全文获取类型
收费全文 | 5573篇 |
免费 | 137篇 |
国内免费 | 22篇 |
专业分类
化学 | 4007篇 |
晶体学 | 41篇 |
力学 | 135篇 |
数学 | 577篇 |
物理学 | 972篇 |
出版年
2023年 | 35篇 |
2022年 | 64篇 |
2021年 | 95篇 |
2020年 | 99篇 |
2019年 | 68篇 |
2018年 | 63篇 |
2017年 | 57篇 |
2016年 | 106篇 |
2015年 | 103篇 |
2014年 | 139篇 |
2013年 | 253篇 |
2012年 | 248篇 |
2011年 | 304篇 |
2010年 | 188篇 |
2009年 | 192篇 |
2008年 | 269篇 |
2007年 | 283篇 |
2006年 | 277篇 |
2005年 | 269篇 |
2004年 | 223篇 |
2003年 | 164篇 |
2002年 | 182篇 |
2001年 | 126篇 |
2000年 | 123篇 |
1999年 | 79篇 |
1998年 | 72篇 |
1997年 | 63篇 |
1996年 | 92篇 |
1995年 | 65篇 |
1994年 | 79篇 |
1993年 | 57篇 |
1992年 | 60篇 |
1991年 | 58篇 |
1990年 | 61篇 |
1989年 | 60篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 47篇 |
1985年 | 59篇 |
1984年 | 56篇 |
1983年 | 55篇 |
1982年 | 54篇 |
1981年 | 44篇 |
1980年 | 44篇 |
1979年 | 40篇 |
1978年 | 45篇 |
1976年 | 31篇 |
1973年 | 28篇 |
1968年 | 29篇 |
1967年 | 36篇 |
排序方式: 共有5732条查询结果,搜索用时 375 毫秒
21.
F. Schreiber M. Hoffmann O. von Geisau J. Pelzl 《Applied Physics A: Materials Science & Processing》1993,57(6):545-551
The conventional and photothermally modulated (PM) ferromagnetic resonance (FMR) of magnetostatic modes (MSM) in yttrium iron garnet (YIG) films have been investigated as a function of temperature. Approaching the ferrimagnetic transition at T
c=560 K a strong enhancement of the PM-FMR signal amplitude is observed which is accompanied by a change of the signal shape. The observations are discussed in the framework of a model that takes into account the temperature derivatives of those quantities that contribute to the high-frequency susceptibility. At temperatures still below T
c a paramagnetic line emerges. The MSM disappear in a state of finite magnetization which is explained on the basis of damping of the MSM being important in the vicinity of the magnetic phase transition. Additionally, frequency and power dependent measurements are presented and the imaging ability of PM-FMR is demonstrated. 相似文献
22.
In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings. 相似文献
23.
24.
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
25.
Raffaello Fusco Alessandro Marchesini Franco Sannicol 《Journal of heterocyclic chemistry》1987,24(3):773-778
The thermal cyclization of a few 2,6-dimethylphenylazo compounds to indazole derivatives is described. 相似文献
26.
We introduce a statistical ensemble for a single vortex filament of a three dimensional incompressible fluid. The core of
the vortex is modeled by a quite generic stochastic process. We prove the existence of the partition function for both positive
and a limited range of negative temperatures.
Received: 31 July 2000 / Revised version: 6 March 2001 / Published online: 20 December 2001 相似文献
27.
28.
W. D. Hoffmann D. Michel I. G. Sorina E. V. Charnaya 《Physics of the Solid State》1998,40(8):1288-1289
The shift in the nuclear magnetic resonance (NMR) line of 71Ga isotopes in GaAs crystals is investigated in the temperature range 160–360 K. It is observed that the position of the resonance
line is temperature-independent. The value of the shift relative to an isolated nucleus is 440 and 420 ppm for the three samples
investigated. The roles of various contributions to the NMR line shift are discussed.
Fiz. Tverd. Tela (St. Petersburg) 40, 1418–1419 (August 1998) 相似文献
29.
Hypothetical helical organic polymers with localized electrons, charges, and/or atoms are described, in which these localized substructures can move along the backbones of the polymers via sigmatropic H shifts. 相似文献
30.