全文获取类型
收费全文 | 727篇 |
免费 | 15篇 |
国内免费 | 15篇 |
专业分类
化学 | 380篇 |
晶体学 | 20篇 |
力学 | 30篇 |
数学 | 153篇 |
物理学 | 174篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 20篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 120篇 |
2012年 | 32篇 |
2011年 | 32篇 |
2010年 | 30篇 |
2009年 | 25篇 |
2008年 | 29篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1990年 | 3篇 |
1987年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 5篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1965年 | 8篇 |
1964年 | 4篇 |
1963年 | 3篇 |
1962年 | 11篇 |
1960年 | 4篇 |
1959年 | 3篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1933年 | 4篇 |
1923年 | 2篇 |
排序方式: 共有757条查询结果,搜索用时 15 毫秒
61.
Combined experimental and computational studies on molecular structure of newly synthesised transtirans 1,2,3-tribromo-1,2,3-trihydro-1H-benz[f]indene (TTTBI) were reported. Also, only computational studies were done for cis-trans-1,2,3-tribromo-1,2,3-trihydro-1H-benz[f]indene (CTTBI) and cis-cis-1,2,3-tribromo-1,2,3-trihydro-1H-benz[f]indene (CCTBI) in order to understand the vibrational spectra and molecular parameters of them. The geometry optimization
and vibrational wave numbers of the title molecules were carried out with the Gaussian98 program package by using Hartree-Fock
(HF) and Density Functional Theory (DFT) with B3LYP functional and 6–31G (d) basis set. All calculations were done for the
title compounds in their ground states. Especially for CTTBI and CCTBI, which could not be synthesized yet, these kind of
pre-calculations take an important role for their synthesis process. Also crystal structural parameters of TTTBI by single-crystal
X-ray diffraction method was used as input for computational study of it. Observed and calculated vibrational wave numbers
were compared. Because the use of benz[f]indene as a cyclopentadienyl ligand attracted much attention because an annulated
benzo ring might increase both the stereocontrol and productivity of catalytic system, TTTBI and other computationally studied
and modeled two molecules may play an important role of other types of compounds as a starting structures. 相似文献
62.
It is shown that a mixed Ricci-flat twisted product semi-Riemannian manifold can be expressed as a warped product semi-Riemannian
manifold. As a consequence, any Einstein twisted product semi-Riemannian manifold is in fact, a warped product semi-Riemannian
manifold.
Received: 8 March 2001 / Revised version: 25 July 2001 相似文献
63.
Nail H Ibragimov Gazanfer Ünal 《Journal of Mathematical Analysis and Applications》2004,297(1):152-168
A new definition for the approximate symmetries of Itô dynamical system is given. Determining systems of approximate symmetries for Itô and Stratonovich dynamical systems have been obtained. It has been shown that approximate conservation laws can be found from the approximate symmetries of stochastic dynamical systems which do not arise from a Hamiltonian. The results have been applied to an example. 相似文献
64.
Let (W,H,μ) be an abstract Wiener space, assume that is a second probability measures on such that , with lower bounded and H-convex. Let , be the solution of the Monge problem transporting μ to ν and realizing the H-Wasserstein distance between μ and ν. We prove that hence the Gaussian Jacobian is well-defined and T is the strong solution of the Monge–Ampère equation ΛL°T=1 a.s. on W. To cite this article: D. Feyel, A.S. Üstünel, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
65.
A new definition for the symmetries of Itô and Stratonovich dynamicalsystem is given. Determining systems of symmetries for Itô andStratonovich systems have been obtained, and their relation has beendiscussed. It has been shown that some of the Lie point symmetries ofthe Fokker–Planck equation can be constructed using the symmetries ofItô dynamical systems. Conserved quantities can be found from thesymmetries of stochastic dynamical systems which do not arise from aHamiltonian. The results have been applied to an example. 相似文献
66.
Summary Let (W, H, ) be an abstract Wiener space and letR(w) be a strongly measurable random variable with values in the set of isometries onH. Suppose that Rh is smooth in the Sobolev sense and that it is a quasi-nilpotent operator onH for everyhH. It is shown that (R(w)h) is again a Gaussian (0, |h|
H
2
)-random variable. Consequently, if (e
i
,i)W
* is a complete, orthonormal basis ofH, then
defines a measure preserving transformation, a rotation, onW. It is also shown that if for some strongly measurable, operator valued (onH) random variableR, (R(w+k)h) is (0, |h|
H
2
)-Gaussian for allk, hH, thenR is an isometry and Rh is quasi-nilpotent for allHH. The relation between the stochastic calculi for these Wiener pathsw and
, as well as the conditions of the inverbibility of the map
are discussed and the problem of the absolute continuity of the image of the Wiener measure under Euclidean motion on the Wiener space (i.e.
composed with a shift) is studied.The research of the second author was supported by the Fund for the Promotion of Research at the TechnionDedicated to the memory of Albert Badrikian 相似文献
67.
Ülo Lumiste 《Results in Mathematics》1995,27(3-4):284-301
The orbits of Lie groups acting in Euclidean spaces by isometries are extrinsically symmetric iff they are parallel, i.e. satisfy ${\overline \nabla} h =0 $ Submanifolds characterized by the integrability condition $ {\overline R}\o\ h =0 $ of this system ${\overline \nabla} h =0$ are called semi-parallel (or semi-symmetric, extrinsically); they are the 2nd order envelopes of the symmetric orbits. For the orthogonal Veronese action, corresponding to the map well-known from the algebraic geometry, all symmetric orbits will be determined, as well as their 2nd order envelopes. The results are essential for the classification of the semi-parallel submanifolds. 相似文献
68.
循环水槽中试验测量了腔体内水动力自噪声,并与模态法建立的湍流脉动压力引起腔体自噪声预报进行比较验证。透声窗振动以简支边界为条件,腔体内部声波以刚性边界为条件模态展开,通过辐射边界条件建立模态耦合振动方程。在随机湍流脉动压力作用下,推导了模态振动方程在随机力激励下的自噪声功率谱响应。对循环水槽中5 m/s和8 m/s两种流速工况下的腔体水动力自噪声和湍流脉动压力进行了测试,结合测量的脉动压力预报方法可以计算腔体水动力自噪声量值,理论预报与试验测量结果大致吻合,趋势一致,为声呐罩材料选取及声学环境控制提供了一种分析方法。 相似文献
69.
70.
A. Ülger 《Monatshefte für Mathematik》1996,121(4):353-379
LetA be a commutative Banach algebra with a nonempty spectrum A. By weak we denote the relative weak topology induced on A by (A
*,A
**). In this note we study some properties of the topological space (A, weak) and present some applications of the results obtained and tools used to amenability, weakly compact homomorphisms, weakly compact subsets of the spectrum of the uniform algebras and to a characterization of the synthesizable ideals of the algebraA. 相似文献