全文获取类型
收费全文 | 752篇 |
免费 | 72篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 29篇 |
综合类 | 72篇 |
化学工业 | 73篇 |
金属工艺 | 75篇 |
机械仪表 | 52篇 |
建筑科学 | 99篇 |
矿业工程 | 13篇 |
能源动力 | 14篇 |
轻工业 | 40篇 |
水利工程 | 82篇 |
石油天然气 | 24篇 |
武器工业 | 15篇 |
无线电 | 55篇 |
一般工业技术 | 97篇 |
冶金工业 | 21篇 |
原子能技术 | 9篇 |
自动化技术 | 85篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 26篇 |
2021年 | 45篇 |
2020年 | 31篇 |
2019年 | 26篇 |
2018年 | 36篇 |
2017年 | 27篇 |
2016年 | 21篇 |
2015年 | 40篇 |
2014年 | 41篇 |
2013年 | 43篇 |
2012年 | 45篇 |
2011年 | 44篇 |
2010年 | 27篇 |
2009年 | 47篇 |
2008年 | 27篇 |
2007年 | 34篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 29篇 |
2003年 | 12篇 |
2002年 | 21篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 16篇 |
1998年 | 24篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有855条查询结果,搜索用时 31 毫秒
41.
The marine operation of floating liquefied natural gas (FLNG) demands process compactness, flexibility, simplicity of operation, safety, and higher efficiency. The modified single mixed refrigerant (MSMR) process satisfies the FLNG process requirements and is accepted as a suitable technology for FLNG operation. The aim of this study was to develop a plant-wide control structure or strategy that can sustain the economic efficiency of the MSMR process. The NGL recovery and liquefaction units were integrated in the MSMR process to provide a compact plant structure with an efficient operation. Steady-state optimality analysis was intensively conducted in a rigorous dynamic simulation environment to determine the correct variable to sustain the economic efficiency of MSMR process. The results showed that the flow rate ratio of heavy and light mixed refrigerant (HK/LK ratio) is a promising self-optimizing controlled variable. Controlling this variable can sustain the MSMR optimality, even when the process is operated under off-design operating conditions or in the presence of disturbances. Based on the control structure tests, the control configuration with the HK/LK ratio loop showed excellent performance, maintaining the process stability against a range of disturbances. The proposed approach can also be applied to any cryogenic liquefaction technology for determining a possible optimizing controlled variable. 相似文献
42.
Effects of Process Parameters on the Temperature Field in Ti-6A1-4V Alloy Blade Precision Forging Process 总被引:1,自引:0,他引:1
Blade precision forging is a high temperature and large plastic deformation process. Process parameters have a great effect on temperature distribution in billet, so in this paper, by taking a Ti-6Al-4V alloy blade with a tenon as an object, the influence of process parameters on the temperature distribution in precision forging process was investigated using 3D coupled thermo-mechanical FEM (finite element method) code developed by the authors. The results obtained illustrate that: (1) the gradient of temperature distribution increases with increasing the deformation degree; (2) with increasing the initial temperature of the billet, the zones of high temperature become larger, and the gradient of temperature distribution hardly has any increase; (3)friction factors have little effect on the distribution of temperature field; (4) with increasing upper die velocity,temperature of the billet increases while the temperature gradient in billet decreases. The results are helpful to the design and optimization of the process parameters in precision forging process of Ti-alloy blade. 相似文献
43.
44.
45.
基于决策树的MPEG视频镜头分割算法 总被引:1,自引:0,他引:1
压缩视频镜头的分割是视频内容分析中的一个难点,由于镜头在组织和索引视频中起关键性的作用,提出了一种基于决策树的MPEG视频镜头分割算法。该算法采用决策树这种机器学习方法对样本视频进行训练,通过融合运动信息、颜色、边缘等特征获得镜头分割的最佳阈值,较好地解决了压缩视频处理中检测镜头突变和渐变难题,同时还能够检测出镜头是否产生闪光现象和相机运动的产生。实验证明本算法在压缩视频镜头检测方面取得了较好的检测结果。 相似文献
46.
针对南关煤矿3205运输巷道工作面掘进与支护困难、巷道变形严重且维修频繁的现状,为破解复杂应力情况下煤柱合理留设宽度这一关键性问题,借助FLAC 3D软件进行了应力场与位移场仿真分析。研究结果表明:显著的水平应力场、邻近的采动应力场与劣化的围岩稳定性三重因素的综合作用是制约3205运输巷正常掘进作业的瓶颈。在不同煤柱宽度方案比选过程中,窄煤柱在应对较强水平应力与剪切应力作用时处于劣势。煤柱宽度越大,采动应力场对煤柱及工作面的影响越小,采掘活动更为安全。经过方案比选,最终确立留设煤柱在复杂应力区段的合理宽度为30 m。 相似文献
47.
利用纳米压痕仪通过连续刚度测量法对单晶硅片在压入过程中的接触刚度、硬度、弹性模量进行了连续测量.结果表明:当接触深度在20~32 nm左右时,单晶硅片的接触刚度与接触深度成直线关系,硬度和弹性模量基本保持不变,此时所测得的是单晶硅片表面氧化层的硬度和弹性模量,分别约为10.2 GPa和140.3 GPa.当接触深度在32~60 nm左右时,单晶硅片的接触刚度与接触深度成非直线关系,硬度和弹性模量随接触深度急剧增加,表明单晶硅片表面氧化层的硬度和弹性模量受到了基体材料的影响.当接触深度在60 nm以上时,单晶硅片的接触刚度与接触深度成直线关系,硬度和弹性模量基本保持不变,测得值为单晶硅的硬度和弹性模量,分别约为12.5 GPa和165.6 GPa. 相似文献
48.
49.
合成了1种线性聚醚聚氨酯,并以此聚合物为基体加入O/Li=16(摩尔比)的锂盐,分别掺入纳米SiO2、纳米TiO2制备了两类复合聚合物固体电解质(CSPE).在室温下,纳米SiO2复合型聚合物固体电解质的电导率最大,达到6.40×10-6S/cm.通过红外光谱、热分析及交流阻抗等手段研究了电解质本体,以及掺入无机氧化物粒子之后其质量分数与离子电导率之间的关系.结果表明,纳米SiO2质量分数达到15%,纳米TiO2质量分数达到25%时,离子电导率最大.在室温下,加入纳米SiO2比加入纳米TiO2的离子电导率要高;但随着温度的升高,这种差距越来越小. 相似文献
50.
Kun Gao Jianbo Chen Yanhua Wang Yuli Qi Lixue Chen Shanshan Li Yinshi Sun 《Food and Bioprocess Technology》2018,11(9):1627-1638
Fresh ginseng was irradiated with 60Co-γ or an electron beam at the dose of 2 and 4 kGy and stored at 2 °C. The quality of ginseng was evaluated after 60 and 120 days. Results suggest that when the storage time was 120 days, 2 kGy EI-treated ginseng had the lowest decay rate. During the 2 storage periods, the amounts of most of 9 ginsenosides decreased with an increase in the irradiation dose. The total saponin content of both 60Co-γ-irradiated and EI-treated samples decreased with an increase in the irradiation dose. Significant (P <?0.05) upregulation of total polysaccharide content was observed in the 4 kGy EI samples after storage. Samples irradiated at 2 or 4 kGy by electron beam irradiation had the highest concentration of total saponin and ginseng polysaccharides, respectively. Levels of most of 17 amino acids decreased with the increasing irradiation dose. Exposure to irradiation doses up to 4 kGy affected the amino acid content of fresh ginseng. Ginseng irradiated at 4 kGy by 60Co-γ irradiation and stored for 120 days had a significantly higher activity of superoxide dismutase (P <?0.05). A significant difference was observed in the total concentration of nucleosides and nucleobases between irradiated and un-irradiated ginseng samples (P <?0.05). These data suggest that the combination of a lower irradiation dose and low temperature is an optimal condition for extending the shelf-life of fresh ginseng without detriment to its ingredients. 相似文献