全文获取类型
收费全文 | 149159篇 |
免费 | 7175篇 |
国内免费 | 3575篇 |
专业分类
电工技术 | 5116篇 |
技术理论 | 3篇 |
综合类 | 6859篇 |
化学工业 | 22206篇 |
金属工艺 | 8760篇 |
机械仪表 | 7384篇 |
建筑科学 | 7355篇 |
矿业工程 | 2617篇 |
能源动力 | 2994篇 |
轻工业 | 8528篇 |
水利工程 | 2486篇 |
石油天然气 | 4608篇 |
武器工业 | 653篇 |
无线电 | 16324篇 |
一般工业技术 | 23996篇 |
冶金工业 | 5509篇 |
原子能技术 | 924篇 |
自动化技术 | 33587篇 |
出版年
2024年 | 349篇 |
2023年 | 1308篇 |
2022年 | 2326篇 |
2021年 | 3105篇 |
2020年 | 2473篇 |
2019年 | 1985篇 |
2018年 | 16307篇 |
2017年 | 15527篇 |
2016年 | 11893篇 |
2015年 | 3446篇 |
2014年 | 3895篇 |
2013年 | 4191篇 |
2012年 | 7391篇 |
2011年 | 13941篇 |
2010年 | 12281篇 |
2009年 | 9280篇 |
2008年 | 10368篇 |
2007年 | 11112篇 |
2006年 | 3530篇 |
2005年 | 4014篇 |
2004年 | 3162篇 |
2003年 | 2919篇 |
2002年 | 2322篇 |
2001年 | 1635篇 |
2000年 | 1583篇 |
1999年 | 1646篇 |
1998年 | 1374篇 |
1997年 | 1177篇 |
1996年 | 1085篇 |
1995年 | 864篇 |
1994年 | 698篇 |
1993年 | 503篇 |
1992年 | 444篇 |
1991年 | 294篇 |
1990年 | 216篇 |
1989年 | 174篇 |
1988年 | 135篇 |
1987年 | 83篇 |
1986年 | 69篇 |
1985年 | 46篇 |
1984年 | 36篇 |
1983年 | 35篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1959年 | 37篇 |
1958年 | 37篇 |
1957年 | 36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 31 毫秒
101.
采用了双极晶体管作为双极工艺的测试结构,将在线工艺的统计分析理论应用于双极工艺,研制了双极工艺的统计分析软件。最后给出了双极工艺的某些分析结果。 相似文献
102.
Li Yu-cheng He Ming Dept.of Civil Engineering Dalian Univ.of Technology Dalian P.R.China 《水动力学研究与进展(B辑)》1993,(4)
Based on model test,the statistical distribution of extreme values of wave-current in-line forces acting on vertical circular cylinder is analyzed in this paper.It is shownthat the results calculated by the simplified method,proposed by authors,agree well with the testdata;Weibull distribution is also adoptable in the region of high KC number, and the shapeparameter a and scale parameter β are related well with KC number respectively. 相似文献
103.
104.
Ting Gang Zhu Uttiya Chowdhury Michael M. Wong Jonathan C. Denyszyn Russell D. Dupuis 《Journal of Electronic Materials》2002,31(5):406-410
In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky
rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers
grown on SiC with a relatively thin “i” region of 2 μm, a breakdown voltage over 400 V, and forward voltage as low as 4.5
V at 100 A/cm2 are exhibited for a 60-μm-diameter device. A GaN Schottky diode with a 2-μm-thick undoped layer exhibits a blocking voltage
in excess of ∼230 V at a reverse-leakage current density below 1 mA/cm2, and a forward-voltage drop of 3.5 V at a current density of 100 A/cm2. It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC
substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge
terminations in mesageometry GaN Schottky rectifiers has also been studied. 相似文献
106.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
107.
108.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献
109.
110.
This paper generalizes an algebraic method for the design of a correct compiler to tackle specification and verification of an optimized compiler. The main optimization issues of concern here include the use of existing contents of registers where possible and the identification of common expressions. A register table is introduced in the compiling specification predicates to map each register to an expression whose value is held by it. We define different kinds of predicates to specify compilation of programs, expressions and Boolean tests. A set of theorems relating to these predicates, acting as a correct compiling specification, are presented and an example proof within the refinement algebra of the programming language is given. Based on these theorems, a prototype compiler in Prolog is produced. 相似文献