全文获取类型
收费全文 | 408962篇 |
免费 | 4671篇 |
国内免费 | 1305篇 |
专业分类
化学 | 223294篇 |
晶体学 | 6586篇 |
力学 | 16702篇 |
综合类 | 13篇 |
数学 | 44192篇 |
物理学 | 124151篇 |
出版年
2020年 | 3223篇 |
2019年 | 3643篇 |
2018年 | 4367篇 |
2017年 | 4342篇 |
2016年 | 6741篇 |
2015年 | 4451篇 |
2014年 | 6796篇 |
2013年 | 18682篇 |
2012年 | 13386篇 |
2011年 | 16563篇 |
2010年 | 11248篇 |
2009年 | 11156篇 |
2008年 | 14823篇 |
2007年 | 14849篇 |
2006年 | 13815篇 |
2005年 | 12713篇 |
2004年 | 11467篇 |
2003年 | 10429篇 |
2002年 | 10081篇 |
2001年 | 12023篇 |
2000年 | 9054篇 |
1999年 | 7088篇 |
1998年 | 5800篇 |
1997年 | 5761篇 |
1996年 | 5371篇 |
1995年 | 5133篇 |
1994年 | 4830篇 |
1993年 | 4762篇 |
1992年 | 5604篇 |
1991年 | 5551篇 |
1990年 | 5329篇 |
1989年 | 5296篇 |
1988年 | 5340篇 |
1987年 | 5329篇 |
1986年 | 5072篇 |
1985年 | 6722篇 |
1984年 | 6847篇 |
1983年 | 5509篇 |
1982年 | 5963篇 |
1981年 | 5891篇 |
1980年 | 5564篇 |
1979年 | 5917篇 |
1978年 | 6074篇 |
1977年 | 6120篇 |
1976年 | 6106篇 |
1975年 | 5480篇 |
1974年 | 5566篇 |
1973年 | 5835篇 |
1972年 | 3775篇 |
1968年 | 3080篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
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
872.
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
873.
Grafov B. M. Davydov A. D. Damaskin B. B. Lazorenko-Manevich R. M. 《Russian Journal of Electrochemistry》2003,39(4):439-440
Russian Journal of Electrochemistry - 相似文献
874.
L. G. Smirnova Yu. B. Grunin S. V. Krasil'nikova M. A. Zaverkina D. R. Bakieva E. V. Smirnov 《Colloid Journal》2003,65(6):778-781
The pulsed NMR, isopiestic and pycnometric methods are applied to investigate the physicochemical properties of softwood [GOST (State Standard) 9571-89] and hardwood [GOST 28172-89] celluloses, as well as flax cellulose [GOST 10330-76, 9394-76], both in the initial state and subjected to chemical treatment. Possible changes occurring in the supramolecular structure of a polymer are analyzed. The structural and sorption characteristics of the investigated samples are calculated. Their water absorption capacities are determined. 相似文献
875.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
876.
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
877.
S. R. Tuikina 《Computational Mathematics and Modeling》2007,18(1):10-18
We consider a mathematical model of sorption that allows for external diffusion kinetics and a redox reaction. Two inverse
problems are considered for this model, uniqueness is proved, and numerical solution methods are proposed. The efficiency
of the numerical methods is investigated by computer experiments.
__________
Translated from Prikladnaya Matematika i Informatika, No. 23, pp. 15–23, 2006. 相似文献
878.
879.
880.
The aim of this paper is to highlight the added value of the generalized Gouy phase shift introduced by Siegman. Although suited for optical systems study, including those more complex than free space, we note that it did not meet the use that it deserves so far. The analysis of the whole of the ideas and analytical approaches associated to the important concept of the Gouy phase proves its effectiveness.
Usually, the resonance condition is systematically built on the basis of the equivalent empty cavity. Unfortunately, this approach does not cover some of the useful parameters of the real resonator. By means of the generalized Gouy phase and the self-consistent complex parameter q, we derive here a new approach for the calculation of the resonance condition for the real cavity. Moreover, the use of the generalized Gouy phase clearly simplifies the study of resonators, while making it possible to avoid the use of the Huygens’ Fresnel integral. 相似文献