全文获取类型
收费全文 | 191564篇 |
免费 | 882篇 |
国内免费 | 431篇 |
专业分类
化学 | 81793篇 |
晶体学 | 2758篇 |
力学 | 11640篇 |
综合类 | 18篇 |
数学 | 34737篇 |
物理学 | 61931篇 |
出版年
2021年 | 1033篇 |
2020年 | 1183篇 |
2019年 | 1374篇 |
2018年 | 10480篇 |
2017年 | 11320篇 |
2016年 | 6518篇 |
2015年 | 2066篇 |
2014年 | 2203篇 |
2013年 | 3886篇 |
2012年 | 7656篇 |
2011年 | 16210篇 |
2010年 | 10102篇 |
2009年 | 10239篇 |
2008年 | 14061篇 |
2007年 | 17587篇 |
2006年 | 3365篇 |
2005年 | 9360篇 |
2004年 | 5937篇 |
2003年 | 5942篇 |
2002年 | 4026篇 |
2001年 | 2805篇 |
2000年 | 2252篇 |
1999年 | 1514篇 |
1998年 | 1388篇 |
1997年 | 1250篇 |
1996年 | 1282篇 |
1995年 | 1133篇 |
1994年 | 1074篇 |
1993年 | 1105篇 |
1992年 | 1151篇 |
1991年 | 1232篇 |
1990年 | 1193篇 |
1989年 | 1223篇 |
1988年 | 1099篇 |
1987年 | 1069篇 |
1986年 | 1031篇 |
1985年 | 1205篇 |
1984年 | 1337篇 |
1983年 | 1159篇 |
1982年 | 1176篇 |
1981年 | 1059篇 |
1980年 | 1037篇 |
1979年 | 1151篇 |
1978年 | 1308篇 |
1977年 | 1233篇 |
1976年 | 1249篇 |
1975年 | 1155篇 |
1974年 | 1202篇 |
1973年 | 1223篇 |
1972年 | 942篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
961.
A general framework is developed to treat inverse problems with parameters that are random fields. It involves a sampling
method that exploits the sensitivity derivatives of the control variable with respect to the random parameters. As the sensitivity
derivatives are computed only at the mean values of the relevant parameters, the related extra cost of the present method
is a fraction of the total cost of the Monte Carlo method. The effectiveness of the method is demonstrated on an example problem
governed by the Burgers equation with random viscosity. It is specifically shown that this method is two orders of magnitude
more efficient compared to the conventional Monte Carlo method. In other words, for a given number of samples, the present
method yields two orders of magnitude higher accuracy than its conventional counterpart. 相似文献
962.
An experimental apparatus and related procedures for the determination of the effective thermal conductivity of sintered powder-metal
plates saturated with distilled water at temperatures in the range 20–150°C are discussed. The apparatus and procedures are
applied to two samples of sintered powder-metal plates, one made of nickel 200 and the other of stainless steel 316, with
porosities of 28.10 and 46.45%, respectively, and each of nominal dimensions 127 mm × 127 mm × 6.35 mm. The experimental
results are compared with corresponding predictions yielded by several correlations available in the literature. The correlations
based on experimental data for packed beds of spherical particles and also porous plates made of cold-pressed (but not sintered)
particles of angular shapes do not apply well to sintered powder-metal plates. A new correlation, which is based on extensions
of ideas contained in earlier works and provides improved predictions, is proposed. 相似文献
963.
Hyperfine structure of a hydrogen-like atom due to orbit-orbit,spin-orbit,and spin-spin interactions
A nonrelativistic model of a hydrogen-like atom is considered. This model is used to calculate corrections to the energy spectrum of the atom. The analysis is based on a Hamiltonian that includes the intratomic fields generated by the electron and the nucleus. 相似文献
964.
A. V. Pastukhov V. A. Davankov E. V. Sidorova E. I. Shkol’nikov V. V. Volkov 《Russian Chemical Bulletin》2007,56(3):484-493
An automated procedure was developed for monitoring fast changes in the size of spherical samples of polymers during their
contact with a solvent or drying. The kinetics of bulk deformation in these processes was studied for a series of cross-linked
polymers, viz., gel-type and porous styrene—divinylbenzene copolymers and poly(divinylbenzenes), and hypercrosslinked polystyrenes. Gel,
macroporous, and hypercrosslinked polystyrenes are substantially different in the rate, mechanism, and degree of swelling,
which is associated with the principal differences in their physical structures. An unusual effect of a sharp decrease followed
by a temporary increase in the volume of porous polystyrene and poly(divinylbenzene) materials were observed during desorption
(evaporation) of organic solvents. Water desorption is accompanied by an excessive bulk compression of porous granules giving
rise to negative deformations, which gradually relax to the state equilibrium for the dry polymer. The results of dynamic
desorption porometry (for water desorption) are indicative of a bimodal size distribution of micropores in hypercrosslinked
polystyrene.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 467–476, March, 2007. 相似文献
965.
Exact relations for the dependence of the positions of extrema of the aggregation work on the aggregation number axis on the surfactant monomer concentration are found for a dilute micellar solution. Relations for the half-widths of the vicinities of the extrema of the aggregation work are determined also. These half-widths are determined by the condition that, within the boundaries of their values, the aggregation work deviates from its extreme values by a thermal unit. The relations derived are illustrated by calculations based on the droplet and quasi-droplet models of spherical aggregates of nonionic surfactant. Some important applications of the obtained results to the theory of relaxation in micellar solutions are considered. 相似文献
966.
In this work preliminary results of amorphous zirconium crystallization using ion beam pulses are presented. Energetic argon- and oxygen-ion beams generated by a plasma focus device were used to promote crystallization on amorphous ZrO2-2.5 mol% Y2O3 film deposited by chemical solution deposition onto silica glass substrate. The films were burnt at 370 °C for 1 h in normal atmosphere previous to plasma irradiation. The irradiation was performed by means of successive pulses of ion beams. The evolution of the surface morphology and crystallization was followed by AFM and X-rays diffraction in a grazing incidence asymmetric Bragg geometry (GIAB), respectively. Argon-irradiated films showed highly nucleated cubic zirconia after 10 pulses. On the other hand, oxygen-irradiated films showed a delayed and less extensive cubic nucleation, but a more ordered structure and well-defined grains. 相似文献
967.
M. Yu. Kulikov 《Radiophysics and Quantum Electronics》2004,47(9):662-673
On the example of the effect of an atmospheric wave with given amplitude on the density oscillations of minor gas constituents near the mesopause (at heights 80–90 km, we consider the influence of the quasi-resonant periodic spatial transport on a distributed system responding subharmonically to a periodic external action (diurnal sunlight variations). Numerical modeling revealed the formation of a coherent horizontal distribution of the dynamical variables (i.e., the concentrations of small constituents). Application of this effect to the mesopause conditions is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 739–752, September, 2004. 相似文献
968.
Ya. A. Éyubov 《International Applied Mechanics》1991,27(1):48-55
Azerbaidzhan Institute of Construction Engineering, Baku. Translated from Prikladnaya Mekhanika, Vol. 27, No. 1, pp. 55–64, January, 1991. 相似文献
969.
S. E. Weal 《The Journal of the Operational Research Society》1991,42(12):1047-1059
Much of the debate over OR education over the last ten years has been confined to the relevance of the content and style of programmes at the postgraduate level. This paper focuses on the undergraduate level and discusses the way in which practical elements have been successfully incorporated at this level in Australia. These elements include the use of case study material from the literature, case problem solving groups, industrial projects and 12 months paid employment through a co-operative education programme. The use of each of the above and the context with which they fit into the programme is covered as are the benefits and problems associated with the programme. 相似文献
970.
R. S. Srivastava 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(5):832-842
The diffraction of normal shock with yawed wedges of small angles have been considered in this paper. Vorticity distribution
of the fluid particle over the diffracted shock has been determined for several Mach numbers of the shock wave. The Mach reflection
effects have also been investigated when the bend is concave to the flow. 相似文献