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841.
842.
Massimiliano Aschi Giorgia Toto Brocchi Gustavo Portalone 《Molecules (Basel, Switzerland)》2021,26(11)
Although natural or artificial modified pyrimidine nucleobases represent important molecules with valuable properties as constituents of DNA and RNA, no systematic analyses of the structural aspects of bromo derivatives of cytosine have appeared so far in the literature. In view of the biochemical and pharmaceutical relevance of these compounds, six different crystals containing proton-transfer derivatives of 5-bromocytosine are prepared and analyzed in the solid-state by single crystal X-ray diffraction. All six compounds are organic salts, with proton transfer occurring to the Nimino atom of the pyridine ring. Experimental results are then complemented with Hirshfeld surface analysis to quantitively evaluate the contribution of different intermolecular interactions in the crystal packing. Furthermore, theoretical calculations, based on different arrangements of molecules extracted from the crystal structure determinations, are carried out to analyze the formation mechanism of halogen bonds (XBs) in these compounds and provide insights into the nature and strength of the observed interactions. The results show that the supramolecular architectures of the six molecular salts involve extensive classical intermolecular hydrogen bonds. However, in all but one proton-transfer adducts, weak to moderate XBs are revealed by C–Br…O short contacts between the bromine atom in the fifth position, which acts as XB donor (electron acceptor). Moreover, the lone pair electrons of the oxygen atom of adjacent pyrimidine nucleobases and/or counterions or water molecules, which acts as XB acceptor (electron donor). 相似文献
843.
Polytetrafluoroethylene (PTFE) is an important engineering material with a low coefficient of friction but a high rate of wear. As a semi‐crystalline polymer, its wear resistance is related to its micro‐morphology. Friction and wear properties of semi‐crystalline non‐spherulitic PTFE have been widely studied, but no investigation is reported about tribological properties of spherulitic PTFE due to difficulties in finding such properties. In this paper, friction and wear properties of PTFE with spherulitic micro‐morphology are studied for the first time. The results show that, first, under the same experimental condition, when two kinds of PTFE are rubbed against the steel disc, the number and size of debris of spherulitic PTFE are much less and smaller than that of debris of PTFE without spherulitic crystals. This means that the wear resistance of spherulitic PTFE is better than that of semi‐crystalline PTFE without spherulitic micro‐morphology. Second, the friction property of spherulitic PTFE is also different from that of PTFE without spherulitic crystals. Finally, the friction and wear mechanisms of spherulitic PTFE and non‐spherulitic PTFE are compared. 相似文献
844.
Dr. Shannon J. Lee Gayatri Viswanathan Dr. Scott L. Carnahan Dr. Colin P. Harmer Dr. Georgiy Akopov Prof. Dr. Aaron J. Rossini Prof. Dr. Gordon J. Miller Prof. Dr. Kirill Kovnir 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202104319
Centrosymmetric skutterudite RhP3 was converted to a nonsymmorphic and chiral compound RhSi0.3P2.7 (space group P212121) by means of partial replacement of Si for P. The structure, determined by a combination of X-ray crystallography and solid state 31P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis-RhSi2P4 and fac-RhSi3P3 fragments is π-electron back-donation between the Rh t2g-type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi0.3P2.7. Electronic structure calculations predicted centrosymmetric cubic RhP3 to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi0.3P2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor. 相似文献
845.
Dr. Kuthuru Suresh Andre P. Kalenak Dr. Ania Sotuyo Prof. Adam J. Matzger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(18):e202200334
Exerting morphological control over metal-organic frameworks (MOFs) is critical for determining their catalytic performance and to optimize their packing behavior in areas from separations to fuel gas storage. A mechanism-based approach to tailor the morphology of MOFs is introduced and experimentally demonstrated for five cubic Zn4O-based MOFs. This methodology provides three key features: 1) computational screening for selection of appropriate additives to change crystal morphology based on knowledge of the crystal structure alone; 2) use of additive to metal cluster geometric relationships to achieve morphologies expressing desired crystallographic facets; 3) potential for suppression of interpenetration for certain phases. 相似文献
846.
847.
848.
849.
Binyu Zhang Yang Zhou Yang Cao Xiaohong Wang Kexi Zhang Jinchun Tu Lei Ding 《Chemphyschem》2022,23(3):e202100697
Modulating the local electronic state of metal compounds through interfacial interaction has become a key method for manufacturing high-performance hydrogen evolution reaction (HER) electrocatalysts. The electron-rich active sites can promote the adsorption of hydrogen, which accelerates the Volmer step and thereby enhances the electrocatalytic performance of HER. Here, we found that the strong interfacial interaction between TiO nanodots (TiO/Co−S) and Co−S nanosheets could advantageously improve the performance toward HER of electrocatalyst. Meanwhile, XPS results showed that modulating the local electronic structure of the TiO nanodots produces electron-rich regions on Co. As a result, the overpotential of the TiO/Co−S nanocomposite at 10 mA cm−2 was 107 mV, and the Tafel slope was 83.3 mV dec−1. This study focused on the effect of the solid-solid interface on the local electronic structure of the catalytic metal active sites and successfully improved the catalytic activity of transition metal materials in HER catalysis. 相似文献
850.
Zeinu Mussa Belew Michal Poborsky Hussam Hassan Nour-Eldin Barbara Ann Halkier 《Current Opinion in Green and Sustainable Chemistry》2022
Transport engineering strategies use altered expression of transporter proteins to change metabolite distribution within an organism. The production of plant specialized metabolites in microbial cell factories encounters a set of challenges that could benefit from the implementation of transport engineering technology. The range of challenges includes premature pathway termination due to secretion of intermediates, feedback inhibition due to inefficient export of final products, low yields in bioconversion processes due to inefficient import of precursors, and poor connectivity between subcellular compartments expressing different parts of complex biosynthetic pathways. We highlight the latest examples of transport engineering in microbial cell factories producing plant specialized metabolites, identify the current knowledge gap, and propose future research for advancing the field. 相似文献