全文获取类型
收费全文 | 94273篇 |
免费 | 14607篇 |
国内免费 | 9811篇 |
专业分类
化学 | 50845篇 |
晶体学 | 657篇 |
力学 | 4739篇 |
综合类 | 310篇 |
数学 | 8194篇 |
物理学 | 28824篇 |
无线电 | 25122篇 |
出版年
2024年 | 415篇 |
2023年 | 2409篇 |
2022年 | 3019篇 |
2021年 | 3803篇 |
2020年 | 3791篇 |
2019年 | 3501篇 |
2018年 | 3018篇 |
2017年 | 2875篇 |
2016年 | 4153篇 |
2015年 | 4345篇 |
2014年 | 5175篇 |
2013年 | 6510篇 |
2012年 | 8104篇 |
2011年 | 8037篇 |
2010年 | 5722篇 |
2009年 | 5648篇 |
2008年 | 5957篇 |
2007年 | 5307篇 |
2006年 | 4972篇 |
2005年 | 4203篇 |
2004年 | 3111篇 |
2003年 | 2636篇 |
2002年 | 2338篇 |
2001年 | 1982篇 |
2000年 | 1926篇 |
1999年 | 2135篇 |
1998年 | 1838篇 |
1997年 | 1686篇 |
1996年 | 1683篇 |
1995年 | 1414篇 |
1994年 | 1229篇 |
1993年 | 1005篇 |
1992年 | 900篇 |
1991年 | 761篇 |
1990年 | 618篇 |
1989年 | 439篇 |
1988年 | 379篇 |
1987年 | 298篇 |
1986年 | 273篇 |
1985年 | 233篇 |
1984年 | 171篇 |
1983年 | 123篇 |
1982年 | 93篇 |
1981年 | 75篇 |
1980年 | 76篇 |
1979年 | 39篇 |
1978年 | 35篇 |
1977年 | 46篇 |
1976年 | 39篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
51.
Image registration by "Super-curves" 总被引:4,自引:0,他引:4
Minghui Xia Bede Liu 《IEEE transactions on image processing》2004,13(5):720-732
We solve the 2-D affine image registration problem by curve matching and alignment. Our approach starts with a super-curve, which is formed by superimposing two affine related curves in one coordinate system. We use B-spline fusion technique to find a single B-spline approximation of the super-curve and a registration between the two curves simultaneously. This approach achieves superior accuracy and efficiency in curve matching and alignment. We then address the occlusion problem by finding partial match between the curves segmented using inflections and cusps, which are affine invariant. The combination of edge detection and curve alignment lead to accurate image registration. 相似文献
52.
53.
Navid Ehsan Mingyan Liu Roderick J. Ragland 《International Journal of Communication Systems》2003,16(6):513-534
Performance enhancing proxies (PEPs) are widely used to improve the performance of TCP over high delay‐bandwidth product links and links with high error probability. In this paper we analyse the performance of using TCP connection splitting in combination with web caching via traces obtained from a commercial satellite system. We examine the resulting performance gain under different scenarios, including the effect of caching, congestion, random loss and file sizes. We show, via analysing our measurements, that the performance gain from using splitting is highly sensitive to random losses and the number of simultaneous connections, and that such sensitivity is alleviated by caching. On the other hand, the use of a splitting proxy enhances the value of web caching in that cache hits result in much more significant performance improvement over cache misses when TCP splitting is used. We also compare the performance of using different versions of HTTP in such a system. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
54.
Haiyan Chen Jizhi Dai Yongzhi Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(5):749-757
The effect of fog and clouds in millimeter communication is discussed, and the attenuation caused by fog and clouds is reviewed. Signal-to-noise ratio (SNR) of image is derived using relating models of fog and clouds attenuation. According to the relation of image quality and its signal-to-noise ratio, the system behavior is forecasted theoretically. It is shown that the signal-to-noise ratio of receiver at certain transmitter power is inverse with radio wave frequency, from about 70dB at 10GHz to 48dB for fog and 49dB for clouds. The image quality of received signal at certain transmitter power is inverse with radio wave frequency, from about 7 grade at 10GHz to 5.27 grade for fog and 5.37 grade for clouds. The above calculated results are consistent with experimental results. 相似文献
55.
Bijian Lan Chunming Liu Xiang Yin Hua Zhang Wei Xu Zhongyi Hua 《Frontiers of Chemistry in China》2006,1(3):296-299
Organic materials of D-π-A type MR-X (MR-1: p-dimethylaminophenylethenetrica-rbonitrile and MR-2: p-diphenylaminophenylethene tricarbonitrile) were designed and synthesized. The device with a sandwich structure shows good
rectificative phenomena. The highest rectification ratio 10000 was achieved in device Cu/MR-1/Ag, and about 100 in other device
M/MR-X/M (M: Cu, Ag). It has been found that rectificative phenomena exist only in the atmosphere-liquid interface region
by means of liquid adsorption, and electric field could help form the oriented molecular film.
__________
Translated from Journal of Fudan University (Natural Science), 2005, 44(4) (in Chinese) 相似文献
56.
57.
58.
Ion-ripple laser, which consists of a relativistic electron beam obliquely propagating through an ion-ripple in a plasma, is investigated by nonlinear numerical simulation. The influence of the component of the ion-ripple field parallel to the beam direction on beam-wave interaction is analyzed. The results show that the longitudinal component of the ion-ripple field has a considerable influence on ion-ripple laser. The operating parameters are also optimized. 相似文献
59.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
60.
A distributed problem solving system can be characterized as a group of individual cooperating agents running to solve common problems. As dynamic application domains continue to grow in scale and complexity, it becomes more difficult to control the purposeful behavior of agents, especially when unexpected events may occur. This article presents an information and knowledge exchange framework to support distributed problem solving. From the application viewpoint the article concentrates on the stock trading domain; however, many presented solutions can be extended to other dynamic domains. It addresses two important issues: how individual agents should be interconnected so that their resources are efficiently used and their goals accomplished effectively; and how information and knowledge transfer should take place among the agents to allow them to respond successfully to user requests and unexpected external situations. The article introduces an architecture, the MASST system architecture, which supports dynamic information and knowledge exchange among the cooperating agents. The architecture uses a dynamic blackboard as an interagent communication paradigm to facilitate factual data, business rule, and command exchange between cooperating MASST agents. The critical components of the MASST architecture have been implemented and tested in the stock trading domain, and have proven to be a viable solution for distributed problem solving based on cooperating agents 相似文献