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101.
Pérez Pavón JL Guerrero Peña A García Pinto C Moreno Cordero B 《Journal of chromatography. A》2004,1047(1):101-109
The direct coupling of a headspace sampler with a mass spectrometer is proposed as a screening tool for the rapid detection of soil pollution by hydrocarbons from petroleum and derivatives. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of the sample analysed. Suitable treatment of the signal by chemometric techniques allows unequivocal characterisation of the different types of sample. The use of fast gas chromatography with a mass spectrometer detector coupled to the headspace sampler allows identification of the major hydrocarbons present in the mineral and organic polluted samples, interpretation of the results obtained, and demonstrates the analytical potential of headspace-mass spectrometry coupling. 相似文献
102.
本文介绍了尼龙1010的结晶过程与动力学、晶体的熔融与转化;并论述了其稀溶液、热降解与动态力学性质及共聚、共混、填充、增强、交联改性方面的研究进展。 相似文献
103.
104.
105.
Annealing experiments have been carried out at a few degrees below the melting point of different polyethylenes (LDPE, LLDPE,
HDPE), of polypropylene (PP) and of Nylon-6. The heat capacities decrease during the annealing, within a 2-4 min time scale,
to a lower value which corresponds to the extrapolated heat capacity values obtained for the cooling cycle when the polymer
is cooled from the melt. Heat capacities in the heating cycle following the cooling cycle of PP, Nylon-6 and HDPE have the
same value as during the cooling section. This is not the case for LDPE and LLDPE.
Exothermic total heat flow in the cooling section following the annealing indicates that the crystallisation takes place during
the cooling rather than during the annealing period. The total melting enthalpy measured before and after the annealing cycle
is the same.
The reversing heat flow shows an excellent fit to the change of the crystallinity measured by small angle scattering of synchrotron
radiation during a heating cycle at temperatures below the melting peak.
A coupled thermodynamic interaction of the crystalline and the amorphous phases is concluded from this study. This kind of
interaction is possible at the lateral end of polymeric chains incorporated into the crystalline phase. This is an indication
of the portion of tie molecules in the system, i.e. the portion of fringed micelle type of crystalline morphology with respect
to that of folded chain lamellae.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
106.
J. Kaloustian 《Journal of Thermal Analysis and Calorimetry》1992,38(6):1377-1389
Nineteen different polymers having no melting endotherm (foam urea-formol, PVC, vinyl polyacetate, vinyl polybutyral, polymethacrylates, polystyrene and its copolymers) are studied by DTA. The identification is realized due to endothermic decomposition peak and exothermic peaks, according to the general method which has been described previously.
Zusammenfassung Mittels DTA wurden neunzehn verschiedene Polymere ohne endothermen Peak beim Schmelzen untersucht (Schaum Carbamid-Formol, PVC, Vinylpolyacetat, Vinylpolybutyral, Polymethacrylate, Polystyrol und seine Kopolymere). Die Identifizierung erfolgte in Übereinstimmung mit der unlängst beschriebenen allgemeinen Methode anhand der endothermen Zersetzung speaks und der exothermen Peaks.相似文献
107.
The nucleation frequency of isotactic polypropylene shows for certain molecular weight distributions during isothermal crystallization
a “stepwise” development of the nuclei as a function of time. The resulting curve can be fitted by a superposition of exponential
functions assuming a separate nucleation density for each nucleation step. The multimodal nucleation is discussed as a consequence
of molecular fractionation effects during crystallization.
Received: 23 October 1997 Accepted: 12 May 1998 相似文献
108.
Wei-ping Gao Yu Bai Er-qiang Chen~ 《高分子科学》2005,(3):275-284
Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer(PEO-b-PB)in THFsolution were obtained by adding a selective solvent for PB blocks,followed by cross-linking the PB shells.Themorphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy andtransmission electron microscopy.The average behaviors of the PEO crystallization and melting confined within thenanostructured particles were studied by using differential scanning calorimetry experiments.For the deeply cross-linkedsample(SCL-1),the crystallization of the PEO blocks was fully confined.The individual nanoparticles only crystallized atvery low crystallization temperatures(T_cs),wherein the homogenous primary nucleation determined the overallcrystallization rate.For the lightly cross-linked sample(SCL-2),the confinement effect was T_c dependent.At T_c(?)42℃,thecrystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer.At T_c>42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same T_c. 相似文献
109.
Plant cells have been immobilized in alginate, where they have been shown to retain their biological activity. Such systems
can be utilized for bioconversions. 相似文献
110.
René Androsch 《European Polymer Journal》2007,43(1):93-108
The melt-crystallization of an oligo[(R)-3-hydroxybutyrate] with five repeating units has been analyzed using standard and temperature-modulated calorimetry, optical microscopy, and atomic force microscopy. Specimens of different crystallinity and supermolecular structure were generated by variation of the rate of cooling of a quiescent melt, or by variation of the temperature of isothermal crystallization. Completely amorphous samples can be obtained by cooling of the melt at a rate of 40 K min−1, or faster, to a temperature lower than the glass transition. The crystallinity depends on the crystallization temperature. The maximum enthalpy-based crystallinity of about 40-45% is obtained by crystallization at temperatures lower than the temperature of the maximum crystallization rate, which is between 310 and 320 K. Analysis of the apparent heat capacity in metastable structural equilibrium reveals reversible melting at temperatures between 320 and 370 K by observation of an excess heat capacity above the level of the vibrational heat capacity, i.e., in the temperature range of irreversible reorganization and melting. The reversible melting is discussed in the context of coupling of the crystalline and amorphous phases, and compared to earlier studies on oligoethylene and oligo(oxyethylene). The presence of crystals causes formation of a rigid amorphous fraction of about 30% at a crystallinity of 40%. Optical and atomic force microscopy reveal spherulitic crystallization. At relatively high crystallization temperature, and in the early stage of the crystallization process, dendrites are observed which finally yield spherulites of decreased perfection. Larger spherulites of higher perfection grow at relatively low crystallization temperature, as deduced from the appearance of the Maltese cross, and the regularity of banding. The band spacing is less than 5 μm, as is accurately determined by atomic force microscopy. The temperature dependence of the spherulitic growth rate is in accord with the calorimetric analysis of the crystallization rate. 相似文献