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41.
The two techniques of luminescence and of infra-red spectrophotometry have been used in an attempt to characterize surface states of η-alumina. Infra-red absorption bands of hydroxyl groups of different coordinations are observed, in agreement with previous results, and evolution of hydroxyl groups according to different treatments allows a luminescence at about 440–450 nm excited at 350–360 nm to be ascribed to these groups. Luminescence with an apparent maximum of 390 nm excited at 250 nm is attributed to internal vacancies, and luminescence with a maximum at 480–500 nm excited at 270–280 nm is attributed to surface vacancies. 相似文献
42.
Glinec Y Faure J Dain LL Darbon S Hosokai T Santos JJ Lefebvre E Rousseau JP Burgy F Mercier B Malka V 《Physical review letters》2005,94(2):025003
An electron beam from a laser-plasma accelerator is converted into a gamma-ray source using bremsstrahlung radiation in a dense material. The gamma-ray beam has a pointlike source size because it is generated by a high quality electron beam with a small source size and a low divergence. Using this gamma-ray source, the radiography of complex and dense objects with submillimeter resolution is performed. It is the first evidence of a gamma-ray source size of a few hundreds micrometers produced with laser-driven accelerators. This size is consistent with results from Monte Carlo simulations. 相似文献
43.
Frédéric?Faure Stéphane?NonnenmacherEmail author 《Communications in Mathematical Physics》2004,245(1):201-214
We consider the quantized hyperbolic automorphisms on the 2-dimensional torus (or generalized quantum cat maps), and study the localization properties of their eigenstates in phase space, in the semiclassical limit. We prove that if the semiclassical measure corresponding to a sequence of normalized eigenstates has a pure point component (phenomenon of strong scarring), then the weight of this component cannot be larger than the weight of the Lebesgue component, and therefore admits the sharp upper bound 1/2. 相似文献
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Sorensen JL Auclair K Kennedy J Hutchinson CR Vederas JC 《Organic & biomolecular chemistry》2003,1(1):50-59
Two mutants of Aspergillus terreus with either the lovC or lovA genes disrupted were examined for their ability to transform nonaketides into lovastatin 1, a cholesterol-lowering drug. The lovC disruptant was able to efficiently convert dihydromonacolin L 5 or monacolin J 9 into 1, and could also transform desmethylmonacolin J 15 into compactin 3. In contrast, the lovA mutant has an unexpectedly active beta-oxidation system and gives only small amounts of 1 upon addition of the immediate precursor 9, with most of the added nonaketide being degraded to heptaketide 22. Similarly, the lovA mutant does not accumulate the polyketide synthase product 5 and rapidly degrades any 5 added as a precursor via two cycles of beta-oxidation and hydroxylation at C-6 to give 20. The possible involvement of epoxides 21a and 21b in the biosynthesis of 1 was also examined, but their instability in fermentation media and fungal cells will require purified enzymes to establish their role. 相似文献
46.
Jean-Marc Jancu Jean-Christophe Harmand Gilles Patriarche Anne Talneau Karine Meunier Frank Glas Paul Voisin 《Comptes Rendus Physique》2007,8(10):1174-1183
A new attempt to solve the phase matching problem for semiconductor-based frequency conversion devices, based on the implementation of intrinsic birefringence in artificial materials, is discussed. The first results concerning the growth and characterization of ultrashort period superlattices are presented. To cite this article: J.-M. Jancu et al., C. R. Physique 8 (2007). 相似文献
47.
Altitude-resolved volume mixing ratio profiles of CFC-113 have recently become available on a global scale with the Atmospheric Chemistry Experiment (ACE) satellite mission. However, the accuracy of the retrieval is currently limited by the uncertainties on the spectroscopic parameters of CFC-113. This paper reports on the geometrical structure, harmonic frequencies and intensities in the mid-infrared region of the two conformers of CFC-113 and the evaluation of whether theoretical calculations reproduce measurements. The calculations are performed using density functional theory at the B3LYP/6-311+G(3df) level. The molecular geometry parameters, the enthalpy difference and the potential barrier between conformers are calculated. The harmonic frequency of the normal modes of vibration are presented and accurately compared to experimental data. Overtones and combination bands are assigned in the 1200-2500 cm−1 region. 相似文献
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Gilles Casano Maxime Robin Pascale Barbier Vincent Peyrot Robert Faure 《Magnetic resonance in chemistry : MRC》2010,48(9):738-744
The complete 1H and 13C NMR assignment of 9 acetamidochalcones, 18 acetamidoflavones, 18 aminoflavones, 9 acetamidoflavonols and 9 aminoflavonols has been performed using one‐ and two‐dimensional NMR techniques including COSY, HMQC and HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献