全文获取类型
收费全文 | 468950篇 |
免费 | 4009篇 |
国内免费 | 1306篇 |
专业分类
化学 | 236050篇 |
晶体学 | 7473篇 |
力学 | 23621篇 |
综合类 | 17篇 |
数学 | 56781篇 |
物理学 | 150323篇 |
出版年
2021年 | 4301篇 |
2020年 | 4563篇 |
2019年 | 5301篇 |
2018年 | 7403篇 |
2017年 | 7591篇 |
2016年 | 10327篇 |
2015年 | 5665篇 |
2014年 | 9731篇 |
2013年 | 21701篇 |
2012年 | 16841篇 |
2011年 | 20127篇 |
2010年 | 15226篇 |
2009年 | 15315篇 |
2008年 | 18407篇 |
2007年 | 18275篇 |
2006年 | 16651篇 |
2005年 | 14570篇 |
2004年 | 13649篇 |
2003年 | 12174篇 |
2002年 | 12193篇 |
2001年 | 14155篇 |
2000年 | 10482篇 |
1999年 | 8095篇 |
1998年 | 6825篇 |
1997年 | 6731篇 |
1996年 | 6229篇 |
1995年 | 5455篇 |
1994年 | 5503篇 |
1993年 | 5281篇 |
1992年 | 5898篇 |
1991年 | 6189篇 |
1990年 | 5836篇 |
1989年 | 5852篇 |
1988年 | 5557篇 |
1987年 | 5691篇 |
1986年 | 5345篇 |
1985年 | 6794篇 |
1984年 | 6951篇 |
1983年 | 5770篇 |
1982年 | 5806篇 |
1981年 | 5586篇 |
1980年 | 5344篇 |
1979年 | 5887篇 |
1978年 | 5833篇 |
1977年 | 6015篇 |
1976年 | 5990篇 |
1975年 | 5654篇 |
1974年 | 5545篇 |
1973年 | 5659篇 |
1972年 | 4142篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
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
172.
For three‐dimensional flows with one inhomogeneous spatial coordinate and two periodic directions, the Karhunen–Loeve procedure is typically formulated as a spatial eigenvalue problem. This is normally referred to as the direct method (DM). Here we derive an equivalent formulation in which the eigenvalue problem is formulated in the temporal coordinate. It is shown that this so‐called method of snapshots (MOS) has some numerical advantages when compared to the DM. In particular, the MOS can be formulated purely as a matrix composed of scalars, thus avoiding the need to construct a matrix of matrices as in the DM. In addition, the MOS avoids the need for so‐called weight functions, which emerge in the DM as a result of the non‐uniform grid typically employed in the inhomogeneous direction. The avoidance of such weight functions, which may exhibit singular behaviour, guarantees satisfaction of the boundary conditions. The MOS is applied to data sets recently obtained from the direct simulation of turbulence in a channel in which viscoelasticity is imparted to the fluid using a Giesekus model. The analysis reveals a steep drop in the dimensionality of the turbulence as viscoelasticity is increased. This is consistent with the results that have been obtained with other viscoelastic models, thus revealing an essential generic feature of polymer‐induced drag reduced turbulent flows. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
173.
A new grid‐free upwind relaxation scheme for simulating inviscid compressible flows is presented in this paper. The non‐linear conservation equations are converted to linear convection equations with non‐linear source terms by using a relaxation system and its interpretation as a discrete Boltzmann equation. A splitting method is used to separate the convection and relaxation parts. Least squares upwinding is used for discretizing the convection equations, thus developing a grid‐free scheme which can operate on any arbitrary distribution of points. The scheme is grid free in the sense that it works on any arbitrary distribution of points and it does not require any topological information like elements, faces, edges, etc. This method is tested on some standard test cases. To explore the power of the grid‐free scheme, solution‐based adaptation of points is done and the results are presented, which demonstrate the efficiency of the new grid‐free scheme. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
174.
175.
176.
A. P. S. Selvadurai 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1987,38(5):674-688
The paper examines the problem related to the axisymmetric interaction between an external circular crack and a centrally placed penny-shaped rigid inclusion located in the plane of the crack. The interface between the inclusion and the elastic medium exhibits a Mindlin-type imperfect bi-lateral contact. Analytical results presented in the paper illustrate the manner in which the lateral translational stiffness of the inclusion and the stress intensity factor at the boundary of the external circular crack are influenced by the inclusion/crack radii ratio. 相似文献
177.
N. I. Alekseev V. B. Kaplan A. M. Martsinovskii I. I. Stolyarov 《Technical Physics》1997,42(6):599-605
Results are presented from a systematic investigation of the conditions under which anomalously high rates of plasma generation
are observed in the anode region of a low-voltage Knudsen arc in grid plasma switch elements. The phenomenon develops over
a wide range of currents and switched voltages under conditions for which the plasma density in the cathode-grid region is
noticeably higher than the density in the anode region. and its onset is characterized by a pronounced pressure threshold
of ∼2×10−2 Torr. The results are analyzed from the standpoint of the possible mechanisms for anomalous plasma generation — collisional
nonresonance diffusion of electrons in velocity space, leading to enrichment of the distribution function in fast particles,
and the collapse of Langmuir waves in the gap at the high energies of the beam produced when the wires of the grid are bridged
by the quenching pulse and and the current is blocked.
Zh. Tekh. Fiz. 67, 15–21 (June 1997) 相似文献
178.
S. M. Dunaevskii A. L. Malyshev V. A. Trunov V. V. Popov 《Physics of the Solid State》1997,39(10):1636-1637
The results of investigating the temperature dependence of the resistivity, the differential magnetic susceptibility, and
the magnetoresistance of a partially substituted perovskite Sm1−x
SrxMnO3 (x=0.16–0.4) are presented. Colossal intrinsic magnetoresistance, reaching 90% in an external magnetic field of 30 kOe, is discovered
in the compound with x=0.30 at 77 K.
Fiz. Tverd. Tela (St. Petersburg) 39, 1831–1832 (October 1997) 相似文献
179.
Consideration is given to the special features of the excitation of spectra of metals (Ag, Au, Fe, Hg, Pt, and Sb) that manifest
themselves in investigating spectral sources with combined glow discharge (glow discharge and capillary discharge). It is
established that the proposed method for introducing a substance into a plasma makes it possible to realize two fundamentally
different regimes: without evaporation and with complete evaporation and matrix atomization. It is shown that a spectral source
of combined glow discharge with a nonequilibrium plasma has significant advantages for the most important analytical characteristics
over quasi-equilibrium combined discharge at atmospheric pressure. The gold and platinum sensitivity in combined glow discharge
is 10−7%, and the reproducibility of spectral determinations is 0.001–0.100, depending on the measurement range. A fractional separation
of elements that makes it possible to analyze the phase composition of substances, particularly metals, with high sensitivity
is revealed in glow discharge.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 143–147, March–April, 1997. 相似文献
180.
S. Gukov 《JETP Letters》1997,65(8):694-700
The manifestly supersymmetric four-dimensional Wess-Zumino model with quenched disorder is considered at the one-loop level.
The infrared fixed points of a beta function form the moduli space ℳ=RP
2, where two types of phases are found: with and without replica symmetry. While the former phase possesses only a trivial
fixed point, this point become unstable in the latter phase, which may be interpreted as a spin glass phase.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 657–662 (25 April 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献