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51.
PbO2 is widely employed as an electrocatalyst for anodic oxidation processes including the generation of oxygen and the degradation of various organic species in aqueous solution. However, despite extensive investigation, the precise mechanism of action remains obscure. In this paper we establish a previously unrecognized strong correlation between the morphology of the PbO2 deposits and their electrocatalytic activity. Cyclic voltammetric results are described for the electrodeposition of PbO2 on boron-doped diamond (BDD) electrodes from 2.5 mM solutions of lead(II) nitrate in nitric acid at pH values between approximately 0 and 7. A likely change in mechanism is observed around pH 4, consistent with the Pourbaix diagram of lead. The morphology of the PbO2 films is observed as a function of time and potential, using in situ AFM in each of the lead solutions. Information on the growth rates of the films is extracted, and the limitations of using AFM in such an application are discussed. It is shown that the deposit morphology depends strongly on the specific conditions used. The oxidation of a 100 mM glucose solution on electrodes modified by PbO2 deposition at a range of potentials and pH values is used as an indicator of the catalytic activity of the corresponding films, leading to the observation of the correlation between deposit morphology and catalytic activity mentioned above. 相似文献
52.
Investigations are reported that identify the biosynthetic source and origins of the pseudopterosins, pharmacologically important diterpene glycosides, in the gorgonian coral Pseudopterogorgia elisabethae. We report here the isolation of physiologically significant levels of endogenous pseudopterosins A, B, C, and D from purified symbionts identified as the dinoflagellate Symbiodinium sp. Biosynthetic studies in photosynthesizing symbiont isolates utilizing 14C-labeled inorganic carbon and the tritiated intermediate geranylgeranyl diphosphate yielded radiochemically pure pseudopterosins A through D and the first committed intermediate, elisabethatriene. The 14CO(2) uptake into the pseudopterosin pathway occurred at low levels compared to the 14CO(2) uptake into total lipids, suggesting a large reserve pool of the compounds. These results reveal for the first time that pseudopterosin biosynthesis is occurring within the algal symbiont and suggests the physiological implications of this biosynthesis. 相似文献
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Herminghaus S. Jacobs K. Seemann R. 《The European physical journal. E, Soft matter》2001,5(1):531-538
The European Physical Journal E - A simple and predictive model is put forward explaining the experimentally observed substantial shift of the glass transition temperature, T g, of sufficiently... 相似文献
57.
The influence of all effective two- and three-particle interactions appearing in second order of perturbation theory was investigated for the 5d-shell atoms Hf, Ta, W, Re, and Os. The radial parts of the effective operators were treated as free parameters which were determined by a least squares fit of calculated energy levels to the observed ones. An appreciable reduction of the mean deviation was achieved in all spectra considered. A test of the eigenvectors of the effective Hamiltonian was performed by a comparison of calculatedg J values andg J values, which were measured with high precision by radiofrequency spectroscopy. The agreement found is typically better than a few parts in 104. 相似文献
58.
Novel thermoplastic segmented poly(urethane-thiourea)s (PURs) were synthesized via one-step polymerization from aromatic diols containing sulfur (thiourea linkage) in the main-chain, including terephthaloyl bis (3-(2-hydroxopyridyl) thiourea) (TBHPT) and terephthaloyl bis (3-(5-naphtholyl) thiourea) (TBNT), along with 1,4-phenylene diisocyanate (PDI) as hard segment and 20, 50 and 80 mol% polyethylene glycol (PEG) as a soft segment. The prepared chain extenders and polymers were characterized by conventional methods, and physical properties such as ηinh, solubility, thermal stability and thermal behavior were studied. Easily processable PURs with excellent thermal stability were obtained by incorporating 20 mol% PEG in the soft segment. Thermogravimetric analysis indicated that poly(urethane-thiourea)s were fairly stable above 500 °C and own high glass transition temperatures about 263-266 °C. These polymers also showed partially crystalline structures. Ultimately, weight average molecular weights (Mw) of PURs were up to 109 × 103. Compared to typical polyurethanes, PURs exhibited better thermal stability and Tg’s owing to rigid hard segment structure. 相似文献
59.
Ellingson D Potts B Anderson P Burkhardt G Ellefson W Sullivan D Jacobs W Ragan R 《Journal of AOAC International》2010,93(6):1897-1904
An improved method for direct determination of available carbohydrates in low-level products has been developed and validated for a low-carbohydrate soy infant formula. The method involves modification of an existing direct determination method to improve specificity, accuracy, detection levels, and run times through a more extensive enzymatic digestion to capture all available (or potentially available) carbohydrates. The digestion hydrolyzes all common sugars, starch, and starch derivatives down to their monosaccharide components, glucose, fructose, and galactose, which are then quantitated by high-performance anion-exchange chromatography with photodiode array detection. Method validation consisted of specificity testing and 10 days of analyzing various spike levels of mixed sugars, maltodextrin, and corn starch. The overall RSD was 4.0% across all sample types, which contained within-day and day-to-day components of 3.6 and 3.4%, respectively. Overall average recovery was 99.4% (n = 10). Average recovery for individual spiked samples ranged from 94.1 to 106% (n = 10). It is expected that the method could be applied to a variety of low-carbohydrate foods and beverages. 相似文献
60.
Asma Rehman Muhammad Irfan Majeed Ayesha Ihsan Syed Zajif Hussain Saif-ur-Rehman Muhammad Afzal Ghauri Zafar M. Khalid Irshad Hussain 《Journal of nanoparticle research》2011,13(12):6747-6754