全文获取类型
收费全文 | 877篇 |
免费 | 174篇 |
国内免费 | 34篇 |
专业分类
化学 | 243篇 |
晶体学 | 2篇 |
力学 | 111篇 |
综合类 | 18篇 |
数学 | 146篇 |
物理学 | 565篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 21篇 |
2020年 | 43篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 44篇 |
2016年 | 41篇 |
2015年 | 25篇 |
2014年 | 48篇 |
2013年 | 95篇 |
2012年 | 57篇 |
2011年 | 50篇 |
2010年 | 40篇 |
2009年 | 46篇 |
2008年 | 64篇 |
2007年 | 57篇 |
2006年 | 66篇 |
2005年 | 40篇 |
2004年 | 41篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 19篇 |
2000年 | 36篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 19篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1085条查询结果,搜索用时 46 毫秒
71.
72.
In the last years the development of light emitting electrochemical cells on a polymer base has made a great progress. They
are extremely interesting due to their low cost, but still, problems concerning the stability and lifetime of these elements
remain.
The performance of light-emitting electrochemical cells (LEC) is strongly influenced by the inhomogeneous distribution of
the three main components (light emitting polymer, ion conductive polymer, ionic molecules) in the device. The local ions
distribution of lithium and triflate (short for the CF3SO3
− species) ions in a blend with the ionic conducting polymer poly(ethylene oxide) (PEO) and the conjugated polymer m-LPPP (methyl
substituted poly(para phenylene)) throughout the polymer layer has been investigated by secondary ion mass spectroscopy (SIMS).
Different combinations of top- and base-electrodes have been investigated and have been found to influence the distribution
of the ions strongly.
Received January 13, 1999. Revision June 16, 2000. 相似文献
73.
In this article, the depth‐averaged transport equations are written in a new way so that it is possible to solve the transport equations for very small water depths. Variables are interpolated into the cell face with two different schemes and, the schemes are compared in terms of computational cost and accuracy. The bed source terms are computed using two different assumptions. The effect of these assumptions on numerical simulations is then investigated. Solutions of transport equations on different types of unstructured triangular grids are compared and, an appropriate choice of grid is suggested. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
74.
BEPCII是一个多束团、大流强的装置, 由于高频腔的高次模和电阻壁阻抗等因素,不可避免地会出现束流不稳定性。BEPCII中采用束流反馈系统来抑制束流不稳定性。横向束流反馈系统主要包括前端电子学、信号处理电子学、反馈器件和放大器等几个部分。梳状滤波器是信号处理电子学的重要部件,利用两根长短不同的电缆以及一个功分器和合成器构成了一种简单有效的梳状滤波器,其梳状深度达到-41 dB,使用这种梳状滤波器的横向反馈系统成功地抑制了束流中出现的不稳定性。 相似文献
75.
Catherine Westfall 《Physics in Perspective (PIP)》2006,8(2):189-213
I explore the fifty-year development of M?ssbauer spectroscopy by focusing on three episodes in its development at Argonne
National Laboratory: work by nuclear physicists using radioactive sources in the early 1960s, work by solid-state physicists
using radioactive resources from the mid- 1960s through the 1970s,and work by solid-state physicists using the Advanced Photon
Source from the 1980s to 2005. These episodes show how knowledge about the properties of matter was produced in a national-laboratory
context and highlights the web of connections that allow nationallaboratory scientists working at a variety of scales to produce
both technological and scientific innovations. 相似文献
76.
在对作者原有工作改进的基础上,应用自行研制的“光纤探针深度计”首次精确测定了Kr+紫激光406.7~415.4um和He-Ne激光632.8nm波长处新鲜离休人肺组织中光能流率分布,获得这两种重要波长处人肺正常组织和人肺腺鳞癌组织中光能流率的分布规律及光穿透深度的数值:(1)δnormal=0.08mm,δtumour=0.32mm(λ=406.7~415.4nm);(2)δnormal=1.19mm,δturmour=1.70mm(λ=632.8nm),并对现有人肺组织的光穿透深度数据作了总结和讨论. 相似文献
77.
In this paper the methods of wave theory based prestack depth migration and their implementation are studied. Using the splitting of wave operator, the wavefield extrapolation equations are deduced and the numerical schemes are presented. The numerical tests for SEG/EAEG model with MPI are performed on the PC-cluster. The numerical re- 相似文献
78.
Three-dimensional (3D) laser carving is a new, very flexible process and is very useful for machining the hard and/or brittle materials such as ceramics, carbide and hardened steel with high precision, excellent productivity and surface quality. In this paper, the effects of laser processing parameters on single-layer carving depth and surface quality are analyzed by laser carving on an Al2O3 ceramic with different processing parameters. The mechanisms of laser carving are also studied. A mathematical model of the relationship between the laser processing parameters and the laser carving depth is established, which is useful in obtaining the best machining parameters with the shortest time. Finally, a 3D pattern is successfully carved using the optimum parameters. 相似文献
79.
V. I. Bukreev 《Fluid Dynamics》2005,40(5):769-776
Theoretical and experimental data which make it possible to find the flow-rate, momentum and energy of the fluid that enters the lower pool after a discontinuity breakdown (dam break) in a rectangular channel with an even bottom, a step (sharp downstream rise in the bottom), a shelf (sharp drop in the bottom), and a threshold on the bottom are presented. 相似文献
80.
水面/水下目标深度辨识可以在主动声呐探测过程中快速筛选感兴趣目标。根据目标多径返回信号到达时间与目标深度的关联性,该文提出了基于水平线阵的主动脉冲响应匹配目标深度辨识方法,该方法利用主动信号传播特性结合阵不变量理论提取脉冲响应,并与拷贝声场匹配实现目标深度估计。在校正了目标多径回波的方位变化后,该方法提取的时域特征较为稳定,并且只在时延估计距离处进行深度搜索。通过水平阵收集的宽带实验数据,在连续的多次回波中实现了对水面/水下目标92%的辨识成功率,验证了该方法在浅海环境下的目标深度估计能力。 相似文献