全文获取类型
收费全文 | 97577篇 |
免费 | 9284篇 |
国内免费 | 5301篇 |
专业分类
电工技术 | 7702篇 |
技术理论 | 6篇 |
综合类 | 9920篇 |
化学工业 | 9214篇 |
金属工艺 | 4283篇 |
机械仪表 | 5894篇 |
建筑科学 | 18523篇 |
矿业工程 | 4641篇 |
能源动力 | 2930篇 |
轻工业 | 6042篇 |
水利工程 | 5191篇 |
石油天然气 | 5950篇 |
武器工业 | 1529篇 |
无线电 | 6403篇 |
一般工业技术 | 8493篇 |
冶金工业 | 4647篇 |
原子能技术 | 973篇 |
自动化技术 | 9821篇 |
出版年
2024年 | 384篇 |
2023年 | 1241篇 |
2022年 | 2416篇 |
2021年 | 2908篇 |
2020年 | 3092篇 |
2019年 | 2504篇 |
2018年 | 2345篇 |
2017年 | 2996篇 |
2016年 | 3333篇 |
2015年 | 3594篇 |
2014年 | 5913篇 |
2013年 | 5445篇 |
2012年 | 7058篇 |
2011年 | 7400篇 |
2010年 | 5642篇 |
2009年 | 5833篇 |
2008年 | 5271篇 |
2007年 | 6535篇 |
2006年 | 5970篇 |
2005年 | 5268篇 |
2004年 | 4404篇 |
2003年 | 3833篇 |
2002年 | 3272篇 |
2001年 | 2790篇 |
2000年 | 2278篇 |
1999年 | 1855篇 |
1998年 | 1433篇 |
1997年 | 1155篇 |
1996年 | 1092篇 |
1995年 | 945篇 |
1994年 | 713篇 |
1993年 | 557篇 |
1992年 | 461篇 |
1991年 | 295篇 |
1990年 | 311篇 |
1989年 | 252篇 |
1988年 | 189篇 |
1987年 | 140篇 |
1986年 | 105篇 |
1985年 | 82篇 |
1984年 | 71篇 |
1983年 | 36篇 |
1981年 | 52篇 |
1980年 | 92篇 |
1979年 | 76篇 |
1965年 | 32篇 |
1964年 | 36篇 |
1959年 | 34篇 |
1956年 | 30篇 |
1955年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
为研究喷射混凝土套拱加固前后二次衬砌与混凝土套拱的受力状况,依托陕西汉中至留坝段八里关隧道,运用有限元软件建立隧道混凝土结构套拱加固分析模型,并通过现场监测获取二次衬砌与套拱间的接触压力、套拱格栅拱架钢筋应力、套拱混凝土应力,将数值模拟结果与现场测试结果相结合,得出套拱结构的一般受力变化规律。结果表明:套拱加固前衬砌结构的最不利荷载位置位于施工缝附近的拱顶、拱肩与拱脚处; 由于衬砌局部变形与温度应力的影响,套拱混凝土应力变化呈现反复“上升-下降-上升”最后趋于稳定的特点; 套拱的作用是控制二次衬砌的进一步变形,套拱施作后所承受荷载较小,套拱反作用力远小于围岩作用于衬砌的应力,在应力计算中不应将衬砌与套拱作为整体计算; 套拱结构数值模拟所得的结果与现场测试套拱结构内力(轴力、弯矩)的大小及分布相似度高,但在衬砌裂损严重部位,数值模拟所得结果误差较大,应以现场测试结果为准。 相似文献
22.
23.
This paper is prepared in honour of Professor E.T. Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author's research career in geomechanics and geotechnical engineering. As a result, we have picked a topic that reflects two key research areas in which Professor E.T. Brown has made seminal contributions over a long and distinguished career. These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials.Partially due to Professor Brown's influence, the first author has also been conducting research in these two areas over many years. In particular, this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils. 相似文献
24.
25.
With the circulation of misinformation about the COVID-19 pandemic, the World Health Organization has raised concerns about an “infodemic,” which exacerbates people’s misperceptions and deters preventive measures. Against this backdrop, this study examined the conditional indirect effect of social media use and discussion heterogeneity preference on COVID-19-related misinformation beliefs in the United States, using a national survey. Findings suggested that social media use was positively associated with misinformation beliefs, while discussion heterogeneity preference was negatively associated with misinformation beliefs. Furthermore, worry of COVID-19 was found to be a significant mediator as both associations became more significant when mediated through worry. In addition, faith in scientists served as a moderator that mitigated the indirect effect of discussion heterogeneity preference on misinformation beliefs. That is, among those who had stronger faiths in scientists, the indirect effect of discussion heterogeneity preference on misinformation belief became more negative. The findings revealed communication and psychological factors associated with COVID-19-related misinformation beliefs and provided insights into coping strategies during the pandemic. 相似文献
26.
对射频电缆幅相稳定性进行了介绍,阐述了射频测试电缆相位和幅度变化的因素,并详细分析了射频电缆相位性能以及幅度性能的不同测试方法,最后通过实测数据的展示,总结说明了在日常测试中该如何正确使用测试电缆。 相似文献
27.
As the development of cloud computing and the convenience of wireless sensor netowrks, smart devices are widely used in daily life, but the security issues of the smart devices have not been well resolved. In this paper, we present a new NTRU-type public-key cryptosystem over the binary field. Specifically, the security of our scheme relies on the computational intractability of an unbalanced sparse polynomial ratio problem (DUSPR). Through theoretical analysis, we prove the correctness of our proposed cryptosystem. Furthermore, we implement our scheme using the NTL library, and conduct a group of experiments to evaluate the capabilities and consuming time of encryption and decryption. Our experiments result demonstrates that the NTRU-type public-key cryptosystem over the binary field is relatively practical and effective. 相似文献
28.
29.
《Geotextiles and Geomembranes》2021,49(5):1256-1269
This study investigates the seismic performance of geosynthetic-reinforced modular block retaining walls backfilled with cohesive, fine grained clay-sand soil mixture. Shaking table tests were performed for three ½ scaled (wall height 190 cm) and ¼ scaled model walls to investigate the effects of backfill type, the influence of reinforcement length and reinforcement stiffness effects. The El Centro and Kobe earthquake records of varying amplitudes were used as base acceleration. Displacement of the front wall, accelerations at different locations, strains on the reinforcements, and the visual observations of the facing and the backfill surface were used to evaluate the seismic performance of model walls. The model walls were subjected to rigorous shaking and the walls did not exhibit any stability problems or signs of impending failure. The maximum deformations observed on the models with cohesive backfill was less than half of the deformation of the sand model. The load transfers between the geogrid and cohesive soil was comparable to that of sand and hence the needed reinforcement length was similar as well. As a result; the model walls with cohesive backfills performed within acceptable limits under seismic loading conditions when compared with granular backfilled counterparts. 相似文献
30.