全文获取类型
收费全文 | 5465篇 |
免费 | 161篇 |
国内免费 | 12篇 |
专业分类
化学 | 3838篇 |
晶体学 | 73篇 |
力学 | 121篇 |
数学 | 407篇 |
物理学 | 1199篇 |
出版年
2023年 | 49篇 |
2022年 | 59篇 |
2021年 | 77篇 |
2020年 | 92篇 |
2019年 | 101篇 |
2016年 | 119篇 |
2015年 | 116篇 |
2014年 | 128篇 |
2013年 | 217篇 |
2012年 | 173篇 |
2011年 | 240篇 |
2010年 | 147篇 |
2009年 | 133篇 |
2008年 | 192篇 |
2007年 | 171篇 |
2006年 | 182篇 |
2005年 | 154篇 |
2004年 | 134篇 |
2003年 | 120篇 |
2002年 | 111篇 |
2001年 | 92篇 |
2000年 | 86篇 |
1999年 | 82篇 |
1998年 | 62篇 |
1997年 | 71篇 |
1996年 | 82篇 |
1995年 | 91篇 |
1994年 | 80篇 |
1993年 | 108篇 |
1992年 | 67篇 |
1991年 | 64篇 |
1990年 | 61篇 |
1989年 | 70篇 |
1988年 | 48篇 |
1987年 | 66篇 |
1986年 | 62篇 |
1985年 | 66篇 |
1984年 | 63篇 |
1983年 | 51篇 |
1982年 | 59篇 |
1981年 | 68篇 |
1980年 | 73篇 |
1979年 | 52篇 |
1978年 | 66篇 |
1977年 | 54篇 |
1976年 | 77篇 |
1975年 | 73篇 |
1974年 | 58篇 |
1973年 | 71篇 |
1967年 | 45篇 |
排序方式: 共有5638条查询结果,搜索用时 0 毫秒
141.
We consider a one-dimensional charge density wave insulator formed by umklapp processes in a quarter-filled band. The spectrum of the model consists of gapless, uncharged excitations carrying spin +/- 1/2 (spinons) and gapped, spinless excitations carrying charge -/+ signe/2 (solitons and antisolitons). We calculate the low-energy behavior of the single-electron Green's function at zero temperature. The spectral function exhibits a featureless scattering continuum of two solitons and many spinons. The theory predicts that the gap observed by angle resolved photoemission is twice the activation gap in the dc conductivity. We comment on possible applications to PrBa(2)Cu(3)O(7) and to the Bechgaard salts. 相似文献
142.
Zhu Y Moodenbaugh AR Schneider G Davenport JW Vogt T Li Q Gu G Fischer DA Tafto J 《Physical review letters》2002,88(24):247002
We use x-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) to study the fine structure at the K edge of boron in MgB(2). We observe in XAS a peak of width 0.7 eV at the edge threshold, signaling a narrow energy region with empty boron p states near the Fermi level. The changes in the near edge structure observed in EELS with direction of the momentum transfer imply that these states have p(x)p(y) symmetry. Our observations are consistent with electronic structure calculations indicating a narrow energy window of empty p(x)p(y) states that falls to zero at 0.8 eV above the Fermi level. The disappearance of the p(x)p(y) feature in EELS at grain boundaries suggests that this signature may become powerful in probing superconductivity at nanoscale. 相似文献
143.
Richard P. Fischer Arne W. Fliflet 《International Journal of Infrared and Millimeter Waves》2002,23(9):1297-1313
This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements. 相似文献
144.
M. Winkelmann G. Fischer B. Pilawa E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):199-209
Nuclear magnetic resonance (NMR) and relaxation of 63Cu and 65Cu in a powder sample of the heavy-fermion paramagnet CeCu6 is measured and analysed quantitatively. Five different Cu sites are accessible to a detailed analysis. We derive quadrupolar
splitting frequencies, Ce to Cu transferred hyperfine field coupling constants, and transversal as well as longitudinal relaxation
behaviour. Only small relaxation anomalies are observed at the orthorhombic to monoclinic structural phase transition of CeCu6. We point to the different importance of transferred hyperfine interaction and local conduction electron density for static
or dynamic part, respectively, of Cu hyperfine interaction. The different sign of the transferred hyperfine interaction from
Ce3+ to different Cu neighbours reveals the different competing interaction mechanisms, giving rise to the heavy-fermion paramagnetic
behavior of CeCu6.
Received 20 November 2001 相似文献
145.
A model for the interaction of near-infrared laser pulses with metal powders in selective laser sintering 总被引:4,自引:0,他引:4
P. Fischer N. Karapatis V. Romano R. Glardon H.P. Weber 《Applied Physics A: Materials Science & Processing》2002,74(4):467-474
A thermal model of the interaction of pulsed near-infrared laser radiation from a Nd:YAG laser was made, taking the measured
powder properties such as reflectance, optical penetration depth and thermal conductivity into account. It allows an estimation
of the evolution of two different temperatures: the average temperature of the powder (taken over the grains in a volume given
by the laser beam diameter and the optical penetration depth) and the temperature distinction within a single grain. It showed
that in pulsed mode consolidation can be achieved at much lower average power as the surface of the powder particles are molten
but their cores remain at nearly room temperature. This leads to a much lower average temperature and therefore a dramatic
decrease in residual thermal stresses in the finished piece. The results of the model were experimentally tested and confirmed.
Received: 26 July 2001 / Accepted: 23 November 2001 / Published online: 23 January 2002 相似文献
146.
Fischer J Hammerschmidt K Cheney DL Seyfarth RM 《The Journal of the Acoustical Society of America》2002,111(3):1465-1474
The acoustic structure of loud calls ("wahoos") recorded from free-ranging male baboons (Papio cynocephalus ursinus) in the Moremi Game Reserve, Botswana, was examined for differences between and within contexts, using calls given in response to predators (alarm wahoos), during male contests (contest wahoos), and when a male had become separated from the group (contact wahoos). Calls were recorded from adolescent, subadult, and adult males. In addition, male alarm calls were compared with those recorded from females. Despite their superficial acoustic similarity, the analysis revealed a number of significant differences between alarm, contest, and contact wahoos. Contest wahoos are given at a much higher rate, exhibit lower frequency characteristics, have a longer "hoo" duration, and a relatively louder "hoo" portion than alarm wahoos. Contact wahoos are acoustically similar to contest wahoos, but are given at a much lower rate. Both alarm and contest wahoos also exhibit significant differences among individuals. Some of the acoustic features that vary in relation to age and sex presumably reflect differences in body size, whereas others are possibly related to male stamina and endurance. The finding that calls serving markedly different functions constitute variants of the same general call type suggests that the vocal production in nonhuman primates is evolutionarily constrained. 相似文献
147.
A. Krimmel P. Fischer B. Roessli H. Maletta C. Geibel C. Schank A. Grauel A. Loidl F. Steglich 《Zeitschrift für Physik B Condensed Matter》1992,86(2):161-162
An elastic neutron scattering study was performed on the new superconducting heavy fermion systems UPd2Al3 and UNi2Al3. The neutron diffraction patterns reveal unambiguously long range antiferromagnetic order in UPd2Al3 with an ordered magnetic moment
U
= (0.85±0.03)
B
, which coexists with the superconducting state. This is by far the largest
U
value observed for any heavy fermion superconductor. For UNi2Al3, no long-range magnetic order could be observed for temperaturesT1.5 K, yielding an upper limit of the ordered moment of 0.2
B
. 相似文献
148.
149.
Hitherto it has not been possible to produce a microscopic image with adequate resolution of the high-impact two-phase system poly(vinyl chloride) (PVC)/chlorinated polyethylene (CPE) due to inadequate phase contrast. With the aid of various chemical staining methods and through ion etching, a way has been found for studying the microstructure of the PVC/CPE system by light microscopy and electron microscopy. These independent visualization techniques and scanning electron micrographs of fracture surfaces show, as the morphology with optimal mechanical and rheological properties, networklike distribution of the rubber phase and, imbedded in this, a PVC phase consisting of primary particles. 相似文献
150.
A. Michel V. Pierron-Bohnes J.P. Jay P. Panissod S. Lefebvre M. Bessière H.E. Fischer G. Van Tendeloo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):225-239
Epitaxial Co/Mn multilayers (0.75 to 6 nm Co, 0.4 nm Mn layer thickness) have been grown on mica substrates covered by a (0002)
Ru buffer layer. The structural properties of these layers have been studied using X-ray diffraction, nuclear magnetic resonance
(NMR), and high resolution transmission electron microscopy (HRTEM). The Co layers, grown as face centred cubic (fcc), were
found to be stabilised by the very thin Mn layers. Data obtained using X-ray diffraction and NMR were analysed and found to
be in good agreement, while Monte-Carlo simulations were used to interpret the data and calculate the expected diffracted
intensity and NMR spectra. The HRTEM data show that the Mn layers give rise to a large strain contrast extending, in the growth
direction, over a distance which exceeds the thickness of the Mn layers. The superlattices could be described as having an
fcc structure containing randomly located stacking faults with varying densities. The results verify the presence of a dominant,
almost perfect phase of fcc stacking, and of a faulted hcp phase, while the number of defects increases with the Co layer
thickness.
Received 27 October 1999 and Received in final form 29 May 2000 相似文献