全文获取类型
收费全文 | 676956篇 |
免费 | 6423篇 |
国内免费 | 1800篇 |
专业分类
化学 | 353655篇 |
晶体学 | 10211篇 |
力学 | 32246篇 |
综合类 | 19篇 |
数学 | 83693篇 |
物理学 | 205355篇 |
出版年
2021年 | 5785篇 |
2020年 | 6280篇 |
2019年 | 7063篇 |
2018年 | 9338篇 |
2017年 | 9427篇 |
2016年 | 13272篇 |
2015年 | 7488篇 |
2014年 | 12241篇 |
2013年 | 29342篇 |
2012年 | 22170篇 |
2011年 | 26635篇 |
2010年 | 19708篇 |
2009年 | 19470篇 |
2008年 | 24904篇 |
2007年 | 24890篇 |
2006年 | 22802篇 |
2005年 | 20420篇 |
2004年 | 19017篇 |
2003年 | 17090篇 |
2002年 | 16901篇 |
2001年 | 18702篇 |
2000年 | 14518篇 |
1999年 | 11293篇 |
1998年 | 9555篇 |
1997年 | 9501篇 |
1996年 | 8971篇 |
1995年 | 8112篇 |
1994年 | 8030篇 |
1993年 | 7759篇 |
1992年 | 8497篇 |
1991年 | 8865篇 |
1990年 | 8553篇 |
1989年 | 8518篇 |
1988年 | 8275篇 |
1987年 | 8158篇 |
1986年 | 7751篇 |
1985年 | 9924篇 |
1984年 | 10317篇 |
1983年 | 8672篇 |
1982年 | 9055篇 |
1981年 | 8532篇 |
1980年 | 8185篇 |
1979年 | 8784篇 |
1978年 | 9263篇 |
1977年 | 9071篇 |
1976年 | 8945篇 |
1975年 | 8530篇 |
1974年 | 8340篇 |
1973年 | 8618篇 |
1972年 | 6213篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
C.H. Chen 《Journal of sound and vibration》2003,263(4):797-813
A neural-network-based method is offered to determine the flutter derivatives of section models under smooth and turbulent flows. The approach uses the observed dynamic responses to train an appropriate neural network. Subsequently, the modal parameters of the model for different mean velocities of wind flow are directly estimated using weight matrices in the neural network. The flutter derivatives can then be determined accurately. The validity of the present method is verified through numerical studies. Finally, the procedure is employed to process experimental data from an inverted-U-type section model, obtained from wind tunnel tests. 相似文献
992.
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
993.
994.
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
995.
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
996.
Jayanth R. Banavar Oscar Gonzalez John H. Maddocks Amos Maritan 《Journal of statistical physics》2003,110(1-2):35-50
Physical strands or sheets that can be modelled as curves or surfaces embedded in three dimensions are ubiquitous in nature, and are of fundamental importance in mathematics, physics, biology, and engineering. Often the physical interpretation dictates that self-avoidance should be enforced in the continuum model, i.e., finite energy configurations should not self-intersect. Current continuum models with self-avoidance frequently employ pairwise repulsive potentials, which are of necessity singular. Moreover the potentials do not have an intrinsic length scale appropriate for modelling the finite thickness of the physical systems. Here we develop a framework for modelling self-avoiding strands and sheets which avoids singularities, and which provides a way to introduce a thickness length scale. In our approach pairwise interaction potentials are replaced by many-body potentials involving three or more points, and the radii of certain associated circles or spheres. Self-interaction energies based on these many-body potentials can be used to describe the statistical mechanics of self-interacting strands and sheets of finite thickness. 相似文献
997.
998.
It is a well-known feature of odd space-time dimensions d that there exist two inequivalent fundamental representations A and B of the Dirac gamma matrices. Moreover, the parity transformation swaps the fermion fields living in A and B. As a consequence, a parity-invariant Lagrangian can only be constructed by incorporating both the representations. Based upon these ideas and contrary to long-held belief, we show that in addition to a discrete exchange symmetry for the massless case, we can also define chiral symmetry provided the Lagrangian contains fields corresponding to both the inequivalent representations. We also study the transformation properties of the corresponding chiral currents under parity and charge-conjugation operations. We work explicitly in 2 + 1 dimensions and later show how some of these ideas generalize to an arbitrary number of odd dimensions. 相似文献
999.
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
1000.