全文获取类型
收费全文 | 97743篇 |
免费 | 3604篇 |
国内免费 | 371篇 |
专业分类
电工技术 | 1361篇 |
综合类 | 718篇 |
化学工业 | 14514篇 |
金属工艺 | 2607篇 |
机械仪表 | 3805篇 |
建筑科学 | 2042篇 |
矿业工程 | 439篇 |
能源动力 | 2547篇 |
轻工业 | 6067篇 |
水利工程 | 842篇 |
石油天然气 | 254篇 |
武器工业 | 5篇 |
无线电 | 11776篇 |
一般工业技术 | 14473篇 |
冶金工业 | 27152篇 |
原子能技术 | 813篇 |
自动化技术 | 12303篇 |
出版年
2023年 | 692篇 |
2022年 | 415篇 |
2021年 | 1440篇 |
2020年 | 1001篇 |
2019年 | 1052篇 |
2018年 | 1772篇 |
2017年 | 1981篇 |
2016年 | 2664篇 |
2015年 | 2060篇 |
2014年 | 2433篇 |
2013年 | 3869篇 |
2012年 | 5304篇 |
2011年 | 6299篇 |
2010年 | 3621篇 |
2009年 | 3902篇 |
2008年 | 3504篇 |
2007年 | 3075篇 |
2006年 | 2786篇 |
2005年 | 5211篇 |
2004年 | 4257篇 |
2003年 | 3632篇 |
2002年 | 2455篇 |
2001年 | 2018篇 |
2000年 | 1475篇 |
1999年 | 1794篇 |
1998年 | 8328篇 |
1997年 | 5220篇 |
1996年 | 3617篇 |
1995年 | 2396篇 |
1994年 | 1778篇 |
1993年 | 1764篇 |
1992年 | 723篇 |
1991年 | 791篇 |
1990年 | 715篇 |
1989年 | 672篇 |
1988年 | 605篇 |
1987年 | 492篇 |
1986年 | 447篇 |
1985年 | 395篇 |
1984年 | 267篇 |
1983年 | 231篇 |
1982年 | 277篇 |
1981年 | 304篇 |
1980年 | 317篇 |
1979年 | 161篇 |
1978年 | 191篇 |
1977年 | 730篇 |
1976年 | 1475篇 |
1975年 | 176篇 |
1974年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
91.
92.
A new polymer electrolyte poly(acrylonitrile)-dimethylsulphoxide-salt for electrochemical capacitors
The PAN-DMSO-Et4NBF4 and PAN-DMSO-Et4NTf (Tf is triflate ion) electrolytes were prepared as white, turbid foils with a thickness in the range of 0.1-0.5 mm, using the casting technique. Room temperature conductance of the electrolytes, detected from ac impedance experiments, was at the level of 8 and 14 mS cm−1 for Et4NBF4 and Et4NTf salts, respectively. The electrochemical stability window of approximately 2.6-2.8 V was estimated using a glassy carbon electrode. Temperature dependence of the conductivity is of the Arrhenius-type for both electrolytes, with an activation energy of approximately 34 kJ mol−1. The double-layer capacitors built with these electrolytes, serving both as separators and activated carbon powder (ACP) binders, showed a specific capacity of 50 F g−1 of carbon material. Capacitors were assembled by sandwiching the PAN-DMSO-salt electrolyte between two PAN-salt-DMSO-ACP-AB electrodes and pressing across the system; the resulting devices had a coin-like shape with 8 mm diameter and thickness between 2.0 and 2.5 mm. 相似文献
93.
Vehicle detection by means of stereo vision-based obstacles features extraction and monocular pattern analysis. 总被引:2,自引:0,他引:2
Gwena?lle Toulminet Massimo Bertozzi Stéphane Mousset Abdelaziz Bensrhair Alberto Broggi 《IEEE transactions on image processing》2006,15(8):2364-2375
This paper presents a stereo vision system for the detection and distance computation of a preceding vehicle. It is divided in two major steps. Initially, a stereo vision-based algorithm is used to extract relevant three-dimensional (3-D) features in the scene, these features are investigated further in order to select the ones that belong to vertical objects only and not to the road or background. These 3-D vertical features are then used as a starting point for preceding vehicle detection; by using a symmetry operator, a match against a simplified model of a rear vehicle's shape is performed using a monocular vision-based approach that allows the identification of a preceding vehicle. In addition, using the 3-D information previously extracted, an accurate distance computation is performed. 相似文献
94.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region. 相似文献
95.
Soo Jin Kim Wha Young Lee Yeungho Park Wansoo Huh Young Gwan Ko 《Polymer Engineering and Science》2003,43(5):1011-1017
Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes. 相似文献
96.
Sébastien Ambellouis Fran?ois Cabestaing Jack-Gérard Postaire 《IEEE transactions on image processing》2006,15(6):1601-1609
Energy-based methods for motion estimation in image sequences process the input data either in the spatiotemporal or in the frequency domain. In both cases, the algorithms already described in the literature often require a huge number of elementary operations. In this paper, we describe a class of velocity selective filters which yield an accurate detection of the edges moving in the sequence. We first present a filtering scheme based on a convolution operation computed on a finite size neighborhood and describe its properties in the spatiotemporal and frequency domains. Then, we show that filters with similar properties can be implemented recursively, i.e., as convolutions computed on infinite-size neighborhoods. As an example, we finally show the filters' responses in the case of two superimposed translational motions. 相似文献
97.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
98.
Presents an obituary and information about the life and accomplishments of Josef Maria Bro?ek. Born August 14, 1913, in the ancient town of Melnik, in central Bohemia, today the Czech Republic, Josef spent his childhood in Poland (Warsaw, 1913- 1915) and in Siberia (1915-1920). His education in Czechoslovakia culminated with a thesis on "Memory, Its Measurement and Structure" and a PhD awarded in June 1937. In the history of psychology, his lifetime project bore the title "Historiography of Psychology Around the World," and it covered about 20 geographical areas. Extensive attention was devoted to institutional and organizational developments as journals, academic settings, archives, museums, research groups, conferences, and institutes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
Evaluation and optimization of package processing and design through solder joint profile prediction 总被引:1,自引:0,他引:1
Solder joints are generated using a variety of methods to provide both mechanical and electrical connection for applications such as flip-chip, wafer level packaging, fine pitch, ball-grid array, and chip scale packages. Solder joint shape prediction has been incorporated as a key tool to aid in process development, wafer level and package level design and development, assembly, and reliability enhancement. This work demonstrates the application of an analytical model and the Surface Evolver software in analyzing a variety of solder processing methods and package types. Bump and joint shape prediction was conducted for the design of wafer level bumping, flip-chip assembly, and wafer level packaging. The results from the prediction methodologies are validated with experimentally measured geometries at each level of design. 相似文献
100.
Jeong-Soo Lee Yang-Kyu Choi Daewon Ha Balasubramanian S. Tsu-Jae King Bokor J. 《Electron Device Letters, IEEE》2003,24(3):186-188
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin. 相似文献