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排序方式: 共有186条查询结果,搜索用时 15 毫秒
1.
A. Hertz 《Graphs and Combinatorics》1989,5(1):149-157
We consider the graphs that can be obtained by deleting in a Meyniel graphG all the edges induced by an arbitrary set of nodes. These graphs will be called Slim and we prove that they are perfect. We study relations between Slim graphs and other well known classes of perfect graphs; particularly we show that the perfection of Slim graphs gives a proof to the conjecture of M. Preissmann that Meyniel graphs are locally perfect. 相似文献
2.
It has been described earlier that imaging measurements of laser-induced fluorescence (LIF) in flames can be calibrated to number densities with an integrated absorption measurement provided the integrated absorption is small. In this paper a method is presented that extends the technique to flames with substantial absorption, improves the number density determination and allows the experimental parameters to be chosen more freely. The method is based on an iterative computer procedure that reconstructs the 1-D spatially resolved absorption profile from laser measurements of the 1-D spatially resolved LIF and the integrated absorption of the laser beam. The technique is experimentally demonstrated by measurements of OH number densities in atmospheric flames. It is potentially a single-pulse method. Other applications of the iterative procedure are mentioned. 相似文献
3.
W E May S N Chesler S P Cram B H Gump H S Hertz D P Enagonio S M Dyszel 《Journal of chromatographic science》1975,13(11):535-540
The low concentration of hydrocarbons anticipated in pollution baseline studies necessitates the development of analytical techniques sensitive at the sub-microgram per kilogram concentration level. The method of analysis developed in this laboratory involves dynamic headspace sampling for volatile hydrocarbon components of the sample, followed by coupled-column liquid chromatography for the non-volatile components. These techniques require minimal sample handling, reducing the risk of sample component loss and/or sample contamination. Volatile sample components are separated from the matrix in a closed system and concentrated on a TENAX-GC packed pre-column, free from large amounts of solvent and ready for GC/GC-MS analysis. Non-volatile compounds, such as the benzpyrenes, may be extracted from large volumes of water and concentrated on a Bondapak C18 packed pre-column for coupled-column liquid chromatographic separation and analysis. Results of the application of these techniques to the analysis of samples from sites of known low level hydrocarbon contamination are presented and discussed. 相似文献
4.
Enemaerke RJ Hertz T Skrydstrup T Daasbjerg K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(20):3747-3754
The fundamental nature of samarium(II) complexes in THF/HMPA (HMPA = hexamethylphosphoramide) solutions containing SmI2 has been clarified by means of cyclic voltammetry, conductivity measurements, UV spectroscopy, and kinetic measurements. The principal species is not [SmI2(hmpa)4] as previously suggested, but either the ionic cluster [Sm(hmpa)4(thf)2+2I- if four equivalents of HMPA is present in the THF solution or [Sm(hmpa)6]2+ 2I- in the presence of at least 10 equivalents of HMPA. The formal potential of the [Sm(hmpa)4(thf)2]3+ 2I-/[Sm(hmpa)4(thf)2]2- 2I- redox couple determined by cyclic voltammetry was -1.79 +/- 0.08 V versus SCE. The order of reactivity of the samarium(II) complexes was found to be [Sm(hmpa)6]2+2I- > [Sm(hmpa)4(thf)2]2+2I- > SmI2 in their respective reactions with 1-iodobutane and with benzyl chloride. Very high rate enhancements, of the order of 1,000-15,000-fold, were observed upon addition of HMPA to the THF solution containing SmI2, Comparison of these rate constants with the corresponding rate constants for electron transfer (ET) reactions involving aromatic radical anions revealed that none of the reactions studied can be classified as outer-sphere ET processes and that the inner-sphere electron-donating abilities of the [Sm(hmpa)4(thf)2]2+ 2I- and SmI2 complexes are comparable. The inner-sphere ET character of the transition state increases on going from 1-iodobutane and benzyl bromide to benzyl chloride and acetophenone. 相似文献
5.
Proton relaxation time measurements are performed for 6m aqueous solutions of7LiI and6LiI in D2O containing small amounts of H2O. The measurements are done at low temperatures and yield maxima of the relaxation rate plotted against 1/T. From the maxima of the relaxation rates, proteon-I– and proton-Li+ distances in the first coordination sphere of the ions are determined, and from the knowledge of the ion-water oxygen distance it is shown that for iodide a somewhat broadened H-bonded configuration is valid and that for Li+ the electric dipole orientation deviates from the radial direction. In order to test the reliability of the method a proton-127I interaction study is also performed in KI solution in glycerol. The I-H distance obtained is in satisfactory agreement with that found in the aqueous system. 相似文献
6.
R. Hertz‐Schünemann R. Dorfner C. Yeretzian T. Streibel R. Zimmermann 《Journal of mass spectrometry : JMS》2013,48(12):i-i
Resonance‐enhanced multiphoton ionisation time‐of‐flight mass spectrometry (REMPI‐TOFMS) enables the fast and sensitive on‐line monitoring of volatile organic compounds (VOC) formed during coffee roasting. On the one hand, REMPI‐TOFMS was applied to monitor roasting gases of an industrial roaster (1500 kg/h capacity), with the aim of determining the roast degree in real‐time from the transient chemical signature of VOCs. On the other hand, a previously developed μ‐probe sampling device was used to analyse roasting gases from individual coffee beans. The aim was to explore fundamental processes at the individual bean level and link these to phenomena at the batch level. The pioneering single‐bean experiments were conducted in two configurations: (1) VOCs formed inside a bean were sampled in situ, i.e. via a drilled μ‐hole, from the interior, using a μ‐probe (inside). (2) VOCs were sampled on‐line in close vicinity of a single coffee bean's surface (outside). The focus was on VOCs originating from hydrolysis and pyrolytic degradation of chlorogenic acids, like feruloyl quinic acid and caffeoyl quinic acid. The single bean experiments revealed interesting phenomena. First, differences in time–intensity profiles between inside versus outside (time shift of maximum) were observed and tentatively linked to the permeability of the bean's cell walls material. Second, sharp bursts of some VOCs were observed, while others did exhibit smooth release curves. It is believed that these reflect a direct observation of bean popping during roasting. Finally, discrimination between Coffea arabica and Coffea canephora was demonstrated based on high‐mass volatile markers, exclusively present in spectra of Coffea arabica. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Stroiney S Sun WM Wilksen T Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N 《Physical review letters》2006,96(9):092003
We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively. 相似文献
8.
Artuso M Blusk S Butt J Li J Menaa N Mountain R Nisar S Randrianarivony K Sia R Skwarnicki T Stone S Wang JC Zhang K Bonvicini G Cinabro D Dubrovin M Lincoln A Asner DM Edwards KW Naik P Briere RA Ferguson T Tatishvili G Vogel H Watkins ME Rosner JL Adam NE Alexander JP Cassel DG Duboscq JE Ehrlich R Fields L Galik RS Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Mohapatra D Onyisi PU Patterson JR Peterson D Pivarski J 《Physical review letters》2007,99(19):191801
Using a 281 pb{-1} data sample collected at the psi(3770) with the CLEO-c detector, we present the first absolute branching fraction measurement of the decay D0-->K(-)pi(+)pi(-)e(+)nu(e) at a statistical significance of about 4.0 standard deviations. We find 10 candidates consistent with the decay D0-->K(-)pi(+)pi(-)e(+)nu(e). The probability that a background fluctuation accounts for this signal is less than 4.1 x 10{-5}. We find B(D0-->K(-)pi(+)pi(-)e(+)nu(e)) = [2.8{-1.1}{+1.4}(stat)+/-0.3(syst)]x10{-4}. By restricting the invariant mass of the hadronic system to be consistent with K1(1270), we obtain the product of branching fractions B(D{0}-->K{1}{-}(1270)e{+}nu{e})xB(K1-(1270)-->K{-}pi{+}pi{-})=[2.5{-1.0}{+1.3}(stat)+/-0.2(syst)]x10{-4}. Using B(K1-(1270)-->K{-}pi{+}pi{-})=(33+/-3)%, we obtain B(D{0}-->K{1}{-}(1270)e{+}nu{e})=[7.6{-3.0}{+4.1}(stat)+/-0.6(syst)+/-0.7]x10{-4}. The last error accounts for the uncertainties in the measured K1-(1270)-->K{-}pi{+}pi{-} branching fractions. 相似文献
9.
The Team Orienteering Problem (TOP) is the generalization to the case of multiple tours of the Orienteering Problem, known
also as Selective Traveling Salesman Problem. A set of potential customers is available and a profit is collected from the
visit to each customer. A fleet of vehicles is available to visit the customers, within a given time limit. The profit of
a customer can be collected by one vehicle at most. The objective is to identify the customers which maximize the total collected
profit while satisfying the given time limit for each vehicle. We propose two variants of a generalized tabu search algorithm
and a variable neighborhood search algorithm for the solution of the TOP and show that each of these algorithms beats the
already known heuristics. Computational experiments are made on standard instances. 相似文献
10.
We address in this paper the problem of finding an optimal strategy for dealing with bottleneck machines and bottleneck parts in the cell formation process in group technology. Three types of economic decisions are considered: subcontracting, machine duplication and intercell moves. The problem is formulated as a minimum weighted node covering problem in a hypergraph, and we show that it can be solved in polynomial time by finding a maximum weighted stable set in a bipartite graph. We extend this result to cellular manufacturing systems in which the sequence of operations of each part is known in advance. 相似文献