全文获取类型
收费全文 | 477625篇 |
免费 | 3964篇 |
国内免费 | 1347篇 |
专业分类
化学 | 227354篇 |
晶体学 | 7688篇 |
力学 | 24469篇 |
综合类 | 5篇 |
数学 | 67203篇 |
物理学 | 156217篇 |
出版年
2020年 | 3261篇 |
2019年 | 3692篇 |
2018年 | 11907篇 |
2017年 | 12521篇 |
2016年 | 10228篇 |
2015年 | 5011篇 |
2014年 | 7079篇 |
2013年 | 17736篇 |
2012年 | 17002篇 |
2011年 | 26559篇 |
2010年 | 17454篇 |
2009年 | 17339篇 |
2008年 | 23610篇 |
2007年 | 26621篇 |
2006年 | 14518篇 |
2005年 | 18447篇 |
2004年 | 14704篇 |
2003年 | 13456篇 |
2002年 | 11658篇 |
2001年 | 12131篇 |
2000年 | 9516篇 |
1999年 | 7323篇 |
1998年 | 6000篇 |
1997年 | 5905篇 |
1996年 | 5701篇 |
1995年 | 5174篇 |
1994年 | 5023篇 |
1993年 | 4990篇 |
1992年 | 5383篇 |
1991年 | 5494篇 |
1990年 | 5231篇 |
1989年 | 5024篇 |
1988年 | 5177篇 |
1987年 | 5025篇 |
1986年 | 4705篇 |
1985年 | 6314篇 |
1984年 | 6699篇 |
1983年 | 5456篇 |
1982年 | 5804篇 |
1981年 | 5711篇 |
1980年 | 5446篇 |
1979年 | 5651篇 |
1978年 | 5831篇 |
1977年 | 5732篇 |
1976年 | 5861篇 |
1975年 | 5404篇 |
1974年 | 5369篇 |
1973年 | 5607篇 |
1972年 | 3746篇 |
1971年 | 3049篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
152.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
153.
The problem of the stability of a heavy rigid body, bounded by the surface of an ellipsoid and with a cavity in the form of a coaxial ellipsoid, rolling along a straight line on a horizontal rough plane is investigated. It is shown that in the case of a body that is close to being dynamically symmetrical, parametric resonance always occurs leading to instability of the rolling. Each ellipsoid has its own “individual” resonance angular velocity. In the general case, regions in which the necessary stability conditions are satisfied can be distinguished in parameter space. The problem of calculating the resonance coefficient corresponding to instability for parametric resonance in a reversible third-order system is solved. 相似文献
154.
P Vincent A BrioudeC Journet S RabasteS.T Purcell J Le BrusqJ.C Plenet 《Journal of Non》2002,311(2):130-137
We report here the successful inclusion of carbon nanotubes (CNs) into a TiO2 matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed. 相似文献
155.
156.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
157.
E. P. Gordov 《Russian Physics Journal》1981,24(11):1039-1041
An evolution operatior is described, which acts on the operators of a problem to take it into the solutions of the corresponding problem of semiclassical electrodynamics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 66–69, November, 1981. 相似文献
158.
Dominant nonlinear electric dipole polarizations at the interaction of fundamental and second harmonic waves in centrosymmetric media without and with memory are treated in this paper. The process of forming a permanent spatially periodic quadratic susceptibility grating in the medium with memory is described from the phenomenological point of view.Dedicated to the Czechoslovak Student Movement '89. 相似文献
159.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985. 相似文献
160.
D. A. Tikhomirov O. S. Slyadevskaya A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1991,27(9):966-969
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991. 相似文献