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161.
Piotr Król Bożena Król Stanisław Pikus Maciej Kozak 《Colloid and polymer science》2006,285(2):169-175
Small angle X-ray scattering and differential scanning calorimetry methods were employed to characterise the internal order of structural phases present in polyurethane coatings obtained as a result of water evaporation from anionomer dispersions. Those anionomers were produced in the reaction of aromatic, cycloaliphatic and aliphatic diisocyanates with polyoxyethylene glycol, 2,2-bis-(hydroxymethyl)propionic acid and 1,6-hexamethylenediamine. The decisive effects were found from ionic and polar structures within the rigid urethane and urea segments on the ordered arrangement degree of the supermolecular structures in the obtained anionomers. That becomes apparent in differential scanning calorimetry thermograms and contributes to improved thermal stability of the produced polyurethane coatings. 相似文献
162.
Maria Cristina Righetti Maria Laura Di Lorenzo Elpidio Tombari 《European Polymer Journal》2007,43(11):4726-4738
The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (Mw = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (Mw = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the Tm = f(Tc) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated. 相似文献
163.
Measurement of the degree of crystallinity of the polymer matrix in a composite is complicated by the presence of the reinforcing additive. This is particularly the case in APC-2 in which as much as 70% can be carbon fibre. A First Law procedure, developed for determining the degree of crystallinity of PEEK, which involves direct measurement of the enthalpy changes associated with melting, crystallization and heat capacity changes, has found to be an effective method for the determination of the crystallinity of the PEEK matrix. The procedure has been applied to carbon fibre and glass fibre PEEK composites. 相似文献
164.
V Parvanova 《Journal of Thermal Analysis and Calorimetry》2006,86(2):443-447
Bi-peroxotitanate
was synthesized by a peroxo method and after thermal decomposition Bi2Ti2O7
was obtained. DTA, TG and DSC curves of Bi2[Ti2(O2)4(OH)6]5H2O were recorded and used to determine
isothermal conditions suitable for obtaining the intermediate samples corresponding
to the phases observed during the thermal decomposition. The samples were
identified by quantitative analysis, IR spectroscopy and X-ray analysis. The
experimental results were used to propose a mechanism of thermal decomposition
of the investigated compound to a nanosized Bi2Ti2O7.
The optimum conditions were also determined for obtaining Bi2Ti2O7,
which is applicable for piezosensors. 相似文献
165.
In order to understand the non-isothermal melting kinetics in the ice slurry, a differential scanning calorimetry (DSC) was used. Experimental results were compared to those obtained by a numerical simulation in which a general enthalpy method was applied. In this work the ice slurry studied consists of ice particles uniformly dispersed within a water-antifreeze liquid mixture. The effects of the heating rate and the initial antifreeze mass fraction are discussed. It has been found that the temperature gradients inside the sample of the solution become important if either heating rate increases or initial antifreeze mass fraction decreases. 相似文献
166.
A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R1‐C6H4‐{OC2N2}‐C6H4‐R2 (R1=R2=C10H21O 1 a , p‐C10H21O‐C6H4‐C?C 3 a , p‐CH3O‐C6H4‐C?C 3 b ; R1=C10H21O, R2=CH3O 1 b , (CH3)2N 1 c ; F 1 d ; R1=C10H21O‐C6H4‐C?C, R2=C10H21O 2 a , CH3O 2 b , (CH3)2N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH2Cl2 solution, these compounds displayed a room‐temperature emission with λmax at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions. 相似文献
167.
New methods are suggested for the determination of the charge density of acrylamide/acrylate copolymers.13C nuclear magnetic resonance spectroscopy was used to determine the comonomer ratio by comparing the peak intensities of the methine carbon in acrylamide and acrylate monomers. Results were compared with those obtained by conductometric and potentiometric titration and were found to be in good agreement. Differential scanning calorimetry was employed to determine the glass transition temperatures (T
g) of the copolymers. A master curve was established by plottingT
g versus charge density of the copolymers previously determined by NMR and conductometric titration. Compositions of poly(acrylamide-co-acrylate) samples can thus be determined by measuring theT
g and reading the percent composition directly from the master curve. 相似文献
168.
Rodová M. Brožek J. Knížek K. Nitsch K. 《Journal of Thermal Analysis and Calorimetry》2003,71(2):667-673
Phase transitions in ternary caesium lead bromide (CsPbBr3) were studied by means of DSC, TMA and high temperature X-ray diffraction. The samples were prepared from the solution by
water evaporation and from the melt. on the DSC curves as well as on the temperature dependence of the lattice constants of
CsPbBr3 only two effects were found belonging to the earlier published phase transitions at 88 and 130°C and no further effects.
Linear thermal expansion coefficient α of individual CsPbBr3 modifications were calculated from both TMA and high temperature X-ray diffraction. The structural parameters of the room
temperature orthorhombic phase were refined and the results are presented. CsPbBr3 prepared from the solution contained about 10% of CsPb2Br5 and so the DSC curve of pure CsPb2Br5 was also measured and an effect at a temperature of 68.5°C was found.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
169.
This paper presents DSC and NMR study of how the kerotolytic drug, salicylic acid (SA), affects the thermotropic and morphological behavior of a model membrane, dipalmitoyl phosphatidic acid (DPPA). The membrane-drug system has been studied in the multilamellar vesicular (MLV) and in the unilamellar vesicular (ULV) forms, for SA/DPPA molar ratios from 0 to 0.5. The mode of interaction of SA molecules with DPPA is similar in MLV and ULV. Chain-melting transition becomes sharper and shifts to higher temperatures in the presence of the drug, implying an enhanced co-operativity of the acyl chains. NMR and DSC data indicate that the drug molecules are located in the aqueous interfacial region neighboring the lipid headgroups. The membrane becomes more rigid in the presence of the drug molecules, due to a stronger interaction between the lipid headgroups leading to reduced permeability. ULVs are destroyed by even a short equilibration at room temperature, whereas prolonged equilibration of the MLV only leads to a slightly reduced interaction between the lipid headgroups due to sequestering of the drug molecules in the interfacial aqueous region. 相似文献
170.
Giorgio Parisi 《Journal of statistical physics》1980,23(1):49-82
We review the physical principles which are at the basis of recent field-theoretic computations of the critical exponents in two- and three-dimensional systems. We concentrate on those points that do not show up explicitly in the more standard-expansion: they must be discussed with care if one uses a perturbative approach at fixed space dimensions (the loop expansion). We present in detail simple computations of the critical exponents, while we summarize the results of longer and more accurate computations. 相似文献