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821.
I. Capek J. Chudej S. Janí
kov 《Journal of polymer science. Part A, Polymer chemistry》2003,41(6):804-820
The sterically stabilized emulsion polymerization of styrene initiated by a water‐soluble initiator at different temperatures has been investigated. The rate of polymerization (Rp) versus conversion curve shows the two non‐stationary‐rate intervals typical for the polymerization proceeding under non‐stationary‐state conditions. The shape of the Rp versus conversion curve results from two opposite effects—the increased number of particles and the decreased monomer concentration at reaction loci as the polymerization advances. At elevated temperatures the monomer emulsion equilibrates to a two‐phase or three‐phase system. The upper phase is transparent (monomer), and the lower one is blue colored, typical for microemulsion. After stirring such a multiphase system and initiation of polymerization, the initial coarse polymer emulsion was formed. The average size of monomer/polymer particles strongly decreased up to about 40% conversion and then leveled off. The initial large particles are assumed to be highly monomer‐swollen particles formed by the heteroagglomeration of unstable polymer particles and monomer droplets. The size of the “highly monomer” swollen particles continuously decreases with conversion, and they merge with the growing particles at about 40–50% conversion. The monomer droplets and/or large highly monomer‐swollen polymer particles also serve as a reservoir of monomer and emulsifier. The continuous release of nonionic (hydrophobic) emulsifier from the monomer phase increases the colloidal stability of primary particles and the number of polymer particles, that is, the particle nucleation is shifted to the higher conversion region. Variations of the square and cube of the mean droplet radius with aging time indicate that neither the coalescence nor the Ostwald ripening is the main driving force for the droplet instability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 804–820, 2003 相似文献
822.
Delauré B. Beck M. Golovko V. V. Kozlov V. Phalet T. Schuurmans P. Severijns N. Vereecke B. Versyck S. Beck D. Quint W. Ames F. Reisinger K. Forstner O. Deutsch J. Bollen G. Schwarz S. 《Hyperfine Interactions》2003,150(1-4):91-105
We present data from three seasons of experimental field work designed to recreate ancient Andean coastal ceramic firing techniques. Based on the recent discovery of two different archaeological ceramic production sites in the La Leche river valley of northern coastal Peru, the opportunity arose to apply Mössbauer spectroscopy and other analytical methods to reconstruct ancient firing procedures. Two sets of firings took place in 1993 and 1997 in Batán Grande using a partially restored Formative kiln from about 800 BC, local hardwood and cow dung as fuel. A third experiment followed in 2000 after the discovery of a Middle Sicán ceramics workshop in use between ca. AD 950 and 1050 at Huaca Sialupe, where an exact replica of an ancient kiln was built from local clay, and fired with local wood and cow dung. Additionally, inverted urns found at Huaca Sialupe were tested for their potential use as furnaces for metal working. Mössbauer spectroscopy was used to compare the physical and chemical state of specimens produced in the field experiments with ancient ceramics and with specimens produced in controlled laboratory experiments. 相似文献
823.
P. Pellegrino B. Garrido C. García R. Ferr J. A. Moreno J. R. Morante 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):424
The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO2 has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO2 interface (Pb centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of Pb centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the Pb defects, increasing at the same time the PL yield and the lifetime. 相似文献
824.
This paper describes how parametric cubic splines and cubicBezier curves may be used in designing a two dimensional shape.A simple aerofoil shape is designed using both methods. Themathematics is described and the shape drawn using Excel. Theeffect of varying parameters is shown in both methods. 相似文献
825.
826.
Role of the microstructure on the transport properties of Y-doped zirconia and Gd-doped ceria 总被引:1,自引:1,他引:0
Transmission electron microscopy characterizations and XPS analyses have allowed us to show the influence of the microstructure
and nanochemistry on the transport properties of Y2O3-(9 mol%)-stabilized zirconia (YSZ) and Gd2O3 (10 mol%)-doped ceria (GDC). The grain boundary electrical conductivity (σgb) and oxygen diffusion coefficient (Do) of conventional YSZ ceramics increase with the grain size, while an opposite behavior was found for GDC samples. This difference
was attributed to glassy precipitates present at YSZ grain boundaries. Furthermore, it was shown that kinetic demixing processes
take place during cooling, at the end of sintering. This causes important changes in the cationic species distribution at
interfaces and plays an important role on the transport properties of these two materials.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
827.
J.-P. Blaizot E. Iancu A. Rebhan 《The European Physical Journal C - Particles and Fields》2003,27(3):433-438
We compare our previously proposed hard-thermal-loop (HTL) resummed calculation of quark number susceptibilities using a
self-consistent two-loop approximation to the quark density with a recent calculation of the same quantity at the one-loop
level in a variant of HTL-screened perturbation theory. Besides pointing out conceptual problems with the latter approach,
we show that it severely over-includes the leading-order interaction effects, while including none of the plasmon terms, which
is the main reason for requiring improved resummation schemes.
Received: 27 June 2002 / Revised version: 23 September 2002 / Published online: 31 January 2003 相似文献
828.
829.
Y. V. Bludov A. J. Kirichenko A. E. Kogut V. V. Kutuzov V. A. Solodovnik 《Radiophysics and Quantum Electronics》2005,48(12):927-933
We experimentally study a new type of resonator, namely, a barrel-shaped dielectric resonator with whispering-gallery modes
which is formed by the cutting dielectric hemisphere. Compared with a hemispherical dielectric resonator, the E type oscillation
spectrum of such a resonator is rarefied with respect to the azimuthal index. Comparative analysis of the electromagnetic
characteristics of the barrel-shaped dielectric resonator and half-disk dielectric resonators shows that the radiation losses
of the mode energy from the spherical surface are smaller than those from the cylindrical surface. This fact stimulates the
high values of the internal Q-factor of modes of the barrel-shaped dielectric resonator.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 12, pp. 1041–1048, December 2005. 相似文献
830.
E.J. Avital 《Journal of sound and vibration》2004,270(3):483-494
A new Dispersion-Relation-Preserving (DRP) scheme has been developed using the Lax-Wendroff methodology. Two collocated grids are placed in a staggered formation and a staggered DRP scheme is used to calculate the spatial differentiation of the propagation and convection terms. A staggered filtering scheme of a six points stencil is developed to complete the transformation from one grid to another. Existing DRP Runge-Kutta schemes are used for the time marching. Stability limits and accuracy issues are investigated using a simple 1D advection equation. The new method is then tested for monopole and quadrupole radiation, diffraction effects of an aperture in a wall, and convection effects of shear flow. All demonstrate the good accuracy and numerical stability of the new method. 相似文献