全文获取类型
收费全文 | 16897篇 |
免费 | 2206篇 |
国内免费 | 1089篇 |
专业分类
化学 | 910篇 |
晶体学 | 18篇 |
力学 | 558篇 |
综合类 | 273篇 |
数学 | 2710篇 |
物理学 | 4136篇 |
无线电 | 11587篇 |
出版年
2024年 | 48篇 |
2023年 | 166篇 |
2022年 | 339篇 |
2021年 | 577篇 |
2020年 | 478篇 |
2019年 | 319篇 |
2018年 | 347篇 |
2017年 | 565篇 |
2016年 | 645篇 |
2015年 | 810篇 |
2014年 | 1315篇 |
2013年 | 1225篇 |
2012年 | 1194篇 |
2011年 | 1192篇 |
2010年 | 917篇 |
2009年 | 1014篇 |
2008年 | 1240篇 |
2007年 | 1253篇 |
2006年 | 996篇 |
2005年 | 881篇 |
2004年 | 772篇 |
2003年 | 701篇 |
2002年 | 561篇 |
2001年 | 424篇 |
2000年 | 373篇 |
1999年 | 330篇 |
1998年 | 261篇 |
1997年 | 263篇 |
1996年 | 194篇 |
1995年 | 165篇 |
1994年 | 120篇 |
1993年 | 108篇 |
1992年 | 82篇 |
1991年 | 67篇 |
1990年 | 55篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 3篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1959年 | 6篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 348 毫秒
101.
José Martínez-Aroza Ramón Román-Roldán 《Multidimensional Systems and Signal Processing》1995,6(1):7-35
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government. 相似文献
102.
This paper presents a partial scan algorithm, calledPARES (PartialscanAlgorithm based onREduced Scan shift), for designing partial scan circuits. PARES is based on the reduced scan shift that has been previously proposed for generating short test sequences for full scan circuits. In the reduced scan shift method, one determines proch FFs must be controlled and observed for each test vector. According to the results of similar analysis, PARES selects these FFs that must be controlled or observed for a large number of test vectors, as scanned FFs. Short test sequences are generated by reducing scan shift operations using a static test compaction method. To minimize the loss of fault coverage, the order of test vectors is so determined that the unscanned FFs are in the state required by the next test vector. If there are any faults undetected yet by a test sequence derived from the test vectors, then PARES uses a sequential circuit test generator to detect the faults. Experimental results for ISCAS'89 benchmark circuits are given to demonstrate the effectiveness of PARES. 相似文献
103.
The coarse acquisition performance of a direct sequence spread-spectrum receiver is analyzed when a linear prediction filter is used for narrowband interference suppression. We show that once an appropriate matching strategy is identified, the linear prediction filter can provide favorable performance when narrowband interference is present over a considerable range of both interference power and bandwidth. In addition, the presence of the filter dramatically improves the performance over the case where there is no filter, except when the interference bandwidth and the power are both small (i.e., when the processing gain provides sufficient interference immunity without the filter). If long spreading sequences are used with moderately sized observation windows, the acquisition performance can be severely degraded when a parallel acquisition scheme is used due to the linear predication filter. We show, however, that a slower serial receiver will provide reliable performance.This work was supported in part by the Office of Naval Research under contract ONR N00014-91-J-1234, the Army Research Office under contract ARO DAAL03-91-0071, and the NSF Center for Ultra-High Speed Circuits and Systems (ICAS). 相似文献
104.
关于独立同分布随机变量部分和的增量有多小问题,目前已有了著名的结果.本文通过与独立同分布情形时完全不同的途径,讨论了独立不同分布情形时相应的问题.在矩母函数存在的条件下,获得了与同分布情形相近的结论. 相似文献
105.
Ari Paasio Adam Dawidziuk Kari Halonen Veikko Porra 《Analog Integrated Circuits and Signal Processing》1997,12(1):59-70
The paper presents a Cellular Neural Network implementation based on a high gain sigmoid operation. The required simplifications to the original theory are described that allow the use of high gain. With this design black and white images can be processed. The basic building blocks in a cell are described. A 16×16 cells network has been designed and processed with 1.2 micron CMOS technology. Measurement results which show the operation of the network are presented. 相似文献
106.
钙—铈氟碳酸盐矿物中BmSn型新多型的发现及其微结构研究 总被引:7,自引:2,他引:5
利用Philips CM-12分析型透射电镜对四川昌北大型稀土矿床中钙铈氟碳酸盐矿物进行了研究。除证实氟碳钙铈矿(BS)存在3R和6R2种多型外,首次发现和研究了氟碳钙铈矿(BS)存在4H、12H、18R、24R、30R和36R6种新多型;伦琴矿(BS_2)1种6R新多型和B_2S新规则混层矿物2H、12R和24R3种中新多型。电子衍射和晶格象分析表明:该类矿物中众多新多型的产生,主要是由于矿物结构单元层沿(?)轴有序堆垛和[CO_3]的定向周期性变化所致。 相似文献
107.
108.
109.
110.
设σ(k,n)表示最小的正整数m,使得对于每个n项正可图序列,当其项和至少为m时,有一个实现含k 1个顶点的团作为其子图。Erdos等人猜想:σ(k,n)=(k-1)(2n-k) 2.Li等人证明了这个猜想对于k≥5,n≥(^k2))+3是对的,并且提出如下问题:确定最小的整数N(k),使得这个猜想对于n≥N(k)成立。他们同时指出:当k≥5时,[5k-1/2]≤N(k)≤(^k2) 3.Mubayi猜想:当k≥5时,N(k)=[5k-1/2]。在本文中,我们证明了N(8)=20,即Mubayi猜想对于k=8是成立的。 相似文献