全文获取类型
收费全文 | 642307篇 |
免费 | 6905篇 |
国内免费 | 1963篇 |
专业分类
化学 | 323382篇 |
晶体学 | 9323篇 |
力学 | 33024篇 |
综合类 | 22篇 |
数学 | 97672篇 |
物理学 | 187752篇 |
出版年
2021年 | 5020篇 |
2020年 | 5412篇 |
2019年 | 6133篇 |
2018年 | 17779篇 |
2017年 | 17479篇 |
2016年 | 17470篇 |
2015年 | 7868篇 |
2014年 | 11592篇 |
2013年 | 26278篇 |
2012年 | 23461篇 |
2011年 | 33858篇 |
2010年 | 22919篇 |
2009年 | 23297篇 |
2008年 | 28641篇 |
2007年 | 30326篇 |
2006年 | 20816篇 |
2005年 | 19615篇 |
2004年 | 18535篇 |
2003年 | 17040篇 |
2002年 | 16089篇 |
2001年 | 17106篇 |
2000年 | 13048篇 |
1999年 | 10128篇 |
1998年 | 8446篇 |
1997年 | 8260篇 |
1996年 | 7985篇 |
1995年 | 7134篇 |
1994年 | 7068篇 |
1993年 | 6831篇 |
1992年 | 7614篇 |
1991年 | 7787篇 |
1990年 | 7420篇 |
1989年 | 7298篇 |
1988年 | 7263篇 |
1987年 | 7133篇 |
1986年 | 6745篇 |
1985年 | 8705篇 |
1984年 | 8907篇 |
1983年 | 7165篇 |
1982年 | 7261篇 |
1981年 | 7184篇 |
1980年 | 6668篇 |
1979年 | 7307篇 |
1978年 | 7437篇 |
1977年 | 7464篇 |
1976年 | 7407篇 |
1975年 | 6834篇 |
1974年 | 6736篇 |
1973年 | 6893篇 |
1972年 | 4989篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Journal of Statistical Physics - We study high-energy asymptotics of the steady velocity distributions for model kinetic equations describing various regimes in dilute granular flows. The main... 相似文献
992.
The kinetics of formation and relaxation of transient holographic gratings recorded in a system of saturable three-level centers is studied. Distortions in the shape of the profile of recorded and decaying structures of population and of the refractive index are taken into account. The analysis of the time dependences of diffraction efficiencies of different orders is performed for phase (thermal) and amplitude (concentration) gratings. 相似文献
993.
994.
We examine several interesting relationships and expressions involving Fourier-Feynman transform, convolution product and
first variation for functionals in the Fresnel class F(B) of an abstract Wiener space B. We also prove a translation theorem and Parseval's identity for the analytic Feynman integral.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
995.
In the direct simulation Monte‐Carlo (DSMC) method for simulating rarefied gas flows, the velocities of simulator particles that cross a simulation boundary and enter the simulation space are typically generated using the acceptance–rejection procedure that samples the velocities from a truncated theoretical velocity distribution that excludes low and high velocities. This paper analyses an alternative technique, where the velocities of entering particles are obtained by extending the simulation procedures to a region adjacent to the simulation space, and considering the movement of particles generated within that region during the simulation time step. The alternative method may be considered as a form of acceptance–rejection procedure, and permits the generation of all possible velocities, although the population of high velocities is depleted with respect to the theoretical distribution. Nevertheless, this is an improvement over the standard acceptance–rejection method. Previous implementations of the alternative method gave a number flux lower than the theoretical number required. Two methods for obtaining the correct number flux are presented. For upstream boundaries in high‐speed flows, the alternative method is more computationally efficient than the acceptance–rejection method. However, for downstream boundaries, the alternative method is extremely inefficient. The alternative method, with the correct theoretical number flux, should therefore be used in DSMC computations in favour of the acceptance–rejection method for upstream boundaries in high‐speed flows. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
996.
Jacob Schach Møller 《Annales Henri Poincare》2005,6(6):1091-1135
In this paper we analyze the bottom of the energy-momentum spectrum of the translation invariant Nelson model, describing
one electron linearly coupled to a second quantized massive scalar field. Our results are valid for all values of the coupling
constant and include an HVZ theorem, non-degeneracy of ground states, existence of isolated groundstates in dimensions 1 and
2, non-existence of ground states embedded in the bottom of the essential spectrum in dimensions 3 and 4, (i.e., at total
momenta where no isolated groundstate eigenvalue exists), and we study regularity and monotonicity properties of the bottom
of the essential spectrum, as a function of total momentum.
Communicated by Joel Feldman
submitted 04/11/04, accepted 17/02/05 相似文献
997.
998.
K. K. Turgunov B. Tashkhodzhaev L. V. Molchanov Kh. M. Shakhidoyatov 《Journal of Structural Chemistry》2004,45(5):912-916
The structure of bis-(2,3-pentamethylene-3,4-dihydro-4-oxoquinazolinium) tetrachlorocuprate (II) sesquihydrate, (C13H15N2O)2[CuCl4]·1.5H2O, was determined by single crystal X-ray diffraction. In contrast to the previously studied analogs, the compound contains crystallization water molecules.Original Russian Text Copyright © 2004 by K. K. Turgunov, B. Tashkhodzhaev, L. V. Molchanov, and Kh. M. Shakhidoyatov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 955–959, September–October, 2004. 相似文献
999.
1000.
Lígia M. Rodrigues 《Tetrahedron》2004,60(40):8929-8936
Tetrapeptides containing one of a set of four different α,α-dialkyl glycines at the C-terminus were synthesized by conventional methods in solution and their conformational behavior investigated by 1H NMR spectroscopy in connection with molecular mechanics calculations. The results were consistent with conformations stabilized by a γ-turn in the case of compounds with alkyl groups larger than methyl, while the corresponding Aib derivative did not exhibit intramolecular hydrogen bonding. 相似文献