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101.
The reaction of 2 equiv of LiSeCC-n-C(5)H(11) (1) with cis-PtCl(2)(Ph(3)P)(2) (2) gives a mixture of the cis and trans isomers of Pt(Ph(3)P)(2)(SeCC-n-C(5)H(11))(2) (3), which slowly isomerizes in CH(2)Cl(2) to the preferred trans form trans-3. The closely related cis-[Pt(dppf)(2)(SeCC-n-C(5)H(11))(2)] (4) (dppf = bis(diphenylphosphino)ferrocene) was prepared by a similar metathetical reaction using the platinum chloride complex of the chelating dppf to impose the cis geometry. The structures of the cis and trans complexes have been investigated in solution by heteronuclear NMR ((31)P, (77)Se, and (195)Pt) and, in the cases of trans-3 and 4, characterized in the solid state by single-crystal X-ray diffraction. Changing the coordination geometry from cis to trans induces significant changes in the structural and spectroscopic parameters, which do not comply with the previously anticipated donor-acceptor properties of selenolate ligands. 相似文献
102.
The Amsterdam Density Functional (ADF) package has been used to constrain Kohn-Sham DFT in such a fashion that a transition from KS-DFT to ligand-field theory in the form of the parametrical d(q)() model is completely well-defined. A relationship is established between the strong-field approximation of the parametrical d(2) model for the tetrahedral complexes VCl(4)(-) and VBr(4)(-) and certain fixed-orbital ADF-computed energies. In this way values for all the parameters of the d(2)() model may be computed, thus allowing the ADF results to be expressed in terms of a KS-DFT energy matrix that can be diagonalized. This means that the KS-DFT deficiency with regard to computation of nondiagonal elements has been overcome and the KS-DFT eigenenergies have become available through the KS-DFT mimicking of the ligand-field plus repulsion model. By using mutually orthogonal strong-field energy matrices, the mimicking has been further elucidated. The computed values for the empirical parameters of VCl(4)(-) and VBr(4)(-) are in good agreement with experimental data. The spectrochemical and the nephelauxetic series have been computed by including the remaining halide complexes and the quantitatively special position of F(-)() among the halides corroborated for both series. 相似文献
103.
Single crystal structure determinations prove the two pyridine substituents in di(2-pyridyl)ketone (H4C4NC)2C=O to be twisted out of the carbonyl skeleton plane by torsion angles (OCCN) of 41° and –163°, in contrast to their planar arrangement in azo-di(2-pyridine) H4C4NC)-N=N-(CNC4H4). In order to rationalize the surprising difference between the two isoelectronic molecules, approximate PM3 enthalpy of formation hypersurfaces have been calculated for each of the two ring torsions, which are assumed to be the dominant ones among the 3N – 6 = 60 degrees of freedom. For both the ketone and the azo derivative, global minima are calculated, the torsion angles of which deviate from the crystal structure results, and, therefore, support the assumption that both the experimentally determined twisting of di(2-pyridyl)ketone as well as the flattening of azo-di(2-pyridine) might be affected by the crystal packing. 相似文献
104.
We present sets of real 3- symbols which correspond to explicitly given irreducible matrix representations for the two double group hierarchies T* C
3
*
and T* C
2
*
. They fit into the formalism exposed in a previous paper [1] on the general theory of 3- symbols and coupling coefficients and illustrate much of the discussion in a subsequent one [2] treating the particular properties of the double groups. 相似文献
105.
Gerd Eyring Thomas Schönherr Hans -Herbert Schmidtke 《Theoretical chemistry accounts》1983,64(2):83-96
The 90 K diffuse reflectance spectra of some octahedral Rh(III), Ir(III) and Pt(IV) complex compounds with chloride, thiocyanate and amine ligands are reported. The spectra show in the visible and near ultraviolet distinct bands due to spin-orbit components of singlet-triplet d-d transitions which are explained by ligand field calculations including spin-orbit coupling considering all possible d-electron configurations. Model parameter sets are obtained by fitting the measured band peaks to possible transitions between calculated energy levels. For some of the bands the vibrational structure could be resolved which is assigned to metal-ligand stretching vibrations of the electronically excited complex octahedra with vibrational fundamentals lower than those of the ground state. 相似文献
106.
Wolfgang A. Herrmann Ricardo Serrano Adolf Schäfer Ulrich Küsthardt Manfred L. Ziegler Ernst Guggolz 《Journal of organometallic chemistry》1984,272(1):55-71
Short-wavelength photolysis of tricarbonyl(η5-pentamethylcyclopentadienyl)rhenium (1) (λ < 300 nm, quartz-glass) in tetrahydrofuran yields under partial or complete decarbonylation three novel organorhenium compounds, with the relative yields depending upon the irradiation time. Formed by exhaustive oxidative decarbonylation, the complex trioxo(η5-pentamethylcyclopentadienyl)rhenium(VII) (5) represents the first example of the new class of oxo half-sandwich complexes. The derivatives (μ-O)[(η5-C5Me5)Re(CO)2]2 (2; Me = CH3) and (η5-C5Me5)2Re2(CO)2O2 (3; Me = CH3) containing both oxo and carbonyl ligands are formed from 1 at shorter irradiation times. Both compounds are isolable intermediates along the mechanistically not yet fully established sequence 1 → → 5 as they are degraded to 5 under CO2 elimination in the presence of air and/or light. The mixed oxo carbonyl complex 2 has been characterized by means of single-crystal X-ray diffraction techniques (triclinic, space group P-Ci1; a 907.4(2), b 1040.2(3), c 1414.3(4) pm; α 79.99(2), β 88.42(2), γ 66.18(2)°; Riso = 0.068, Raniso = 0.037, Rw = 0.031). The molecular structure centres around an isosceles Re2O triangle whose metal centres exhibit a strongly distorted square-pyramidal geometry; the metal-metal distance recorded at 281.7(1) pm is in agreement with a single bond by the EAN rule. The centrically coordinated, planar five-membered ring ligands are parallel to each other (interplanar angle 2°) and occupy trans-positions with respect to the central Re2O geometry. 相似文献
107.
The ternary bodides HfCo3B2 and ZrCo3B2 crystallize with the hexagonal D 2d structure type, space group P 6/mmm,a=4.840,c=3.036Å,c/a=0.627 anda=4.863,c=3.043Å,c/a=0.625, respectively. The boron atoms are located inside a trigonal prism that is familiar from other metal-rich borides. The ternary CaCu5 type has good space filling at a theoretical axial ratioc/a=0.75 and a theoretical radius ratio of 1.5 ∶ 1 ∶ 0.81. 相似文献
108.
A close coupling between the structure and size of hematite flocs formed in suspension and the permeability of the cake that accumulates on ultrafiltration membranes is observed. Specific resistances of cakes formed from flocs generated under diffusion-limited aggregation conditions are at least an order of magnitude lower than those of cakes formed from flocs generated under reaction-limited aggregation conditions. Similar effects are observed whether the aggregation regime is controlled by salt concentration, pH, or added organic anions. This dramatic difference in cake resistance is considered to arise from the size and fractal properties of the hematite assemblages. The ease of fluid flow through these assemblages will be influenced both by the fractal dimension of the aggregates and by their size relative to primary particle size (since, for fractal aggregates, porosity increases as the size of the aggregate increases). The size and strength of aggregates are also important determinants of the relative effects of permeation drag, shear-induced diffusion, and inertial lift and result, in the studies reported here, in relatively similar rates of particle deposition for both rapidly and slowly formed aggregates. The results presented here suggest that control of cake permeability (and mass) via control of aggregate size and structure is an area with scope for further development though the nature and extent of compaction effects in modifying the fractal properties of aggregates generated in suspension requires attention. Copyright 1999 Academic Press. 相似文献
109.
Ralf Eiden Ralf Falter Barbara Augustin-Castro Heinz Friedrich Schöler 《Analytical and bioanalytical chemistry》1997,357(4):439-441
Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high
performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for
the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this
method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within
their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition
method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples
were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight.
Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996 相似文献
110.
Zusammenfassung Es wird über Strom-Spannungskurven in Phenylphosphoroxydichlorid berichtet, welche mit verschiedenen Elektrodenkombinationen erhalten wurden. Die bei der Polarographie leitsalzfreier Phenylphosphoroxydichloridlösungen beobachteten Erscheinungen werden auf Migrationsströme zurückgeführt.Mit 3 Abbildungen3. Mitt.:H. Dehn, V. Gutmann undG. Schöber, Mh. Chem.94, 312 (1963). 相似文献