全文获取类型
收费全文 | 115399篇 |
免费 | 11969篇 |
国内免费 | 6961篇 |
专业分类
电工技术 | 8410篇 |
技术理论 | 8篇 |
综合类 | 8896篇 |
化学工业 | 17277篇 |
金属工艺 | 6433篇 |
机械仪表 | 7761篇 |
建筑科学 | 9612篇 |
矿业工程 | 3731篇 |
能源动力 | 3503篇 |
轻工业 | 7749篇 |
水利工程 | 2561篇 |
石油天然气 | 6373篇 |
武器工业 | 1263篇 |
无线电 | 14285篇 |
一般工业技术 | 12546篇 |
冶金工业 | 4676篇 |
原子能技术 | 1563篇 |
自动化技术 | 17682篇 |
出版年
2024年 | 641篇 |
2023年 | 2040篇 |
2022年 | 4002篇 |
2021年 | 5646篇 |
2020年 | 4229篇 |
2019年 | 3331篇 |
2018年 | 3684篇 |
2017年 | 4142篇 |
2016年 | 3668篇 |
2015年 | 5236篇 |
2014年 | 6651篇 |
2013年 | 7742篇 |
2012年 | 8787篇 |
2011年 | 9268篇 |
2010年 | 8198篇 |
2009年 | 7645篇 |
2008年 | 7378篇 |
2007年 | 6698篇 |
2006年 | 6177篇 |
2005年 | 5025篇 |
2004年 | 3438篇 |
2003年 | 2947篇 |
2002年 | 3074篇 |
2001年 | 2558篇 |
2000年 | 2076篇 |
1999年 | 2064篇 |
1998年 | 1419篇 |
1997年 | 1228篇 |
1996年 | 1188篇 |
1995年 | 941篇 |
1994年 | 794篇 |
1993年 | 590篇 |
1992年 | 409篇 |
1991年 | 325篇 |
1990年 | 237篇 |
1989年 | 203篇 |
1988年 | 203篇 |
1987年 | 120篇 |
1986年 | 77篇 |
1985年 | 46篇 |
1984年 | 36篇 |
1983年 | 21篇 |
1982年 | 33篇 |
1981年 | 25篇 |
1980年 | 30篇 |
1979年 | 26篇 |
1976年 | 3篇 |
1971年 | 3篇 |
1959年 | 14篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
82.
An account is given of some principal observations made from a series of experiments in which three-span pipe beams were subjected to central impact by indenters with different nose shapes. These pipes were filled and pre-pressurized with water in order to identify the main effects produced by the fluid–structure interaction. In comparison, the impact experiments of the pipes with no water were also carried out. The perforation failure modes and corresponding critical impact energies were obtained in different test conditions. The experimental results indicated that the critical perforation energy and the deformation of the wall of the pipe were significantly influenced by the presence of the water and the pressure. 相似文献
83.
84.
The semiconductor device trend for increasing functionalities and performances yet with smaller overall feature sizes presents escalating obstacles to the decreasing form factor along with demanding thermal carrying capability required at the package level. To confront this compounding issue, ultrafine-pitch wirebond interconnect coupled with thermally enhanced copper heat spreader attached to the package are introduced. However, the additional copper heat spreader thickness introduced within the package challenges the design of the package's wire, its loop height, and the molding process control to prevent wire sweeping occurrences. This study investigates the impact of different ultrafine pitched wire types, wire loop designs, copper heat spreader structures, and mold material types on eliminating device short from occurring due to the wire sweeping phenomena. A full factorial experiment is performed using an active silicon device packaged in a thermally enhanced ball grid array (BGA) test vehicle. In addition, test characterization is carried out using x-ray and multiinsertions hot/cold continuity tests. Then, a detailed failure analysis is performed by package decapsulation and scanning electron microscopy/energy-dispersive x-ray (SEM/EDX) to confirm the experimental findings. In conclusion, the study finds that for an ultrafine-pitched thermally enhanced BGA package, wire type is insignificant to reduce wire shorting occurrences. However, mold material and copper heat spreader structure using an optimized wire loop design are significant factors in eliminating wiresweep shorting phenomena. This study concludes with a wirebond interconnect and heat slug design recommended along with an improved process parameters and assembly material sets found from the experiment. 相似文献
85.
MX345芯片用于产生模拟信令—CTCSS单音.本文在介绍MX345编码/解码器工作原理的基础上,设计出MX345芯片与单片机的接口电路.最后给出控制软件. 相似文献
86.
Crystallite growth characteristics of coprecipitated superfine zirconia powders have been investigated. It was found that the crystallite growth in powders follows a cubic law at 800 and 1000°C; however, the crystallite size data for compacts of both Y-TZP and YSZ cannot be fitted with a traditional parabolic or cubic law, but with a linear relation between crystallite size and the logarithm of time. In addition, it was also found that the degree of agglomeration of the powders can affect the crystallite growth. 相似文献
87.
88.
高度有序多孔氧化铝模板的制备工艺与生长机制的研究 总被引:4,自引:0,他引:4
采用二次氧化法制备出高度有序的多孔氧化铝模板,结合扫描电镜和原子力显微镜对其结构、形貌进行观察和表征。研究了铝箔预处理和温度等对多孔氧化铝模板孔洞有序性的影响,讨论了有序孔洞的自组织生长机理。 相似文献
89.
Guanghui Wang Lei Huang Rong Yu Nansheng Deng 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):601-608
BACKGROUND: Endocrine disruptors in the aquatic environment and their potential adverse effects are currently issues of concern. One of these endocrine disruptors is 2,2‐bis(4‐hydroxy‐3‐methylphenyl)propane (BPP). In this work the molecular recognition interaction of BPP with β‐cyclodextrin (β‐CD) was studied using IR spectroscopy and steady state fluorescence spectroscopy, and the photocatalytic degradation behaviour of BPP based on molecular recognition interaction was investigated in a TiO2/UV–visible (λmax = 365 nm) system. This might provide a new method for the treatment of some organic pollutants in wastewater. RESULTS: β‐CD reacts with BPP to form a 1:1 inclusion complex, the formation constant of which is 4.94 × 103 L mol?1. The photodegradation rate constant of BPP after molecular recognition by β‐CD showed a 1.42‐fold increase in the TiO2/UV–visible (λmax = 365 nm) system. The photodegradation of BPP depended on the concentration of β‐CD, the pH value, the gaseous medium and the initial concentration of BPP. The photodegradation efficiency of BPP with molecular recognition was higher than that without molecular recognition. After 100 min of irradiation the mineralisation efficiency of BPP after molecular recognition by β‐CD reached 94.8%, whereas the mineralisation efficiency of BPP before molecular recognition by β‐CD was only 40.6%. CONCLUSION: The photocatalytic degradation of BPP after molecular recognition by β‐CD can be enhanced in the TiO2/UV‐visible (λmax = 365 nm) system. This enhancement is dependent on the enhancement of the adsorption of BPP, the moderate inclusion depth of BPP in the β‐CD cavity and the increase in the frontier electron density of BPP after molecular recognition. Copyright © 2008 Society of Chemical Industry 相似文献
90.
Xianfu Lei Pingzhi Fan 《Communications Letters, IEEE》2008,12(10):720-721
We point out that a simpler expression could be derived for the outage probability considered by Chalise and Vandendorpe (2008). As a result, the computation of confluent hypergeometric function of two variables is not needed and the required computational effort is significantly reduced. 相似文献