全文获取类型
收费全文 | 157585篇 |
免费 | 13097篇 |
国内免费 | 6960篇 |
专业分类
电工技术 | 8761篇 |
技术理论 | 3篇 |
综合类 | 8385篇 |
化学工业 | 25133篇 |
金属工艺 | 8565篇 |
机械仪表 | 10176篇 |
建筑科学 | 9479篇 |
矿业工程 | 3327篇 |
能源动力 | 5305篇 |
轻工业 | 11213篇 |
水利工程 | 2812篇 |
石油天然气 | 4953篇 |
武器工业 | 1287篇 |
无线电 | 22284篇 |
一般工业技术 | 21774篇 |
冶金工业 | 9918篇 |
原子能技术 | 2179篇 |
自动化技术 | 22088篇 |
出版年
2024年 | 483篇 |
2023年 | 1825篇 |
2022年 | 3513篇 |
2021年 | 5262篇 |
2020年 | 3884篇 |
2019年 | 3457篇 |
2018年 | 3966篇 |
2017年 | 4430篇 |
2016年 | 4587篇 |
2015年 | 5553篇 |
2014年 | 7489篇 |
2013年 | 9834篇 |
2012年 | 10678篇 |
2011年 | 12229篇 |
2010年 | 10763篇 |
2009年 | 10633篇 |
2008年 | 10471篇 |
2007年 | 9745篇 |
2006年 | 9038篇 |
2005年 | 7354篇 |
2004年 | 5865篇 |
2003年 | 4996篇 |
2002年 | 4838篇 |
2001年 | 3987篇 |
2000年 | 3339篇 |
1999年 | 2732篇 |
1998年 | 3177篇 |
1997年 | 2263篇 |
1996年 | 1875篇 |
1995年 | 1508篇 |
1994年 | 1128篇 |
1993年 | 1018篇 |
1992年 | 712篇 |
1991年 | 671篇 |
1990年 | 555篇 |
1989年 | 528篇 |
1988年 | 397篇 |
1987年 | 339篇 |
1986年 | 310篇 |
1985年 | 257篇 |
1984年 | 221篇 |
1983年 | 182篇 |
1982年 | 172篇 |
1981年 | 154篇 |
1980年 | 147篇 |
1979年 | 112篇 |
1978年 | 101篇 |
1977年 | 136篇 |
1976年 | 170篇 |
1975年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
农村通信如何"突围" 总被引:2,自引:0,他引:2
农村通信作为农村地区信息化的基础,对于全面建设小康具有特殊的重要地位。介绍了我国农村通信的发展现状,分析了农村通信发展的困难压其原因,最后对农村压边远、欠发达地区通信的均衡震展提出了一些建议。 相似文献
152.
153.
154.
文中详细地阐述了取河水、井水、水库水、跨流城引(排)水等不同情况进行还原的具体方法步骤。并对水量还原成果提出合理性检查措施。 相似文献
155.
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
156.
Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry 相似文献
157.
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
158.
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
159.
160.