全文获取类型
收费全文 | 147086篇 |
免费 | 1460篇 |
国内免费 | 396篇 |
专业分类
化学 | 80275篇 |
晶体学 | 2390篇 |
力学 | 6098篇 |
综合类 | 3篇 |
数学 | 13622篇 |
物理学 | 46554篇 |
出版年
2021年 | 1033篇 |
2020年 | 1181篇 |
2019年 | 1249篇 |
2018年 | 1639篇 |
2017年 | 1694篇 |
2016年 | 2541篇 |
2015年 | 1564篇 |
2014年 | 2354篇 |
2013年 | 6052篇 |
2012年 | 4847篇 |
2011年 | 5947篇 |
2010年 | 4184篇 |
2009年 | 4219篇 |
2008年 | 5733篇 |
2007年 | 5518篇 |
2006年 | 5385篇 |
2005年 | 4952篇 |
2004年 | 4457篇 |
2003年 | 4123篇 |
2002年 | 4016篇 |
2001年 | 5553篇 |
2000年 | 3979篇 |
1999年 | 3081篇 |
1998年 | 2119篇 |
1997年 | 2211篇 |
1996年 | 2077篇 |
1995年 | 1919篇 |
1994年 | 1918篇 |
1993年 | 1727篇 |
1992年 | 2219篇 |
1991年 | 2299篇 |
1990年 | 2136篇 |
1989年 | 2104篇 |
1988年 | 2078篇 |
1987年 | 2088篇 |
1986年 | 1913篇 |
1985年 | 2373篇 |
1984年 | 2395篇 |
1983年 | 1914篇 |
1982年 | 1917篇 |
1981年 | 1759篇 |
1980年 | 1743篇 |
1979年 | 2027篇 |
1978年 | 2106篇 |
1977年 | 2054篇 |
1976年 | 1978篇 |
1975年 | 1862篇 |
1974年 | 1844篇 |
1973年 | 1876篇 |
1972年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献
212.
To elucidate the fundamental process underlying the semiconductor surface fabrication, isothermal desorption from a Cl/Si(111)-‘1×1’ surface was monitored by means of second-harmonic generation with 1064 nm light. During the desorption, surface Cl-coverages were obtained in real time. The temperature dependence of the desorption rates revealed that the energy barrier against chloride desorption is 2.1 eV. A very slow second phase in the recovery of the second-harmonic intensity is associated with reconstruction of 7×7 DAS structure following the desorption. The activation energy for the reconstruction was 2.4 eV. 相似文献
213.
214.
Chemisorption at interfaces between organic semiconductors and metals: role of the electron affinity
Chemisorption is a well-known phenomenon for many interfaces between organic semiconductors and metals. It is shown that many published data indicate that the occurrence of chemisorption can be rationalized upon the consideration of the metal work function versus the electron affinity of the organic semiconductor. 相似文献
215.
216.
J. Berkemeier T. Dirksmeyer G. Klempt H. G. Purwins 《Zeitschrift für Physik B Condensed Matter》1986,65(2):255-258
It is observed experimentally that a periodic array of resistively coupled LC-oscillators with ans-shaped nonlinearity exhibits stable non-uniform voltage and current distributions. The dependence of the resulting structure on the coupling resistance and the boundary conditions is investigated. The structure is rather insensitive to variations of the boundary values. The experiments are well described by a two-variable reaction-diffusion equation. 相似文献
217.
B. Saha S. Bhattacharyya T. K. Mukherjee P. K. Mukherjee 《International journal of quantum chemistry》2003,92(5):413-418
In the framework of nonrelativistic variational formalism a new type of basis set is proposed, to estimate separately the effect of radial and angular correlations on the ground‐state energy for helium isoelectronic sequence H? to Ar16+. Effect of radial correlation is incorporated by using multiexponential functions arising from product basis sets suitably formed out of Slater‐type one‐particle orbitals. The angular correlation can be switched on by incorporating an expansion in terms of basis involving interparticle coordinates. With a set of six‐term Slater‐type one‐particle basis and five‐term interparticle expansion, the ground‐state energy of helium is estimated as ?2.9037236 (a.u.) compared with the multiterm variational estimates ?2.9037244 (a.u.) due to Pekeris and Thakkar and Smith and Drake. Matrix elements of different operators in the ground state have been calculated and found to be in good agreement with available accurate results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
218.
E.Ann Hallinan Clifford R. DornWilliam M. Moore Gina M. JeromePamela T. Manning Barnett S. Pitzele 《Tetrahedron letters》2003,44(39):7345-7347
Described is a method of introducing trifluoroalkyl groups at C-6 of lysine. This chemistry has the potential to introduce a variety of functionality at C-6 of lysine. 相似文献
219.
N. V. Vysotina A. S. Naumov N. N. Rozanov R. L. Sabirov V. E. Semenov V. A. Smirnov T. V. Starchikova S. V. Fedorov S. A. Chizhov V. E. Yashin 《Optics and Spectroscopy》2004,97(3):411-415
The final stage of self-focusing of 500-ps pulses of a neodymium laser in silicate and phosphate glasses and in the nonlinear liquids perfluorooctane, benzene, and toluene is studied theoretically and experimentally. The formation of spatial solitons, which are stable due to the nonlinearity saturation, is demonstrated. It is found that the intensity of the nonlinearity saturation is close to that of the threshold breakdown for glasses and the role of stimulated Raman scattering is significant for liquids. 相似文献
220.
Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed. 相似文献