全文获取类型
收费全文 | 9390篇 |
免费 | 835篇 |
国内免费 | 494篇 |
专业分类
电工技术 | 616篇 |
综合类 | 812篇 |
化学工业 | 1727篇 |
金属工艺 | 515篇 |
机械仪表 | 405篇 |
建筑科学 | 1270篇 |
矿业工程 | 303篇 |
能源动力 | 386篇 |
轻工业 | 247篇 |
水利工程 | 346篇 |
石油天然气 | 448篇 |
武器工业 | 97篇 |
无线电 | 671篇 |
一般工业技术 | 1474篇 |
冶金工业 | 302篇 |
原子能技术 | 112篇 |
自动化技术 | 988篇 |
出版年
2024年 | 31篇 |
2023年 | 156篇 |
2022年 | 245篇 |
2021年 | 301篇 |
2020年 | 293篇 |
2019年 | 268篇 |
2018年 | 240篇 |
2017年 | 306篇 |
2016年 | 314篇 |
2015年 | 352篇 |
2014年 | 522篇 |
2013年 | 563篇 |
2012年 | 641篇 |
2011年 | 675篇 |
2010年 | 575篇 |
2009年 | 569篇 |
2008年 | 471篇 |
2007年 | 592篇 |
2006年 | 528篇 |
2005年 | 458篇 |
2004年 | 410篇 |
2003年 | 370篇 |
2002年 | 295篇 |
2001年 | 264篇 |
2000年 | 197篇 |
1999年 | 163篇 |
1998年 | 145篇 |
1997年 | 132篇 |
1996年 | 116篇 |
1995年 | 79篇 |
1994年 | 72篇 |
1993年 | 48篇 |
1992年 | 43篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 32篇 |
1988年 | 32篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1959年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Nordic hydropower flexibility and transmission expansion to support integration of North European wind power 下载免费PDF全文
The expected increase of wind power production in the North and Baltic Seas will substantially increase the variability of the generation portfolio in Northern Europe. Access to available resources of flexible power production will be necessary to support the power system against this variability. Since the Nordic hydro‐based power system can provide such resources, a stronger interconnection between continental Europe and the Nordic region seems to be beneficial. This paper assesses the challenges related to wind power production variability, especially offshore, in the North and Baltic Seas. Assessment on the transmission grid needed for both harvesting the available wind production located far away from load centres and to enable the optimal use of hydropower flexibility is studied in a long‐term cost‐benefit analysis. Special focus is devoted to the role of an offshore grid structure and the impact of onshore grid constraints. The analysis includes two interrelated simulation steps. The first step focuses on the strategic use of hydro energy in the day‐ahead market, where detailed modelling of water courses and hydro production in the Nordic region is considered. Then, in a second step, flow‐based simulations are conducted on a detailed grid model for the whole European system. The results show that long‐term strategies for the expansion of offshore and onshore grids must be defined in a coordinated way to ensure optimal developments. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
992.
针对中国原子能科学研究院100 MeV质子回旋加速器上的单粒子效应辐照装置进行了二期管道设计,采用八极磁铁校正法对束流进行了扩束及均匀化,最终在靶上得到了一个30 cm×30 cm、均匀性好于92%的均匀分布的束斑,满足了单粒子效应实验的需求。为降低靶站处的束流能散及中子本底,采用两级降能的方案,在偏转磁铁前放置1个降能片,将能量分为100 MeV和40 MeV两档,并分别针对这两个能量点进行方案设计,束流利用率均在42%以上。公差分析结果表明,四极磁铁对靶上束斑均匀性的影响大于八极磁铁,安装过程中应优先保证四极磁铁的安装公差。 相似文献
993.
994.
Many factors contribute to the planning process of power systems. In the context of expansion planning, focus is paid to selection criteria that enable the optimization of related factors that will result in the best performance. This is described as meeting demand whilst reducing costs and maintaining minimal risk in operation. In this paper, different criteria used in the planning of power system expansion studies are investigated with the objective of identifying their impact on the expansion plan. The results of these criteria on the expansion study of the Jordanian power system are presented. Results show good correspondence to the actual adopted solutions. The spinning reserve is the most influential planning criterion on the overall system expansion cost. This is followed by the peak load changes, and the forced outage rate of the candidate units used for capacity additions to meet future expected demand. Finally, the loss of load expectation and cost of energy not served have the least effect on the overall system expansion cost. These results highlight the importance to be placed on performing sensitivity analyses to determine the most cost effective and acceptable expansion plan of the electric power system. There is a need to continually update the planning criteria to cater for changes and developments in the power system and the economic situation. Finally, the methodology of this study can be generalized to other power systems. 相似文献
995.
一种新颖的求解离散Gabor展开对偶窗的方法 总被引:1,自引:0,他引:1
本文给出了一种新颖的简捷的求解离散Gabor展开最佳对偶窗的方法.首先推导了离散Gabor展开的公式,给出了连续Gabor展开和离散Gabor展开间的关系.最后利用连续展开和离散展开间的关系给出了一求解离散Gabor展开最佳对偶窗的表达式及实例. 相似文献
996.
997.
Statistical continuum mechanics is used to predict the coefficient of thermal expansion (CTE) for solid oxide fuel cell glass-ceramic seal materials with different morphology and crystallinity. Two-point correlation functions are utilized to represent the heterogeneous microstructure morphology and phase distribution. The model uses two-point correlation functions in conjunction with local properties to predict the effective CTE. Prediction results are comparable to experimental CTE results. The advantage of using the statistical continuum mechanics model in predicting the effective properties of anisotropic media is shown, using the ability to take the microstructure into consideration. 相似文献
998.
Christian Thieme 《Journal of the American Ceramic Society》2022,105(5):3544-3554
Glass-ceramics from the studied system are able to precipitate a crystalline phase with an anomalous and low coefficient of thermal expansion. Besides the crystalline phase called LEAZit (Low Expansion Alkaline Earth Zinc Silicate), other phases appear within those glass-ceramics. In order to understand the thermal expansion behavior of the whole material, the phase content has to be known as a function of the composition and the chosen heat treatment. In this paper, a glass with the molar composition 5 BaO · 12 SrO · 35 ZnO · 46.2 SiO2 · 1.5 Sb2O3 · 0.3 Ag is studied using X-ray tomography. With this method, the phase content can be studied in detail together with the microstructure. An ex-situ workflow was used to study one and the same sample after different heat treatments, which makes it possible to characterize the structures (crystalline phase, residual matrix, and porosity) inside the sample in a nondestructive way. The size of the different phases was characterized with a strut thickness analysis of the three-dimensional datasets. The tomographic results are supported by results from X-ray diffraction as well as scanning electron microscopy in combination with elemental analysis. 相似文献
999.
《Displays》2021
The air conditioning method based on radiation heat exchange has the characteristics of small vertical temperature gradient, high thermal comfort and energy saving, and has become a hot spot of attention. The Fluent numerical simulation, the experiment in this paper studies the direct expansion multi-line radiant air conditioner under the artificially simulated climate environment in winter heating, summer cooling and dehumidification. The temperature difference of the radiation + fresh air mode at the same time indoors under heating conditions is less than 2.5 °C, and the time to reach the indoor set temperature of 24 °C is about 2–3 h. Under cooling conditions, the temperature difference of the radiation + fresh air mode at the same time in the room is about 0.5–2 °C, and the time to reach the indoor set temperature of 26 °C is about 1–3 h. In the fresh air mode, the indoor temperature difference and response time at the same time are slightly larger than the radiation + fresh air mode. The freezing and dehumidification effect of fresh air is obvious, the moisture content of dehumidifying fresh air is between 6.3 and 10.5 g/kg, and the dehumidification efficiency can reach 50%. Under the same artificial simulated climate environment, the consumption of the three modes is not much different. When the outdoor temperature in heating conditions is higher than 9 °C, the fresh air mode can get better, and the radiation + fresh air mode can achieve better comfort when running indoors under various conditions. 相似文献
1000.
Values reported for the expansion of worts and of sugar solutions are examined and those which are concordant are used in the construction of a Gravity Lost Table for 20°C. 相似文献