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排序方式: 共有676条查询结果,搜索用时 46 毫秒
111.
112.
Jin Koo Kim Sun Young Jeong Sae Hoon Lim Jang Hyeok Oh Seung‐Keun Park Jung Sang Cho Yun Chan Kang 《化学:亚洲杂志》2019,14(18):3127-3140
Increasing demand for sodium‐ion batteries (SIBs), one of the most feasible alternatives to lithium ion batteries (LIBs), has resulted because of their high energy density, low cost, and excellent cycling stability. Consequently, the design and fabrication of suitable electrode materials that govern the overall performance of SIBs are important. Aerosol‐assisted spray processes have gained recent prominence as feasible, scalable, and cost‐effective methods for preparing electrode materials. Herein, recent advances in aerosol‐assisted spray processes for the fabrication of nanostructured metal chalcogenides (e.g., metal sulfides, selenides, and tellurides) for SIBs, with a focus on improving the electrochemical performance of metal chalcogenides, are summarized. Finally, the improvements, limitations, and direction of future research into aerosol‐assisted spray processes for the fabrication of various electrode materials are presented. 相似文献
113.
114.
T. William Bentley Robert O. Jones Dae Ho Kang In Sun Koo 《Journal of Physical Organic Chemistry》2009,22(9):799-806
Rate constants for a wide range of binary aqueous mixtures and product selectivities (S) in ethanol–water (EW) and methanol–water (MW) mixtures, are reported at 25 °C for solvolyses of benzenesulfonyl chloride and the 4‐chloro‐derivative. S is defined as follows using molar concentrations: S = ([ester product]/[acid product]) × ([water solvent]/[alcohol solvent]). Additional selectivity data are reported for solvolyses of 4‐Z‐substituted sulfonyl chlorides (Z = OMe, Me, H, Cl and NO2) in 2,2,2‐trifluoroethanol–water. To explain these results and previously published data on kinetic solvent isotope effects (KSIEs) and on other solvolyses of 4‐nitro and 4‐methoxybenzenesulfonyl chloride, a mechanistic spectrum involving a change from third order to second order is proposed. The molecularity of these reactions is discussed, along with new term ‘SN3–SN2 spectrum’ and its connection with the better established term ‘SN2–SN1 spectrum’. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
115.
The capacitance characteristics of platinum nanoparticle (NP)-embedded metal–oxide–semiconductor (MOS) capacitors with gate Al2O3 layers are studied in this work. The capacitance versus voltage (C–V) curves obtained for a representative MOS capacitor exhibit flat-band voltage shifts, demonstrating the presence of charge storages in the platinum NPs. The counterclockwise hysteresis and flat-band voltage shift, observed from the C–V curves imply that electrons are stored in a floating gate layer consisting of the platinum NPs present between the tunneling and control oxide layers in the MOS capacitor and that these stored electrons originate from the Si substrate. Moreover, the charge remains versus time curve for the platinum NP-embedded MOS capacitor is investigated in this work. 相似文献
116.
Hyun-Joo Koo 《Solid State Communications》2009,149(21-22):847-851
The magnetic properties of Ag2V OP2O7 were examined by evaluating its spin exchange interactions in terms of spin dimer analysis based on tight binding calculations and mapping analysis based on first principles density functional theory calculations. Both calculations show that a strong spin exchange interaction occurs through the super-superexchange path J1 with the V…V distance of 5.293 Å. This strong antiferromagnetic interaction forms isolated spin dimer units, which are coupled antiferromagnetically by the spin exchange path J3 to form a two-leg spin ladder that has no spin frustration. The inter–dimer interaction J2 is found to be ferromagnetic, and does not lead to spin frustration. 相似文献
117.
T. -K. Hong B. -H. Koo S. -Y. Ly M. -H. Kim M. -Z. Czae 《Journal of Analytical Chemistry》2009,64(11):1158-1165
A theoretical model for the potentiometric analysis of precipitation titrations using a pH electrode has been developed and
tested. The new analytical method is possible by introducing a mediator which must be a weak acid and must be able to form
an insoluble salt with a cation (a titrant). Theoretical expressions of pH, as well as the concentrations of all other species,
were derived and solved numerically using bisection method. Among the various factors that influence pH during the titration,
concentrations of the mediator and initial values of pH were proved to be very critical. The experimental potentiometric titration
curves agree well with those predicted from the theoretical model. Crossing point method was adopted to determine an equivalence
point from the titration curves. The method is tested using a known system of chloride determination. Among the several mediators
tested (bisulfite, chromate, phosphate, cyanide, arsenate and EDTA), phosphate yielded the best results with an error of 0.1%;
bisulfite, chromate and arsenate yielded comparably good results with an error of 0.3∼0.5%, but cyanide and EDTA yielded unsatisfactory
results. The optimum mediator concentration found to be in a range of 1–2 mM. 相似文献
118.
119.
Nguyen Van Duc Long Thai‐Hoang Le Jin‐Il Kim Ju Weon Lee Yoon‐Mo Koo 《Journal of separation science》2009,32(11):1987-1995
Simulated moving bed (SMB) processes have been widely used in the sugar industries with ion‐exchange resin as a stationary phase. D ‐Psicose, a rare monosaccharide known as a valuable pharmaceutical substrate, was synthesized by the enzymatic conversion from D ‐fructose. The SMB process was adopted to separate D ‐psicose from D ‐fructose. Before the SMB experiment, the reaction mixture including D ‐psicose and D ‐fructose was treated by a deashing process to remove contaminants, such as buffers, proteins, and other organic materials. Four columns packed with Dowex 50WX4‐Ca2+ (200–400 mesh) ion‐exchange resins were used in the four‐zone SMB. Single‐step frontal analysis was performed to estimate the isotherm parameters of each monosaccharide. The operating conditions of the SMB process were determined based on the Equilibrium Theory. According to the simulation of the SMB process, the purity and yield of extract product (D ‐psicose) achieved were 99.04 and 97.46%, respectively and those of raffinate product (D ‐fructose) were 99.06 and 99.53%, respectively. Under the optimized operating condition, complete separation (extract purity = 99.36%, raffinate purity = 99.67%) was achieved experimentally. 相似文献
120.
Despite intensive studies of the neutral tropyl radical, none of its structure, energetics, and vibrational modes are still clear. This system has puzzled scientists for over a decade since one vibrational mode frequency sharply varies from imaginary number 3000i cm-1 to the real number 6000 cm-1, depending on the calculation methods employed. We find that the origin of this peculiar mode is due to the pseudorotation (omegairot) involved in the interconversion of two nearly isoenergetic Jahn-Teller configurations (elongated structure 2B1 and compressed structure 2A2 with C2v symmetry). Here, we first report that this interconversion is not via D7h or C2v symmetry configuration but via Cs symmetry (i.e., by changing the C2v axis). This interconversion barrier is found negligibly small. Thus, the two conformers are considered to be not two different structures but a dynamically identical structure with partial quantum statistical distributions on the potential energy surface. Owing to the nearly barrierless pseudorotation, the overall structure in a short time scale (less than femtosecond) would be Cs-like between 2A2 and 2B1 configurations with small fluctuation of bond distances. However, the dynamical transitions between the 2B1 and 2A2 configurations via 14 different pseudorotation pathways would make the tropyl radical have the effective D7h structure in either a nonshort time scale (greater than femtosecond) or at nonlow temperatures, which explains the high temperature electron spin resonance experiments. 相似文献