全文获取类型
收费全文 | 3799篇 |
免费 | 936篇 |
国内免费 | 382篇 |
专业分类
化学 | 218篇 |
晶体学 | 9篇 |
力学 | 1042篇 |
综合类 | 159篇 |
数学 | 1292篇 |
物理学 | 2397篇 |
出版年
2024年 | 39篇 |
2023年 | 112篇 |
2022年 | 136篇 |
2021年 | 149篇 |
2020年 | 90篇 |
2019年 | 156篇 |
2018年 | 95篇 |
2017年 | 161篇 |
2016年 | 140篇 |
2015年 | 186篇 |
2014年 | 296篇 |
2013年 | 224篇 |
2012年 | 214篇 |
2011年 | 261篇 |
2010年 | 230篇 |
2009年 | 310篇 |
2008年 | 251篇 |
2007年 | 218篇 |
2006年 | 197篇 |
2005年 | 173篇 |
2004年 | 211篇 |
2003年 | 194篇 |
2002年 | 145篇 |
2001年 | 153篇 |
2000年 | 128篇 |
1999年 | 94篇 |
1998年 | 70篇 |
1997年 | 76篇 |
1996年 | 76篇 |
1995年 | 85篇 |
1994年 | 85篇 |
1993年 | 40篇 |
1992年 | 41篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 5篇 |
1985年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有5117条查询结果,搜索用时 15 毫秒
141.
142.
给出了一种利用网格点的预报雨量来模拟区域内任一点预报雨量的方法,建立了预报雨量函数,进而得出预报雨量与实测雨量的整体偏方差的数学模型;利用QPF方法建立出准确率、预报效率、空报率、漏报率等评价预报方法优劣指标的数学模型,并对两种预报方法得出的数据进行了计算,得出上述模型中的数值如下:方案方法总体偏方差预报准确率漏报率空报率预报效率方法1 0.99987×10679.431%11.463%25.621%62.256%方法2 1.00518×10657.509%26.976%31.705%58.936%比较这些指标,可得第一种预报结果较好. 相似文献
143.
A novel micromirror based on the PolyMUMPs process is designed and presented. The hexagonal micromirror with a diameter of 450 μm consists of three supporting bilayer cantilevers and a mirror plate. The bilayer cantilevers, formed with a polysilicon layer and a gold layer, elevate the mirror plate according to residual stress-induced bending. Both analytical and finite element analysis (FEA) models are built to calculate the elevated height of the free end of the cantilever. The analytical solution is in accordance with the FEA simulation results, with longitudinal stresses applied only. Results of a three-dimensional (3D) simulation with two direction stresses applied also show the elevated height to be proportional to the width of the cantilever and the length of the gold layer. Due to the torque of the joint, the elevated heights of the two kinds of cantilevers assembled with the mirror plates are much smaller than those of the free end of the cantilevers. Both micromirrors with different cantilevers are fabricated. The elevated heights of the fabricated micromirrors are measured using Veeco optical profiler, which show good coincidence with simulation results. 相似文献
144.
Zhigang Suo 《Acta Mechanica Solida Sinica》2010,23(6):549-578
In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material (SAM). This review focuses on one class of soft active materials: dielectric elastomers. When a membrane of a dielectric elastomer is subject to a voltage through its thickness, the membrane reduces thickness and expands area, possibly straining over 100%. The dielectric elastomers are being developed as transducers for broad applications, including soft robots, adaptive optics, Braille displays, and electric generators. This paper reviews the theory of dielectric elastomers, developed within continuum mechanics and thermodynamics, and motivated by molecular pictures and empirical observations. The theory couples large deformation and electric potential, and describes nonlinear and nonequilibrium behavior, such as electromechanical instability and viscoelasticity. The theory enables the finite element method to simulate transducers of realistic configurations, predicts the efficiency of electromechanical energy conversion, and suggests alternative routes to achieve giant voltage-induced deformation. It is hoped that the theory will aid in the creation of materials and devices. 相似文献
145.
Based on the LaSalle invariance principle, we propose a simple adaptive-feedback for controlling the unified chaotic system. We show explicitly with numerical proofs that our method can easily achieve the control of chaos in the unified chaotic system using only a single variable feedback. The present controller, to our knowledge, is the simplest control scheme for controlling a unified chaotic system. 相似文献
146.
148.
克服线性回归模型中设计矩阵的复共线性,主要有三种方法追加数据自变量选择和非量小二乘法,本文研究追加数据在减少条件数中的作用,我们的研究表明,在可能情况下适当地选择追加数据,设计矩阵的条件指数可以被减少。我们用在回归最优设计中广泛初研Gaylor-Merrill数据说明了本文理论结果的实用意义。 相似文献
149.
Zi-qing Xie Chuan-miao Chen Institute of Computation Hunan Normal University Changsha Hunan China 《应用数学学报(英文版)》2004,20(2):317-322
The multiple solutions for one-dimensional cubic nonlinear problem u" u~3=0,u(0)=u(π)=0are computed,on the basis of the eigenpairs of-φ"_k=λ_(kφk),k=1,2,3....There exist two nonzero solutions±u_k corresponding to each k,and their Morse index MI(k) for 1(?)k(?)20 is to be exactly determined.It isshown by the numerical results that MI(k)(?)k. 相似文献
150.
钝体后湍流预混燃烧的PDF模拟 总被引:3,自引:0,他引:3
本文采用PDF方法对矩形燃烧室内钝体后的湍流预混火焰进行了数值模拟。脉动速度-频率-标量联合的PDF输运方程用Monte Carlo方法求解,质量、动量和能量的平均值由基于无结构网格的有限体积法求解,压力通过状态方程获得。PDF方程中所需的平均密度、平均速度和压力由有限体积法提供,并将用Monte Carlo方法求出的雷诺应力、化学反应源项和比热比传递给有限体积法。本文对丙烷和空气燃烧的不同简化化学反应机理进行了研究,并与实验结果进行比较,获得满意的结果。 相似文献