全文获取类型
收费全文 | 2107篇 |
免费 | 58篇 |
国内免费 | 9篇 |
专业分类
化学 | 1354篇 |
晶体学 | 7篇 |
力学 | 26篇 |
数学 | 315篇 |
物理学 | 472篇 |
出版年
2020年 | 23篇 |
2019年 | 20篇 |
2018年 | 19篇 |
2016年 | 45篇 |
2015年 | 27篇 |
2014年 | 33篇 |
2013年 | 76篇 |
2012年 | 70篇 |
2011年 | 65篇 |
2010年 | 44篇 |
2009年 | 38篇 |
2008年 | 64篇 |
2007年 | 62篇 |
2006年 | 73篇 |
2005年 | 81篇 |
2004年 | 58篇 |
2003年 | 66篇 |
2002年 | 61篇 |
2001年 | 50篇 |
2000年 | 31篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 30篇 |
1996年 | 34篇 |
1995年 | 31篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 30篇 |
1985年 | 38篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 31篇 |
1980年 | 36篇 |
1979年 | 28篇 |
1978年 | 39篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1975年 | 28篇 |
1974年 | 22篇 |
1973年 | 23篇 |
1972年 | 22篇 |
1971年 | 20篇 |
1970年 | 17篇 |
排序方式: 共有2174条查询结果,搜索用时 171 毫秒
991.
This paper discusses the droplet imaging velocimeter and sizer (DIVAS), a two-dimensional technique to measure droplet size
from very small droplets (a few microns) to very large drops (millimeters), as well as droplet velocity and concentration.
DIVAS uses a particle imaging velocimetry (PIV) configuration; that is, pulsed lasers illuminate the droplets in the measurement
plane and CCD cameras collect the off-axis scattered light, thus yielding a small measurement volume and correspondingly a
high number density measurement capability. DIVAS is based on glare point imaging as described by van de Hulst and Wang (Appl
Opt 30(33):4755–4763, 1991). By measuring the separation of cross-polarized glare points, DIVAS is capable of measuring droplet size down to a few microns
with sub-pixel resolution. The measurement of large drops from the separation of glare points is straightforward. However,
the paper discusses that large drops are often non-spherical and more advanced signal processing is required to retrieve their
size. Both analytical studies and experiments are presented to demonstrate the feasibility of the technique. 相似文献
992.
993.
Carla Pinto Moura Luís Miguel Cunha Helena Vilarinho Maria Joo Cunha Diamantino Freitas Miguel Palha Siegfried M. Pueschel M. Pais-Clemente 《Journal of voice》2008,22(1):34-42
Down syndrome (DS) is the most frequent chromosomal disorder. Commonly, individuals with DS have difficulties with speech and show an unusual quality in the voice. Their phenotypic characteristics include general hypotonia and maxillary hypoplasia with relative macroglossia, and these contribute to particular acoustic alterations. Subjective perceptual and acoustic assessments of the voice (Praat-4.1 software) were performed in 66 children with DS, 36 boys and 30 girls, aged 3 to 8 years. These data were compared with those of an age-matched group of children from the general population. Perceptual evaluations showed significant differences in the group of children with DS. The voice of children with DS presented a lower fundamental frequency (F(0)) with elevated dispersion. The conjunction of frequencies for formants (F(1) and F(2)) revealed a decreased distinction between the vowels, reflecting the loss of articulatory processing. The DS vocalic anatomical functional ratio represents the main distinctive parameter between the two groups studied, and it may be useful in conducting assessments. 相似文献
994.
995.
Tetsu Narumi Kenji Yasuoka Makoto Taiji Siegfried Höfinger 《Journal of computational chemistry》2009,30(14):2351-2357
Scientific applications do frequently suffer from limited compute performance. In this article, we investigate the suitability of specialized computer chips to overcome this limitation. An enhanced Poisson Boltzmann program is ported to the graphics processing unit and the application specific integrated circuit MDGRAPE‐3 and resulting execution times are compared to the conventional performance obtained on a modern central processing unit. Speed Up factors are measured and an analysis of numerical accuracy is provided. On both specialized architectures the improvement is increasing with problem size and reaches up to a Speed Up factor of 39 × for the largest problem studied. This type of alternative high performance computing can significantly improve the performance of demanding scientific applications. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
996.
F. Hess 《Fresenius' Journal of Analytical Chemistry》1881,20(1):298
Ohne Zusammenfassung 相似文献
997.
998.
999.
1000.
Ali Alaaeddine Andrew Hess Frédéric Boschet Harry Allcock Bruno Ameduri 《Journal of polymer science. Part A, Polymer chemistry》2013,51(4):977-986
The synthesis and characterization of novel poly(CTFE‐g‐oligoEO) graft copolymers [chlorotrifluoroethylene (CTFE) and ethylene oxide (EO)] are presented. First, vinyl ether monomers bearing oligo(EO) were prepared by transetherification of ω‐hydroxyoligo(EO) with ethyl vinyl ether catalyzed by a palladium complex in 70–84% yields. Two vinyl ethers of different molecular weights (three and 10 EO units) were thus obtained. Then, radical copolymerization of the above vinyl ethers with CTFE led to alternating poly(CTFE‐alt‐VE) copolymers that bore oligo(OE) side chains in satisfactory yields (65%). These original poly(CTFE‐g‐oligoEO) graft copolymers were characterized by 1H, 19F, and 13C NMR spectroscopy. Their molecular weights reached 19,000 g mol?1, and their thermal properties were investigated while their glass transition temperatures ranged between ?42 and ?36 °C. Their thermogravimetric analyses under air showed decomposition temperatures of 270 °C with 10% weight loss (Td,10%). These novel copolymers are of potential interest as polymer electrolytes in lithium ion batteries, showing room temperature conductivities ranging from 4.49 × 10?7 to 1.45 × 10?6 S cm?1 for unplasticized material. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献