全文获取类型
收费全文 | 3972篇 |
免费 | 118篇 |
国内免费 | 34篇 |
专业分类
化学 | 2955篇 |
晶体学 | 33篇 |
力学 | 85篇 |
综合类 | 1篇 |
数学 | 536篇 |
物理学 | 514篇 |
出版年
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 31篇 |
2020年 | 55篇 |
2019年 | 54篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 89篇 |
2015年 | 90篇 |
2014年 | 99篇 |
2013年 | 212篇 |
2012年 | 206篇 |
2011年 | 324篇 |
2010年 | 120篇 |
2009年 | 126篇 |
2008年 | 257篇 |
2007年 | 259篇 |
2006年 | 257篇 |
2005年 | 251篇 |
2004年 | 224篇 |
2003年 | 162篇 |
2002年 | 158篇 |
2001年 | 41篇 |
2000年 | 48篇 |
1999年 | 40篇 |
1998年 | 37篇 |
1997年 | 42篇 |
1996年 | 60篇 |
1995年 | 35篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 35篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 46篇 |
1984年 | 39篇 |
1983年 | 30篇 |
1982年 | 54篇 |
1981年 | 43篇 |
1980年 | 41篇 |
1979年 | 32篇 |
1978年 | 40篇 |
1977年 | 32篇 |
1976年 | 24篇 |
1975年 | 31篇 |
1974年 | 19篇 |
排序方式: 共有4124条查询结果,搜索用时 15 毫秒
1.
2.
A practical Sonogashira alkynylation protocol for the preparation of 8-alkynylated adenosines and guanosines has been developed. Protection of the sugar hydroxyl substituents is not required; protection hinders the purification of these products. A preliminary fluorescent study is reported, which shows that the presence of a substituent on the phenylene ring influences the fluorescent properties considerably, an outcome that could be utilized in biological applications. 相似文献
3.
A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature 总被引:5,自引:0,他引:5
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables. 相似文献
4.
In this paper we prove the equivalence of various algebraically or geometrically defined assembly maps used in formulating the main conjectures in K- and L-theory, and C*-theory.Partially supported by NSERC grant A4000 and NSF grant DMS 9104026. The authors also wish to thank the SFB für Geometrie und Analysis, Münster, and the Max Planck Institut für Mathematik, Bonn, for their hospitality and support.Received: 7 May 2001 相似文献
5.
6.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
7.
8.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
9.
Ian Kiming 《manuscripta mathematica》1995,87(1):101-129
For an imaginary quadratic fieldK we study the asymptotic behaviour (with respect top) of the number of integers inK with norm of the formk(p−k) for some 1≤k≤p−1, wherep is a prime number. The motivation for studying this problem is that it is known by recent results due to G. Frey and E. Kani
that knowledge of this asymptotic behaviour can lead to statements of existence of curves of genus 2 with elliptic differentials
in particular cases.
We give a general, and from one point of view complete, answer to this question on asymptotic behaviour. This answer is derived
from a theorem concerning the number of representations of a natural number by certain quaternary quadratic forms. This second
result may be of some independent interest because it can be seen as a generalisation of the classical theorem of Jacobi on
the number of representations of a natural number as a sum of 4 squares. 相似文献
10.
John M. Davis Ian A. Gravagne 《Journal of Mathematical Analysis and Applications》2007,332(2):1291-1307
In this work, we reexamine the time scale Laplace transform as defined by Bohner and Peterson [M. Bohner, A. Peterson, Dynamic Equations on Time Scales: An Introduction with Applications, Birkhäuser, Boston, 2001; M. Bohner, A. Peterson, Laplace transform and Z-transform: Unification and extension, Methods Appl. Anal. 9 (1) (2002) 155-162]. In particular, we give conditions on the class of functions which have a transform, develop an inversion formula for the transform, and further, we provide a convolution for the transform. The notion of convolution leads to considering its algebraic structure—in particular the existence of an identity element—motivating the development of the Dirac delta functional on time scales. Applications and examples of these concepts are given. 相似文献