全文获取类型
收费全文 | 32245篇 |
免费 | 3200篇 |
国内免费 | 1565篇 |
专业分类
电工技术 | 5090篇 |
技术理论 | 2篇 |
综合类 | 2264篇 |
化学工业 | 1394篇 |
金属工艺 | 763篇 |
机械仪表 | 2638篇 |
建筑科学 | 3986篇 |
矿业工程 | 2662篇 |
能源动力 | 905篇 |
轻工业 | 761篇 |
水利工程 | 3100篇 |
石油天然气 | 938篇 |
武器工业 | 150篇 |
无线电 | 2870篇 |
一般工业技术 | 1609篇 |
冶金工业 | 717篇 |
原子能技术 | 505篇 |
自动化技术 | 6656篇 |
出版年
2024年 | 108篇 |
2023年 | 397篇 |
2022年 | 885篇 |
2021年 | 1094篇 |
2020年 | 1109篇 |
2019年 | 750篇 |
2018年 | 725篇 |
2017年 | 999篇 |
2016年 | 1241篇 |
2015年 | 1484篇 |
2014年 | 2608篇 |
2013年 | 2264篇 |
2012年 | 3202篇 |
2011年 | 3088篇 |
2010年 | 2009篇 |
2009年 | 1937篇 |
2008年 | 1739篇 |
2007年 | 1966篇 |
2006年 | 1754篇 |
2005年 | 1542篇 |
2004年 | 1347篇 |
2003年 | 1091篇 |
2002年 | 830篇 |
2001年 | 616篇 |
2000年 | 515篇 |
1999年 | 380篇 |
1998年 | 302篇 |
1997年 | 244篇 |
1996年 | 192篇 |
1995年 | 158篇 |
1994年 | 105篇 |
1993年 | 66篇 |
1992年 | 45篇 |
1991年 | 45篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
Based on an idea introduced by Benjamin and Cornell (1970. Probability, statistics and decision for civil engineers. New York: McGaw Hill) and previous works by the authors it is demonstrated how condition indicators may be formulated for the general purpose of quality control and for assessment and inspection planning in particular. The formulation facilitates quality control based on sampling of indirect information about the condition of the considered components. This allows for a Bayesian formulation of the indicators whereby the experience and expertise of the inspection personnel may be fully utilized and consistently updated as frequentistic information is collected. The approach is illustrated on an example considering a concrete structure subject to corrosion. It is shown how half-cell potential measurements may be utilized to update the probability of excessive repair after 50 years. Furthermore in the same example it is shown how the concept of condition indicators might be applied to develop a cost optimal maintenance strategy composed of preventive and corrective repair measures. 相似文献
45.
46.
Airframe riveting is a critical process that requires high levels of process monitoring and quality assurance due to the very
high risk associated with the failure of such joints. This paper describes the development of the enabling technology developed
for a machine vision-based process monitoring system. One of the key factors affecting the performance of a machine vision
system is the quality of the lighting. In the application described in this paper the available lighting was severely limited
by the confined space in which the system had to operate. The problem was also compounded by the reflective nature of the
objects to be examined. The initial images obtained were not suitable for further processing due to the presence of significant
shadows and specular reflections. A novel solution to this problem based on multiple wavelength illumination and signal processing
is presented along with results from experimental trials of the approach. 相似文献
47.
Conceptual damage-sensitive features for structural health monitoring: Laboratory and field demonstrations 总被引:2,自引:0,他引:2
F. Necati Catbas Mustafa Gul Jason L. Burkett 《Mechanical Systems and Signal Processing》2008,22(7):1650-1669
The use of damage-sensitive features to evaluate structural condition or health is a very critical aspect of structural health monitoring. The purpose of this paper is to investigate the potential of two different damage-sensitive features for detecting damage. Different damage scenarios are simulated on a large-scale laboratory structure and a three-span highway bridge for demonstration. The features presented in this paper are the modal flexibility-based deflection and curvature both of which are obtained directly from dynamic properties. In the literature, flexibility associated with mode shapes and mode shapes curvatures have been mostly explored. In this study, multi-input–multi-output dynamic data are used to obtain modal flexibility, which is a close approximation to the actual flexibility. A main novelty is that the curvature is calculated from the deflected shapes using the modal flexibility as opposed to using modal vectors. In this paper, the theory of the methodology is explained and then experimental studies and results are presented. For the experimental studies, the laboratory specimen and the three-span bridge were gradually damaged. It is shown that both deflection and curvature are conceptual and physically meaningful features for damage detection and localization. The issues and the requirements for these features to perform successfully are also presented. 相似文献
48.
There is widespread application of indicators to the assessment of environmental condition of streams. These indicators are intended for use by managers in making various comparative and absolute assessments and often have a role in resource allocation and performance assessment. Therefore, the problem of formally defining confidence in the results is important but difficult because the sampling strategies used are commonly based on a compromise between the requirements of statistical rigour and the pragmatic issues of access and resources. It is rare to see this compromise explicitly considered and consequently there is seldom quantification of the uncertainty that could affect the confidence a manager has in an indicator. In this paper, we present a method for quantitatively assessing the tradeoffs between sampling density and uncertainty in meeting various monitoring objectives. Assessments using judgement‐based representative reaches are shown to be unreliable; instead a sampling approach is recommended based on the random selection of measuring sites. A detailed dataset was collected along two streams in Victoria, Australia, and the effect of sampling density was assessed by subsampling from this dataset with precision related to the number of sites assessed per reach length and the intensity of the sampling at each site. The sampling scheme to achieve a given precision is shown to depend on the monitoring objective. In particular, three objectives were considered: (1) making a baseline assessment of current condition; (2) change detection; and (3) detection of a critical threshold in condition. Change detection is shown to be more demanding than assessing baseline condition with additional sampling effort required to achieve the same precision. Sampling to detect a critical threshold depends on nominating acceptable values of Type I and II error and the size of the effect to be detected. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
49.
波分复用系统将不同波长的光复用在一起进行传输,以满足对传输容量和传输距离的各种需求。介绍了一种开销监视与提取的设计方法,使用VSC8150提取承载在波分复用系统相应波长上SDH信号的开销。分析了VSC8150的工作原理,管脚和外部接口,以及与FPGA、单片机共同完成B1重新计算,开销提取,B1,J0提取。此外,还提出将帧丢失,帧失步等错误状态传送给单片机和网管的方法。本设计增强了波分复用系统网管管理参数,功能和灵活性,这会在系统维护时带来较大的方便。该设计已经成熟应用在实际的波分复用系统中。 相似文献
50.
储运罐区计算机监测系统的开发与应用 总被引:3,自引:1,他引:2
储运罐区计算机监测系统是石化企业自动控制的薄弱环节。中国石油集团公司抚顺石油一厂使用ZYG-101型电子智能液位仪,以及使用FIX组态软件完成该系统的数据库组态、工艺流程显示、实时和历史趋势显示、报警和报表等处理过程,通过二次表的串行口与计算机进行通信,由计算机实时监测每个罐的各种重要参数。运行证明:该系统测量误差小,数据实时性好.易于存储及远程传送,较理想地达到储运罐区的自动检测功能。 相似文献