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1.
We construct for each n2 an isometric C-imbedding HnE6n–6 of the n-dim. hyperbolic space into the Euclidean space E6n–6 whose image is the graph of a C-map RnR5n–6. This generalizes a well known result of D. Blanusa 1955 (the case n=2). 相似文献
2.
B. Bastian T. P. Knepper P. Hoffmann H. M. Ortner 《Fresenius' Journal of Analytical Chemistry》1994,348(10):674-679
A method for the identification and quantification of aromatic sulfonic acids in industrial waste water has been developed. The preparation of the samples comprises a clean-up step and an enrichment step, utilizing i) reversed-phase extraction and ii) ion-pair solid phase extraction. The aromatic sulfonic acids are separated by ion-pair chromatography with diode-array detection. An advantage of the developed ion-pair chromatographic method is the separation of linear alkylbenzenesulfonic acids (LAS), lignosulfonic acids and aromatic sulfonic acids in one chromatographic run. Also described is an optimized clean-up procedure for collected fractions of a preparative chromatographic run to identify monosulfonic acids with GC/MS after methylation. The detection limits for aromatic sulfonic acids in industrial waste waters are at the g/l level. 相似文献
3.
The quantitative determination of the quaternary spasmolytic compound ciclotropium and its metabolite N-isopropyltropinium is described for human plasma and urine. The analytical procedure consists of ion-pair extraction from biological material, alkaline hydrolysis, subsequent derivatization with the fluorophor flunoxaprofen chloride and separation by high-performance liquid chromatography on a reversed-phase column with fluorimetric monitoring. The detection limits of 0.5 ng/ml in plasma and 10 ng/ml in urine at signal-to-noise ratios higher than 3 permit the determination of pharmacokinetic parameters after therapeutic doses. 相似文献
4.
5.
Meier H Gerold J Kolshorn H Mühling B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(2):360-370
Four OPV series 1-4 (a-d) with a terminal dialkylamino group as electron donor were prepared by Wittig-Horner reactions. To study the influence of the push-pull effect on the long-wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO(2)). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)-an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor-substituted series 1 a-4 a and the series 1 b-4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c-4 c with terminal CHO groups, so that the absorption maxima are almost independent of the length of the chromophore. A hypsochromic shift is observed for the series 1 d-4 d, which contains the strong acceptor group NO(2). This anomaly disappears on protonation of the dialkylamino group because the push-pull effect disappears in the ammonium salts. The results can be explained by semiempirical quantum mechanics (AM1, INDO/S). The HOMO-LUMO transition, which is mainly responsible for the ICT, becomes less important in the electron transitions S(0)-->S(1) when the distance between donor and acceptor is increased. The commonly used VB model, which contains an electroneutral and a zwitterionic resonance structure, is contrasted with a MO model with dipole segments at both ends of the OPV chains. The latter model turned out to be more appropriate-at least for donor-acceptor-substituted OPVs with n >/= 2. 相似文献
6.
Rudolf Allmann Wolfgang Henke Peter Krommes Jörg Lorberth 《Journal of organometallic chemistry》1978,162(3):283-287
The molecular and crystal structure of tris(bistrimethylsilylamin)thallium was determined by means of single-crystal X-ray spectroscopy: in the space group P1c with a = 16.447(7), c = 8.456(7) Å; and Dc = 1.149 g cm?3 two molecules are located in the unit cell. The compound is isomorphous to the analogues Fe[N(SiMe3)2]3 or Al[N(SiMe3)2]3, respectively, which show a propellar-twist of the Si2N-groups versus the plane of the metal atom and the three nitrogen-atoms: Tl(N)3/Si2N 49.1°; SiNSi 122.6°; NSiC 111.8°; CSiC 107.1°; TlN 2.089 Å;; SiN 1.738 Å;; 1.889 Å;. 相似文献
7.
Henning Henke 《无机化学与普通化学杂志》1993,619(2):311-317
Crystal Structure and Pseudosymmetry of a New Modification of Potassium Hexachloroniobate(V), KNbCl6. Comments on the Cubic Phase Long needles of KNbCl6 – invariably twinned around [100] – are obtained if the material is crystallized from SOCl2 solution. The structure has been determined from X-ray data collected with a single-crystal diffractometer at room temperature [space group P21/n, Z = 16, a = 6.894(1), b = 22.073(4), c = 23.337(3) Å, β = 91.00(1)°, R = 0.032 for 2 909 unique reflexions, 290 structural parameters]. Distorted NbCl6? octahedra and ?interstitial’? K+ ions are found to form similar arrangements, each of them corresponding to a closest packing of spheres with the layer sequence ACAB (stacking symbol hc). The resulting asymmetry in coordination by potassium is coupled with a strong off-centre displacement of the Nb atoms in any of the four independent chlorine polyhedra (0.14 Å on average). A pronounced pseudosymmetry accounts for the twinning. Since P21/m21/n21/b (no. 62) is already a good approximation of the real structure, only one formal step of symmetry reduction (index t2) is needed to create both, the observed twin law and the actual space group P1 21/n1. Above 180°C a reconstructive phase transition leads to the ‘face-centred cubic’ modification with ~ 10% lower density. 相似文献
8.
The crystal structure of [C10N2H10]2[P2Mo5O21(OH)2] · 2H2O, contains the heteropolyanion, [P2Mo5O21(OH)2]4—, together with diprotonated 4, 4′‐bipyridine. The heteropolyanion is built up from five MoO6 octahedra sharing four common edges and one common corner, capped by two PO3(OH) tetrahedra. The structure is stabilized by hydrogen bonds involving the hydrogen atoms of the 4, 4′‐bipyridine, water molecules and the oxygen atoms of the pentamolybdatobisphosphate. This is the first example that this kind of cluster could be isolated in the presence of a poly‐functional aromatic molecule ion. Crystal data: triclinic, P1¯ (No. 2), a = 9.983(2)Å, b = 11.269(2)Å, c = 17.604(4)Å, α = 73.50(3)°, β = 84.07(3)°, γ = 67.96(3)°; V = 1760.0(6)Å3; Z = 2; R1 = 0.037 and wR2 = 0.081, for 9138 reflections [I > 2σ(I)]. 相似文献
9.
Hydrothermal investigations in the system MgO/B2O3/P2O5(/H2O) yielded two new magnesium borophosphates, Mg2(H2O)[BP3O9(OH)4] and Mg(H2O)2[B2P2O8(OH)2]·H2O. The crystal structures were solved by means of single crystal X‐ray diffraction. While the acentric crystal structure of Mg2(H2O)[BP3O9(OH)4] (orthorhombic, P212121 (No. 19), a = 709.44(5) pm, b = 859.70(4) pm, c = 1635.1(1) pm, V = 997.3(3) × 106 pm3, Z = 4) contains 1D infinite chains of magnesium coordination octahedra interconnected by a borophosphate tetramer, Mg(H2O)2[B2P2O8(OH)2]·H2O (monoclinic, P21/c (No. 14), a = 776.04(5) pm, b = 1464.26(9) pm, c = 824.10(4) pm, β = 90.25(1)°, V = 936.44(9) × 106 pm3,Z = 4) represents the first layered borophosphate with 63 net topology. The structures are discussed and classified in terms of structural systematics. 相似文献