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991.
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994.
The search for a nonthrombogenic membrane having high permselectivity to be used for hemodialysis applications continues to be a field of extensive investigation. A series of membranes was prepared by air drying the thin layers of albumin: chitosan [a (1 → 4)-2-amino-2-deoxy-β-d-glucan] blends in a ratio of 7:3 (chitosan:albumin). The albumin blended chitosan membranes showed high permeability properties for low molecular weight compounds. Nonthrombogenic albumin: chitosan blended membranes were derived by immobilizing bioactive molecules like PGE1, hirudin, heparin, or AT-III on liposome modified membranes, via the carbodiimide functional moiety. Such novel membranes demonstrated good permeability properties for small molecules and showed dramatic reduction in platelet attachment; though they exhibited variable degrees of wettability. The interfacial changes arising from surface modifications did not cause any significant interference with their permeability and mechanical properties. 相似文献
995.
The reported pressure-induced amorphization in α-NaVO3 has been re-investigated using Raman spectroscopy. Discontinuous changes are noted in the Raman spectrum above 5.6 GPa implying large structural changes across the transition. The decrease in frequency of the V-O stretching mode across the transition suggests that the vanadium atom may be in octahedral coordination in the high pressure phase. Excessive broadening of the internal modes is observed above 6 GPa. New peaks characteristic of a crystalline phase gain in intensity at higher pressures in the bending modes region; however, the transformation is not complete even at 13 GPa. Co-existence of phases is noted over a significant pressure range above the onset of transition. Pressure released spectrum is found to be a mixture of crystalline α-phase, traces of crystalline β-phase and highly disordered phase consisting of V-O units in five- and six-fold coordination. 相似文献
996.
Aqueous solutions of the hypovalent state indium(I) have been prepared by treatment of In(Hg) with silver triflate in acetonitrile, followed by dilution with oxygen-free water. These solutions are stable for over 5 h at 25 degrees C. In(I)(aq) reacts with oxidants of the type [(NH(3))(5)Co(III)(Lig)](2+) (In(I) + 2Co(III) --> In(III) + 2Co(II)), and kinetic profiles are consistent with a two-step sequence proceeding with formation of the metastable state In(II), which reacts rapidly with Co(III). Rate ratios for reductions of halogeno-substituted oxidants point to predominance of halide-bridged paths for the chloro, bromo and iodo complexes. Reductions of carboxylato-substituted derivatives are slow but appear to entail inner-sphere precursors if aided by an O-donor group in a position favorable for chelation. In no case is there evidence for reaction via initial reduction of the ligand (the radical-cation mechanism) although the potential of the In(I,II) couple (-0.40 V) allows this path for carbonyl-substituted oxidants. Reductions by In(I), like those by Eu(II), make no significant use of bridging by heterocyclic donor nitrogen centers in pyridine and pyrazine complexes. 相似文献
997.
Poly(vinyl chloride)-based membranes of macrocycles 4,11-dimethyl-2,4,9,11-tetraethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (I) and 4,11-dioxa-2,9-dimethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (II) with sodium tetraphenyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutylbutyl phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as magnesium selective electrodes. The best performance was observed having the composition (II)-PVC-STB-DBP in the ratio 2:10:1:7, which works well over a wide concentration range (1.9x10(-6) to 1.0x10(-1) M) with a Nernstian slope of 29 mV per decade of activity between pH 2.5 and 6.5. These electrodes have been found to be chemically inert showing a fast response time of 15 s and were used over a period of 3 months with good reproducibility (S=+/-0.2 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Mg(2+) over a large number of cations. The electrodes have also been used successfully in partially non-aqueous medium and as an indicator electrode in the potentiometric titration of Mg(2+) with EDTA. Anions such as Cl(-) and SO(4)(2-) do not interfere in the working of the electrode. The practical utility of the membrane sensor has also been observed in solutions contaminated with detergents (cetyltrimethyl ammonium bromide and sodium dodecyl sulphate). Above all, the membrane sensor has been very successfully used to analyse some babyfood products and soft drinks for the determination of Mg(2+). 相似文献
998.
Tara Chandra Gupta Abani K. Bhattacharya 《Fresenius' Journal of Analytical Chemistry》1958,161(5):321-323
Summary In the quantitative estimation of barium as barium sulphate it has been recommended that BaSO4 should be precipitated by adding sulphuric acid of N or 2 N strength, because the results are low in more diluted solutions of sulphuric acid. It has been observed that accurate results within the limits of experimental error can be obtained by precipitating barium sulphate in the presence of alcohol or acetone with dilute sulphuric acid up to 0.167 N strength. When barium sulphate is precipitated with dilute sulphuric acid of strength less than 0.5 N the results are low in the absence of alcohol or acetone. 相似文献
999.
When HCrO4 ? is reduced by formate in solutions buffered by 2-ethyl-2-hydroxybutanoic acid and its anion, chelated complexes of both Cr(IV) and Cr(V), both of them stabilized in the medium used, are formed. It appears that Cr(V) is not generated directly from the Cr(VI)-formate reaction but arises instead from oxidation of Cr(IV) by Cr(VI). When the Cr(VI)-formate reaction is allowed to go to completion in the presence of [Cl(NH3)5Co]2+, a scavenger for Cr(II), 84–86% of the Cr(VI) taken is found to be converted to Cr(II), indicating that nearly all of the reacting system proceeds through Cr(IV) and bypasses the more usual state Cr(III). Initial rates for formation of Cr(IV) lead to a rate law pointing to a transition state containing the two redox partners, two ligating carboxyl groups, and two units of H+. Substitution of DCO2 ? for HCO2 ? retards formation of Cr(IV) by a factor of 3.3, whereas the solvent isotope affect, rateD 2O/rateH 2O, favors the deuterated system by a factor of 1.4. Our observations are in accord with a sequence initiated by the ligation of HCrO4 ? to a chelate derived from the buffering carboxylate anion. Conversions of Cr(VI) to Cr(IV), and Cr(IV) to Cr(II) appear to entail hydride shifts from formate to the Cr(=O) function. 相似文献
1000.
Sarju Prasad Ramesh Chandra Srivastava 《Fresenius' Journal of Analytical Chemistry》1964,206(3):171-174
Summary Conductometric determination of Ce3+ has been carried out successfully at 30±0.5°C by titrating it against standard sodium metavanadate solution in 15% ethanol. An overall effect of ethanol concentration on the results has also been studied. The titration curves obtained show a sharp break at the end point and lend support to the formation of Ce(VO3)3. The method has the advantage of being a simple and precise titrimetric procedure for the determination of Ce3+ in microquantities.
Zusammenfassung Es wird eine einfache und genaue Methode zur konduktometrischen Bestimmung von Cer(III) beschrieben. Die Titration erfolgt mit Natriummetavanadat in 15%iger äthanolischer Lösung bei 30±0,5°C. Der Einfluß der Äthanolkonzentration auf die Ergebnisse wurde untersucht. Die Titrationskurven weisen am Endpunkt einen scharfen Knick auf und deuten auf die Bildung von Ce(VO3)3 hin.相似文献