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981.
Joaquín Barber Fernando Navarro Luis Oriol Milagros Piol Jos Luis Serrano 《Journal of polymer science. Part A, Polymer chemistry》1990,28(4):703-715
Some members of four series of polyesters were synthesized by the direct polycondensation of two types of dicarboxylic acids (4,4′-dicarboxy-α,ω-diphenoxyalkanes and 4,4′-dicarboxy-α,ω-dibenzoyloxyalkanes) with two types of bisphenols (4,4′-dihydroxy-α,ω-diphenoxyalkanes and 4,4′-dihydroxy-α,ω-dibenzoyloxyalkanes) using tosyl chloride in pyridine in the presence of N, N-dimethylformamide. The 1H-NMR spectra of the polymers synthesized showed that these polymers have an ordenated structure. The mesogenic properties of these polymers were studied by optical microscopy and differential scanning calorimetry. Many of the polymers show nematic mesomorphism. 相似文献
982.
Tiziana Parasassi Ewa K. Krasnowska Luis Bagatolli Enrico Gratton 《Journal of fluorescence》1998,8(4):365-373
The steady-state and dynamic fluorescence spectral properties of 2-dimethylamino-6-lauroylnaphthalene (LAURDAN) and several other naphthalene derivatives are summarized to illustrate their sensitivity to the polarity of the environment. Results obtained both in solvents of different polarity and in phospholipid vesicles in two phase states are presented. The emission red shift observed in polar solvents and in the phospholipid liquid–crystalline phase is explained on the basis of dipolar relaxation of solvent molecules surrounding the fluorescent naphthalene moiety of these probes. In phospholipid environments, experimental evidence is shown that excludes the intramolecular relative reorientation of the dimethylamino and carbonyl groups in the naphthalene and the reorientation of the entire fluorescent moiety. The solvent dipolar relaxation observed for LAURDAN and PRODAN in phospholipid bilayers has been attributed to a small number of water molecules present at the membrane interface. A comparison between LAURDAN emission in phospholipid vesicles prepared in D2O and in H2O is also presented. The definition and the derivation of the generalized polarization function are also discussed. 相似文献
983.
984.
985.
María Inés Frascaroli Juan Manuel Salas-Peregrin Luis F. Sala Sandra Signorella 《Polyhedron》2009,28(6):1049-1056
The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by CrVI in acid medium yields CrIII, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over CrVI is used. The redox reaction takes place through the combination of CrVI → CrIV → CrII and CrVI → CrIV → CrIII pathways. Intermediacy of free radicals and CrII in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO22+ formed by reaction of CrII with O2. Intermediate oxo-CrV–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO4, intermediate CrV rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate CrV bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with CrVI distinguishes this derivative from glucose, which is oxidized to gluconic acid. 相似文献
986.
In this paper we present an approach to quantum mechanical canonical transformations. Our main result is that time-dependent quantum canonical transformations can always be cast in the form of squeezing operators. We revise the main properties of these operators in regard to its Lie group properties, how two of them can be combined to yield another operator of the same class and how can also be decomposed and fragmented. In the second part of the paper we show how this procedure works extremely well for the time-dependent quantum harmonic oscillator. The issue of the systematic construction of quantum canonical transformations is also discussed along the lines of Dirac, Wigner, and Schwinger ideas and to the more recent work by Lee. The main conclusion is that the classical phase space transformation can be maintained in the operator formalism but the construction of the quantum canonical transformation is not clearly related to the classical generating function of a classical canonical transformation. We hereby propose the much more efficient method given by the squeezing operators. This method has also been proved to be very useful, by one of the authors, in the framework of the dynamical symmetries (Cerveró, J. M. (1999). International Journal of Theoretical Physics
38, 2095–2109). 相似文献
987.
Alberto Marcone 《Mathematical Logic Quarterly》1995,41(3):373-383
In this paper we give a proof of the II12-completeness of the set of countable better quasi orderings (viewed as a subset of the Cantor space). This result was conjectured by Clote in [2] and proved by the author in his Ph.d. thesis [6] (see also [7]). Here we prove it using Simpson's definition of better quasi ordering ([15]) and as little bqo theory as possible. 相似文献
988.
Isobaric vapor–liquid equilibrium data (VLE) at 101.325 kPa have been determined in the miscible region for 1,1-dimethylethoxy-butane (BTBE) + methanol + water and 1,1-dimethylethoxy-butane (BTBE) + ethanol + water ternary systems, and for their constituent binary systems, methanol + BTBE and ethanol + BTBE. Both binary systems show an azeotrope at the minimum boiling point. In the ternary system BTBE + methanol + water no azeotrope has been found, however, the system BTBE + ethanol + water might form a ternary azeotrope near the top of the binodal. Thermodynamically consistent VLE data have been satisfactorily correlated using the UNIQUAC, NRTL and Wilson equations for the activity coefficient of the liquid phase. Temperature and vapor phase compositions have been compared with those calculated by the group-contribution methods of prediction ASOG, and the original and modified UNIFAC. Predicted values are not in good agreement with experimental values. 相似文献
989.
Roberto Floreanini Javier Negro Luis Miguel Nieto Luc Vinet 《Letters in Mathematical Physics》1996,36(4):351-355
Discrete versions of the heat equation on two-dimensional uniform lattices are shown to possess the same symmetry algebra as their continuum limits. Solutions with definite symmetry properties are presented. 相似文献
990.
Hiroshi Aoki Yoshio Umezawa Alberto Vertova Sandra Rondinini 《Analytical sciences》2006,22(12):1581-1584
An ion-channel sensor was demonstrated by immobilizing ETH 1001, an ionophore for ion-selective electrodes, on a gold electrode surface. The approach for preparing the sensor was to incorporate the ionophore into a mixed self-assembled monolayer of 10-mercaptodecanesulfonate and 11-hydroxy-1-undecanethiol formed on the surface. The voltammetric responses for the thus prepared sensor to the primary cation Ca(2+) were observed by using [Fe(CN)(6)](3-/4-) as an electroactive marker. The ionophore was stably immobilized on the electrode surface with the hydrophobic interaction between its alkyl chains and those of the alkanethiol. The introduction of a proper charge density to the electrode surface improved the sensor sensitivity with retaining the selective response to Ca(2+) against Mg(2+) with concentrations above 10(-4) M. 相似文献