全文获取类型
收费全文 | 290871篇 |
免费 | 1882篇 |
国内免费 | 1000篇 |
专业分类
化学 | 140957篇 |
晶体学 | 4016篇 |
力学 | 14953篇 |
综合类 | 6篇 |
数学 | 54508篇 |
物理学 | 79313篇 |
出版年
2020年 | 1971篇 |
2019年 | 2266篇 |
2018年 | 13390篇 |
2017年 | 13158篇 |
2016年 | 10187篇 |
2015年 | 3181篇 |
2014年 | 4085篇 |
2013年 | 9531篇 |
2012年 | 10524篇 |
2011年 | 18603篇 |
2010年 | 11530篇 |
2009年 | 11788篇 |
2008年 | 14499篇 |
2007年 | 16663篇 |
2006年 | 7805篇 |
2005年 | 8159篇 |
2004年 | 7624篇 |
2003年 | 7535篇 |
2002年 | 6466篇 |
2001年 | 6165篇 |
2000年 | 4947篇 |
1999年 | 3595篇 |
1998年 | 3178篇 |
1997年 | 3168篇 |
1996年 | 3004篇 |
1995年 | 2432篇 |
1994年 | 2492篇 |
1993年 | 2541篇 |
1992年 | 2644篇 |
1991年 | 2718篇 |
1990年 | 2608篇 |
1989年 | 2591篇 |
1988年 | 2519篇 |
1987年 | 2490篇 |
1986年 | 2413篇 |
1985年 | 3082篇 |
1984年 | 3236篇 |
1983年 | 2595篇 |
1982年 | 2866篇 |
1981年 | 2740篇 |
1980年 | 2547篇 |
1979年 | 2761篇 |
1978年 | 2866篇 |
1977年 | 2874篇 |
1976年 | 2847篇 |
1975年 | 2703篇 |
1974年 | 2676篇 |
1973年 | 2835篇 |
1972年 | 1892篇 |
1967年 | 1840篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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
152.
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
153.
S. P. Savin L. M. Zelenyi E. Amata J. Buechner J. Blecki S. I. Klimov B. Nikutowski J. L. Rauch S. A. Romanov A. A. Skalsky V. N. Smirnov P. Song K. Stasiewicz 《JETP Letters》2004,79(8):368-371
The study of the interaction between collisionless plasma flow and stagnant plasma revealed the presence of an outer boundary layer at the border of a geomagnetic trap, where the super-Alfvén subsonic laminar flow changes over to the dynamic regime characterized by the formation of accelerated magnetosonic jets and decelerated Alfvén flows with characteristic relaxation times of 10–20 min. The nonlinear interaction of fluctuations in the initial flow with the waves reflected from an obstacle explains the observed flow chaotization. The Cherenkov resonance of the magnetosonic jet with the fluctuation beats between the boundary layer and the incoming flow is the possible mechanism of its formation. In the flow reference system, the incoming particles are accelerated by the electric fields at the border of boundary layer that arise self-consistently as a result of the preceding wave-particle interactions; the inertial drift of the incoming ions in a transverse electric field increasing toward the border explains quantitatively the observed ion acceleration. The magnetosonic jets may carry away downstream up to a half of the unperturbed flow momentum, and their dynamic pressure is an order of magnitude higher than the magnetic pressure at the obstacle border. The appearance of nonequilibrium jets and the boundary-layer fluctuations are synchronized by the magnetosonic oscillations of the incoming flow at frequencies of 1–2 mHz. 相似文献
154.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
155.
Harish C. Bahl Stanley Zionts 《The Journal of the Operational Research Society》1987,38(12):1141-1148
Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method. 相似文献
156.
157.
158.
159.
G. E. Volovik 《JETP Letters》1997,65(7):522-527
The efficiency of conversion of the heat flux into hard x radiation (HXR) is analyzed, via time-dependent two-temperature
one-dimensional non-LTE-radiation-hydrodynamic numerical modeling, for a heat-to-radiation flux converter linked to the edge
of a low-atomic-number hot Z-pinch. The domain of parameters in this scheme is found where about the same HXR yield can be
achieved at values of input energy which are an order of magnitude lower than in the conventional scheme of a radially imploding
plasma.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 502–506 (10 April 1997)
Published in English in the original Russian Journal. Edited by Steve Torstveit. 相似文献
160.