全文获取类型
收费全文 | 492篇 |
免费 | 48篇 |
国内免费 | 2篇 |
专业分类
化学 | 337篇 |
晶体学 | 2篇 |
力学 | 18篇 |
数学 | 30篇 |
物理学 | 155篇 |
出版年
2024年 | 6篇 |
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 26篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 38篇 |
2012年 | 46篇 |
2011年 | 45篇 |
2010年 | 21篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有542条查询结果,搜索用时 15 毫秒
151.
E. Vardaci G. La Rana A. Brondi R. Moro A. Principe D. Fabris G. Nebbia G. Viesti M. Cinausero E. Fioretto G. Prete F. Lucarelli E.M. Fiore L. Fiore V. Paticchio P.F. Bortignon 《The European Physical Journal A - Hadrons and Nuclei》1998,2(1):55-60
The α-particle emission from the 28Si+170Er fusion-evaporation reaction at 165 and 185 MeV has been measured and compared with published data relative to the pre-scission
emission in the same reaction. The spectra in the two channels exhibit nearly the same shape in the low energy region, whereas
in the high energy region the spectrum for the fusion-evaporation case features a larger apparent temperature. The interpretation
of the difference in shape between the two decay channels is based on statistical model calculations which account for the
effects due to the different length of the decay chain. Statistical model calculations with standard parameters describe well
the gross features of the alpha particle spectra in the fusion-evaporation channel and the proton spectra in the pre-scission
channel. On the contrary, the model predictions seem to overestimate by ≃2 MeV the emission barrier for the alpha particles
in the pre-fission channel. This effect is ascribed to the larger elongation of the nucleus during the fission process. An
average axis ratio b/a∼ 2 for the emitter is suggested.
Received 29 April 1997 / Revised version 10 September 1997 相似文献
152.
Early ischemic change after stroke can be demonstrated with diffusion-weighted imaging (DWI) and quantified by measuring the apparent diffusion coefficient (ADC) and/or lesion volume. We examined the reliability and reproducibility of lesion volume and ADC measurement on DWI images, and discuss the implications for clinical studies. Using 38 DWI scans from 15 stroke patients, two observers (a physicist and a neuroscience graduate) blind to each other, recorded the lesion volume on DWI sequences, measured the ADC values in this volume and calculated the ratio of ischemic: control ADC (ADCr). One observer repeated his measurements blind to his first, and also examined the effect on lesion volume and ADC of deliberately varying by only one pixel, the outline of the visible boundary of the lesion. The inter and intra-rater reliability were worse for lesion volume than ADC or ADCr measurements: lesion volume, inter-rater coefficient of variation (CoV) 85 +/- 130%, intra-rater CoV 20+/-SD80% (p < 0.05); ADC inter-rater CoV 7.7 +/- SD 19%, intra-rater CoV 0.2 +/- SD 12% (p = NS); and ADCr inter-rater CoV 8 +/- SD27%, intra-rater CoV 0.8 +/- SD73% (p = NS). Altering the position of the outline tracing of the lesion boundary by one pixel altered the measured volumes by 22 +/- SD25% (p < 0.05), but ADC values were altered by only 2.9 +/- SD4.9% and ADCr by 2.7 +/- SD4.8% (p = NS). ADC and ADCr values are more reliable and reproducible than DWI lesion size in acute ischemic stroke because altering where the lesion boundary is measured has a much greater impact on lesion volume than on the ADC or ADCr. This effect is greatest in large lesions. 相似文献
153.
M. Mazzocco P. Scopel C. Signorini L. Fortunato F. Soramel I. J. Thompson A. Vitturi M. Barbui A. Brondi M. Cinausero D. Fabris E. Fioretto G. La Rana M. Lunardon R. Moro A. Ordine G. F. Prete V. Rizzi L. Stroe M. Trotta E. Vardaci G. Viesti 《The European Physical Journal A - Hadrons and Nuclei》2003,18(4):583-587
The excitation energy above the breakup threshold of the
Li system, after the interaction of 6Li nuclei with a 208Pb target, was deduced from the invariant mass of the
system. Data were collected with a large-solid-angle detector set-up at four beam energies around the Coulomb barrier. The excitation of the 6Li nucleus above the breakup threshold (1.47 MeV) has a quite similar behavior at each measured beam energy and angle; it is peaked at
MeV above the threshold and shows an exponential decay on the high energy side, which is a clear signature of a direct breakup process. The experimental excitation energies are reproduced both in shape and absolute value by 1) fully quantum-mechanical Coupled-Channel calculations with coupling to discretized-continuum 6Li excitations, 2) semi-classical Coupled-Channel approach, where the relative motion is treated along a classical trajectory.Received: 2 June 2003, Published online: 18 November 2003PACS:
25.70.Ji Fusion and fusion-fission reactions - 25.70.Mn Projectile and target fragmentation - 24.10.Eq Coupled-channel and distorted-wave modelsThis revised version was published online in December 2003 with corrections to the communicators name. 相似文献
154.
The preparation of a novel phosphorus species, thiophosphoramidate, has enabled the specific thiophosphorylation of histidine at its 3-position. The rates of phosphorylation and thiophosphorylation of histidine are reported, as well as the spectroscopic properties of both thiophosphoramidate and 3-thiophosphohistidine. Structural assignment of the latter was made by analogy to the NMR properties of the known 3-phosphohistidine. The alkylation of 3-thiophosphohistidine by phenacyl bromide serves as a model for the introduction of labeling or probe reagents into histidine phosphorothioate-containing proteins. 相似文献
155.
156.
Seth's generalized measure of strain is used in the determination of the deformation field produced by radial forces acting on a thin plane sheet of incompressible isotropic elastic material, containing a circular hole or circular rigid inclusion, at its outer edge. Results calculated are comparable with the experimental results obtained by Rivlin and Thomas, employing a vulcanized natural rubber. 相似文献
157.
Mauriello G Marino R D'Auria M Cerone G Rana GL 《Journal of chromatographic science》2004,42(6):299-305
Volatile organic compounds (VOCs) of nine Tuber species and two corresponding forms are identified via solid-phase microextraction-gas chromatography-mass spectrometry analysis. Seventy-five compounds are identified. The most abundant are dimethylsulphide, 2- and 3-methylbutanal, 2-methylpropanol, and butanone. 相似文献
158.
159.
Ozgul Gok Sezin Yigit Meliha Merve Kose Rana Sanyal Amitav Sanyal 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3191-3201
Diblock and triblock dendron–polymer conjugates containing biodegradable polyester dendron blocks and polyethylene glycol (PEG) polymer were synthesized using the Diels–Alder “click” cycloaddition reaction. PEG polymers with furan‐protected maleimide functionality were synthesized and reacted with biodegradable polyester dendrons containing an anthracene moiety at their focal point. First through third generations of biodegradable polyester dendrons containing an anthracene unit at their focal point were synthesized using a divergent strategy. Efficient conjugation of the dendrons to polymers was demonstrated using 1HNMR and size exclusion chromatography. This modular approach provides an easy access to the design of multivalent PEG conjugates. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3191–3201 相似文献
160.
Impedance matching in an indigenously developed 2 kW RF-excited fast axial flow (RF-FAF) CO2 laser was seen to be significantly influenced by the capacitance formed between the laser head and the electrodes. We find in the published literature that this capacitance is generally assumed to be negligible while designing the matching network in the RF-FAF CO2 lasers. It is shown that this capacitance could have a significant value and consequently would modify the design of the matching network remarkably for a specific laser design studied in the present case. The widely used discharge load model for capacitively coupled RF (CCRF) discharge excited CO2 laser plasma is extended to include this capacitance. The method of measurement of this capacitance using a bridge and the ANSYS software based simulation of its formation due to the laser head structure are discussed. 相似文献