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71.
72.
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
73.
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
74.
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
75.
76.
Michael A. Nettleton 《Shock Waves》2000,10(1):9-22
Since much of the early work on the concepts on which ram accelerators are based dates back to the 1960s, although many of
these are still being actively pursued, it is difficult to formulate a completely logical approach. This situation is compounded
by the use of presently unacceptable treatments of unidimensional detonations in the early work and unfortunately extended
to some of the more modern treatments. My approach has been to start by dealing with the early work and recent work impinging
upon it, then to re-emphasise recent work on detonations, particularly that dealing with the influence of changes in confinement
on quenching and re-initiation of detonations. However, some knowledge of this is inferred in suggestions made in Part 2 for
possible improvements in the techniques. Latter sections cover the development of the ram accelerator, the use of various
types of projectiles, developments in experimental techniques and finally on areas in space flight where the results from
ram accelerators might be utilised.
Received 14 January 1999 / Accepted 16 June 1999 相似文献
77.
垂直磁各向异性稀土-铁-石榴石纳米薄膜在自旋电子学中具有重要应用前景.本文使用溅射方法在(111)取向掺杂钇钪的钆镓石榴石(Gd0.63Y2.37Sc2Ga3O12,GYSGG)单晶衬底上外延生长了2—100 nm厚的钬铁石榴石(Ho3Fe5O12,HoIG)薄膜,并进一步在HoIG上沉积了3 nm Pt薄膜.测量了室温下HoIG的磁各向异性和HoIG/Pt异质结构的自旋相关输运性质.结果显示,厚度薄至2 nm的HoIG薄膜(小于2个单胞层)在室温仍具有铁磁性,且由于外延应变,2—60 nm厚HoIG薄膜都具有很强的垂直磁各向异性,有效垂直各向异性场最大达350 mT;异质结构样品表现出非常可观的反常霍尔效应和“自旋霍尔/各向异性”磁电阻效应,前者在HoIG厚度小于4 nm时开始缓慢下降,而后者当HoIG厚度小于7 nm时急剧减小,说明相较于反常霍尔效应,磁电阻效应对HoIG的体磁性相对更加敏感;此外,自旋相关热电压随HoIG厚度减薄在整个厚度范围以指数方式下降,说明遵从热激化磁振子运动规律的自旋塞贝克效应是其主要贡献者.本文结果表明HoIG纳米薄膜具有可调控的垂直磁各向异性,厚度大于4 nm的HoIG/Pt异质结构具有高效的自旋界面交换作用,是自旋电子学应用发展的一个重要候选材料. 相似文献
78.
In this article, analysis is presented to study the effect of Hall current on the rotating flow of a non-Newtonian fluid in
a porous medium taking into consideration the modified Darcy's law. The Oldroyd-B fluid model is used to characterize the
non-Newtonian fluid behavior. The governing equations for unsteady rotating flow have been modeled in a porous medium. The
analysis includes the flows induced by general periodic oscillations and elliptic harmonic oscillations of a plate. The effect
of the various emerging parameters is discussed on the velocity distribution. The analytical results are confirmed mathematically
by giving comparison with previous studies in the literature. It is observed that the velocity distribution increases with
an increase of Hall parameter. The behavior of permeability is similar to that of the Hall parameter. 相似文献
79.
An exact solution of an oscillatory flow is constructed in a rotating fluid under the influence of an uniform transverse magnetic field. The fluid is considered as second-grade (non-Newtonian). The influence of Hall currents and material parameters of the second-grade fluid is investigated. The hydromagnetic flow is generated in the uniformly rotating fluid bounded between two rigid non-conducting parallel plates by small amplitude oscillations of the upper plate. The exact solutions of the steady and unsteady velocity fields are constructed. It is found that the steady solution depends on the Hall parameter but is independent of the material parameter of the fluid. The unsteady part of the solution depends upon both (Hall and material) parameters. Attention is focused upon the physical nature of the solution, and the structure of the various kinds of boundary layers is examined. Several results of physical interest have been deduced in limiting cases. 相似文献
80.
Zdeněk Trávníček Prof. Dr. Richard Pastorek Pavel Štarha Igor Popa Václav Slovák 《无机化学与普通化学杂志》2010,636(8):1557-1564
The nickel(II) N‐benzyl‐N‐methyldithiocarbamato (BzMedtc) complexes [Ni(BzMedtc)(PPh3)Cl] ( 1 ), [Ni(BzMedtc)(PPh3)Br] ( 2 ), [Ni(BzMedtc)(PPh3)I] ( 3 ), and [Ni(BzMedtc)(PPh3)(NCS)] ( 4 ) were synthesized using the reaction of [Ni(BzMedtc)2] and [NiX2(PPh3)2] (X = Cl, Br, I and NCS). Subsequently, complex 1 was used for the preparation of [Ni(BzMedtc)(PPh3)2]ClO4 ( 5 ), [Ni(BzMedtc)(PPh3)2]BPh4 ( 6 ), and [Ni(BzMedtc)(PPh3)2]PF6 ( 7 ). The obtained complexes 1 – 7 were characterized by elemental analysis, thermal analysis and spectroscopic methods (IR, UV/Vis, 31P{1H} NMR). The results of the magnetochemical and molar conductivity measurements proved the complexes as diamagnetic non‐electrolytes ( 1 – 4 ) or 1:1 electrolytes ( 5 – 7 ). The molecular structures of 4 and 5· H2O were determined by a single‐crystal X‐ray analysis. In all cases, the NiII atom is tetracoordinated in a distorted square‐planar arrangement with the S2PX, and S2P2 donor set, respectively. The catalytic influence of selected complexes 1 , 3 , 5 , and 6 on graphite oxidation was studied. The results clearly indicated that the presence of the products of thermal degradation processes of the mentioned complexes has impact on the course of graphite oxidation. A decrease in the oxidation start temperatures by about 60–100 °C was observed in the cases of all the tested complexes in comparison with pure graphite. 相似文献