全文获取类型
收费全文 | 4730篇 |
免费 | 151篇 |
国内免费 | 1篇 |
专业分类
化学 | 2818篇 |
晶体学 | 27篇 |
力学 | 153篇 |
数学 | 730篇 |
物理学 | 1154篇 |
出版年
2021年 | 31篇 |
2020年 | 63篇 |
2019年 | 42篇 |
2018年 | 52篇 |
2017年 | 41篇 |
2016年 | 93篇 |
2015年 | 107篇 |
2014年 | 102篇 |
2013年 | 201篇 |
2012年 | 276篇 |
2011年 | 292篇 |
2010年 | 157篇 |
2009年 | 129篇 |
2008年 | 219篇 |
2007年 | 220篇 |
2006年 | 207篇 |
2005年 | 210篇 |
2004年 | 195篇 |
2003年 | 148篇 |
2002年 | 154篇 |
2001年 | 74篇 |
2000年 | 63篇 |
1999年 | 56篇 |
1998年 | 46篇 |
1997年 | 55篇 |
1996年 | 39篇 |
1995年 | 58篇 |
1994年 | 38篇 |
1993年 | 36篇 |
1992年 | 47篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 51篇 |
1987年 | 43篇 |
1985年 | 33篇 |
1984年 | 32篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 48篇 |
1980年 | 36篇 |
1979年 | 27篇 |
1978年 | 40篇 |
1977年 | 31篇 |
1976年 | 36篇 |
1975年 | 31篇 |
1974年 | 31篇 |
1973年 | 23篇 |
1933年 | 24篇 |
1908年 | 27篇 |
排序方式: 共有4882条查询结果,搜索用时 45 毫秒
31.
Hansen Alex Roux Stéphane Roux Aharony Amnon Feder Jens Jøssang Torstein Hardy H. H. 《Transport in Porous Media》1997,29(3):247-279
We present a spatial renormalization group algorithm to handle immiscibletwo-phase flow in heterogeneous porous media. We call this algorithmFRACTAM-R, where FRACTAM is an acronym for Fast Renormalization Algorithmfor Correlated Transport in Anisotropic Media, and the R stands for relativepermeability. Originally, FRACTAM was an approximate iterative process thatreplaces the L × L lattice of grid blocks, representing the reservoir,by a (L/2) × (L/2) one. In fact, FRACTAM replaces the original L× L lattice by a hierarchical (fractal) lattice, in such a way thatfinding the solution of the two-phase flow equations becomes trivial. Thistriviality translates in practice into computer efficiency. For N=L ×L grid blocks we find that the computer time necessary to calculatefractional flow F(t) and pressure P(t) as a function of time scales as N1.7 for FRACTAM-R. This should be contrasted with thecomputational time of a conventional grid simulator N2.3. The solution we find in this way is an accurateapproximation to the direct solution of the original problem. 相似文献
32.
Summary A new and very general expression is proposed for correlation of data for the effective viscosity of pseudoplastic and dilatant fluids as a function of the shear stress. Most of the models which have been proposed previously are shown to be special cases of this expression. A straightforward procedure is outlined for evaluation of the arbitrary constants.
Nomenclature b arbitrary constant inSisko model (eq. [5]) - n arbitrary exponent in eq. [1] - x independent variable - y(x) dependent variable - y 0(x) limiting behavior of dependent variable asx 0 - y(x) limiting behavior of dependent variable asx - z original dependent variable - arbitrary constant inSisko model (eq. [5]) andBird-Sisko model (eq. [6]) - arbitrary exponent in eqs. [2] and [8] - effective viscosity = shear stress/rate of shear - A effective viscosity at = A - B empirical constant in eqs. [2] and [8] - 0 limiting value of effective viscosity as 0 - 0() limiting behavior of effective viscosity as 0 - limiting value of effective viscosity as - () limiting behavior of effective viscosity as - rate of shear - arbitrary constant inBird-Sisko model (eq.[6]) - shear stress - A arbitrary constant in eqs. [2] and [8] - 0 shear stress at inBingham model - 1/2 shear stress at = ( 0 + )/2 With 8 figures 相似文献
Zusammenfassung Eine neue und sehr allgemeine Formel wird für die Korrelation der Werte der effektiven Viskosität von strukturviskosen und dilatanten Flüssigkeiten in Abhängigkeit von der Schubspannung vorgeschlagen. Die meisten schon früher vorgeschlagenen Methoden werden hier als Spezialfälle dieser Gleichung gezeigt. Ein einfaches Verfahren für die Auswertung der willkürlichen Konstanten wird beschrieben.
Nomenclature b arbitrary constant inSisko model (eq. [5]) - n arbitrary exponent in eq. [1] - x independent variable - y(x) dependent variable - y 0(x) limiting behavior of dependent variable asx 0 - y(x) limiting behavior of dependent variable asx - z original dependent variable - arbitrary constant inSisko model (eq. [5]) andBird-Sisko model (eq. [6]) - arbitrary exponent in eqs. [2] and [8] - effective viscosity = shear stress/rate of shear - A effective viscosity at = A - B empirical constant in eqs. [2] and [8] - 0 limiting value of effective viscosity as 0 - 0() limiting behavior of effective viscosity as 0 - limiting value of effective viscosity as - () limiting behavior of effective viscosity as - rate of shear - arbitrary constant inBird-Sisko model (eq.[6]) - shear stress - A arbitrary constant in eqs. [2] and [8] - 0 shear stress at inBingham model - 1/2 shear stress at = ( 0 + )/2 With 8 figures 相似文献
33.
Control of the flow around a circular cylinder is studied using Large Eddy Simulation. The influence of control by rotation and suction on the flow characteristics is considered for several Reynolds numbers. Comparisons with experiments were conducted at for the flow with and without control. A drag reduction up to 30% is obtained for an usual suction intensity. To cite this article: G. Fournier et al., C. R. Mecanique 333 (2005). 相似文献
34.
Pierre Lubin Stéphane Vincent Jean-Paul Caltagirone Stéphane Abadie 《Comptes Rendus Mecanique》2003,331(7):495-501
The scope of this paper is to show the results obtained for simulating three-dimensional breaking waves by solving the Navier–Stokes equations in air and water. The interface tracking is achieved by a Lax–Wendroff TVD scheme (Total Variation Diminishing), which is able to handle interface reconnections. We first present the equations and the numerical methods used in this work. We then proceed to the study of a three-dimensional plunging breaking wave, using initial conditions corresponding to unstable periodic sinusoidal waves of large amplitudes. We compare the results obtained for two simulations, a longshore depth perturbation has been introduced in the solution of the flow equations in order to see the transition from a two-dimensional velocity field to a fully three-dimensional one after plunging. Breaking processes including overturning, splash-up and breaking induced vortex-like motion beneath the surface are presented and discussed. To cite this article: P. Lubin et al., C. R. Mecanique 331 (2003). 相似文献
35.
Influence of higher harmonics of the undulator in X‐ray polarimetry and crystal monochromator design 下载免费PDF全文
Berit Marx‐Glowna Kai S. Schulze Ingo Uschmann Tino Kämpfer Günter Weber Christoph Hahn Hans‐Christian Wille Kai Schlage Ralf Röhlsberger Eckhart Förster Thomas Stöhlker Gerhard G. Paulus 《Journal of synchrotron radiation》2015,22(5):1151-1154
The spectrum of the undulator radiation of beamline P01 at Petra III has been measured after passing a multiple reflection channel‐cut polarimeter. Odd and even harmonics up to the 15th order, as well as Compton peaks which were produced by the high harmonics in the spectrum, could been measured. These additional contributions can have a tremendous influence on the performance of the polarimeter and have to be taken into account for further polarimeter designs. 相似文献
36.
Using dislocation simulation approach, the basic equation for a finite crack perpendicular to and terminating at a bimaterial
interface is formulated. A novel expansion method is proposed for solving the problem. The complete solution to the problem,
including the explicit formulae for theT stresses ahead of the crack tip and the stress intensity factors are presented. The stress field characteristics are analysed
in detail. It is found that normal stresses {ie27-1} and {ie27-2} ahead of the crack tip, are characterised byQ fields if the crack is within a stiff material and the parameters |p
T
| and |q
T
| are very small, whereQ is a generalised stress intensity factor for a crack normal to and terminating at the interface. If the crack is within a
weak material, the normal stresses {ie27-3} and {ie27-4} are dominated by theQ field plusT stress.
This work was supported by the Swedish Research Council for Engineering Sciences. 相似文献
37.
Dr.-Ing. St. Dorosz Prof. Dr. J. A. König 《Archive of Applied Mechanics (Ingenieur Archiv)》1985,55(3):202-212
Summary The concept of substitutive concentrated elastic-plastic rotations, replacing actual elasticplastic zones is used, together with an iterative method of determination of the bending moment distribution to simplify the evaluation of elastic-plastic deflections of hyperstatic beams and frames.
Eine iterative Methode der Auswertung von elastisch-plastischen Verschiebungen für statisch unbestimmte Rahmen
Übersicht Die Idee von fiktiven Ersatzrotationen, welche die tatsächlichen elastisch-plastischen Zonen modelliert, wird mit einer iterativen Methode kombiniert, um eine relativ einfache Bestimmung von Biegemomentenfeldern in statisch unbestimmten Balken und Rahmen zu ermöglichen. Die resultierenden Verschiebungen, ergeben sich mit ausreichender Genauigkeit.相似文献
38.
Equations of motion are derived for a viscoplastic liquid in a nonuniform medium of type 2 (piecewise uniform) or type 3 (with a variable filtration coefficient) [1] on the assumption that the motion is of steady-state type. Solutions are presented for a parallel flow and a flow with axial symmetry. 相似文献
39.
The use of a sliding plate rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers
at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that
limit the use of rotational rheometers to shear rates often below 1 s−1. However, issues of secondary flow and wall slip must be addressed to obtain reliable data using an SPR. A highly entangled,
monodisperse polybutadiene and a commercial polystyrene were the polymers studied. The inclusion of the polystyrene made it
possible to compare data with those obtained by Lodge using a stressmeter, which is an instrument based on the measurement
of the hole pressure. The data from the two instruments are in good agreement and are also close to the predictions of an
empirical equation of Laun based on the storage and loss moduli. 相似文献
40.
Dr. Victor de Seauve Dr. Marie-Angélique Languille Dr. Mathieu Kociak Dr. Stéphanie Belin Dr. James Ablett Prof. Christine Andraud Prof. Odile Stéphan Dr. Jean-Pascal Rueff Dr. Emiliano Fonda Prof. Bertrand Lavédrine 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9198-9204
The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIXth century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours. 相似文献