全文获取类型
收费全文 | 407609篇 |
免费 | 3450篇 |
国内免费 | 949篇 |
专业分类
化学 | 189662篇 |
晶体学 | 6450篇 |
力学 | 21390篇 |
综合类 | 7篇 |
数学 | 59849篇 |
物理学 | 134650篇 |
出版年
2021年 | 3117篇 |
2020年 | 3329篇 |
2019年 | 3762篇 |
2018年 | 11918篇 |
2017年 | 12617篇 |
2016年 | 10500篇 |
2015年 | 4817篇 |
2014年 | 7122篇 |
2013年 | 16002篇 |
2012年 | 15760篇 |
2011年 | 24768篇 |
2010年 | 16808篇 |
2009年 | 16792篇 |
2008年 | 21812篇 |
2007年 | 24596篇 |
2006年 | 12304篇 |
2005年 | 15892篇 |
2004年 | 12517篇 |
2003年 | 11452篇 |
2002年 | 9859篇 |
2001年 | 10518篇 |
2000年 | 7932篇 |
1999年 | 5998篇 |
1998年 | 5002篇 |
1997年 | 4823篇 |
1996年 | 4645篇 |
1995年 | 3958篇 |
1994年 | 3904篇 |
1993年 | 3777篇 |
1992年 | 4159篇 |
1991年 | 4374篇 |
1990年 | 4167篇 |
1989年 | 4083篇 |
1988年 | 3862篇 |
1987年 | 3994篇 |
1986年 | 3756篇 |
1985年 | 4713篇 |
1984年 | 4777篇 |
1983年 | 3975篇 |
1982年 | 4055篇 |
1981年 | 3781篇 |
1980年 | 3734篇 |
1979年 | 4015篇 |
1978年 | 4016篇 |
1977年 | 3931篇 |
1976年 | 3940篇 |
1975年 | 3722篇 |
1974年 | 3663篇 |
1973年 | 3723篇 |
1972年 | 2638篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Infinite periodic lattices can be used as models for analyzing and understanding various properties of mechanical truss constructions with periodic structures. For infinite lattices, the problems of connectivity and stability are nontrivial from the mathematical point of view and have not been addressed adequately in the literature. In this paper, we will present a set of algebraic algorithms, which are based on ideal theory, to solve such problems.
For the understanding of the notion ``complicated three-dimensional lattices', it is essential to have this paper with colored figures.
922.
B. A. Lukiyanets 《Optics and Spectroscopy》2004,97(5):746-750
Effects related to the periodicity of the carrier dispersion relation in the reciprocal space are investigated. It is shown that, under certain conditions, magnetoabsorption in crystals exhibiting such dispersion significantly differs from the magnetoabsorption in crystals characterized by a parabolic dispersion relation for charge carriers. 相似文献
923.
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
924.
I. M. Batyaev S. M. Begel'dieva E. B. Kleshchinov S. M. Shilov 《Russian Journal of Applied Chemistry》2003,76(10):1694-1695
Synthesis and some chemical properties of the Al2O-SiO2-P2O5 system activated with MnO were studied. 相似文献
925.
An ultrasonic Doppler velocimeter (UDV) is used for an experimental investigation of turbulent pipe flow at eight different Reynolds numbers (22,300–854,900). The UDV is a multipoint probe in the sense that it takes instantaneous measurements of fluid velocities at different locations simultaneously, with remarkable resolutions in space and time. The performances of the instrument with respect to the properties of the overlap layer of the turbulent flow field are investigated; the experimental results are compared with both already existing and more recently proposed scaling laws, and with other data of experimental nature. 相似文献
926.
Nešetřil and Sopena introduced the concept of oriented game chromatic number. They asked whether the oriented game chromatic
number of partial k-trees was bounded. Here we answer their question positively.
Received: January 12, 2001 Final version received: February 25, 2002 相似文献
927.
928.
V. A. Popov S. I. Lopatin L. Sh. Tsemekhman L. A. Pavlinova S. P. Kormilitsyn V. V. Barsegyan 《Russian Journal of Applied Chemistry》2003,76(10):1564-1567
Evaporation of chromium ore and concentrates was studied using high-temperature differential mass-spectrometry. The data obtained, concerning the component vapor pressures in evaporation of complex oxide systems in the range 1700-2100 K, can be used to calculate the evaporation loss in melting and to assess the possibility of utilization of the sublimates formed. 相似文献
929.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
930.
B. Szafran P. S
p J. Adamowski S. Bednarek 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):523-529
We present a theoretical study of the charging spectra in natural and artificial atoms. We apply a model electrostatic potential created by a homogenously charged sphere. This model potential allows for a continuous passage from the Coulomb potential of the nucleus to parabolic confinement potential of quantum dots. We consider electron systems with N=1,…,10 electrons with the use of the Hartree–Fock method. We discuss the qualitative similarities and differences between the chemical potential spectrum of electron systems bound to nucleus and confined in quantum dots. 相似文献