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71.
Summary A new sensitive, spectrophotometric determination of gallium, based on the ternary gallium-Eriochrome Cyanine R-cetyltrimethylammonium system has been developed. At
max=588 nm the molar absorptivity is 1.20×105l·mole–1·cm–1. The maximum absorbance is attained in 5 min in the presence of a 10-fold molar ratio of Eriochrome Cyanine R and an approx. 50-fold ratio of cetyltrimethylammonium bromide (to Ga). Citrate, EDTA and to a lesser extent tartrate, interfere. Interference by metals can be eliminated by a preliminary extraction of gallium with di-isopropyl ether from 7 M hydrochloric acid in the presence of ascorbic acid as reductant. The results for gallium (at a concentration level of 1×10–4%) in aluminium metal and chloride indicate good precision and accuracy.
Empfindliche spektrophotometrische Bestimmung von Gallium mit Eriochromcyanin-R- und Cetyltrimethylammonium-Ionen
Zusammenfassung Ein neues, empfindliches spektrophotometrisches Verfahren zur Galliumbestimmung wurde ausgearbeitet. Es beruht auf der Verwendung des ternären Systems Gallium — EriochromcyaninR — Cetyltrimethylammonium. Bei max=588 nm beträgt die molare Extinktion 1,20·105 1·Mol–1·cm–1. Die maximale Absorption wird innerhalb von 5 min bei Gegenwart der 10fachen molaren Menge EriochromcyaninR und der etwa 50fachen Menge Cetyltrimethylammoniumbromid erreicht. Citrat, ÄDTA und in geringerem Maß Tartrat stören. Störende Wirkung durch Metalle kann durch vorhergehende Extraktion des Galliums mit Diisopropyläther aus 7 M Salzsäure in Gegenwart von Askorbinsäure als Reduktionsmittel vermieden werden. Die Ergebnisse (im Konzentrationsbereich von 10–4% Ga) in metallischem Aluminium und AICI3 sind genau.相似文献
72.
73.
João Paulo R.F. André Hugh D. Burrows Carlos F.G.C. Geraldes Maria Da Graça M. Miguel M.Helena S.F. Teixeira L.F. Vilas Boas 《Polyhedron》1996,15(24):4331-4340
Complexation of europium(III) with glyceryl-1- and -2-phosphates has been studied by metal ion luminescence, 1H and 13C NMR spectroscopy and potentiometry. From the luminescence and NMR studies, the formation of a 1:1 inner-sphere complex, in which the glyceryl phosphate is directly bound to the metal, is confirmed. Similar apparent binding constants at pH 2 were obtained by the three methods. Values obtained by NMR at pH 2 are 53 M−1 and 12 M−1 for glyceryl-1- and -2-phosphate, respectively. By comparison with literature data on related systems it is suggested that the ligands bind through the phosphate group. To obtain structural information from the NMR data, complexation has also been studied with the lanthanide ions Dy(III), Er(III) and Gd(III) using both chemical shift and relaxation data. From this, metal-proton distance ratios have been calculated. Comparison of 1H and 13C NMR spectral data in the presence of paramagnetic lanthanides suggests conformational equilibria in the solutions. From the potentiometric studies, global formation constants have been determined, and speciation diagrams obtained over the pH range 1.5pH7.0 for ligand/metal ratios of 1 and 30. Implications of these results on lanthanide induced fusion of phospholipid membranes are discussed. 相似文献
74.
Maria Helena Araujo Maria D. Vargas Anthony G. Avent Fabrizia Grepioni 《Journal of organometallic chemistry》2004,689(22):3513-3519
The reactions of [HIr4(CO)9(Ph2PCCPh)(μ-PPh2)] (1) or [Ir4(CO)8(μ3-η2-HCCPh)(μ-PPh2)2] (2) with HCCPh gave two isomeric forms of [Ir4(CO)6(μ3-η2-HCCPh)(μ2-η4-C4H2Ph2)(μ-PPh2)2] (3 and 4) in good yields as the only products. These compounds were characterized with analytical and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy and their molecular structures were established by X-ray diffraction studies. Compounds 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two μ-PPh2 that occupy different positions in the structures of the two isomers. Both molecules contain a HCCPh ligand bonded in a μ3-η2-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(H)C(Ph)}(μ-PPh2)2] (3) and tail-to-tail coupling, in that of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(Ph)C(H)}(μ-PPh2)2] (4), and which is linked to two metal atoms of the second wing of the butterfly. 相似文献
75.
Gustavsson S Rosén A Grennberg H Bolton K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(9):2223-2227
Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds. 相似文献
76.
The optimization of lead hydride generation in aqueous ethanolic media and the influence on its generation of the wine components, both white and red, have been studied. These interferences were overcome by careful control of the parameters affecting hydride generation and the procedure was applied to the determination of Pb in wines. The method is fast, accurate and sensitive and can be used to quantify 24 ppb of Pb in wines. 相似文献
77.
Fernando Ferreira 《Tetrahedron letters》2004,45(33):6287-6290
Oligonucleotides protected with N-(trimethylsilylethoxycarbonyl) (Teoc) and P-(trimethylsilylethanol) (Tse) groups were synthesized and deprotected by a single ZnBr2 treatment. Teoc group stabilized dA against depurination. This strategy was applied to the synthesis of base-sensitive oligonucleotide prodrugs bearing S-acetyl-2-thioethyl (Sate) phosphotriesters. 相似文献
78.
Ferreira CM Guedes da Silva MF Fraústo da Silva JJ Pombeiro AJ Kukushkin VY Michelin RA 《Inorganic chemistry》2001,40(6):1134-1142
The dialkylcyanamide complexes cis-[PtCl(NCNR(2))(PPh(3))(2)][BF(4)] 1 and cis-[Pt(NCNR(2))(2)(PPh(3))(2)][BF(4)](2) 2 (R = Me or Et) have been prepared by treatment of a CH(2)Cl(2) solution of cis-[PtCl(2)(PPh(3))(2)] with the appropriate dialkylcyanamide and one or two equivalents of Ag[BF(4)], respectively. Compounds 2 can also be obtained from 1 by a similar procedure. Their reaction with oximes, HON=CR'R' ' (R'R' ' = Me(2) or C(4)H(8)), in CH(2)Cl(2) and in the presence of Ag[BF(4)] or Cu(CH(3)COO)(2), leads to the novel type of azametallacycles cis-[Pt(NH=C(ON=CR'R")-NR2)(PPh3)2][BF4]2 4 upon an unprecedented coupling of the organocyanamides with oximes, in a process that proceeds via the mixed oxime-organocyanamide species cis-[Pt(NCNR(2))(HON=CR'R' ')(PPh(3))(2)][BF(4)](2) 3, and is catalyzed by either Ag(+) or Cu(2+) which activate the ligating organocyanamide by Lewis acid addition to the amide group. In contrast, in the organonitrile complexes cis-[Pt(NCR)(2)(PPh(3))(2)][BF(4)](2) 5 (R = C(6)H(4)OMe-4 or Et), obtained in a similar way as 2 (but by using NCR instead of the cyanamide), the ligating NCR is not activated by the Lewis acid and does not couple with the oximes. The spectroscopic properties of those complexes are reported along with the molecular structures of 2b (R = Et), 4a1 (R = Me, R'R' ' = Me(2)), and 4b1 (R = Et, R'R' ' = Me(2)), as established by X-ray crystallography which indicates that in the former complex the amide-N-atoms are trigonal planar, whereas in the latter (4a1 and 4b1) the five-membered rings are planar with a localized N=C double bond (imine group derived from the cyanamide) and the exocyclic amide and alkylidene groups (in 4b1) are involved in two intramolecular H-bonds to the oxygen atom of the ring. 相似文献
79.
M. G. Ferreira Da Silva J. M. Fernàndez Navarro 《Journal of Sol-Gel Science and Technology》1994,2(1-3):895-901
The effect of thermal treatment on the structural incorporation of Cr2O3 in xCr2O3·(100 – x)SiO2 and 5R
n
O·xCr2O3·(95 – x)SiO2 (where x=0.01–1 mol.% and R=Li, Na and Ca) gel glasses was studied by optical absorption spectrophotometry, DTA-TG, XRD and electron microscopy.Samples heat treated at 60°C have green color due to the presence of Cr3+ in octahedral coordination. The optical transmission, and color (yellow, orange or ambar), of the samples heat treated between 200 and 700°C prove that Cr3+ (octahedrally coordinated) and Cr6+ (tetrahedrally coordinated) are both present. Segregation of Cr2O3 take place at temperatures above 800°C.In reducing conditions the gel glasses were green due to the presence of a high content of Cr3+ ions. Samples containing Li or Na show crystalline phases at temperatures below 850°C. 相似文献
80.
Helena?H?kanssonEmail author Per?Ahlgren Ulf?Germg?rd 《Cellulose (London, England)》2005,12(3):327-335
The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the
point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one
conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results
indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore
only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed
kraft pulp. A model explaining the LODP-results is proposed. 相似文献