全文获取类型
收费全文 | 397579篇 |
免费 | 4607篇 |
国内免费 | 1421篇 |
专业分类
化学 | 217973篇 |
晶体学 | 4979篇 |
力学 | 16593篇 |
综合类 | 6篇 |
数学 | 43363篇 |
物理学 | 120693篇 |
出版年
2019年 | 2987篇 |
2018年 | 3519篇 |
2017年 | 3403篇 |
2016年 | 5670篇 |
2015年 | 3988篇 |
2014年 | 5871篇 |
2013年 | 17620篇 |
2012年 | 12321篇 |
2011年 | 15341篇 |
2010年 | 10165篇 |
2009年 | 10075篇 |
2008年 | 13807篇 |
2007年 | 14000篇 |
2006年 | 13042篇 |
2005年 | 12095篇 |
2004年 | 10950篇 |
2003年 | 9771篇 |
2002年 | 9575篇 |
2001年 | 11714篇 |
2000年 | 8841篇 |
1999年 | 7006篇 |
1998年 | 5695篇 |
1997年 | 5738篇 |
1996年 | 5482篇 |
1995年 | 5116篇 |
1994年 | 4896篇 |
1993年 | 4850篇 |
1992年 | 5405篇 |
1991年 | 5229篇 |
1990年 | 5014篇 |
1989年 | 5037篇 |
1988年 | 5047篇 |
1987年 | 4957篇 |
1986年 | 4659篇 |
1985年 | 6465篇 |
1984年 | 6676篇 |
1983年 | 5420篇 |
1982年 | 5913篇 |
1981年 | 5781篇 |
1980年 | 5548篇 |
1979年 | 5774篇 |
1978年 | 6185篇 |
1977年 | 5934篇 |
1976年 | 6063篇 |
1975年 | 5544篇 |
1974年 | 5570篇 |
1973年 | 5890篇 |
1972年 | 3734篇 |
1968年 | 3259篇 |
1967年 | 3219篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
161.
An analysis is made of the conditions of formation and the stability region of static-soliton-type magnetic nonuniformities
in a (001)-crystal plate with combined anisotropy. It is shown that if demagnetizing fields in the plate are taken into account,
static solitons can localize at certain defects for appropriate parameters of the material. The soliton stability region was
found to be bounded by two extreme values of the material parameters, namely, those at which the soliton is unstable against
collapse and at which it expands. It was also found that the soliton stability region differs considerably from that predicted
theoretically in the model disregarding the finite size of the sample and the presence of defects.
Fiz. Tverd. Tela (St. Petersburg) 40, 1498–1502 (August 1998) 相似文献
162.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
163.
The barotropic compressible Navier–Stokes equations in an unbounded domain are studied. We prove the unique existence of the solution (u, p) of the system (1.1) in the Sobolev spaceHk + 3 × Hk + 2provided that the derivatives of the data of the problem are sufficiently small, wherek ≥ 0 is any integer. The proof follows from an analysis of the linearized problem, the solvability of the continuity equation, and the Schauder fixed point theory. Similar smoothness results are obtained for a linearized form of (1.1). 相似文献
164.
165.
P. Seelig A. Dax S. Faber M. Gerlach G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt H. Winter M. Würtz 《Hyperfine Interactions》1998,114(1-4):135-139
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric
and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique
using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics
from an ion beam at relativistic velocities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
166.
R. Plaga 《Foundations of Physics》1997,27(4):559-577
The many-worlds interpretation of quantum mechanics predicts the formation of distinct parallel worlds as a result, of a quantum
mechanical measurement. Communication among these parallel worlds would experimentally rule out alternatives to this interpretation.
A possible procedure for “interworld” exchange of information and energy, using only state of the art quantum optical equipement,
is described. A single ion is isolated from its environment in an ion trap. Then a quantum mechanical measurement with two
discrete outcomes is performed on another system, resulting in the formation of two parallel worlds. Depending on the outcome
of this measurement the ion is excited from only one of the parallel worlds before the ion decoheres through its interaction
with the environment. A detection of this excitation in the other parallel world is direct evidence for the many-worlds interpretation.
This method could have important practical applications in physics and beyond. 相似文献
167.
C. Waldtmann H.-U. Everts B. Bernu C. Lhuillier P. Sindzingre P. Lecheminant L. Pierre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):501-507
We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagomé lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis
of Néel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather
unusual. The magnetic () excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic () excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless
continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these
states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg
antiferromagnet on the kagomé lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably
they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
Received: 27 November 1997 / Accepted: 29 January 1998 相似文献
168.
Highly sensitive optical reflectivity measurements are used to investigate the layer-by-layer transition in extremely thin
and thick N-(4-n-hexyloxybenzylidene)-4-n-hexylaniline (6O.6) films. The simple power-law form, N=N
0
t
−1/3, for the penetration of the crystal-B order is found to describe the transitions only near the surface. A deviation from
the power law is observed for the interior layers.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 266–269 (25 February 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
169.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
170.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献