全文获取类型
收费全文 | 372篇 |
免费 | 4篇 |
专业分类
化学 | 230篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 30篇 |
物理学 | 108篇 |
出版年
2020年 | 5篇 |
2019年 | 6篇 |
2016年 | 5篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 23篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1970年 | 5篇 |
1969年 | 6篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1965年 | 2篇 |
1959年 | 3篇 |
1939年 | 2篇 |
1932年 | 2篇 |
排序方式: 共有376条查询结果,搜索用时 15 毫秒
31.
Preston S. P.; Jensen O. E.; Richardson G. 《The Quarterly Journal of Mechanics and Applied Mathematics》2008,61(1):1-24
We consider the axisymmetric deformation of an initially spherical,porous vesicle with incompressible membrane having finite resistanceto in-plane shearing, as the vesicle is compressed between parallelplates. We adopt a thin-shell balance-of-forces formulationin which the mechanical properties of the membrane are describedby a single dimensionless parameter, C, which is the ratio ofthe membrane's resistance to shearing to its resistance to bending.This results in a novel free-boundary problem which we solvenumerically to obtain vesicle shapes as a function of plateseparation, h. For small deformations, the vesicle contactseach plate over a small circular area. At a critical value ofplate separation, hTC, there is a transcritical bifurcationfrom which a new branch of solutions emerges, representing buckledvesicles which contact each plate along a circular curve. Forthe values of C investigated, we find that the transcriticalbifurcation is subcritical and that there is a further saddle-nodebifurcation (fold) along the branch of buckled solutions ath = hSN (where hSN > hTC). The resulting bifurcation structureis commensurate with a hysteresis loop in which a sudden transitionfrom an unbuckled solution to a buckled one occurs as h is decreasedthrough hTC and a further sudden transition, this time froma buckled solution to an unbuckled one, occurs as h is increasedthrough hSN. We find that hSN and hTC increase with C, thatis, vesicles that resist shear are more prone to buckling. 相似文献
32.
Song HC Cho S Kang T Hodgkiss WS Preston JR 《The Journal of the Acoustical Society of America》2011,129(3):EL71-EL75
In September 2010 a long-range acoustic communication (LRAC10) experiment was carried out in deep water off the Southern California Coast. The experiment involved two mobile components: (1) a source towed slowly at a speed of 2-3 knots at ~75-m depth and (2) a horizontal line array towed at 3.5 knots at a depth of ~200 m. Phase-coherent communication sequences were transmitted in the frequency band of 200-300 Hz at various ranges (100-700 km). Initial analysis of the LRAC10 data demonstrates that an information rate of 50 bits/s can be achieved over ~550-km range using quadrature-phase shift-keying (QPSK) modulation and error-correction coding combined with beamforming. 相似文献
33.
Argo TF Guild MD Wilson PS Schröter M Radin C Swinney HL 《The Journal of the Acoustical Society of America》2011,129(4):EL101-EL107
Sound propagation in water-saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both the frequency and porosity dependency. To begin to address this deficiency, a fluidized bed technique was used to control the porosity of an artificial sediment composed of glass spheres of 265 μm diameter. Time-of-flight measurements and the Fourier phase technique were utilized to determine the sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to 0.43. A Biot-based model qualitatively describes the porosity dependence. 相似文献
34.
S. Neretina R. A. Hughes G. Stortz J. S. Preston P. Mascher 《Applied Physics A: Materials Science & Processing》2011,102(2):259-264
Cadmium telluride films deposited on amorphous substrates exhibit a grain structure characterized by [111]-oriented grains,
but where the in-plane grain orientation is randomized due to the absence of epitaxy. Here, we explore the viability of promoting
an in-plane grain alignment through graphoepitaxy. Fifteen different substrate surface textures were fabricated using focused
ion beam lithography. This approach allows for the side-by-side deposition of surface textures where both the areal extent
and depth of the surface features are varied in a systematic manner. CdTe films deposited overtop these textures show grain
structures with dramatic variations, revealing that particular length scales have the most pronounced effect on the grain
structure. 相似文献
35.
36.
We report measurements of non-linear charge transport in epitaxial (La1−x
Pr
x
)0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the
highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage
characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven
charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters
dispersed in a CO background. 相似文献
37.
Holland CW Preston JR Abraham DA 《The Journal of the Acoustical Society of America》2007,122(4):1946-1958
Analysis of reverberation measurements in the Straits of Sicily shows high intensity, discrete, scattered returns 10-20 dB above background reverberation. These returns are due to scattering from mud volcanoes. The reverberation from the mud volcanoes at ranges of 15-22 km is reasonably consistent over these spatial scales (i.e., kilometers) and temporal scales of several hours; measurements separated by 4 years are also similar. Statistical characterization indicates that the reverberation associated with a mud-volcano cluster is strongly non-Rayleigh and that the reverberation can be characterized by a single (shape) parameter, roughly independent of frequency. The non-Rayleigh statistics, with a concomitant increase in the probability of false alarm, indicate that mud volcanoes are a likely source of clutter. Mean target strengths were estimated at 1-11 dB over 160-1400 Hz and are consistent with target strengths measured during a different year at short (direct-path) ranges. Accumulated evidence points to small (order 10 m diameter and several meters high) carbonate chimneys on the mud-volcano edifice as the scattering mechanism as opposed to the edifice itself or scattering from gas bubbles in the water column. Thus, the results represent acoustic scattering from mud volcanoes in a quiescent state. 相似文献
38.
In this work we apply infinitesimal variational calculus to the systems of balance equations. We determine a class of the exterior -forms Θ on the jet bundle of infinite order over a configurational bundle similar to the class of Lepage n-forms. Systems of differential equations obtained in the way similar to one used in the Lagrangian field theory, include the Euler–Lagrange equations corresponding to a Lagrangian functions as well as arbitrary regular systems of balance equations. For a balance system with a symmetry group G we present the Noether balance laws corresponding to the generators of the Lie algebra of the group G. 相似文献
39.
Zhang X Mohandessi S Miller LW Snee PT 《Chemical communications (Cambridge, England)》2011,47(12):3532-3534
Small molecular reagents that can efficiently functionalize water soluble CdSe/ZnS nanocrystals (NCs) are reported. These reagents do not cause quenching or precipitation of NCs as seen with commercially available activators. The results demonstrate that controlling the electrostatic character of the materials is critical in the design of functionalization schemes. 相似文献
40.