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71.
72.
Honrubia MA Rodrigo J Cadavid MI Calleja JM Sanz F Loza MI 《Chemical & pharmaceutical bulletin》2002,50(3):395-398
Cyproheptadine is one of the compounds exhibiting the highest activity at 5-HT2B receptors. In a previous work we analysed the relevance of the amino group in diphenylmethylenepiperidines (DPMP), which are open cyproheptadine analogues. Only compounds containing N-H or N-methyl motifs, showed significant 5-HT2B activity. Surprisingly, the corresponding quaternary ammonium salt demonstrated a total lack of activity. Therefore, the question arises whether protonation favours the interaction of these compounds with 5-HT2B receptors. Consequently, we studied the protonation influence (by varying the pH of the medium) on the antagonism of serotonin by some cyproheptadine analogues in rat stomach fundus. The main results were: 1) N-protonation increases the activity of DPMPs. 2) Alkaline pH facilitates the occurrence of a non-surmountable antagonism. 3) The contrast between the activity of protonated DPMPs and the lack of activity of the corresponding quaternary ammonium cation, suggests either that the latter is prevented from acting by steric hindrance, or that the mechanism by which protonation may increase the activity depends not only on the charge of the proton, but also on its ability to form hydrogen bonds. 相似文献
73.
Reacting imine derivatives of resin-bound amino acids with alpha,omega-dihaloalkanes provides highly versatile intermediates to racemic alpha,alpha-disubstituted amino acids with a wide variety of side-chain functionality. Two strategies were developed to convert the intermediate omega-chloro or omega-bromo derivatives to the desired products. Together, they allow the creation of amino acids with diverse functionalities (omega-chlorides, nitriles, azides, acetates, thioacetates, thioethers, secondary and tertiary aliphatic amines, and anilines) placed at varying chain lengths (2-5) from the alpha-center of the amino acid. 相似文献
74.
Sastre G Vidal-Moya JA Blasco T Rius J Jordá JL Navarro MT Rey F Corma A 《Angewandte Chemie (International ed. in English)》2002,41(24):4722-4726
75.
Martínez-Teipel B Teixidó J Pascual R Mora M Pujolà J Fujimoto T Borrell JI Michelotti EL 《Journal of combinatorial chemistry》2005,7(3):436-448
Heterocyclic demonstration libraries for agrochemical screening were prepared from the common intermediates 2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles (1), using standard solution-phase techniques. A total of 18 screening libraries were prepared in good to excellent yields. Several members of these libraries were active in the first level of agrochemical screening, especially in the fungicide screen. 相似文献
76.
Piras A Colussi S Trovarelli A Sergo V Llorca J Psaro R Sordelli L 《The journal of physical chemistry. B》2005,109(22):11110-11118
A series of CeO(2)/Al(2)O(3) samples with different ceria loadings in the range 0-25 wt % (0, 2, 5, 7.5, 15, and 25%) were prepared by incipient wetness and studied using several complementary techniques such as Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman, high-resolution transmission electron microscopy (HRTEM), and extended X-ray absorption fine structure (EXAFS). The aim of the investigation was to understand the behavior of ceria when deposited on alumina and treated under oxidizing and reducing conditions at high temperature (T >/= 1273 K). It is shown that ceria can partially stabilize alumina toward the formation of low-surface-area phases up to 1373 K under oxidizing conditions, while enhanced stabilization is observed under reducing conditions, being effective up to 1473 K. A detailed quantitative temperature-programmed reduction (TPR) analysis made at different loadings and calcination temperatures allowed us to identify three characteristic regions where the reduction of small and large ceria crystallites occurs with the formation of CeAlO(3) crystallites at high temperature. These are likely responsible for surface-area stabilization. For dispersed ceria samples, reduction takes place almost exclusively at low temperature (<700 K), while a shift to higher temperatures is observed upon increasing the ceria particle size. A fraction of Ce, in samples at low loadings, is stable in the lower oxidation state, even if subjected to strongly oxidizing conditions. 相似文献
77.
78.
[reaction: see text] Crystal structures of the one-to-one co-crystals of C(60).perchloroazatriquinacene and C(70).perchloroazatriquinacene show that the rigid, chalice-like azatriquinacene packs between completely ordered fullerene molecules with multiple, close Cl...fullerene contacts. 相似文献
79.
Fernández CE Mancera M Holler E Bou JJ Galbis JA Muñoz-Guerra S 《Macromolecular bioscience》2005,5(2):172-176
Low-molecular-weight poly(alpha-methyl beta,L-malate) made of approximately 25-30 units was prepared from microbial poly(beta,L-malic acid) by treatment with diazomethane. The thermal characterization of the polymalate methyl ester was carried out and its crystalline structure was preliminary examined. Its ability to crystallize both from solution and from the melt was comparatively evaluated. 相似文献
80.
van Dijk EM Hernando J García-López JJ Crego-Calama M Reinhoudt DN Kuipers L García-Parajó MF van Hulst NF 《Physical review letters》2005,94(7):078302
We report the first experimental study of individual molecules with femtosecond time resolution using a novel ultrafast single-molecule pump-probe method. A wide range of relaxation times from below 100 up to 400 fs is found, revealing energy redistribution over different vibrational modes and phonon coupling to the nanoenvironment. Addressing quantum-coupled molecules we find longer decay times, pointing towards inhibited intramolecular decay due to delocalized excitation. Interestingly, each individual system shows discrete jumps in femtosecond response, reflecting sudden breakup of the coupled superradiant state. 相似文献