全文获取类型
收费全文 | 91565篇 |
免费 | 1055篇 |
国内免费 | 407篇 |
专业分类
电工技术 | 909篇 |
综合类 | 2320篇 |
化学工业 | 12232篇 |
金属工艺 | 4879篇 |
机械仪表 | 3154篇 |
建筑科学 | 2328篇 |
矿业工程 | 592篇 |
能源动力 | 1202篇 |
轻工业 | 4281篇 |
水利工程 | 1311篇 |
石油天然气 | 363篇 |
无线电 | 10050篇 |
一般工业技术 | 17242篇 |
冶金工业 | 5813篇 |
原子能技术 | 362篇 |
自动化技术 | 25989篇 |
出版年
2018年 | 14495篇 |
2017年 | 13420篇 |
2016年 | 10016篇 |
2015年 | 652篇 |
2014年 | 307篇 |
2013年 | 372篇 |
2012年 | 3301篇 |
2011年 | 9617篇 |
2010年 | 8459篇 |
2009年 | 5736篇 |
2008年 | 6985篇 |
2007年 | 7991篇 |
2006年 | 313篇 |
2005年 | 1407篇 |
2004年 | 1309篇 |
2003年 | 1328篇 |
2002年 | 677篇 |
2001年 | 243篇 |
2000年 | 341篇 |
1999年 | 265篇 |
1998年 | 808篇 |
1997年 | 488篇 |
1996年 | 422篇 |
1995年 | 244篇 |
1994年 | 228篇 |
1993年 | 279篇 |
1992年 | 162篇 |
1991年 | 170篇 |
1990年 | 143篇 |
1989年 | 164篇 |
1988年 | 156篇 |
1987年 | 117篇 |
1986年 | 138篇 |
1985年 | 123篇 |
1984年 | 91篇 |
1983年 | 92篇 |
1982年 | 83篇 |
1981年 | 68篇 |
1980年 | 70篇 |
1979年 | 78篇 |
1978年 | 85篇 |
1977年 | 117篇 |
1976年 | 182篇 |
1975年 | 59篇 |
1968年 | 65篇 |
1967年 | 60篇 |
1966年 | 61篇 |
1965年 | 63篇 |
1955年 | 65篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
Utilizing multidimensional signaling techniques, a generalized multirate wavelet-based modulation format for orthogonally multiplexed communication systems is presented. Wavelet packet modulation (WPM) employs the basis functions from an arbitrary pruning of a dyadic tree structured filter bank as orthogonal pulse shapes for conventional quadrature amplitude modulation (QAM) symbols. This generalized framework affords an entire library of basis sets with increased flexibility in time-frequency (T-F) partitioning. The bandwidth efficiency and power spectral density figures of merit for the general signal are derived and shown to be that of standard QAM 相似文献
24.
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
25.
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
26.
27.
Russel B. Miller Isaac M. Horowitz Constantine H. Houpis A. Finley Barfield 《国际强度与非线性控制杂志
》1994,4(1):211-230
》1994,4(1):211-230
Nonlinear quantitative feedback theory (QFT) and pilot compensation techniques are used to design a 2 × 2 flight control system for the YF-16 aircraft over a large range of plant uncertainty. The design is based on numerical input-output time histories generated with a FORTRAN implemented nonlinear simulation of the YF-16. The first step of the design process is the generation of a set of equivalent linear time-invariant (LTI) plant models to represent the actual nonlinear plant. It has been proven that the solution to the equivalent plant problem is guaranteed to solve the original nonlinear problem. Standard QFT techniques are then used in the design synthesis based on the equivalent plant models. A detailed mathematical development of the method used to develop these equivalent LTI plant models is provided. After this inner-loop design, pilot compensation is developed to reduce the pilot's workload. This outer-loop design is also based on a set of equivalent LTI plant models. This is accomplished by modelling the pilot with parameters that result in good handling qualities ratings, and developing the necessary compensation to force the desired system responses. 相似文献
28.
29.
Bloomfield R.E. Guerra S. Miller A. Masera M. Weinstock C.B. 《Security & Privacy, IEEE》2006,4(3):66-68
Critical systems are aptly named - from electric power to water and gas to the telephone system and the Internet, they're all critical to some aspect of our daily lives. We're a networked society and as such, it's important to both know whether critical systems are trustworthy and be able to communicate, review, and debate the level of trust achieved in them. In the safety domain, explicit safety cases are increasingly required by law, regulations, and standards. In this article, we outline what a small, international group of experts, spanning various disciplines in safety, security, reliability, and critical infrastructure, been doing with the International Working Group on Assurance Cases (for Security), what we hope to achieve, and where we go next. 相似文献
30.