全文获取类型
收费全文 | 165篇 |
免费 | 27篇 |
国内免费 | 27篇 |
专业分类
化学 | 56篇 |
晶体学 | 1篇 |
力学 | 6篇 |
综合类 | 4篇 |
数学 | 25篇 |
物理学 | 70篇 |
无线电 | 57篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 23篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 7篇 |
2006年 | 18篇 |
2005年 | 5篇 |
2004年 | 16篇 |
2003年 | 10篇 |
2002年 | 23篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有219条查询结果,搜索用时 15 毫秒
1.
After the remarkable increase of Internet users and broadband Internet subscribers at the end of the 20th century, the size of Korean Internet and e-commerce market steadily increased but the growth rate has been either stagnant or decreased. Trends of Korean Internet and e-commerce market are summarized in this paper the trends on Internet usage are introduced. Trends of online games, blogs and wireless Internet are introduced. The trends of Korean Internet market may have implications for China and Japan. 相似文献
2.
S.K. HAY.H. KIM 《Journal of sound and vibration》2002,253(5):1001-1014
Impedance and admittance matrices are presented for the analysis of the beam-type piezoelectric multimorph (PM). Each piezoelectric layer is polarized in the thickness direction. The stacking sequence can be arbitrary, and both the extensional and flexural motions are considered. The variational principle is used for deriving the lumped conjugate parameters: two mechanical ports for the extensional motion, four mechanical ports for the flexural motion, and m electrical ports for the m piezoelectric layers. The resonance and antiresonance frequencies are then easily calculated from the admittance matrices. For the case of all the piezoelectric layers either in series or parallel connection, them +6 ports reduce to the seven ports, and its impedance and admittance matrices are presented. The present methods are applied to the cantilevered PM and their electromechanical behavior is studied. The tip trajectory of the cantilevered piezomotor is also investigated using the presented matrices. It is found that the present methods are very effective in analyzing the multilayer piezoelectric transducers. 相似文献
3.
The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the upper critical magnetic field Hc3 at which superconductivity can nucleate is estimated. In addition, the authors locate the concentration of the order parameter, which depends on the inhomogeneous term a(x). Unlikely to the homogeneous case, the order parameter may concentrate in the interior of the superconducting material, due to the influence of the inhomogeneous term a(x). 相似文献
4.
EFFECT OF FORESTLAND AVAILABILITY BY OWNERSHIP TYPE ON LICENSE SALES FOR HUNTING: A SPATIAL APPROACH
SEONG‐HOON CHO J.M. BOWKER ROLAND K. ROBERTS SEUNG GYU KIM DAYTON M. LAMBERT NEELAM C. POUDYAL 《Natural Resource Modeling》2012,25(4):549-573
Abstract The effect of forestland availability under different ownership types on license sales for hunting in nine Southeastern states is empirically evaluated. An equation that represents license sales for hunting is estimated assuming the sale of hunting licenses in a particular county is related to the characteristics of that county as well as the characteristics and license sales for hunting in its neighboring counties. The positive effects of the amounts of both national and private forestland on license sales reaffirm the potential benefits of maintaining forestland to stimulate hunting. The positive spillover effect of national forests on license sales for hunting suggests that availability and close access to hunting in national forests within neighboring counties are important in supporting hunting license sales in a county. This study contributes to the general understanding of the drivers affecting individuals’ decisions to use natural resources for hunting. Advances in natural resource modeling, specifically the spatial process model and geospatial data used in this research, make it possible to examine the interactions between the spatial dynamics and ownership attributes of the natural system, allowing policy makers to design natural resource management practices that respond to a system characterized by these interactions. 相似文献
5.
Gakhyun Kim Dr. Ranjan Dutta Dr. Won-Young Cha Dr. Seong-Jin Hong Dr. Juwon Oh Dr. Dikhi Firmansyah Hongil Jo Prof. Dr. Kang Min Ok Prof. Dr. Chang-Hee Lee Prof. Dr. Dongho Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16434-16440
π–π Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of π–π stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar β,β’-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24π-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed π–π interactions between the two subunits. 相似文献
6.
This work demonstrates high-performance and current crowding-free InGaN/GaN light-emitting diodes (LEDs) using an electrically-reverse-connected Schottky diode (SD) and an Mg-delta (δ) doped layer.Poss... 相似文献
7.
Xinglong Chen Hongil Jo Kang Min Ok 《Angewandte Chemie (International ed. in English)》2020,59(19):7514-7520
To design high‐performance mid‐infrared (mid‐IR) nonlinear optical (NLO) materials, we have focused on the combination of a heavy metal lone pair cation, Pb2+ and mixed oxyhalides. A systematic investigation in PbO‐PbCl2‐PbBr2 system led us to discover the first examples of NLO lead mixed oxyhalides, namely, Pb13O6Cl4Br10, Pb13O6Cl7Br7, and Pb13O6Cl9Br5. All the reported materials have remarkably comprehensive properties including broad IR transparency (up to 14.0 μm), qualified second harmonic generation (SHG) responses (0.6–0.9×AgGaS2), wide band gaps (3.05–3.21 eV), and ease of crystal growth. Interestingly, a centimeter‐sized single crystal (2.9×1.3×0.5 cm3) of Pb13O6Cl9Br5 revealing a wide transparent range (0.384–14.0 μm) and high laser damage threshold (LDT) (14.6×AgGaS2) has been successfully grown in an open system. The study suggests that all the reported mixed oxyhalides are outstanding candidates for mid‐IR NLO materials. 相似文献
8.
9.
Influence of Excitation Pulse Width on the Second-Order Correlation Functions of the Exciton-Biexciton Emissions
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate theoretically the population dynamics and the second-order correlation functions of photon emissions from the biexciton-exciton system of a single quantum dot with excitation from pulses to continuous wave. The dynamic equations of the correlation functions are deduced by applying quantum regression theorem to optical Bloch equations. The influences of excitation pulse width on the correlation function have been discussed in detail. 相似文献
10.
The influence of γ′ precipitate on the acoustic nonlinearity is investigated for a nickel-based superalloy, which is subjected to creep deformation. During creep deformation, the cuboidal γ′ precipitate is preferentially coarsened in a direction perpendicular to the applied stress axis. The length and shape factor of the γ′ precipitate increase with creep time. The increase of relative acoustic nonlinearity with increasing fraction of creep life is discussed in relation to the rafting of γ′ precipitate, which is closely related to the scattering and distortion of the acoustic wave 相似文献