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911.
912.
913.
Helena Valentová Markéta Ilčíková Klaudia Czaniková Zdenko Špitalský Miroslav Šlouf Jan Nedbal 《Journal of Macromolecular Science: Physics》2014,53(3):496-512
A comparative study of the dielectric and mechanical properties of ethylene vinyl acetate copolymer (EVA) filled with various concentrations of pristine and modified carbon nanotubes is reported. The surface of the carbon nanotubes was modified with 4-(2-(cholesteryloxycarboxy)ethyl) phenyl to improve the interaction of the filler with the block copolymer matrix. The improved interaction and the better dispersion of the modified carbon nanotubes (mMWCNTs) were demonstrated by a detailed study of the EVA molecular mobility through dynamic mechanical analysis and broadband dielectric relaxation spectroscopy. The storage modulus of the nanocomposite with 6 wt.% of mMWCNTs at ?50°C was enhanced by 103%, whereas for the nanocomposite with the same amount of unmodified filler, the storage modulus was only enhanced by 76% compared to the pure elastomeric matrix. This difference is more pronounced in the rubbery region in which the storage moduli were increased by 117% and 48% for the composite with the modified and unmodified fillers, respectively. The morphologies of the nanocomposites were studied with scanning and transmission electron microscopies to demonstrate the dispersion of the mMWCNTs within the EVA matrix. 相似文献
914.
Vesna Đorđević Željka AntićMarko G. Nikolić Miroslav D. Dramićanin 《Journal of Physics and Chemistry of Solids》2014
Eu3+-doped La2O3 nanocrystalline powder was prepared by polymer complex solution method and further used for preparation of Eu3+-doped La(OH)3. Structural and optical characterization was carried out by powder X-ray diffraction and photoluminescent spectroscopy. XRD measurements confirmed the formation of hexagonal La2O3 and its recrystallization into La(OH)3 in a humid atmosphere. Excitation spectra show redshift of host lattice and charge transfer emission bands in La(OH)3 while bands that correspond to Eu3+f–f transitions are placed at same wavelengths in both samples. Photoluminescence spectra recorded over the temperature range from 10 K to 300 K show that intensities of emission lines in Eu3+-doped La2O3 do not depend on temperature as much as in La(OH)3 sample. Observed dominant 5D0→7F2 and markedly visible 5D0→7F0 emissions in doped La2O3 indicate that Eu3+ ion is located in a structural site without an inversion center. On the other hand, in Eu3+-doped La(OH)35D0→7F0 transition is barely visible while 5D0→7F2 is not prominent, and with temperature drop three 5D0→7FJ (J=1, 2, 4) transitions become almost of the same intensity. In both La2O3 and La(OH)3 structures Eu3+ ion replaces La3+ in non-centrosymmetric C3v and C3h crystallographic sites, respectively, and difference in symmetry of the crystal field around europium ion is explained by comparing shape and volume of these sites. Decay times of the 5D0- level recorded over the temperature range 10−300 K revealed that emission lifetime values in La2O3 (~0.7 ms) are almost two times higher than in La(OH)3 (~0.4 ms), and unlike in La2O3, lifetime in La(OH)3 is temperature dependent. 相似文献
915.
We report on the experimental verification of quantum non-Gaussian character of a heralded single-photon state with a positive Wigner function. We unambiguously demonstrate that the generated state cannot be expressed as a mixture of Gaussian states. Sufficient information to witness the quantum non-Gaussian character is obtained from a standard photon anticorrelation measurement. 相似文献
916.
A novel capillary electrophoretic method for the separation of pancuronium (PM) and vecuronium (VM) ions utilizing capacitively coupled contactless conductivity detection was devised and validated. The separation was carried out in bare fused-silica capillaries (50 μm id, 75/45 cm) at 25°C. Optimal BGE was 50 mM borate buffer of pH 9.5 containing 12.5 mg/mL of (2-hydoxypropyl)-γ-CD. The samples were injected hydrodynamically at 1000 mbar for 3 s. Separation was performed at +30 kV. Under such conditions the PM and VM were base-line resolved and the separation took < 4 min. For quantification phenyltrimethylammonium iodide was used as internal standard. Calibration curves were linear for both pancuronium bromide (PMB) and vecuronium bromide (VMB) in the range 25-250 μg/mL with r> 0.9968. The limits of detection were 7 and 6?μg/mL for PMB and VMB, respectively. The accuracy tested by recovery experiment at three concentration levels of added PMB and VMB was satisfactory (95.7-102.7%, n =3, with RSD < 2.61%). The method was successfully applied to the assay of PMB and VMB in commercial injection solutions. 相似文献
917.
Magdaléna Hromadová Viliam Kolivoška Miroslav Gál Lubomír Pospíšil Romana Sokolová Michal Valášek 《Journal of inclusion phenomena and macrocyclic chemistry》2011,70(3-4):461-469
An extended viologen dication 1, containing one viologen subunit, was used as a model for the inclusion complex formation between cyclodextrin (CD) molecules and molecular wires comprising several subunits. UV–Vis and fluorescence spectroscopic measurements confirmed the formation of two types of the inclusion complexes 1:1 and 2:1 between αCD and 1 in the aqueous solution containing 20% of ethanol. The complex formation constants were obtained from the fluorescence spectral changes: K a = 25 ± 3 mM?1 for [αCD–1] complex and K a = 0.21 ± 0.07 mM?2 for [(αCD)2–1] complex, respectively. Cyclodextrins βCD and γCD do not form the inclusion complexes with 1 in these aqueous solutions. The time-dependent differential capacitance measurements confirmed the adsorption of 1 in the form of a complex at the electrode/electrolyte interface. These studies were conducted with the aim to find the most suitable CD cavity that would separate individual molecular wires from each other on the electrode/electrolyte interface. 相似文献
918.
Štěpánek M Matějíček P Procházka K Filippov SK Angelov B Šlouf M Mountrichas G Pispas S 《Langmuir : the ACS journal of surfaces and colloids》2011,27(9):5275-5281
Formation of polyelectrolyte-surfactant (PE-S) complexes of poly[3,5-bis(trimethylammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) and sodium dodecyl sulfate (SDS) in aqueous solution was studied by dynamic and electrophoretic light scattering, small-angle X-ray scattering (SAXS), atomic force microscopy, and fluorometry, using pyrene as a fluorescent probe. SAXS data from the QNPHOS-PEO/SDS solutions were fitted assuming contributions from free copolymer, PE-S aggregates described by a mass fractal model, and densely packed surfactant micelles inside the aggregates. It was found that, unlike other systems of a double hydrophilic block polyelectrolyte and an oppositely charged surfactant, PE-S aggregates of the QNPHOS-PEO/SDS system do not form core-shell particles and the PE-S complex precipitates before reaching the charge equivalence between dodecyl sulfate anions and QNPHOS polycationic blocks, most likely because of conformational rigidity of the QNPHOS blocks, which prevents the system from the corresponding rearrangement. 相似文献
919.
Sulc M Fadrhoncová I Jelínková M Chudomelová M Felsberg J Olšovská J 《Journal of chromatography. A》2011,1218(1):83-91
A new separation and quantification method using ultra high-performance liquid chromatography (UHPLC) with UV detection was developed for the detection of sibiromycin in fermentation broth of Streptosporangium sibiricum. The solid phase extraction method based on cation-exchange was employed to pre-concentrate and purify fermentation broth containing sibiromycin prior to UHPLC analysis. The whole assay was validated and showed a linear range of detector response for the quantification of sibiromycin in a concentration from 3.9 to 250.0 μg mL−1, with correlation coefficient of 0.999 and recoveries ranging from 71.66 ± 3.55% to 74.76 ± 5.18%. Method limit of quantification of the assay was determined as 0.18 μg mL−1 and was verified with resulting RSD of 9.6% and accuracy of 97.6%. The developed assay was used to determine the sibiromycin production in 12 different fermentation broths. Moreover, several natural sibiromycin analogues/derivatives were described with pilot characterization using off-line mass spectrometry: the previously described dihydro-sibiromycin (DH-sibiromycin) and tentative bis-glycosyl forms of sibiromycin and its dihydro-analogue. 相似文献
920.
O. Kaman P. Veverka Z. Jirák M. Maryško K. Knížek M. Veverka P. Kašpar M. Burian V. Šepelák E. Pollert 《Journal of nanoparticle research》2011,13(3):1237-1252
The magnetic nanoparticles of La0.75Sr0.25MnO3 perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent
mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods
and probed by DC magnetic measurements. The nanoparticles of the mean crystallite sizes 11–40 nm exhibit T
C in the range of ≈310–347 K and the sample possessing 20-nm crystallites was identified as the most suitable for hyperthermia
experiments. In order to obtain a colloidally stable suspension and prevent toxic effects, the selected magnetic cores were
further encapsulated into silica shell using tetraethoxysilane. The detailed magnetic studies were focused on the comparison
of the raw product, the bare nanoparticles after mechanical processing and the silica-coated nanoparticles, dealing also with
effects of size distribution and magnetic interactions. The heating experiments were carried out in an AC field of frequencies
100 kHz–1 MHz and amplitude 3.0–8.9 kA m−1 on water dispersions of the samples, and the generated heat was deduced from their warming rate taking into account experimentally
determined thermal losses into surroundings. The experiments demonstrate that the heating efficiency of the coated nanoparticles
is generally higher than that of the bare magnetic cores. It is also shown that the aggregation of the bare nanoparticles
increases heating efficiency at least in a certain concentration range. 相似文献