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991.
Fox PA Griffin ST Reichert WM Salter EA Smith AB Tickell MD Wicker BF Cioffi EA Davis JH Rogers RD Wierzbicki A 《Chemical communications (Cambridge, England)》2005,(29):3679-3681
Readily prepared imidazole-based boronium ions form stable, hydrophobic, room-temperature ionic liquids (RTIL) with unique electronic and spectroscopic characteristics. 相似文献
992.
Versatile and conveniently operated microreactor devices, suitable for long term chemical synthesis for both laboratory and industrial use, are described. Direct fluorination of ethyl acetoacetate by fluorine gas is used as a model reaction to illustrate the successful application of reactors having either 9, 18 or 30 microchannels, with all channels supplied from single reagent sources, to provide significant quantities of fluorinated products. Convenient reactor maintenance, simple design, versatility and the enhanced safety features of using such modular microreactor devices, make these systems appropriate for synthesis on the large scale. 相似文献
993.
Amide nitrogens open episulfonium ions to form pyrrolidines or piperidines selectively, depending on the nitrogen substituent, in either reversible or irreversible reactions. 相似文献
994.
CFD simulation of shear-induced aggregation and breakage in turbulent Taylor-Couette flow 总被引:6,自引:0,他引:6
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing turbulent Taylor-Couette flow was carried out. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method). Excellent agreement between the CFD-QMOM and experimental results was observed for two Reynolds numbers in the turbulent-flow regime. 相似文献
995.
Fox BS Balaj OP Balteanu I Beyer MK Bondybey VE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(24):5534-5540
"Nanodroplets" consisting of a central ion surrounded by a solvation shell of water molecules provide an interesting medium for studies of aqueous transition-metal chemistry in the unusual oxidation state (I). While VI undergoes efficient, solvent shell dependent redox reactions to VII and VIII, the absence of any similar reactivity in aqueous CrI, Mn1, FeI, CoI, NiI, and CuI clusters is explained by a rapid precipitation of the corresponding single monochloride molecules from the nanosolutions. 相似文献
996.
Numerical simulation algorithms for multiplicative noise (white or colored) are tested for accuracy against closed-form expressions for the Kubo oscillator. Direct white noise simulations lead to spurious decay of the modulus of the oscillator amplitude. A straightforward colored noise algorithm greatly reduces this decay and also provides highly accurate results in the white noise limit. 相似文献
997.
Fox A.M. Miller D.A.B. Livescu G. Cunningham J.E. Jan W.Y. 《Quantum Electronics, IEEE Journal of》1991,27(10):2281-2295
The authors studied the effects of changing the barrier design of GaAs-AlxGa1-xAs quantum wells on the electroabsorption, exciton saturation, and carrier sweep-out times. Five samples with x values ranging from 0.2 to 0.4 and barrier thicknesses from 35 to 95 Å were studied. Within this range, the authors find that the electroabsorption is not very sensitive to the barrier thickness, but that the ionization field of the excitons approximately doubles for an increase of x from 0.2 to 0.4. The samples with high, thick barriers have lower internal quantum efficiencies than those with low, thin barriers. It was found that the exciton saturation intensity increases with increasing applied field, and decreasing barrier thickness or height. Time-resolved electroabsorption measurements confirm the variation in sweep-out rates between samples, and indicate that the escape mechanism at low field is probably a thermally-assisted tunneling process 相似文献
998.
999.
Summary We consider a vibrating string fixed at the ends for which the position is known at two different times. This corrisponds
to a classical not well posed problem, theDirichlet problem for the wave equation, which we reconsider here in order to determine under what conditions it is possible to obtain
useful information about the physical phenomenon. This problem is related to a functional equation from which the principal
results can be deduced.
This research was supported in part by the United States Air Force under contract No. AF 49 (638) 228 monitored by the Office of Scientific Research, Air Research and Development Command. 相似文献
Sunto Si riesamina un classico esempio di problema ? non ben posto ?, il problema diDirichlet corrispondente al modello fisico di una corda vibrante, fissa agli estremi e assumente posizioni note in due diversi istanti. Lo studio relativo all'esistenza ed unicità della soluzione è ricondotto a quello di una equazione funzionale ed è strettamente connesso a questioni di teoria dei numeri. Si esamina poi la dipendenza della soluzione dai dati e si discute il problema dal punto di vista delle sue applicazioni.
This research was supported in part by the United States Air Force under contract No. AF 49 (638) 228 monitored by the Office of Scientific Research, Air Research and Development Command. 相似文献
1000.
Bernard D. Coleman Thomas G Fox 《Journal of polymer science. Part A, Polymer chemistry》1996,34(9):1635-1649
When, in a poly-α-olefin, the probability that a given placement be isotactic depends upon the tacticity of only a finite number of immediate predecessors, the resulting diastereosequence distribution obeys the theory of Markoff chains. When this is not the case, one says that the resulting diastereosequence distribution is non-Markoffian. A special case of a Markoffian distribution is given by a simple Markof chain in which the tacticity of a given placement is assumed to be affected by only the tacticity of the immediately preceding placement. Another special case is, of course, the Bernoulli trial distribution in which the probability that a given placement be isotactic is independent of the tacticity of all other placements. A high resolution NMR spectrum can sometimes yield a quantitative determination of the concentrations of isotactic and syndiotactic placements and the concentrations of the three types of possible adjacent pairs of such placements (i.e., isotactic, syndiotactic, and heterotactic pairs). When this is the case, the spectrum can be used to determine whether or not a given diastereosequence distribution is Bernoullian. However, because the longest diastereosequences whose concentration can be measured by NMR spectroscopy involve only two placements, an NMR spectrum cannot check whether a given non-Bernoullian distribution be simple Markoffian or Markoffian in general. In fact, non-Markoffian distributions are compatible with existing NMR spectra on polymers prepared by anionic polymerizations. In this paper we work within the framework of Kac's theory of stationary statistical processes and point out some general results which are valid for both Markoffian and non-Markoffian processes. The results are applied to NMR spectroscopy and it is pointed out which calculations used to check the self-consistency of NMR data and to obtain the mean length of closed diastereosequences are valid for both Markoffian and non-Markoffian distributions. 相似文献