全文获取类型
收费全文 | 27195篇 |
免费 | 3270篇 |
国内免费 | 2024篇 |
专业分类
电工技术 | 2269篇 |
技术理论 | 7篇 |
综合类 | 3849篇 |
化学工业 | 550篇 |
金属工艺 | 238篇 |
机械仪表 | 1429篇 |
建筑科学 | 8310篇 |
矿业工程 | 396篇 |
能源动力 | 347篇 |
轻工业 | 343篇 |
水利工程 | 500篇 |
石油天然气 | 458篇 |
武器工业 | 779篇 |
无线电 | 3380篇 |
一般工业技术 | 1667篇 |
冶金工业 | 304篇 |
原子能技术 | 169篇 |
自动化技术 | 7494篇 |
出版年
2024年 | 49篇 |
2023年 | 347篇 |
2022年 | 625篇 |
2021年 | 708篇 |
2020年 | 773篇 |
2019年 | 641篇 |
2018年 | 660篇 |
2017年 | 800篇 |
2016年 | 978篇 |
2015年 | 1141篇 |
2014年 | 2016篇 |
2013年 | 1637篇 |
2012年 | 2158篇 |
2011年 | 2357篇 |
2010年 | 1989篇 |
2009年 | 1961篇 |
2008年 | 1946篇 |
2007年 | 2165篇 |
2006年 | 1838篇 |
2005年 | 1409篇 |
2004年 | 1117篇 |
2003年 | 938篇 |
2002年 | 745篇 |
2001年 | 656篇 |
2000年 | 582篇 |
1999年 | 440篇 |
1998年 | 328篇 |
1997年 | 251篇 |
1996年 | 211篇 |
1995年 | 216篇 |
1994年 | 163篇 |
1993年 | 123篇 |
1992年 | 125篇 |
1991年 | 67篇 |
1990年 | 58篇 |
1989年 | 60篇 |
1988年 | 49篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1964年 | 3篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
变分自编码器(VAE)作为深度隐空间生成模型的一种,近年来其表现性能取得了极大的成功,尤其是在图像生成方面。变分自编码器模型作为无监督式特征学习的重要工具之一,可以通过学习隐编码空间与数据生成空间的特征映射,进而在输出端重构生成输入数据。梳理了传统变分自编码器模型及其衍生变体模型的发展与研究现状,并就此做了总结和对比,最后分析了变分自编码器模型存在的问题与挑战,并就可能的发展趋势做了展望。 相似文献
22.
空间核反应堆是空间核电源和核推进的研究基础,大功率核反应堆的体积和质量一直是限制航空航天设计的重要因素。针对这一问题,本文对MW级空间核反应堆系统热管式辐射散热器进行建模和分析,建立热管式辐射散热器的热阻模型,利用穷举法和遗传算法在给定工况下探讨裸碳纤维翅片长度Lf和厚度δf、冷却剂质量流量m、辐射散热器入口温度Tf1对散热器质量M的影响。结果表明,当Tf1=800 K、Lf=5 cm、δf=0.16 mm、m=9 kg/s时,M达到最优,为906.593 kg,优化了0.63%的系统质量。 相似文献
23.
M. Sanchiz F. Amadieu P.-V. Paubel A. Chevalier 《Behaviour & Information Technology》2020,39(10):1094-1109
ABSTRACT This study investigates how a search interface that displays users’ ultimate query (i.e. users’ current search goal) can cope with the age-related decrease of fluid abilities and support older users’ search behaviours. 30 young and 18 older adults completed 9 search problems with a regular web browser or with the experimental search interface. Results showed that older adults spent longer time on the search engine result pages, they needed more time to reformulate, and they had more difficulties exploring the search paths elaborated. Age-differences also appeared as soon as the beginning of the search. The support tool helped older users reformulate their queries more rapidly and elaborate more flexible search strategies at the beginning of the activity. Indeed, older adults who interacted with the support tool switched to the processing of a new search path more rapidly instead of exploiting their initial query (i.e. they visited fewer websites for the initial query produced and reformulated a query instead of keeping on conducting a deeper investigation of the search results provided in the search engine result page). Implications of these findings for the design of effective support tools for older users are discussed. 相似文献
24.
A quality-by-design approach was adopted to develop telmisartan potassium (TP) tablets, which were bioequivalent with the commercially available Micardis® (telmisartan free base) tablets. The dissolution pattern and impurity profile of TP tablets differed from those of Micardis® tablets because telmisartan free base is poorly soluble in water. After identifying the quality target product profile and critical quality attributes (CQAs), drug dissolution, and impurities were predicted to be risky CQAs. To determine the exact range and cause of risks, we used the risk assessment (RA) tools, preliminary hazard analysis and failure mode and effect analysis to determine the parameters affecting drug dissolution, impurities, and formulation. The range of the design space was optimized using the face-centered central composite design among the design of experiment (DOE) methods. The binder, disintegrant, and kneading time in the wet granulation were identified as X values affecting Y values (disintegration, hardness, friability, dissolution, and impurities). After determining the design space with the desired Y values, the TP tablets were formulated and their dissolution pattern was compared with that of the reference tablet. The selected TP tablet formulated using design space showed a similar dissolution to that of Micardis® tablets at pH 7.5. The QbD approach TP tablet was bioequivalent to Micardis® tablets in beagle dogs. 相似文献
25.
26.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified. 相似文献
27.
28.
29.
A novel navigation signal design method based on spread code time shift position modulation was proposed,which inherits the idea of separating the pilot signal component and the data signal component,and applies time shift position of the spread code to carry data information.The old pattern of using carrier phase to carry information was changed,the power efficiency of data signal components and the performances of the satellite navigation system were improved.Theoretical analysis and simulation results show that the proposed method can significantly improve the transmission rate of data signal component or power ratio of the pilot signal component to data signal component without increasing the total transmission power.Then,the transmission rate,acquisition and tracking performance,positioning accuracy and other technical indicators of the satellite navigation system can be further improved. 相似文献
30.
相关器的特性变化规律对其实际应用中参数的设定具有重要的指导意义。针对基于比累对切透镜的联合菲涅耳变换相关器,通过数值仿真详细分析了比累对切透镜缝宽变化对相关器输出特性和空变特性的影响。结果表明,比累对切透镜缝宽能一定程度地控制联合菲涅耳变换功率分布的有效面积、相关峰的尖锐度及其空变特性的敏感度。实验采用纯相位空间光调制器编码比累对切透镜相位掩模替代实体透镜的方式搭建了相关器,实验结果与仿真结果一致性好,进一步验证了上述结论的正确性。 相似文献