全文获取类型
收费全文 | 113543篇 |
免费 | 3290篇 |
国内免费 | 1708篇 |
专业分类
电工技术 | 2231篇 |
技术理论 | 6篇 |
综合类 | 4274篇 |
化学工业 | 16652篇 |
金属工艺 | 6713篇 |
机械仪表 | 4906篇 |
建筑科学 | 4510篇 |
矿业工程 | 1399篇 |
能源动力 | 1920篇 |
轻工业 | 5343篇 |
水利工程 | 1777篇 |
石油天然气 | 2410篇 |
武器工业 | 167篇 |
无线电 | 12460篇 |
一般工业技术 | 19952篇 |
冶金工业 | 4242篇 |
原子能技术 | 646篇 |
自动化技术 | 28933篇 |
出版年
2024年 | 126篇 |
2023年 | 499篇 |
2022年 | 822篇 |
2021年 | 1166篇 |
2020年 | 880篇 |
2019年 | 734篇 |
2018年 | 15127篇 |
2017年 | 14172篇 |
2016年 | 10779篇 |
2015年 | 1672篇 |
2014年 | 1661篇 |
2013年 | 1932篇 |
2012年 | 4890篇 |
2011年 | 11350篇 |
2010年 | 10034篇 |
2009年 | 7249篇 |
2008年 | 8360篇 |
2007年 | 9220篇 |
2006年 | 1619篇 |
2005年 | 2539篇 |
2004年 | 2137篇 |
2003年 | 2202篇 |
2002年 | 1598篇 |
2001年 | 1136篇 |
2000年 | 984篇 |
1999年 | 949篇 |
1998年 | 790篇 |
1997年 | 611篇 |
1996年 | 571篇 |
1995年 | 444篇 |
1994年 | 395篇 |
1993年 | 276篇 |
1992年 | 223篇 |
1991年 | 178篇 |
1990年 | 122篇 |
1989年 | 106篇 |
1988年 | 85篇 |
1987年 | 51篇 |
1986年 | 55篇 |
1968年 | 44篇 |
1967年 | 34篇 |
1966年 | 46篇 |
1965年 | 46篇 |
1960年 | 30篇 |
1959年 | 36篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
M. Del C. Ruiz J. A. González J. B. Rivarola 《Metallurgical and Materials Transactions B》2004,35(3):439-448
The mechanism and kinetics of β-Ta2O5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature
range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray
diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters
was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method,
and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature
has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is
144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the
order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable
mechanism for the carbochlorination of β-Ta2O5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta2O5, (3) oxidation of carbon, and (4) recrystallization of β-Ta2O5. 相似文献
42.
43.
44.
45.
This paper reports the findings of a detailed study of Web-based systems design (WBSD) practices in Ireland based on data
collected over a 3-year period (2002–2005), the objectives of which were to (1) contribute towards a richer understanding
of the current “real-world” context of WBSD by characterising the profile of a typical project (team size, timeframe, nature
of requirements, etc.) and identifying the key challenges, constraints, and imperatives (i.e. “mediating factors”) faced by
Web-based system designers, and (2) understand how those contextual parameters and mediating factors influence the activity
of WBSD as regards the selection and enactment of whatever design practices are therefore engaged (i.e. the use of methods,
procedures, etc.). Data was gathered through a survey which yielded 165 usable responses, and later through a series of semi-structured
qualitative interviews. Using grounded theory, an explanatory conceptual framework is derived, based on an extension of the
“method-in-action” model, the application of which to WBSD has not been previously investigated in depth. It is proposed that
this framework of WBSD issues is valuable in a number of ways to educators, researchers, practitioners, and method engineers. 相似文献
46.
47.
应用不同剂量的~(60)Coγ射线照射含NT株弓形虫包囊的鼠脑匀浆后,以0.4%胰蛋白酶液消化,使弓形虫缓殖子从包囊中释放出来,并用生理盐水作连续10倍稀释,使成为含不同数量缓殖子的悬液,将此悬液接种小鼠,用生物检测方法确定其感染性。另设未经照射处理的缓殖子悬液感染小鼠的对照组。结果表明,γ射线0.55kGy剂量为控制鼠脑中NT株弓形虫感染性的最小有效剂量。γ射线0.1kGy剂量对弓形虫缓殖子感染性无明显影响,而0.45kGy照射后,其感染性较前者下降了10~4倍。 相似文献
48.
Keng Siau 《Requirements Engineering》2007,12(4):199-201
49.
Phase-change read-and-write memory (PRAM) is a promising memory that can solve the problems of conventional memory—scalability, read/write speed, and reliability. We will review the opportunities and technical challenges of PRAM. The most important challenge of PRAM is the reduction of the writing current. Various approaches to reduce the writing current will be reviewed and the prospects of PRAM are discussed. 相似文献
50.