全文获取类型
收费全文 | 56923篇 |
免费 | 5394篇 |
国内免费 | 2589篇 |
专业分类
电工技术 | 3925篇 |
技术理论 | 2篇 |
综合类 | 4734篇 |
化学工业 | 7163篇 |
金属工艺 | 2406篇 |
机械仪表 | 4171篇 |
建筑科学 | 8173篇 |
矿业工程 | 2294篇 |
能源动力 | 3669篇 |
轻工业 | 5485篇 |
水利工程 | 813篇 |
石油天然气 | 2667篇 |
武器工业 | 742篇 |
无线电 | 3365篇 |
一般工业技术 | 5083篇 |
冶金工业 | 3268篇 |
原子能技术 | 353篇 |
自动化技术 | 6593篇 |
出版年
2024年 | 171篇 |
2023年 | 1000篇 |
2022年 | 1917篇 |
2021年 | 2305篇 |
2020年 | 2362篇 |
2019年 | 1922篇 |
2018年 | 1841篇 |
2017年 | 2093篇 |
2016年 | 2266篇 |
2015年 | 2334篇 |
2014年 | 3779篇 |
2013年 | 3531篇 |
2012年 | 4363篇 |
2011年 | 4447篇 |
2010年 | 3362篇 |
2009年 | 3371篇 |
2008年 | 2888篇 |
2007年 | 3688篇 |
2006年 | 3131篇 |
2005年 | 2702篇 |
2004年 | 2198篇 |
2003年 | 1842篇 |
2002年 | 1513篇 |
2001年 | 1251篇 |
2000年 | 943篇 |
1999年 | 723篇 |
1998年 | 492篇 |
1997年 | 414篇 |
1996年 | 371篇 |
1995年 | 280篇 |
1994年 | 217篇 |
1993年 | 161篇 |
1992年 | 123篇 |
1991年 | 114篇 |
1990年 | 86篇 |
1989年 | 75篇 |
1988年 | 52篇 |
1987年 | 40篇 |
1986年 | 25篇 |
1985年 | 32篇 |
1984年 | 52篇 |
1983年 | 32篇 |
1982年 | 31篇 |
1980年 | 47篇 |
1964年 | 28篇 |
1963年 | 26篇 |
1961年 | 22篇 |
1959年 | 20篇 |
1956年 | 19篇 |
1955年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
41.
42.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance 下载免费PDF全文
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献
43.
介绍了超高性能混凝土(UHPC)的制备原理和性能特点,对UHPC国内外研究和应用情况进行了综述,指出了我国UHPC研究和应用中存在的问题。结果表明:UHPC是一种具有优异的力学性能、耐久性能和环保效益的新型水泥基复合材料。国外在UHPC理论研究和应用研究方面都取得了大量成果,在实际工程中已经获得了广泛的应用;近年来我国在理论研究和应用方面也得到了快速发展;如何简化UHPC制备工艺、降低生产成本、补偿自收缩是今后的主要研究方向,完善相关规范标准以更好地指导UHPC现浇工程应用是目前首要解决的问题。随着环保和可持续发展理念的日益重视,UHPC这种低碳环保材料将有广阔的发展前景。 相似文献
44.
R. Dwaraka 《Machining Science and Technology》2020,24(4):638-662
AbstractThe performance of electrical discharge machining (EDM) primarily depends on the spark quality generated in the inter-electrode gap (IEG) between the tool and workpiece. A method for obtaining accurate information about the spark gap is required to effectively monitor the EDM process. The rise and fall of thermal energy in the discharge zone at a rapid rate during the dielectric breakdown produces high-pressure shock waves. This work explores the suitability of using acoustic emission (AE) generated from these shock waves and the elastic AE waves released on the workpiece due to the induced stress to monitor the performance and spark gap in EDM. The information content of the AE signals acquired at various machining conditions was extracted using AE RMS, spectral energy and peak amplitude. These features were able to well discriminate the machining condition, tool material, workpiece material, flushing pressure, current density, the initial surface roughness of the tool. Additionally, the AE signal features had a good and consistent correlation with the performance parameters, including material removal rate, surface roughness (Ra and Rq) and tool wear. The findings lay the groundwork to develop an effective, non-intrusive in-situ AE-monitoring system for performance and IEG condition in EDM. 相似文献
45.
汾西矿务局水峪矿部分工作面现已面临带压开采问题,受下伏奥陶系灰岩水害影响,工作面安全回采过程中的防治水工作难度增加,尤其是带压开采工作面底板灰岩水的有效探测变得异常紧迫与重要。为了解决底板带压开采工作面富水区的探测问题,水峪矿引入了并行电透视技术,并对相应工作面进行了探测应用。并行电透视技术相对于传统音频电透视技术具有仪器智能化控制发射接收切换、一发射点并行对应多接收点、仪器智能快速高效跑极施工的3项技术优势,可体现应用现场施工高效、实际探测效果可靠的技术特点。经过对并行电透视技术及探测应用效果分析研究,证明该方法技术领先,现场施工高效,实际探测结果可靠,实用性强。 相似文献
46.
为了预估发射装药的内弹道性能,建立了一种基于密闭爆发器试验检测发射药的静态燃烧性能参数进而预测其装药内弹道性能的方法,采用不同批次的单樟-5/7发射药进行了装药性能预估计算,并基于30 mm火炮对内弹道性能预估精度进行了试验验证。结果表明,采用所建立的基于密闭爆发器试验的发射装药内弹道性能预估方法计算获得的最大膛压为376.0 MPa,与试验测试的膛压平均值388.7 MPa的计算误差为3.27%;计算的炮口初速为1143.5 m/s,与试验测试的炮口初速平均值1156.3 m/s的计算误差为1.11%。所建立的基于密闭爆发器试验的发射装药内弹道性能预估方法具有较高的精度,可对发射药样品不同批次间的内弹道性能进行高效精确的预估,为长期贮存发射药使用寿命的判定及发射药产品的出厂校验提供了一种高效低成本的弹道性能评价方法。 相似文献
47.
Spray quality is the critical factor which decides the efficacy of Small Quantity Lubrication (SQL) technology in a high specific energy involved machining process like grinding. Yet, the understanding about spray quality, the actual process mechanics and its effect on machining performance is inadequate. The present work is an attempt to establish a correlation between the spray input variables, quality of the spray and machining performance of SQL grinding through modelling and experiments. Using computational fluid dynamic techniques, the variation of droplet size, droplet velocity, number of droplets and heat transfer coefficient have been analysed at different input parameters and the computed trends have been verified and validated. CFD modelling of spray indicates that it is possible to produce aerosol medium with high heat dissipation ability at moderately high air pressure and low flow rate. It also shows that any increase in atomising air pressure favourably leads to notable increase in wetting area and also results in substantial enhancement in heat dissipation ability. Reduction of residual stress is thus remarkably good. On the other hand, grinding fluid flow rate, if increased, offers significantly better lubricity and reduces the grinding force which also reduces tensile residual stress. Short spell grinding test results are found to be in good agreement with CFD results. 相似文献
48.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
49.
《Displays》2021
Although many app-based textbooks are available for students, reading have not been thoroughly outlined. This study aimed to understand how changes from paper to electronic textbooks have affected the academic reading task, investigate student users’ perceptions of in-app components and screen sizes, and identify issues affecting in-app components and task requirements. A mixed factorial design experiment was employed. Results showed that there were no significant changes in comprehension and time spent reading between print text and the iPad. Yet, student highlighting, notetaking, and reading behavior and perception significantly changed based on condition. In addition, students struggled to use in-app components and found them frustrating especially when accounting for sentence splitting. The findings presented can assist in understanding the changes in student reading behavior, which can be used to improve interface design of future e-textbooks. 相似文献
50.
为降低烟草中噁霉灵检测中的基质干扰,提高检测灵敏度和和稳定性,通过试验建立了以QuEChERS为样品前处理方法、液相色谱串联质谱仪为检测仪器的烟草中噁霉灵残留检测方法。样品加水浸润后,经丙酮提取、盐析试剂包除水、石墨化炭黑除杂后,采用Agilent ZORBAX 300SB-C8液相色谱柱(2.1 mm×100 mm,1.8 μm)分离,甲醇-水程序洗脱,ESI雾化,串联质谱MRM检测。结果发现,该方法在0.0025~0.0500 mg/L范围内线性良好,决定系数r2=0.9996,定量检测限1.06 μg/L,回收率在90.8%~92.0%之间,相对标准偏差为5.1%。运用该方法测定烟草中的噁霉灵,操作简单,检测精度高,满足CORESTA对烟草农残检测的要求。 相似文献