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101.
We report here solution NMR relaxation measurements that show millisecond time-scale intersubunit dynamics in the homopentameric B subunit (VTB) of the toxin derived from Escherichia coli O157. These data are consistent with interconversion between an axially symmetric form and a low-abundance ( approximately 10%, 45 degrees C) higher energy form. The higher energy state is depopulated on binding of a novel bivalent analogue (P(k) dimer) of the natural carbohydrate acceptor globotriaosylceramide. The isothermal titration calorimetry isotherm for the binding of P(k) dimer to VTB is consistent with a five-site sequential binding model which assumes that cooperative effects arise through communication only between neighboring binding sites. The resulting thermodynamic parameters (K(a1) = 114 +/- 2.2 M(-1), K(a2) = 283 +/- 4.5 M(-1), DeltaH(1) degrees = -116.3 +/- 0.55 kJ/mol, and DeltaH(2) degrees = -50.3 +/- 0.11 kJ/mol) indicate favorable entropic cooperativity that has not previously been observed in multivalent systems.  相似文献   
102.
An optimal algorithm for 3-edge-connectivity is presented. The algorithm performs only one pass over the given graph to determine a set of cut-pairs whose removal leads to the 3-edge-connected components. An additional pass determines all the 3-edge-connected components of the given graph. The algorithm is simple, easy to implement and runs in linear time and space. Experimental results show that it outperforms all the previously known linear-time algorithms for 3-edge-connectivity in determining if a given graph is 3-edge-connected and in determining cut-pairs. Its performance is also among the best in determining the 3-edge-connected components.  相似文献   
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105.
The substitution reactions of 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoyl chloride (Cl2C6H3COCl) and 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoate ion (Cl2C6H5COO) or benzoate ion (C6H5COO) in a two-phase H2O/CH2Cl2 medium using pyridine 1-oxide (PNO) as an inverse phase transfer catalyst were investigated. The reaction of Cl2C6H3COCl and PNO in CH2Cl2 to produce the ionic intermediate, 1-(dichlorobenzoyloxy)-pyridinium chloride (Cl2C6H3COONP+Cl) is the rate-determining step. In the PNO-catalyzed two-phase reaction of Cl2C6H3COCl and C6H5COONa, the order of reactivities of Cl2C6H3COCl toward reaction with PNO is (2,3-, 2,4-)>3,5->3,4-2,6-Cl2C6H3COCl, whereas it is 3,5->(2,3-, 3,4-)>2,4-Cl2C6H3COCl in the PNO-catalyzed two-phase reaction of Cl2C6H3COCl and the corresponding Cl2C6H3COONa. The order of reactivities of Cl2C6H3COO ions towards the reaction with 1-(benzoyloxy)-pyridinium (C6H5COONP+) ion is (3,4-, 3,5-)>(2,3-, 2,4-Cl2C6H3COO).  相似文献   
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107.
This study investigates the decomposition reactions of ethyl formate in the S1 and T1 states. The dissociation channels leading to HCOOH + C2H4, CH3CH2O + HCO, CH3CH2OCO + H, and CH3CH2 + HCO2 were studied. The major reactions of ethyl formate in the S1 and T1 states are isomerization to the biradical CH2CH2OC(OH)H and dissociation to CH3CH2O + HCO. All the stationary and intersection points were optimized at the CAS(10,8) level of theory with the 6‐31G(d,p) and 6‐311G(2df,2pd) basis sets. Single‐point CASPT3 energy was calculated for each of the stationary and intersection points. Microcanonical rate constants were also calculated for each of the reactions by using the RRKM theory.  相似文献   
108.
Novel CO2‐responsive conductive polymer particles based on poly(N‐(3‐amidino)‐aniline) (or PNAAN) are reported in this work. A CO2‐responsive N‐(3‐amidino)‐aniline (NAAN) monomer is firstly synthesized with the pendant amidine group at the meta‐position of aniline (AN) and subsequently polymerized into the PNAAN polymer by chemical oxidation. Self‐assembly of PNAAN in turn forms the polymer particles. In the strong or weak acid media, the amidine group protonates into cationic amidinium and self‐stabilizes the PNAAN particles without the use of any stabilizers. The reaction media are found to affect the polymerization rate and self‐assembly of particles, and hence the size and size distribution of the resultant particles. The particles synthesized in strong basic media show CO2‐responsvie properties since the H+ released by dissolved CO2 (dCO2) can protonate the amidine group into hydrophilic amidinium group and result in swelling of the PNAAN particles. Zeta‐potential measurements show the reversible change of particle surface charges in the presence and absence of dCO2. Dynamic light scattering (DLS) measurements show the particle size linearly changed with dCO2 concentration in the range of 5 × 10?4 and 2.5 × 10?2 atm. This is the first reported CO2‐responsive polyaniline (PANI) particles for dCO2 sensing or reversible fixation of CO2.  相似文献   
109.
Layered growth of molybdenum disulphide (MoS2) was successfully achieved by pulsed laser deposition (PLD) method on c ‐plane sapphire substrate. Growth of monolayer to a few monolayer MoS2, dependent on the pulsed number of excimer laser in PLD is demonstrated, indicating the promising controllability of layer growth. Among the samples with various pulse number deposition, the frequency difference (A1g–E12g) in Raman analysis of the 70 pulse sample is estimated as 20.11 cm–1, suggesting a monolayer MoS2 was obtained. Two‐dimensional (2D) layer growth of MoS2 is confirmed by the streaky reflection high energy electron diffraction (RHEED) patterns during growth and the cross‐sectional view of transmission electron microscopy (TEM). The in‐plane relationship, (0006) sapphire//(0002)MoS2and sapphire//MoS2 is determined. The results imply that PLD is suitable for layered MoS2 growth. Additionally, the oxide states of Mo 3d core level spectra of PLD grown MoS2, analysed by X‐ray photoelectron spectroscopy (XPS), can be effectively reduced by adopting a post sulfurization process. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   
110.
Expanding upon a previous study, the modified double lattice model for mixed-solvent polymer systems was developed by employing new universal constants. The calculated results of the proposed model showed good agreement with Monte Carlo simulation results and hypothetically predicted Types 0 and 3 phase separations of the Treybal classification. To describe real systems, the chain length of the polymer and energy parameters were adjusted to fit experimental data. The proposed model correlated well with experimental data from real systems incorporating low to high molecular weight polymers (PEO 200, dextran 40 350, PS 300 000) using reasonable model parameters.  相似文献   
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