全文获取类型
收费全文 | 146952篇 |
免费 | 1443篇 |
国内免费 | 405篇 |
专业分类
化学 | 80237篇 |
晶体学 | 2388篇 |
力学 | 6063篇 |
综合类 | 20篇 |
数学 | 13598篇 |
物理学 | 46494篇 |
出版年
2021年 | 1033篇 |
2020年 | 1182篇 |
2019年 | 1249篇 |
2018年 | 1638篇 |
2017年 | 1689篇 |
2016年 | 2542篇 |
2015年 | 1560篇 |
2014年 | 2349篇 |
2013年 | 6035篇 |
2012年 | 4843篇 |
2011年 | 5941篇 |
2010年 | 4184篇 |
2009年 | 4211篇 |
2008年 | 5726篇 |
2007年 | 5511篇 |
2006年 | 5385篇 |
2005年 | 4953篇 |
2004年 | 4452篇 |
2003年 | 4125篇 |
2002年 | 4018篇 |
2001年 | 5546篇 |
2000年 | 3972篇 |
1999年 | 3077篇 |
1998年 | 2113篇 |
1997年 | 2210篇 |
1996年 | 2073篇 |
1995年 | 1918篇 |
1994年 | 1914篇 |
1993年 | 1728篇 |
1992年 | 2219篇 |
1991年 | 2304篇 |
1990年 | 2136篇 |
1989年 | 2103篇 |
1988年 | 2083篇 |
1987年 | 2089篇 |
1986年 | 1909篇 |
1985年 | 2371篇 |
1984年 | 2394篇 |
1983年 | 1910篇 |
1982年 | 1914篇 |
1981年 | 1754篇 |
1980年 | 1737篇 |
1979年 | 2028篇 |
1978年 | 2102篇 |
1977年 | 2046篇 |
1976年 | 1975篇 |
1975年 | 1861篇 |
1974年 | 1842篇 |
1973年 | 1874篇 |
1972年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
An upper bound for the best approximation of summable functions of several variables by trigonometric polynomials in the metric of L is determined in terms of Fourier coefficients. We consider functions representable by trigonometric series with certain symmetry of coefficients satisfying a multiple analog of the Sidon–Telyakovskii conditions. 相似文献
112.
113.
Local and nonlocal coercive estimates in Lebesgue, Hölder, and Morrey–Campanato spaces are proved for solutions of linear stationary systems of hydrodynamic type. For this purpose, the technique proposed by Italian mathematicians for the study of solutions to equations and systems of elliptic and parabolic types is developed. Bibliography: 14 titles. 相似文献
114.
S.V.N Bhaskara Rao T.K. Balasubramanian 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,87(2):203-210
Fresh computations of rovibrational matrix elements of the polarizability α[=(α||+2α⊥)/3] and the polarizability anisotropy γ(=α||−α⊥) of the heteronuclear isotopomers, HD, HT, and DT, of the hydrogen molecule are presented. The computations combine the most accurate polarizability functions α(R) and γ(R) (R being the bond distance) on the one hand and the most accurate adiabatic potential on the other. The calculations are extended to the product operators xα and xγ where x is the centre of mass to centre of charge separation in the heteronuclear species. The latter matrix elements are needed, additionally, for elucidating the absorption intensities of some of the zero-phonon rovibrational transitions peculiar to the heteronuclear species in the crystalline phase. 相似文献
115.
The spectrum and the spatial distribution of the emission of scattered particles upon bombardment of Be, Ti, Ta, and W with H and He ions were studied. The quantum yield and the velocity and angular distributions of the scattered excited particles were measured. Computer simulation of the scattering of H ions and He ions from the metals under study was performed with the use of the program TRIM-95. Agreement is observed between the calculated and experimentally measured angular distributions of the scattered particles. 相似文献
116.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
117.
118.
Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa2Cu3Oy with various porosity and also in BiSrCaCu2Oy. A velocity drop of about 400 ppm was found at Tc only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon. 相似文献
119.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program. 相似文献
120.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献