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51.
The magnetic properties of synthetic goethite, precipitated from a SiO2-containing Fe(III) solution, have been studied. The Mössbauer spectra show the coexistence of a quadrupole doublet and a magnetically split component in a large temperature range. The area ratio of these two components depends strongly on temperature, indicating a normal superparamagnetic behaviour of isolated crystallites. This is in contrast to the behaviour normally exhibited by pure samples of microcrystalline goethite, in which strong magnetic interactions among the crystallites lead to a superferromagnetic behaviour. The results show that the magnetic interactions among the crystallites are drastically diminished when amorphous SiO2 separates the goethite crystallites. 相似文献
52.
This paper presents a new spectral model for solving the fully nonlinear potential flow problem for water waves in a single horizontal dimension. At the heart of the numerical method is the solution to the Laplace equation which is solved using a variant of the ‐transform. The method discretizes the spatial part of the governing equations using the Galerkin method and the temporal part using the classical fourth‐order Runge‐Kutta method. A careful investigation of the numerical method's stability properties is carried out, and it is shown that the method is stable up to a certain threshold steepness when applied to nonlinear monochromatic waves in deep water. Above this threshold artificial damping may be employed to obtain stable solutions. The accuracy of the model is tested for: (i) highly nonlinear progressive wave trains, (ii) solitary wave reflection, and (iii) deep water wave focusing events. In all cases it is demonstrated that the model is capable of obtaining excellent results, essentially up to very near breaking. 相似文献
53.
Tommy Sonne Alstrøm Mads Peter Sørensen Niels Falsig Pedersen Søren Madsen 《Acta Appl Math》2011,115(1):63-74
The time-dependent Ginzburg-Landau equation is solved numerically for type-II superconductors of complex geometry using the
finite element method. The geometry has a marked influence on the magnetic vortex distribution and the vortex dynamics. We
have observed generation of giant vortices at boundary defects, suppressing the superconducting state far into the superconductor. 相似文献
54.
Yoshikawa HY Rossetti FF Kaufmann S Kaindl T Madsen J Engel U Lewis AL Armes SP Tanaka M 《Journal of the American Chemical Society》2011,133(5):1367-1374
Thin hydrogel films based on an ABA triblock copolymer gelator [where A is pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) and B is biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC)] were used as a stimulus-responsive substrate that allows fine adjustment of the mechanical environment experienced by mouse myoblast cells. The hydrogel film elasticity could be reversibly modulated by a factor of 40 via careful pH adjustment without adversely affecting cell viability. Myoblast cells exhibited pronounced stress fiber formation and flattening on increasing the hydrogel elasticity. As a new tool to evaluate the strength of cell adhesion, we combined a picosecond laser with an inverted microscope and utilized the strong shock wave created by the laser pulse to determine the critical pressure required for cell detachment. Furthermore, we demonstrate that an abrupt jump in the hydrogel elasticity can be utilized to monitor how cells adapt their morphology to changes in their mechanical environment. 相似文献
55.
X-ray diffraction data of high quality measured to high resolution on crystals of the two pentitol epimers ribitol (centric) and xylitol (acentric) at 101, 141, and 181 K and data on the two compounds previously recorded at 122 K have formed the basis for multipole refinements with the VALRAY system. Our analysis showed that it is possible to obtain a reliable crystal electron density for an acentric compound (xylitol) from X-ray diffraction data and that the thermal motion can be deconvoluted from the static density in this temperature range. The Bader-type topological analysis of the static electron densities revealed virtually identical intramolecular interactions as well as very similar hydrogen bond interactions of ribitol and xylitol; the only minor differences are found in the weaker intermolecular interactions. The high-level periodic DFT calculations are in accordance with the thermodynamic measurements that show that the two pentitols have identical sublimation energies. A rigid body normal coordinate analysis was performed on the atomic displacement parameters obtained at the four different temperatures. The translational and librational mean square deviations derived through this analysis were used in a quantum statistical approach to derive frequencies of the corresponding harmonic oscillators. The analysis showed a consistent vibrational model for all temperatures. The frequencies were subsequently used to calculate crystal entropies assuming an Einstein-type behavior. These calculations show that the crystal entropy of ribitol is 8 J K(-1) mol(-1) higher than the crystal entropy of xylitol, confirming that it is a difference in the entropy of the two compounds that causes the difference in their free energy. Our results presented in this Article show the potential to use X-ray diffraction data to obtain physicochemical properties of crystals. 相似文献
56.
57.
J. H. Bowie P. Y. White J. C. Wilson F. C. V. Larsson S.-O. Lawesson J.
Madsen C. Nolde G. Schroll 《Journal of mass spectrometry : JMS》1977,12(4):191-195
+E spectra derived from the non-decomposing anion of some sulphur compounds are independent of the pressure of the collision gas. The compounds chosen for study contain peaks produced from either ortho effects or skeletal rearrangement fragments in their conventional positive ion spectra. The dissociative +E spectra are either devoid of skeletal rearangement ions or alternatiely contain such peaks in small abundance. In contrast, peaks derived from ortho reactions are present in high abundance. 相似文献
58.
59.
I.E. Grey I.C. Madsen J.A. Watts L.A. Bursill J. Kwiatkowska 《Journal of solid state chemistry》1985,58(3):350-356
A phase study of the Cs2OTiO2 system in the composition range 75–100 mole% TiO2 and the temperature range 850–1200°C revealed the existence of two new cesium titanates, with compositions Cs2Ti5O11 and Cs2Ti6O13. The former compound undergoes a reversible hydration reaction below 200°C to form Cs2Ti5O11 · (1 + x)H2O, 0.5 < x < 1. The structures of the three phases have been determined. They are based on corrugated layers of edge-shared octahedra, with cesium ions (and H2O) packing between the layers. In Cs2Ti6O13, the layers are continuous in two dimensions, whereas in Cs2Ti5O11 and Cs2Ti5O11 · (1 + x)H2O, the layers are periodically stepped to give 5-octahedra wide, corner-linked ribbons. 相似文献
60.
G. Perrin D. Lebrun J. Chauvin P. Martin P. De Santignon D. Eppel H.V. Geramb H.L. Yadav V.A. Madsen 《Physics letters. [Part B]》1977,68(1):55-57
Angular distributions for polarized proton inelastic scattering cross sections along with the analysing power for the reaction at Ep=42.5, 44.0 and 49.3 MeV have been measured. A semidirect reaction analysis augments the evidence for octupole giant resonance strength in the 30 to 50 MeV energy region. 相似文献