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91.
Comparison of phantom materials for use in quality assurance of microbeam radiation therapy
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Matthew Cameron Iwan Cornelius Dean Cutajar Jeremy Davis Anatoly Rosenfeld Michael Lerch Susanna Guatelli 《Journal of synchrotron radiation》2017,24(4):866-876
Microbeam radiation therapy (MRT) is a promising radiotherapy modality that uses arrays of spatially fractionated micrometre‐sized beams of synchrotron radiation to irradiate tumours. Routine dosimetry quality assurance (QA) prior to treatment is necessary to identify any changes in beam condition from the treatment plan, and is undertaken using solid homogeneous phantoms. Solid phantoms are designed for, and routinely used in, megavoltage X‐ray beam radiation therapy. These solid phantoms are not necessarily designed to be water‐equivalent at low X‐ray energies, and therefore may not be suitable for MRT QA. This work quantitatively determines the most appropriate solid phantom to use in dosimetric MRT QA. Simulated dose profiles of various phantom materials were compared with those calculated in water under the same conditions. The phantoms under consideration were RMI457 Solid Water (Gammex‐RMI, Middleton, WI, USA), Plastic Water (CIRS, Norfolk, VA, USA), Plastic Water DT (CIRS, Norfolk, VA, USA), PAGAT (CIRS, Norfolk, VA, USA), RW3 Solid Phantom (PTW Freiburg, Freiburg, Germany), PMMA, Virtual Water (Med‐Cal, Verona, WI, USA) and Perspex. RMI457 Solid Water and Virtual Water were found to be the best approximations for water in MRT dosimetry (within ±3% deviation in peak and 6% in valley). RW3 and Plastic Water DT approximate the relative dose distribution in water (within ±3% deviation in the peak and 5% in the valley). PAGAT, PMMA, Perspex and Plastic Water are not recommended to be used as phantoms for MRT QA, due to dosimetric discrepancies greater than 5%. 相似文献
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93.
Dependence of electrical performance on structural organization in polymer field effect transistors
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Emily G. Bittle Hyun Wook Ro Chad R. Snyder Sebastian Engmann R. Joseph Kline Xinran Zhang Oana D. Jurchescu Dean M. DeLongchamp David J. Gundlach 《Journal of Polymer Science.Polymer Physics》2017,55(14):1063-1074
Organic semiconductors (OSCs) are strong contenders for use in printed, flexible electronics. Although organic electronic materials have been studied for many years, the physics of charge transport is still under investigation. This is in part due to variability resulting from the large variety of molecules that can be synthesized and inconsistency in electrical characterization due to device and processing conditions. Molecular ordering in OSCs is known to alter the charge transport characteristics and attention to long range and short range ordering provides clues as to the nature of transport pathways. Here, we study ordered regioregular poly(3‐hexylthiophene‐2,5‐diyl) films carefully prepared to obtain a set of three samples with incrementally increasing order on identical transistor architectures. Ordering was characterized using a variety of short and long range techniques to probe the coherence and number of crystallites formed during processing, and the correlation between these different measures of order are quantified. We observe three changes in transistor behavior that show a shift from non‐ideal to more textbook‐like characteristics with increasing order: reduction of the contact resistance, shift to field‐independent mobility, and a shift from a diode‐like (S‐shaped) to linear response at low lateral fields. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1063–1074 相似文献
94.
95.
Dean Shi Xiao‐Yang Wang Hengchong Shi Jing‐Hua Yin Robert K. Y. Li Guo‐Hua Hu 《Journal of Polymer Science.Polymer Physics》2010,48(1):65-73
TEM micrographs show that the PA grafts of PS‐g‐PA6 graft copolymers, which are obtained directly by extracting homo‐PA6 out from the homo‐PA6/PS‐g‐PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50–60 nm. This article reports on a unique crystallization behavior of the PA6 grafts in PS‐g‐PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 65–73, 2010 相似文献
96.
Chris Capaccio Nikolay S. Stoykov Raji Sundararajan David A. Dean 《Journal of Electrostatics》2009,67(4):652-662
The application of appropriate electric fields to cells and tissues, termed electroporation, can result in efficient and safe gene transfer. We have shown previously that this approach results in high level gene transfer to and expression in the vasculature of living animals. This paper presents the results of an electric field distribution study of a rat mesenteric vasculature model using the Finite-Element Time-Domain (FETD) technique. A novelty of this work is the use of Debye dispersive dielectric parameters, as the electrical response of biological tissues is inherently frequency-dependent. The results compare fairly well with experimental findings. 相似文献
97.
98.
Motivated by a computer science algorithm known as "linear probing with hashing," we study a new type of percolation model whose basic features include a sequential "dropping" of particles on a substrate followed by their transport via a "pushing" mechanism. Our exact solution in one dimension shows that, unlike the ordinary random percolation model, the drop-push model has nontrivial spatial correlations generated by the dynamics itself. The critical exponents in the drop-push model are also different from those of the ordinary percolation. The relevance of our results to computer science is pointed out. 相似文献
99.
Dean P. Stull Thomas A. Scales Randy Daughenbaugh Neil A. Jans David T. Bailey 《Applied biochemistry and biotechnology》1995,54(1-3):133-140
Taxol® (paclitaxel) has been hailed by many as the most promising new cancer treatment in two decades. The FDA requires that paclitaxel intended for human consumption be obtained only from the bark ofTaxus brevifolia, the Pacific yew. As this may become increasingly uneconomical, new strategies must be explored to ensure the continued availability of taxol and related molecules. This article examines the planning that must be engaged in and the contingencies that must be prepared for in this changing arena. 相似文献
100.
The theoretical model for multiple bound excitons (MBE) recently introduced by Dean et al1 is used to discuss uniaxial stress effects in silicon. The fine structures observed in MBE spectra for SiC and Si are qualitatively strikingly similar. However, the interpretation of the strongest features in terms of a specific model for excited states suggested by Kirczenow2 and Thewalt3 is not valid for SiC. 相似文献