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101.
102.
103.
Two solid-membrane methods exist for separating mixtures of organic liquids. They are pervaporation, in which the product phase is a vapour, and hyperfiltration in which feed and product phases are both liquid. Technically hyperfiltration is similar to reverse osmosis but, if that term is to be used at all, it should be restricted to dilute solutions of solutes to which the membrane is almost semi-permeable. The polymer membranes which have been found so far to give significant degrees of separation and fluxes with organic liquid mixtures have been crystalline polar polymers with high glass temperatures. The problems of membrane preparation are thus more severe than with almost amorphous, freely soluble polymers such as cellulose acetate.The absorption of liquids from a mixture by a polymer and their permeation in the polymer have received relatively little attention and it is not yet possible to infer the behaviour from that of the polymer towards each liquid alone. Nevertheless a theory of hyperfiltration can be developed based on Henry's and Fick's laws and neglecting any direct coupling of flows. The equations which predict the separation and fluxes are useful in the first place to predict the thermodynamic restraints on any potentially useful separation process. It turns out that relatively large pressures are required, 100 atm or more, and hyperfiltration is better adapted to further purifying a relatively good product than to recovering a small amount of a valuable substance from a large volume of waste.The equations lend themselves to a direct experimental test. An apparatus for doing this has been constructed and two liquid mixtures and membranes have been studied. They are toluene + n-heptane with an asymmetric polyacrylonitrile membrane and methanol + isobutanol with a uniform cellulose membrane. The mixtures were chosen as being thermodynamically close to ideal because this simplifies the interpretation of the data. Their nonideality has been taken fully into account.The results show that the simple theory accounts very well for the observed facts. For the first system the selectivity coefficient was about 2 and for the second, about 15.The mechanism of transport is found to be the normal solution-diffusion mechanism for permeation of organic solvents in polymers. There is some positive frictional coupling between the two liquids as a result of which the improvements in separation to be expected from an increase in the applied pressure are not achieved quantitatively. The increasing absorption of liquid by the membrane as the mole fraction of the preferentially absorbed liquid in the mixture is increased increases its permeability to both components by about 相似文献
104.
105.
Savici AT Fukaya A Gat-Malureanu IM Ito T Russo PL Uemura YJ Wiebe CR Kyriakou PP MacDougall GJ Rovers MT Luke GM Kojima KM Goto M Uchida S Kadono R Yamada K Tajima S Masui T Eisaki H Kaneko N Greven M Gu GD 《Physical review letters》2005,95(15):157001
Muon spin relaxation measurements in high transverse magnetic fields [FORMULA: SEE TEXT] revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)2CuO4 and La1.875Ba0.125CuO4, existing well above Tc and TN. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T approximately 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7. 相似文献
106.
The hydrozirconation of alkynes with zirconocene hydrochloride and the dimethylzinc-mediated addition of alkenylzirconocenes to diphenylphosphinoyl imines can be greatly accelerated with microwave irradiation, resulting in a convenient and rapid one-pot process for the preparation of synthetically useful allylic amines. 相似文献
107.
Vivekananda S Sadílek M Chen X Adams LE Turecek F 《Journal of the American Society for Mass Spectrometry》2004,15(7):1068-1079
The title radical (1) is generated in the gas-phase by collisional neutralization of carbonyl-protonated oxolan-3-one. A 1.5% fraction of 1 does not dissociate and is detected following reionization as survivor ions. The major dissociation of 1 (approximately 56%) occurs as loss of the hydroxyl H atom forming oxolan-3-one (2). The competing ring cleavages by O[bond]C-2 and C-4[bond]C-5 bond dissociations combined account for approximately 42% of dissociation and result in the formation of formaldehyde and 2-hydroxyallyl radical. Additional ring-cleavage dissociations of 1 resulting in the formation of C(2)H(3)O and C(2)H(4)O cannot be explained as occurring competitively on the doublet ground (X) electronic state of 1, but are energetically accessible from the A and higher electronic states accessed by vertical electron transfer. Exothermic protonation of 2 also produces 3-oxo-(1H)-oxolanium cation (3(+)) which upon collisional neutralization gives hypervalent 3-oxo-(1H)-oxolanium radical (3). The latter dissociates spontaneously by ring opening and expulsion of hydroxy radical. Experiment and calculations suggest that carbohydrate radicals incorporating the 3-hydroxyoxolan-3-yl motif will prefer ring-cleavage dissociations at low internal energies or upon photoexcitation by absorbing light at approximately 590 and approximately 400 nm. 相似文献
108.
Vinyl acetate formation by the reaction of ethylene with acetate species on oxygen-covered Pd(111) 总被引:1,自引:0,他引:1
Stacchiola D Calaza F Burkholder L Tysoe WT 《Journal of the American Chemical Society》2004,126(47):15384-15385
The reaction pathway of vinyl acetate synthesis is scrutinized by reacting gas-phase ethylene (at an effective pressure of 1 x 10-4 Torr) with eta2-acetate species (with a coverage of 0.31 +/- 0.02 monolayer) on a Pd(111)-O(2x2) model catalyst surface in ultrahigh vacuum. It is found that the 1414 cm-1 infrared feature due to the symmetric OCO stretching mode of the acetate species decreases in intensity due to reaction with gas-phase ethylene, while temperature-programmed desorption experiments demonstrate that vinyl acetate is formed. The formation of ethylidyne species is detected when almost all of the acetate species have been removed. The experimental removal kinetics are reproduced by a model in which adsorbed acetates react with an ethylene-derived (possibly ethylene or vinyl) species, where ethylene adsorption is blocked by the acetate present on the surface. 相似文献
109.
Higham LT Kreher UP Mulder RJ Strauss CR Scott JL 《Chemical communications (Cambridge, England)》2004,(20):2264-2265
A member of a new class of novel macrocycles possessing both polyether and phenolic functionalities, forms dimers in both the solid-state and in solution when exposed to chloroform, dichloromethane or toluene, but does not self-associate in the presence of dimethyl sulfoxide. 相似文献
110.
Peter Rapta Krzysztof R. Idzik Vladimír Lukeš Rainer Beckert Lothar Dunsch 《Electrochemistry communications》2010,12(4):513-516
The role of the chemical structure in an alternative charge stabilisation and a changing reactivity of star-shaped compounds with a central triazine ring linked to aryl groups like thiophene, furan or ethylenedioxythiophene synthesized by a Stille cross-coupling procedure, is followed by spectroelectrochemical measurements. While cathodic reduction leads to stable anion radicals with a delocalised spin on the central triazine moiety, dimerisation and oligomerisation occurs upon anodic oxidation. The stability of the charged states in the polymer film increased substantially using an EDOT (3,4-ethylenedioxythiophene) side group. The location of the charged states on the molecules has been proved by computations. These star-shaped molecules are excellent model structures for studies of the competition of dimerisation and oligomerisation processes based on the variation of the electron and spin distribution in the molecules. 相似文献