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91.
Sulphite (1–80 × 10?5 M) in formaldehyde-stabilized solutions is determined by injection into a flowing stream of pH 8.5 phosphate buffer, passing through a mini-column of sulphite oxidase immobilized on controlled-pore glass, with amperometric detection of the hydrogen peroxide produced. Sulphite oxidase (5–100 U l?) is determined by injection into a flowing stream of formaldehyde-stabilized 2 × 10?3 M sodium sulphite in pH 8.0 phosphate buffer; hydrogen peroxide is again monitored. 相似文献
92.
Alan E. Tonelli 《European Polymer Journal》1978,14(4):305
The Flory-Williams rotational isomeric state models describing the conformational characteristics of polyesters and polyamides are combined to calculate the dimensions of the alternating polyesteramide (PEA) of the type 6NT6. The calculated ratio of unperturbed dimensions is in excellent agreement with the value recently obtained from an intrinsic viscosity-molecular weight study of PEA. 相似文献
93.
Conway B Hevia E Kennedy AR Mulvey RE Weatherstone S 《Dalton transactions (Cambridge, England : 2003)》2005,(8):1532-1544
Synthesised either by an unusual tert-butyl metathesis between tert-butyllithium and a n,s-butylmagnesium amide or by reaction of an alkyl Grignard reagent and a sodium amide, five tert-butylmagnesium amides, Bu(t)MgDBA (5)(DBA=dibenzylamide), Bu(t)MgDA (6)(DA=diisopropylamide), Bu(t)MgHMDS (7)(HMDS=1,1,1,3,3,3-hexamethyldisilazide), Bu(t)MgTMP (8)(TMP=2,2,6,6-tetramethylpiperidide) and Bu(t)MgNCy2 (9)(cy=cyclohexyl) have been isolated as crystalline solids. All five amides have been characterised by X-ray crystallography and solution NMR spectroscopic studies. The former studies reveal a common dimeric molecular structure with amido bridges in a planar (MgN)2 ring and terminal Bu(t) ligands on the Mg atoms. Also described is the dodecameric primary amide [Bu(n)MgN(H)Dipp]12 (10a) and its monomeric solvate Bu(n)MgN(H)Dipp.TMEDA (10b)(Dipp=2,6-diisopropylphenyl; TMEDA=N,N,N',N'-tetramethylethylenediamine). The crystal structures of the oxo-insertion products Bu(t)MgOBu(t).THF (11), Bu(t)Mg(mu-OBu(t))(mu-TMP)MgTMP (12) and Mg(OBu(n))HMDS.solv [solv=THF (13a) or Et2O (13b)], made fortuitously during the course of this work, are also presented. 相似文献
94.
Alan H. Cowley 《Journal of organometallic chemistry》2004,689(24):3866-3872
A survey of some recent developments and past achievements in low-valent main group chemistry is presented. Some emerging implications of this area of chemistry in materials science, catalysis and new reagent development are also discussed. 相似文献
95.
Grossfield A 《The Journal of chemical physics》2005,122(2):024506
The solvation of simple ions in water is studied using molecular dynamics simulations with a polarizable force field. Previous simulations using this potential demonstrated that anions are more favorably solvated in water than cations. The present work is an attempt to explain this result by examining the effects of ions on the surrounding water structure, with particular focus on the first solvation shell and its interactions with the surrounding water. We conclude that while the first solvation shell surrounding cations is frustrated by competition between ion-water and water-water interactions, solvation of anions is compatible with good water-water interactions. 相似文献
96.
Leonid Mashlyakovskiy Elena Khomko Natalya Volynkina Claudio Tonelli 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3771-3795
The kinetics of the dibutyltin dilaurate (DBTDL)‐catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z‐DOL H‐1000 of various molecular weights (100–1084 g mol?1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30–60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl‐containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero‐order, first‐order, second‐order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771–3795, 2002 相似文献
97.
The thiols Cp2M(SH)2, where M = Ti and Zr, react to form the complexes Cp2MS5 when treated with mono- and di-sulfur transfer reagents. Treatment of Cp2MCl2 with Li2S2 and sulfur gave Cp2MS5, M = Ti, Zr and Hf, in better yield. The new Zr and Hf complexes have a six-membered MS5 ring in a chair conformation similar to the previously observed for M = Ti. Variable temperature NMR studies show that the barriers to MS5 ring inversion decrease in the order Ti > Hf > Zr. 相似文献
98.
Propane fuel cells using H(3)PO(4)-doped polybenzimidazole polymer membranes produce low and unsustainable current densities at temperatures up to 250 degrees C under anhydrous conditions. Stable intermediate species blocked the surface of noble metal anode catalysts, and the intermediate species could not react further into desorbable final products. In contrast, when water was introduced by light humidification (S(r) 0.08%) of the propane stream, sustainable and higher current densities were achieved. Water participated in the reaction sequence to form surface-bound hydrocarbon and then oxygen-containing intermediates and thereby generated CO and CO(2) as the only carbon-containing products. 相似文献
99.
The effect of isocyanides as axial ligands on the formation and stability of verdoheme by oxidation has been examined. The reaction of [Fe(III)(OEPO)]2 with t-butyl isocyanide under dioxygen-free conditions results in the formation of (t-BuNC)2Fe(II)(OEPO*) with an electron paramagnetic resonance at g=2.009 with a peak-to-peak separation of 23.5 G at 4 K. (OEPO is the trianion of octaethyloxophlorin and OEPO* is the radical dianion obtained from OEPO by one-electron oxidation.) Exposure of chloroform solutions of either (2,6-xylylNC)2Fe(II)(OEPO*) or (t-BuNC)2Fe(II)(OEPO*) to dioxygen followed by the addition of ammonium hexafluorophosphate results in their transformation into the diamagnetic verdohemes, [(2,6-xylylNC)2Fe(II)(OEOP)](PF6) and [(t-BuNC)2Fe(II)(OEOP)](PF6), yields 68 and 70%, respectively. (OEOP is the anion of octaethyl-5-oxaporphyrin.) The oxidation reactions of (2,6-xylylNC)2Fe(II)(OEPO*) and (t-BuNC)2Fe(II)(OEPO*) have also been monitored by 1H NMR spectroscopy. No resonances due to paramagnetic products could be detected, the reactions appear to result only in the formation of the diamagnetic verdohemes, and the products are not susceptible to further oxidation. 相似文献
100.
D. Tonelli Renato Seeber Claudio Ciavatta Carlo Gessa 《Analytical and bioanalytical chemistry》1997,359(7-8):555-560
Fractions of humic acids, resolved by ultrafiltration of extracts from a sample of peat treated with alkaline pyrophosphate
solution, have been submitted to high-performance size-exclusion chromatography, with the aim of determining the molecular
weight distributions. Anomalous peaks, located at retention volumes higher than those corresponding to the main signal, are
present in the elution profiles relative to the lightest fractions. These peaks are more intense when using a refractive index
detector rather than a UV detector. Elemental analysis data for the lightest fractions suggested that the spurious peaks are
due to the presence of inorganic material. The hypothesis that pyrophosphate interacts with humic acids in the course of the
extraction has been confirmed by colorimetric determination of the phosphorus content in the different fractions. As a consequence,
the extraction procedure has been modified by using 0.1 mol/L NaOH as extractant.
The average molecular weights of the various fractions, following NaOH extraction, result in substantial agreement with those
obtained following pyrophosphate solution extraction (if the ‘pyrophosphate peaks’ present in the chromatographic profile
are discarded in the calculations).
Received: 18 November 1996 / Revised: 18 February 1997 / Accepted: 23 February 1997 相似文献