全文获取类型
收费全文 | 152492篇 |
免费 | 1567篇 |
国内免费 | 382篇 |
专业分类
化学 | 81955篇 |
晶体学 | 2028篇 |
力学 | 6657篇 |
综合类 | 7篇 |
数学 | 15279篇 |
物理学 | 48515篇 |
出版年
2020年 | 1111篇 |
2019年 | 1171篇 |
2018年 | 1475篇 |
2017年 | 1452篇 |
2016年 | 2467篇 |
2015年 | 1545篇 |
2014年 | 2422篇 |
2013年 | 6315篇 |
2012年 | 4925篇 |
2011年 | 6257篇 |
2010年 | 4277篇 |
2009年 | 4289篇 |
2008年 | 5691篇 |
2007年 | 5763篇 |
2006年 | 5404篇 |
2005年 | 4992篇 |
2004年 | 4409篇 |
2003年 | 3854篇 |
2002年 | 3883篇 |
2001年 | 4337篇 |
2000年 | 3319篇 |
1999年 | 2573篇 |
1998年 | 2243篇 |
1997年 | 2186篇 |
1996年 | 1981篇 |
1995年 | 1898篇 |
1994年 | 1887篇 |
1993年 | 1726篇 |
1992年 | 1991篇 |
1991年 | 2119篇 |
1990年 | 1917篇 |
1989年 | 1916篇 |
1988年 | 1856篇 |
1987年 | 1755篇 |
1986年 | 1692篇 |
1985年 | 2192篇 |
1984年 | 2324篇 |
1983年 | 1897篇 |
1982年 | 2078篇 |
1981年 | 1964篇 |
1980年 | 1888篇 |
1979年 | 2029篇 |
1978年 | 2197篇 |
1977年 | 2067篇 |
1976年 | 2112篇 |
1975年 | 2019篇 |
1974年 | 2072篇 |
1973年 | 2060篇 |
1972年 | 1354篇 |
1971年 | 1210篇 |
排序方式: 共有10000条查询结果,搜索用时 63 毫秒
61.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
62.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献
63.
F. A. van Goor S. V. Mitko V. N. Ochkin W. J. Witteman 《Journal of Russian Laser Research》1997,18(2):107-120
Experimental and theoretical results are presented on an XeF(C?A) blue-green laser driven by 5-kJ energy. The laser was pumped by a ferrite-induced discharge of 90 cm in length. The output energy of 0.22 J was obtained with a plane-parallel resonator. A program to simulate laser operation has been developed. Numerical results for a wide range of conditions are compared with experiments performed by us and by other authors. It is found that intracavity refractive losses limit laser operation for XeF pressures above 3 torr. The laser efficiency strongly depends on the discharge-to-cavity length ratio. Possible ways to increase the laser power and efficiency are discussed. 相似文献
64.
Translated from Khimiya Geterotsiklicheskikh Soedinenii. Vol. 30. No. 3, pp. 424–425, March, 1994. 相似文献
65.
V. D. Orlov Z. Kaluski N. P. Borob'eva E. Figas A. A. Tishchenko F. G. Yaremko 《Chemistry of Heterocyclic Compounds》1994,30(8):964-971
We have measured the PMR spectra of 5, 7-diaryl-1, 4-diazabicyclo[4. ].O]hept-4-enes. We have studied the structure of the 5-(4-nitrophenyl)-7-phenyl derivative by x-ray diffraction. We show that the six-membered heterocycle has the half-chair form. The 6-H and 7-H protons of the aziridine ring are trans, while the 7-aryl is exo relative to the six-membered ring. Introduction of substituents into the aromatic ring has practically no effect on the geometry of the bicycle.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1124, August, 1994.For Communication 11, see [1]. 相似文献
66.
67.
68.
A. N. Komissarenko T. P. Nadezhina N. F. Komissarenko 《Chemistry of Natural Compounds》1994,30(4):521-522
State Scientific Center for Drugs, Khar'kov. Ukrainian Pharmaceutical Academy, Khar'kov. Botanical Gardem, Russian Academy
of Sciences, St. Petersburg. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 564–565, July–August, 1994. 相似文献
69.
70.
D. N. Dalimov M. B. Gafurov Z. Tilyabaev F. G. Kamaev A. A. Abdugakhabov 《Chemistry of Natural Compounds》1994,30(1):61-64
The synthesis has been effected of alkyl anabasinoprop-2-yl and alkyl piperidinoprop-2-yl methylphosphonothionates. It has been shown by1H,13C and31P NMR spectroscopies that the anabasine derivatives exist in solution as four diastereomeric forms. The kinetics of the interaction of the compounds synthesized with two types of cholinesterases has been studied.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Fax 627071. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 70–74, January–February, 1994. 相似文献