全文获取类型
收费全文 | 38248篇 |
免费 | 3990篇 |
国内免费 | 2538篇 |
专业分类
电工技术 | 6105篇 |
综合类 | 3196篇 |
化学工业 | 1950篇 |
金属工艺 | 1263篇 |
机械仪表 | 5743篇 |
建筑科学 | 2137篇 |
矿业工程 | 1142篇 |
能源动力 | 944篇 |
轻工业 | 994篇 |
水利工程 | 768篇 |
石油天然气 | 901篇 |
武器工业 | 660篇 |
无线电 | 5798篇 |
一般工业技术 | 4534篇 |
冶金工业 | 1465篇 |
原子能技术 | 861篇 |
自动化技术 | 6315篇 |
出版年
2024年 | 80篇 |
2023年 | 398篇 |
2022年 | 740篇 |
2021年 | 875篇 |
2020年 | 1008篇 |
2019年 | 731篇 |
2018年 | 767篇 |
2017年 | 1209篇 |
2016年 | 1408篇 |
2015年 | 1573篇 |
2014年 | 2382篇 |
2013年 | 2048篇 |
2012年 | 2874篇 |
2011年 | 2940篇 |
2010年 | 2182篇 |
2009年 | 2230篇 |
2008年 | 2371篇 |
2007年 | 2832篇 |
2006年 | 2597篇 |
2005年 | 2129篇 |
2004年 | 1914篇 |
2003年 | 1638篇 |
2002年 | 1255篇 |
2001年 | 1074篇 |
2000年 | 937篇 |
1999年 | 767篇 |
1998年 | 608篇 |
1997年 | 686篇 |
1996年 | 501篇 |
1995年 | 369篇 |
1994年 | 358篇 |
1993年 | 284篇 |
1992年 | 201篇 |
1991年 | 141篇 |
1990年 | 132篇 |
1989年 | 87篇 |
1988年 | 84篇 |
1987年 | 61篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 44篇 |
1983年 | 25篇 |
1982年 | 29篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1977年 | 10篇 |
1964年 | 7篇 |
1959年 | 11篇 |
1956年 | 7篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
R. Hughes 《Information Systems Journal》1994,4(3):169-183
Abstract. This paper examines critically the function point analysis mark II (FPA mark II) method of measuring the functionality of information systems. Although the focus of the paper is on FPA mark II as devised by Symons, both this and the Albrecht method, from which the FPA mark II was developed, are briefly discussed. The published attempts to validate FPA mark II are reviewed and then the problems encountered by the author in applying the approach are described. The final part of the paper is concerned with the fit between SSADM and FPA mark II. 相似文献
92.
93.
94.
本文详细叙述了海上靶场角度量录取糸统的组成、测试原理及其功能设计,简要介绍了该系统在靶扬的应用情况. 相似文献
95.
提出了一种快速自动测试光栅光谱衍射效率的新方法。重点推导了测试平面光栅绝对光谱衍射效率与相对光谱衍射效率公式,介绍了双光束高精度自动测试光栅光谱衍射效率曲线的基本原理、方案与方法,并分析了测试精度。研究表明,本方案的测试速度和精度均比一般测试方法提高一倍,并能有效地消除光源波动对测量结果的影响,测量误差小于5×10-3。 相似文献
96.
The GaSb layers investigated were grown directly on GaAs substrates by molecular beam epitaxy (MBE) using SnTe source as the
n-type dopant. By using admittance spectroscopy, a dominant deep level with the activation energy of 0.23-0.26 eV was observed
and its concentration was affected by the Sb4/Ga flux ratio in the MBE growth. A lowest deep-level concentration together with a highest mobility was obtained for GaSb
grown at 550°C under a Sb4/Ga beam equivalent pressure (BEP) ratio around 7, which should correspond to the lowest ratio to maintain a Sb-stabilized
surface reconstruction. In the Hall measurement, an analysis of the temperature-dependent mobility shows that the ionized
impurity concentration increases proportionally with the sample’s donor concentration, suggesting that the ionized impurity
was introduced by an SnTe source. In addition, optical properties of an undoped p-, a lightly and heavily SnTe-doped GaSb
layers were studied by comparing their photoluminescence spectra at 4.5K. 相似文献
97.
应用水文过河缆道测验在传统水文测验中是一种行之有效的测验手段。本文主要结合黄河水文近年来开展的水文测报水平升级活动和现代化建设过程中取得的成功经验,分析说明水文过河缆道建设施工过程中的质量控制措施和方法。 相似文献
98.
A.H. Wonders T.H.M. Housmans V. Rosca M.T.M. Koper 《Journal of Applied Electrochemistry》2006,36(11):1215-1221
We present the construction and some first applications of an On-line electrochemical mass spectrometry system for detecting volatile products formed during electrochemical reactions at a single-crystal electrode in hanging meniscus configuration. The system is based on a small inlet tip made of porous Teflon and a Peek holder, which is brought in close proximity (ca. 10–20 μm) to the electrode surface. The tip is connected to the mass spectrometer by glass and metal tubing. Because of the small amount of gas entering the mass spectrometer, no differential pumping is needed during the measurement. The tip construction and preparation introduced here leads to reproducible voltammetry with very good cleanliness characteristics. The presence of the tip has no significant influence on the blank voltammetry of a Pt(111) in sulfuric acid, and on voltammetric responses for CO adlayer oxidation, methanol oxidation, and hydroxylamine electrochemistry on Pt(111). The formation of gaseous products in these reactions can be followed accurately and is in good agreement with earlier results obtained by other mass spectrometric or spectroscopic techniques. The time response and tailing of the setup is on the order of seconds and mainly determined by the distance between the tip and the electrode. 相似文献
99.
Due to the fact that human activities and most sustainability issues are closely related to energy use, the energy system is a sound framework for providing lead indicators for sustainable development. Common energy-economic models enable the estimation of future states of the energy system. An energy system-based lead indicator set can be used to develop consistent and coherent future indicator estimates and to track sustainability, a clear advantage over existing sets. 相似文献