全文获取类型
收费全文 | 85篇 |
免费 | 100篇 |
国内免费 | 48篇 |
专业分类
化学 | 61篇 |
晶体学 | 5篇 |
力学 | 15篇 |
综合类 | 2篇 |
数学 | 25篇 |
物理学 | 125篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 12篇 |
2013年 | 4篇 |
2012年 | 7篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 12篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1988年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 109 毫秒
101.
利用从头算RHF方法研究了聚芳醚酮单体4,4’-对苯二酚、4,4’-联苯二酚及4,4’-二氟苯酮。结果表明,它们的苯环皆存在一定的扭转,首次给出联苯二酚全优化结构,其苯环二面角为51.8°,活性稍强于对苯二酚,但引入更多的链支化活特点,含联苯基聚芳醚醚酮的链支化比不含联苯基的PEEK严重,故前者结晶性差,反应机理及实验还表明:前者凝胶化的浓硫酸溶液中存在一种羰基被极化后的红色阴离子。 相似文献
102.
封建湖 《纯粹数学与应用数学》1996,12(2):12-16
研究了如何利用迎风格式的耗散性构造中心差分TVD格式的方法,给 相应的定理,构造出新的耗散表达式。新格式既保留了二阶中心差分格式灵活方便的优点,又吸收了迎风格式耗散项比较精细的特点,同时具有TVD性质,使得新格式具有较同的激波分辨率。 相似文献
103.
104.
用不同的工艺和原料制备了3个名义成分相同的Mn1.2Fe0.8P0.48S i0.52化合物。X射线衍射结果表明,3个化合物均为Fe2P型六角结构(空间群为P-62m),并且存在少量的(Fe,Mn)3S i相。通过磁性测量发现,3个样品的居里温度有所不同,但是都在室温附近(270~290 K)。以Fe2P为原料制备的化合物具有较大的磁熵变,在1.5 T的磁场变化下其最大磁熵变为13.6 J.(kg.K)-1。以行星样品球磨机制备的化合物具有较小的热滞,最小热滞为6.7 K。这些表明不同的制备工艺和原料对化合物的居里温度、热滞和磁熵变都具有一定的影响。同时低成本的原料、简单的制备工艺、较小的热滞和较大的磁熵变使得Mn1.2Fe0.8P0.48S i0.52化合物成为一种理想的室温磁致冷候选材料。 相似文献
105.
We fabricated a set of symmetric gate-recess devices with gate length of 70 nm.We kept the source-to-drain spacing(LSD)unchanged,and obtained a group of devices with gate-recess length(Lrecess)from 0.4μm to 0.8μm through process improvement.In order to suppress the influence of the kink effect,we have done SiNX passivation treatment.The maximum saturation current density(IDmax)and maximum transconductance(gm,max)increase as Lrecess decreases to 0.4μm.At this time,the device shows IDmax=749.6 mA/mm at VGS=0.2 V,VDS=1.5 V,and gm,max=1111 mS/mm at VGS=?0.35 V,VDS=1.5 V.Meanwhile,as Lrecess increases,it causes parasitic capacitance Cgd and gd to decrease,making fmax drastically increases.When Lrecess=0.8μm,the device shows fT=188 GHz and fmax=1112 GHz. 相似文献
106.
Heterogeneous integrated InP high electron mobility transistors(HEMTs)on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene(BCB)bonding technology.The channel of the new device is In0.7Ga0.3As,and the gate length is 100 nm.A maximum extrinsic transconductance gm,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained.The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz.In addition,a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance. 相似文献
107.
A double-recessed offset gate process technology for InP-based high electron mobility transistors (HEMTs) has been developed in this paper. Single-recessed and double-recessed HEMTs with different gate offsets have been fabricated and characterized. Compared with single-recessed devices, the maximum drain-source current (ID,max) and maximum extrinsic transconductance (gm,max) of double-recessed devices decreased due to the increase in series resistances. However, in terms of RF performance, double-recessed HEMTs achieved higher maximum oscillation frequency (fMAX) by reducing drain output conductance (gds) and drain to gate capacitance (Cgd). In addition, further improvement of fMAX was observed by adjusting the gate offset of double-recessed devices. This can be explained by suppressing the ratio of Cgd to source to gate capacitance (Cgs) by extending drain-side recess length (Lrd). Compared with the single-recessed HEMTs, the fMAX of double-recessed offset gate HEMTs was increased by about 20%. 相似文献
108.
2-μm single longitudinal mode GaSb-based laterally coupled distributed feedback laser with regrowth-free shallow-etched gratings by interference lithography
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report a type-I Ga Sb-based laterally coupled distributed-feedback(LC-DFB) laser with shallow-etched gratings operating a continuous wave at room temperature without re-growth process. Second-order Bragg gratings are fabricated alongside the ridge waveguide by interference lithography. Index-coupled LC-DFB laser with a cavity of 1500 μm achieves single longitudinal mode continuous-wave operation at 20℃ with side mode suppression ratio(SMSR) as high as 24 dB.The maximum single mode continuous-wave output power is about 10 mW at room temperature(uncoated facet). A low threshold current density of 230 A/cm~2 is achieved with differential quantum efficiency estimated to be 93 mW/A. The laser shows a good wavelength stability against drive current and working temperature. 相似文献
109.
The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots(SQDs) to raise the growth repeatability.Here,through many growth tests on rotating substrates,we develop a proper In deposition amount(θ) for SQD growth,according to the measured critical θ for test QD nucleation(θ_c).The proper ratio θ/θ_c,with a large tolerance of the variation of the real substrate temperature(T_(sub)),is 0.964-0.971 at the edge and 0.989 but 0.996 in the center of a 1/4-piece semi-insulating wafer,and around 0.9709 but 0.9714 in the center of a 1/4-piece N~+ wafer as shown in the evolution of QD size and density as θ/θ_c varies.Bright SQDs with spectral lines at 905 nm-935 nm nucleate at the edge and correlate with individual 7 nm-8 nm-height QDs in atomic force microscopy,among dense 1 nm-5 nm-height small QDs with a strong spectral profile around 860 nm-880 nm.The higher T_(sub) in the center forms diluter,taller and uniform QDs,and very dilute SQDs for a proper θ/θ_c:only one 7-nm-height SQD in25 μm~2.On a 2-inch(1 inch = 2.54 cm) semi-insulating wafer,by using θ/θ_c = 0.961,SQDs nucleate in a circle in 22%of the whole area.More SQDs will form in the broad high-T_(sub) region in the center by using a proper θ/θ_c. 相似文献
110.