全文获取类型
收费全文 | 221篇 |
免费 | 7篇 |
国内免费 | 8篇 |
专业分类
化学 | 75篇 |
力学 | 4篇 |
综合类 | 1篇 |
数学 | 4篇 |
物理学 | 29篇 |
综合类 | 123篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 27篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
221.
222.
印刷电路板固定故障的热模式 总被引:1,自引:0,他引:1
在研究TTL集成电路和CMOS集成电路功耗的基础上,提出了一种新的印刷电路板(PCB)故障的描述方法,即PCB故障的热模式.并详细分析了两类PCB固定故障(SAF)即固定开路(SAO)故障和固定短路(SAS)故障的热模式,指出利用PCB故障热模式进行故障检测和诊断的可行性 相似文献
223.
Micro via and line patterning for PCB using imprint technique 总被引:1,自引:0,他引:1
Seunghyun Ra Choonkeun Lee Jaechoon Cho Sangmoon Lee Jungwoo Lee Myungho Hong Jungbok Kwak 《Current Applied Physics》2008,8(6):675-678
Today’s electronic devices such as mobile phones, PDA, computers, etc. have more functions in a smaller size. Thus conducting lines and via holes of PCB (printed circuit board) which has a role of land for all kinds of electronic components are getting finer. In this study, the conducting lines and via holes are produced using thermal imprint technique rather than the conventional photo-lithography process. Imprint technique is a press process that transfers patterns of stamp to resins. Imprint technique is used to produce micro size trench lines and via holes in epoxy resins.Resins used in this work are silica (SiO2) reinforced epoxy. Resins were imprinted using 10 * 10 mm size Ni or polymer stamp. Line/space of pattern is 10/10 μm while diameter of via hole is 30 μm. The depths of lines and via holes are 15 and 30 μm, respectively. The anti-sticking treated stamp and epoxy resins were pressed at 100 °C for 30 min in vacuum. The stamp was released after resins were cured for 1 h at 130 °C. All patterns of stamp were successfully transferred with high fidelity and any noticeable defect was not observed within imprinted area. Imprinted resins were de-smeared to remove the residue at the bottom of via holes and to enhance the adhesion of resins with Cu. Electro/less copper plating was followed to fill in the imprinted patterns. Since the excess Cu layer was formed on the resins during Cu plating, the planarization process was introduced to obtain isolated lines and via holes. 相似文献
224.
A comparison of two electrochemical immunosensing strategies for PCBs detection, based on the use of two different solid phases, is here discussed. In both cases, carbon-based screen-printed electrodes (SPEs) are used as transducers in a direct competitive immunoassay scheme, where PCBs in solution compete with the tracer PCB28-alkaline phosphatase (AP) labeled for antibodies immobilized onto the solid-phase.In the standard format (called EI strategy), SPEs are both the solid-phase for immunoassay and electrochemical transducers: in this case the immunochemical reaction occurs onto the working electrode. Finally, the enzymatic substrate is added and an electroactive product is generated and detected by electrochemical measurement. In order to improve the performances of the system, a new approach (called EMI strategy) is developed by using functionalized magnetic beads as solid phase for the competitive assay; only after the immunosensing step they are captured by a magnet onto the working surface of the SPE for the electrochemical detection.Experimental results evidenced that the configuration based on the use of separate surfaces for immunoassay and for electrochemical detection gave the best results in terms of sensitivity and speed of the analysis. The improvement of analytical performances of the immunosensor based on EMI strategy was also demonstrated by the analysis of some spiked samples. 相似文献
225.
In order to solve the problem of digital radiography for printed circuit board (PCB) defect inspection, a new inspection system for PCB defect inspection with high resolution X-ray is proposed and implemented in this paper. The influence of the focus size of X-ray source on imaging formation is analyzed to get the best geometrical magnification. Moreover, the relationship between the resolution of intensifier and geometrical magnification is presented by analyzing the performance of MCP-X intensifier, which results in calculating the comprehensive resolution of this system. The experiment result indicates that the measurements on defect character is achieved by inspection software, and the defect analysis accuracy on ball grid array (BGA) solder joint of circuit board achieves minimum resolution of 0.03 mm. As a result, this system succeeds in implementing invisible solder joint defect inspection on BGA. 相似文献
226.
由于引脚、印制电路板和焊接剂的热-机材料属性不同,在受到热载荷或机械载荷时,引脚焊接界面端会产生奇异性应力,有可能产生界面开裂.为了基于界面端奇异场来评价QFP结构引脚界面端力学行为,本文拟采用数值方法求解引脚焊缝任意角度尖劈界面端的应力强度系数.具体步骤为:首先,基于高次内插有限元特征分析法确定两相任意角度尖劈界面端的奇异性指数和应力角分布函数,并引入常数热应力项,获得热-机耦合奇异性应力场表达式;采用有限元分析技术和最小二乘拟合法来获得应力强度系数的数值解.文中考察了热-机材料属性对热载荷下焊接剂/印制电路板界面端应力强度系数的影响,并给出改善界面端热应力状态的建议. 相似文献
227.
228.
R. O. Harrison N. Melnychuk 《International journal of environmental analytical chemistry》2013,93(2-4):179-185
Abstract A commercially available kit has been applied successfully to screening for polychlorinated biphenyls (PCB's) in soil samples. The kit uses a competitive inhibition Enzyme ImmunoAssay (EIA) for recognition of the PCB structure. Test specificity is restricted to PCB's, primarily Aroclors 1016, 1242, 1248, 1254, and 1260. Soil sample preparation and analysis can be performed in the field or lab using disposable kit components. Screening of unidentified Aroclors at 4 levels from 1 to 50 μg/g in soil is possible using the calibrators in the kit. This screening use has been reviewed by the USEPA Office of Solid Waste and will be proposed for inclusion in the 4000 series of screening methods in the next SW846 update. Conventional analysis (Soxhlet/GC-ECD) and the EIA kit were compared by Manitoba Hydro using 112 field samples over one year. EIA technology was found to be an effective screening tool for determining PCB concentration at contaminated sites. Routine use of these kits in conjunction with conventional Soxhlet extraction procedures has increased the lab's testing capability and reduced the amount of samples requiring conventional testing, providing substantial savings to the corporation. 相似文献
229.
Kimitaka Kawamura Spencer Steinberg I. R. Kaplan 《International journal of environmental analytical chemistry》2013,93(3):175-188
Abstract A capillary GC and GC-MS method, employing dibutyl esters is described for determining short-chain dicarboxylic acids in rain, fog and mist samples collected in the Los Angeles area. Approximately twenty dicarboxylic acids (C2-C10) were identified in the water samples, including cis (maleic) and trans (fumaric) unsaturated, saturated, normal, branched and aromatic. Oxalic acid is the dominant acid, followed by succinic and malonic acids. The total concentrations measured are 2.9–51μM, 64–66 μM and 12 μM for rain, fog and mist samples, respectively. These diacids are probably produced by photooxidation of anthropogenic and possibly biogenic organic compounds in the atmosphere. 相似文献
230.