全文获取类型
收费全文 | 223909篇 |
免费 | 2388篇 |
国内免费 | 287篇 |
专业分类
化学 | 116907篇 |
晶体学 | 2862篇 |
力学 | 10121篇 |
综合类 | 8篇 |
数学 | 29581篇 |
物理学 | 67105篇 |
出版年
2021年 | 2179篇 |
2020年 | 2500篇 |
2019年 | 2885篇 |
2018年 | 4321篇 |
2017年 | 4375篇 |
2016年 | 5797篇 |
2015年 | 3216篇 |
2014年 | 4900篇 |
2013年 | 9957篇 |
2012年 | 8300篇 |
2011年 | 9167篇 |
2010年 | 7227篇 |
2009年 | 7083篇 |
2008年 | 8611篇 |
2007年 | 8363篇 |
2006年 | 7456篇 |
2005年 | 6878篇 |
2004年 | 6444篇 |
2003年 | 5706篇 |
2002年 | 5687篇 |
2001年 | 5866篇 |
2000年 | 4579篇 |
1999年 | 3455篇 |
1998年 | 3090篇 |
1997年 | 2879篇 |
1996年 | 2803篇 |
1995年 | 2438篇 |
1994年 | 2467篇 |
1993年 | 2475篇 |
1992年 | 2521篇 |
1991年 | 2759篇 |
1990年 | 2721篇 |
1989年 | 2725篇 |
1988年 | 2620篇 |
1987年 | 2619篇 |
1986年 | 2430篇 |
1985年 | 3079篇 |
1984年 | 3060篇 |
1983年 | 2610篇 |
1982年 | 2680篇 |
1981年 | 2586篇 |
1980年 | 2346篇 |
1979年 | 2651篇 |
1978年 | 2805篇 |
1977年 | 2896篇 |
1976年 | 2987篇 |
1975年 | 2763篇 |
1974年 | 2702篇 |
1973年 | 2884篇 |
1972年 | 2296篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
String theory at nonzero temperature is reviewed. A bosonic string at nonzero temperature is studied and the calculation of its free energy in both the one-loop approximation and the case of arbitrary genus (multiloop analysis) is discussed. A string at nonzero temperature is compared with a string compacted on a one-dimensional torus. The properties of modular invariance and dual symmetry are discussed at both the one-loop and multiloop levels. The thermodynamics of superstrings, including also superstrings compactified on a torus, is also studied. Possible cosmological applications are briefly considered. It is shown that many features of string thermodynamics (in particular, the existence of the Hagedorn temperature and dual symmetry) also occur in the theory of noncritical strings.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–49, December, 1991. 相似文献
992.
993.
The length-distribution of stereoregular sequences in low-density polyethylene (LDPE) is determined by a computer-aided analysis of cp-melting curves within the framework of thermodynamics of eutectoid copolymers. Small-angle x-ray scattering patterns are then described by using the structure data derived. One of the results is that fluctuations of the mean electron-density are increasingly reduced with an increasing degree of crystallinity.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday 相似文献
994.
M.S. Anagnostou I. Panagiotopoulos A. Kostikas D. Niarchos G. Zouganelis 《Journal of magnetism and magnetic materials》1994,130(1-3):57-62
From the analysis of Mössbauer data for Y2Fe17 and Y2Fe17N3−δ at various temperatures the hyperfine fields for 4f, 6g, 12j, 12k iron sites were estimated as a function of temperature. The reduced magnetizations calculated from the values of the hyperfine fields are fitted with a mean field model for four interacting sublattices using a computer program. The estimated exchange interaction from the fitting procedure between the 4f sites is found strongly negative (antiferromagnetic) in Y2Fe17 whereas in Y2Fe17N3−δ it increases and becomes weak negative following a modified Slater-Néel curve. The rest of the exchange interactions are found positive or weak negative depending on the distances between the Fe atoms. 相似文献
995.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions. 相似文献
996.
Robert Andreu Gerard Lligadas Joan Carles Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4965-4973
A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ~ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007 相似文献
997.
998.
999.
1000.
P. V. Pavlov I. V. Babushkin N. A. Loiko N. N. Rosanov S. V. Fedorov 《Radiophysics and Quantum Electronics》2004,47(10-11):898-904
We consider spatial dissipative solitons arising in the system of two nonlinear thin films which interact resonantly with light. Symmetric and nonsymmetric solitons and methods of their exciting and switching are studied. 相似文献