全文获取类型
收费全文 | 194738篇 |
免费 | 2158篇 |
国内免费 | 611篇 |
专业分类
化学 | 107767篇 |
晶体学 | 3292篇 |
力学 | 7836篇 |
综合类 | 4篇 |
数学 | 18392篇 |
物理学 | 60216篇 |
出版年
2016年 | 2271篇 |
2015年 | 1685篇 |
2014年 | 2392篇 |
2013年 | 7836篇 |
2012年 | 5249篇 |
2011年 | 6608篇 |
2010年 | 4419篇 |
2009年 | 4359篇 |
2008年 | 5985篇 |
2007年 | 6154篇 |
2006年 | 5905篇 |
2005年 | 5410篇 |
2004年 | 4952篇 |
2003年 | 4424篇 |
2002年 | 4304篇 |
2001年 | 5777篇 |
2000年 | 4388篇 |
1999年 | 3513篇 |
1998年 | 2742篇 |
1997年 | 2779篇 |
1996年 | 2726篇 |
1995年 | 2521篇 |
1994年 | 2395篇 |
1993年 | 2290篇 |
1992年 | 2786篇 |
1991年 | 2668篇 |
1990年 | 2617篇 |
1989年 | 2640篇 |
1988年 | 2579篇 |
1987年 | 2587篇 |
1986年 | 2402篇 |
1985年 | 3269篇 |
1984年 | 3285篇 |
1983年 | 2713篇 |
1982年 | 2910篇 |
1981年 | 2848篇 |
1980年 | 2756篇 |
1979年 | 2898篇 |
1978年 | 3141篇 |
1977年 | 2960篇 |
1976年 | 2897篇 |
1975年 | 2754篇 |
1974年 | 2702篇 |
1973年 | 2715篇 |
1972年 | 1759篇 |
1971年 | 1467篇 |
1968年 | 1930篇 |
1967年 | 2129篇 |
1966年 | 1921篇 |
1965年 | 1497篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
The consequences of Ge deposition on Br-terminated Si(1 0 0) were studied with scanning tunneling microscopy at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This is possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. The deposition of 7 ML of Ge resulted in a rough surface characterized by irregularly shaped clusters. A short 800 K anneal desorbed the Br and allowed Ge atoms to reorganize into the more energetically favorable “hut” structures produced by conventional Ge overlayer growth on Si(1 0 0). 相似文献
92.
M. A. H. Dempster 《Journal of Mathematical Sciences》2006,133(4):1422-1444
This paper gives a comprehensive treatment of EVPI-based sequential importance sampling algorithms for dynamic (multistage)
stochastic programming problems. Both theory and computational algorithms are discussed. Under general assumptions it is shown
that both an expected value of perfect information (EVPI) process and the corresponding marginal EVPI process (the supremum
norm of the conditional expectation of its generalized derivative) are nonanticipative nonnegative supermartingales. These
processes are used as importance criteria in the class of sampling algorithms treated in the paper. When their values are
negligible at a node of the current sample problem scenario tree, scenarios descending from the node are replaced by a single
scenario at the next iteration. On the other hand, high values lead to increasing the number of scenarios descending from
the node. Both the small sample and asymptotic properties of the sample problem estimates arising from the algorithms are
established, and the former are evaluated numerically in the context of a financial planning problem. Finally, current and
future research is described. Bibliography: 49 titles.
__________
Published in Zapiski Nauchnykh Seminarov POMI, Vol. 312, 2004, pp. 94–129. 相似文献
93.
V. De Sabbata C. Sivaram H.-H. v. Borzeszkowski H.-J. Treder 《Annalen der Physik》1991,503(7):497-502
It is shown that in gravitational theories with torsion one is led to commutation rules corresponding to Landau-Peierls type uncertainty relations. 相似文献
94.
95.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
96.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
97.
P. David J. Hartfiel H. Janszen R. von Mutius J. Arvieux L. Farvacque B. Berthier B. Bonin J. C. Lugol 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(4):367-372
The excitation function of the fission probability P E E x) for238U has been measured in the reaction238U(α, α′ f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowB nf , the threshold for second chance fission, and aboveB nf up toE x =37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityP f at excitation energies well aboveB nE . The role of the quasi-elastic knock-out process in this reaction is discussed. 相似文献
98.
H. Mazaheri 《分析论及其应用》2006,22(2):141-145
The concepts of quasi-Chebyshev and weakly-Chebyshev and σ-Chebyshev were defined [3 - 7], andas a counterpart to best approximation in normed linear spaces, best coapprozimation was introduced by Franchetti and Furi^[1]. In this research, we shall define τ-Chebyshev subspaces and τ-cochebyshev subspaces of a Banach space, in which the property τ is compact or weakly-compact, respectively. A set of necessary and sufficient theorems under which a subspace is τ-Chebyshev is defined. 相似文献
99.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement. 相似文献
100.
Johan Håstad 《Random Structures and Algorithms》2006,29(4):466-474
We show that the operations of permuting columns and rows separately and independently mix a square matrix in constant time. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献