全文获取类型
收费全文 | 3210篇 |
免费 | 149篇 |
国内免费 | 17篇 |
专业分类
化学 | 1643篇 |
晶体学 | 48篇 |
力学 | 48篇 |
数学 | 273篇 |
物理学 | 668篇 |
无线电 | 696篇 |
出版年
2023年 | 27篇 |
2022年 | 33篇 |
2021年 | 54篇 |
2020年 | 61篇 |
2019年 | 60篇 |
2018年 | 69篇 |
2017年 | 58篇 |
2016年 | 107篇 |
2015年 | 81篇 |
2014年 | 89篇 |
2013年 | 200篇 |
2012年 | 190篇 |
2011年 | 226篇 |
2010年 | 115篇 |
2009年 | 137篇 |
2008年 | 183篇 |
2007年 | 183篇 |
2006年 | 152篇 |
2005年 | 113篇 |
2004年 | 126篇 |
2003年 | 117篇 |
2002年 | 98篇 |
2001年 | 81篇 |
2000年 | 68篇 |
1999年 | 51篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 37篇 |
1995年 | 33篇 |
1994年 | 37篇 |
1993年 | 35篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 28篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1975年 | 19篇 |
1974年 | 13篇 |
排序方式: 共有3376条查询结果,搜索用时 9 毫秒
991.
Min-Seung Yoon Min-Ku Ko Oh-Han Kim Young-Bae Park William D. Nix Young-Chang Joo 《Journal of Electronic Materials》2007,36(5):562-567
The real-time microstructural evolution during electromigration of eutectic SnPb solder lines with an edge drift structure
was examined using an in-situ scanning electron microscope (SEM) technique. The test temperature and the current density were
either 100°C or 50°C and 6 × 104 A/cm2 or 8 × 104 A/cm2, respectively. In-situ microstructural observation of the depleted phases and quantitative analysis of the number of hillock
phases made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb at room temperature, respectively,
while both dominant migrating element and dominant hillock phase were Pb at 100°C. Such temperature dependence of the dominant
hillock phase in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions.
We suggest that at high temperature, it is easier for Pb atoms to be injected into the Pb phase (Pb-phase hillocks); while
at low temperature, Pb-phase hillocks were squeezed by Sn, which penetrated the Pb phase. 相似文献
992.
Su Houng Lee Shigehiro Yasui Wei Liu Che Ming Ko 《The European Physical Journal C - Particles and Fields》2008,54(2):259-265
Based on the color–spin interaction in diquarks, we argue that charmed multiquark hadrons are likely to exist. Because of
the appreciable number of charm quarks produced in central nucleus–nucleus collisions at ultrarelativistic energies, the production
of charmed multiquark hadrons is expected to be enhanced in these collisions. Using both the quark coalescence model and the
statistical hadronization model, we estimate the yield of charmed tetraquark mesons, Tcc, and pentaquark baryons, Θcs, in heavy ion collisions at RHIC and LHC. We further discuss the decay modes of these charmed exotic hadrons in order to
facilitate their detections in experiments.
PACS 25.75.Dw; 14.20.Lq; 14.40.Lb 相似文献
993.
An experimental investigation was made of the flow over a grooved circular cylinder of different aspect ratios. Based on the drag coefficient, Strouhal number and mean shear stress, three flow regimes of subcritical, critical and supercritical were found, all of which are below the subcritical Reynolds number of a smooth cylinder. Boundary layer characteristics within the different flow regimes were measured. The shift of the boundary layer away from the grooves and an estimated change in the virtual origin are used to establish the similarity of the flow characteristics of grooved and smooth cylinders.Now at Development and Planning Division, Hong Kong Electric Co. Ltd., Hong Kong 相似文献
994.
Sammy Chan Moshe Zukerman Eric W. M. Wong K. T. Ko Edmund Yeung Bartek Wydrowski 《International Journal of Communication Systems》2002,15(4):341-357
Fair packet discarding (FPD) is a mechanism which provides incentives to users to co‐operate in congestion control, so that ATM networks can operate more efficiently. In this paper, we propose a simple congestion control framework consisting of a combination of FPD and ATM Forum's explicit‐rate flow control scheme. We show by simulations that this frame‐work achieves all objectives of congestion control: (1) control congestion, (2) achieve high user‐perceived throughput, (3) maintain fairness and (4) provide protection from misbehaving users. In addition, we equip this framework with two enhancements to improve efficiency, and reduce end‐to‐end delay. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
995.
L. Kronik R. Fromherz E. Ko G. Ganteför J. R. Chelikowsky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):33-36
We compare experimentally measured and
ab initio computed
photoelectron spectra of negatively charged deuterated silicon
clusters (
, 4m10, 0n2) produced in a plasma environment.
Based on this comparison, we discuss the kinetics and
thermodynamics of the cluster formation and the effect of
deuterium on the geometrical and electronic structure of the
clusters. 相似文献
996.
Coalescence of minijet partons with partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum. The resulting enhanced antiproton and pion yields at intermediate transverse momenta give a plausible explanation for the observed large antiproton to pion ratio. With further increasing momentum, the ratio is predicted to decrease and approach the small value given by independent fragmentations of minijet partons after their energy loss in the quark-gluon plasma. 相似文献
997.
Optical coherence microscopy (OCM) is demonstrated with a high-speed, broadband, reflective-grating phase modulator and a femtosecond Ti:Al2O3 laser. The novel system design permits high-resolution OCM imaging in a new operating regime in which a short coherence gate is used to relax the requirement for high-numerical-aperture confocal axial sectioning. In vivo cellular imaging is demonstrated in the Xenopus laevis tadpole and in human skin with a 3-microm coherence gate and a 30-microm confocal gate. The ability to achieve cellular imaging with a lower numerical aperture should facilitate the development of miniaturized probes for in vivo imaging applications. 相似文献
998.
Ciprian?FoiasEmail author Il?Bong?Jung Eungil?Ko Carl?Pearcy 《Israel Journal of Mathematics》2005,145(1):83-91
We consider the question of which operators on Hilbert space admit a moment sequence, and show, in particular, that ifT is any operator inL(itH) that can be written asT=N+K, whereN is normal andK is compact, andM⊂itH is any invariant subspace forT, then the restrictionT/itM admits such a sequence. 相似文献
999.
Chui HC Shaw SY Ko MS Liu YW Shy JT Lin T Cheng WY Roussev RV Fejer MM 《Optics letters》2005,30(6):646-648
The iodine molecule has frequently been used as a frequency reference from the green to the near-infrared wavelength region (500-900 nm). We describe the frequency locking of the second-harmonic signal of a 197.2-THz (1520.25-nm) distributed-feedback diode laser to the absorption lines of the iodine hyperfine structure; a frequency jitter below 0.1 MHz was achieved at a 300-ms time constant. This scheme provides a simple, compact, and high-performance frequency reference in the optical communication band. 相似文献
1000.
One-dimensional colloidal metal oxide nanocrystals are of great importance in materials chemistry, but reports on these materials are rare due to lack of well-defined synthetic protocols. In this paper, we present a general and highly effective one-pot synthetic protocol to produce 1-dimensional nanostructures of transition metal oxide (e.g., W(18)O(49), TiO(2), Mn(3)O(4), and V(2)O(5)) through thermally induced crystal growth processes from a mixture of metal chloride and surfactants. 相似文献