全文获取类型
收费全文 | 116880篇 |
免费 | 11283篇 |
国内免费 | 6598篇 |
专业分类
电工技术 | 8854篇 |
技术理论 | 7篇 |
综合类 | 8812篇 |
化学工业 | 17169篇 |
金属工艺 | 7003篇 |
机械仪表 | 8195篇 |
建筑科学 | 9256篇 |
矿业工程 | 3742篇 |
能源动力 | 3466篇 |
轻工业 | 8404篇 |
水利工程 | 2827篇 |
石油天然气 | 6828篇 |
武器工业 | 1344篇 |
无线电 | 13544篇 |
一般工业技术 | 12416篇 |
冶金工业 | 4884篇 |
原子能技术 | 1430篇 |
自动化技术 | 16580篇 |
出版年
2024年 | 572篇 |
2023年 | 1976篇 |
2022年 | 3715篇 |
2021年 | 5080篇 |
2020年 | 3956篇 |
2019年 | 3094篇 |
2018年 | 3555篇 |
2017年 | 4010篇 |
2016年 | 3545篇 |
2015年 | 5152篇 |
2014年 | 6450篇 |
2013年 | 7380篇 |
2012年 | 8387篇 |
2011年 | 9262篇 |
2010年 | 8182篇 |
2009年 | 7598篇 |
2008年 | 7737篇 |
2007年 | 7290篇 |
2006年 | 6754篇 |
2005年 | 5511篇 |
2004年 | 3882篇 |
2003年 | 3068篇 |
2002年 | 2925篇 |
2001年 | 2523篇 |
2000年 | 2230篇 |
1999年 | 2197篇 |
1998年 | 1679篇 |
1997年 | 1413篇 |
1996年 | 1262篇 |
1995年 | 1061篇 |
1994年 | 839篇 |
1993年 | 595篇 |
1992年 | 518篇 |
1991年 | 319篇 |
1990年 | 257篇 |
1989年 | 196篇 |
1988年 | 148篇 |
1987年 | 100篇 |
1986年 | 80篇 |
1985年 | 51篇 |
1984年 | 38篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 33篇 |
1979年 | 16篇 |
1959年 | 8篇 |
1951年 | 7篇 |
1940年 | 3篇 |
1928年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
设计了一种以STM32F103微控制器为控制核心,基于24位高精度模数转换器的钻孔深度测量仪器。利用弹性波回波测距原理,通过测量出钻孔中钻杆的长度,实现钻孔深度的快速、无损、准确的测量,主要用于井下瓦斯抽放钻孔、探放水钻孔等煤矿通防工作的施工验收。仪器小巧轻便,操作简单,单人即可完成测量工作,节约下井的人力物力,提高生产效率,最长测量长度可达250米,误差不超过1米。 相似文献
13.
14.
15.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
16.
Shuang Shao Yong Liu Chun-Shui Xu Ying-Xuan Xu Bin Wu Xiao-Shu Zeng Xian-Feng Lu Xiang-Jie Yang 《金属学报(英文版)》2015,(1):7-14
The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y(wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing(SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates(Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0:45:45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction(Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory. 相似文献
17.
Climate change raises many concerns for urban water management because of the effects on all aspects of the hydrological cycle. Urban water infrastructure has traditionally been designed using historical observations and assuming stationary climatic conditions. The capability of this infrastructure, whether for storm-water drainage, or water supply, may be over- or under-designed for future climatic conditions. In particular, changes in the frequency and intensity of extreme rainfall events will have the most acute effect on storm-water drainage systems. Therefore, it is necessary to take future climatic conditions into consideration in engineering designs in order to enhance water infrastructure investment planning practices in a long time horizon. This paper provides the initial results of a study that is examining ways to enhance urban infrastructure investment planning practices against changes in hydrologic regimes for a changing climate. Design storms and intensity-duration-frequency curves that are used in the engineering design of storm-water drainage systems are developed under future climatic conditions by empirically adjusting the general circulation model output, and using the Gumbel distribution and the Chicago method. Simulations are then performed on an existing storm-water drainage system from NE Calgary to investigate the resiliency of the system under climate change. 相似文献
18.
梁斌 《冶金标准化与质量》2006,44(6):41-43
质量管理永远是企业生命的源泉,质量管理体系是一个复杂的系统工程,企业只有不断完善质量体系,进行质量管理创新,保持质量管理体系的长期有效的进行,才能在市场竞争中保持领先。 相似文献
19.
1概述
近十多年来,随着电力电子技术、微电子技术及现代控制理论的发展,变频调速技术已经广泛地用于交流电动机的速度控制,其最主要的特点是具有高效率的驱动性能及良好的控制特性.它是一种高新技术电力节能装置,它通过改变(降低)电源工作频率,来降低动力设备(电机)的转速,减少设备的输出功率,达到输出功率与工作负荷的最佳匹配,实现节能目的,有效地提高了经济效益和产品质量.几乎可以说,有电动机的地方就有变频器,在一切需要进行速度控制的场合,变频器以其操作方便、体积小、控制性能高而获得广泛应用. 相似文献
20.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献