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221.
222.
Ohne Zusammenfassung 相似文献
223.
Rate coefficients and products were determined for the title reactions employing a drift tube mass spectrometer apparatus. The implications of these reactions for the ion chemistry of the stratosphere is discussed. 相似文献
224.
Meyer N Nestler K Engisch L Marx G Füting M Kiesow A Heilmann A Wartewig S Kleinebudde P 《Fresenius' Journal of Analytical Chemistry》2001,370(6):789-791
First results of experiments on the surface characterization of cellulose derivatives are presented. Different water contents of the surface of microcrystalline cellulose have been investigated by means of Raman spectroscopy, SERS, and environmental scanning electron microscopy (ESEM). 相似文献
225.
Britta Vortmann-Westhoven Marcel Diehl Martin Winter Sascha Nowak 《Chromatographia》2018,81(7):995-1002
We present a method for the separation and determination of transition metals in electrolytes based on ion chromatography (IC) with post-column reaction (PCR) and serial conductivity and spectrophotometric detection. Three IC columns [Metrosep C4—250/4.0 (column A), Metrosep C6—250/4.0 (column B), and Nucleosil 100-5SA—250/4.6 (column C)] with different capacities, and stationary phases were used and compared with each other for method development. All spectrophotometric measurements were carried out with 4-(2-pyridylazo)resorcinol (PAR) as PCR reagent at a wavelength of 500 nm. To characterize the precision of the separation, the selectivity for the analysis of transition metals (nickel, cobalt, copper, and manganese) in the presence of large amounts of lithium and the resolution of the peaks were determined and compared with one another. Furthermore, the limits of detection (LOD) and quantification (LOQ) were determined for the transition metals. The LODs and LOQs determined by column C were as follows: cobalt (LOD/LOQ): 9.4 µg L?1/31.3 µg L?1, manganese (LOD/LOQ): 7.0 µg L?1/23.5 µg L?1, and nickel (LOD/LOQ): 6.3 µg L?1/21.1 µg L?1. Finally, the concentration of transition metal dissolution of the cathode material Li1Ni1/3Co1/3Mn1/3O2 (NCM) was investigated for different charge cut-off voltages by the developed IC method. 相似文献
226.
Tina Nestler Kay Potzger Hartmut St?cker Barbara Abendroth Ralph Strohmeyer Robert Zierer Dirk C. Meyer 《Applied Physics A: Materials Science & Processing》2011,105(1):103-109
Electrical properties of SrTiO3 single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated
in the temperature range of 35 K–300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization
and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as
well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping.
Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge
has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature
T
C
at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain
fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously
pin tetragonal domains. Thus, microregions of the tetragonal phase persist above T
C
causing the hysteresis in resistivity up to ∼12%. This effect possibly provides new chances for future oxide based non-volatile
data-storage devices. 相似文献
227.
Mohammed HA Ba LA Burkholz T Schumann E Diesel B Zapp J Kiemer AK Ries C Hartmann RW Hosny M Jacob C 《Natural product communications》2011,6(1):31-34
Flavones such as chrysin show structural similarities to androgens, the substrates of human aromatase, which converts androgens to estrogens. Aromatase is a key target in the treatment of hormone-dependent tumors, including breast cancer. Flavone-based aromatase inhibitors are of growing interest, and chrysin in particular provides a (natural) lead structure. This paper reports multicomponent synthesis as a means for facile modification of the chrysin core structure in order to add functional elements. A Mannich-type reaction was used to synthesize a range of mono- and disubstituted chrysin derivatives, some of which are more effective aromatase inhibitors than the benchmark compound, aminoglutethimide. Similarly, the reaction of chrysin with various isonitriles and acetylene dicarboxylates results in a new class of flavone derivatives, tricyclic pyrano-flavones which also inhibit human aromatase. Multicomponent reactions involving flavones therefore enable the synthesis of a variety of derivatives, some of which may be useful as anticancer agents. 相似文献
228.
We develop a model, based on pairwise additive He-Mg and He-O interactions, for the potential energy of He adsorbates above a rigid MgO(100) surface. The attractive long-range He-Mg and He-O interactions are assumed to have the form C(6)/r(6), with the C(6) coefficients determined from atomic data within the context of the Slater-Kirkwood approximation. The repulsive short-range He-Mg and He-O interactions are assumed to have the form C(p)/r(p), with the exponent p and the C(p) coefficients taken as adjustable parameters. We find that for p = 9, the C(p) coefficients can be chosen so that the laterally averaged He-MgO(100) pairwise additive interaction supports low-lying selective adsorption states, some of whose energies agree very well with the states' apparent energies inferred from experimental measurements. However, for realistic values of the adjustable parameters that define our model, the lateral corrugation of the model pairwise additive He-MgO(100) potential energy surface far exceeds the corrugation that has been inferred both from experimental measurements and from density functional calculations of the short-range He-MgO(100) interaction. 相似文献
229.
Vinzenz X Grosse W Linne U Meissner B Essen LO 《Chemical communications (Cambridge, England)》2011,47(39):11071-11073
The suitability for chemical engineering of the highly symmetrical Mycobacterium tuberculosis dodecin was investigated, its inner cavity providing a large compartment shields introduced compounds from bulk solvent. Hybrids were obtained by S-alkylation of cysteine mutants and characterized by spectroscopic methods, including the crystal structures of wild type and biohybrid dodecins. 相似文献
230.