全文获取类型
收费全文 | 106369篇 |
免费 | 9218篇 |
国内免费 | 6609篇 |
专业分类
电工技术 | 6791篇 |
技术理论 | 1篇 |
综合类 | 7358篇 |
化学工业 | 18878篇 |
金属工艺 | 17780篇 |
机械仪表 | 5558篇 |
建筑科学 | 12403篇 |
矿业工程 | 2270篇 |
能源动力 | 5039篇 |
轻工业 | 7723篇 |
水利工程 | 1637篇 |
石油天然气 | 6514篇 |
武器工业 | 1060篇 |
无线电 | 5303篇 |
一般工业技术 | 11151篇 |
冶金工业 | 4886篇 |
原子能技术 | 891篇 |
自动化技术 | 6953篇 |
出版年
2024年 | 527篇 |
2023年 | 1863篇 |
2022年 | 3557篇 |
2021年 | 4340篇 |
2020年 | 4142篇 |
2019年 | 3542篇 |
2018年 | 3272篇 |
2017年 | 4135篇 |
2016年 | 4180篇 |
2015年 | 4197篇 |
2014年 | 6390篇 |
2013年 | 6485篇 |
2012年 | 7496篇 |
2011年 | 8161篇 |
2010年 | 6011篇 |
2009年 | 6392篇 |
2008年 | 5268篇 |
2007年 | 6595篇 |
2006年 | 6070篇 |
2005年 | 5030篇 |
2004年 | 4345篇 |
2003年 | 3731篇 |
2002年 | 3056篇 |
2001年 | 2535篇 |
2000年 | 2050篇 |
1999年 | 1724篇 |
1998年 | 1261篇 |
1997年 | 1106篇 |
1996年 | 902篇 |
1995年 | 798篇 |
1994年 | 622篇 |
1993年 | 448篇 |
1992年 | 358篇 |
1991年 | 274篇 |
1990年 | 217篇 |
1989年 | 190篇 |
1988年 | 124篇 |
1987年 | 92篇 |
1986年 | 53篇 |
1985年 | 51篇 |
1984年 | 65篇 |
1983年 | 44篇 |
1982年 | 49篇 |
1981年 | 30篇 |
1980年 | 71篇 |
1964年 | 29篇 |
1963年 | 27篇 |
1961年 | 24篇 |
1959年 | 28篇 |
1955年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
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
113.
Behavior of Magnesium‐Alloys for Automotive Applications under Mechanical and Environmental Loading: Influence of Passivating Films and Mechanisms of Local Breakdown To assure an efficient design of components under cyclic loading, all available data concerning fatigue have to be observed. Therefore the influences of manufacturing on the material condition, the mechanical loads and environmental effects have to be analysed. Magnesium‐alloys are of special interest for lightweight applications because of their excellent strength‐density ratio. The corrosion resistance of magnesium‐alloys depends on the same factors that are critical to other metals. The alloys have a good stability to atmospheric exposure and a good resistance to attack by alkali, chromic and hydrofluoric acids. However, because of the electrochemical activity of magnesium, the relative importance of some factors is greatly amplified. The nature and composition of passive films formed on magnesium‐alloys depend on the prevailing conditions, viz. alloy‐composition, passivation potential, pH, electrolyte composition and temperature. Passive films may be damaged by local breakdown. Because of this, magnesium‐alloys suffer a degradation of their properties when exposed to an aqueous environment. The main topic of the present investigations is the verification of mechanisms of the local breakdown of the protecting film. At least two mechanisms are possible for this localization: mechanical breakdown by slip steps and electrochemical breakdown (for e.g. by the effects of chloride ions). Corrosion and passivation of different high purity alloys have been studied in different solutions (neutral, alkaline with specific anions and cations) using electrochemical techniques. The diecasted alloys were tested as produced and machined. The results clarified that depending on alloy/material and surface condition/corrosion environment different mechanisms for electrochemical breakdown of the protecting films are possible. Hence fatigue life under environmental loading is influenced by surface and testing conditions. 相似文献
114.
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
115.
116.
腐蚀引起钻柱刺漏的机理分析及预防措施 总被引:7,自引:7,他引:0
详细分析了腐蚀引起钻柱刺漏的机理,得知:造成钻柱刺漏的主要原因是空气中的O2、地层中的硫化氢和二氧化碳、钻井液残液、钻井液中的盐类对钻柱的腐蚀和钻井液对钻柱的冲蚀。针对引起钻柱刺漏的原因,制定了去除钻井液中的O2、监测钻井液腐蚀性并加入相应的添加剂去除CO2和H2S、定期对钻杆进行检测、对存放的钻杆进行防腐处理、使用厚过渡区改进型钻杆等措施。在苏丹某区块现场实践证明,采取这些措施,由腐蚀引起的钻柱刺漏事故大大减少,在该区块的T-1井和D-1井钻进的3个月中,仅发生一次钻柱刺漏事故。 相似文献
117.
阳离子型高温酸化缓蚀剂的合成及其性能评价 总被引:3,自引:3,他引:0
针对Mannich碱型缓蚀剂存在的溶解性不好和缓蚀率不高等问题,以甲醛、环己酮和苯胺为原料,合成了一种Mannich碱型缓蚀剂CH-9,将其阳离子化后,再与丙炔醇复配,得到了阳离子型高温酸化缓蚀剂CH-10。由室内性能评价可知,CH-10在盐酸中有良好的溶解分散性;与酸液中其他添加剂如粘土稳定剂和铁离子稳定剂的配伍性良好,不会对酸化地层造成堵塞;在90℃和常压下,在20%HCl溶液中加入浓度为1%的CH-10,其对N80钢片的腐蚀速率为4.765g/(m2·h);在120℃时,浓度为2%的CH-10对N80钢片的腐蚀速率为14.30g/(m2·h),均达到了SY/T5405-1996标准中的一级标准。 相似文献
118.
介绍了中国石油天然气股份有限公司大庆石化分公司地下输水管网的腐蚀现状与调查分析情况,提出了对地下输水管网实施以深井阳极地床外加电流阴极保护为主、局部欠保护区辅以镁合金牺牲阳极的阴极保护方案。经分析,采取上述防护措施后,每年可产生2488万元的经济效益。 相似文献
119.
120.