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91.
Sara K. Metcalf Elizabeth M. Holt 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(10):1228-1231
Diethyl 4‐(2,5‐dimethoxyphenyl)‐2,6‐dimethyl‐1,4‐dihydropyridine‐3,5‐dicarboxylate, C21H27NO6, (I), diethyl 4‐(3,4‐dimethoxyphenyl)‐2,6‐dimethyl‐1,4‐dihydropyridine‐3,5‐dicarboxylate, C21H27NO6, (II), and diethyl 2,6‐dimethyl‐4‐(3,4,5‐trimethoxyphenyl)‐1,4‐dihydropyridine‐3,5‐dicarboxylate, C22H29NO7, (III), crystallize with hydrogen‐bonding networks involving the H atom bonded to the N atom of the 1,4‐dihydropyridine ring and carbonyl O atoms in (I) and (II). Unusually, (III) shows O atoms of methoxy groups serving as hydrogen‐bond acceptors. 相似文献
92.
Aicha Benabad Karima Bakhous Fatima Cherkaoui Elizabeth M. Holt 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1292-1293
BiV0.4Fe3IIIO(PO4)3 crystallizes with two Fe atoms (one on an inversion centre and one on a mirror plane) displaying octahedral geometry and a third Fe atom (on a mirror plane) with trigonal bipyramidal coordination. Fe atoms are seen in oxygen‐bridged chains. BiV atoms are found in the interstitial sites between these chains. Bi shows sevenfold coordination, with Bi—O distances between 2.357 (7) and 2.529 (6) Å. 相似文献
93.
David W. Holt 《Accreditation and quality assurance》2000,5(9):389-391
This report addresses the proposition: current proficiency testing (PT) schemes for therapeutics and toxicology can easily
engender complacency. The proposition was based on the premise that there are substantial between-laboratory differences and
objectives in the supply of services for the measurement of drugs, as a result of which it is difficult to design PT schemes
which adequately cover the requirements of all laboratories. Thus, acceptable performance in a PT scheme may lead participants
to consider that they have tested their procedures more rigorously than is the case. Four areas, validity of the PT scheme,
PT material, frequency of testing and acceptance criteria are examined.
Received: 15 April 2000 · Accepted: 15 April 2000 相似文献
94.
Frank Marken Yu-Chen Tsai Andrew J. Saterlay Barry A. Coles Daniel Tibbetts Katherine Holt Christiaan H. Goeting John S. Foord Richard G. Compton 《Journal of Solid State Electrochemistry》2001,5(5):313-318
Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and
control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon
and boron-doped diamond electrodes. Deposition of both Pb metal and PbO2 from an aqueous solution of Pb2+ (0.1 M HNO3) are affected by microwave radiation. The formation of PbO2 on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room
temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature
at the electrode|solution (electrolyte) interface with the Fe3+/2+ (0.1 M HNO3) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore
consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO2 on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An
increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO2/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution
of solid microparticles of PbO2 abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation.
Electronic Publication 相似文献
95.
96.
J. A. Atanasiu A. J. Velculescu J. A. Boltunow M. A. Worssina M. L. Holt L. Kahlenberg L. H. Baldinger L. Wolf M. L. Nichols S. R. Cooper und A. Holmqvist 《Fresenius' Journal of Analytical Chemistry》1938,115(1-2):37-42
Ohne Zusammenfassung 相似文献
97.
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98.
The ion exchange equilibrium between KCl and SrCl2 solutions and the cation selective membrane CR61 AZL386 has been examined. Equilibrium isotherms are measured for membrane—electrolyte equilibria for two total concentrations of Cl?in the electrolyte solution and at three different temperatures. The results show that Sr2+ is strongly preferred to K+ in the membrane. Selectivity increases with temperature in the range 10°C to 40°C. It decreases with increasing total concentration from 0.01 N to 0.03 N. Electrolyte absorption in the membrane was not detected for the experimental conditions used. Contents of water in the membrane is constant for external salt concentrations between 3 x 10?8N and 3 x 10?2N. The difference in water content between the pure K form and the pure Sr form is approximately 5%.A thermodynamic treatment of ion exchange is presented. The thermodynamic equilibrium constant for the exchange reaction 2 KR + SrCl2 = SrR2+ 2 KCl has been determined by two different integration procedures, R being an ion exchange site in the membrane. The variations of the thermodynamic functions ΔGmix, ΔHmix and ΔSmix are calculated from experimental data for an assumed mixing process of membranes in the pure forms.Activity coefficients for the membrane components are calculated from experimental data. Results are compared to two lattice models. A model with a random distribution of K+, Sr2+ and a vacant site seems preferred at low concentration of Sr2+. At high concentrations, Sr2+ and the vacant site associate. 相似文献
99.
100.