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161.
负权最短路问题的新算法 总被引:3,自引:0,他引:3
Bellman-Ford算法自1958年以来一直是负权最短路问题的公认的最好算法之一.1970年,Yen对其进行了改进,理论上可以节省一半的计算量.本文得到了一种比Bellman-Ford算法更加优越的算法.尽管在理论上新算法无法保证完全超越于Yen的改进算法,但在许多情况下需要更少的计算量. 相似文献
162.
The evolution and the steady-state structure of gasdynamic disturbances in a thermodynamically nonequilibrium gas are investigated both analytically and numerically. It is shown that in a medium with negative viscosity steady-state structures different from those in an equilibrium medium can exist. The conditions of existence of stationary shock waves with a discontinuous front and a smooth increase or decrease in the amplitude behind the front, waves with an oscillatory structure, and a stationary self-wave pulse with a power-law trailing front are determined.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 181–191. Original Russian Text Copyright © 2004 by Makaryan and Molevich. 相似文献
163.
164.
分析了以Na2CO3-NaHCO3混合溶液为淋洗液,离子色谱法测定碱性样品时,色谱负峰产生的原因。通过计算和试验,采用在样品中加入适量NaHCO3进行中和的方法,解决了负峰影响HCOO^-测定的问题。 相似文献
165.
Wen-yu SUN~ 《中国科学A辑(英文版)》2007,50(10)
In this paper,an unconstrained optimization method using the nonmonotone second order Goldstein's line search is proposed.By using the negative curvature information from the Hessian, the sequence generated is shown to converge to a stationary point with the second order optimality conditions.Numerical tests on a set of standard test problems confirm the efficiency of our new method. 相似文献
166.
167.
The optical symmetry of many crystals is lower than would be expected from their external form and X-ray diffraction data. Recently such optical anomalies have been attributed to nonequilibrium structures resulting from kinetically controlled crystal growth. Impurities are incorporated to different extents at various surface sites that would otherwise have become symmetry-related within the bulk crystal. After their discovery by Brewster in 1815, optically anomalous crystals were the subject of lively debate throughout the 19th century among some of the most distinguished contributors to the development of crystallography including Biot, Berzelius, Herschel, Mitscherlich, Frankenheim, Pasteur, Mallard, Klein, Groth, Wyrouboff, Barlow, Brauns, Rinne, Pockels, and Friedel. From a sea of wild speculation two conflicting postulates emerged: that the symmetric form resulted from accidental twinning of segments with lower symmetry, or that the optical peculiarities resulted from stress due to impurities or external perturbations. Neither postulate expresses the present view. Interest in this research waned at the turn of the century, and after 1917 no one pursued Tammann's alternative correct insight. The problem of anomalous double refraction attracted no attention for more than half a century until its recent solution. This review discusses both mineral and organic systems with particular emphasis on the phyllosilicate apophyllite and on 1,5-dichloro-2,3-dinitrobenzene. These nonequilibrium structures relate to questions of crystal order, crystal growth, molecular recognition, and the design of new materials. The review provides a reminder of the enduring value of the polarizing microscope as a research tool in chemistry. 相似文献
168.
Boerio-Goates J. Stevens R. Lang B. Woodfield B. F. 《Journal of Thermal Analysis and Calorimetry》2002,69(3):773-783
Experimental heat capacity measurements of α-ZrW2O8, and zeolitic polymorphs of SiO2, BEA and MFI, have been made from 0.6 to 400 K. Measurements on β-ZrMo2O8 have been made from 8 to 400 K. Analysis of the results yields evidence for very low frequency modes in all four materials.
These modes are responsible for negative thermal expansion behavior in α-ZrW2O8 and β-ZrMo2O8. Negative thermal expansion has been observed in some pure SiO2 zeolites, but no studies have been made to look for it in BEA and MFI. The appearance of low frequency modes in these two
zeolites suggests that temperature dependent structural investigations would be worthwhile. These modes are lower in energy
than the Boson peak in vitreous silica.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
169.
受自然界树型结构的启发,设计了分叉树型微结构单元,用电路板刻蚀技术制作了非对称开口六边形谐振单环及其组合结构.采用计算机模拟和实验研究了单个和多个谐振环在微波段(7—12 GHz)的电磁响应行为.研究结果表明:该结构具有负磁导率特性,开口谐振环几何尺寸影响环的磁谐振频率;两环环间距较小时出现二次谐振;带高级分支的辐射状环列相对于不带分支环列透射峰向低频移动.实验和模拟结果相符.
关键词:
负磁导率
开口谐振环
透射率 相似文献
170.
Summary In this paper, the reflection and refraction of a plane wave at an interface between two half-spaces composed of triclinic crystalline material is considered. It is shown that due to incidence of plane wave three types of waves, namely quasi-P (qP), quasi-SV (qSV) and quasi-SH (qSH), will be generated governed by the propagation condition involving the acoustic tensor. A simple procedure has been presented for the calculation of all the three phase velocities of the quasi waves. It has been established that the direction of particle motion is neither parallel nor perpendicular to the direction of propagation. Relations are established between directions of motion and propagation, respectively. The expressions for reflection and refraction coefficients of qP, qSV and qSH waves are obtained. Numerical results of reflection and refraction coefficients are presented for different types of anisotropic media and for different types of incident waves. Graphical representations have been made for incident qP waves, and for incident qSV and qSH waves numerical data are presented in tables.The work was completed while the author was visiting the University of Kaiserslautern, Department of Geomathematics as Visiting Professor. The Author is grateful to Professor Dr. W. Freeden for providing DAAD fellowship and all the facilities for conducting research, as well as to Dr. V.Michel for various discussions about the research work and also for all kinds of help during his stay at Kaiserslautern, Germany. This award is very gratefully acknowledged. 相似文献