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661.
Absorption spectra of V2O5 layers deposited from gels of various V4+ contents C were studied from near UV down to near IR. The high absorption region due to the charge transfer transition extends above ≈ 2 eV. Whatever C the optical gap is ≈ 2.25 eV. On the low energy side an Urbach tail is observed whose slope increases with C. In the near infrared absorption is related to the V4+ ions and increases linearly with C. The absorption band due to the optically induced polaron hopping is detected. The corresponding maximum Emax suffers a red shift when C increases. The experimental Emax data are very close to the values predicted from the polaron and disorder energies as deduced from the conductivity study in an earlier paper. The slight difference between the two sets of data allowed us to estimate the transfer integral J ≈ 0.015 eV. 相似文献
662.
We develop a flexible discrete-time hedging methodology that minimizes the expected value of any desired penalty function of the hedging error within a general regime-switching framework. A numerical algorithm based on backward recursion allows for the sequential construction of an optimal hedging strategy. Numerical experiments comparing this and other methodologies show a relative expected penalty reduction ranging between 0.9% and 12.6% with respect to the best benchmark. 相似文献
663.
We demonstrate a position-sensing technique that relies on the inherent sensitivity of chaos, where we illuminate a subwavelength object with a complex structured radio-frequency field generated using wave chaos and nonlinear feedback. We operate the system in a quasiperiodic state and analyze changes in the frequency content of the scalar voltage signal in the feedback loop. This allows us to extract the object's position with a one-dimensional resolution of ~λ/10,000 and a two-dimensional resolution of ~λ/300, where λ is the shortest wavelength of the illuminating source. 相似文献
664.
Jean-Philippe Gauthier Sébastien Cauet Pascal Martin 《Journal of sound and vibration》2011,330(24):5785-5790
This article presents a real-life application for the extremal harmonic active control of power [1] applied on a hybrid engine setup. The active control was adapted for a hybrid powertrain constituted of a one-cylinder diesel engine coupled with a permanent magnet synchronous machine. The problem was formulated in the harmonic domain and the control objective was to extremalize energetic criterions. Three criterions were considered: minimizing the speed ripple of the engine, maximizing the mechanical reactive power (mechanical impedance adaptation) and maximizing the active electric power for energy harvesting. The results show that, for the first and second orders of the ripple, speed oscillations can be completely cancelled and reactive power and active power can be optimized on-line. The implicit extremal controller converged rapidly, remaining stable even when the mean engine speed changed abruptly. These results confirm the robustness and the applicability of the extremal harmonic active control for industrial applications. 相似文献
665.
R. Chaplin D. MacManus F. Leopold T. Gauthier B. Martinez T. Birch 《Experiments in fluids》2011,50(2):491-507
Aerodynamic interference between high-speed slender bodies can detrimentally affect the force and moment characteristics.
This is investigated through a wind tunnel study using pressure sensitive paint and force measurements on a receiver body
placed adjacent to a generator body. The aim of this paper is to understand both the force and moment changes as well as the
underlying aerodynamics of the interference loads which are induced by the disturbance flowfield. The impact of receiver incidence
and the strength of the disturbance field are also assessed. The observed interference loads primarily depend on a complex
balance of static pressure footprints and tend to be bespoke to each configuration. As a result, overall trends are difficult
to extract, but in general the magnitude of the interference loads increases when the receiver is at incidence and also when
the strength of the imposed disturbance flowfield increases. 相似文献
666.
Cissampelos capensis, commonly known by the Afrikaans name "dawidjies" or "dawidjieswortel", is the most important and best known medicinal plant of the family Menispermaceae used by the Khoisan and other rural people in the western region of South Africa. The main alkaloids in the leaves, stems and rhizomes were isolated and identified. Several of the main compounds were previously found in species of the related genus Antizoma and this similarity indicates that the two genera are closely related if not congeneric. Bulbocapnine (an aporphine alkaloid), dicentrine (an aporphine alkaloid) and salutaridine (a morphinane alkaloid) were the main alkaloids in the leaves, while bulbocapnine, cissacapine, cycleanine and insularine (the last three are bisbenzyltetrahydro-isoquinoline alkaloids) are the major compounds in the stems. The rhizome contains mostly bisbenzyltetrahydroisoquinoline alkaloids, with 12-O-methylcurine, cissacapine and cycleanine as the main ones. Alkaloids appear to be quite variable within different plant parts and different provenances, as confirmed by the difference in alkaloid patterns between coastal and inland forms of Cissampelos capensis (the morphinane alkaloid salutaridine, for example, is the major leaf alkaloid along the coast but is practically absent from the inland form of the species). The variety of alkaloids identified may contribute to the medicinal value of this species. The data on alkaloidal variation in the species has potential value and practical applications in chemotaxonomy, toxicology and pharmacognosy. 相似文献
667.
We present a novel method for passive separation of microfluidic droplets by size at high throughput using deterministic lateral displacement (DLD). We also show that droplets containing Saccharomyces cerevisiae shrink significantly during incubation while droplets containing only yeast media retain or slightly increase their size. We demonstrate the DLD device by sorting out shrunken yeast-cell containing droplets from 31% larger diameter droplets which were generated at the same time containing only media, present at a >40-fold excess. This demonstrates the resolving power of droplet separation by DLD and establishes that droplets can be separated for a biological property of the droplet contents discriminated by a change of the physical properties of the droplet. Thus suggesting that this technique may be used for e.g. clonal selection. The same device also separates 11 μm from 30 μm droplets at a rate of 12,000 droplets per second, more than twofold faster than previously demonstrated passive hydrodynamic separation devices. 相似文献
668.
Alexandre François-Heude Emmanuel Richaud Julien Leprovost Michel Heninger Helene Mestdagh Eric Desnoux Xavier Colin 《Polymer Testing》2013,32(5):907-917
Analysis of volatile organic compounds (VOCs) during PP thermal oxidation under three oxygen partial pressures (0%, 21% and 100% of atmospheric pressure) at 140 °C was performed by proton transfer reaction coupled with Fourier transform ion cyclotron resonance mass spectrometry. Six main VOCs were identified: acetone, acetic acid, 2,4-pentanedione, acetaldehyde, formaldehyde and methyl acrolein. Their formation was shown to obey two main reaction pathways, both involving methyne units as driving oxidation sites: (i) the widely accepted chain scission mechanism of tertiary alkoxy radicals, which generates primary radicals undergoing secondary reactions leading to the oxidation of methylene units; (ii) the chain scission mechanism occurring on tertiary alkyl radical, which is proposed here as a realistic path leading to methyl acrolein. The relative proportions of the six main VOCs depend on the oxygen partial pressure, which mostly impacts the oxidation of methylene units rather than the competition between the two previous paths. 相似文献
669.
Dr. Jun Zhu Dr. Heather A. Fogarty Dr. Helene Möllerstedt Dr. Maria Brink Dr. Henrik Ottosson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10698-10707
A density functional theory study on olefins with five‐membered monocyclic 4n and 4n+2 π‐electron substituents (C4H3X; X=CH+, SiH+, BH, AlH, CH2, SiH2, O, S, NH, and CH?) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet‐state (T1) potential‐energy surface (PES) for twisting about olefinic C?C bonds. It exploited both Hückel’s rule on aromaticity in the closed‐shell singlet ground state (S0) and Baird’s rule on aromaticity in the lowest ππ* excited triplet state. The compounds CH2?CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0‐antiaromatic/T1‐aromatic (C5H4+) to strongly S0‐aromatic/T1‐ antiaromatic (C5H4?). Our hypothesis is that the shapes of the T1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T1 [ΔE(T1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ΔE(T1) and the (anti)aromaticity changes of the C4H3X groups, as measured by the zz‐tensor component of the nucleus‐independent chemical shift ΔNICS(T1;1)zz, are found both for sets A and B separately (linear fits; r2=0.949 and 0.851, respectively) and for the two sets combined (linear fit; r2=0.851). For sets A and B combined, strong correlations are also found between ΔE(T1) and the degree of S0 (anti)aromaticity as determined by NICS(S0,1)zz (sigmoidal fit; r2=0.963), as well as between the T1 energies of the planar olefins and NICS(S0,1)zz (linear fit; r2=0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T1 PESs suitable for adiabatic Z/E photoisomerization. 相似文献
670.
Abstract Ultrasonic (70 W, 20 kHz) solution (2% THF) degradations of polystyrene (PS), poly(α-methylstyrene) (PαMeS), poly(p-isopropyl α-methylstyrene) (PpiPrαMeS), poly(p-chlorostyrene) (PpCIS), poly(p-bromostyrene) (PpBrS), and poly(p-methoxystyrene) (PpOMeS) have been carried out in tetrahydrofuran at 27° C. The average number of chain scissions S (where S = [(M n)0/(M n)t] - 1), computed from the overall values of [(M n)0 and (M n)t, were found to be different from those of S' (where S' = α([(M n)0/(M n)t] - 1)) based on the component (only that part of the polymer which is involved in degradation) data of the weight fraction (α), (M n)0, and (M n)t), S' for polystyrene and substituted polystyrene follows the order PS gt; PpCIS gt; PpiPrαMeS gt; PpBrS gt; PpOMeS gt; PαMeS. In the case of PS where degradations were also carried out at -20°C, lowering of the temperature increased the weight fraction of polymer degraded as well as S. Based on the viscosity and GPC data, it is concluded that the ultrasonic solution degradation of PS does not lead to branched polymers. 相似文献