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101.
The divinyl carbinols and furnished octalinols and respectively on treatment with base. 相似文献
102.
Guliants VV Bhandari R Swaminathan B Vasudevan VK Brongersma HH Knoester A Gaffney AM Han S 《The journal of physical chemistry. B》2005,109(50):24046-24055
The outermost surfaces and subsurface layers of the orthorhombic (M1) Mo-V-O catalysts promoted with Te, Nb, and Sb oxide species at submonolayer surface coverage were examined by low-energy ion scattering (LEIS). This study indicated that the Nb oxide species was preferentially located at the topmost surface, while the subsurface Te and Sb concentrations declined gradually into the bulk. Although the original Mo-V-O catalyst was essentially unselective in propane oxidation to acrylic acid, significant improvement in the selectivity to acrylic acid was observed when Te, Nb, and Sb oxides were present as the surface species at submonolayer coverage. These findings further suggested that the formation of the surface V-O-M bonds (M = Nb, Te, or Sb) was highly beneficial for both the activity and selectivity of the orthorhombic Mo-V-O catalysts in propane oxidation to acrylic acid. The highest selectivity was observed when both Nb and Te (or Sb) oxide species were present at the surface. The selectivity trends established for the surface-promoted Mo-V-O catalyst parallel those found previously for the corresponding bulk Mo-V-M-O catalysts. These results further indicated that the introduction of surface metal oxide species is a highly promising method to prepare well-defined model catalysts for studies of the structure-activity/selectivity relationships as well as optimize the catalytic performance of the bulk mixed Mo-V-M-O catalysts for selective (amm)oxidation of propane. 相似文献
103.
Paul A Jass Victor W RossoSaibaba Racha Nachimuthu SoundararajanJohn J Venit Andrew RusowiczShankar Swaminathan Julia LivshitzEdward J Delaney 《Tetrahedron》2003,59(45):9019-9029
The use of protected amino acid chlorides for peptide coupling reactions has long been avoided due to the extensive racemization that commonly occurs during either the acid chloride formation or the coupling reaction itself. Conditions are described which allow N-trifluoroacetyl-protected amino acid chlorides to be generated in high purity and with high retention of stereochemical integrity. Control of temperature is the predominant factor in controlling racemization, and rapid formation of acid chlorides under low temperature can be conveniently achieved using Vilsmeier reagent. Stereochemical integrity is further maintained when coupling of N-trifluoroacetyl acid chlorides is carried out with amino acid esters under Schotten-Baumann conditions using specific controls on pH, temperature, and agitation. Second order rate constants for coupling and the azlactone formation associated with racemization were measured to be 4260 and 3.6 L/mol s, respectively. This high rate differential allows for the reaction to be run with a minimum excess of amine ester, and makes it suitable for continuous processing. The applicability of the preferred coupling conditions to a range of amino acid couplings is described. 相似文献
104.
105.
106.
S K Nayaki M Swaminathan 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(7):1361-1367
The absorption and fluorescence spectra of 2-aminodiphenylamine (2ADA) have been studied as a function of solvent polarity and acid concentration. Analysis of solvatochromic and prototropic shifts of 2ADA reveals: (i) the presence of intramolecular hydrogen bonding between imino and amino groups in the ground state, (ii) dual fluorescence (360 and 430 nm) of the monocation (2ADA+) formed by the protonation of amino group; and (iii) proton-induced quenching of the monocation (2ADA+) fluorescence. In the dual fluorescence of 2ADA+, the longer wavelength emission at 430 nm is found to be from the twisted form of the monocation. The rate constants of the proton-induced quenching of 2ADA+ are determined. 相似文献
107.
Biosorption of copper (II) and cadmium (II) by live Phanerochaete chrysosporium immobilized by growing onto polyurethane foam material in individual packed bed columns over two successive cycles of sorption–desorption
were investigated in this study. Initial pH and concentrations of the metals in their respective solutions were set optimum
to each of those: 4.6 and 35 mg·l−1 in case of copper and 5.3 and 11 mg·l−1 for cadmium. The breakthrough curves obtained for the two metals during sorption in both the cycles exhibited a constant
pattern at various bed depths in the columns. The maximum yield of the columns in removing these metals were found to be,
respectively, 57% and 43% for copper and cadmium indicating that copper biosorption by the immobilized fungus in its column
was better than for cadmium. Recovery values of the sorbed copper and cadmium metals from the respective loaded columns by
using 0.1 N HCl as eluant was observed to be quite high at more than 65% and 75%, respectively, at the end of desorption in
both the cycles. Breakthrough models of bed-depth service time, Adams–Bohart, Wolborska, and Clark were fitted to the experimental
data on sorption of copper and cadmium in the columns, and only the Clark model could fit the sorption performance of the
columns well over the entire range of ratios of concentrations of effluent to influent, i.e., C/C
0 for both copper and cadmium biosorption. The kinetic coefficients of mass transfer and other suitable parameters in the system
were determined by applying the experimental data at C/C
0 ratios lower than 0.5 to the other three models. 相似文献
108.
We introduce new classes of n-by-n matrices with complex entries which can be scaled by a diagonal matrix with complex entries to be normal or Hermitian and study the Schur-type stability properties of these matrices. 相似文献
109.
The radiative and Forster type of energy transfer processes in a dye mixture laser of 7-diethylamino-4-methyl coumarin (donor) and fluorescein disodium salt (acceptor) under nitrogen laser pumping were investigated. The Forster transfer rate calculated from the absorption and emission spectra of acceptor and donor is 1.3 × 1011 liter mole?1sec?1. The gain of acceptor at 550 nm was measured for acceptor concentrations NA from 10?3M to 3 × 10?3M for a fixed ratio F = 1 of donor to acceptor concentrations at different pump powers. The results agreed with the rate equation model proposed for the dye mixture laser. The radiative rate constant calculated from these results is 3.1 × 1010 liter mole?1sec?1. Numerical simulation of the rate equations showed that the acceptor reaches peak emission with a time lag of 3 ns with respect to the donor peak emission for F = 0.998, NA = 10?5M. This time lag decreases with increasing NA and becomes zero for NA = 10?1M, F = 0.048. 相似文献
110.
The earlier structural assignment as 1 for the product obtained by the condensation of phenyl ethynyl ketone with cyclopentadiene is now revised to the dimeric structure 5d. 相似文献