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371.
The single-phase Stefan problem was modelled numerically in approximation of the classical solution in application to melting
of a flat semitransparent sample by radiant-conductive technique in a wide range of emissivity of the phase transition front. 相似文献
372.
Duncan TV Ghoroghchian PP Rubtsov IV Hammer DA Therien MJ 《Journal of the American Chemical Society》2008,130(30):9773-9784
Formed through cooperative self-assembly of amphiphilic diblock copolymers and electronically conjugated porphyrinic near-infrared (NIR) fluorophores (NIRFs), NIR-emissive polymersomes (50 nm to 50 microm diameter polymer vesicles) define a family of organic-based, soft-matter structures that are ideally suited for deep-tissue optical imaging and sensitive diagnostic applications. Here, we describe magic angle and polarized pump-probe spectroscopic experiments that: (i) probe polymersome structure and NIRF organization and (ii) connect emitter structural properties and NIRF loading with vesicle emissive output at the nanoscale. Within polymersome membrane environments, long polymer chains constrain ethyne-bridged oligo(porphinato)zinc(II) based supermolecular fluorophore (PZn n ) conformeric populations and disperse these PZn n species within the hydrophobic bilayer. Ultrafast excited-state transient absorption and anisotropy dynamical studies of NIR-emissive polymersomes, in which the PZn n fluorophore loading per nanoscale vesicle is varied between 0.1-10 mol %, enable the exploration of concentration-dependent mechanisms for nonradiative excited-state decay. These experiments correlate fluorophore structure with its gross spatial arrangement within specific nanodomains of these nanoparticles and reveal how compartmentalization of fluorophores within reduced effective dispersion volumes impacts bulk photophysical properties. As these factors play key roles in determining the energy transfer dynamics between dispersed fluorophores, this work underscores that strategies that modulate fluorophore and polymer structure to optimize dispersion volume in bilayered nanoscale vesicular environments will further enhance the emissive properties of these sensitive nanoscale probes. 相似文献
373.
Upul JayarathneKia Williams Valeriy M. KasyanenkoJoel T. Mague Igor V. Rubtsov 《Polyhedron》2012,31(1):98-103
The iron dithiolene compounds [Fe2(mnt)4]2− [1]2− and [Fe(NO)(mnt)2]n (n = 1−, [2]1−; n = 2−, [2]2−) ([mnt]2− = maleonitriledithiolate = [(NC)2C2S2]2−) have been characterized structurally by X-ray diffraction as their [Et4N]+ salts at 100 K. Dianion [2]2− is prepared from [2]1− by reduction with Na[Et3BH] and is observed to have a bent Fe-NO angle at 149.9(5)° in contrast to the linear configuration of Fe-NO in [2]1− (180.0°). The change from linear to bent binding mode for NO, an increase of more than 0.1 Å in the Fe-N bond length, and the relative invariance of the Fe-S distances for [2]2− versus [2]1− indicate that the NO ligand is the site of reduction. The [Et3NH]+ complex of [2]1− was also identified by crystallography and found to have hydrogen bonding contacts between [Et3NH]+ and the cyano nitrogen atom of an [mnt]2− ligand. Furthermore, relatively close S?S contacts (3.602-3.615 Å) occur between [2]1− anions, which pack together in an offset, head-to-head fashion. These S?S contacts are absent in the structure of [Et4N][2]. Infrared spectra show an energy decrease for, and a significant broadening of, the NO bond stretching absorption peak in [2]2−, which is consistent with a bent NO ligand sampling a range of conformations both by facile pivoting about the Fe-N axis and by a breathing of the Fe-NO angle. 相似文献
374.
N. M. Rubtsov B. S. Seplyarskii V. I. Chernysh G. I. Tsvetkov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(5):891-895
High-speed color filming was used to study laminar spherical flame propagation at the initial stage in preliminarily mixed
stoichiometric mixtures of natural gas and isobutylene with oxygen containing krypton and carbon dioxide and in hydrogen-air
mixtures at atmospheric pressure in a bomb with a constant volume. Under experimental conditions (T
0 = 298 K, p
0 = 100 torr, spark discharge energy E
0 = 0.91 J), the dilution of mixtures with Kr and CO2 increased the time of formation of a stable flame front by more than 10 times. The introduction of a small chemically active
admixture (1.2% isobutylene) into a stoichiometric mixture of hydrogen and air sharply increased the time of formation of
a stable flame front, which was evidence of an important role played by the chemical mechanism of the reaction in the formation
of the combustion field. 相似文献
375.
The Pierre Auger collaboration have recently put forward the hypothesis that the arrival directions of the highest energy cosmic rays correlate with the subset of local active galactic nuclei (AGNs). We perform a blind test of AGN hypothesis using publicly available event sets collected by Yakutsk, AGASA, and HiRes experiments. The consistency of the procedure requires the event energies to be normalized towards the common energy scale. The number of correlating events in resulting data-set is 3 of 21 which is consistent with expected random background. 相似文献
376.
The properties of phase transitions in two-dimensional and layered systems are investigated on the basis of a discrete φ4 model by numerical and analytical methods. The only parameter a of the discrete φ4 model determines the behavior of the system and makes it possible to investigate phase transitions ranging from transitions of the displacement type (a → +0) to order-disorder type (a → +∞). The behavior of a two-dimensional system is investigated in a wide range of values of the parameter a. The temperature dependences of the squared order parameter η2(T) and the phase transition temperature T c as a function of the thickness N of the system are obtained for three characteristic values of the parameter a using the Monte Carlo method. The properties of phase transitions in the discrete φ4 model are investigated on the basis of the mean-field approximation and the independent-mode approximation. The results obtained in the numerical experiments are compared with the analytical approximations. It is shown that the mean-field approximation qualitatively describes the behavior of the phase-transition temperature T c as a function of the thickness N of the system for a wide range of values of the parameter a, and the independent-mode approximation describes quantitatively, to within 5%, the results of the numerical simulation for small values of a. 相似文献