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排序方式: 共有993条查询结果,搜索用时 31 毫秒
71.
Jürgen Brem Weston B. Struwe Anna M. Rydzik Hanna Tarhonskaya Inga Pfeffer Emily Flashman Sander S. van Berkel James Spencer Timothy D. W. Claridge Michael A. McDonough Justin L. P. Benesch Christopher J. Schofield 《Chemical science》2015,6(2):956-963
Metallo-β-lactamases (MBLs) catalyse the hydrolysis of almost all β-lactam antibiotics. We report biophysical and kinetic studies on the São Paulo MBL (SPM-1), which reveal its Zn(ii) ion usage and mechanism as characteristic of the clinically important di-Zn(ii) dependent B1 MBL subfamily. Biophysical analyses employing crystallography, dynamic 19F NMR and ion mobility mass spectrometry, however, reveal that SPM-1 possesses loop and mobile element regions characteristic of the B2 MBLs. These include a mobile α3 region which is important in catalysis and determining inhibitor selectivity. SPM-1 thus appears to be a hybrid B1/B2 MBL. The results have implications for MBL evolution and inhibitor design. 相似文献
72.
Functional Hydride Transfer by a Thiolate‐Containing Model of Mono‐Iron Hydrogenase featuring an Anthracene Scaffold 下载免费PDF全文
Spencer A. Kerns Anne‐Clarisse Magtaan Pisey R. Vong Michael J. Rose 《Angewandte Chemie (International ed. in English)》2018,57(11):2855-2858
We report the synthesis, X‐ray structure and functional biomimetic activity of a model complex of mono‐iron hydrogenase (Hmd). To achieve the desired biomimetic fac‐CNS(thiolate) ligation motif, an anthracene framework is used to provide the requisite donors in a single chelate. A bulky aryl thiolate (ortho dimethylphenyl) is included to achieve mononuclearity. In addition to exhibiting structural (X‐ray) and spectroscopic (NMR, IR) similarity to the enzyme, the complex is competent for H2 activation (heterolysis) and hydride transfer to a model substrate—mimicking the functional behavior of the enzyme in a biomimetic CNS coordination sphere for the first time. 相似文献
73.
Keita B Kortz U Brudna Holzle LR Brown S Nadjo L 《Langmuir : the ACS journal of surfaces and colloids》2007,23(19):9531-9534
Original and simple procedures for glassy carbon electrode modification with polyoxometalates (POMs), phosphotungstate [H7P8W48O184]33-, and Co(II)-containing silicotungstates [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(beta-SiW8O31)3}]5- and [{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29OH)2}2]22- give stable and very active surfaces for the hydrogen-evolution reaction (HER). For this purpose, the selected POMs fixed on Vulcan XC-72 were adsorbed on the electrode surface or were directly entrapped in polyvinylpyridine films on the electrode. Cyclic voltammetry and confocal microscopy results converge to indicate that the activation is related to the proton and electron reservoir-like behaviors of these molecular oxides and not to any electrode surface area increase. However, the Tafel parameters of the HER process, which are different from one POM to the next, are in the range of those of the best metallic electrodes. 相似文献
74.
Griffith GA Percy JM Pintat S Smith CA Spencer N Uneyama E 《Organic & biomolecular chemistry》2005,3(15):2701-2712
Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT (19)F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers. 相似文献
75.
The distribution of the chromatic number on random graphsG
n, p
is quite sharply concentrated. For fixedp it concentrates almost surely in √n ω(n) consecutive integers where ω(n) approaches infinity arbitrarily slowly. If the average degreepn is less thann
1/6, it concentrates almost surely in five consecutive integers. Large deviation estimates for martingales are used in the proof. 相似文献
76.
Zirconia powders were prepared by forming gels by desiccation of aqueous precursor solutions of zirconium acetate containing nitric or sulfuric acid at pH 2.4 and 1.4 and pyrolyzing the gels to temperatures up to 825°C. The structure development in the gels and solid pyrolysis products was investigated. The crystalline zirconia structures produced monoclinic (m), metastable cubic (c) and tetragonal (t) polymorphs. The structure transition temperatures were strongly dependent on the pH, the anions and the stoichiometry of the zirconium complex in the precursor solution. The monoclinic polymorph fraction in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing sulfuric acid at pH 2.4 to 750°C approaches zero while this ratio in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing nitric acid at pH 1.4 to 825°C is 0.7. 相似文献
77.
78.
Dale R. Harshman Ralph Eric Turner Jess H. Brewer David P. Spencer 《Hyperfine Interactions》1986,32(1-4):527-533
Muonium (μ
+
e
−) in bulk fused quartz is a unique system in that theμ
+ spin polarization (in the muonium state) relaxes almost entirely via random anisotropic hyperfine distortions (RAHD). As
such, this system provides an excellent test case for a new RAHD spin relaxation theory. This theory is quantitatively compared
to static zero field data and the functional characteristics in both the high field and dynamic limits are considered as well. 相似文献
79.
80.
M. Manickam Alun Smith Maura Belloni Elwyn J. Shelley Peter R. Ashton Neil Spencer Jon A. Preece 《Liquid crystals》2002,29(4):497-504
The synthesis and characterization of four C 60 Bingel cyclopropanation adducts incorporating bis-biphenylene (three adducts) and bis-triphenylene (one adduct) moieties are described. The thermal analysis (POM and DSC) of these materials reveals that they are not liquid crystalline. However, two of the precursor bis-biphenylene malonate esters possess monotropic mesophases. Furthermore, each of the corresponding C 60 adducts is miscible in the melts of the precursor malonate ester, and at low dopings, retains the liquid crystalline monotropic mesophases of the precursor. 相似文献