全文获取类型
收费全文 | 13420篇 |
免费 | 451篇 |
国内免费 | 488篇 |
专业分类
电工技术 | 352篇 |
综合类 | 1151篇 |
化学工业 | 593篇 |
金属工艺 | 191篇 |
机械仪表 | 995篇 |
建筑科学 | 1311篇 |
矿业工程 | 747篇 |
能源动力 | 359篇 |
轻工业 | 590篇 |
水利工程 | 325篇 |
石油天然气 | 540篇 |
武器工业 | 88篇 |
无线电 | 768篇 |
一般工业技术 | 1270篇 |
冶金工业 | 529篇 |
原子能技术 | 390篇 |
自动化技术 | 4160篇 |
出版年
2024年 | 8篇 |
2023年 | 44篇 |
2022年 | 225篇 |
2021年 | 152篇 |
2020年 | 159篇 |
2019年 | 122篇 |
2018年 | 130篇 |
2017年 | 155篇 |
2016年 | 256篇 |
2015年 | 294篇 |
2014年 | 748篇 |
2013年 | 788篇 |
2012年 | 900篇 |
2011年 | 1171篇 |
2010年 | 920篇 |
2009年 | 749篇 |
2008年 | 805篇 |
2007年 | 922篇 |
2006年 | 889篇 |
2005年 | 777篇 |
2004年 | 710篇 |
2003年 | 684篇 |
2002年 | 584篇 |
2001年 | 427篇 |
2000年 | 391篇 |
1999年 | 330篇 |
1998年 | 237篇 |
1997年 | 168篇 |
1996年 | 129篇 |
1995年 | 100篇 |
1994年 | 80篇 |
1993年 | 52篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 30篇 |
1988年 | 19篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(12):8130-8144
Compared to liquid/gas hydrogen tank, the pipeline is an economical way for hydrogen transportation. With the quick development of utility tunnel in China, hydrogen pipeline enters the gas compartment can be expected soon. However, all the safety requirements of the gas compartment in the current standards are designed for natural gas, and the applicability for hydrogen is unknown. Therefore, a series of studies were started to investigate the safety of hydrogen in utility tunnel. In this work, a real utility tunnel locates at Shanghai was selected as the physical object. A 3D numerical model was built and successfully validated by a scaled tunnel test. The model has the maximum deviation of +9.5%. After that, a comparatively study of the dispersion behavior of CH4 and H2 was conducted. The assumed scenario was a 20 mm small-hole leaks with gauge pressure of 1.0 MPa in the middle of the tunnel. Numerical results shown that, H2 has a larger dispersion velocity and higher concentration, and is more dangerous compared to CH4. The current emergency ventilation strategy of air change rate of 12 times/h is not effective enough to dilute the H2 flammable cloud. The alarm time of the testing points shown strong linear law. There was a sharp variation in the range of 20%–100% LFL (Lower Flammable Limit), so the alarm strategy in the tunnel standards is too ideal for both CH4 and H2. The numerical results in the present study could provide a guidance for the design and safety management of the hydrogen tunnel. 相似文献
2.
3.
4.
5.
《International Journal of Hydrogen Energy》2022,47(57):24242-24253
As hydrogen refueling stations become increasingly common, it is clear that a high level of economic efficiency and safety is crucial to promoting their use. One way to reduce costs is to use a simple orifice instead of an excess flow valve, which Japanese safety regulations have identified as a safety device. However, there is concern about its effect on refueling time and on risk due to hydrogen leakage. To clarify the effect, we did a study of model-based refueling time evaluation and quantitative risk assessment for a typical refueling station. This study showed that an orifice is an effective alternative safety device. The increase in refueling time was less than 10%, based on simulations using a dynamic physical model of the station. Neither was there a significant difference in the risk between a configuration with excess flow valves and one with an orifice. 相似文献
6.
Hitoshi Muta 《Journal of Nuclear Science and Technology》2019,56(5):367-368
Recent activities in the field of Nuclear Operational Management and Nuclear Safety Engineering, the studies related to risk analysis methodology, design, and operational management, physical phenomena, and emergency preparedness and nuclear security, have been progressed. Especially, ‘risk analysis methodology’ and ‘design and operational management’ are the main categories of the field, in which more than half of published articles on Journal of Nuclear Science and Technology are related to these categories. 相似文献
7.
Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties. 相似文献
8.
The activation of safety valves causes the development of flow reaction forces that have to be transferred in an adequate way via the piping to the steel structure or via the connected vessel into the foundation. If the safety valve outlet piping is connected to a blowdown system or, in case of blowing off into the atmosphere, are equipped with a T‐piece at the outlet, the stationary reaction forces are compensated completely. The transient opening process, however, develops flow reaction forces which culminate in peaks of short duration. In this article, a simple method will be proposed for the estimation of the resulting reaction forces as a function of the length of the pipe at the safety valve outlet. CFD calculations and blowdown tests executed with a full‐lift safety valve have confirmed this method on principle. Special importance is attributed to the short duration of the effect of the reaction forces which seems to have only a negligible impact on the supporting steel structure. 相似文献
9.
论文比较详细地阐述了涉密网主机系统所面临的安全隐患,提出了涉密网主机安全防护所要解决的几个技术问题,并就可能实现的技术方法进行了探讨和比较。 相似文献
10.
通过对广州市电视台综合信息平台网络系统的应用现状及安全风险进行分析,提出基于网络层、系统层、用户层和安全策略管理全方位的网络信息安全体系. 相似文献