全文获取类型
收费全文 | 390436篇 |
免费 | 24653篇 |
国内免费 | 12639篇 |
专业分类
电工技术 | 17746篇 |
技术理论 | 31篇 |
综合类 | 20944篇 |
化学工业 | 64114篇 |
金属工艺 | 22486篇 |
机械仪表 | 22780篇 |
建筑科学 | 26900篇 |
矿业工程 | 10837篇 |
能源动力 | 9710篇 |
轻工业 | 21873篇 |
水利工程 | 6520篇 |
石油天然气 | 21773篇 |
武器工业 | 2461篇 |
无线电 | 42770篇 |
一般工业技术 | 51957篇 |
冶金工业 | 18752篇 |
原子能技术 | 3407篇 |
自动化技术 | 62667篇 |
出版年
2024年 | 1356篇 |
2023年 | 5136篇 |
2022年 | 8880篇 |
2021年 | 12785篇 |
2020年 | 9570篇 |
2019年 | 8099篇 |
2018年 | 21994篇 |
2017年 | 22210篇 |
2016年 | 17938篇 |
2015年 | 12967篇 |
2014年 | 15414篇 |
2013年 | 18336篇 |
2012年 | 22350篇 |
2011年 | 29877篇 |
2010年 | 25902篇 |
2009年 | 22403篇 |
2008年 | 23164篇 |
2007年 | 23704篇 |
2006年 | 17262篇 |
2005年 | 16292篇 |
2004年 | 10788篇 |
2003年 | 9536篇 |
2002年 | 8335篇 |
2001年 | 6978篇 |
2000年 | 7646篇 |
1999年 | 8953篇 |
1998年 | 7210篇 |
1997年 | 6107篇 |
1996年 | 5738篇 |
1995年 | 4717篇 |
1994年 | 3935篇 |
1993年 | 2737篇 |
1992年 | 2225篇 |
1991年 | 1690篇 |
1990年 | 1223篇 |
1989年 | 977篇 |
1988年 | 797篇 |
1987年 | 551篇 |
1986年 | 412篇 |
1985年 | 271篇 |
1984年 | 191篇 |
1983年 | 124篇 |
1982年 | 137篇 |
1981年 | 96篇 |
1980年 | 77篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 46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
101.
102.
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
103.
104.
105.
106.
Zhen-Qiu Lu Yan-Yun Zhang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):296-302
Reconstruction algorithms and their numerical examples of acoustical tomography based on the second-order Born transform perturbation approximation are presented. The reconstruction algorithms in the second-order Born approximation are similar in form to those in the first-order Born approximation. Replacing the angular spectrum of the scattered wave in the first-order case by the result of applying a first-order operator to the angular spectrum of the scattered wave or applying a second-order operator to the angular spectrum of the incident wave leads to the second-order reconstruction algorithms. Also, comparisons of reconstruction algorithms of the first- and second-order Born approximations are given, and they show that the second-order Born approximation algorithms have a distinct advantage over the first-order approximations in many cases 相似文献
107.
108.
Zhang Sheng-ming Yangtze River Scientific Research Institute Wuhan Hubei P. R. China 《水动力学研究与进展(B辑)》1992,(2)
Through a series of model tests of five scales for 2-D free hydraulic jump, the da-ta of fluctuating pressure acting on the floor level within the hydraulic jump were obtained. Dur-ing the experiments, Froude number varied from 2.94 to 8.61, and Reynolds number rangedfrom 2×10~4 to 6×10~5. Experiment results indicate that the amplitude scale of fluctuating pres-sure is the length scale of model, i. e. P'=L, which agrees with gravity similarity law: Thefrequency scale of the fluctuating pressure is a unity i. e., f=1, which does not satisfy thegravity similarity law. 相似文献
109.
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
110.
By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed. 相似文献