全文获取类型
收费全文 | 268824篇 |
免费 | 2480篇 |
国内免费 | 1138篇 |
专业分类
化学 | 139428篇 |
晶体学 | 3929篇 |
力学 | 11198篇 |
综合类 | 14篇 |
数学 | 35679篇 |
物理学 | 82194篇 |
出版年
2020年 | 1779篇 |
2019年 | 2044篇 |
2018年 | 3619篇 |
2017年 | 3788篇 |
2016年 | 4467篇 |
2015年 | 3102篇 |
2014年 | 4317篇 |
2013年 | 11731篇 |
2012年 | 10919篇 |
2011年 | 12083篇 |
2010年 | 8090篇 |
2009年 | 7799篇 |
2008年 | 9454篇 |
2007年 | 9663篇 |
2006年 | 8892篇 |
2005年 | 12014篇 |
2004年 | 10648篇 |
2003年 | 8364篇 |
2002年 | 6566篇 |
2001年 | 7404篇 |
2000年 | 5434篇 |
1999年 | 4353篇 |
1998年 | 3631篇 |
1997年 | 3627篇 |
1996年 | 3320篇 |
1995年 | 3159篇 |
1994年 | 2975篇 |
1993年 | 3013篇 |
1992年 | 3420篇 |
1991年 | 3461篇 |
1990年 | 3244篇 |
1989年 | 3178篇 |
1988年 | 3230篇 |
1987年 | 3075篇 |
1986年 | 2954篇 |
1985年 | 4017篇 |
1984年 | 4170篇 |
1983年 | 3419篇 |
1982年 | 3765篇 |
1981年 | 3655篇 |
1980年 | 3528篇 |
1979年 | 3573篇 |
1978年 | 3794篇 |
1977年 | 3621篇 |
1976年 | 3884篇 |
1975年 | 3419篇 |
1974年 | 3552篇 |
1973年 | 3855篇 |
1972年 | 2360篇 |
1971年 | 1810篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
H. Fawcett S. Barlag H. Becker E. Belau T. Böhringer M. Bosman V. Castillo V. Chabaud D. Bucholz C. Damerell C. Daum G. De Rijk H. Dietl S. Gill A. Gillman R. Gilmore T. Gooch P. Gras Z. Hajduk E. Higon B. Hyams D. Kelsey J. Kemmer R. Klanner U. Kötz S. Kwan B. Lücking G. Lütjens G. Lutz J. Malos W. Männer E. Neugebauer H. Palka M. Pepé G. Polok J. Richardson M. Rozanska K. Rybicki H. Seebrunner U. Stierlin R. Tapper H. Tiecke M. Turala G. Waltermann S. Watts P. Weilhammer F. Wickens L. Wiggers A. Wylie T. Zeludziewicz ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1990,46(4):513-519
The production of the neutralK ? (892) resonances by 200 GeVK ? andπ ? has been studied over the kinematic range 0.0<x f<1.0 andp t 2 <5.0 GeV2. Longitudinal and transverse momentum distributions are presented. In addition the decay angular distributions inK ? fragmentation to \(\bar K^{0*} \) have been investigated. 相似文献
992.
The development and the use of the diamond anvil cell for Mössbauer Spectroscopy (MS) to pressures nearing 100 GPa are discussed. Three types of cells and their typical performance are given. Pressure calibration, hydrostatic media, gasketing, collimation, -ray absorption, and sample size for MS are reviewed. New MS results showing hysteresis in the room temperature high pressure transition in iron and showing the rapid rise ofT
N in NiI2 with pressure are presented. 相似文献
993.
D. R. Rowland 《Optical and Quantum Electronics》1990,22(4):369-373
A geometrical method for determining the power transfer between piecewise uniform, alternating , twin-core linear directional couplers is presented. Phase space provides the basis for the method. 相似文献
994.
We use the topological tool of Nielsen fixed-point theory to study the controllability of perturbed linear control processes whose control space can be reduced to a finite-dimensional one. These methods produce a lower bound on the number of controls that achieve a given target. We concentrate particularly on the case where the perturbation has sublinear growth, and we exhibit examples of multiple controls of various types that are detected by the Nielsen theory method.This research was partly supported by the Research Grant Teoria del Controllo dei Sistemi Dinamici, Ministero della Pubblica Istruzione, Roma, Italy. 相似文献
995.
Chvátal introduced the idea of viewing cutting planes as a system for proving that every integral solution of a given set of linear inequalities satisfies another given linear inequality. This viewpoint has proven to be very useful in many studies of combinatorial and integer programming problems. The basic ingredient in these cutting-plane proofs is that for a polyhedronP and integral vectorw, if max(wx|x P, wx integer} =t, thenwx t is valid for all integral vectors inP. We consider the variant of this step where the requirement thatwx be integer may be replaced by the requirement that
be integer for some other integral vector
. The cutting-plane proofs thus obtained may be seen either as an abstraction of Gomory's mixed integer cutting-plane technique or as a proof version of a simple class of the disjunctive cutting planes studied by Balas and Jeroslow. Our main result is that for a given polyhedronP, the set of vectors that satisfy every cutting plane forP with respect to a specified subset of integer variables is again a polyhedron. This allows us to obtain a finite recursive procedure for generating the mixed integer hull of a polyhedron, analogous to the process of repeatedly taking Chvátal closures in the integer programming case. These results are illustrated with a number of examples from combinatorial optimization. Our work can be seen as a continuation of that of Nemhauser and Wolsey on mixed integer cutting planes.Supported by Sonderforschungsbereich 303 (DFG) and by NSF Grant Number ECS-8611841.Supported by NSF Grant Number ECS-8418392 and Sonderforschungsbereich 303 (DFG), Institut für Ökonometrie und Operations Research, Universität Bonn, FR Germany. 相似文献
996.
K.J. Devlin has extended Jensen's construction of a model ofZFC andCH without Souslin trees to a model without Kurepa trees either. We modify the construction again to obtain a model with these properties, but in addition, without Kurepa trees inccc-generic extensions. We use a partially defined -sequence, given by a fine structure lemma. We also show that the usual collapse of Mahlo to
2 will give a model without Kurepa trees not only in the model itself, but also inccc-extensions. 相似文献
997.
It is proved that if a graphG has maximum degreed, then its vertices can be represented by distinct unit vectors inR
2d so that two vectors are orthogonal if and only if the corresponding vertices are adjacent. As a corollary it follows that if a graph has maximum degreed, then it is isomorphic to a unit distance graph inR
2d. 相似文献
998.
Joel L. Lebowitz Christian Maes Eugene R. Speer 《Journal of statistical physics》1990,59(1-2):117-170
We investigate the behavior of discrete-time probabilistic cellular automata (PCA), which are Markov processes on spin configurations on ad-dimensional lattice, from a rigorous statistical mechanics point of view. In particular, we exploit, whenever possible, the correspondence between stationary measures on the space-time histories of PCAs on
d
and translation-invariant Gibbs states for a related Hamiltonian on (
d+1). This leads to a simple large-deviation formula for the space-time histories of the PCA and a proof that in a high-temperature regime the stationary states of the PCA are Gibbsian. We also obtain results about entropy, fluctuations, and correlation inequalities, and demonstrate uniqueness of the invariant state and exponential decay of correlations in a high-noise regime. We discuss phase transitions in the low-noise (or low-temperature) regime and review Toom's proof of nonergodicity of a certain class of PCAs. 相似文献
999.
We investigate the topology of the phase diagram of binary alloys on the fee lattice with first-neighbor antiferromagnetic interactions around the superdegenerate point, where the L10 and L12 phases meet. We treat the system as a hard-constraint lattice gas, following a procedure previously described by Lebowitzet al. We perform cluster variation method calculations in theT0 limit and Monte Carlo simulations directly atT=0 K on the ground states of the superdegenerate point. We find that: (i) there is no disordered phase in the neighborhood of this point; (ii) a phase L for which two of the four cubic sublattices have the same average occupancy and each of the two others are different appears between L10 and L12; (iii) the transition L/L12 is of first order. 相似文献
1000.
For an exactly soluble classical spin model with long-range inhomogeneous coupling it is proved that in the absence of external magnetic field the free energy is aC
function of the temperature at the critical point. 相似文献