全文获取类型
收费全文 | 81678篇 |
免费 | 2859篇 |
国内免费 | 286篇 |
专业分类
化学 | 53484篇 |
晶体学 | 447篇 |
力学 | 2298篇 |
综合类 | 2篇 |
数学 | 13799篇 |
物理学 | 14793篇 |
出版年
2023年 | 482篇 |
2022年 | 502篇 |
2021年 | 834篇 |
2020年 | 1070篇 |
2019年 | 1011篇 |
2018年 | 1365篇 |
2017年 | 1190篇 |
2016年 | 2253篇 |
2015年 | 2127篇 |
2014年 | 2192篇 |
2013年 | 4548篇 |
2012年 | 5009篇 |
2011年 | 5409篇 |
2010年 | 3236篇 |
2009年 | 2695篇 |
2008年 | 4638篇 |
2007年 | 4621篇 |
2006年 | 4357篇 |
2005年 | 4120篇 |
2004年 | 3681篇 |
2003年 | 2973篇 |
2002年 | 2702篇 |
2001年 | 1453篇 |
2000年 | 1276篇 |
1999年 | 1012篇 |
1998年 | 865篇 |
1997年 | 861篇 |
1996年 | 947篇 |
1995年 | 702篇 |
1994年 | 799篇 |
1993年 | 744篇 |
1992年 | 758篇 |
1991年 | 704篇 |
1990年 | 641篇 |
1989年 | 645篇 |
1988年 | 553篇 |
1987年 | 509篇 |
1986年 | 505篇 |
1985年 | 781篇 |
1984年 | 763篇 |
1983年 | 583篇 |
1982年 | 711篇 |
1981年 | 678篇 |
1980年 | 639篇 |
1979年 | 579篇 |
1978年 | 584篇 |
1977年 | 510篇 |
1976年 | 520篇 |
1975年 | 454篇 |
1974年 | 468篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
251.
We solve numerically the Monge–Ampère equation with periodic boundary condition using a Newton's algorithm. We prove convergence of the algorithm, and present some numerical examples, for which a good approximation is obtained in 10 iterations. To cite this article: G. Loeper, F. Rapetti, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
252.
253.
Standard ODE methods such as linear multistep methods encounter difficulties when applied to differential-algebraic equations (DAEs) of index greater than 1. In particular, previous results for index 2 DAEs have practically ruled out the use of all explicit methods and of implicit multistep methods other than backward difference formulas (BDFs) because of stability considerations. In this paper we embed known results for semi-explicit index 1 and 2 DAEs in a more comprehensive theory based on compound multistep and one-leg discretizations. This explains and characterizes the necessary requirements that a method must fulfill in order to be applicable to semi-explicit DAEs. Thus we conclude that the most useful discretizations are those that avoid discretization of the constraint. A freer use of e.g. explicit methods for the non-stiff differential part of the DAE is then possible.Dedicated to Germund Dahlquist on the occasion of his 70th birthdayThis author thanks the Centro de Estadística y Software Matemático de la Universidad Simón Bolivar (CESMa) for permitting her free use of its research facilities.Partial support by the Swedish Research Council for Engineering Sciences TFR under contract no. 222/91-405. 相似文献
254.
Design theory crosses the boundary between mathematics and statistics, and includes a wide range of disparate types of design. In this paper we present a classification scheme which aims to include as many important types as possible, based on a balance among concept, representation and use. 相似文献
255.
A time-dependent model corresponding to an Oldroyd-B viscoelastic fluid is considered, the convective terms being disregarded.
Global existence in time is proved in Banach spaces provided the data are small enough, using the implicit function theorem
and a maximum regularity property for a three fields Stokes problem. A finite element discretization in space is then proposed.
Existence of the numerical solution is proved for small data, so as a priori error estimates, using again an implicit function
theorem.
Supported by the Swiss National Science Foundation. Fellowship PBEL2–114311. 相似文献
256.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
257.
Manfred Brun Peter Hubner Dieter Oelkrug 《Fresenius' Journal of Analytical Chemistry》1992,344(4-5):209-213
Summary A theoretical model is derived that describes the influence of lateral light diffusion in a scattering medium on the absorptivity of an absorber spot on top of the substrate. The model uses the lateral resolved reflectivity under point irradiation that has been analyzed experimentally with a scanning-micro-laser-reflectometer. The model allows quantification of the absorptivity by one single equation that contains only the mean radial diffusion length of light and the spot area. Experiment and theory are applied to typical substrates for thin layer chromatography (alumina, silica, cellulose). The diffusion lengths in these substrates are given and the absorptivities of the spots are calculated as a function of the spot area. 相似文献
258.
E. Beinrohr M. Németh P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(3):93-99
Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10–9 to 10–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.
One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia 相似文献
259.
José A. Anquela Teresa Cortés Miguel Gómez-Lozano Mercedes Siles-Molina 《Acta Mathematica Hungarica》2004,103(3):177-196
We investigate the basic properties of the different socles that can be considered in not necessarily semiprime associative
systems. Among other things, we show that the socle defined as the sum of minimal (or minimal and trivial) inner ideals is
always an ideal. When trivial inner ideals are included, this inner socle contains the socles defined in terms of minimal
left or right ideals.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
260.
Mátyás Bognár 《Acta Mathematica Hungarica》2004,102(1-2):37-84
The following generalization of the Hahn-Mazurkiewicz theorem is proved: Let (E,e) be a locally compact locally connected metric space. Let M be a continuum in this space and let d,e∈ M. Then there is a continuous mapping f: [0,1]→E such that f(0) = d, f(1)= e and M⊂f([0,1]). Also some corollaries of this theorem are proved. 相似文献