全文获取类型
收费全文 | 248346篇 |
免费 | 5072篇 |
国内免费 | 2227篇 |
专业分类
化学 | 136376篇 |
晶体学 | 4039篇 |
力学 | 11136篇 |
综合类 | 99篇 |
数学 | 23878篇 |
物理学 | 80117篇 |
出版年
2018年 | 2138篇 |
2017年 | 1954篇 |
2016年 | 3501篇 |
2015年 | 2763篇 |
2014年 | 3819篇 |
2013年 | 10672篇 |
2012年 | 7912篇 |
2011年 | 9734篇 |
2010年 | 6616篇 |
2009年 | 6508篇 |
2008年 | 8598篇 |
2007年 | 8586篇 |
2006年 | 8137篇 |
2005年 | 7366篇 |
2004年 | 6653篇 |
2003年 | 5956篇 |
2002年 | 5784篇 |
2001年 | 7981篇 |
2000年 | 6004篇 |
1999年 | 4825篇 |
1998年 | 3770篇 |
1997年 | 3720篇 |
1996年 | 3540篇 |
1995年 | 3301篇 |
1994年 | 3101篇 |
1993年 | 2911篇 |
1992年 | 3553篇 |
1991年 | 3481篇 |
1990年 | 3335篇 |
1989年 | 3252篇 |
1988年 | 3160篇 |
1987年 | 3200篇 |
1986年 | 2927篇 |
1985年 | 3974篇 |
1984年 | 3925篇 |
1983年 | 3171篇 |
1982年 | 3347篇 |
1981年 | 3283篇 |
1980年 | 3151篇 |
1979年 | 3381篇 |
1978年 | 3665篇 |
1977年 | 3454篇 |
1976年 | 3366篇 |
1975年 | 3144篇 |
1974年 | 3119篇 |
1973年 | 3084篇 |
1972年 | 1956篇 |
1968年 | 2048篇 |
1967年 | 2248篇 |
1966年 | 1992篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Summary A non-destructive method is described for the determination of major and minor constituents in archeological specimens by energy-dispersive X-ray fluorescence. Homogeneity tests are made by measuring at various sites of the specimen. In the same way, mean values are obtained for inhomogeneous specimen without taking samples. For calibration, powder standards are used. In case of the determination of elements with numbers up to 14 (Si) a vacuum chamber is used and the dimensions of the specimens are limited by the dimensions of that vacuum chamber, whereas for the determination of elements from K up to U specimens of any size, form or weight are suitable.
Zerstörungsfreie Analyse von archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse
Zusammenfassung Eine zerstörungsfreie Methode für die Bestimmung von Haupt- und Nebenbestandteilen in archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse wird beschrieben. Für Homogenitätstests wird an mehreren Stellen der Probe gemessen. In der gleichen Weise werden für inhomogene Proben Mittelwerte erhalten ohne Probenahme. Für die Eichung werden Pulverstandards verwendet. Im Falle der Bestimmung von Elementen mit Ordnungszahlen bis 14 (Si) wird eine Vakuumkammer eingesetzt, und die Dimensionen der Proben sind durch die Dimensionen dieser Vakuumkammer begrenzt, während für die Bestimmung der Elemente K bis U Proben jeder Größe, jeder Form oder jeden Gewichts verwendbar sind.相似文献
942.
943.
Recently commercial equipment using sedimentation field flow fractionation (SFFF) has become available for analysis of particulate materials in the sub-micron range. This paper describes the DuPont instrument and discusses its performance. A particular study is described on the comparison of the SFFF technique with that of quasi-elastic light scattering (QELS). The paper concludes that the instrument is capable of measuring particle size distributions with high resolution and precision, provided that no particles above the upper size limit — about 1 μm — are present. 相似文献
944.
945.
Microemulsions (dispersions of water droplets, typical radius about 10 nm, in oil) show a particular percolation pattern, a so-called dynamical percolation. Predictions of scaling theory and Monte Carlo simulations were compared with experimental static and frequency dependent conductivity data. The latter gives evidence of two different time scales of charge transport.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday 相似文献
946.
R. Möller und H. Viefhaus 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):331
947.
948.
H. Hakemi 《Journal of Polymer Science.Polymer Physics》1986,24(11):2445-2458
Poly(γ-benzyl-L-glutamate) (PBLG), was utilized as a surface coating agent in order to obtain parallel molecular orientation in thin layers of PBLG liquid-crystalline solutions confined between coated surfaces. It was found that in a thickness range much larger than the cholesteric pitch value, the texture was predominantly planar cholesteric. At film thickness comparable or smaller than the pitch, isotropic spherulites developed from a homeotropic nematic phase. Because of the coupling between the solution concentration and nematic director, as well as large differences in the elastic moduli of PBLG liquid-crystalline solutions, the long-range intermolecular interaction was unfavorable. Competition between parallel orientation induced by the surface coating of PBLG and inherent perpendicular orientation induced by PBLG molecules in the bulk would favor a short-range helix-coil transition mechanism, which results into a reentrant isotropic phase. 相似文献
949.
We prove both geometric ergodicity and regular variation of the stationary distribution for a class of nonlinear stochastic recursions that includes nonlinear AR-ARCH models of order 1. The Lyapounov exponent for the model, the index of regular variation and the spectral measure for the regular variation all are characterized by a simple two-state Markov chain. 相似文献
950.
A flow visualization of the two-dimensional rigid fling-clap motions of the flat-plate wing is performed to get the knowledge
of fling-clapping mechanism that might be employed by insects during flight. In this numerical visualization, the time-dependent
Navier-Stokes equations are solved for two types of wing motion; ‘fling followed by clap and pause motion’ and ‘cyclic fling-clapping
motion’. The result is observed regarding the main flow features such as the sequential development of the two families of
separation vortex pairs and their movement. For the ‘fling followed by clap and pause motion’, a strong separation vortex
pair of counterrotation develops in the opening between the wings in the fling phase and they then move out from the opening
in the following clap phase. For ‘the cyclic fling-clapping motion’, the separation vortex pair developed in the outside space
in the clap phase move into the opening in the following fling phase. The separation vortex pair in the opening developed
in the fling phase of the cyclic motion is observed to be stronger than those of the ‘fling followed by clap and pause motion’.
Regarding the strong fling separation vortex and the weak clap separation vortex above it in the opening, the flow pattern
of the fling phase of the cyclic fling and clap motion is different to that of the fling phase of the first cycle. The flow
pattern of the third cycle of the cyclic fling-clapping motion is observed to be almost same as that of the second cycle.
Therefore, a periodicity of the flow pattern is established after the second cycle. 相似文献