全文获取类型
收费全文 | 808篇 |
免费 | 27篇 |
国内免费 | 1篇 |
专业分类
化学 | 503篇 |
晶体学 | 8篇 |
力学 | 21篇 |
数学 | 34篇 |
物理学 | 270篇 |
出版年
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 33篇 |
2012年 | 28篇 |
2011年 | 37篇 |
2010年 | 23篇 |
2009年 | 15篇 |
2008年 | 32篇 |
2007年 | 41篇 |
2006年 | 26篇 |
2005年 | 40篇 |
2004年 | 46篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 52篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 14篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1973年 | 5篇 |
1923年 | 4篇 |
排序方式: 共有836条查询结果,搜索用时 437 毫秒
71.
72.
Fera A Dolbnya IP Grubel G Muller HG Ostrovskii BI Shalaginov AN de Jeu WH 《Physical review letters》2000,85(11):2316-2319
Coherent dynamic x-ray scattering has been used to study the thermally excited layer fluctuations in freely suspended smectic films of the compound 4O.8. Using 8-keV x rays and films with a thickness around 0.3 &mgr;m we resolve relaxation times down to a few &mgr;s. A combination of damped and oscillatory behavior is observed for the layer undulations, which can be attributed to inertial effects. These are due to the surface contribution to the free energy which cannot be disregarded for thin films. 相似文献
73.
A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions, forbids certain cosmological singularities, and is compatible with entropy bounds. This second law is based on the conjecture that causal boundaries and not only event horizons have geometric entropies proportional to their area. In string cosmology the second law provides new information about nonsingular solutions. 相似文献
74.
The effects of viscous heating on the stability of Taylor-Couette flow were investigated through flow visualization experiments for Newtonian and viscoelastic fluids. For highly viscous Newtonian fluids, viscous heating drives a transition to a new, oscillatory mode of instability at a critical Reynolds number significantly below that at which the inertial transition is observed in isothermal flows. The effects of viscous heating may explain the discrepancies between the observed and predicted critical conditions and the symmetry of the disturbance flow for viscoelastic instabilities. 相似文献
75.
The detection and evaluation of defects in industrial components relies strongly on ultrasonic inspection techniques. Distance gain size (DG) or reference reflector methods can be improved concerning their localization, signal-to-noise ratio and sizing accuracy by the synthetic aperture focusing technique (SAFT). To obtain a high quality image, parameters like focal probe versus contact technique probe, achieved resolution or features of SAFT images compared with B-scan images are discussed. The implementation of SAFT in a CAD environment allows us to present stacked 2D reconstructions dynamically. On a cladded testblock with half-penny shaped cracks the advantage of combining CAD with SAFT is shown. A 3D SAFT example finalizes the overview of two decades of experience in applying this technique. 相似文献
76.
Anthony D'Aléo Jide Xu King Do Gilles Muller Kenneth N. Raymond 《Helvetica chimica acta》2009,92(11):2439-2460
The synthesis of the cyclen derivative H4 L 1 ?2 HBr containing four 2‐hydroxybenzamide groups is described. The spectroscopic properties of the LnIII conplexes of L 1 (Ln=Gd, Tb, Yb, and Eu) reveal changes of the UV/VIS‐absorption, circular‐dichroism‐absorption, luminescence, and circularly polarized luminescence spectra. It is shown that at least two metal‐complex species are present in solution, whose relative amounts are pH dependent. At pH>8.0, an intense long‐lived emission is observed (for [Tb L 1 ] and [Yb L 1 ]), while at pH<8.0, a weaker, shorter‐lived species predominates. Unconventional LnIII emitters (Pr, Nd, Sm, Dy, and Tm) were sensitized in basic solution, both in the VIS and in the near‐IR, to measure the emission of these ions. 相似文献
77.
Audrey Hecka Benoît Maunit Frédéric Aubriet Jean‐François Muller 《Rapid communications in mass spectrometry : RCM》2009,23(6):885-898
Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSn. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSn experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
78.
79.
Self-organized filaments in dielectric barrier glow discharges 总被引:1,自引:0,他引:1
Muller L. Punset C. Ammelt E. Purwins H.-G. Boeuf J.P. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(1):20-21
The filamentation of a plasma created by a dielectric barrier discharge in conditions of low pd products (i.e., Townsend breakdown and not streamer breakdown) is investigated both experimentally and with a two-dimensional numerical discharge model. Complex stationary and dynamical domains and filaments are observed experimentally. Some of the properties of these systems are reproduced by the model 相似文献
80.
J. A. Muller M. Centnerszwer J. Szedrowicz H. Walde und K. A. Schuch 《Fresenius' Journal of Analytical Chemistry》1942,124(1-2):57-58
Ohne Zusammenfassung 相似文献