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91.
92.
Athermal lattice gases of particles with first neighbor exclusion have been studied for a long time as simple models exhibiting a fluid-solid transition. At low concentration the particles occupy randomly both sublattices, but as the concentration is increased one of the sublattices is occupied preferentially. Here, we study a mixed lattice gas with excluded volume interactions only in the grand-canonical formalism with two kinds of particles: small ones, which occupy a single lattice site and large ones, which, when placed on a site, do not allow other particles to occupy its first neighbors also. We solve the model on a Bethe lattice of arbitrary coordination number q. In the parameter space defined by the activities of both particles, at low values of the activity of small particles (z(1)) we find a continuous transition from the fluid to the solid phase as the activity of large particles (z(2)) is increased. At higher values of z(1) the transition becomes discontinuous, both regimes are separated by a tricritical point. The critical line has a negative slope at z(1) = 0 and displays a minimum before reaching the tricritical point, so that a re-entrant behavior is observed for constant values of z(2) in the region of low density of small particles. The isobaric curves of the total density of particles as a function of the density or the activity of small particles show a minimum in the fluid phase. 相似文献
93.
Marcelo Kobelnik Douglas Lopes Cassimiro Diógenesdos Dos Santos Clóvis Augusto Ribeiro Marisa Spirandeli Crespi 《中国化学》2011,29(11):2271-2277
Solid state compounds of general formula Sr(Diclof)2·5.7H2O and Ba(Diclof)2·4.8H2O were obtained. Thermogravimetry (TG), differential scanning calorimetry (DSC), X‐ray diffraction powder patterns and microscopy analysis were used to characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters have been described here. The kinetic behaviors of these stages were evaluated from several heating rates with samples masses of 2 and 5 mg in open crucibles under a nitrogen atmosphere. The results of the present study improve the knowledge on these compounds including their dehydration and thermal stability. The obtained data depend on the mass of the sample which results in two kinetic behavior patterns. 相似文献
94.
Hydrochlorothiazide is a common diuretic antihypertensive drug of the thiazide family. Its poor aqueous solubility is one of the reasons for its limited bioavailability after oral administration. This work aimed at the development of a hydrochlorothiazide:β-cyclodextrin (HTZ:β-CD) pharmaceutical composition in order to improve water solubility and bioavailability of the drug. The HTZ:β-CD complexes were prepared by three different methods: spray-drying, freeze-drying and fluid bed. Complexes were characterized by thermal analysis, Fourier transform-infrared (FTIR) spectroscopy, powder X-ray diffractometry, NMR (2D-ROESY), scanning electron microscopy (SEM), particle analysis and intrinsic dissolution. The findings reveal that three binary systems prepared presented better solubility results in comparison with free HTZ. Increased diuretic effect was observed to HTZ:β-CD obtained by fluid bed in comparison to free drug in rats. Results taken together suggest that pharmacological effect of HTZ in complex was increased by solubility improvement promoted by cyclodextrin. 相似文献
95.
Wang Y Markwick PR de Oliveira CA McCammon JA 《Journal of chemical theory and computation》2011,7(10):3199-3207
Accelerated molecular dynamics (aMD) is an enhanced sampling technique that expedites conformational space sampling by reducing the barriers separating various low-energy states of a system. Here, we present the first application of the aMD method on lipid membranes. Altogether, ~1.5 μs simulations were performed on three systems: a pure POPC bilayer, a pure DMPC bilayer, and a mixed POPC:DMPC bilayer. Overall, the aMD simulations are found to produce significant speedup in trans-gauche isomerization and lipid lateral diffusion versus those in conventional MD (cMD) simulations. Further comparison of a 70-ns aMD run and a 300-ns cMD run of the mixed POPC:DMPC bilayer shows that the two simulations yield similar lipid mixing behaviors, with aMD generating a 2-3-fold speedup compared to cMD. Our results demonstrate that the aMD method is an efficient approach for the study of bilayer structural and dynamic properties. On the basis of simulations of the three bilayer systems, we also discuss the impact of aMD parameters on various lipid properties, which can be used as a guideline for future aMD simulations of membrane systems. 相似文献
96.
Pedroso MP Ferreira EC Hantao LW Bogusz S Augusto F 《Journal of separation science》2011,34(13):1547-1554
Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications. 相似文献
97.
Augusto Visintin 《Journal of Differential Equations》2011,250(3):1521-1552
This work deals with the homogenization of hysteresis-free processes in ferromagnetic composites. A degenerate, quasilinear, parabolic equation is derived by coupling the Maxwell-Ohm system without displacement current with a nonlinear constitutive law:
98.
Marcelo Kobelnik Douglas Lopes Cassimiro Adélia Emilia de Almeida Clóvis Augusto Ribeiro Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2011,105(2):415-419
The Al and In-diclofenac compounds were prepared. Thermogravimetry (TG) and X-ray diffraction powder patterns were used to
characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters
have been described here. The kinetic studies of these stages were evaluated from several heating rates with mass sample of
2 and 5 mg in open crucibles under nitrogen atmosphere. The results of the present study improve the knowledge on these compounds
including their dehydration and thermal stability. The obtained data leads to a dependence on the sample mass, which results
in two kinetic behavior patterns. 相似文献
99.
Renato Vessecchi Lourenço Marcelo Kobelnik Clóvis Augusto Ribeiro Fernando L. Fernonani 《Journal of Thermal Analysis and Calorimetry》2011,106(3):735-740
The Brazilian sugarcane industry shows a great amount of generated sludge which should be utilized adequately. Two sludge
samples, aerobic and anaerobic, were collected. Both were evaluated by thermogravimetry and differential thermal analysis
(DTA) as well as X-ray power diffraction. These compounds show variations of mass between 30 and 140 °C due to the dehydration
stage. The DTA curves show that the compounds have an exothermic reaction between 450 and 550 °C, which indicates that this
can be used as an energy source. Details concerning the kinetic parameters of the dehydration and thermal decomposition have
also been described here. The kinetic study of these stages was evaluated in open crucibles under nitrogen atmosphere. The
obtained data were evaluated with the isoconversional kinetic method. The results show that different activation energies
were obtained for thermal decomposition. 相似文献
100.
Pereira AM Soares AR Hausmann A Neves MG Tomé AC Silva AM Cavaleiro JA Guldi DM Torres T 《Physical chemistry chemical physics : PCCP》2011,13(25):11858-11863
In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin-phthalocyanine (P-Pc) conjugates and a pyridylfullerene. The ZnP-ZnPc conjugate was synthesized in three steps starting with a Diels-Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2(1),2(2)-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H(2)P-ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin-phthalocyanine-fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H(2)P to ZnPc followed by an intramolecular charge transfer to yield ZnP-(ZnPc)˙(+)-(C(60))˙(-) and H(2)P-(ZnPc)˙(+)-(C(60))˙(-), respectively. 相似文献