全文获取类型
收费全文 | 24761篇 |
免费 | 2697篇 |
国内免费 | 1169篇 |
学科分类
工业技术 | 28627篇 |
出版年
2024年 | 82篇 |
2023年 | 402篇 |
2022年 | 789篇 |
2021年 | 991篇 |
2020年 | 955篇 |
2019年 | 775篇 |
2018年 | 778篇 |
2017年 | 831篇 |
2016年 | 1121篇 |
2015年 | 1042篇 |
2014年 | 1723篇 |
2013年 | 1898篇 |
2012年 | 1859篇 |
2011年 | 2108篇 |
2010年 | 1613篇 |
2009年 | 1556篇 |
2008年 | 1437篇 |
2007年 | 1574篇 |
2006年 | 1386篇 |
2005年 | 1148篇 |
2004年 | 857篇 |
2003年 | 722篇 |
2002年 | 633篇 |
2001年 | 456篇 |
2000年 | 353篇 |
1999年 | 272篇 |
1998年 | 234篇 |
1997年 | 173篇 |
1996年 | 169篇 |
1995年 | 129篇 |
1994年 | 119篇 |
1993年 | 80篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 33篇 |
1989年 | 34篇 |
1988年 | 38篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1971年 | 3篇 |
1965年 | 14篇 |
1961年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
71.
The analysis of recently collected wind data at five sites in Saudi Arabia namely, Dhulum, Arar, Yanbu, Gassim and Dhahran is presented. The five sites represent different geographically and climatologically conditions. The data collected over a period spanned between 1995 and 2002 with different collection periods for each site. Daily, monthly and frequency profiles of the wind speed at the sites showed that Dhulum and Arar sites have higher wind energy potential with annual wind speed average of 5.7 and 5.4 m/s and speeds higher than 5 m/s for 60 and 47% of the time, respectively. The two sites are candidates for remote area wind energy applications. The costal site's, i.e. Yanbu and Dhahran wind speed data indicated that the two sites have lower annual wind speed averages and wind blows at speed higher than 5 m/s during afternoon hours. That makes the two sites candidates for grid connected wind systems for electrical load peak shaving. The data of Gassim site showed that the site has the lowest wind energy potential compared to the others. The annual energy produced by a Nordex N43 wind machine is estimated to be 1080, 990, 730, 454 and 833 MWh for Dhulum, Arar, Yanbu, Gassim and Dhahran, respectively. The analysis showed that the estimated annual energy produced by the machine based on 10 min averaged data is 2.5% higher than the estimated energy based on 30 min averaged data. 相似文献
72.
通过对TN S系统接地方式中重复接地的探讨 ,介绍了重复接地对N线和PE线的不同作用 ,明确了TN S系统接地方式中重复接地的设计和施工方法。 相似文献
73.
In the framework of joint effort between the Nuclear Energy Agency (NEA) of OECD, the United States Department of Energy (US DOE), and the Commissariat a l'Energie Atomique (CEA), France a coupled three-dimensional (3D) thermal-hydraulics/neutron kinetics benchmark for VVER-1000 was defined. The benchmark consists of calculation of a pump start-up experiment labelled V1000CT-1 (Phase 1), as well as a vessel mixing experiment and main steam line break (MSLB) transient labelled V1000CT-2 (Phase 2), respectively. The reference nuclear plant is Kozloduy-6 in Bulgaria. The overall objective is to assess computer codes used in the analysis of VVER-1000 reactivity transients. A specific objective is to assess the vessel mixing models used in system codes. Plant data are available for code validation consisting of one experiment of pump start-up (V1000CT-1) and one experiment of steam generator isolation (V1000CT-2). The validated codes can be used to calculate asymmetric MSLB transients involving similar mixing patterns. This paper summarizes a comparison of CATHARE and TRAC-PF1 system code results for V1000CT-1, Exercise 1, which is a full plant point kinetics simulation of a reactor coolant system (RCS) pump start-up experiment. The reference plant data include integral and sector average parameters. The comparison is made from the point of view of vessel mixing and full system simulation. CATHARE used a six-sector multiple 1D vessel thermal-hydraulic model with cross flows and TRAC used a six-sector, 18-channel coarse-mesh 3D vessel model. Good agreement in terms of integral parameters and inter-loop mixing is observed. 相似文献
74.
A practical approach to develop a more realistic fault-tree model with a consideration of various conditions endured by a human operator is proposed. In safety-critical systems, the generation failure of an actuation signal is caused by the concurrent failures of the automated systems and an operator action. These two sources of safety signals are complicatedly correlated. The failures of sensors or automated systems will cause a lack of necessary information for a human operator and result in error-forcing contexts such as the loss of corresponding alarms and indications. It is well known that the error-forcing contexts largely affect the operator's performance. An automated system which consists of multiple processing channels and complex components is also affected by the availability of the sensors. This paper proposes a condition-based human reliability assessment (CBHRA) method in order to address these complicated conditions in a practical way. We apply the CBHRA method to the manual actuation of the safety features such as a reactor trip and auxiliary feedwater actuation in Korean Standard Nuclear Power Plants. Even the human error probability of each given condition is simply assumed, the application results prove that the CBHRA effectively accommodates the complicated error-forcing contexts into the fault trees. 相似文献
75.
76.
农业重组微生物生物安全研究进展 总被引:2,自引:2,他引:0
综述了近年来农业重组微生物的研究现状和进展 ,详细介绍农业重组微生物环境释放的监控方法以及对环境的冲击作用 ,对一些有关生物安全研究的热点问题进行了探讨 相似文献
77.
分析铝电解多功能天车轨道接头的受力情况、轮轨磨损机理和现场采集的数据照片,指出轨道经过碾压后的硬度变化以及氧化铝灰对天车轨道接头磨损的影响,提出相应措施. 相似文献
78.
79.
介绍了高坝洲水电厂一次主接线改造后2号发电机组同期回路改造的情况. 相似文献
80.
通过一起由二次回路接线错误引发的事故分析,阐述二次回路的重要性。从设计、安装、调试和管理上对二次回路进行探讨,提出反事故措施和对策,以防止类似事故的发生。 相似文献