全文获取类型
收费全文 | 2906篇 |
免费 | 299篇 |
国内免费 | 93篇 |
专业分类
化学 | 221篇 |
晶体学 | 11篇 |
力学 | 1617篇 |
综合类 | 34篇 |
数学 | 479篇 |
物理学 | 936篇 |
出版年
2024年 | 6篇 |
2023年 | 19篇 |
2022年 | 51篇 |
2021年 | 40篇 |
2020年 | 65篇 |
2019年 | 54篇 |
2018年 | 49篇 |
2017年 | 68篇 |
2016年 | 99篇 |
2015年 | 79篇 |
2014年 | 144篇 |
2013年 | 134篇 |
2012年 | 118篇 |
2011年 | 168篇 |
2010年 | 101篇 |
2009年 | 157篇 |
2008年 | 159篇 |
2007年 | 190篇 |
2006年 | 168篇 |
2005年 | 156篇 |
2004年 | 124篇 |
2003年 | 129篇 |
2002年 | 100篇 |
2001年 | 78篇 |
2000年 | 86篇 |
1999年 | 81篇 |
1998年 | 99篇 |
1997年 | 86篇 |
1996年 | 62篇 |
1995年 | 60篇 |
1994年 | 59篇 |
1993年 | 48篇 |
1992年 | 56篇 |
1991年 | 50篇 |
1990年 | 53篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1957年 | 2篇 |
排序方式: 共有3298条查询结果,搜索用时 15 毫秒
71.
An investigation of heat transfer and pressure drop from some louvered surfaces is presented. The test rig and the measuring as well as the data evaluating procedures are described. The measured data are transferred and presented in a nondimenswnal form. The heal transfer data are provided mainly as Stanton numbers versus Reynolds number, and the pressure drop is given as Darcy friction factors versus Reynolds number. For comparing the performance of the various louvered surfaces, the flow area goodness factors and the so-called volume goodness factors are presented. All the louvered surfaces have been found to be more efficient than the corresponding smooth surface. The standard multilouvered fin surfaces were found to be most efficient, but one of the new surfaces also performed very well. 相似文献
72.
The growth of a prolate or oblate elliptic micro-void in a fiber reinforced anisotropic incompressible hyper-elastic rectangular thin plate subjected to uniaxial extensions is studied within the framework of finite elasticity. Coupling effects of void shape and void size on the growth of the void are paid special attention to. The deformation function of the plate with an isolated elliptic void is given, which is expressed by two parameters to solve the differential equation. The solution is approximately obtained from the minimum potential energy principle. Deformation curves for the void with a wide range of void aspect ratios and the stress distributions on the surface of the void have been obtained by numerical computation. The growth behavior of the void and the characteristics of stress distributions on the surface of the void are captured. The combined effects of void size and void shape on the growth of the void in the thin plate are discussed. The maximum stresses for the void with different sizes and different void aspect ratios are compared. 相似文献
73.
SUI GuoFa LI JinShan SUN Feng* MA Bei & LI HongWei State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi’an China 《中国科学:物理学 力学 天文学(英文版)》2011,(5)
A 3D finite element model of the explosive welding process of three-layer plates with materials of steel-copper-copper is established. Based on the presented model, the bonding mechanism is simulated and analyzed, different detonation modes are also comparatively studied to indicate the driving force spread in few microseconds. The results show that the three layer plates bond together after many times of impact between the flyers and the base driven by detonation wave, which is damping rapidly at each impa... 相似文献
74.
飞机水上迫降以及船体在高速行驶时,均会发生结构物砰击水面的现象,当结构物底面较为平坦,砰击水面时会捕获空气,在板底形成空气垫。研究空气垫的形成及影响,有助于对结构物进行更准确的载荷分析。该问题的研究涉及到气固液三相的相互作用,在数值模拟中仍是一个挑战,本文使用光滑粒子流体动力学(SPH)方法对该问题进行模拟。首先,与实验结果进行对比;其次,系统地研究了平板形成空气垫以及砰击水面的过程,考查了空气、水和平板的动能变化。对比了在SPH模拟中考虑空气与不考虑空气得到的水压力场和平板所受压力,说明了空气对结果的影响;最后,研究了平板宽度对空气垫形成的影响,从而进一步影响加速度。 相似文献
75.
This paper experimentally studies the natural convection heat transfer characteristics on horizontal and vertical plates at pressures lower than atmospheric value. Eight different pressures ranging from 10Pa to 101.325kPa, and three heating loads were used in the experiments. It is found that natural convection heat transfer characteristics at reduced pressures are independent of the plate arrangements and present different behaviors in two pressure ranges, 10Pa < p < 1000Pa and p > 1000Pa. The experimental heat transfer results are correlated into a non-dimensional equation to help the thermal design of stratosphere aircrafts and airborne equipment. 相似文献
76.
Flapping-powered propulsion is used by many animals to locomote through air or water. Here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These studies improve our understanding of the mutual interaction between actively flapping bodies and surrounding fluids. The results obtained in these works provide not only new insights into biolocomotion but also useful information for the bio-mimetic design of artificial flyers and swimmers. 相似文献
77.
Vando Narciso 《Mathematical Methods in the Applied Sciences》2015,38(4):775-784
This paper is concerned with the existence of a global attractor for the nonlinear viscoelastic beam equation with past history memory where g(ut) is a damping like | ut | rut and f(u) is a source term like | u | αu ? | u | βu, by considering 0 ≤ β < α and r > 0. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
78.
B. Shankar Goud Y. Dharmendar Reddy S.R. Mishra M. Ijaz Khan Kamel Guedri Ahmed M. Galal 《印度化学会志》2022,99(8):100618
For this research, an examination on the magnetohydrodynamic flow of a micropolar fluid across a moving vertical porous plate for the presence of thermal radiation is achieved. It is necessary to translate the partial differential equations regulating the flow, heat, & mass transfer into dimensionless form employing proper non-dimensional variables, which are then cracked numerically by utilizing the Finite difference approach. Graphs are used to represent numerical values of various flow profiles; however, tables are used to represent the simulated values of rate coefficients. The velocity rises when the value of Grashof number, dimensionless viscosity ratio is raised, and the opposite effect is seen when the value of magnetic parameter, micro-gyration factor is raised. The result in skin friction coefficient improves when the values of magnetic parameter, micro-gyration factor, Prandtl number, and radiation are raised higher. 相似文献
79.
The present study demonstrates ultrasound-induced cell injury using a nickel–titanium dioxide (Ni–TiO2) alloy plate as a sonocatalyst and a cell culture surface. Ultrasound irradiation of cell-free Ni–TiO2 alloy plates with 1 MHz ultrasound at 0.5 W/cm2 for 30 s led to an increased generation of hydroxyl (OH) radicals compared to nickel–titanium (Ni–Ti) control alloy plates with and without ultrasound irradiation. When human breast cancer cells (MCF-7 cells) cultured on the Ni–TiO2 alloy plates were irradiated with 1 MHz ultrasound at 0.5 W/cm2 for 30 s and then incubated for 48 h, cell density on the alloy plate was reduced to approximately 50% of the controls on the Ni–Ti alloy plates with and without ultrasound irradiation. These results indicate the injury of MCF-7 cells following sonocatalytic OH radical generation by Ni–TiO2. Further experiments demonstrated cell shrinkage and chromatin condensation after ultrasound irradiation of MCF-7 cells attached on the Ni–TiO2 alloy plates, indicating induction of apoptosis. 相似文献
80.
In situ X‐ray data collection and structure phasing of protein crystals at Structural Biology Center 19‐ID
下载免费PDF全文
![点击此处可从《Journal of synchrotron radiation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Karolina Michalska Kemin Tan Changsoo Chang Hui Li Catherine Hatzos‐Skintges Michael Molitsky Randy Alkire Andrzej Joachimiak 《Journal of synchrotron radiation》2015,22(6):1386-1395
A prototype of a 96‐well plate scanner for in situ data collection has been developed at the Structural Biology Center (SBC) beamline 19‐ID, located at the Advanced Photon Source, USA. The applicability of this instrument for protein crystal diffraction screening and data collection at ambient temperature has been demonstrated. Several different protein crystals, including selenium‐labeled, were used for data collection and successful SAD phasing. Without the common procedure of crystal handling and subsequent cryo‐cooling for data collection at T = 100 K, crystals in a crystallization buffer show remarkably low mosaicity (<0.1°) until deterioration by radiation damage occurs. Data presented here show that cryo‐cooling can cause some unexpected structural changes. Based on the results of this study, the integration of the plate scanner into the 19‐ID end‐station with automated controls is being prepared. With improvement of hardware and software, in situ data collection will become available for the SBC user program including remote access. 相似文献