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101.
Veetil AT Solomek T Ngoy BP Pavlíková N Heger D Klán P 《The Journal of organic chemistry》2011,76(20):8232-8242
Various synthetically readily accessible S-phenacyl xanthates are shown to undergo photoinitiated homolytic scission of the C-S bond in the primary step. The resultant fragments, phenacyl and xanthic acid radicals, recombine to form symmetrical 1,4-diketones and xanthogen disulfides, respectively, in high to moderate chemical yields in chemically inert solvents. They can also be efficiently trapped by a hydrogen-atom-donating solvent to give acetophenone and xanthic acid derivatives. The latter compound is in situ thermally converted to the corresponding alcohol in high chemical yields. S-Phenacyl xanthates could thus be utilized as synthetic precursors to the above-mentioned compounds or as photoremovable protecting groups for alcohols in which the xanthate moiety represents a photolabile linker. The photochemically released phenacyl radical fragments efficiently but reversibly add to the thiocarbonyl group of the parent xanthate molecule. The kinetics of this degenerative reversible addition-fragmentation transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) mechanism was studied using laser flash photolysis (LFP) and density functional theory (DFT) calculations. The rate constants of the RAFT addition step, k(add) ~ 7 × 10(8) M(-1) s(-1), and phenacyl radical addition to a double bond of 1,1-diphenylethylene, k(add) ~ 10(8) M(-1) s(-1), in acetonitrile were experimentally determined by LFP. In addition, photoinitiation of the methyl methacrylate polymerization by S-phenacyl xanthate is demonstrated. The polydispersity index of the resulting poly(methyl methacrylate) was found to be ~1.4. We conclude that S-phenacyl xanthates can serve simultaneously as photoinitiators as well as RAFT/MADIX agents in polymerization reactions. 相似文献
102.
Kwan P Schmitt D Volosin AM McIntosh CL Seo DK Jones AK 《Chemical communications (Cambridge, England)》2011,47(45):12367-12369
Stable immobilization of two redox proteins, cytochrome c and azurin, in a thin film of highly mesoporous antimony-doped tin oxide is demonstrated via UV-vis spectroscopic and electrochemical investigation. 相似文献
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Dominik Völker 《Bl?tter der DGVFM》2007,28(2):291-309
In this article loss-reserves are handled with the methods and models for financial assets. In particular, the stochastic processes number of payments and size of the payment are modelled by an (inhomogeneous) poisson-process resp. an geometric brownian motion. In this model the cumulative payments are given by the stochastic integral. In an first step the conditional expectation, i.?e. the best estimator, of the payment-process is derived, where in an second step this expression is approximated by observations. Furthermore, the mean-square-error and an estimator of this expression is given. 相似文献
107.
Summary The probability to predict correctly a protein structure can be enhanced through introduction of spatial constraints – either
from NMR experiments or from homologous structures. However, the additional constraints lead often to new local energy minima
and worse sampling efficiency in simulations. In this work, we present a new parallel tempering variant that alleviates the
energy barriers resulting from spatial constraints and therefore yields to an enhanced sampling in structure prediction simulations. 相似文献
108.
Paul Houston Ilaria Perugia Anna Schneebeli Dominik Schötzau 《Numerische Mathematik》2005,100(3):485-518
Summary In this paper, we introduce and analyze the interior penalty discontinuous Galerkin method for the numerical discretization of the indefinite time-harmonic Maxwell equations in the high-frequency regime. Based on suitable duality arguments, we derive a-priori error bounds in the energy norm and the L2-norm. In particular, the error in the energy norm is shown to converge with the optimal order (hmin{s,}) with respect to the mesh size h, the polynomial degree , and the regularity exponent s of the analytical solution. Under additional regularity assumptions, the L2-error is shown to converge with the optimal order (h+1). The theoretical results are confirmed in a series of numerical experiments.Supported by the EPSRC (Grant GR/R76615).Supported by the Swiss National Science Foundation under project 21-068126.02.Supported in part by the Natural Sciences and Engineering Council of Canada. 相似文献
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