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31.
W. Wojnowski J. Pikies K. Peters E.-M. Peters D. Thiery H. G. Von Schnering 《无机化学与普通化学杂志》1994,620(2):377-384
Formation and Structures of N-(tri-t-butoxysilyl)aniline Compounds Para-substituted N-(tri-t-butoxysilyl)anilines (t-BuO)3SiNRC4H4X-p, R = H, CH3, with substituents of high electron affinity (X = CN, NO2) were prepared by a one-pot reaction of tri-t-butoxychlorsilane, potassium t-butanolate and substituted anilines. Corresponding compounds with substituents of low electron affinity (X = OMe, H) preferably were prepared by metalation of anilines with sodium amide. Four crystal structures were determined. N-(tri-t-butoxysilyl)-p-nitro-aniline, N-methyl-(N-tri-t-butoxysilyl)-p-nitroaniline and N-(tri-t-butoxysilyl)-p-cyanoaniline crystallize at 298 K monoclinically, N-(tri-t-butoxysilyl)aniline crystallizes orthorhombically. 相似文献
32.
van Apeldoorn AA van Manen HJ Bezemer JM de Bruijn JD van Blitterswijk CA Otto C 《Journal of the American Chemical Society》2004,126(41):13226-13227
Understanding the degradation behavior of polymeric microspheres is crucial for the successful application of such devices in controlled drug delivery. The degradation mechanism of poly(lactic-co-glycolic acid) (PLGA) microspheres inside phagocytic cells is not known, but different models for degradation in aqueous solution have been proposed. We have used confocal Raman spectroscopy and imaging to study the intracellular degradation of PLGA microspheres inside individual macrophages. Our results show that ingested microspheres degrade in a heterogeneous manner, with a more rapid degradation in the center. Comparison of Raman spectra from degrading beads with those of uningested beads reveals that ester hydrolysis occurs throughout the phagocytosed microspheres, with a selective loss of glycolic acid units. Furthermore, we show that PLGA degradation is a cell-mediated process, possibly caused by the low pH of the phagosome and/or the presence of hydrolytic enzymes. In conclusion, we have demonstrated that the chemical composition of degrading polymers inside cells can be probed by Raman spectral imaging. This technique will expand the capabilities of investigating biomaterial degradation in vivo. 相似文献
33.
Ren Traber Camilla Keller-Jusln Hans-Rudolf Loosli Max Kuhn Albert Von Wartburg 《Helvetica chimica acta》1979,62(4):1252-1267
Cyclopeptide antibiotics from Aspergillus species. Structure of echinocandins C and D The echinocandins B, C and D are antifungal antibiotics produced by a strain of Aspergillus rugulosus. All three metabolites are closely related representing cyclic oligopeptides composed of six amino acids and a linolic acid residue in an amide linkage. The complete structure of echinocandin B ( 1 ) has recently been established by X-ray analysis. Structural assignments to the new minor metabolites C and D have now been made by hydrolytic and oxidative cleavage reactions, formation of N-acyl-α-aminoethers as well as by chemical correlations and extensive NMR. examinations. Echinocandin C ( 2 ), C52H81N7O15, contains 3-hydroxyhomotyrosine in the place of 3, 4-dihydroxyhomotyrosine present in 1 . Echinocandin D ( 3 ), C52H81N7O13, differs in two amino acids: 3, 4-dihyroxyhomotyrosine and 4, 5-dihydroxyornithine, unusual units of 1 being replaced by 3-hydroxyhomotyrosine and ornithine. 相似文献
34.
On the Temperature Dependence of the 13C-NMR.-Spectra of Tetracarbonyl (η-( Z )-cyclooctene)iron and of ( Z )-Cyclooctene Reaction of (Z)-cyclooctene (1) with Fe2(CO)9 in pentane at 0° yielded tetracarbonyl(η-(Z)-cyclooctene)iron (2) as a yellow oil which can be stored over a longer period only at ?78°. It is shown that the title compounds ( 1 and 2 , respectively) are fluxional. The activation parameters for the conformational C-atom site exchange of (Z)-cyclooctene (1) and tetracarbonyl (η-(Z)-cyclooctene)iron (2) (in CCl2F2) have been determined between 113 K and 151 K for 1 and between 151 K and 205 K for 2 , respectively, by a complete line shape analysis of the temperature dependent proton noise-decoupled 13C-NMR. signals of the olefinic C-atom. The kinetic data and activation parameters are given in Tables 1 and 2. 相似文献
35.
Clemens Puppe 《Annals of Operations Research》1994,52(1):67-81
This paper studies vague preferences. In contrast to the concept of fuzzy preferences, the more general notion of vague preferences does not entail the assumption that the different degrees of preference are completely ordered. It is shown that the more general concept of a vague preference order arises very naturally in the context of aggregating a set of (exact) weak orders. Furthermore, necessary and sufficient conditions for the rationalizability of an exact choice function by means of a vague preference order are given. It turns out that in the general case these conditions are weaker than in the case where the degrees of preference are completely ordered. Consequently, there exist choice functions which are rationalizable by a general vague preference order but which are not rationalizable by a fuzzy preference order, or more generally by any vague preference order which induces a complete ranking of the degrees of preference. Examples of such choice functions are provided.This is a revised version of a discussion paper which was written at the University of Karlsruhe. I am grateful to Georg Bol and an anonymous referee for valuable comments. The research has been made possible by a fellowship of the DFG (Deutsche Forschungsgemeinschaft) which is also gratefully acknowledged. 相似文献
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Chemical and electronic properties of scrapecleaned YBa2Cu3O7–(YBCO) ceramics, which were also annealed in vacuum or exposed to H atoms or O2 molecules, were studied at room temperature by applying Auger electron (AES) and low-energy electron energy-loss spectroscopy (LEELS). Scanning electron micrographs showed such scraped surfaces to consist mainly of small, fractured YBCO crystallites, i.e. of clean YBCO surfaces. With only one exception, all low-energy AES lines were found to be shifted in energy compared to data recorded with surfaces of metallic Cu and Y. The analysis of the high-energy AES lines indicated the existence of non-stoichiometric material in grain boundaries. At least 25 different LEELS features were recorded. The 24.9-eV energy loss, which is due to the excitation of bulk valence-electron plasmons, indicates an enhanced oxygen deficit s 0.8 at scrape-cleaned YBCO surfaces. Annealing of scraped YBCO samples at approximately 700 K in vacuum and also their exposure to hydrogen atoms resulted in an additional oxygen depletion within a few atomic layers near to the surfaces. These oxygen deficiencies were found to increase the intensity ratios of low-and high-energy AES lines of Cu, Ba, and Y and to intensify the energy-loss peak at 4.4 eV which has been attributed to O–Cu–O dumbbells. 相似文献
40.