全文获取类型
收费全文 | 70677篇 |
免费 | 6741篇 |
国内免费 | 3504篇 |
专业分类
电工技术 | 4192篇 |
技术理论 | 4篇 |
综合类 | 6713篇 |
化学工业 | 8086篇 |
金属工艺 | 2455篇 |
机械仪表 | 4100篇 |
建筑科学 | 13400篇 |
矿业工程 | 2228篇 |
能源动力 | 3967篇 |
轻工业 | 5981篇 |
水利工程 | 2295篇 |
石油天然气 | 3121篇 |
武器工业 | 920篇 |
无线电 | 4266篇 |
一般工业技术 | 5946篇 |
冶金工业 | 3179篇 |
原子能技术 | 490篇 |
自动化技术 | 9579篇 |
出版年
2024年 | 318篇 |
2023年 | 1173篇 |
2022年 | 2282篇 |
2021年 | 2693篇 |
2020年 | 2699篇 |
2019年 | 2273篇 |
2018年 | 2123篇 |
2017年 | 2516篇 |
2016年 | 2695篇 |
2015年 | 2824篇 |
2014年 | 4538篇 |
2013年 | 4246篇 |
2012年 | 5002篇 |
2011年 | 5384篇 |
2010年 | 4154篇 |
2009年 | 4295篇 |
2008年 | 3872篇 |
2007年 | 4886篇 |
2006年 | 4178篇 |
2005年 | 3536篇 |
2004年 | 2919篇 |
2003年 | 2479篇 |
2002年 | 2066篇 |
2001年 | 1649篇 |
2000年 | 1287篇 |
1999年 | 1003篇 |
1998年 | 687篇 |
1997年 | 560篇 |
1996年 | 509篇 |
1995年 | 350篇 |
1994年 | 286篇 |
1993年 | 222篇 |
1992年 | 176篇 |
1991年 | 140篇 |
1990年 | 117篇 |
1989年 | 83篇 |
1988年 | 71篇 |
1987年 | 50篇 |
1986年 | 29篇 |
1985年 | 43篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 30篇 |
1981年 | 21篇 |
1980年 | 49篇 |
1964年 | 29篇 |
1963年 | 27篇 |
1961年 | 22篇 |
1959年 | 23篇 |
1955年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
51.
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
52.
掌握了理论知识并不等于有了实战经验,更不等于有实战能力。从理论到有实战能力的飞跃,只有亲临生产线,在不断解决问题过程中实现。 相似文献
53.
Spatial collaboration is an everyday activity in which people work together to solve a spatial problem. For example, a group of people will often arrange furniture together or exchange directions with one another. Collaborative virtual environments using desktop PCs are particularly useful for spatial activities when the participants are distributed. This work investigates ways to enhance distributed, collaborative spatial activities. This paper explores how different frames of reference affect spatial collaboration. Specifically, it reports on an experiment that examines different combinations of exocentric and egocentric frames of reference with two users. Tasks involve manipulating an object, where one participant knows the objective (director) and the other performs the interactions (actor). It discusses the advantages and disadvantages of the different combinations for a spatial collaboration task. Findings from this study demonstrate that frames of reference affect collaboration in a variety of ways and simple exocentric-egocentric combinations do not always provide the most usable solution. 相似文献
54.
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
55.
56.
钻井、地震、测井及测试资料综合研究认为:渤海湾盆地济阳—临清东部地区石炭—二叠系主要发育一套浅海碳酸盐岩台地相灰岩、障壁—潟湖、潮坪、沼泽及三角洲相陆源碎屑岩和煤层.从纵向发育的沉积特征来看,上石炭统本溪组发育浅海台地相碳酸盐岩和浅海陆棚相(陆表海)砂泥岩,太原组主要发育障壁—潟湖、潮坪、沼泽相碳酸盐岩、陆源碎屑岩和煤的混合沉积;二叠系山西组主要发育三角洲相和三角洲平原沼泽相砂泥岩及煤,下石盒子组和上石盒子组则以发育近海陆相碎屑岩沉积为主,局部有河流沼泽的泥炭和煤发育.沉积环境总体具有自下而上、由南向北由浅海相、海陆交互相逐步过渡为陆相的基本特点.成煤环境以晚石炭世—早二叠世太原、山西期潮坪、潟湖过渡带之潮坪沼泽环境及三角洲平原沼泽环境为最佳. 相似文献
57.
58.
59.
60.
为实现电源设备乃至通信机房的少人或无人值守和集中维护,必须建立一套完善的电信局动力环境集中监控系统。文中结合番禺区电信局的实际,讨论了提高系统运行可靠性的几点措施,包括硬件方面与软件方面的手段,关键在于加强系统的运行管理。 相似文献