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51.
De la Fuente JR Jullian C Saitz C Neira V Poblete O Sobarzo-Sánchez E 《The Journal of organic chemistry》2005,70(22):8712-8716
[reaction: see text] Photoreduction of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the N-hydrogen oxoisoaporphine anion. When triethylamine, TEA, was used as the electron donor in anaerobic conditions, 1-diethylaminobutadiene, DEAB, was one of the oxidation products of TEA, among diethylamine and acetaldehyde. DEAB was identified by (1)H NMR and GC-MS experiments by comparison with the authentic 1-diethylaminobutadiene. This is the first report of a butadienyl derivative formed in the dye-sensitized photooxidation of TEA. In addition, isotopic exchange experiments with TEA-d(15) and D(2)O show that the hydrogens at carbon-2 and carbon-4 of the butadienyl moiety are exchangeable. The observed isotopic exchange pattern could be explained by the head-to-tail coupling of an N,N-diethylvinylamine intermediate that exchanges hydrogens at the C-beta via the enammonium ion. 相似文献
52.
The modeling of liquid–vapor equilibrium in ternary mixtures that include substances found in alcoholic distillation processes of wine and musts is analyzed. In particular, vapor–liquid equilibrium in ternary mixtures containing water + ethanol + cogener has been modeled using parameters obtained from binary mixture data only. The congeners are substances that although present in very low concentrations, of the order of part per million, 10−6 to 10−4 mg/L, are important enological parameters [1] and [2]. In this work two predictive models, the PSRK equation of state and the UNIFAC liquid phase model and two semipredictive activity coefficient models: NRTL and UNIQUAC have been used. The results given by these different models have been compared with literature data and conclusions about the accuracy of the models studied are drawn, recommending the best models for correlating and predicting the phase equilibrium in this type of mixtures. 相似文献
53.
Rodella Cristiane B. Franco Roberto W.A. Magon Claudio J. Donoso Jose P. Nunes Luis A.O. Saeki Margarida J. Aegerter Michel A. Sargentelli Vagner Florentino Ariovaldo O. 《Journal of Sol-Gel Science and Technology》2002,25(1):83-88
Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V2O5/TiO2 catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm–1 and 770 to 850 cm–1. The Raman spectra do not exhibit characteristic peaks of crystalline V2O5. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V4+ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V4+ ions are located in sites with octahedral symmetry substituting for Ti4+ ions in the rutile structure. Magnetically interacting V4+ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V2O5, a partial oxidation of V4+ to V5+ is apparent from the EPR results. 相似文献
54.
The electronic structure and the spectroscopic properties of [Au2(CS3)2]?2, [Au2(pym‐2‐S)2] (pym = pyrimidethiolate), [Au2(dpm)2]+2 (dpm = bis(diphosphino)methane) were studied using density functional theory (DFT) at the B3LYP level. The absorption spectrum of these binuclear gold(I) complexes was calculated by single excitation time‐dependent (TD) method. All complexes showed a 1(5dσ* → 6pσ) transition associated with a metal–metal charge transfer, which is strongly interrelated with the gold–gold distance. Furthermore, we have calculated the frequency of the gold–gold vibration (νAu2) on the above complexes. The values obtained are theoretically in agreement with experimental range. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
55.
Giovanni Greco Ettore Novellino Maurizio Pellecchia Carlo Silipo Antonio Vittoria 《Journal of computer-aided molecular design》1994,8(2):97-112
Summary An example of a CoMFA study is described with the aim to discuss one of the major problems of this 3D QSAR method: lack of variable selection. It is shown that the use of nonrelevant energy parameters might produce CoMFA contour maps which poorly reflect the actual nature of the binding site and are in part statistical artefacts. The data set employed in our analysis comparises triazine inhibitors of dihydrofolate reductase (DHFR), isolated from chicken liver, which have already been the object of a QSAR study by other authors. Since three-dimensional structures of triazine-DHFR complexes are known, it was possible not only to reduce ambiguities in the superimposition of the ligands, but also to compare the resulting CoMFA contour maps with the enzyme active site.Supplementary material available: The Cartesian coordinates and the atomic charges of the PM3-optimized structures used in the CoMFA study are available as MOL2 files upon request.To whose memory this paper is dedicated. 相似文献
56.
Pettinari C Pettinari R Fianchini M Marchetti F Skelton BW White AH 《Inorganic chemistry》2005,44(22):7933-7942
New [CpM(Q)Cl] complexes (M = Rh or Ir, Cp = pentamethylcyclopentadienyl, HQ = 1-phenyl-3-methyl-4R(C=O)-pyrazol-5-one in general, in detail HQ(Me), R = CH(3); HQ(Et), R = CH(2)CH(3); HQ(Piv), R = CH(2)-C(CH(3))(3); HQ(Bn), R = CH(2)-(C(6)H(5)); HQ(S), R = CH-(C(6)H(5))(2)) have been synthesized from the reaction of [CpMCl(2)](2) with the sodium salt, NaQ, of the appropriate HQ proligand. Crystal structure determinations for a representative selection of these [CpM(Q)Cl] compounds show a pseudo-octahedral metal environment with the Q ligand bonded in the O,O'-chelating form. In each case, two enantiomers (S(M)) and (R(M)) arise, differing only in the metal chirality. The reaction of [CpRh(Q(Bn))Cl] with MgCH(3)Br produces only halide exchange with the formation of [CpRh(Q(Bn))Br]. The [CpRh(Q)Cl] complexes react with PPh(3) in dichloromethane yielding the adducts CpRh(Q)Cl/PPh(3) (1:1) which exist in solution in two different isomeric forms. The interaction of [CpRh(Q(Me))Cl] with AgNO(3) in MeCN allows generation of [CpRh(Q(Me))(MeCN)]NO(3).3H(2)O, whereas the reaction of [CpRh(Q(Me))Cl] with AgClO(4) in the same solvent yields both [CpRh(Q(Me))(H(2)O)]ClO(4) and [CpRh(Cl)(H(2)O)(2)]ClO(4); the H(2)O molecules derive from the not-rigorously anhydrous solvents or silver salts. 相似文献
57.
de Farias Robson Fernandes Martínez Leandro Airoldi Claudio 《Transition Metal Chemistry》2002,27(7):748-750
This paper describes the synthesis, characterization and a thermogravimetric (t.g.) study of 11 adducts of general formula MCl2·nL (M = Cu, Co and Sn; n = 1 and 2 for Sn, and 2 for Cu and Co; L = ethyleneurea eu, ethylenethiourea etu, and propyleneurea pu). The i.r. results shows that the eu and pu adducts are coordinated through oxygen, whereas for etu nitrogen is the coordination site. The (C=O) or (C=S) trend is: Cu > Co > Sn. The t.g. curves show that the adducts release ligand molecules in a single mass loss step. As regards considering adducts with the same stoichiometry, the observed thermal stability trend is: etu > pu > eu. 相似文献
58.
This paper presents some new data on nitrophenol formation from phenol under illumination, and reviews the studies performed on phenol photonitration, from its discovery in 1988 to the very recent elucidation of its reaction pathway by the authors. Recent experimental results account for the pH effect on phenol photonitration. The nitrogen sources so far investigated are nitrate and nitrite, which undergo photolysis upon absorption of near-UV light. These studies have given a relevant information on the role of both nitrate and nitrite as environmental factors. Such processes can take place both in natural waters and in atmospheric hydrometeors. 相似文献
59.
Chromatographic evaluations of a C18 dimethylurea phase in 150 mm x 3.9 mm HPLC columns were performed using the Tanaka and Engelhardt test mixtures. The applicability of the new C18 dimethylurea phase was also evaluated with a mixture of some herbicides and their metabolites. An artificial aging procedure was also performed by passing a potassium phosphate mobile phase buffered at pH 7.0 through C18 50 mm x 3.9 mm dimethylurea columns. The column stability was evaluated by means of the chromatographic parameters obtained for the separation of some compounds from the Neue test mixture, using apolar, polar and highly basic analytes. 相似文献
60.
Claudio Bernardi 《Annali di Matematica Pura ed Applicata》1980,126(1):253-266
Summary This paper is concerned with the Stone space X of a direct product
of infinitely many Boolean algebras. In paragraph 2, after recalling that X is the Stone-ech compactification of the sum (disjoint union)
of the Stone spaces of the algebras Bi, we exhibit a compactification of
which is not a Stone space and we give a method to construct all the «Stone compactifications» of
(the corresponding Boolean algebras are easily characterised). In paragraph 3, a set of ultrafilters of B (the «decomposable» ultrafilters) are introduced: this set properly contains
, but, as is shown in paragraph 5, there are direct products that admit nondeeomposable ultrafilters (this is the case iff the set {Card Bi: i I } is not bounded by a natural number). In paragraph 4, among other things, we prove, for the set of decomposable ultrafilters, a weak form of countable compactness, in the sense that every countable clopen cover has a finite subcover; then, we deduce that the set of decomposable ultrafilters is pseudocompact, while obviously
is not. Lastly, in paragraph 6, we give a second characterisation of the Stone space of B, showing that every ultrafilter of B can be obtained by iterating in a suitable way the procedure which leads to the construction of decomposable ultrafilters.
Lavoro eseguito nell'ambito dell'attività del Comitato Nazionale per le Scienze Matematiche del C.N.R. 相似文献
Lavoro eseguito nell'ambito dell'attività del Comitato Nazionale per le Scienze Matematiche del C.N.R. 相似文献