全文获取类型
收费全文 | 51015篇 |
免费 | 4862篇 |
国内免费 | 2279篇 |
专业分类
电工技术 | 6064篇 |
技术理论 | 7篇 |
综合类 | 5656篇 |
化学工业 | 1387篇 |
金属工艺 | 413篇 |
机械仪表 | 1900篇 |
建筑科学 | 4451篇 |
矿业工程 | 1266篇 |
能源动力 | 672篇 |
轻工业 | 3650篇 |
水利工程 | 1753篇 |
石油天然气 | 857篇 |
武器工业 | 454篇 |
无线电 | 11607篇 |
一般工业技术 | 2340篇 |
冶金工业 | 3317篇 |
原子能技术 | 248篇 |
自动化技术 | 12114篇 |
出版年
2024年 | 115篇 |
2023年 | 687篇 |
2022年 | 1215篇 |
2021年 | 1672篇 |
2020年 | 1712篇 |
2019年 | 1263篇 |
2018年 | 1247篇 |
2017年 | 1496篇 |
2016年 | 1761篇 |
2015年 | 1963篇 |
2014年 | 3409篇 |
2013年 | 3208篇 |
2012年 | 3873篇 |
2011年 | 3979篇 |
2010年 | 3056篇 |
2009年 | 2893篇 |
2008年 | 3149篇 |
2007年 | 3419篇 |
2006年 | 3291篇 |
2005年 | 2818篇 |
2004年 | 2339篇 |
2003年 | 2222篇 |
2002年 | 1545篇 |
2001年 | 1245篇 |
2000年 | 895篇 |
1999年 | 746篇 |
1998年 | 477篇 |
1997年 | 421篇 |
1996年 | 375篇 |
1995年 | 313篇 |
1994年 | 245篇 |
1993年 | 156篇 |
1992年 | 115篇 |
1991年 | 67篇 |
1990年 | 71篇 |
1989年 | 79篇 |
1988年 | 61篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 44篇 |
1983年 | 30篇 |
1982年 | 45篇 |
1981年 | 23篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1977年 | 18篇 |
1964年 | 22篇 |
1959年 | 16篇 |
1955年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
ABSTRACTIndividuals, (media-) organisations, and crisis responders who are involved in ad hoc crisis communication steadily deploy social media to contribute to collective sense-making as an endeavour to create meaning in highly uncertain situations. Exerting sense-giving in order to shape others’ conceptions is causally preceded by an initial breakup of existing understanding. This study aims to explore patterns of sense-breaking in social media crisis communication and its impact on collective sense-making and sense-giving. To this end, we conducted a case study of the Manchester bombing in 2017, including a social network analysis of 708,147 Twitter postings and a content analysis of 2006 original tweets. We found individual role types to be initiators of sense-breaking in early crisis stages when uncertainty is at its height. Exerting successive sense-giving becomes more challenging if the collective sense-making has progressed along with the sequence of events. This understanding aims to encourage emergency management organisations to move their sense-giving actions closer to the point in time when sense-breaking occurs. 相似文献
82.
In May 2018,the primetime news casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2 200 Bq/m3.After a humble,the Nuclear Safety and Security Commission(NSSC) of Korea confirmed that significant amount of thoron gas is emanated from several mattress models marketed by a company claiming beneficial health effects of negative ions.Laboratory analysis showed that some internal fabric sheets of those mattresses contain high concentration of Th-232.It was revealed that the manufacture treated the material with so-called ‘negative ion powder’ procured from the market and NSSC found that its radioactive content is the monazite powder.Although measurements with reliable instruments resulted in somewhat lower values,the tentative but conservative estimates of doses to the users are still remarkable,ranging from a few to 14 mSv a year.Most of the affected models have been marketed from 2010 but earlier models,with lower thorium content,were supplied from 2006.As many as 88,000 mattresses have been produced.The manufacturer with help of the government,recalled all the affected models and separated the radioactive internals.A large amount of waste is waiting for the government decision on disposal method.Similar problems were identified in other consumer products including latex mattresses and pillows imported,hot pads,and several models of sanitary or health-aid goods.These episodes called for revisiting NORM control strategy in Korea. 相似文献
83.
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
84.
Lakshmi Krishnasamy Rama Mohan Rao Arumulla Gopalakrishnan Naga 《Structure and Infrastructure Engineering》2018,14(10):1412-1431
An approach to enhance the sensitivity of the damage index using the prediction errors of autoregressive – autoregressive exogenous models by augmenting Singular Spectrum Analysis (SSA) to detect and locate minor damage is presented. Numerical simulation studies are carried out by considering a simply supported beam with single and multiple cracks. An experimental study on a reinforced cement concrete beam has been carried out to validate the technique using different levels of damage. The studies emphasise that the SSA improves the sensitivity of the damage index for detection and also localisation, handling environmental/operational variability and measurement noise. 相似文献
85.
Xiaojia Wang Mi Chen Wei Xia Keyu Zhu Shanshan Zhang Weiqun Xu Yuxiang Guan 《Expert Systems》2020,37(2):e12484
In China, Type 2 diabetes mellitus (T2DM) is increasingly affecting people's health. Although many risk factors related to T2DM have been researched, the association between social relationships and risk management of T2DM in China has not been fully researched. Therefore, we obtained 2,969 valid cases from the National Chinese Medicine Clinical Research Base-Key Disease of Diabetes Mellitus Study to evaluate the role of social relationships in the risk management of T2DM. We first establish an indicators system of social relationship factors and then propose a comprehensive method that integrates subjective (analytical network process) and objective (entropy weight method) evaluations to rank the importance of the 17 social relationship factors that were the most important and commonly used. The results suggest that different social relationship factors have different effects on the risk management of T2DM. Patients and health workers should pay more attention to the high-benefit factors and thus improve the efficiency of the risk management of T2DM. These findings provided theoretical support for patients and health workers by developing the positive effects of social relationships in improving the risk management of T2DM to the fullest degree. 相似文献
86.
我国有许多种类的地质矿产资源,地质矿产资源的勘查与开发有效地促进了我国工业生产的进步。整个社会的发展对于地质矿产资源的需求也非常高,所以必须开展高效的矿产资源勘查活动。但是目前地质矿产资源勘查中经常会存在一系列的风险,会对勘查人员及整个矿床造成不同程度的损害。相关企业必须采取有效的应对策略,有效降低企业的勘查风险。本文主要是基于地质矿产勘查风险原因的分析及应对策略两方面来展开进一步论述的。 相似文献
87.
针对卫星激光通信粗跟踪系统的跟踪稳定精度指标要求高的特点,建立了基于永磁同步电机直接驱动的粗跟踪系统模型并进行了跟踪稳定误差分析。在采用传统PID控制策略存在跟踪误差较大、动态性能较差等不足的基础上,提出了一种基于粗跟踪系统的改进型前馈复合控制策略。从理论上分析了前馈复合控制策略提高了粗跟踪系统的动态性能,为降低跟踪稳定误差提供了改善方案。地面实验验证结果表明,与传统控制策略相比,改进型复合控制策略极大地降低了系统的动态跟踪误差,动态跟踪误差由606μrad降低至13μrad(1δ)。进一步的在轨实验也验证了改进型复合控制策略的合理性和先进性,总体指标满足了卫星激光通信终端的极高精度要求。本文所提出的控制策略对其他高性能跟踪伺服系统设计也具有较大的借鉴意义。 相似文献
88.
89.
Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs. 相似文献
90.
ABSTRACT This article synthesizes the literature on Dutch flood risk governance to analyze how external conditions shaped past and present dynamics of cross-sector collaboration for integrated flood risk management in the Netherlands. It traces the extent to which policy and legal frameworks, socio-economic circumstances, political realities, power relations and conflict situations have influenced attempts at collaboration between flood safety, spatial planning, environmental protection and other sectors. Despite the growing interdependences, existing power relations between the sectors are characterized by the dominance of the water sector. Hence, cross-sector collaboration can develop as long as it does not compromise flood safety. 相似文献