全文获取类型
收费全文 | 137852篇 |
免费 | 6308篇 |
国内免费 | 3065篇 |
专业分类
电工技术 | 4275篇 |
技术理论 | 8篇 |
综合类 | 5878篇 |
化学工业 | 20660篇 |
金属工艺 | 7673篇 |
机械仪表 | 6242篇 |
建筑科学 | 6119篇 |
矿业工程 | 2050篇 |
能源动力 | 2848篇 |
轻工业 | 7036篇 |
水利工程 | 2354篇 |
石油天然气 | 3180篇 |
武器工业 | 650篇 |
无线电 | 16076篇 |
一般工业技术 | 22833篇 |
冶金工业 | 5500篇 |
原子能技术 | 944篇 |
自动化技术 | 32899篇 |
出版年
2024年 | 258篇 |
2023年 | 919篇 |
2022年 | 1820篇 |
2021年 | 2465篇 |
2020年 | 1834篇 |
2019年 | 1531篇 |
2018年 | 15923篇 |
2017年 | 15018篇 |
2016年 | 11469篇 |
2015年 | 2867篇 |
2014年 | 2928篇 |
2013年 | 3617篇 |
2012年 | 6669篇 |
2011年 | 13083篇 |
2010年 | 11504篇 |
2009年 | 8690篇 |
2008年 | 9803篇 |
2007年 | 10632篇 |
2006年 | 3083篇 |
2005年 | 3660篇 |
2004年 | 2963篇 |
2003年 | 2775篇 |
2002年 | 2199篇 |
2001年 | 1626篇 |
2000年 | 1490篇 |
1999年 | 1389篇 |
1998年 | 1211篇 |
1997年 | 1018篇 |
1996年 | 846篇 |
1995年 | 679篇 |
1994年 | 507篇 |
1993年 | 438篇 |
1992年 | 340篇 |
1991年 | 291篇 |
1990年 | 183篇 |
1989年 | 179篇 |
1988年 | 153篇 |
1987年 | 86篇 |
1986年 | 88篇 |
1985年 | 78篇 |
1982年 | 37篇 |
1968年 | 46篇 |
1967年 | 36篇 |
1966年 | 48篇 |
1965年 | 49篇 |
1959年 | 38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
101.
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
102.
Yuhua Cheng Chih-Hung Chen Matloubian M. Deen M.J. 《Electron Devices, IEEE Transactions on》2002,49(3):400-408
High-frequency (HF) AC and noise modeling of MOSFETs for radio frequency (RF) integrated circuit (IC) design is discussed. A subcircuit RF model incorporating the HF effects of parasitics is presented. This model is compared with the measured data for both y parameter and fT characteristics. Good model accuracy is achieved against measurements for a 0.25 μm RF CMOS technology. The HF noise predictivity of the model is also examined with measured data. Furthermore, a methodology to extract the channel thermal noise of MOSFETs from HF noise measurements is presented. By using the extracted channel thermal noise, any thermal noise models can be verified directly. Several noise models including the RF model discussed in this paper have been examined, and the results show that the RF model can predict the channel thermal noise better than the other models 相似文献
103.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
104.
介绍新型低压抽屉式开关柜的结构性能和特点,并与早期低压柜作了比较。阐述了新型低压抽屉式开关柜在冶金系统应用中的几点改进情况。 相似文献
105.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 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.
杨承志 《自动化与仪器仪表》1994,(4):38-41
本文论述了对小型工业炉窑燃烧过程进行智能控制的一种设计思想。该控制器用智能PID调节器控制炉温作为主控回路,用自寻最优控制空燃比作为副控回路。是一种既满足燃烧过程多目标要求,又造价低廉的智能控制器。 相似文献
109.
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
110.