全文获取类型
收费全文 | 71221篇 |
免费 | 1448篇 |
国内免费 | 349篇 |
专业分类
化学 | 34900篇 |
晶体学 | 468篇 |
力学 | 2301篇 |
综合类 | 22篇 |
数学 | 15565篇 |
物理学 | 19762篇 |
出版年
2023年 | 233篇 |
2021年 | 415篇 |
2020年 | 583篇 |
2019年 | 441篇 |
2018年 | 1707篇 |
2017年 | 1921篇 |
2016年 | 1839篇 |
2015年 | 1515篇 |
2014年 | 1574篇 |
2013年 | 2992篇 |
2012年 | 5005篇 |
2011年 | 4592篇 |
2010年 | 3012篇 |
2009年 | 2549篇 |
2008年 | 2684篇 |
2007年 | 2663篇 |
2006年 | 2439篇 |
2005年 | 6080篇 |
2004年 | 5227篇 |
2003年 | 3467篇 |
2002年 | 1578篇 |
2001年 | 1183篇 |
2000年 | 866篇 |
1999年 | 679篇 |
1998年 | 557篇 |
1997年 | 524篇 |
1996年 | 621篇 |
1995年 | 538篇 |
1994年 | 559篇 |
1993年 | 635篇 |
1992年 | 671篇 |
1991年 | 537篇 |
1990年 | 555篇 |
1989年 | 465篇 |
1988年 | 452篇 |
1987年 | 406篇 |
1986年 | 366篇 |
1985年 | 537篇 |
1984年 | 504篇 |
1983年 | 461篇 |
1982年 | 469篇 |
1981年 | 484篇 |
1980年 | 431篇 |
1979年 | 410篇 |
1978年 | 446篇 |
1977年 | 421篇 |
1976年 | 433篇 |
1975年 | 373篇 |
1974年 | 365篇 |
1973年 | 372篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Montgomery and Vaughan improved a theorem of Erd?s and Fuchs for an arbitrary sequence. Sárközy extended this theorem of Erd?s and Fuchs for two arbitrary sequences which are "near" in a certain sense. Using the idea of Jurkat (differentiation of the generating function), we will extend similarly the result of Montgomery and Vaughan for "sufficiently near" sequences. 相似文献
72.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献
73.
B. Sun Yu. A. Litvinov P. M. Walker K. Beckert P. Beller F. Bosch D. Boutin C. Brandau L. Chen C. Dimopoulou H. Geissel R. Knöbel C. Kozhuharov J. Kurcewicz S. A. Litvinov M. Mazzocco J. Meng C. Nociforo F. Nolden W. R. Plass C. Scheidenberger M. Steck H. Weick M. Winkler 《The European Physical Journal A - Hadrons and Nuclei》2007,31(3):393-394
A new long-lived isomeric state in the near proton dripline nucleus 125Ce has been identified with Schottky mass spectrometry at GSI. The excitation energy E
* = 103(12)keV and the decay time of 193(1)s have been obtained from a single stored fully ionized 125m
Ce58+ ion. The data implies an E3 transition and a 1/2+ assignment for the spin of the isomer. 相似文献
74.
Søren Riis 《Archive for Mathematical Logic》1997,36(3):157-188
For each there exists a model of which satisfies the Count() principle. Furthermore, if contains all prime factors of there exist and a bijective map mapping onto . A corollary is a complete classification of the Count() versus Count() problem. Another corollary shows that the pigeon-hole principle for injective maps does not follow from any of the Count() principles. This solves an open question [Ajtai 94].
Received August 16, 1994 / Revised version received April 29, 1996 相似文献
75.
76.
We study general relativity in the framework of non-commutative differential geometry. As a prerequisite we develop the basic notions of non-commutative Riemannian geometry, including analogues of Riemannian metric, curvature and scalar curvature. This enables us to introduce a generalized Einstein-Hilbert action for non-commutative Riemannian spaces. As an example we study a space-time which is the product of a four dimensional manifold by a two-point space, using the tools of non-commutative Riemannian geometry, and derive its generalized Einstein-Hilbert action. In the simplest situation, where the Riemannian metric is taken to be the same on the two copies of the manifold, one obtains a model of a scalar field coupled to Einstein gravity. This field is geometrically interpreted as describing the distance between the two points in the internal space.Dedicated to H. ArakiSupported in part by the Swiss National Foundation (SNF) 相似文献
77.
P E S?rensen R A McClelland R D Gandour 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(6):558-566
The ring-chain tautomerism in aqueous solution of some aryl-substituted morpholinium salts (bromides), has been studied and equilibrium constants are reported. In the crystals the substrates exist entirely in their cyclic forms as hemiacetals, but in aqueous solution NMR measurements reveal that an equilibrium is established between the cyclic (hemiacetal) and the noncyclic (ketone) form, the degree of ring-opening being more pronounced with electron-donating aryl substituents at the carbonyl carbon. The kinetics of the ring-chain interconversion in water has been investigated spectrophotometrically by a 'pH jump' stopped-flow technique. General base catalysis is observed with a Br?nsted beta value apparently independent of substituent and equal to 0.60. The Hammett rho values for various base catalysts are close to those for very similar intermolecular reactions involving hemiacetal breakdown, leading to the suggestion of a 'normal' class n mechanism for base catalysis. For acid catalysis, however, a quite different situation is encountered, since no general acid but only (weak) catalysis by the hydronium ion can be detected. We believe this deviation from 'normal' general acid catalysis is caused by an electrostatic interaction, and we suggest that it might result from a change in the usual class e mechanism for general acid catalysis by a situation in which rate-limiting concerted proton transfer is replaced by rate-limiting preprotonation. This is supported by the observed drastic change in Hammett rho value for catalysis by the hydronium ion, compared with the 'normal' case. An interesting case is encountered for the 4-aminophenyl-substituted substrate, in which the amino group becomes protonated in acid solution, thus representing a new substituent. Despite this complication, the various equilibrium and rate constants may also be evaluated experimentally for this substrate. 相似文献
78.
79.
The focus of this paper is on the following problem. Given a linear space F of complex-valued functions on a set X and a polynomial p(z), is there an algebraic composition operator on F whose characteristic polynomial equals p(z)? We show that the supply of all the polynomials p(z) for which the answer to this question is affirmative depends heavily on the structure of the space F. 相似文献
80.
F. Cannata J. P. Dedonder L. Le?niak 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(4):451-460
We investigate the origin of the attraction in theK¯K channel around the threshold by introducing an additional channel to theππ andK¯K channels in a separable potential formalism assuming, in general, no direct interaction in theK¯K channel. To reproduce the features of the data, we find that the threshold of the additional channel is much above thef 0(975) meson position. We show that this three-channel problem can be reduced to an effective two-channel problem where thef 0(975) behaves as if it were aK¯K molecule bound by the coupling to the exotic channel. This picture is also supported by the fact that a single pole only, in the complexK¯K momentum plane, is associated to thef 0(975) meson. Various physical observables, like the decay branching ratio and theK¯K scattering length, are then discussed in an effective two-channel framework. 相似文献