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931.
Xidos JD Gosse TL Burke ED Poirier RA Burnell DJ 《Journal of the American Chemical Society》2001,123(23):5482-5488
A computational examination of the four modes of addition in the Diels-Alder reactions of 3-substituted cyclopropene derivatives (substituents: BH(2), CH(3), SiH(3), NH(2), PH(2), OH, SH, F, and Cl) with butadiene have been carried out at the B3LYP/6-31++G(d)//HF/6-31++G(d) level. The degree of stabilization of these derivatives at the ground state correlates with the electronegativity of the substituent. This attenuation of reactivity and differences in steric interactions are the only factors needed to explain both the high facial selectivity and the differences in the endo-exo selectivity seen in these reactions. Furthermore, evidence is presented that indicates that stabilization by an interaction involving the syn C-3 hydrogen of cyclopropene and butadiene is small or irrelevant in controlling the endo-exo selectivity of the Diels-Alder reaction. 相似文献
932.
Donald A. Kangas Ronald R. Pelletier 《Journal of polymer science. Part A, Polymer chemistry》1970,8(12):3543-3555
Copolymers of 2-sulfoethyl methacrylate, (SEM) were prepared with ethyl methacrylate, ethyl acrylate, vinylidene chloride, and styrene in 1,2-dimethoxyethane solution with N,N′-azobisisobutyronitrile as initiator. The monomer reactivity ratios with SEM (M1) were: vinylidene chloride, r1 = 3.6 ± 0.5, r2 = 0.22 ± 0.03; ethyl acrylate, r1 = 3.2 ± 0.6, r2 = 0.30 ± 0.05; ethyl methacrylate, r1 = 2.0 ± 0.4, r2 = 1.0 ± 0.1; styrene, r1 = 0.6 ± 0.2, r2 = 0.37 ± 0.03. The values of the copolymerization parameters calculated from the monomer reactivity ratios were e = +0.6 and Q = 1.4. Comparison of the monomer reactivities indicates that SEM is similar to ethyl methacrylate with regard to copolymerization reactivity in 1,2-dimethoxyethane solution. The sodium salt of 2-sulfoethyl methacrylate, SEM?Na⊕, was copolymerized with 2-hydroxyethyl methacrylate (M2) in water solution. Reactivity ratios of r1 = 0.7 ± 0.1 and r2 = 1.6 ± 0.1 were obtained, indicating a lower reactivity of SEM?Na⊕ in water as compared to SEM in 1,2-dimethoxyethane. This decreased reactivity was attributed to greater ionic repulsion between reacting species in the aqueous medium. 相似文献
933.
Xue Kui Ji Stephen B. Colbran Donald C. Craig Khaled M. Edbey Jason B. Harper Gary D. Willett 《Tetrahedron》2005,61(45):10705-10712
Two new meso-indanyl-substituted calix[4]pyrrole receptors, 2 and 3, have been synthesized. A range of calix[4]pyrrole host-neutral molecule complexes crystallise from solutions of 2 in a variety of solvents and the structures of four have been elucidated by X-ray crystallography. The F− and Cl− anion affinities of 2 have been measured in acetonitrile, and are significantly different from the corresponding affinities of the prototypical calix[4]pyrrole, the octamethyl-derivative, 1. ESI-FTICR-MS has been used to determine the relative F− and Cl− anion affinities of receptors 1 and 2 in methanol-acetonitrile solution. Deprotonation of 1 and 2 by fluoride is observed (under the conditions of the MS experiment). 相似文献
934.
935.
Decken A Jenkins HD Nikiforov GB Passmore J 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2496-2504
NO[Al(OC(CF(3))(2)Ph)(4)] 1 and NO[Al(OC(CF(3))(3))(4)] 2 were obtained by the metathesis reaction of NO[SbF(6)] and the corresponding Li[Al(OR)(4)] salts in liquid sulfur dioxide solution in ca 40% (1) and 85% (2) isolated yield. 1 and 2, as well as Li[NO(3)] and N(2)O, were also given by the reaction of an excess of mixture of (90 mol%) NO, (10 mol%) NO(2) with Li[Al(OR)(4)] followed by extraction with SO(2). The unfavourable disproportionation reaction of 2NO(2)(g) to [NO](+)(g) and [NO(3)](-)(g)[DeltaH degrees = +616.2 kJ mol(-1)] is more than compensated by the disproportionation energy of 3NO(g) to N(2)O(g) and NO(2)(g)[DeltaH degrees =-155.4 kJ mol(-1)] and the lattice energy of Li[NO(3)](s)[U(POT)= 862 kJ mol(-1)]. Evidence is presented that the reaction proceeds via a complex of [Li](+) with NO, NO(2)(or their dimers) and N(2)O. NO(2) and Li[Al(OC(CF(3))(3))(4)] gave [NO(3)(NO)(3)][Al(OC(CF(3))(3))(4)](2), NO[Al(OC(CF(3))(3))(4)] and (NO(2))[Al(OC(CF(3))(3))(4)] products. The aluminium complex [Li[AlF(OC(CF(3))(2)Ph)(3)]](2) 3 was prepared by the thermal decomposition of Li[Al(OC(CF(3))(2)Ph)(4)]. Compounds 1 and 3 were characterized by single crystal X-ray structural analyses, 1-3 by elemental analyses, NMR, IR, Raman and mass spectra. Solid 1 contains [Al(OC(CF(3))(2)Ph)(4)](-) and [NO](+) weakly linked via donor acceptor interactions, while in the SO(2) solution there is an equilibrium between the associated [NO](+)[Al(OC(CF(3))(2)Ph)(4)](-) and separated solvated ions. Solid 2 contains essentially ionic [NO](+) and [Al(OC(CF(3))(3))(4)](-). Complex 3 consists of two [Li[AlF(OC(CF(3))(2)Ph)(3)]] units linked via fluorine lithium contacts. Compound 1 is unstable in the SO(2) solution and decomposes to yield [AlF(OC(CF(3))(2)Ph)(3)](-), [(PhC(CF(3))(2)O)(3)Al(mu-F)Al(OC(CF(3))(2)Ph)(3)](-) anions as well as (NO)C(6)H(4)C(CF(3))(2)OH, while compound 2 is stable in liquid SO(2). The [small nu](NO(+)) in 1 and [NO](+)(toluene)[SbCl(6)] are similar, implying similar basicities of [Al(OC(CF(3))(2)Ph)(4)](-) and toluene. 相似文献
936.
Abstract— Weighted and unweighted UV spectral irradiances were measured under a 2-lamp fluorescent fixture containing Westinghouse FS-40 fluorescent sunlamps filtered with (6 h aged) 0.127 mm (0.005 in.) cellulose acetate by use of newly developed broadband UV radiometers and an automated UV spectro-radiometer. Measurements were taken at 10-cm intervals between 20 and 110 cm from the lamps. Correlations were determined between sets of data measured with the broadband radiometers and the UV spectroradiometer.
By use of linear regression analyses on the weighted and unweighted spectral data, regression equations were developed for predicting UV-B irradiance (unweighted mWm-2 ), biologically effective UV (BUV) (weighted mWm) in the 280–320 nm (UV-B) region, UV-B sun equivalents, and incident flux density in the UV-B region in photons m-2 × 1021 integrated over a 6-h exposure. Examination of the correlation coefficients ( r values) indicated that agreement was excellent between measured and predicted values for all comparisons (r values from 0.9972 to 0.9998).
Use of regression equations should permit accurate. rapid estimation of both weighted and unweighted UV irradiances at any location in an experimental set-up and provide a useful means for intra- and inter-laboratory comparisons of spectral measurements, made in the interagency BACER program under FS-40 fluorescent sunlamps filtered with 0.127 mm cellulose acetate (aged for 6h). 相似文献
By use of linear regression analyses on the weighted and unweighted spectral data, regression equations were developed for predicting UV-B irradiance (unweighted mWm-
Use of regression equations should permit accurate. rapid estimation of both weighted and unweighted UV irradiances at any location in an experimental set-up and provide a useful means for intra- and inter-laboratory comparisons of spectral measurements, made in the interagency BACER program under FS-40 fluorescent sunlamps filtered with 0.127 mm cellulose acetate (aged for 6h). 相似文献
937.
Lin H Zhao Y Ellingson BA Pu J Truhlar DG 《Journal of the American Chemical Society》2005,127(9):2830-2831
We report here a theoretical study of the 13C kinetic isotope effect (KIE) and its temperature dependence for the reaction OH + CH4 --> H2O + CH3, the major sink of atmospheric methane in the troposphere. The KIE values at various atmospherically significant temperatures were determined by direct dynamics using variational transition state theory with multidimensional tunneling contributions (VTST/MT). The potential energy surfaces (PESs) were generated by hybrid density functional theory as well as by recently developed doubly hybrid density functional theory methods. Comparisons of our calculated KIEs with experimental data and theoretical values in the literature reveal the critical contributions due to multidimensional tunneling and torsion anharmonicity as well as the critical issue of the choice of internal rotational axis. 相似文献
938.
The oxidation of aluminum nanoparticles is studied with classical molecular dynamics and the Streitz-Mintmire (Streitz, F. H.; Mintmire, J. W. Phys. Rev. B 1994, 50, 11996) electrostatic plus (ES+) potential that allows for the variation of electrostatic charge on all atoms in the simulation. The structure and charge distributions of bulk crystalline alpha-Al(2)O(3), a surface slab of alpha-Al(2)O(3) with an exposed (0001) basal plane, and an isolated Al(2)O(3) nanoparticle are studied. Constant NVT simulations of the oxidation of aluminum nanoparticles are also performed with different oxygen exposures. The calculations simulate a thermostated one-time exposure of an aluminum nanoparticle to different numbers of surface oxygen atoms. In the first set of oxidation studies, the overall approximate ratios of Al to O in the nanoparticle are 1:1 and 2:1. The nanoparticles are annealed to 3000 K and are then cooled to 500, 1000, or 1500 K. The atomic kinetic energy is scaled during the simulation to maintain the desired temperature. The structure and charge distributions in the oxidized nanoparticles differ from each other and from those of the bulk Al(2)O(3) phases. In the Al(1)O(1) simulation, an oxide shell forms that stabilizes the shape of the particle, and thus the original structure of the nanoparticle is approximately retained. In the case of Al(1)O(0.5), there is insufficient oxygen to form a complete oxide shell, and the oxidation results in particles of irregular shapes and rough surfaces. The particle surface is rough, and the nanoparticle is deformed. 相似文献
939.
Green DR Fenker HC Lai KW LeBritton J Lin YC Pifer AE Davenport TF Goldman JH Hagopian SL Lannutti JE Canough G Chang CC Davis TC Joyner RW Poirier JA Georgiopoulos CH Napier A Schneps J Marraffino JM Waters JW Webster MS Williams EG Woosley J Ficenec JR Torres S Trower WP 《Physical review letters》1986,56(16):1639-1642
940.
Matthew J. Donald 《Communications in Mathematical Physics》1986,105(1):13-34
ForA any subset of () (the bounded operators on a Hilbert space) containing the unit, and and restrictions of states on () toA, ent
A
(|)—the entropy of relative to given the information inA—is defined and given an axiomatic characterisation. It is compared with ent
A
A
(|)—the relative entropy introduced by Umegaki and generalised by various authors—which is defined only forA an algebra. It is proved that ent and ent
S
agree on pairs of normal states on an injective von Neumann algebra. It is also proved that ent always has all the most important properties known for ent
S
: monotonicity, concavity,w* upper semicontinuity, etc. 相似文献