全文获取类型
收费全文 | 518篇 |
免费 | 173篇 |
国内免费 | 10篇 |
专业分类
化学 | 82篇 |
晶体学 | 13篇 |
力学 | 36篇 |
综合类 | 10篇 |
数学 | 59篇 |
物理学 | 501篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 10篇 |
2020年 | 27篇 |
2019年 | 5篇 |
2018年 | 14篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 45篇 |
2012年 | 43篇 |
2011年 | 41篇 |
2010年 | 38篇 |
2009年 | 26篇 |
2008年 | 44篇 |
2007年 | 35篇 |
2006年 | 38篇 |
2005年 | 20篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 23篇 |
2001年 | 24篇 |
2000年 | 31篇 |
1999年 | 16篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有701条查询结果,搜索用时 15 毫秒
131.
132.
完善系统集成环境提高光电总体技术水平 总被引:1,自引:1,他引:0
以系统工程方法论述光电总体技术的特征、内容及方法。阐述了光电总体技术研究环境。 相似文献
133.
N. Kulatilaka 《Annals of Operations Research》1985,3(2):35-57
This paper investigates the financial-economic decision process for investments in flexible manufacturing systems (FMS). Contrary to popular belief, we show that conventional capital budgeting techniques can be used to make such investment decisions. First, we identify theoverall impact of installing an FMS and present guidelines for a cash flow forecasting model. We then present ways in which to incorporate uncertainty in these cash flows within a risk-adjusted discount rate. These expected cash flows and the discount rate are used in calculating the net present value (NPV). Once the capital budgeting analysis is completed, a critical issue facing the firm is the optimal timing of the installation. We reinterpret the general results on optimal timing of investments within the special context of an FMS project. Finally, we illustrate the above technique via a stylized example. 相似文献
134.
An apodized cubic phase mask used in a wavefront coding system to extend the depth of field
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The point spread function (PSF) caused by a wavefront coding system with a cubic phase mask has big side-lobes which leads to bad image restoration. This paper proposes a novel apodized cubic phase mask to suppress the side-lobes of the PSF. Simulated annealing algorithm is used to optimize the cubic and the truncation parameter of the phase mask. The system with the novel phase mask has better performance in the modulation transfer function (MTF) especially in low-and-medium spatial frequency region. The simulation results show that the restored images with the novel phase mask are superior to the one with the classic cubic phase mask in contrast and ringing effect. The experimental results show that the side-lobes of the PSF are suppressed by using the apodized cubic phase mask. 相似文献
135.
Compounds with the same chiral terminal chain but different structure of rigid core and non-chiral terminal chain were added to basic highly tilted ferroelectric compound in the aim of establishing whether the miscibility of phases, especially ferroelectric phase, exists in these compounds and what are the helical pitch and tilt angle temperature dependence in bicomponent systems. In certain systems, we obtained a mixture with very short helical pitch at broad temperature range of ferroelectric phase, which open opportunities for the formulation of multicomponent mixtures for fast switching ferroelectric liquid crystals modes. 相似文献
136.
Effects of Motion, Implied Direction and Displacement of a Large-Visual-Stimulus on Postural Control
Effects of motion, implied direction in a static stimulus and displacement on postural control were examined independently.
In Experiment 1, rotation of a random-dot stimulus was presented. In Experiments 2 and 3, photographic slides of natural scenes
were used; participants closed their eyes during stimulus rotation to eliminate motion information. In Experiment 2, the stimulus
was presented upright initially, then presented again with a tilt. In Experiment 3, the order was reversed to separate the
effects of implied direction and displacement. Results showed that all information of motion, implied direction, and displacement
had some effect on postural control, although visual information of motion has been presumed to have a principal effect on
postural control. Results suggested that the effects of implied direction might reflect an immediate processing of information.
The effects of displacement and motion might reflect a continuous processing of information. 相似文献
137.
An approach based on depth-sensitive skew-angle x-ray diffraction (SAXRD) is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that (103) plane and (101) plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive (103)/(101) ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach. 相似文献
138.
This paper presents our study of the nonlinear stability of a new anisotropic continuum traffic flow model in which the dimensionless parameter or anisotropic factor controls the non-isotropic character and diffusive influence. In order to establish traff~c flow stability criterion or to know the critical parameters that lead, on one hand, to a stable response to perturbations or disturbances or, on the other hand, to an unstable response and therefore to a possible congestion, a nonlinear stability criterion is derived by using a wavefront expansion technique. The stability criterion is illustrated by numerical results using the finite difference method for two different values of anisotropic parameter. It is also been observed that the newly derived stability results are consistent with previously reported results obtained using approximate linearisation methods. Moreover, the stability criterion derived in this paper can provide more refined information from the perspective of the capability to reproduce nonlinear traffic flow behaviors observed in real traffic than previously established methodologies. 相似文献
139.
Nonlinear Stability of Traveling Wavefronts for a Discrete Cooperative Lotka-Volterra System With Delays北大核心CSCD
下载免费PDF全文
![点击此处可从《应用数学和力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The stability of traveling wave solutions of the reaction diffusion model is a very important research topic. The globally nonlinear stability of traveling wavefronts for a discrete cooperative Lotka-Volterra system with delays was studied. More precisely, for the initial perturbation decaying exponentially to the traveling wavefronts with a relatively large speed at infinity, but arbitrarily large speeds in other positions, by means of the L2⁃ weighted energy method, the comparison principle and the squeezing technique, such traveling wavefronts were obtained and proved to be of exponentially asymptotic stability. Moreover, the problem of establishing the energy estimates was solved under the actions of the discrete dispersal operator and the time delays. In short, the extension of the weighted energy method to discrete systems with delays, enriches the relative research. © 2023 Editorial Office of Applied Mathematics and Mechanics. All rights reserved. 相似文献
140.