全文获取类型
收费全文 | 928篇 |
免费 | 56篇 |
国内免费 | 45篇 |
专业分类
化学 | 225篇 |
晶体学 | 5篇 |
力学 | 24篇 |
数学 | 5篇 |
物理学 | 83篇 |
无线电 | 687篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 26篇 |
2021年 | 43篇 |
2020年 | 24篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 33篇 |
2016年 | 23篇 |
2015年 | 33篇 |
2014年 | 46篇 |
2013年 | 37篇 |
2012年 | 64篇 |
2011年 | 63篇 |
2010年 | 42篇 |
2009年 | 58篇 |
2008年 | 64篇 |
2007年 | 77篇 |
2006年 | 61篇 |
2005年 | 50篇 |
2004年 | 40篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 28篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 22篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有1029条查询结果,搜索用时 15 毫秒
111.
Amine Kassouf Maria El Rakwe Hanna Chebib Violette Ducruet Douglas N. Rutledge Jacqueline Maalouly 《Analytica chimica acta》2014
Olive oil is one of the most valued sources of fats in the Mediterranean diet. Its storage was generally done using glass or metallic packaging materials. Nowadays, plastic packaging has gained worldwide spread for the storage of olive oil. However, plastics are not inert and interaction phenomena may occur between packaging materials and olive oil. In this study, extra virgin olive oil samples were submitted to accelerated interaction conditions, in contact with polypropylene (PP) and polylactide (PLA) plastic packaging materials. 3D-front-face fluorescence spectroscopy, being a simple, fast and non destructive analytical technique, was used to study this interaction. Independent components analysis (ICA) was used to analyze raw 3D-front-face fluorescence spectra of olive oil. ICA was able to highlight a probable effect of a migration of substances with antioxidant activity. The signals extracted by ICA corresponded to natural olive oil fluorophores (tocopherols and polyphenols) as well as newly formed ones which were tentatively identified as fluorescent oxidation products. Based on the extracted fluorescent signals, olive oil in contact with plastics had slower aging rates in comparison with reference oils. Peroxide and free acidity values validated the results obtained by ICA, related to olive oil oxidation rates. Sorbed olive oil in plastic was also quantified given that this sorption could induce a swelling of the polymer thus promoting migration. 相似文献
112.
《Microelectronics Reliability》2014,54(11):2594-2603
When encountering a particular reliability problem at the design, fabrication, testing, or an operation stage of a product’s life, and considering the use of predictive modeling to assess the seriousness and the likely consequences of the a detected failure, one has to choose whether a statistical, or a physics-of-failure-based, or a suitable combination of these two major modeling tools should be employed to address the problem of interest and to decide on how to proceed. A three-step concept (TSC) is suggested as a possible way to go in such a situation. The classical statistical Bayes’ formula can be used at the first step in this concept as a technical diagnostics tool. Its objective is to identify, on the probabilistic basis, the faulty (malfunctioning) device(s) from the obtained signals (“symptoms of faults”). The recently suggested physics-of-failure-based Boltzmann–Arrhenius–Zhurkov’s (BAZ) model and particularly the multi-parametric BAZ model can be employed at the second step to assess the remaining useful life (RUL) of the faulty device(s). If the RUL is still long enough, no action might be needed; if it is not, corrective restoration action becomes necessary. In any event, after the first two steps are carried out, the device is put back into operation (testing), provided that the assessed probability of its continuing failure-free operation is found to be satisfactory. If the operational failure nonetheless occurs, the third, technical diagnostics step should be undertaken to update reliability. Statistical beta-distribution, in which the probability of failure is treated as a random variable, is suggested to be used at this step. While various statistical methods and approaches, including Bayes’ formula and beta-distribution, are well known and widely used in numerous applications for many decades, the BAZ model was introduced in the microelectronics reliability (MR) area only several years ago. Its attributes are addressed and discussed therefore in some detail. The suggested concept is illustrated by a numerical example geared to the use of the prognostics-and-health-monitoring (PHM) effort in actual operation, such as, e.g., en-route flight mission. 相似文献
113.
《Microelectronics Reliability》2014,54(6-7):1223-1227
3D-integration becomes more and more an important issue for advanced LED packaging solutions as it is a great challenge for the thermo-mechanical reliability to remove heat from LEDs to the environment by heat spreading or specialized cooling technologies. Thermal copper-TSVs provide an elegant solution to effectively transfer heat from LED to the heat spreading structures on the backside of a substrate. But, the use of copper-TSVs generates also novel challenges for reliability as well as also for reliability analysis and prediction, i.e. to manage multiple failure modes acting combined – interface delamination, cracking and fatigue, in particular. In this case, the thermal expansion mismatch between copper and silicon yields to risky stress situations.To overcome cracking and delamination risks in the vicinity of thermal copper-TSVs the authors performed extensive simulative work by means of fracture mechanics approaches – an interaction integral approach within a simulative DoE and the X-FEM methodology to help clarifying crack propagation paths in silicon. The results provided a good insight into the role of model parameters for further optimizations of the intended thermal TSV-approaches in LED packaging applications. 相似文献
114.
杨建生 《电子工业专用设备》2011,40(5):15-20
包含微机电系统(MEMS)混合元器件的埋置型叠层封装,此封装工艺为目前用于微电子封装的挠曲基板上芯片(COF)工艺的衍生物.COF是一种高性能、多芯片封装工艺技术,在此封装中把芯片包入模塑塑料基板中,通过在元器件上形成的薄膜结构构成互连.研究的激光融除工艺能够使所选择的COF叠层区域有效融除,而对封装的MEMS器件影响... 相似文献
115.
116.
117.
Cristina BlascoYolanda Picó 《Trends in analytical chemistry : TRAC》2011,30(1):84-99
Nanotechnology has emerged as one of the most innovative technologies and has the potential to improve food quality and safety. However, there are a few studies demonstrating that nanomaterials (NMs) are not inherently benign.This review highlights some current applications of NMs in food, food additives and food-contact materials, and reviews analytical approaches suitable to address food-safety issues related to nanotechnology.We start with a preliminary discussion on the current regulatory situation with respect to nanotechnology in relation to foods. We cover sample preparation, imaging techniques (e.g., electron microscopy, scanning electron microscopy and X-ray microscopy), separation methods (e.g., field-flow fractionation and chromatographic techniques) and detection or characterization techniques (e.g., light scattering, Raman spectroscopy and mass spectrometry). We also show the first applications of the analysis of NMs in food matrices. 相似文献
118.
119.
In this study, a microcapillary pumped loop (MCPL) that can be used as a cooling device for small electronic and telecommunications equipment has been developed. For thin devices such as an MCPL, securing a vapor flow space is a critical issue for enhancing the thermal performance. In this letter, such enhancement in thermal performance was accomplished by eliminating condensed droplets from the vapor line. By fabricating the grooves in the vapor line to eliminate droplets, a decrease in thermal resistance of about 63.7% was achieved. 相似文献
120.
Wire bonding is one of the main processes of the LED packaging which provides electrical interconnection between the LED chip and lead frame. The gold wire bonding process has been widely used in LED packaging industry currently. However, due to the high cost of gold wire, copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving. In this paper, the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation. This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging. 相似文献