全文获取类型
收费全文 | 2963篇 |
免费 | 516篇 |
国内免费 | 207篇 |
专业分类
化学 | 633篇 |
晶体学 | 15篇 |
力学 | 618篇 |
综合类 | 13篇 |
数学 | 294篇 |
物理学 | 383篇 |
无线电 | 1730篇 |
出版年
2024年 | 22篇 |
2023年 | 114篇 |
2022年 | 65篇 |
2021年 | 151篇 |
2020年 | 175篇 |
2019年 | 163篇 |
2018年 | 132篇 |
2017年 | 137篇 |
2016年 | 150篇 |
2015年 | 134篇 |
2014年 | 159篇 |
2013年 | 181篇 |
2012年 | 170篇 |
2011年 | 215篇 |
2010年 | 122篇 |
2009年 | 132篇 |
2008年 | 159篇 |
2007年 | 150篇 |
2006年 | 161篇 |
2005年 | 146篇 |
2004年 | 128篇 |
2003年 | 126篇 |
2002年 | 84篇 |
2001年 | 70篇 |
2000年 | 61篇 |
1999年 | 69篇 |
1998年 | 50篇 |
1997年 | 45篇 |
1996年 | 32篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1957年 | 6篇 |
1936年 | 1篇 |
排序方式: 共有3686条查询结果,搜索用时 19 毫秒
2.
目前需求预测在整个印制电路板产业的生产活动控制中正扮演着越来越重要的角色。分析了影响印制电路板需求的因素和现有的预测方法,提出了一种适用于PCB产业需求预测的有效方法——遗传/BP—神经网络。实验表明该方法能够进一步改善印制电路板预测的准确度和减少生产成本的消耗。 相似文献
3.
对电子机柜传统的走线方式进行了分析、解剖,提出了新的走线方案模式,从工艺角度对机柜走线结构进行了改进设计,使之更适合于车载机柜的布线要求。 相似文献
4.
对微波陶瓷基印制板的制造工艺流程进行了简单的介绍,对所采用的工艺技术的有效性进行了较为详细的论述。 相似文献
5.
气垫导轨在刚体转动惯量测定实验中的应用 总被引:1,自引:0,他引:1
本文介绍了一种测量刚体转动惯量的新方法。即把气垫导轨和刚体转动仪结合起来来测量刚体的转动惯量,使传统的气垫导轨实验和刚体转动惯量测定实验得以更新,提高了实验测量的精度,拓展了实验内容。 相似文献
6.
7.
L. Brian Lawrence 《Transactions of the American Mathematical Society》2005,357(7):2535-2556
Working in ZFC, we give an example as indicated in the title.
8.
Experiments concerning the properties of soap films have recently been carried out and these systems have been proposed as experimental versions of theoretical two‐dimensional liquids. A silk filament introduced into a flowing soap film, was seen to demonstrate various stable modes, and these were, namely, a mode in which the filament oscillates and one in which the filament is stationary and aligns with the flow of the liquid. The system could be forced from the oscillatory mode into the non‐ oscillatory mode by varying the length of the filament. In this article we use numerical and computational techniques in order to simulate the strongly coupled behaviour of the filament and the fluid. Preliminary results are presented for the specific case in which the filament is seen to oscillate continuously for the duration of our simulation. We also find that the filament oscillations are strongly suppressed when we reduce the effective length of the filament. We believe that these results are reminiscent of the different oscillatory and non‐oscillatory modes observed in experiment. The numerical solutions show that, in contrast to experiment, vortices are created at the leading edge of the filament and are preferentially grown in the curvature of the filament and are eventually released from the trailing edge of the filament. In a similar manner to oscillating hydrofoils, it seems that the oscillating filaments are in a minimal energy state, extracting sufficient energy from the fluid to oscillate. In comparing numerical and experimental results it is possible that the soap film does have an effect on the fluid flow especially in the boundary layer where surface tension forces are large. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques 总被引:1,自引:0,他引:1
Hideo Fujikake Hiroto Sato Takeshi Murashige Yoshihide Fujisaki Taiichiro Kurita Tadahiro Furukawa Fumio Sato 《Optical Review》2006,13(1):14-19
This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black
matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate.
While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates
by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced
by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active
matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight
illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by
illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system
is useful in various information displays because of its freedom of setting and location. 相似文献
10.
Jaroslav Neetil 《Journal of Graph Theory》2002,39(2):108-110
A graph G is called rigid if the identical mapping V(G)→V(G) is the only homomorphism G→G. In this note we give a simple construction of a rigid oriented graph on every set. © 2002 John Wiley & Sons, Inc. J Graph Theory 39: 108–110, 2002 相似文献