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981.
982.
Vera Lúcia Carbone José Gaspar Ruas-Filho 《Journal of Mathematical Analysis and Applications》2005,303(1):220-241
In this paper we study one dimensional parabolic problems that arise from composite materials. We show that the eigenvalues and eigenfunctions of the associated linear unbounded operator have the Sturm-Liouville property and the nonincrease of the lap number along the solutions. These results are used to show that the stable and unstable manifolds of equilibrium points are transversal. 相似文献
983.
A dispersive liquid–liquid microextraction procedure was developed to extract nine fluoroquinolones in porcine blood, six of which were quantified using a univariate calibration method. Extraction parameters including type and volume of extraction and dispersive solvent and pH, were optimized using a full factorial and a central composite designs. The optimum extraction parameters were a mixture of 250 μL dichloromethane (extract solvent) and 1250 μL ACN (dispersive solvent) in 500 μL of porcine blood reached to pH 6.80. After shaking and centrifugation, the upper phase was transferred in a glass tube and evaporated under N2 steam. The residue was resuspended into 50 μL of water–ACN (70:30, v/v) and determined by CE method with DAD, under optimum separation conditions. Consequently, a tenfold enrichment factor can potentially be reached with the pretreatment, taking into account the relationship between initial sample volume and final extract volume. Optimum separation conditions were as follows: BGE solution containing equal amounts of sodium borate (Na2B4O7) and di‐sodium hydrogen phosphate (Na2HPO4) with a final concentration of 23 mmol/L containing 0.2% of poly (diallyldimethylammonium chloride) and adjusted to pH 7.80. Separation was performed applying a negative potential of 25 kV, the cartridge was maintained at 25.0°C and the electropherograms were recorded at 275 nm during 4 min. The hydrodynamic injection was performed in the cathode by applying a pressure of 50 mbar for 10 s. 相似文献
984.
Dr. Uvinduni I. Premadasa Dr. Vera Bocharova Audrey R. Miles Diana Stamberga Stella Belony Dr. Vyacheslav S. Bryantsev Adnan Elgattar Prof. Yi Liao Dr. Joshua T. Damron Dr. Michelle K. Kidder Dr. Benjamin Doughty Dr. Radu Custelcean Dr. Ying-Zhong Ma 《Angewandte Chemie (International ed. in English)》2023,62(29):e202304957
One of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO2 release, making the massive scale (GtCO2/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically-driven approach for CO2 release by exploiting the unique properties of an indazole metastable-state photoacid (mPAH). Our measurements on simulated and amino acid-based DAC systems revealed the potential of mPAH to be used for CO2 release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ≈55 % and ≈68 % to ≈78 % conversion of total inorganic carbon to CO2 was found for the simulated and amino acid-based DAC systems, respectively. Our results confirm the feasibility of on-demand CO2 release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents. 相似文献
985.
Bharadwaj Mysore Ramesha Bram Pawlak Dr. Daniel Arenas Esteban Dr. Gunter Reekmans Prof. Dr. Sara Bals Prof. Dr. Wouter Marchal Prof. Dr. Robert Carleer Prof. Dr. Peter Adriaensens Prof. Dr. Vera Meynen 《Chemphyschem》2023,24(22):e202300437
The hydrolysis of the phosphonate ester linker during the synthesis of hybrid (organic-inorganic) TiO2 nanoparticles is important when forming porous hybrid organic-inorganic metal phosphonates. In the present work, a method was utilized to control the in-situ partial hydrolysis of diphosphonate ester in the presence of a titania precursor as a function of acid content, and its impact on the hybrid nanoparticles was assessed. Organodiphosphonate esters, and more specific, their hydrolysis degree during the formation of hybrid organic-inorganic metal oxide nanoparticles, are relatively under explored as linkers. Here, a detailed analysis on the hydrolysis of tetraethyl propylene diphosphonate ester (TEPD) as diphosphonate linker to produce hybrid TiO2 nanoparticles is discussed as a function of acid content. Quantitative solution NMR spectroscopy revealed that during the synthesis of TiO2 nanoparticles, an increase in acid concentration introduces a higher degree of partial hydrolysis of the TEPD linker into diverse acid/ester derivatives of TEPD. Increasing the HCl/Ti ratio from 1 to 3, resulted in an increase in degree of partial hydrolysis of the TEPD linker in solution from 4 % to 18.8 % under the applied conditions. As a result of the difference in partial hydrolysis, the linker-TiO2 bonding was altered. Upon subsequent drying of the colloidal TiO2 solution, different textures, at nanoscale and macroscopic scale, were obtained dependent on the HCl/Ti ratio and thus the degree of hydrolysis of TEPD. Understanding such linker-TiO2 nanoparticle surface dynamics is crucial for making hybrid organic-inorganic materials (i. e. (porous) metal phosphonates) employed in applications such as electronic/photonic devices, separation technology and heterogeneous catalysis. 相似文献
986.
987.
Anatoliy I. Polyakov Vera A. Eryomina Lidiya A. Medvedeva Nadezhda I. Tihonova LeoniD. G. Voskressensky 《Journal of heterocyclic chemistry》2008,45(6):1589-1596
988.
Two rapid, accurate and sensitive methods are developed and validated for the quantitative simultaneous determination of cefotaxime (CFX) and its active metabolite desacetylcefotaxime (DCFX) in urine.Based on the previous results which showed the four electron reduction of CFX at ≈ −0.5 V, and the new findings that DCFX reduction occurred at more positive potential (−0.23 V), the new adsorptive stripping differential pulse voltammetric (AdSDPV) method was developed for determination of CFX in the presence of DCFX. Linear responses were observed over a wide concentration range (0.07-0.52 μg/ml for CFX and 0.22-1.3 μg/ml for DCFX) in urine.The second assay involves subsequent separation on a reversed-phase HPLC column, with ultraviolet detection at 262 nm. Retention times were 4.057 and 1.960 min for CFX and DCFX, respectively. Linear responses were observed over a wide range, 0.55-6.60 μg/ml for CFX and 1.10-11.00 μg/ml for DCFX, in urine.The statistical evaluation for both methods was examined by means of within-day repeatability (n = 5) and day-to-day precision (n = 3) and was found to be satisfactory with high accuracy and precision. 相似文献
989.
Homogeneous chitosan films of various thicknesses (10-65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe(3+) were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe(3+) of 9.49 x 10(5) M(-1) was determined with a detection limit as low as 250 ppb. 相似文献
990.
Maria das Dores M.C. Ribeiro da Silva Manuel A.V. Ribeiro da Silva Vera L.S. Freitas Maria Victoria Roux Pilar Jiménez Manuel Temprado Juan Z. Dávalos Pilar Cabildo Rosa M. Claramunt José Elguero 《The Journal of chemical thermodynamics》2008,40(3):386-393
A thermophysical and thermochemical study has been carried out for crystalline imidazolidin-2-one and N,N′-trimethyleneurea [tetrahydropyrimidin-2(1H)-one]. The thermophysical study was made by differential scanning calorimetry, d.s.c., in the temperature intervals between T = 268 K and their respective melting temperatures. Several solid–solid transitions have been detected in imidazolidin-2-one. The standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for crystalline imidazolidin-2-one and N,N′-trimethyleneurea [tetrahydropyrimidin-2(1H)-one], were determined using static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, for the two compounds were derived from the variation of their vapour pressures, measured by the Knudsen effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpies of formation of the two cyclic urea compounds studied in the gaseous phase at T = 298.15 K. These values are discussed in terms of molecular structural contributions and interpreted on the bases of the “benzo-condensed effect” and of the ring strain of imidazolidin-2-one. 相似文献