全文获取类型
收费全文 | 53845篇 |
免费 | 5135篇 |
国内免费 | 3389篇 |
专业分类
电工技术 | 6123篇 |
综合类 | 4670篇 |
化学工业 | 4636篇 |
金属工艺 | 2628篇 |
机械仪表 | 6381篇 |
建筑科学 | 3127篇 |
矿业工程 | 1399篇 |
能源动力 | 1744篇 |
轻工业 | 1698篇 |
水利工程 | 1099篇 |
石油天然气 | 1575篇 |
武器工业 | 745篇 |
无线电 | 8236篇 |
一般工业技术 | 6781篇 |
冶金工业 | 1849篇 |
原子能技术 | 1058篇 |
自动化技术 | 8620篇 |
出版年
2024年 | 186篇 |
2023年 | 696篇 |
2022年 | 1191篇 |
2021年 | 1447篇 |
2020年 | 1596篇 |
2019年 | 1284篇 |
2018年 | 1284篇 |
2017年 | 1786篇 |
2016年 | 1909篇 |
2015年 | 2177篇 |
2014年 | 3289篇 |
2013年 | 3031篇 |
2012年 | 3795篇 |
2011年 | 4125篇 |
2010年 | 3009篇 |
2009年 | 3159篇 |
2008年 | 3187篇 |
2007年 | 3653篇 |
2006年 | 3307篇 |
2005年 | 2763篇 |
2004年 | 2425篇 |
2003年 | 2140篇 |
2002年 | 1753篇 |
2001年 | 1460篇 |
2000年 | 1279篇 |
1999年 | 1088篇 |
1998年 | 868篇 |
1997年 | 911篇 |
1996年 | 661篇 |
1995年 | 548篇 |
1994年 | 495篇 |
1993年 | 392篇 |
1992年 | 303篇 |
1991年 | 236篇 |
1990年 | 206篇 |
1989年 | 131篇 |
1988年 | 124篇 |
1987年 | 86篇 |
1986年 | 66篇 |
1985年 | 46篇 |
1984年 | 50篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 9篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
动态波前相位的高分辨率测量 总被引:4,自引:0,他引:4
动态波前相位信息测量是大气光学,气动光学和激光技术等领域的重要实验手段。提出了一种具有高的时间和空间分辨率以及长的测量持续时间的动态波前相位测量方法。应用Hartmann-Shack波前传感器获得高空间分辨率的相位信息,采用高帧频CCD摄象机获得高时间分辨率图象数据。 相似文献
42.
Abstract. This paper examines the capacity of the research designs of 37 empirical studies of information systems (IS) effectiveness to provide a basis for the development of theories about behaviour related to IS effectiveness. The power of each study to support causal inference was evaluated in terms of (a) its handling of the time dimension, (b) its ability to weigh differences and (c) its resistance to internal validity threats that pose alternative explanations for its reported findings. Of the reviewed studies, 29.7% could account for the time dimension, 32.4% employed a comparison group and 16.2% were not susceptible to any internal validity threats. Only 13.5% of the studies combined an accounting for the time dimension with the use of a comparison group. Of these, however, only 5.4% were also invulnerable to internal validity threats. The research designs of nearly 95% of these published studies were deficient in supporting causal inference. In those studies, suggestions that one variable was causally related to another variable could not be substantiated. Encouragement for the future capacity of IS effectiveness research to support causal inference was found in a trend towards the use of quasiexperimental designs. Recommendations are made regarding ways to increase the inferential capacity of research designs employed in the study of IS effectiveness. 相似文献
43.
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
44.
45.
46.
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
47.
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
48.
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
49.
本文利用选区电子衍射,并结合X射线衍射对六种不同成份的急冷合金及其退火后的相组成进行了鉴定,得到了它们的相组成。 相似文献
50.
In this study a thermodynamic model for the phase behavior of aqueous salt+polymer solutions is developed. The model is based on the solution theory of Hill, which included scaling laws for the polymer molecular mass dependence and Pitzer–Debye–Hückel theory. This model was tested for systems composed of two different molecular mass of polyethylene glycols (PEG) and five different inorganic salts. All the model parameters were determined from independent measurements. The agreement between the experimental and predicted phase diagrams by this model is good. 相似文献