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811.
Marian ?erňansky P?emysl Vaněk Karel Král Radmila Krupková 《Monatshefte für Chemie / Chemical Monthly》2002,105(3):799-806
In this investigation the crystallization of PbTiO3 upon annealing of pure nanopowders and PbTiO3–SiO2 (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the
start of PbTiO3 crystallization in pure PbTiO3 powders was detected at 400°C. Distinct crystallization of PbTiO3 in PbTiO3–SiO2 nanocomposites starts at 700°C, whereas SiO2 remains amorphous. There are indications that an interface interaction between the PbTiO3 and the SiO2 phase plays an important role in hindering the crystallization of PbTiO3. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line
profiles. The average size of PbTiO3 nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than
that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect
to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution
of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites
(coherently scattering regions). 相似文献
812.
Stefan Lis Bronisław Marciniak Marian Elbanowski 《Monatshefte für Chemie / Chemical Monthly》1989,120(10):821-826
Summary The Tb(III)-acetylacetone system in ethanol solution has been studied by spectroscopic methods. The formation of a Tb(III)/acetylacetone (1:1) complex in the ground state has been proved and its stability constant determined,K=(0.97±0.06)·104dm3mol–1. The role of this complex in the spectrofluorimetric determination ofLn(III) ions in the presence of acetylacetone has been discussed.
Über die Rolle eines Tb(III)-Acetylaceton-Komplexes im Grundzustand in der sensibilisierten Emission von Tb(III) in Ethanol-Lösung
Zusammenfassung Das Tb(III)-Acetylaceton-System in Ethanol-Lösung wurde mit spektroskopischen Methoden untersuchung. Die Bildung eines Tb(III)-Acetylaceton(1:1)-Komplexes im Grundzustand wurde bestätigt und seine Stabilitätskonstante bestimmt,K=(0.97±0.06)·104dm3mol–1. Die Rolle dieses Komplexes in der spektrofluorimetrischen Bestimmung vonLn(III)-Ionen in Gegenwart von Acetylaceton wurde erörtert.相似文献
813.
The solution and solid state structures of two octahedral Ru(II) complexes, cis,cis,cis-RuCl(2)(Me(2)SO)(2)(py)(Me(3)Bzm) (Me(3)Bzm = 1,5,6-trimethylbenzimidazole, py = pyridine) (1) and cis,cis,cis-RuCl(2)(Me(2)SO)(2)(Me(3)Bzm)(2) (2), were compared. 2, the subject of a preliminary report, is described in more detail here. 1 has two possible geometric isomers with py trans to Cl in one (position "a") and trans to Me(2)SO in the other (position "b"), Me(3)Bzm occupying the other position in each isomer. The X-ray structure of 1 revealed that py is at "a". Since Me(3)Bzm is lopsided, each Me(3)Bzm has two possible orientations related by a rotation of approximately 180 degrees about the Ru-N3 bond; there are two possible atropisomers for each geometric isomer of 1 and four for 2. For 1, the solid state structure shows that Me(3)Bzm adopts the orientation with H2 (H on C between the two N's) pointing between the two cis Cl ligands, the same disposition as Me(3)Bzm "b" in 2 in the solid. For 1, the py signals (two broad py alpha and beta signals, a sharp gamma signal) in CDCl(3) show that py "a" is rotating on the NMR time scale and that only one atropisomer is present. This interpretation was supported by ROESY and EXSY (1)H NMR spectra. The (1)H NMR shift pattern and the NOE data can be understood best if Me(3)Bzm "b" remains primarily in the orientation found in the solid. The solution data for 1, with the nonlopsided and sterically less demanding py ligand, provide insight into the more complicated properties of 2. For 2, there is a marked dispersion of (1)H NMR signals of Me(3)Bzm "a" between the two atropisomers, which have nearly equal stability. One atropisomer is a head-to-head (HH) and the other a head-to-tail (HT) species. Me(3)Bzm "a" flips between the two species. Thus, ligand "a" is fluxional in both complexes. The dispersion of Me(3)Bzm "a" signals is due to the effect of Me(3)Bzm "b" anisotropy. For 1 and both atropisomers of 2, Me(3)Bzm "b" prefers one orientation, which appears to be the most hindered orientation. We postulate that the H2 of Me(3)Bzm "b" is electrostatically attracted to the two cis halides, accounting for this surprising result. Crystallographic details for 1 are as follows: C(19)H(29)Cl(2)N(3)O(2)RuS(2), P2(1)/c, a = 10.947(1) ?, b = 9.046(1) ?, c = 24.221(2) ?, D(calcd) = 1.580 g cm(-)(3), Z = 4, R = 0.026 for 4627 independent reflections. 相似文献
814.
Bryan MC Fazio F Lee HK Huang CY Chang A Best MD Calarese DA Blixt O Paulson JC Burton D Wilson IA Wong CH 《Journal of the American Chemical Society》2004,126(28):8640-8641
A covalent array for the display of complex oligosaccharides in microtiter plates has been developed. This strategy is conducive to the display of carbohydrates to proteins of interest such as lectins and antibodies, including the broadly neutralizing antibody 2G12 against HIV envelope oligomannose and can be cleaved from the surface for further characterization by mass spectrometry. The system was used to probe the multivalent interaction of 2G12 with an optimal epitope (Kd 0.1 muM). 相似文献
815.
The evolution of the surface roughness during cementation of Ag+ conducted either in O2‐free or O2‐saturated aqueous H2SO4/CuSO4 was investigated at two different initial concentrations of Ag+. The kinetics data of the process determined previously in the rotating cylinder were linked directly with scanning‐electron‐microscope (SEM) images and surface‐height‐distribution diagrams calculated for various cementation times. It was found that, at the beginning of the process, the surface roughness decreases due to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O2 in the system. With increasing reaction time, an increase in the surface roughness was observed. The rate enhancement of the process is mainly responsible for the increase of the surface roughness in the O2‐saturated solutions, especially at the higher initial Ag+ concentration (100 mg/dm3). The rate enhancement observed at a latter stage of the process, connected with the increase of the effective surface area of the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process occurring in O2‐free solution. The difference in the mechanisms of the processes conducted under aerobic and anaerobic conditions was reflected in the surface‐heigth distributions calculated from the SEM images. 相似文献
816.
Double-layer and hydration interactions have been coupled into a single set of equations because both are dependent on the polarization of the water molecules. The coupled equations involve the electric fields generated by the surface charge and surface dipoles, as well as the field due to the neighboring dipoles in water. The dipoles on the surface are generated through the counterions' binding to sites of opposite charge. The equations obtained were employed to explain the restabilization observed experimentally at large ionic strengths for colloidal particles on which protein molecules were adsorbed. Polar molecules adsorbed on a charged surface of colloidal particle can generate a field either in the same direction as that generated by the charge or in the opposite direction. The effect of the sign of the dipole of the adsorbed polar molecules on the interaction between surfaces was also examined. 相似文献
817.
Chiarizia R Jensen MP Rickert PG Kolarik Z Borkowski M Thiyagarajan P 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):10798-10808
Small-angle neutron scattering (SANS) data for the tri-n-butyl phosphate (TBP)-n-octane, HNO(3)-Zr(NO(3))(4) solvent extraction system, obtained under a variety of experimental conditions, have been interpreted using the Baxter model for hard spheres with surface adhesion. The increase in scattering intensity in the low Q range observed when increasing amounts of Zr(NO(3))(4) were extracted into the organic phase was interpreted as arising from interactions between small reverse micelle-like particles containing two to three TBP molecules. Upon extraction of Zr(NO(3))(4), the particles interact through attractive forces between their polar cores with a potential energy that exceeds 2 k(B)T. The interparticle attraction, under suitable conditions, leads to third phase formation. A linear relationship exists between the derivative of the potential energy of attraction with respect to the concentration of nitrate ions in the organic phase and the ionization potential or the hydration enthalpy of the extracted metal cations. 相似文献
818.
Agnaldo de Souza Gonçalves Sergio Antonio Marques de Lima Marian Rosaly Davolos Selma Gutierrez Antônio Carlos de Oliveira Paiva-Santos 《Journal of solid state chemistry》2006,179(5):1330-1334
Gallium-doped zinc oxide (ZnO:Ga 1, 2, 3, 4 and 5 at%) samples were prepared in powder form by modifying the Pechini method. The formation of zinc gallate (ZnGa2O4) with the spinel crystal structure was observed even in ZnO:Ga 1 at% by X-ray diffraction. The presence of ZnGa2O4 in ZnO:Ga samples was also evidenced by luminescence spectroscopy through its blue emission at 430 nm, assigned to charge transfer between Ga3+ at regular octahedral symmetry and its surrounding O2− ions. The amount of ZnGa2O4 increases as the dopant concentration increases, as observed by the quantitative phase analysis by the Rietveld method. 相似文献
819.
Narayani Ramakrishnan Marian E. Clay Libby R. Friedman Antonio R. Antunez Nancy L. Oleinick 《Photochemistry and photobiology》1990,52(3):555-559
The interaction of chloroaluminum phthalocyanine-sensitized photodynamic treatment and gamma-irradiation was studied in confluent murine L929 fibroblasts. When the cells were given the combined treatments and immediately subcultured for determination of cell survival by colony formation, the data indicate independent actions of each modality. However, when subculture was delayed for 1 h, a substantial fraction of cells treated with a sub-lethal dose of PDT followed by 5 Gy gamma-radiation detached from the monolayer. Most of these detached cells were no longer clonogenic. The mode of photosensitized cell killing was found to be different from that of ionizing radiation-induced cell killing. Photosensitized cell killing was accompanied by morphological changes in the cells and extensive DNA degradation within one hour following the treatment. When chloroaluminum phthalocyanine pretreated cells were exposed to a sublethal fluence of light (6 kJ/m2) and a lethal dose of gamma-radiation (5 Gy), DNA degradation was enhanced, and about 20% of the cell population appeared to undergo the type of cell death typical of photodynamic treatment. Thus, although different initial lethal lesions are induced by photodynamic treatment and by ionizing radiation, interactions may occur during processing of the damage. 相似文献
820.
Marian Grabowski 《International Journal of Theoretical Physics》1978,17(8):635-641
We investigateA-entropy with respect to certain semispectral measures in a given state. It is shown that the entropy with respect to an observable describing simultaneous measurement of position and momentum is greater than the von Neumann entropy. Similar results are obtained for the fuzzy and sharp positions. The continuity properties of this entropy are also examined. 相似文献