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排序方式: 共有229条查询结果,搜索用时 16 毫秒
111.
Inga Ronova 《Structural chemistry》2010,21(3):541-553
This article focuses on the influence of the geometric structure of the polymer chain on the physical properties of polymers.
It is shown that for polyheteroarylenes the Kuhn segment calculated based on the geometric structure of the polymer chain
has a good correlation with the physical properties of those polymers. For aliphatic polymers, a volume factor is suggested
that equals the ratio of the Van der Waals volume of pendant substitute to the volume of the whole polymer chain. It is shown
that the properties of aliphatic polymers that depend on free volume are well described by this value. 相似文献
112.
Irradiation (350 nm) of the newly synthesized 3‐(alk‐1‐ynyl)cyclohept‐2‐en‐1‐ones 1 and 2 leads to the selective formation of tricyclic head‐to‐head dimers. In the presence of 2,3‐dimethylbuta‐1,3‐diene, the (monocyclic) enone 1 affords trans‐fused 7‐alkynyl‐bicyclo[5.2.0]nonan‐2‐ones as major photoproducts, whereas photocycloaddition of benzocyclohept‐5‐en‐7‐one 2 to the same diene gives preferentially the eight‐membered cyclic allene 16 via ‘end‐to‐end’ cyclization of the intermediate allyl‐propargyl biradical 22 . On contact with acid, cycloocta‐1,2,5‐triene 16 isomerizes to cycloocta‐1,3,5‐triene 18 . 相似文献
113.
We consider a control volume discretization with a multi-point flux approximation to model Discrete Fracture–Matrix systems for anisotropic and fractured porous media in two and three spatial dimensions. Inspired by a recently introduced approach based on a two-point flux approximation, we explicitly account for the fractures by representing them as hybrid cells between the matrix cells. As well as simplifying the grid generation, our hybrid approach excludes small cells in the intersection of the fractures and hence avoids severe time-step restrictions associated with small cells. Excluding the small cells also reduces the condition number of the discretization matrix. For examples involving realistic anisotropy ratios in the permeability, numerical results show significant improvement compared to existing methods based on two-point flux approximations. We also investigate the hybrid method by studying the convergence rates for different apertures and fracture/matrix permeability ratios. Finally, the effect of removing the cells in the intersections of the fractures are studied. Together, these examples demonstrate the efficiency, flexibility and robustness of our new approach. 相似文献
114.
Inga Susvilo Algirdas Brukstus Sigitas Tumkevicius 《Journal of heterocyclic chemistry》2006,43(2):267-276
Methyl N‐methyl‐N‐(6‐substituted‐5‐nitropyrimidin‐4‐yl)glycinates ( 4a‐n ), obtained from 6‐substituted‐4‐chloro‐5‐nitropyrimidines and sarcosine methyl ester (methyl 2‐(methylamino)acetate), in the reaction with sodium alkoxides underwent transformations to give different products. N‐methyl‐N‐(5‐nitropyrimidin‐4‐yl)glycinates ( 4a,i,j ) bearing amino and arylamino groups in the position 6 of the pyrimidine ring gave corresponding 6‐substituted‐4‐methylamino‐5‐nitrosopyrimidines ( 5a,i,j ). In the reaction of N‐(6‐alkylamino‐5‐nitropyrimidin‐4‐yl)‐N‐methylglycinates ( 4b,f‐h ) with sodium alkoxides the corresponding 6‐alkylamino‐4‐methylamino‐5‐nitrosopyrimidines ( 5b,f‐h ) and 5‐hydroxy‐8‐methyl‐5,8‐dihydropteridine‐6,7‐diones ( 6b,f‐h ) were formed. The main products of the reaction of N‐(6‐dialkylamino‐5‐nitropyrimidin‐4‐yl)‐N‐methylglycinates ( 4c‐e,k,l ), after work‐up, were the corresponding 6‐dialkylamino‐9‐methylpurin‐8‐ones ( 7c‐e,k,l ) and 8‐alkoxy‐6‐dialkylamino‐9‐methylpurines ( 9c,1,10c,l ). Methyl N‐methyl‐N‐{[6‐(2‐methoxy‐oxoethyl)thio]‐5‐nitropyrimidin‐4‐yl}glycinate ( 4n ) under the same conditions gave methyl 7‐methylaminothiazolo[5,4‐d]pyrimidine‐2‐carboxylate ( 13 ). Mechanisms of the observed transformations are discussed. 相似文献
115.
Bardelang D Rockenbauer A Karoui H Finet JP Biskupska I Banaszak K Tordo P 《Organic & biomolecular chemistry》2006,4(15):2874-2882
The free radical trapping properties of eight 5-alkoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO) type nitrones and those of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were evaluated for trapping of superoxide anion radicals in the presence of 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CD). (1)H-NMR titrations were performed to determine both stoichiometries and binding constants for the diamagnetic nitrone-DM-beta-CD equilibria. EPR titrations were then performed and analyzed using a two-dimensional EPR simulation program affording 1 : 1 and 1 : 2 stoichiometries for the nitroxide spin adducts with DM-beta-CD and the associated binding constants after spin trapping. The nitroxide spin adducts associate more strongly with DM-beta-CD than the nitrones. The ability of the nitrones to trap superoxide, the enhancement of the EPR signal intensity and the supramolecular protection by DM-beta-CD against sodium L-ascorbate reduction were evaluated. 相似文献
116.
Electrochemistry of Methyl Viologen and Anthraquinonedisulfonate at Diamond and Diamond Powder Electrodes: The Influence of Surface Chemistry 下载免费PDF全文
The electrochemical behaviour of methyl viologen and anthraquinonedisulfonate was studied at electrodes produced from differing forms of diamond, including microcrystalline boron doped diamond, boron doped diamond powder and detonation nanodiamond powder. Two types of electrode pretreatment were employed to produce two dissimilar surface terminations: hydrophobic H‐terminated and hydrophilic O‐terminated. In the case of methyl viologen, it was found that the reduced neutral molecule adsorbed on all three electrodes if they were hydrogen terminated, but not if they were oxygen terminated. For anthraquinonedisulfonate, no adsorption was found on the solid diamond electrode, although again significant adsorption was noted on the powder electrodes, provided they were hydrogen terminated. The reasons underlying these observations are discussed in terms of hydrophobic and electrostatic interactions and the electrode morphology. The work provides information into the likely occurrence of adsorption and concomitant electrode fouling, which may be experienced in electroanalytical applications using solid and powdered forms of diamond. 相似文献
117.
Inga Leinemann Weihao Zhang Tiit Kaljuvee Kaia Tõnsuaadu Rainer Traksmaa Jaan Raudoja Maarja Grossberg Mare Altosaar Dieter Meissner 《Journal of Thermal Analysis and Calorimetry》2014,118(2):1313-1321
The present study deals with chemical reactions and enthalpies during the synthesis of Cu2ZnSnSe4 (CZTSe) from CuSe, SnSe, and ZnSe in molten NaI as flux material in closed degassed ampoules. Differential thermal analysis (DTA) at heating rates 5 °C min?1 and cooling rates 10 °C min?1 were used for the determination of temperatures of phase transitions and/or chemical reactions. XRD and Raman analyses confirmed that the formation of CZTSe starts already at 380 °C after the melting of Se that deliberates from the transformation of CuSe to Cu1.8Se, and the CZTSe formation process impedes to a great extent due to the presence of solid NaI. After the melting of NaI, the formation of CZTSe is completed. For the determination of enthalpy values, the calibration with pure NaI was performed. The thermal effects and enthalpies were compared with the available known thermodynamical values. The specific enthalpy of exothermic Cu2ZnSnSe4 formation at 661 °C in NaI ?36 ± 3 kJ mol?1 was determined experimentally for the first time. Ternary compound Na2SnSe3 was formed during the synthesis process. NaI·2H2O, if present in NaI, was found to be a critical issue in the synthesis process of CZTSe monograin powders in molten NaI—it gave rise to the formation of oxygen-containing by-products Na2SeO4 and Na2Cu(OH)4. The complete dehydration of NaI·2H2O at T ≤ 70 °C in vacuum is necessary to avoid the formation of oxygen-containing compounds. 相似文献
118.
Monitoring Conformational Changes in the NDM‐1 Metallo‐β‐lactamase by 19F NMR Spectroscopy 下载免费PDF全文
Anna M. Rydzik Jürgen Brem Sander S. van Berkel Inga Pfeffer Anne Makena Dr. Timothy D. W. Claridge Prof. Christopher J. Schofield 《Angewandte Chemie (International ed. in English)》2014,53(12):3129-3133
The New Delhi metallo‐β‐lactamase (NDM‐1) is involved in the emerging antibiotic resistance problem. Development of metallo‐β‐lactamases (MBLs) inhibitors has proven challenging, due to their conformational flexibility. Here we report site‐selective labeling of NDM‐1 with 1,1,1‐trifluoro‐3‐bromo acetone (BFA), and its use to study binding events and conformational changes upon ligand–metal binding using 19F NMR spectroscopy. The results demonstrate different modes of binding of known NDM‐1 inhibitors, including L ‐ and D ‐captopril by monitoring the changing chemical environment of the active‐site loop of NDM‐1. The method described will be applicable to other MBLs and more generally to monitoring ligand‐induced conformational changes. 相似文献
119.
Tatyana A. Mastryukova Inga M. Aladzheva Olga V. Bykhovskaya Dmitrii I. Lobanov Alexey M. Nemeryuk Konstantin A. Lyssenko 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1701-1704
A novel convenient "one-pot" synthesis of 2-oxo-1,2 u 5 -azaphosphacyclanes 1 and 1,2 u 4 -azaphosphacyclanium salts 2 via intramolecular N-alkylation of y -halogenalkyl-substituted iminophosphoryl compounds 3 has been developed. The common nature of the reaction of intramolecular cyclization of iminophosphoryl compounds having an alkoxy group at the phosphorus atom and the Arbuzov reaction has been established. 相似文献
120.
Inga A. Ronova Lev N. Nikitin Ekaterina A. Sokolova Irina Bacosca Ion Sava Maria Bruma 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):929-936
Two series of polyheteroarylenes have been investigated with regard to their physical properties before and after swelling with supercritical carbon dioxide. The study of the dependence of glass transition temperature and free volume of polymers on their conformational rigidity showed that the process of swelling in supercritical carbon dioxide is influenced by the voluminous side groups and by the high boiling solvent N-methylpyrolidinone used for the preparation of the polymers which facilitates the formation of crosslinks or complexes with the macromolecular chains. 相似文献