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991.
The electrochemical reduction of NO(2)ClO(4) solutions at a platinum electrode in sulpholane has been studied. The results suggest the following scheme for the reduction of NO(+)(2) : 2NO(+)(2) + 2e(-) right harpoon over left harpoon 2NO(2) right harpoon over left harpoon N(2)O(4). A fast dimerization of nitrogen dioxide, which is favoured by the high donor number of sulpholane, follows the charge-transfer step. The NO(+)(2) ion is much more oxidative than the NO(+) ion in sulpholane, whereas the oxidizing power of the two species is nearly the same in nitromethane or acetonitrile solution. This result can be used to explain the role of water present at trace level. 相似文献
992.
Highly diastereoselective Lewis acid mediated aza-Diels-Alder reactions of chiral auxiliary derivatized 2H-azirines have been accomplished for the first time, yielding bi and tri-cyclic heterocyclic compounds, comprising aziridine and tetrahydropyridine substructures, in up to 97% de; with the absolute stereochemistry of the major product confirmed by X-ray crystallography. 相似文献
993.
Absolute rate constants for the addition of the highly nucleophilic 2-hydroxy-2-propyl radical to eight fast-reacting 1- and 1,1-disubstituted alkenes in MeOH at room temperature have been determined by laser flash photolysis. Also the absorption spectra of the 2-hydroxy-2-propyl and the benzylic and alkyl-type adduct radicals are presented. The rate constants were obtained using various methods for the analysis of the kinetic traces and support earlier findings. 相似文献
994.
Zusammenfassung Die Darstellung eines neuartigen, zum gas-chromatographischen Nachweis geeigneten Phosphorderivats von Oestron wird beschrieben. Der Oestron-dimethylphosphinsäureester läßt sich sehr empfindlich mit dem Alkaliflammenionisationsdetektor (AFID) nachweisen. Die Umsetzung von Dimethylaminodimethylphosphin mit Oestron ist unter den angegebenen Bedingungen quantitativ und sehr gut reproduzierbar. Bezugskurven mit Oestronkonzentrationen von 2–50 g Oestron im Ansatz hatten bei Nachweis mit dem FID einen Korrelationskoeffizienten von 0,999, bei Nachweis mit dem AFID von 0,998. 200 pg des Derivats konnten noch gut gemessen werden. Die Reaktionsbedingungen werden diskutiert. Auf die erfolgreiche Derivatisierung anderer Steroidhormone wird abschließend hingewiesen.
Estrone-dimethylphosphinic ester, a new type of derivatives for the sensitive, gas chromatographic determination of steroids
The synthesis of estrone-dimethyl phosphinic ester, with good gas chromatographic properties is described. This ester is very sensitively detectable with the alkali detector. The reaction of dimethyl-amino-dimethylphosphine with estrone is quantitative and reproducible. Calibration curves with concentrations of estrone varying from 2 to 50 g per sample detected by a FID yielded a correlation coefficient of 0.999, detected by an AFID one of 0.998. The smallest amount which could be measured was 200 pg. The reaction conditions are discussed. The possibility of the derivatisation of other steroid hormones is shown.相似文献
995.
S. Mlinko E. Fischer und J. F. Diehl 《Fresenius' Journal of Analytical Chemistry》1972,261(3):203-208
Zusammenfassung Zur Ermittlung des natürlichen Tritiumgehaltes von Lebensmitteln wurde eine Verbrennungsanlage entwickelt, in der aus Lebensmitteln beliebiger Zusammensetzung in einem Arbeitsvorgang etwa 100 ml Wasser gewonnen werden. Zur Messung der Tritiumaktivität dieses Verbrennungswassers im Flüssigkeitsszintillationsspektrometer wird das Wasser von störenden Verbrennungsprodukten durch Destillation gereinigt. Aufbau und Arbeitsweise der Verbrennungsanlage und des Wasserreinigungssystems werden beschrieben.Die Teilnahme von S. Mlinko an diesen Untersuchungen wurden durch ein Stipendium der Alexander von Humboldt-Stiftung ermöglicht, wofür wir hier unseren herzlichen Dank sagen wollen.Frl. I. Kuschel wird für die wertvolle Mitarbeit bei den Untersuchungen gedankt. 相似文献
996.
Patrick Chaumette Hubert Mimoun Lucien Saussine Jean Fischer Andre Mitschler 《Journal of organometallic chemistry》1983,250(1):291-310
Novel oxoperoxomolybdenum(VI) complexes with the general formula MoO(O2)L2X2 (III, L = DMF, HMPT) and MoO(O2)Cl(ON)L(IV, ON) = pyridin-2-carboxylate (Pic), 8-hydroxyquinolinate (Quin) were prepared from the reaction of Ph3COOH or H2O2 with the corresponding cis-dioxo complexes. In the reaction with Ph3COOH both oxygen atoms of the peroxo moiety were found, by 18O labeling experiments, to come from the hydroperoxide. The X-ray crystal structure of MoO(O2)Cl(Pic)(HMPT) revealed a bipyramidal pentagonal surounding with a rather short OO distance (1.41 Å). Complexes III were found to be more reactive than MoO(O2)2,HMPT for the epoxidation of olefins (oxidative cleavage products are consecutively formed) but react by the same cyclic peroxymetalation mechanism. The absence of reaction in the case of complexes IV illustrates the necessity for the metal to possess an equatorial releasable coordination site adjacent to the peroxo group for the oxygen transfer to occur. Catalytic oxidation of olefins using Ph3COOH gave a selectivity in oxygenated products very different from that using t-BuOOH, and 18O labeling studies showed that alkyl-peroxidic rather than peroxo species are intermediates in this latter reaction. The mechanism of epoxidation of olefins by alkyl hydroperoxides catalyzed by d0 metal complexes is discussed. 相似文献
997.
Li QS Schwaneberg U Fischer P Schmid RD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(9):1531-1536
The self-sufficient cytochrome P450 BM-3 enzyme from Bacillus megaterium catalyzes subterminal hydroxylation of saturated long-chain fatty acids and structurally related compounds. Since the primary structure of P450 BM-3 is homologous to that of mammalian P450 type II, it represents an excellent model for this family of enzymes. During studies on the directed evolution of P450 BM-3 into a medium-chain fatty-acid hydroxylase, several mutants, in particular the triple mutant Phe87Val, Leu188Gln, Ala74Gly, were observed to hydroxylate indole, producing indigo and indirubin at a catalytic efficiency of 1365 M(-1)s(-1) (kcat=2.73 s(-1) and Km=2.0 mM). Both products were unequivocally characterized by NMR and MS analysis. Wild-type P450 BM-3 is incapable to hydroxylate indole. These results demonstrate that an enzyme can be engineered to catalyze the transformation of substrates with structures widely divergent from those of its native substrate. 相似文献
998.
Karel Cizek Jiri Barek Jan Fischer Karolina Peckova Jiri Zima 《Electroanalysis》2007,19(12):1295-1299
The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10?8–1×10?6 mol L?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10?7–1×10?5 mol L?1, respectively. Limits of determination were 3×10?8 mol L?1 (3‐nitrofluoranthene) and 2×10?7 mol L?1 (3‐aminofluoranthene). 相似文献
999.
Molar conductances of dilute aqueous benzoic acid solutions are presented for temperatures from 5 to 80°C. The data have been analyzed to give acid dissociation constants as well as ΔH o, ΔS o, and ΔC p o for the ionization process and the limiting conductance of the benzoate ion. The conductance-viscosity product changes less than 4% over the temperature range, indicating that the interaction of the benzoate ion with the solvent changes little if at all with increasing temperature. The pK a(m) vs.T data show that ΔH o decreases quadratically while ΔC p o increases linearly withT although, over the 75°C range, ΔC p o increases only about 6 cal-mole?1 deg?1 around an average of ?37 cal-mole?1deg?1. The acid dissociation constants as derived from the conductance-molal concentration analysis show an average uncertainty of about 0.1% and are fitted to within about 0.01% by the equation $$p{\text{K}}_{\text{a}} (m) = - 75.5422 + 3136.34/T + 28.7965 log T - 6.8139 {\text{x}} 10^{ - 3{\text{T}}} $$ whereT is the absolute temperature. 相似文献
1000.
The salt elimination reaction of the transition carbonyl metal-lates [L(CO)nM](Na/K) (M = Cr, Mo, W, Mn, Re, Fe, Co, Ni; L= CO, n5-C5R5, PR3; n= 1-4; R= alkyl, aryl) with the base-stabilized galliumhalides ClaGaR3 -a(Do) (R = H, alkyl, halide; Do = THF, N(CH3)3, NC7H13) or ClaGa[(CH2)3N-R2](R)2 - a yielded almost quantitatively the transition metal-substituted, gallanes [L(CO)nM]aGaR3 - a(Do) and [L(CO)n-M]aGa[(CH2)3NR2](R)2 - a, respectively. Residual halide functionalities in these complexes were selectively replaced by various other groups. The new compounds were characterized by means of elemental analysis, 1H-, 13C-, 31P-NMR, MS, and lR v(CO) data. The single-crystal X-ray structure analysis of trans-(Ph3P)(CO)3Co-Ga[(CH2) 3N(C2H5)2](R)( 6s : R = Cl, 6t : R= CH3) showed s̀(Co-Ga) lengths of 237.78(4) and 249.5(1) pm, respectively. A short s̀(Fe-Ga) contact of 236.18(3) pm was found for (n5-C5H5)(CO)2Fe-Ga-Cl2[N(CH 3)3] ( 5a ). Low-pressure MOCVD experiments were performed to give thin films of analytically pure CoGa alloy. 相似文献