全文获取类型
收费全文 | 27229篇 |
免费 | 2599篇 |
国内免费 | 1074篇 |
专业分类
电工技术 | 1648篇 |
综合类 | 1632篇 |
化学工业 | 7966篇 |
金属工艺 | 1421篇 |
机械仪表 | 914篇 |
建筑科学 | 902篇 |
矿业工程 | 542篇 |
能源动力 | 724篇 |
轻工业 | 5852篇 |
水利工程 | 205篇 |
石油天然气 | 1080篇 |
武器工业 | 142篇 |
无线电 | 2542篇 |
一般工业技术 | 3094篇 |
冶金工业 | 1267篇 |
原子能技术 | 287篇 |
自动化技术 | 684篇 |
出版年
2024年 | 135篇 |
2023年 | 381篇 |
2022年 | 594篇 |
2021年 | 715篇 |
2020年 | 837篇 |
2019年 | 708篇 |
2018年 | 691篇 |
2017年 | 947篇 |
2016年 | 941篇 |
2015年 | 912篇 |
2014年 | 1462篇 |
2013年 | 2604篇 |
2012年 | 2017篇 |
2011年 | 2033篇 |
2010年 | 1494篇 |
2009年 | 1480篇 |
2008年 | 1264篇 |
2007年 | 1770篇 |
2006年 | 1698篇 |
2005年 | 1403篇 |
2004年 | 1200篇 |
2003年 | 1050篇 |
2002年 | 800篇 |
2001年 | 749篇 |
2000年 | 597篇 |
1999年 | 508篇 |
1998年 | 371篇 |
1997年 | 359篇 |
1996年 | 241篇 |
1995年 | 215篇 |
1994年 | 166篇 |
1993年 | 135篇 |
1992年 | 104篇 |
1991年 | 81篇 |
1990年 | 65篇 |
1989年 | 39篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 639 毫秒
51.
This research investigates the utility of passive microwave remote sensing instruments to accurately determine snow water equivalent (SWE) over large spatial extents. Three existing Special Sensor Microwave Imager (SSM/I) snow water equivalent algorithms produced by Chang, Tait and Goodison were evaluated for their ability to determine snow water equivalent in a snowpack containing substantial depth hoar, large faceted snow crystals. The Kuparuk River Watershed (8140 km2) test site on the North Slope of Alaska was chosen for its snowpack containing a think depth hoar layer and long history of ground truth data. A new regional snow water equivalent algorithm was developed to determine if it could produce better results than the existing algorithms in an area known to contain significant depth hoar. The four algorithms were tested to see how well they could determine snow water equivalent: (1) on a per pixel basis, (2) across swath-averaged spatial bands of approximately 850 km2, and (3) on a watershed scale. The algorithms were evaluated to see if they captured the annual spatial distribution in snow water equivalent over the watershed. Results show that the algorithms developed by Chang and from this research are generally within 3 cm of the spatially averaged snow water equivalents over the entire watershed. The algorithms produced by Chang, Tait, and in this research were able to predict the basin-wide ground measured snow water equivalent value within a percent error range from −32.4% to 24.4% in the years with a typical snowpack. None of the algorithms produce accurate results on a pixel-by-pixel scale, with errors ranging from −26% to 308%. 相似文献
52.
The wettability of the lithium surface by liquid alkali metals Na, K and Rb is investigated for the first time by the sessile drop method in an all-soldered instrument under conditions of a high vacuum. The presence of the temperature threshold of wetting is found in Li–Na and Li–K systems at temperatures of 325°C and 160°C, respectively. A conclusion is drawn that an abrupt decrease in wetting angles in the investigated systems is associated with a marked decrease in the interfacial tension at lithium-lithium, lithium-potassium, and lithium--rubidium interfaces owing to the beginning of a noticeable mutual solubility of the components at relatively high temperatures. 相似文献
53.
54.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
55.
56.
混凝土早期收缩开裂是加剧混凝土劣化并导致最终失效的一个重要因素.分析混凝土早期的自由收缩量值是进行收缩开裂研究的基础。为此,基于湿度扩散理论建立了混凝士早期的自生收缩与干燥收缩计算分析模型,经实例验证,计算结果与试验结果有较好的一致性。 相似文献
57.
58.
59.
介绍了500W宽频带功率负载的设计及实验结果,并将研究成果扩展到10~1000W范围。负载主要技术指标:输入阻抗50Ω,频带宽度0~1000MHz,电压驻波比≤1.1.表面最高温升△t≤100℃。 相似文献
60.
介绍抚顺石油化工公司石油一厂东蒸馏装置的改造情况,通过技术改造,使减压蒸馏塔由生产燃料型改造成生产石蜡-润滑油型,满足了该厂对石蜡和润滑油料的质量要求。 相似文献