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961.
A continuous surface stretched with velocity u
w=u
w (x) and having the temperature distribution T
w=T
w (x) interacts with the viscous fluid in which it is immersed both mechanically and thermally. The thermal interaction is characterized by the surface heat flux q
w=q
w (x) and the mechanical one by the skin friction τ w=τ w (x). In the whole previous theoretical research concerned with such processes, either (u
w and T
w) or (u
w and q
w) have been prescribed as known boundary conditions. The goal of the present paper is to initiate the investigation of the boundary layer flows induced by stretching processes for which either (τ w and T
w ) or (τ w and q
w) are the prescribed quantities. The case of an isothermal surface stretched with constant skin friction, (τ w=const., T
w=const. ≠ T
∞) is worked out in detail. The corresponding flow and heat transfer characteristics are compared to those obtained for the (well known) case of a uniformly moving isothermal surface (u
w=const., T
w=const. ≠ T
∞). 相似文献
962.
963.
The well known steady free convection forward boundary layer (FBL) flows ascending over a heated upwards projecting semi-infinite flat plate embedded in a fluid saturated porous medium are compared in this paper to their less well known backward (BBL) counterparts descending over a cooled (also upwards projecting!) semi-infinite flat plate. The circumstance that the definite edge of the plate (x = 0) in the former case is a leading edge and in the latter one a trailing edge, leads to substantially different mathematical and physical features of the FBL and BBL flows, respectively. The paper considers under this aspect the case of similar flows corresponding to surface temperature distributions which are power-law functions of the distance x from the definite edge. For permeable plates the effect of an adequate lateral suction and injection of the fluid is also taken into account. The detailed investigation, however, is restricted to the particular values m = +1 and m = –1/3 of the power-law exponent m, where both FBL and BBL solutions are available in exact analytic form. For each of these values, both exponentially and algebraically decaying BBL solutions were found. In addition, the existence of an exact algebraic BBL solution valid for any value of m is reported. 相似文献
964.
E. Popova H. Ndilimabaka B. Warot-Fonrose M. Bibes N. Keller B. Berini F. Jomard K. Bouzehouane Y. Dumont 《Applied Physics A: Materials Science & Processing》2008,93(3):669-674
The understanding and control of the ilmenite–hematite solid solutions (Fe2−x
Ti
x
O3±δ
or IH) thin film structure and properties are crucial for spintronics applications. Good quality films of Fe2−x
Ti
x
O3±δ
on Al2O3(0001) substrates were obtained by pulsed laser deposition. For the studied compositions (x=1, 0.7, 0.5) in a wide oxygen pressure range all the films were epitaxial, with flat interfaces, and without secondary phases.
Unconventional lattice strain relaxation with the increase of in-plane lattice parameter above its relaxed bulk value was
observed for different film compositions, oxygen pressures, substrate temperatures, and film growth rates. This phenomenon
is most likely explained by the buckling of a few first film monolayers because of a significant compressive stress induced
on the film by the sapphire substrate. The IH thin films with x=0.7 and 0.5 exhibited the properties of a room temperature magnetic semiconductor. The resistivity changed over three orders
of magnitude in the studied pressure range, thus clearly demonstrating the important role of oxygen stoichiometry in the creation
of carriers. 相似文献
965.
Dunkelman Orr Eichlseder Maria Kales Daniel Keller Nathan Leurent Gatan Schofnegger Markus 《Designs, Codes and Cryptography》2022,90(4):983-1007
Designs, Codes and Cryptography - FlexAEAD is a block cipher candidate submitted to the NIST Lightweight Cryptography standardization project, based on repeated application of an... 相似文献
966.
Harry F. Keller 《Fresenius' Journal of Analytical Chemistry》1890,29(1):71-73
Ohne Zusammenfassung 相似文献
967.
R. Paschotta J. Aus der Au G.J. Spühler S. Erhard A. Giesen U. Keller 《Applied physics. B, Lasers and optics》2001,72(3):267-278
We recently demonstrated that passive mode locking of a thin-disk Yb:YAG laser is possible and that this concept leads to
sources of femtosecond pulses with very high average power. Here we discuss in detail the effect of spatial hole burning on
the mode-locking behavior of such lasers. We have developed an efficient numerical model and arrive at quantitative stability
criteria which agree well with experimental data. The main result is that stable soliton mode locking can in general be obtained
only in a certain range of pulse durations. We use our model to investigate the influence of various cavity parameters and
the situation for different gain media. We also consider several methods to reduce the effect of spatial hole burning in order
to expand the range of possible pulse durations.
Received: 4 September 2000 / Published online: 10 January 2001 相似文献
968.
M. W. Keller 《The European physical journal. Special topics》2009,172(1):297-309
This review covers various aspects of the single-electron tunneling pumps based on Al junctions studied at NIST over the past
15 years. The operation of a pump is described, and some important error mechanisms are summarized, which allows for a sketch
of the basic pump parameters required for metrological accuracy. Fabrication of pumps, filtering of leads in the cryostat,
and the electronics used to drive the pump are described next. The shuttle error technique that allows measurement of very
rare errors is then described, and some outstanding questions about limitations of pumps based on Al junctions are mentioned.
A detailed algorithm for cancelling the cross capacitance in a pump is described in an appendix.
Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. 相似文献
969.
É. Maréchal S. Guibal J.-L. Bossennec M.-P. Gorza R. Barbé J.-C. Keller O. Gorceix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):195-198
The mechanical Stern-Gerlach effect is investigated in the case of a slow atomic cloud falling through an inhomogeneous magnetic
field featuring a strong longitudinal gradient. The resulting Zeeman sublevel state selection is demonstrated under various
experimental conditions. Longitudinal spatial separations are in agreement with numerical simulations that take into account
the gravitational acceleration and both the transverse and axial magnetic forces. Since separations greater than 20 cm are
obtained, potential applications in atom optics are outlined.
Received: 16 February 1998 / Received in final form: 1 April 1998 / Accepted: 6 April 1998 相似文献
970.
Monique Brunet Lubor Lej
ek Laurence Navailles Patrick Keller Tinh Huu Nguyen Eric Polossat Emmanuel Rouy 《Liquid crystals》2006,33(9):961-978
In the chiral smectic C phase of liquid crystals with the phase transition N*-SmC*, texture development depending on the sample thickness is reported. In very thin samples, domains of rectangular-like shape are observed. As two possible tilts of smectic layers are possible for one anchoring direction, smectic layers inside a domain, called twin-like domains, are tilted with respect to layers in outer regions, similarly to crystalline planes in solid crystalline twins. An elastic model of such a twin domain is proposed and its energy determined. 相似文献