全文获取类型
收费全文 | 3357篇 |
免费 | 118篇 |
国内免费 | 24篇 |
专业分类
化学 | 2358篇 |
晶体学 | 14篇 |
力学 | 111篇 |
数学 | 443篇 |
物理学 | 573篇 |
出版年
2022年 | 25篇 |
2021年 | 22篇 |
2020年 | 49篇 |
2019年 | 39篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 67篇 |
2015年 | 62篇 |
2014年 | 74篇 |
2013年 | 143篇 |
2012年 | 181篇 |
2011年 | 224篇 |
2010年 | 80篇 |
2009年 | 96篇 |
2008年 | 234篇 |
2007年 | 236篇 |
2006年 | 189篇 |
2005年 | 198篇 |
2004年 | 162篇 |
2003年 | 141篇 |
2002年 | 122篇 |
2001年 | 54篇 |
2000年 | 35篇 |
1999年 | 37篇 |
1998年 | 33篇 |
1997年 | 35篇 |
1996年 | 49篇 |
1995年 | 38篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 27篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 33篇 |
1984年 | 36篇 |
1983年 | 37篇 |
1982年 | 37篇 |
1981年 | 40篇 |
1980年 | 30篇 |
1979年 | 33篇 |
1978年 | 40篇 |
1977年 | 33篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1974年 | 29篇 |
1973年 | 25篇 |
排序方式: 共有3499条查询结果,搜索用时 15 毫秒
1.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
2.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic. 相似文献
3.
Aminonaphthols are easily transformed into a variety of 1- and 2-naphthyl piperazines using a sequence of diazotization, iodide substitution and Pd(0) catalyzed coupling reactions. 相似文献
4.
Stuart S. Antman 《Journal of Elasticity》2003,70(1-3):55-64
The introduction of artificial viscosity into the partial differential equations of mechanics is often useful for both analytic and numerical studies. The traditional forms of artificial viscosity, originally designed to treat problems for fluids, when applied to problems for solids often lead to equations describing material properties that are not invariant under rigid motions. Consequently, for rapidly rotating bodies, artificial viscosity could produce serious errors. In this paper it is shown how to introduce artificial viscosity in a properly invariant way, and that the resulting systems have a rich and attractive structure, which beckons analysis. 相似文献
5.
Christopher E. Stuart Paul Abraham 《Journal of Mathematical Analysis and Applications》2004,300(2):224-361
Generalizations of the Nikodym boundedness and Vitali–Hahn–Saks theorems for scalar-valued measures on rings of sets that are in general not σ-rings are presented. As a consequence, the rings of subsets of N with density zero and uniform density zero are shown to have the Nikodym property. In addition, vector measure generalizations of the Vitali–Hahn–Saks theorem are given. 相似文献
6.
Stuart P. RomerilVictor Lee Jack E. Baldwin Timothy D.W. ClaridgeBarbara Odell 《Tetrahedron letters》2003,44(42):7757-7761
The absolute configuration of the marine sponge alkaloid pyrinodemin A is established by organic synthesis. 相似文献
7.
R. Hart P. Hue D. Burton G. F. Robertshaw F. G. H. Tate L. A. Warren und P. Eisenstein 《Fresenius' Journal of Analytical Chemistry》1938,115(7-8):272-274
Ohne Zusammenfassung 相似文献
8.
For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of
the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of
this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an
example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a
C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat
ambient metric in the sense of Fefferman and Graham.
Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse
9, 1090 Vienna, Austria
Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany 相似文献
9.
Joe Warren Scott Schaefer Anil N. Hirani Mathieu Desbrun 《Advances in Computational Mathematics》2007,27(3):319-338
In this paper we provide an extension of barycentric coordinates from simplices to arbitrary convex sets. Barycentric coordinates
over convex 2D polygons have found numerous applications in various fields as they allow smooth interpolation of data located
on vertices. However, no explicit formulation valid for arbitrary convex polytopes has been proposed to extend this interpolation
in higher dimensions. Moreover, there has been no attempt to extend these functions into the continuous domain, where barycentric
coordinates are related to Green’s functions and construct functions that satisfy a boundary value problem. First, we review
the properties and construction of barycentric coordinates in the discrete domain for convex polytopes. Next, we show how
these concepts extend into the continuous domain to yield barycentric coordinates for continuous functions. We then provide
a proof that our functions satisfy all the desirable properties of barycentric coordinates in arbitrary dimensions. Finally,
we provide an example of constructing such barycentric functions over regions bounded by parametric curves and show how they
can be used to perform freeform deformations.
相似文献
10.
Mauel M.E. Warren H.H. Hasegawa A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(6):626-630
A new laboratory terrella has been constructed in order to study collisionless radial diffusion of particles trapped within a dipole magnetic field. Columbia's collisionless terrella experiment (CTX) aims to reproduce the process of wave-induced radial transport and does not try to simulate magnetospheric structure. The first experiment planned for CTX is the direct measurement of stochastic radial diffusion induced from wave-particle drift resonances. The motivation for the CTX experiment is described, and the procedures to be used to measure the intensity and spectrum of fluctuations generating chaos, the rate of radial transport, and the evolution of the density and pressure profiles are illustrated. Because of the success of similar experiments conducted earlier in a long thin magnetic mirror, these dipole experiments can be performed with a high degree of confidence. An example from these earlier experiments is presented 相似文献