全文获取类型
收费全文 | 226374篇 |
免费 | 15496篇 |
国内免费 | 8704篇 |
专业分类
电工技术 | 11866篇 |
技术理论 | 11篇 |
综合类 | 15013篇 |
化学工业 | 32773篇 |
金属工艺 | 13457篇 |
机械仪表 | 12413篇 |
建筑科学 | 13515篇 |
矿业工程 | 5018篇 |
能源动力 | 5275篇 |
轻工业 | 16861篇 |
水利工程 | 4590篇 |
石油天然气 | 7544篇 |
武器工业 | 1670篇 |
无线电 | 24616篇 |
一般工业技术 | 30812篇 |
冶金工业 | 7978篇 |
原子能技术 | 2070篇 |
自动化技术 | 45092篇 |
出版年
2024年 | 586篇 |
2023年 | 2255篇 |
2022年 | 4708篇 |
2021年 | 6490篇 |
2020年 | 4778篇 |
2019年 | 3728篇 |
2018年 | 18118篇 |
2017年 | 17827篇 |
2016年 | 13876篇 |
2015年 | 6896篇 |
2014年 | 8274篇 |
2013年 | 9430篇 |
2012年 | 14100篇 |
2011年 | 21035篇 |
2010年 | 18759篇 |
2009年 | 15600篇 |
2008年 | 16733篇 |
2007年 | 17123篇 |
2006年 | 8969篇 |
2005年 | 8270篇 |
2004年 | 6090篇 |
2003年 | 5160篇 |
2002年 | 4518篇 |
2001年 | 3449篇 |
2000年 | 3004篇 |
1999年 | 2417篇 |
1998年 | 1698篇 |
1997年 | 1319篇 |
1996年 | 1166篇 |
1995年 | 847篇 |
1994年 | 688篇 |
1993年 | 494篇 |
1992年 | 402篇 |
1991年 | 326篇 |
1990年 | 203篇 |
1989年 | 169篇 |
1988年 | 112篇 |
1987年 | 82篇 |
1986年 | 61篇 |
1981年 | 34篇 |
1980年 | 39篇 |
1968年 | 43篇 |
1966年 | 43篇 |
1965年 | 46篇 |
1959年 | 52篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
91.
92.
93.
针对流体输送埋地管道泄漏问题,设计了一种利用管道机器人携带封堵气囊进行快速应急封堵修复的埋地管道泄漏内封堵装置。采用矩阵变换方法建立了牵引系统驱动轮过弯方程,利用MATLAB软件对过弯方程进行了验证,同时利用ADAMS软件仿真分析过弯路径与驱动轮转角对牵引系统行走速度的影响。研究结果表明:由两个串联封堵器组成的应急封堵系统可满足复杂工况下的管道泄漏封堵要求;牵引系统驱动轮在弯管内部行走时,单轮速度呈周期性变化,但三个驱动轮整体周期运动特性一致;驱动轮转角在25°~40°时,牵引系统行走速度与驱动轮转角成正比,且转角为30°时驱动效果最好。该内封堵装置的结构设计可为管道泄漏应急封堵领域装备的研发提供重要参考。 相似文献
94.
The physical mechanism of highly efficient photoluminescence (PL) emission from p-type silicon is described by a comparative study of the effectiveness of the etching parameters in an electrochemical anodization technique. Two series of porous silicon samples were prepared in a combination of anodization current and time, to maintain the total amount of anodic charge transfer constant. Photoluminescence studies show that irrespective of the amount of charge transfer, the samples prepared with comparatively higher current density show an efficient PL as well as stronger blueshift in the emission energy vis-à-vis the samples prepared for longer durations. An overall decrease in crystallite size, as estimated by Raman spectral analysis, was observed for both series of samples with the progress of charge transfer. Comparative analysis shows a marginal difference in crystallite size for both series of samples in the initial state of charge transfer, whereas major differences arise at higher values. This is explained with the formation of silicon suboxide on the porous surface at higher current density, leading to initiation of side wall reaction, and higher reduction rate in crystallite size as well as strong luminescence due to the carrier quantum confinement effect. 相似文献
96.
该文基于对上海市出租汽车行业历史群体性事件的梳理,通过深入分析群体性事件发生原因及特征表现,重点总结历史事件的处置经验,从群体性事件发生的事前事中事后各个环节提出应对管理建议. 相似文献
97.
Hong Wei Li Li Ya‐Li Ma Ru‐Xue Liu Shuang‐Yan Meng Li‐Tong Niu Zhe Zhang Zhi‐Wang Yang 《火与材料》2019,43(7):868-879
Through the simple precipitation of palygorskite (PGS) by zinc borate (ZB) (to make PGS@ZB) and the decoration of PGS@ZB by dodecylamine (N), a novel organic‐inorganic@inorganic hybrid flame retardant of PGS@ZB‐N was prepared and was incorporated with ethylene vinyl acetate copolymer (EVA) to improve its flame retardance. The structure and morphology of PGS@ZB‐N were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM), and it was confirmed that the PGS@ZB‐N hybrid had been successfully prepared. The flame retardancy and burning behavior of EVA/PGS@ZB‐N/EG (EG = expandable graphite) composite were studied through thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL‐94 (by the vertical burning test), and cone calorimeter test (CCT) characterizations. The prepared EVA/PGS@ZB‐N/EG composite obtained an LOI value of 41.2% with the addition of 30 wt% PGS@ZB‐N/EG. It was found that EVA/PGS@ZB‐N/EG was protected through a gas phase and condensed phase alternating synergistic effect mechanism. 相似文献
98.
Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
99.
分析研究国家标准中液压支架让缩性能试验的技术要求,设计开发让缩性能试验系统,以双伸缩立柱液压支架为研究对象进行让缩性能试验分析与研究,为让缩性能试验的开展提供了试验条件,为液压支架国标的实施提供基础。 相似文献
100.
As accessing computing resources from the remote cloud inherently incurs high end-to-end (E2E) delay for mobile users, cloudlets, which are deployed at the edge of a network, can potentially mitigate this problem. Although some research works focus on allocating workloads among cloudlets, the cloudlet placement aiming to minimize the deployment cost (i.e., consisting of both the cloudlet cost and average E2E delay cost) has not been addressed effectively so far. The locations and number of cloudlets have a crucial impact on both the cloudlet cost in the network and average E2E delay of users. Therefore, in this paper, we propose the Cost Aware cloudlet PlAcement in moBiLe Edge computing (CAPABLE) strategy, where both the cloudlet cost and average E2E delay are considered in the cloudlet placement. To solve this problem, a Lagrangian heuristic algorithm is developed to achieve the suboptimal solution. After cloudlets are placed in the network, we also design a workload allocation scheme to minimize the E2E delay between users and their cloudlets by considering the user mobility. The performance of CAPABLE has been validated by extensive simulations. 相似文献