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71.
A method for simultaneous analysis of eight azolic fungicides: cyproconazole, diniconazole, tetraconazole, thiabendazole, flusilazole, triadimenol, triadimefon, carbendazim and the degradation product 2-aminobenzimidazole in wine samples is described. The compounds are isolated from the samples and concentrated by solid-phase extraction on polymeric cartridges. The determination is carried out by liquid chromatography with mass spectrometric detection in positive ionization and selected ion monitoring modes. The influence of parameters such as the mobile phase composition, column temperature, corona current and fragmentor voltage is studied and the proposed method is validated. Recoveries of the nine compounds added to wine samples range from 83 to 109%, with relative standard deviations below 10%. The quantitation limits are between 9 and 31 microg/L. Real wine samples are analyzed by the proposed method, also. 相似文献
72.
Phosphate selective electrodes have been produced based upon rubbery membranes containing heterocylic macrocycles as sensors covalently bound to a cross-linked polystyrene-block–polybutadiene-block–polystyrene (SBS) polymer. The membranes were robust and the best HPO42−-selective membrane fabricated was composed of 7.1% (m/m) dicumyl peroxide, 28.3% (m/m) 2-nitrophenyloctylether, 9.8% (m/m) 3-(10-undecenyl)-1,5,8-triazacyclodecane-2,4-dione, 31.0% (m/m) SBS and 23.8% (m/m) PoleStar™ 200R (clay-based filler). The characteristics of this electrode were a linear Nernstian range of 3.9×10−3 to 1×10−6 mol dm−3 HPO42− with a limit of detection of 1.0×10−6 mol dm−3 HPO42−, a slope of −29.7±0.9 mV per activity decade and a pH range from 6 to 8. Selectivity coefficients for phosphate against various interfering anions (chloride, sulfate and nitrate) were determined. Response times were 2 min or under, stability of response and electrode lifetime in continuous use were also very satisfactory. The response behavior of HPO42−-ISEs based upon mobile and bound ionophores was comparable and suggests that mobility of the ionophore is not necessary to obtain a working ISE and that covalent binding of ionophores can be used to produce ISEs of increased stability and robustness. 相似文献
73.
Maria Luisa Moyá Antonio Barrios Maria del Mar Graciani Rafael Jiménez Ernestina Muñoz Francisco Sánchez John Burgess 《Transition Metal Chemistry》1991,16(2):165-168
Summary The kinetics of replacement of 4,4-bipyridine, (4,4-bipy), and 4-cyanopyridine, (4-CNpy), by cyanide in [Fe(CN)5-(4,4-bipy)]3-. at 298 K have been studied in binary aqueous mixtures containing different amounts of t-butanol, methanol, glycerol, ethyleneglycol and sucrose. The plots of logarithms of the limiting rate constantsversus the mole fraction of water are linear over the entire composition range studied, showing the importance of solvation phenomena. A different straight line of log (kL/s–1)versus XH2O is obtained for each mixture, indicating the influence of other solvent parameters on the reaction rate. A multiparameter regression of G
exp
with A (acidity vector), B (basicity vector) and GE is used for both reactions; plots of G
calc
versus G
exp
are linear with slopes of near unity. 相似文献
74.
A spectrofluorimetric method for the simultaneous determination of dysprosium, europium, gadolinium and terbium in ternary and quaternary mixtures by the use of pyridine-2,6-dicarboxylic acid as a chelating agent was developed. The influence of chemical variables affecting the analytical reaction was evaluated. A partial least-squares procedure and PC Quant software were used to assess data obtained from a variable number of calibration solutions and wavelengths. The ensuing method was validated by applying it to the analysis of synthetic ternary (Eu-Dy-Tb) and quaternary mixtures (Eu-Dy-Gd-Tb) over the concentration ranges 60-550 mug Eu l(-1), 30-400 mug Dy l(-1) and 30-400 mug Tb l(-1) in the former, and 20-220 mug Eu l(-1), 20-235 mug Dy l(-1), 25-230 mug Gd l(-1) and 75-230 mug Tb l(-1) in the latter. The results obtained by using the two quantitation procedures are compared. The relative errors in the determinations were less than 8% in most cases. 相似文献
75.
Jim Agler 《Integral Equations and Operator Theory》1982,5(1):608-631
We develop techniques which allow one to describe in simple terms the set of operators on Hilbert space of the form M* () |M, where M is multiplication by z on a Hilbert space of analytic functions satisfying certain technical assumptions, M* () is the direct sum of a countably infinite number of copies of M*, andM is invariant for M* (). One of the main ingredients in our technique is the Arveson Extension Theorem and this paper illustrates the great power and tractability of that theorem in a concrete setting.Research partially supported by NSF grant MCS 81-02518 相似文献
76.
Jiménez JC Chavarría B López-Macià A Royo M Giralt E Albericio F 《Organic letters》2003,5(12):2115-2118
[reaction: see text] A solid-phase method for the synthesis of tentoxin has been developed. Two key steps-dehydration and N-alkylation-are carried out while the peptide is anchored to the resin. The method, which has been validated by the preparation of a library of tentoxin analogues, should be applicable to the generation of further libraries that have the tentoxin scaffold structure, as well as other structures containing N-alkylated didehydroamino acids. 相似文献
77.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,28(4):941-949
The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
78.
Pericàs MA Puigjaner C Riera A Vidal-Ferran A Gómez M Jiménez F Muller G Rocamora M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(18):4164-4178
New families of enantiopure bis(oxazolines) with 4,5-trans (5 a-g) or 4,5-cis (6 c) stereochemistry at the individual rings have been prepared in high yield. Their eta(3)-allyl palladium complexes (8 a-g, 9 c and 10) have been used as catalytic precursors in allylic alkylation reactions with excellent enantioselectivities (up to 96 %) for the trans oxazoline derivatives, while Pd/6 c system was inactive. NMR studies on palladium eta(3)-1,3-diphenylallyl intermediates (11 a, c and e) showed the presence of syn/syn- and syn/anti-allyl isomers in solution; this resembles the first example of eta(3)-eta(1)-eta(3) isomerism in Pd allylic complexes containing bis(oxazolines) derived from malonic acid. 相似文献
79.
Silica obtained by acid treatment of sepiolite was used as a support for catalysts consisting of palladium complexes of 2‐ and 3‐thiophenecarbaldehyde. The support and the catalysts were characterized by X‐ray diffraction, and solid‐state 29Si and 13C nuclear magnetic resonance spectroscopies. The supported palladium catalysts were used in the Suzuki reaction of bromobenzene with phenylboronic acid. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
80.
Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo‐heterocycles
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María Inés Flores‐Conde Fabiola N. de la Cruz Julio López J. Óscar C. Jiménez‐Halla Eduardo Peña‐Cabrera Marcos Flores‐Álamo Francisco Delgado Miguel A. Vázquez 《应用有机金属化学》2018,32(3)
The unprecedented reaction of ketone‐containing aromatic pyridinium salts 3a ‐ e and alkynyl Fischer complexes 1a ‐ f proceeds via a mild domino process to provide 4,6‐disubstituted pyran‐2‐ones 5a ‐ k and 2,3,5‐trisubstituted furans 6a ‐ h (45‐97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products. 相似文献