全文获取类型
收费全文 | 921篇 |
免费 | 71篇 |
国内免费 | 42篇 |
专业分类
化学 | 556篇 |
晶体学 | 2篇 |
力学 | 21篇 |
综合类 | 1篇 |
数学 | 50篇 |
物理学 | 161篇 |
无线电 | 243篇 |
出版年
2023年 | 15篇 |
2022年 | 11篇 |
2021年 | 28篇 |
2020年 | 20篇 |
2019年 | 34篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 35篇 |
2014年 | 58篇 |
2013年 | 48篇 |
2012年 | 56篇 |
2011年 | 53篇 |
2010年 | 42篇 |
2009年 | 34篇 |
2008年 | 43篇 |
2007年 | 58篇 |
2006年 | 51篇 |
2005年 | 46篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 33篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 7篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1034条查询结果,搜索用时 15 毫秒
61.
The forced-convection film condensation on a horizontal cylinder with wavy surface structure was performed by boundary-layer-approximation.
The local/mean heat fluxes were obtained for the effects of tube temperature, wave number, and wave amplitude. The mean heat
flux increases with decreasing wavy amplitude and tube temperatures. Furthermore, when β = 20 and α = 0.005, the mean heat
flux slightly increases from 1.1 to 3.6% compared with that of smooth tube, depending on tube temperature. 相似文献
62.
1.5 mu m band travelling-wave semiconductor optical amplifiers (TWAs), characterised by their window facet structure and symmetrised active waveguide, have been developed. 1.5 dB spectral gain ripple and 1.3 dB TE-TM mode gain difference at 22 dB signal gain were achieved simultaneously. An average facet reflectivity as low as 0.06% was estimated.<> 相似文献
63.
Young Chul Choi Ho-Young Cha Eastman L.F. Spencer M.G. 《Electron Devices, IEEE Transactions on》2005,52(9):1940-1948
A novel silicon carbide (SiC) normally off lateral channel vertical junction field-effect transistor (LC-VJFET), namely a source-inserted double-gate structure with a supplementary highly doped region (SHDR), was proposed for achieving extremely low power losses in high-power switching applications. The proposed architecture was based on the combination of an additional source electrode inserted between two adjacent surface gate electrodes and a unique SHDR in the vertical channel region. Two-dimensional numerical simulations for the static and resistive switching characteristics were performed to analyze and optimize the SiC LC-VJFET structures for this purpose. Based on the simulation results, the excellent performance of the proposed structure was compared with optimized conventional structures with regard to total power losses. Finally, the proposed structure showed about a 20% reduction in on-state loss (P/sub on/) compared to the conventional structures, due to the effective suppression of the JFET effect. Furthermore, the switching loss (P/sub sw/) of the proposed structure was found to be much lower than the results of the conventional structures, about a 75% /spl sim/ 95% reduction, by significantly reducing both input capacitance (C/sub iss/) and reverse transfer capacitance (C/sub rss/) of the device. 相似文献
64.
65.
Ho-Young Cha Y. C. Choi R. M. Thompson V. Kaper J. R. Shealy L. F. Eastman M. G. Spencer 《Journal of Electronic Materials》2004,33(8):908-911
The SiC metal-semiconductor field-effect transistors (MESFETs) have been reported to have current instability and strong dispersion
caused by trapping phenomena at the surface and in the substrate, which degrade direct-current (DC) and radio-frequency (RF)
performance. This paper illustrates the change in electrical characteristics of SiC MESFETs after Si3N4 passivation. Because of a reduction of surface trapping effects, Si3N4 passivation can diminish current collapse under pulsed DC conditions, increasing the RF power performance. The reduction
of surface trapping effects is verified by the change in the ratio of the drain current to the gate current under pinch-off
conditions. 相似文献
66.
Byeong Hee Hwang Jae Won Lee Hyung Joon Cha 《Applied biochemistry and biotechnology》2010,162(4):1187-1194
The polymerase chain reaction (PCR) technique is widely used for efficient detection of food-borne pathogens because of speed and specificity. However, PCR methods have focused mostly on species-specific detection. In the present work, we describe a PCR-based method for the simultaneous detection of all Vibrio species because lots of them are notorious food-borne human pathogens. We then combined this total detection method with specific detection of Vibrio cholerae pathogen. Using a degenerate primer set based on the sequence of the potassium uptake gene, trkA, we were able to successfully detect all Vibrio species. Specific detection of V. cholerae was also possible using primer sets based on putative flagellin sequence. Importantly, simultaneous total and species-specific Vibrio detection was possible using all two primer sets in a multiplexed PCR strategy. Thus, the PCR method we have developed is applicable to both simultaneous and two-step detection of total and specific Vibrio species. 相似文献
67.
Hwang S. H. Lim J. W. Lee W.-J. Kim G. W. Cho C. H. An J. B. Jung K. Y. Cha K. S. Rho B. S. 《Photonics Technology Letters, IEEE》2010,22(3):167-169
68.
69.
In this paper, we will show our latest results on high-efficiency blue phosphorescent organic light-emitting diodes (PHOLEDs). Effects of triplet exciton confinement, exciton energy transfer and charge trapping, and charge balance on iridium(III)bis [(4,6-di-fluorophenyl)-pyridinato-N,C2'] picolinate (FIrpic)-based blue PHOLEDs will be presented. By optimizing the aforementioned device parameters, a high-efficiency blue PHOLED with 59 cd/A (48 lm/W at 100 cd/m2) was demonstrated. 相似文献
70.
Keunho Kim Jin Kun Cha Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(29):5334-5336
A stereoselective synthesis of cyathin A3 and cyathin B2 has been achieved by a Prins‐type reaction of a cycloalkenyl cyclopropanol. Particularly noteworthy is the use of a spirocyclobutanone moiety as a convenient scaffold for an efficient ring‐closing metathesis to stereoselectively construct a suitably functionalized seven‐membered ring (see scheme).