全文获取类型
收费全文 | 32285篇 |
免费 | 4033篇 |
国内免费 | 2065篇 |
专业分类
电工技术 | 5249篇 |
技术理论 | 4篇 |
综合类 | 4011篇 |
化学工业 | 1412篇 |
金属工艺 | 1435篇 |
机械仪表 | 2550篇 |
建筑科学 | 3766篇 |
矿业工程 | 906篇 |
能源动力 | 955篇 |
轻工业 | 461篇 |
水利工程 | 1854篇 |
石油天然气 | 1044篇 |
武器工业 | 476篇 |
无线电 | 4744篇 |
一般工业技术 | 2735篇 |
冶金工业 | 777篇 |
原子能技术 | 322篇 |
自动化技术 | 5682篇 |
出版年
2024年 | 43篇 |
2023年 | 525篇 |
2022年 | 989篇 |
2021年 | 1099篇 |
2020年 | 1500篇 |
2019年 | 1757篇 |
2018年 | 827篇 |
2017年 | 1140篇 |
2016年 | 1216篇 |
2015年 | 1330篇 |
2014年 | 2324篇 |
2013年 | 1875篇 |
2012年 | 2552篇 |
2011年 | 2714篇 |
2010年 | 1964篇 |
2009年 | 2047篇 |
2008年 | 1917篇 |
2007年 | 2247篇 |
2006年 | 1837篇 |
2005年 | 1649篇 |
2004年 | 1325篇 |
2003年 | 1082篇 |
2002年 | 901篇 |
2001年 | 790篇 |
2000年 | 566篇 |
1999年 | 464篇 |
1998年 | 324篇 |
1997年 | 301篇 |
1996年 | 227篇 |
1995年 | 204篇 |
1994年 | 145篇 |
1993年 | 104篇 |
1992年 | 98篇 |
1991年 | 67篇 |
1990年 | 53篇 |
1989年 | 60篇 |
1988年 | 45篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 108 毫秒
1.
《Soils and Foundations》2022,62(3):101159
Suffusion erosion, characterized as the selective detachment and transportation of finer particles by seepage flow, is hazardous to the stability and serviceability of geotechnical structures. The removal of finer particles deteriorates the structure and fabric of the soil, leading to the degradation of its mechanical properties. Studies into the effects of suffusion on mechanical behavior have so far produced disparate results depending on the pre-erosion relative density of the specimens tested. To investigate this issue, small cyclic and monotonic loading tests were performed on intact and eroded gap-graded silty sand specimens in three dispersed density states, using a triaxial cell modified for the purpose of erosion. The variation of Young's modulus showed an inverse relationship with the pre-erosion density of the specimen, as the small strain stiffness decreased in the dense cases and increased in the loose cases. Conversely, Poisson's ratio increased in value as suffusion progressed regardless of the initial density of the specimens. In the contractive phase of monotonic loading, the densification of the coarse soil skeleton by the downward seepage flow resulted in a decrease in contractiveness and an increase in secant stiffness. In the dilative phase, the increase in porosity by the erosion of finer particles reduced the dilatancy and peak strength of the specimens. The results suggest that the pre-suffusion density determines the primary locus of affected mechanical behavior in triaxial compression, which shifts from the contractive phase to the dilative phase with the increase in pre-suffusion density. The critical state strength, inferred using stress–dilatancy theory, was largely unaffected by the erosion of finer particles. As the results indicate, pre-erosion density may be of practical significance in assessing the vulnerability to deterioration and collapse of geotechnical formations and structures subjected to suffusion erosion. 相似文献
2.
《Soils and Foundations》2022,62(6):101224
Internal erosion is a major threat to hydraulic earth structures, such as river levees and dams. This paper focuses on suffusion and suffosion phenomena which are caused by the movement of fine particles in the granular skeleton due to seepage flow. The present study investigates the impact of internal erosion on the dynamic response under cyclic torsional shear and monotonic responses under triaxial compression and torsional simple shear. A series of experiments, using a gap-graded silica mixture with a fines content of 20%, is performed under loose, medium, and dense conditions using a novel erosion hollow cylindrical torsional shear apparatus. The erosion test results indicate that the critical hydraulic gradient and the rate of erosion are density-dependent, where a transition from suffosion to suffusion is observed as the seepage continues. Regardless of the sample density, variations in the radial strain and particle size distribution, along the specimen height after erosion, are no longer uniform. Furthermore, the dynamic shearing results show that the small-strain shear modulus increases, but the initial damping ratio decreases after internal erosion, probably due to the removal of free fines. In addition, the elastic threshold strain and reference shear strain values are found to be higher for the eroded and non-eroded specimens, respectively. Finally, based on drained monotonic loading, the post-erosion peak stress ratio increases remarkably under triaxial compression, while that under torsional simple shear depends on the relative density where the direction of loading is normal to the direction of seepage. These observations indicate that the horizontal bedding plane becomes weaker, while the vertical one becomes stronger after downward erosion. 相似文献
3.
为快速准确评估受拉纵筋锈蚀对钢筋混凝土梁正截面受弯承载力的影响,采用解析方法计算受弯破坏时锈蚀钢筋混凝土梁正截面应力和应变分布,识别并定义锈蚀钢筋混凝土梁的3个界限锈蚀率和6种正截面受弯破坏模式,提出预判破坏模式再计算承载力的锈蚀钢筋混凝土梁正截面受弯承载力简化计算方法。采用该简化方法,计算相关文献中235根锈蚀钢筋混凝土梁的正截面受弯承载力,并与试验结果对比,验证该简化方法的准确性。通过两个算例,分别研究初始超筋梁和初始适筋梁的正截面受弯破坏模式及承载力随受拉纵筋锈蚀率的变化规律。研究结果表明:随着受拉纵筋锈蚀率的增大,初始超筋钢筋混凝土梁的正截面受弯破坏模式按照从“类似超筋”、“类似适筋”、“类似超筋”到“类似少筋”依次转变;初始适筋钢筋混凝土梁的正截面受弯破坏模式按照从“类似适筋”、“类似超筋”到“类似少筋”依次转变;钢筋混凝土梁正截面受弯承载力近似呈多段线性降低,最终退化为素混凝土梁的开裂弯矩,转折点位置为界限及临界锈蚀率。 相似文献
4.
5.
为研究冲击速度和热处理温度对黑云母花岗岩动态力学特性的影响,利用改进的霍普金森压杆系统对25~800 ℃共9个温度等级的热处理试样分别进行3种弹速下的冲击压缩试验。试验结果表明:随着冲击速度的增加,25~700 ℃热处理试样的应力—应变曲线由“Ⅱ型”转变为“Ⅰ型”,而800 ℃热处理试样均表现出“Ⅰ型”应力—应变曲线特征。同一温度热处理下试块的峰值应力、应变和平均应变均随动荷载的升高而增大。相同的冲击速度下,300 ℃热处理试样的动力学性能有所改善,500 ℃后试样的动力学性能开始逐渐劣化。同一温度热处理试样的破碎程度随冲击速度的增加而增加;相同冲击速度下,热处理试样的破碎程度随温度的升高先减弱后增强。 相似文献
6.
首钢迁钢2号高炉开炉2年后炉缸便发生水温差异常升高现象,长期被迫加钛护炉,控制冶炼强度。研究炭砖的侵蚀是探索炉缸侵蚀的关键。通过化学成分分析、SEM和EDS等手段,研究2号高炉炉缸炭砖异常侵蚀状态和机理。结果表明,13号风口下方象脚区炭砖主要受铁、钾、硫等侵蚀,其中铁的侵蚀深度最深;20号风口下方象脚区炭砖除受铁、钾和硫侵蚀外,受锌侵蚀也较为严重,但锌的侵蚀深度小于铁、钾和硫的侵蚀深度;出铁口区炭砖主要受锌和硫侵蚀,该区炭砖附近存在串气现象,炭砖表层有裂纹,裂纹处主要为锌和硫。炭砖芯部存在混料不均现象,其将导致碳砖随着炉缸温度和压力的变化而产生裂纹。 相似文献
7.
8.
在不同路面行走过程中,为了提高轮式机器人的响应速度,降低外部扰动对调速系统的影响,改善系统抖振,根据分数阶微积分原理,结合滑模控制与内模控制策略,提出一种分数阶滑模内模控制(Fractional Order Sliding Mode Internal Mode Control,FOSMIMC)新方法,应用于轮式机器人调速系统。通过MATLAB/Simulink与Carsim仿真软件建立四轮差速运动模型。实验结果表明,分数阶滑模内模调速方法不仅能够有效消除系统受干扰时产生的稳态误差和降低调节时间,而且可以削弱系统抖振现象,同时提升了系统的鲁棒性。 相似文献
9.
张阅 《计算机应用与软件》2022,39(3):89-95
针对复杂飞行环境下的多四旋翼飞行器系统,提出一种基于有限时间扩张状态观测器的主从编队控制策略(FTESO-LFFC)。对于领航者子系统,提出一种积分滑模控制(ISM)策略,通过引入的积分项,消除了传统滑模控制中的趋近阶段,提高了系统的鲁棒性。对于跟随者子系统,提出一种非奇异终端滑模控制(NTSM)策略,该方法在解决了奇异性问题的同时也具有有限时间收敛特性,其控制效果更佳。针对外界扰动,提出一种有限时间扩张状态观测器(FTESO)实现了对扰动的准确观测。通过稳定性分析可知,所提出的控制策略可以实现闭环系统的有限时间稳定。仿真结果验证了该方法的可靠性与优越性。 相似文献
10.
Ayman M. Abdalla Mohammad Abu Awad Omar AlZoubi La'aly A. Al-Samrraie 《计算机、材料和连续体(英文)》2022,72(1):797-814
The enlarged veins in the pampiniform venous plexus, known as varicocele disease, are typically identified using ultrasound scans. The medical diagnosis of varicocele is based on examinations made in three positions taken to the right and left testicles of the male patient. The proposed system is designed to determine whether a patient is affected. Varicocele is more frequent on the left side of the scrotum than on the right and physicians commonly depend on the supine position more than other positions. Therefore, the experimental results of this study focused on images taken in the supine position of the left testicles of patients. There are two possible vein structures in each image: a cross-section (circular) and a tube (non-circular) structure. This proposed system identifies dilated (varicocele) veins of these structures in ultrasound images in three stages: preprocessing, processing, and detection and measurement. These three stages are applied in three different color modes: Grayscale, Red-Green-Blue (RGB), and Hue, Saturation, and Value (HSV). In the preprocessing stage, the region of interest enclosing the pampiniform plexus area is extracted using a median filter and threshold segmentation. Then, the processing stage employs different filters to perform image denoising. Finally, edge detection is applied in multiple steps and the detected veins are measured to determine if dilated veins exist. Overall implementation results showed the proposed system is faster and more effective than the previous work. 相似文献