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971.
972.
973.
Mario Blumthaler Walter Ambach Roland Silbernagl Johannes Staehelin 《Photochemistry and photobiology》1994,59(S1):657-659
Abstract –Robertson-Berger sunburn meter data recorded from August 1992 to May 1993 (Innsbruck, 577 m above sea level, Austria) were compared with measurements taken in previous years. In February and March 1993 instantaneous values on clear days were found to be higher by up to 37% than those registered in previous years (1986–1988). However, in winter/spring 1993 daily totals for all days, averaged over 7 days, were within the range of standard deviation of the previous years (1981–1988). Therefore the cumulative UV-B exposure of the ecosystem is within the general range of variability even under the record low ozone values in winter/spring 1993, while single peak doses were enhanced significantly. 相似文献
974.
Zusammenfassung Das Transportproblem wird dahingehend verallgemeinert, daß nicht der Transport eines einheitlichen Gutes, sondern der Transport verschiedener Sorten betrachtet wird. Gesucht ist ein optimaler Verteilungsplan, der gleichzeitig vorschreibt, in welchen Mengen die einzelnen Sorten in den Versandorten am besten produziert werden, wobei für diese Mengen obere Schranken gegeben sind. Es wird gezeigt, daß sich die geschilderte Aufgabe auf ein gewöhnliches Transportproblem zurückführen läßt. Diese Tatsache ist vor allem deshalb interessant, da dadurch der Aufwand für die numerische Bearbeitung solcher Aufgaben wesentlich herabgesetzt wird.
Summary The transportation-problem is generalized by considering not the transport of a uniform commodity, but of goods of various kinds. The obejetive is to find an optimal distribution plan, prescribing at the same time the quantities in which the different kinds of goods have to be produced in the places of dispatch, if maximum amounts are given for these goods. It is shown that the problem in question can be reduced to a normal transportation-problem. This is especially important on account of the fact that it leads to a considerable reduction of the cost of treating problems of this kind.相似文献
975.
976.
John M. Patterson Nabeel F. Haidar Loren L. Braun Walter T. Smith 《Journal of Analytical and Applied Pyrolysis》1981,2(4):331-337
The controlled pyrolysis of ethylenetetracarboxyclic acid at 220°C followed by methylation of the pyrolyzate results in the formation of methyl propiolate as the major product along with lesser amounts of methyl fumarate. Evidence is presented which indicates that the methyl fumarate probably arises from some precursor in the pyrolyzate during the methylation reaction. Extended heating of the tetra acid at its melting point produces, in addition to the substances cited above, ethylenetetracarboxylic dianhydride and dicarboxymaleic anhydride. The high-temperature (300–400°C) pyrolysis of the tetraacid gives l0–20% yields of dimethylmaleic anhydride. 相似文献
977.
Colin D Walter 《Journal of Combinatorial Theory, Series B》1983,35(2):201-204
It is shown that the intersection numbers of a coherent configuration are closely related to the determinant of a generic matrix for the corresponding adjacency algebra. This is important as both concepts provide isomorphism invariants for graphs. 相似文献
978.
We consider solutions of the scalar wave equation vanishing on the boundary of an obstacle which undergoes periodic motion. In analogy with the Lax-Phillips theory, we show that the scattering matrix, as a function of frequency, is holomorphic in a lower half-plane, and meromorphic in an upper half-plane, provided rays are not trapped. The poles of the scattering matrix correspond to certain outgoing eigenfunctions, and there is a near-field expansion of finite energy solutions in terms of these eigenfunctions. 相似文献
979.
980.
Kostelansky CN Pietron JJ Chen MS Dressick WJ Swider-Lyons KE Ramaker DE Stroud RM Klug CA Zelakiewicz BS Schull TL 《The journal of physical chemistry. B》2006,110(43):21487-21496
Ligand-stabilized platinum nanoparticles (Pt NPs) can be used to build well-defined three-dimensional (3-D) nanostructured electrodes for better control of the catalyst architecture in proton exchange membrane fuel cells (PEMFCs). Platinum NPs of 1.7 +/- 0.5 nm diameter stabilized by the water-soluble phosphine ligand, tris(4-phosphonatophenyl)phosphine (TPPTP, P(4-C6H4PO3H2)3), were prepared by ethylene glycol reduction of chloroplatinic acid and subsequent treatment of the isolated nanoparticles with TPPTP. The isolated TPPTP-stabilized Pt NPs were characterized by multinuclear magnetic resonance spectroscopy (31P and 195Pt NMR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). The negatively charged TPPTP-Pt NPs were electrostatically deposited onto a glassy carbon electrode (GCE) modified with protonated 4-aminophenyl functional groups (APh). Multilayers were assembled via electrostatic layer-by-layer deposition with cationic poly(allylamine HCl) (PAH). These multilayer films are active for the key hydrogen fuel cell reactions, hydrogen oxidation (anode) and oxygen reduction (cathode). Using a rotating disk electrode configuration, fully mass-transport limited kinetics for hydrogen oxidation was obtained after 3 layers of TPPTP-Pt NPs with a total Pt loading of 4.2 microg/cm2. Complete reduction of oxygen by four electrons was achieved with 4 layers of TPPTP-Pt NPs and a total Pt loading of 5.6 microg/cm2. A maximum current density for oxygen reduction was reached with these films after 5 layers resulting in a mass-specific activity, i(m), of 0.11 A/mg(Pt) at 0.9 V. These films feature a high electrocatalytic activity and can be used to create systematic changes in the catalyst chemistry and architecture to provide insight for building better electrocatalysts. 相似文献