全文获取类型
收费全文 | 120733篇 |
免费 | 3681篇 |
国内免费 | 1861篇 |
专业分类
电工技术 | 2694篇 |
技术理论 | 2篇 |
综合类 | 4485篇 |
化学工业 | 17653篇 |
金属工艺 | 6850篇 |
机械仪表 | 5262篇 |
建筑科学 | 5087篇 |
矿业工程 | 1477篇 |
能源动力 | 1977篇 |
轻工业 | 5827篇 |
水利工程 | 1785篇 |
石油天然气 | 2977篇 |
武器工业 | 201篇 |
无线电 | 13741篇 |
一般工业技术 | 20862篇 |
冶金工业 | 4689篇 |
原子能技术 | 658篇 |
自动化技术 | 30048篇 |
出版年
2024年 | 142篇 |
2023年 | 628篇 |
2022年 | 943篇 |
2021年 | 1415篇 |
2020年 | 1074篇 |
2019年 | 891篇 |
2018年 | 15251篇 |
2017年 | 14364篇 |
2016年 | 10882篇 |
2015年 | 1946篇 |
2014年 | 1947篇 |
2013年 | 2396篇 |
2012年 | 5263篇 |
2011年 | 11772篇 |
2010年 | 10395篇 |
2009年 | 7518篇 |
2008年 | 8738篇 |
2007年 | 9728篇 |
2006年 | 2149篇 |
2005年 | 2973篇 |
2004年 | 2328篇 |
2003年 | 2209篇 |
2002年 | 1553篇 |
2001年 | 967篇 |
2000年 | 1086篇 |
1999年 | 1166篇 |
1998年 | 1008篇 |
1997年 | 865篇 |
1996年 | 872篇 |
1995年 | 643篇 |
1994年 | 560篇 |
1993年 | 391篇 |
1992年 | 355篇 |
1991年 | 281篇 |
1990年 | 196篇 |
1989年 | 169篇 |
1988年 | 146篇 |
1987年 | 105篇 |
1986年 | 78篇 |
1985年 | 58篇 |
1984年 | 57篇 |
1982年 | 37篇 |
1968年 | 45篇 |
1967年 | 36篇 |
1966年 | 44篇 |
1965年 | 46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 15 毫秒
11.
12.
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
13.
14.
本文阐述了通过Friedel-Crafts反应合成邻-(4-乙基苯甲酰基)苯甲酸的方法.研究了影响产物质量的因素,提出了适宜的工艺条件. 相似文献
15.
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
16.
17.
Following up on recent studies of the Zn-rich corners of the Zn-Fe-Ni and Zn-Fe-Si ternary systems, a 450 °C isothermal section
of the Zn-Fe-Ni-Si quaternary phase diagram with the Zn composition being fixed at 93 at.% was determined experimentally using
optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), and x-ray
diffractometry (XRD). FeSi was found to be in equilibrium with almost all phases in the section, including the T, ζ, Ni-δ,
NiSi2, and FeSi2 phases, as well as the liquid phase (L). Silicon solubilities in the T, ζ, and Ni-δ phases were rather limited. However,
the solubilities of Fe and Zn in the NiSi2 phase, at 4.5 at.% and 7.2 at.%, respectively, were appreciable. The existence of the (L+NiSi2+Ni-δ) three-phase equilibrium state apparently prevents other Ni-Si compounds from entering equilibrium with the liquid at
450 °C. No true quaternary compound was found in the study. 相似文献
18.
19.
飞机液压系统污染及控制 总被引:2,自引:2,他引:0
本文全面分析了收音机液压系统污染的危害和主要原因,并在此基础上有针对性地提出了预防措施。 相似文献
20.
Three interesterified vegetable oils (IVOs) prepared from palm, cottonseed, and olive oil, respectively, have been studied for application to Frankfurters. Beef fat (10%) was replaced by one of the IVOs at 20, 60 or 100%. Fatty acid composition of the lipid fraction in the Frankfurters and saturated/unsaturated ratios were established for all batches. We found that total or partial replacement of beef fat by IVOs did not lead to significant changes in appearance, colour, texture, flavour or sensory score. We conclude that IVOs may be successfully applied as beef fat substitutes in Frankfurters. 相似文献