全文获取类型
收费全文 | 73959篇 |
免费 | 6557篇 |
国内免费 | 3523篇 |
专业分类
电工技术 | 4783篇 |
技术理论 | 2篇 |
综合类 | 5968篇 |
化学工业 | 9072篇 |
金属工艺 | 3218篇 |
机械仪表 | 4718篇 |
建筑科学 | 10380篇 |
矿业工程 | 2035篇 |
能源动力 | 4093篇 |
轻工业 | 6704篇 |
水利工程 | 1514篇 |
石油天然气 | 3881篇 |
武器工业 | 1284篇 |
无线电 | 7012篇 |
一般工业技术 | 6789篇 |
冶金工业 | 3439篇 |
原子能技术 | 626篇 |
自动化技术 | 8521篇 |
出版年
2024年 | 291篇 |
2023年 | 1056篇 |
2022年 | 1960篇 |
2021年 | 2351篇 |
2020年 | 2409篇 |
2019年 | 2087篇 |
2018年 | 2013篇 |
2017年 | 2409篇 |
2016年 | 2590篇 |
2015年 | 2640篇 |
2014年 | 4280篇 |
2013年 | 4125篇 |
2012年 | 5232篇 |
2011年 | 5407篇 |
2010年 | 4159篇 |
2009年 | 4254篇 |
2008年 | 4208篇 |
2007年 | 5434篇 |
2006年 | 4695篇 |
2005年 | 4072篇 |
2004年 | 3377篇 |
2003年 | 2857篇 |
2002年 | 2249篇 |
2001年 | 1966篇 |
2000年 | 1545篇 |
1999年 | 1212篇 |
1998年 | 895篇 |
1997年 | 735篇 |
1996年 | 677篇 |
1995年 | 521篇 |
1994年 | 402篇 |
1993年 | 308篇 |
1992年 | 258篇 |
1991年 | 214篇 |
1990年 | 173篇 |
1989年 | 137篇 |
1988年 | 110篇 |
1987年 | 71篇 |
1986年 | 61篇 |
1985年 | 52篇 |
1984年 | 51篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 24篇 |
1980年 | 58篇 |
1966年 | 24篇 |
1964年 | 32篇 |
1963年 | 26篇 |
1961年 | 24篇 |
1955年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
51.
Spherical LiNi1/3Co1/3Mn1/3O2 cathode particles were resynthesized by a carbonate co-precipitation method using spent lithium-ion batteries (LIBs) as a raw material. The physical characteristics of the Ni1/3Co1/3Mn1/3CO3 precursor, the (Ni1/3Co1/3Mn1/3)3O4 intermediate, and the regenerated LiNi1/3Co1/3Mn1/3O2 cathode material were investigated by laser particle-size analysis, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of the regenerated LiNi1/3Co1/3Mn1/3O2 was studied by continuous charge–discharge cycling and cyclic voltammetry. The results indicate that the regenerated Ni1/3Co1/3Mn1/3CO3 precursor comprises uniform spherical particles with a narrow particle-size distribution. The regenerated LiNi1/3Co1/3Mn1/3O2 comprises spherical particles similar to those of the Ni1/3Co1/3Mn1/3CO3 precursor, but with a narrower particle-size distribution. Moreover, it has a well-ordered layered structure and a low degree of cation mixing. The regenerated LiNi1/3Co1/3Mn1/3O2 shows an initial discharge capacity of 163.5 mA h g?1 at 0.1 C, between 2.7 and 4.3 V; the discharge capacity at 1 C is 135.1 mA h g?1, and the capacity retention ratio is 94.1% after 50 cycles. Even at the high rate of 5 C, LiNi1/3Co1/3Mn1/3O2 delivers the high capacity of 112.6 mA h g?1. These results demonstrate that the electrochemical performance of the regenerated LiNi1/3Co1/3Mn1/3O2 is comparable to that of a cathode synthesized from fresh materials by carbonate co-precipitation. 相似文献
52.
The present study investigates the impact of different key solutions of mobile phones on users' effectiveness and efficiency using the devices. In the first experiment, 36 children (9 - 14 years) and in the second experiment 45 young adults (19 - 33 years) completed four common phone tasks twice consecutively on three simulated phones that had identical menus, but different key solutions. An approach was undertaken to quantify the complexity of keys in three models, incorporating different factors contributing to the keys' complexity (number of key options, number of modes and number of modes with a semantically dissimilar meaning), in order to predict users' performance decrements. As a further main factor, the degree of the users' locus of control (LOC) was measured and interactions with performance outcomes were studied. As dependent measures, the number of inefficient keystrokes, the number of tasks solved and the processing time were determined. Results showed a significant effect of control key solutions on users' efficiency and effectiveness for both children and young adults. Moreover, children's LOC values significantly interacted with performance: children with low LOC values showed the lowest performance and no learnability, especially when using keys with a high complexity. From the three factors contributing to the complexity of keys, keys exerting different functions with semantically inconsistent meanings had the worst effect on performance. It is concluded that in mobile user interface design keys with semantically inconsistent meanings should be generally avoided. 相似文献
53.
WANG Jiqing 《声学技术》2003,22(Z1)
The traditional performing arts and theatrical buildings in China can be traced back to a long history and were well developed during Song and Yuan Dynasties, 11th-14th centuries. Pavilion stage, opened on three sides and thrusting into the audience area, was unique and the most popular form in the open-air theatres, the courtyard theatres, and the indoor theatres up to the present day. As the traditional Chinese opera is performed in an abstract way, no stage settings are required and used. Therefore, the pavilion stage including the flat or domed ceiling and the back wall is virtually functioned as a reflective shell, which increases the early reflections and also intensifies the sound in the audience area. Meanwhile, it provides sufficient self-support to the performers. Acoustical parameters including reverberation time RT, early decay time EDT, acoustic ratio C50, strength index (loudness) G, and stage support factor ST1 were measured and reported on several traditional theatrical buildings. 相似文献
54.
55.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
56.
57.
移动通信系统中功率控制研究 总被引:2,自引:0,他引:2
在阐述功率控制在移动通信系统中的发展过程的基础上,着重研究了WCDMA系统的功率控制,最后对功率控制未来的研究方向做了简要的分析。 相似文献
58.
59.
60.
天然气水合物和天然气脱水新工艺探讨 总被引:3,自引:0,他引:3
探讨了天然气水合物的发展过程、形成条件以及对天然气输送管道的腐蚀堵塞作用,对我国天然气脱水创新技术———膜法脱水、汽提脱水的原理与工艺过程进行了全面论述。考察了气体处理量及操作压力等对我国1.2×105m3/d天然气膜法脱水的工业试验装置的脱水过程的影响。 相似文献