 |
力学 | 390篇 |
综合类 | 1篇 |
数学 | 2311篇 |
物理学 | 3161篇 |
出版年
2023年 | 89篇 |
2022年 | 127篇 |
2021年 | 203篇 |
2020年 | 226篇 |
2019年 | 261篇 |
2018年 | 185篇 |
2017年 | 175篇 |
2016年 | 419篇 |
2015年 | 319篇 |
2014年 | 350篇 |
2013年 | 775篇 |
2012年 | 703篇 |
2011年 | 747篇 |
2010年 | 522篇 |
2009年 | 488篇 |
2008年 | 698篇 |
2007年 | 761篇 |
2006年 | 619篇 |
2005年 | 699篇 |
2004年 | 566篇 |
2003年 | 447篇 |
2002年 | 434篇 |
2001年 | 230篇 |
2000年 | 207篇 |
1999年 | 173篇 |
1998年 | 146篇 |
1997年 | 182篇 |
1996年 | 212篇 |
1995年 | 187篇 |
1994年 | 141篇 |
1993年 | 163篇 |
1992年 | 136篇 |
1991年 | 140篇 |
1990年 | 137篇 |
1989年 | 121篇 |
1988年 | 121篇 |
1987年 | 134篇 |
1986年 | 122篇 |
1985年 | 165篇 |
1984年 | 171篇 |
1983年 | 142篇 |
1982年 | 143篇 |
1981年 | 133篇 |
1980年 | 150篇 |
1979年 | 123篇 |
1978年 | 146篇 |
1977年 | 109篇 |
1976年 | 103篇 |
1975年 | 120篇 |
1974年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We prove that for every fixed k and ? ≥ 5 and for sufficiently large n, every edge coloring of the hypercube Qn with k colors contains a monochromatic cycle of length 2 ?. This answers an open question of Chung. Our techniques provide also a characterization of all subgraphs H of the hypercube which are Ramsey, that is, have the property that for every k, any k‐edge coloring of a sufficiently large Qn contains a monochromatic copy of H. © 2006 Wiley Periodicals, Inc. J Graph Theory 53: 196–208, 2006 相似文献
42.
Jan E. Åman Ingemar Bengtsson Narit Pidokrajt 《General Relativity and Gravitation》2006,38(8):1305-1315
The Hessian of either the entropy or the energy function can be regarded as a metric on a Gibbs surface. For two parameter families of asymptotically flat black holes in arbitrary dimension one or the other of these metrics are flat, and the state space is a flat wedge. The mathematical reason for this is traced back to the scale invariance of the Einstein–Maxwell equations. The picture of state space that we obtain makes some properties such as the occurence of divergent specific heats transparent.Supported by VR. 相似文献
43.
Th. Friedrich I. Kath A. Moroianu U. Semmelmann 《Journal of Geometry and Physics》1997,23(3-4):259-286
A nearly parallel G2-structure on a seven-dimensional Riemannian manifold is equivalent to a spin structure with a Killing spinor. We prove general results about the automorphism group of such structures and we construct new examples. We classify all nearly parallel G2-manifolds with large symmetry group and in particular all homogeneous nearly parallel G2-structures. 相似文献
44.
6-Thia-l-aza-5λ5-phosphabicyclo[3.2.0]hept-3-enes and Isothiocyanatophosphine-sulfides from (Methylidenamino)phosphines, Carbon Disulfide, and Acetylene- or Ethylene Derivatives (Methylidenamino)phosphines react with carbon disulfide to 1,3,2-thiazaphosphete derivatives 2 . Acetylenedicarboxylates give with 2 6-thia-l-aza-5λ5-phosphabicyclo[3.2.0]hept-3-enes 4a , b , and acrylates yield isothio-cyanatophosphin-sulfides 5a – c . The structures of 4a and 5a are proven by an X-ray diffraction analysis. 相似文献
45.
46.
47.
Polymer lightguides of PMMA doped with the azo dyes methyl-red and N, N-dihexyl-4-amino-4'-nitro-azobenzene (DHANA) are investigated with respect to their opto-optical properties. The trans-cis photoisomerisation of the dyes leads to reversible polarization-dependent optically induced refractive index changes. The index changes are anisotropic. Birefringence is measured using index matched lightguides. The changes with respect to each polarization are determined by leaky mode spectroscopy and by using a half-integrated interferometer. These changes are intensity dependent and, with a suitable geometry, bistability at low intensities (3 mW/mm3) can be obtained. 相似文献
48.
49.
Boena N. Kolarz Maria Wojaczyska Jan Kaczmarczyk Teresa Siemieniewska Kazimierz Tomkw 《Journal of Polymer Science.Polymer Physics》1994,32(12):1977-1990
Sulfonic cation exchangers with two ion exchange group concentrations (0.5 and 2.4 mmol/g, samples A and B, respectively) were obtained by sulfonation of a porous styrene (S) and divinylbenzene (DVB) copolymer with chlorosulfonic acid. Strong thermal decomposition of the sulfonated copolymer A, accompanied by significant changes in its porous structure, starts at ca. 400°C. The char has no sulfonic groups. After heat treatment at 400°C in steam, a sorbent was obtained (yield 65%) that shows higher phenol sorption than the untreated sample when related to the bed volume. The chlorosulfonic derivatives of the initial copolymer were less thermally resistant than the sulfonic ones obtained by hydrolysis. Pyrolysis of the cation exchanger B, in its H+ and Ca2+ forms, was carried out at 900°C (yield of both chars close to 30%). By subsequent steam activation at 800°C to a 50% burn-off of the char, sorbents with well-developed, but distinctly different, porous structures were obtained. The activated char from the sulfonated copolymer in its hydrogen form was highly microporous and indicated an effective surface area of 1180 m2/g. However, because of a low contribution of mesopores, its ability to adsorb phenol from the liquid phase was not very high. The activated char from the calcium-doped copolymer, indicating a smaller surface area (580 m2/g) but characterized by a well-developed mesoporosity, was a better sorbent for phenol. © 1994 John Wiley & Sons, Inc. 相似文献
50.