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51.
采用多晶LaB6材料制成平板二极管阴极,阳极采用钼材料,阴极采用热传导与热辐射加热,加热体为石墨。实验研究了不同阴极温度、不同真空度下的脉冲发射特性,并对热发射稳定性进行了分析。结果表明: 在动态真空系统中, 阴极发射面积为0.012 1 cm2, 工作真空度为2×10-4 Pa, 阴极温度分别为1 600, 1 650和1 700 ℃,在脉冲宽度为40 ms、重复频率为107 Hz的条件下,最大脉冲发射电流密度分别为34.0,44.0和53.8 A/cm2; 2×10-4,5×10-4和2×10-3 Pa压强下的发射能力没有明显的差异;脉冲宽度的变化不影响发射电流密度的变化。 相似文献
52.
J. Adam K. Katovsky A. Balabekyan V. G. Kalinnikov M. I. Krivopustov H. Kumawat A. A. Solnyshkin V. I. Stegailov S. G. Stetsenko V. M. Tsoupko-Sitnikov W. Westmeier 《Pramana》2007,68(2):201-212
Target-blanket facility ‘Energy + Transmutation’ was irradiated by proton beam extracted from the Nuclotron Accelerator in
Laboratory of High Energies of Joint Institute for Nuclear Research in Dubna, Russia. Neutrons generated by the spallation
reactions of 0.7, 1.0, 1.5 and 2 GeV protons and lead target interact with subcritical uranium blanket. In the neutron field
outside the blanket, radioactive iodine, neptunium, plutonium and americium samples were irradiated and transmutation reaction
yields (residual nuclei production yields) have been determined using γ-spectroscopy. Neutron field's energy distribution
has also been studied using a set of threshold detectors. Results of transmutation studies of 129I, 237Np, 238Pu, 239Pu and 241Am are presented.
相似文献
53.
V. Wagner A. Krása M. Majerle F. Křížek O. Svoboda A. Kugler J. Adam V. M. Tsoupko-Sitnikov M. I. Krivopustov I. V. Zhuk W. Westmeier 《Pramana》2007,68(2):297-306
The set-up ‘energy plus transmutation’, consisting of a thick lead target and a natural uranium blanket, was irradiated by
relativistic proton beams with the energy from 0.7 GeV up to 2 GeV. Neutron field was measured in different places of this
set-up using different activation detectors. The possibilities of using the obtained data for benchmark studies are analyzed
in this paper. Uncertainties of experimental data are shown and discussed. The experimental data are compared with results
of simulation with MCNPX code.
相似文献
54.
J. Blomgren 《Pramana》2007,68(2):269-278
One of the outstanding new developments in the field of partitioning and transmutation (P&T) concerns accelerator-driven systems
(ADS) which consist of a combination of a high-power, high-energy accelerator, a spallation target for neutron production
and a sub-critical reactor core. The development of the commercial critical reactors of today motivated a large effort on
nuclear data up to about 20 MeV, and presently several million data points can be found in various data libraries. At higher
energies, data are scarce or even non-existent. With the development of nuclear techniques based on neutrons at higher energies,
nowadays there is a need also for higher-energy nuclear data. To provide alternative to this lack of data, a wide program
on neutron-induced data related to ADS for P&T is running at the 20–180 MeV neutron beam facility at ‘The Svedberg Laboratory’
(TSL), Uppsala. The programme encompasses studies of elastic scattering, inelastic neutron production, i.e., (n, xn′) reactions, light-ion production, fission and production of heavy residues. Recent results are presented and future program
of development is outlined.
相似文献
55.
Gun Sang Jeon Chia-Chen Chang Jainendra K. Jain 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):271-282
We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model
of composite fermions is unsatisfactory for the qualitative physics at high angular momenta.
Extensive numerical calculations demonstrate that the microscopic CF theory,
which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account
of the quantum dot ground state down to the largest angular momenta studied,
and allows systematic improvements by inclusion of mixing between composite
fermion Landau levels (called Λ levels). 相似文献
56.
Roland Wittje 《Physics in Perspective (PIP)》2007,9(4):406-433
In the late 1940s and the 1950s, Norwegian nuclear scientists, engineers, and administrators were deeply split over their
nation’s goals, organization, politics, and tools for research in nuclear physics. One faction was determined to build a nuclear
reactor in Norway, while another fiercely opposed the reactor plans and focused on particle accelerators. The first faction
comprised scientific entrepreneurs and research technologists, the second academic scientists, most of whom began their research
careers in nuclear physics in the 1930s. To understand this conflict, I trace the development of nuclear research in Norway
from the early 1930s to the mid-1950s, placing it within an international context.
Roland Wittje is working on his habilitation thesis in the History of Science Unit at the University of Regensburg, Germany. 相似文献
57.
58.
An experimental investigation has been undertaken to improve understanding of the role of the obturator and detonations in
the subdetonative ram accelerator starting process. Ram accelerator start experiments were conducted with various obturator
geometries to determine the obturator dynamics and assess its effect on the outcome of a start attempt. The obturator rapidly
decelerates upon entrance and then moves backwards. Reversal of direction occurs more rapidly after propellant ignition, for
less massive obturators, and solid geometries. Perforated geometries and decreasing obturator mass are less conducive to igniting
a given propellant, as evidenced by the flowfield and start attempt outcome data presented. Wave unstarts were observed to
occur with and without detonations, indicating more than one mechanism responsible for this type of start failure. Piston-initiated
detonation experiments were conducted by firing the obturators without the ram accelerator projectile. The piston experiments
identified the detonation limits for a wide range of propellants, but were found to not always be indicative of the upper
Mach number at which a ram accelerator can be successfully started. In some instances a successful start or wave fall-off
would occur at Mach numbers above which a piston alone detonated the propellant. Thus, the projectile can play a mitigating
role in detonation initiation and use of piston detonation limits to quantitatively define a detonation wave unstart limit
was not realized.
Received 6 April 1998 / Accepted 15 January 1999 相似文献
59.
The excitation spectra in the wavelength range of 19—40 nm for highly ionized sulphur ions were measured by using the beam-foil
method at the Heavy lon Research Facility in Lanzhou. In this experiment, more than 30 spectral lines were observed, which
belonged to the transitions of the excitation energy levels for highly ionized SX—SXV ions, and 5 new lines were determined.
The experimental results were compared with those from other experiments and theoretical calculations. 相似文献
60.
Milica V. Milovanovi Efrat Shimshoni 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We study bulk and edge correlations in the compressible half-filled state, using a modified version of the plasma analogy. The corresponding plasma has anomalously weak screening properties, and as a consequence we find that the correlations along the edge do not decay algebraically as in the Laughlin (incompressible) case, while the bulk correlations decay in the same way. The results suggest that due to the strong coupling between charged modes on the edge and the neutral fermions in the bulk, reflected by the weak screening in the plasma analogue, the (attractive) correlation hole is not well defined on the edge. Hence, the system there can be modeled as a free Fermi gas of electrons. We finally comment on a possible scenario, in which the Laughlin-like dynamical edge correlations may nevertheless be realized. 相似文献