全文获取类型
收费全文 | 474339篇 |
免费 | 4499篇 |
国内免费 | 1921篇 |
专业分类
化学 | 241323篇 |
晶体学 | 6805篇 |
力学 | 22251篇 |
综合类 | 67篇 |
数学 | 66988篇 |
物理学 | 143325篇 |
出版年
2020年 | 3402篇 |
2019年 | 3764篇 |
2018年 | 11847篇 |
2017年 | 12508篇 |
2016年 | 10431篇 |
2015年 | 5053篇 |
2014年 | 6860篇 |
2013年 | 16845篇 |
2012年 | 16710篇 |
2011年 | 26013篇 |
2010年 | 17085篇 |
2009年 | 16971篇 |
2008年 | 23671篇 |
2007年 | 26633篇 |
2006年 | 14733篇 |
2005年 | 18291篇 |
2004年 | 14500篇 |
2003年 | 13422篇 |
2002年 | 11576篇 |
2001年 | 11433篇 |
2000年 | 9095篇 |
1999年 | 6537篇 |
1998年 | 5524篇 |
1997年 | 5532篇 |
1996年 | 5493篇 |
1995年 | 4654篇 |
1994年 | 4780篇 |
1993年 | 4656篇 |
1992年 | 5040篇 |
1991年 | 5128篇 |
1990年 | 4874篇 |
1989年 | 4797篇 |
1988年 | 4667篇 |
1987年 | 4603篇 |
1986年 | 4548篇 |
1985年 | 5909篇 |
1984年 | 6130篇 |
1983年 | 5019篇 |
1982年 | 5458篇 |
1981年 | 5177篇 |
1980年 | 4796篇 |
1979年 | 5178篇 |
1978年 | 5458篇 |
1977年 | 5424篇 |
1976年 | 5469篇 |
1975年 | 5067篇 |
1974年 | 5199篇 |
1973年 | 5379篇 |
1972年 | 3931篇 |
1967年 | 3260篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
We obtain a lower bound on the number of prime divisors of integers whose g-ary expansion contains a fixed number of nonzero digits.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
982.
983.
O. A. Alekseeva N. I. Sorokina I. A. Verin T. Yu. Losevskaya V. I. Voronkova V. K. Yanovskii V. I. Simonov 《Crystallography Reports》2003,48(2):205-211
This study is a continuation of research into the atomic structure and physical properties of niobium-doped potassium titanyl phosphate crystals, KTiOPO4 (KTP: Nb). Crystals containing 7 and 11 at. % of niobium were grown and studied. With an increase in niobium content, the number of vacancies and additional potassium positions in the structure also increase. This fact accounts for an increase in both the intensities of relaxation peaks and the conductivity of KTP: Nb crystals. 相似文献
984.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
985.
Until recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering 1 ns pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to >100 kHz.Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to >1 W average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser. 相似文献
986.
V. I. Tsoy 《Optics and Spectroscopy》2003,94(4):607-612
In the framework of the matrix formulation of the coupled plane wave approach, a method is proposed for increasing the stability of the numerical analysis of vector electromagnetic fields in periodic structures, including dielectric and metallic anisotropic layers and relief boundaries. 相似文献
987.
The operating principles, design, and characteristics of an ion source with a cold magnetron cathode and magnetic plasma compression are described. The source is intended for the injector of a linear proton accelerator. 相似文献
988.
The local vibrational spectra of copper crystals containing vacancies are calculated using the pair atomic potential derived in the framework of the resonance pseudopotential theory. The calculations are performed by a recursive method with due regard for the symmetry of the defect region. The frequencies of the vacancy-induced resonance vibrations of different symmetries are determined. 相似文献
989.
Yu. M. Pechatnikov 《Technical Physics》2003,48(12):1522-1526
Transition (molecular-viscous) isothermal channel flow of rarefied gases is considered. Present-day engineering physical models of transition gas flow and methods of simulation are analyzed and verified in terms of the kinetic theory on the micro-and macrolevels. 相似文献
990.
L. M. Vasilyak M. N. Vasil’ev S. P. Vetchinin D. N. Polyakov V. E. Fortov 《Journal of Experimental and Theoretical Physics》2003,96(3):440-443
The action of an electron beam on ordered dust structures in glow and low-pressure RF discharges was studied experimentally. The electron beam produces destruction and dynamic displacement of the dust structure. In the center of a dust structure, an electron beam with a low electron energy (tens of eV) at currents up to 1 mA caused structural disordering and “melting” in the region of its action but did not excite external crystal regions. Local action of an electron beam with a high electron energy (25 keV) and a beam current above 10 mA caused deformation of the whole dust structure and shifted it in the horizontal direction so that it was carried away from the RF discharge zone. The effect of dust structure displacements can be used to locally remove particles from a plasma. 相似文献