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51.
Nb-silicide in situ composites have great potential for high-temperature turbine applications. Nb-silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3 and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb-silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation. 相似文献
52.
S. A. Dodds T. L. Estle G. A. Gist Qiuan Zhu S. L. Rudaz D. P. Spencer E. J. Ansaldo J. H. Brewer D. R. Noakes R. Keitel 《Hyperfine Interactions》1986,32(1-4):869-872
Magnetic resonance of a spin system which is acted upon by a large near-resonance oscillating magnetic field transverse to
a static field has been studied experimentally and theoretically for many years. The technique of DEMUR (Double Electron Muon
Resonance) has many advantages for such studies. This paper will describe the results of an experiment to study the precession
of the muonium triplet near magnetic resonance using DEMUR. 相似文献
53.
Increased Water Reduction Efficiency of Polyelectrolyte‐Bound Trimetallic [Ru,Rh,Ru] Photocatalysts in Air‐Saturated Aqueous Solutions 下载免费PDF全文
Theodore R. Canterbury Dr. Shamindri M. Arachchige Prof. Robert B. Moore Prof. Karen J. Brewer 《Angewandte Chemie (International ed. in English)》2015,54(43):12819-12822
The groundbreaking use of polyelectrolytes to increase the efficiency of supramolecular photocatalysts in solar H2 production schemes under aqueous aerobic conditions is reported. Supramolecular photocatalysts of the architecture [{(TL)2Ru(BL)}2RhX2]5+ (BL=bridging ligand, TL=terminal ligand, X=halide) demonstrate high efficiencies in deoxygenated organic solvents but do not function in air‐saturated aqueous solution because of the quenching of the metal‐to‐ligand charge‐transfer (MLCT) excited state under these conditions. The new photocatalytic system incorporates poly(4‐styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)2Ru(dpp)}2RhCl2]5+ (bpy=2,2′‐bipyridine, dpp=2,3‐bis(2‐pyridyl)pyrazine). PSS has a profound impact on the photocatalyst efficiency, increasing H2 production over three times that of deoxygenated aqueous solutions alone. H2 photocatalysis proceeds even under aerobic conditions for PSS‐containing solutions, an exciting consequence for solar hydrogen‐production research. 相似文献
54.
A Districtwide Study of Automaticity When Included in Concept‐Based Elementary School Mathematics Instruction 下载免费PDF全文
Daniel McGee Patrick Richardson Meredith Brewer Funda Gonulates Theodore Hodgson Rebecca Weinel 《School science and mathematics》2017,117(6):259-268
While conceptual understanding of properties, operations, and the base‐ten number system is certainly associated with the ability to access math facts fluently, the role of math fact memorization to promote conceptual understanding remains contested. In order to gain insight into this question, this study looks at the results when one of three elementary schools in a school district implements mandatory automaticity drills for 10 minutes each day while the remaining two elementary schools, with the same curriculum and very similar demographics, do not. This study looks at (a) the impact that schoolwide implementation of automaticity drills has on schoolwide computational math skills as measured by the ITBS and (b) the relationship between automaticity and conceptual understanding as measured by statewide standardized testing. The results suggest that while there may be an association between automaticity and higher performance on standardized tests, caution should be taken before assuming there are benefits to promoting automaticity drills. These results are consistent with those that support a process‐driven approach to automaticity based on familiarity with properties and strategies associated with the base‐ten number system; they are not consistent with those that support an answer‐driven approach to automaticity based on memorization of answers. 相似文献
55.
Given A. Brewer 《Experimental Mechanics》1972,12(3):159-168
The failure at sea of a number of merchantship propeller blodes initiated a research program supported by the Maritime Administration, the American Bureau of Shipping, the American President Lines and the States Steamship Company. Although extensive theoretical work has been carried out in the past (predicting propeller operating stresses), very little full-scale experimental stress measurements have been obtained. Brewer Engineering Laboratories, Inc. was retained by the sponsors to attach and protect fifty strain gages on the test propeller at the locations chosen by Littleton Research and Engineering Corporation. The propeller strain gages were protected from the severe environment by means of synthetic rubber and metallic overlays. The gage wiring was led down each blade and into a specially machined, hollow tailshaft through a waterproof bulkhead. The S.S. “Michigan”, with the test group aboard, sailed from Long Beach, Calif., in April 1970. The ship called at the ports of San Francisco, Yokohama, Naha, Manila, Bogo and Hong Kong during the test period. Throughout the trip across the Pacific, the gaging and instrumentation functioned without degradation or evidence of distress after onemillion propeller shaft turns. At the end of five weeks at sea and two-million turns, all but eight gages exhibited low ground resistance. The S.S. “Michigan” went into dry dock at the Bethlehem Steel Shipyard at Terminal Island, Calif., on June 15, 1970. The propeller was removed and all strain gages checked for continuity and ground resistance. Forty-two of the original 50 strain gages were found to be intact. No sign of deterioration due to cavitation or electrolysis attack existed on the metallic overlays or spot welding. Wire chafing within the fairwater adapter cap accounted for the low ground resistance values observed at the end of the voyage to Hong Kong. 相似文献
56.
This paper describes certain tests and techniques employed in measuring stresses within an experimental nuclear-reactor head of unusual design. The incorporation of certain desired design features necessitated that the head be extremely thick. Due to the thickness and its complex geometry, it was considered desirable to determine stress distribution within the head under conditions of steady-state pressure combined with rapid heating and cooling transients within the reactor, in order to determine safe limits for the operation of the head. A photoelastic study of a three-dimensional model of the reactor head was completed in 1956; this study permitted prediction of the stress distribution throughout the head as a function of internal pressure, but it was not possible to assimilate the head thermal stresses by photoelastic means. It is the purpose of this paper to describe the technique employed in measuring thermal stresses in the interior of the head, under simulated operating conditions of steady-state pressure and temperature transients. 相似文献
57.
58.
Vaschenko G Brizuela F Brewer C Grisham M Mancini H Menoni CS Marconi MC Rocca JJ Chao W Liddle JA Anderson EH Attwood DT Vinogradov AV Artioukov IA Pershyn YP Kondratenko VV 《Optics letters》2005,30(16):2095-2097
Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a free-standing imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology. 相似文献
59.
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