全文获取类型
收费全文 | 24906篇 |
免费 | 3268篇 |
国内免费 | 3349篇 |
专业分类
化学 | 14140篇 |
晶体学 | 282篇 |
力学 | 739篇 |
综合类 | 264篇 |
数学 | 1967篇 |
物理学 | 5666篇 |
无线电 | 8465篇 |
出版年
2024年 | 36篇 |
2023年 | 319篇 |
2022年 | 459篇 |
2021年 | 647篇 |
2020年 | 624篇 |
2019年 | 700篇 |
2018年 | 621篇 |
2017年 | 547篇 |
2016年 | 903篇 |
2015年 | 1025篇 |
2014年 | 1218篇 |
2013年 | 1670篇 |
2012年 | 1894篇 |
2011年 | 1978篇 |
2010年 | 1596篇 |
2009年 | 1594篇 |
2008年 | 1881篇 |
2007年 | 1732篇 |
2006年 | 1603篇 |
2005年 | 1395篇 |
2004年 | 1274篇 |
2003年 | 1148篇 |
2002年 | 1294篇 |
2001年 | 1091篇 |
2000年 | 810篇 |
1999年 | 612篇 |
1998年 | 387篇 |
1997年 | 390篇 |
1996年 | 343篇 |
1995年 | 297篇 |
1994年 | 241篇 |
1993年 | 233篇 |
1992年 | 201篇 |
1991年 | 144篇 |
1990年 | 132篇 |
1989年 | 107篇 |
1988年 | 68篇 |
1987年 | 62篇 |
1986年 | 43篇 |
1985年 | 43篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
101.
Gunapala S.D. Bundara S.V. Liu J.K. Winn Hong Mani Sundaram Maker P.D. Muller R.E. Shott C.A. Carralejo R. 《Electron Devices, IEEE Transactions on》1998,45(9):1890-1895
A 9-μm cutoff 640×486 snap-shot quantum well infrared photodetector (QWIP) camera has been demonstrated. The performance of this QWIP camera is reported including indoor and outdoor imaging. The noise equivalent differential temperature (NEΔT) of 36 mK has been achieved at 300 K background with f/2 optics. This is in good agreement with expected focal plane array sensitivity due to the practical limitations on charge handling capacity of the multiplexer, read noise, bias voltage, and operating temperature 相似文献
102.
103.
104.
钢管内径光电检测装置 总被引:3,自引:0,他引:3
介绍了一种检测细长钢管内径的光电检测装置。该装置利用线阵CCD作传感器,采用8031单片机作为主控制。 相似文献
105.
主要介绍了丝绸之路上多元文化的典型代表——艾德莱斯绸.文章重点介绍了艾德莱斯绸的历史和传说,扎经染色工艺,各类艾德莱斯绸的特点及典型的艾德莱斯绸图案. 相似文献
106.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
107.
Transformations for nonideal uniform circular arrays operating in correlated signal environments 总被引:2,自引:0,他引:2
Buon Kiong Lau Yee Hong Leung Yanqun Liu Kok Lay Teo 《Signal Processing, IEEE Transactions on》2006,54(1):34-48
The Davies transformation is a method to transform the steering vector of a uniform circular array (UCA) to one with Vandermonde form. As such, it allows techniques such as spatial smoothing for direction-of-arrival (DOA) estimation in a correlated signal environment, developed originally for uniform linear arrays, to be applied to UCAs. However, the Davies transformation can be highly sensitive to perturbations of the underlying array model. This paper presents a method for deriving a more robust transformation using optimization techniques. The effectiveness of the method is illustrated through a number of DOA estimation examples. 相似文献
108.
A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion
Vinh Trong Le Xiaohong Jiang Son Hong Ngo Susumu Horiguchi Yasushi Inoguchi 《Optical Switching and Networking》2006,3(3-4):173-190
In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied. 相似文献
109.
Dual-Mode Microstrip Open-Loop Resonators and Filters 总被引:1,自引:0,他引:1
A miniature dual-mode microstrip open-loop resonator is proposed. Distinct characteristics of this new type of dual-mode resonator are investigated using full-wave electromagnetic simulations. It is shown that the two operating modes, i.e., the even and odd modes, within a single dual-mode resonator of this type do not couple. It is also found that there is a finite-frequency transmission zero inherently associated with the even mode. Two two-pole filters using this type of dual-mode resonator are demonstrated with opposite asymmetric responses, which result from different locations of the transmission zero. Higher order filters of this type are also investigated. Both simulated and measured results are presented. 相似文献
110.