全文获取类型
收费全文 | 195篇 |
免费 | 42篇 |
国内免费 | 19篇 |
专业分类
化学 | 27篇 |
晶体学 | 1篇 |
力学 | 5篇 |
综合类 | 3篇 |
数学 | 35篇 |
物理学 | 40篇 |
无线电 | 145篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 8篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 30篇 |
2006年 | 13篇 |
2005年 | 10篇 |
2004年 | 15篇 |
2003年 | 22篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有256条查询结果,搜索用时 9 毫秒
251.
252.
The microstructure of the ultrasmall eutectic Bi-Sn solder bumps on Au/Cu/Ti and Au/Ni/Ti under-bump metallizations (UBMs)
was investigated as a function of cooling rate. The ultrasmall eutectic Bi-Sn solder bump, about 50 μm in diameter, was fabricated
by using the lift-off method and reflowed at various cooling rates using the rapid thermal annealing system. The microstructure
of the solder bump was observed using a backscattered electron (BSE) image and the intermetallic compound was identified using
energy dispersive spectroscopy (EDS) and an x-ray diffractometer (XRD). The Bi facet was found at the surface of the ultrasmall
Bi-Sn solder bumps on the Au/Cu/Ti UBM in almost all specimens, and the interior microstructure of the bumps was changed with
the solidification rate. The faceted and polygonal intermetallic compound was found in the case of the Bi-Sn solder bump on
the Au (0.1 μm)/Ni/Ti UBM, and it was confirmed to be the (Au1−x−yBixNiy)Sn2 phase by XRD. The intermetallic compounds grown form the Au (0.1 μm)/Ni/Ti UBM interface, and they interrupted the growth
of Bi and Sn phases throughout the solder bump. The ultrasmall eutectic Bi-Sn solder bumps on the Au (0.025 μm)/Ni/Ti UBM
showed similar microstructures to those on the Au/Cu/Ti UBM. 相似文献
253.
倒装焊SnPb焊点热循环失效和底充胶的影响 总被引:3,自引:5,他引:3
采用实验方法 ,确定了倒装焊 Sn Pb焊点的热循环寿命 .采用粘塑性和粘弹性材料模式描述了 Sn Pb焊料和底充胶的力学行为 ,用有限元方法模拟了 Sn Pb焊点在热循环条件下的应力应变过程 .基于计算的塑性应变范围和实验的热循环寿命 ,确定了倒装焊 Sn Pb焊点热循环失效 Coffin- Manson经验方程的材料参数 .研究表明 ,有底充胶倒装焊 Sn Pb焊点的塑性应变范围比无底充胶时明显减小 ,热循环寿命可提高约 2 0倍 ,充胶后的焊点高度对可靠性的影响变得不明显 相似文献
254.
The spin polarization phenomenon in lepton circular accelerators had been known for many years.It provides a new approach for physicists to study the spin feature of fundamental particles and the dynamics of spin-orbit coupling,such as spin resonances.We use numerical simulation to study the features of spin under the modulation of orbital motion in an electron storage ring.The various cases of depolarization due to spin-orbit coupling through an emitting photon and misalignment of magnets in the ring are discussed. 相似文献
255.
Pure Ni, the Ni-Cu alloy, and pure Cu layers as the under bump metallurgy (UBM) for a flip-chip solder joint were deposited
by electrolytic plating. For the pure Ni layer, residual stress can be controlled by adding a wetting agent and decreasing
current density, and it is always under tensile stress. The Ni-Cu alloys of different Cu compositions from ∼20wt.%Cu to 100wt.%Cu
were deposited with varying current density in a single bath. The residual stress was a strong function of current density
and Cu composition. Decreasing current density and increasing Cu content simultaneously causes the residual stress of the
metal layers to sharply decrease. For the pure Cu layer, the stress is compressive. The Cu layer acts as a cushion layer for
the UBM. The residual stress of the UBM strongly depends on the fraction of the Cu cushion layer. Interfacial reaction of
the UBM with Sn-3.5 wt.% Ag was studied. As the Cu contents of Ni-Cu alloys increased, the dissolution rate increased. Several
different intermetallic compounds (IMCs) were found. The lattice constants of alloys and the IMC increase with increasing
Cu contents because the larger Cu atoms substitute for the smaller Ni atoms in the crystallites. The Cu content of the IMC
are strongly dependent on the composition of the alloys. Ball shear tests were done with different metal-layer schemes. The
failure occurs through the IMC and solder. 相似文献
256.
Nonlocal Andreev reflection with Rashba spin-orbital interaction in a triple-quantum-dot ring 下载免费PDF全文
We theoretically studied the nonlocal Andreev reflection with Rashba spin-orbital interaction in a triple-quantumdot(QD) ring,which is introduced as Rashba spin-orbital interaction to act locally on one component quantum dot.It is found that the electronic current and spin current are sensitive to the systematic parameters.The interdot spin-flip term does not play a leading role in causing electronic and spin currents.Otherwise the spin precessing term leads to shift of the peaks of the the spin-up and spin-down electronic currents in different directions and results in the spin current.Moreover,the spin-orbital interaction suppresses the nonlocal Andreev reflection,so we cannot obtain the pure spin current. 相似文献