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151.
152.
Claudia Della Rosa 《Tetrahedron letters》2007,48(8):1435-1438
N-Tosyl-2-nitropyrroles react at high temperature with poorly and strongly activated dienes. They exhibit a dienophilic character similar to N-tosyl-3-nitropyrroles producing the corresponding indoles through a classical Diels-Alder process. A similar behaviour was observed in disubstituted N-tosyl-pyrroles. 相似文献
153.
R. Zanoni R. Psaro C. Dossi L. Garlaschelli R. Della Pergola D. Roberto 《Journal of Cluster Science》1990,1(3):241-247
The initial stage of Ir4(CO)12 physisorption on SiO2 from solutions and the subsequent modifications induced by heating under different atmospheres are discussed with the help of XPS results obtained on samples treatedin situ. Ir4(CO)12 is shown to physisorb as crystallites. A good dispersion of crystallites on SiO2 is obtainedvia heating at 373 K under Ar. Ir4(CO)12-supported clusters can be reduced to metal under mild conditions, with complete loss of ligands on controlled heating under Ar or H2. The final products of the process are metal clusters, which are obtained at different nuclearities, depending on the duration of the process. We present the first report on the obtainment of Ir on SiO2 at the same Ir4f7/2 binding energy (b.e.) of bulk Ir. 相似文献
154.
Frank P Benfatto M Szilagyi RK D'Angelo P Della Longa S Hodgson KO 《Inorganic chemistry》2005,44(6):1922-1933
The structure of [Cu(aq)]2+ has been investigated by using full multiple-scattering theoretical (MXAN) analysis of the copper K-edge X-ray absorption (XAS) spectrum and density functional theory (DFT) to test both ideal Td and square-planar four-coordinate, five-coordinate square-pyramidal, and six-coordinate octahedral [Cu(aq)]2+ models. The best fit was an elongated five-coordinate square pyramid with four Cu-O(eq) bonds (2 x 1.98 +/- 0.03 A and 2 x 1.95 +/- 0.03 A) and a long Cu-O(ax) bond (2.35 +/- 0.05 A). The four equatorial ligands were D2d-distorted from the mean equatorial plane by +/-(17 +/- 4) degrees, so that the overall symmetry of [Cu(H2O)5]2+ is C2v. The four-coordinate MXAN fit was nearly as good, but the water ligands (4 x 1.96 +/- 0.02 A) migrated +/-(13 +/- 4) degrees from the mean equatorial plane, making the [Cu(H2O)4]2+ model again D2d-distorted. Spectroscopically calibrated DFT calculations were carried out on the C2v elongate square-pyramidal and D2d-distorted four-coordinate MXAN copper models, providing comparative electronic structures of the experimentally observed geometries. These calculations showed 0.85e spin on Cu(II) and 0.03e electron spin on each of the four equatorial water oxygens. All covalent bonding was restricted to the equatorial plane. In the square-pyramidal model, the electrostatic Cu-O(ax) bond was worth only 96.8 kJ mol(-1), compared to 304.6 kJ mol(-1) for each Cu-O(eq) bond. Both MXAN and DFT showed the potential well of the axial bond to be broad and flat, allowing large low-energy excursions. The irregular geometry and D2d-distorted equatorial ligand set sustained by unconstrained [Cu(H2O)5]2+ warrants caution in drawing conclusions regarding structural preferences from small molecule crystal structures and raises questions about the site-structural basis of the rack-induced bonding hypothesis of blue copper proteins. Further, previously neglected protein folding thermodynamic consequences of the rack-bonding hypothesis indicate an experimental disconfirmation. 相似文献
155.
156.
The molecular structure of S-methyl thioacetate, CH3C(O)SCH3, was determined by gas electron diffraction (GED) with the assistance of quantum chemical calculations (B3LYP/6-31G and MP2/6-31G). Experimental and theoretical methods result in a structure with syn conformation (C=O double bond syn with respect to the S-C(H3) single bond). The following skeletal geometric parameters were derived from the GED analysis (ra values with 3sigma uncertainties): C=O = 1.214(3), C-C = 1.499(5), S-C(sp2) = 1.781(6), S-C(sp3) = 1.805(6) angstroms, O=C-C = 123.4(8) degrees, O=C-S = 122.8(5) degrees and C-S-C = 99.2(9) degrees. 相似文献
157.
Della Védova CO Downs AJ Novikov VP Oberhammer H Parsons S Romano RM Zawadski A 《Inorganic chemistry》2004,43(13):4064-4071
Pure fluorocarbonyl trifluoromethanesulfonate, FC(O)OSO(2)CF(3), is prepared in about 70% yield by the ambient-temperature reaction between FC(O)SCl and AgCF(3)SO(3). The geometric structure and conformational properties of the gaseous molecule have been studied by gas electron diffraction (GED), vibrational spectroscopy [IR(gas), IR(matrix), and Raman(liquid)] and quantum chemical calculations (HF, MP2, and B3LYP with 6-311G basis sets); in addition, the solid-state structure has been determined by X-ray crystallography. FC(O)OSO(2)CF(3) exists in the gas phase as a mixture of trans [FC(O) group trans with respect to the CF(3) group] and gauche conformers with the trans form prevailing [67(8)% from GED and 59(5)% from IR(matrix) measurements]. In both conformers the C=O bond of the FC(O) group is oriented synperiplanar with respect to the S-O single bond. The experimental free energy difference between the two forms, DeltaG degrees = 0.49(13) kcal mol(-1) (GED) and 0.22(12) kcal mol(-1) (IR), is slightly smaller than the calculated value (0.74-0.94 kcal mol(-1)). The crystalline solid at 150 K [monoclinic, P2(1)/c, a = 10.983(1) A, b = 6.4613(6) A, c = 8.8508(8) A, beta = 104.786(2) degrees ] consists exclusively of the trans conformer. 相似文献
158.
159.
Summary The object of this work was to optimize and validate an analytical method for the analysis of glyphosate and its main metabolite
AMPA (aminomethylphosphonic acid) in natural and drinking water, for sanitary control. The method uses a derivatization step
which transforms glyphosate and AMPA into fluorescent products by reaction with 9-fluorenylmethylchloroformate (FMOC-Cl).
The kinetics and yield of this reaction were studied by use of different samples. The derivatization products were injected
directly into the liquid chromatograph and separated on an amino-functionalized silica gel column. The performance of the
method (detection limit, quantification limit, linearity, and relative standard deviation) was studied and the results obtained
showed the method was suitable for routine analysis of glyphosate and AMPA. An interlaboratory test with five laboratories
confirmed that good results were obtained by use of this method. 相似文献
160.
V. Vitagliano G. Borriello C. Della Volpe O. Ortona 《Journal of solution chemistry》1986,15(10):811-826
The four diffusion coefficients for the system sucrose (0.097M)-NaCl-(0.291M)-water at 25°C have been measured by the Gouy interferometric technique. The cross terms D12 and D21 are small However, if sucrose or NaCl are chosen as component 3 instead of water, one of the cross terms becomes very large. Several runs were used to test the McDougall analysis of gravitational instability in diffusion boundaries for three component systems. Growth of convective motions at the center and at the edges of the boundary have been observed that confirm the McDougall model. 相似文献