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951.
Rehan H.Zuberi 《Acta Mechanica Solida Sinica》2009,22(2):180-188
This paper presents a new approach to the structural topology optimization of continuum structures. Material-point independent variables are presented to illustrate the existence condition,or inexistence of the material points and their vicinity instead of elements or nodes in popular topology optimization methods. Topological variables field is constructed by moving least square approximation which is used as a shape function in the meshless method. Combined with finite element analyses,not only checkerboard patterns and mesh-dependence phenomena are overcome by this continuous and smooth topological variables field,but also the locations and numbers of topological variables can be arbitrary. Parameters including the number of quadrature points,scaling parameter,weight function and so on upon optimum topological configurations are discussed. Two classic topology optimization problems are solved successfully by the proposed method. The method is found robust and no numerical instabilities are found with proper parameters. 相似文献
952.
分析了小型专题博物馆在国内外的发展特点和趋势;针对宁波服装博物馆项目的设计实践,从地域文化、空间形态、展陈互动结合、传统现代结合等几个方面提出了小型专题博物馆的创新设计理念和设计方法. 相似文献
953.
Three-dimensional interfacial wave theory of dendritic growth: (Ⅰ). multiple variables expansion solutions 下载免费PDF全文
Dendritic pattern formation at the interface between liquid and
solid is a commonly observed phenomenon in crystal growth and
solidification process. The theoretical investigation of dendritic
growth is one of the most profound and highly challenging subjects
in the broad areas of interfacial pattern formation, condensed
matter physics and materials science, preoccupying many researchers
from various areas. Some longstanding key issues on this subject
finally gained a breakthrough in the late of last century, via the
`{Interfacial Wave} (IFW) Theory' on the ground of systematical
global stability analysis of the basic state of dendritic growth.
The original form of the IFW theory mainly focus on the
investigation of various axi-symmetric unsteady perturbed modes
solutions around the axi-symmetric basic state of system of
dendritic growth. In reality, the system may allow various
non-axi-symmetric, unsteady perturbed states. Whether or not the
system of dendritic growth allows some growing non-axi-symmetric
modes? Will the stationary dendritic pattern be destroyed by some of
such non-axi-symmetric modes? Or, in one word, what is the stability
property of the system, once the non-axi-symmetric modes can be
evoked? The answers for these questions are important for the solid
foundation of IFW theory. The present work attempts to settle down
these issues and develop a three-dimensional (3D) interfacial wave
theory of dendritic growth. Our investigations verify that dendritic
growth indeed allows a discrete set of non-axi-symmetric unstable
global wave modes, which gives rise to a set of multiple arms spiral
waves propagating along the Ivantsov's paraboloid. 相似文献
954.
Sebastián Bouzat Damián H. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):557-565
We study an SIS epidemiological model for a sexually
transmitted infection in a monogamous population where the formation
and breaking of couples is governed by individual preferences. The
mechanism of couple recombination is based on the so-called bar
dynamics for the marriage problem. We compare the results with those
of random recombination – where no individual preferences exist –
for which we calculate analytically the infection incidence and the
endemic threshold. We find that individual preferences give rise to
a large dispersion in the average duration of different couples,
causing substantial changes in the incidence of the infection and in
the endemic threshold. Our analysis yields also new results on the
bar dynamics, that may be of interest beyond the field of
epidemiological models. 相似文献
955.
基于微机电系统工艺,设计并制作了一种电磁驱动大尺寸的二维扫描振镜.分析了两种不同的电磁驱动方式产生的力的大小,选择驱动力较大的双极子方式作为驱动.运用有限元法模拟了器件的谐振频率静态及动态响应,仿真结果与实际测得的结果一致.描述了振镜的工艺流程及封装方式,并制备了振镜.实验测得振镜在120mA静态电流驱动下,慢轴和快轴分别能达到的最大转角为±4.5°及±5°,慢轴及快轴的谐振频率分别为348Hz及660Hz,并得到在此谐振频率下的李萨如图形.将器件用于激光成像系统之中,使得散斑对比度下降到4.2%,激光成像质量得到很大提升. 相似文献
956.
为实现面阵相机对沿轨方向长条带区域一定重叠率的推凝视成像,设计了高分辨CMOS传感器的钟摆式搜索成像模型.通过长条带逐层区域划分和成像重叠率渐近变化构建,计算了钟摆式搜索成像参量和卫星实时推凝指向姿态,并利用多次小幅逼近的PD控制器分析了搜索成像姿态控制精度与成像像移失配量.利用高分CMOS原理样机和小卫星姿控仿真平台对P5型曲面LED靶标系统进行地面等比缩放的长条带钟摆式搜索成像仿真试验.结果表明:帧间重叠率大于85%的钟摆式搜索成像比全凝视成像区域扩大了4倍;控制周期为10 Hz时,其姿态控制精度优于0.05°,姿态稳定度优于0.003°/s,搜索成像对应的图像传递函数能够达到0.141 1. 相似文献
957.
城市绿地是城市自然生态系统的重要组成部分, 我国东南沿海地区是城市化速度最快的区域之一, 快速城市化导致建设用地的大量增加, 并引起区域绿地景观格局及生态价值的显著变化. 本文选取东南沿海中部的宁波市北仑区为研究区域, 以其1990、1995、2000、2005、2010和2015年6期土地利用变化数据为基础提取绿地, 借助ArcGIS和Fragstats软件, 应用景观生态学方法和基于专家知识的生态系统服务价值化方法对快速城市化背景下北仑区绿地景观动态演化及其生态价值变化进行了研究. 结果表明: (1)绿地是北仑区的主要景观类型, 1990~2015年间快速城市化导致北仑区1406hm2绿地转化为建设用地; (2)北仑区绿地景观异质性减弱, 趋于集中式发展, 整体破碎度降低; (3)截止2015年, 绿地的生态服务价值总量比1990年减少了6%, 生态环境出现恶化, 主要是建设用地占用绿地导致生态总价值下降; (4)北仑区绿地系统生态价值等级由中心向外围降低呈不规则环状, 且高价值区逐渐向东南方向减少并转变为较低价值区. 相似文献
958.
This paper presents a new fringe projection method for surface-shape measurement that uses background and amplitude encoded high-frequency fringe patterns. The background and amplitude, combined as a codeword, identify the wrapped phase fringe order to partially unwrap the phase to a low frequency. The low-frequency wrapped phase map is then directly used to reconstruct the surface based on geometry constraints without requiring additional images as in other temporal phase-unwrapping methods. Measurements performed on a double-hemisphere, mask, and manikin head, using projected fringe patterns with 48 periods, demonstrated the ability of the method to perform 3D shape measurement with only four projected patterns and captured images, using a single camera and projector. 相似文献
959.
Completely random allocation of the treatment combinations to the experimental units is appropriate only if the experimental units are homogeneous. Such homogeneity may not always be guaranteed when the size of the experiment is relatively large. Suitably partitioning inhomogeneous units into homogeneous groups, known as blocks, is a practical design strategy. How to partition the experimental units for a given design is an important issue. The blocked general minimum lower order confounding is a new criterion for selecting blocked designs. With the help of doubling theory and second order saturated design, we present a theory on constructing optimal blocked designs under the blocked general minimum lower order confounding criterion. 相似文献
960.
使用二维有限体积方法,对在管流中固定位置处注入静止固体粒子的可压缩含灰气体流动进行数值模拟,讨论流场和粒子在过程中的耦合,研究质量增加和热量变化所产生的非定常波系,分析物理参数在过程中的变化.结果表明,在添质和加热过程中,流场会产生不同类型和不同强度的非定常波,在分析其物理规律的同时,讨论添质和加热相互作用导致的波系间转换,最后求解流场中各区域的热力学参数,得到不同的流场速度和粒子温度情况下各非定常波波强的相图,定量解释改变参数引起的非定常波变化规律. 相似文献