全文获取类型
收费全文 | 444159篇 |
免费 | 6958篇 |
国内免费 | 2325篇 |
专业分类
化学 | 240120篇 |
晶体学 | 6571篇 |
力学 | 19171篇 |
综合类 | 115篇 |
数学 | 50943篇 |
物理学 | 136522篇 |
出版年
2021年 | 4080篇 |
2020年 | 4565篇 |
2019年 | 4891篇 |
2018年 | 6163篇 |
2017年 | 6047篇 |
2016年 | 9262篇 |
2015年 | 5985篇 |
2014年 | 9076篇 |
2013年 | 20822篇 |
2012年 | 16459篇 |
2011年 | 20025篇 |
2010年 | 14007篇 |
2009年 | 13817篇 |
2008年 | 18219篇 |
2007年 | 18097篇 |
2006年 | 16700篇 |
2005年 | 14951篇 |
2004年 | 13795篇 |
2003年 | 12122篇 |
2002年 | 11945篇 |
2001年 | 13622篇 |
2000年 | 10286篇 |
1999年 | 8089篇 |
1998年 | 6736篇 |
1997年 | 6457篇 |
1996年 | 6235篇 |
1995年 | 5613篇 |
1994年 | 5497篇 |
1993年 | 5293篇 |
1992年 | 5902篇 |
1991年 | 5984篇 |
1990年 | 5726篇 |
1989年 | 5511篇 |
1988年 | 5530篇 |
1987年 | 5405篇 |
1986年 | 5116篇 |
1985年 | 6595篇 |
1984年 | 6708篇 |
1983年 | 5315篇 |
1982年 | 5402篇 |
1981年 | 5371篇 |
1980年 | 4959篇 |
1979年 | 5358篇 |
1978年 | 5493篇 |
1977年 | 5387篇 |
1976年 | 5332篇 |
1975年 | 4914篇 |
1974年 | 4885篇 |
1973年 | 4880篇 |
1972年 | 3455篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
153.
154.
ABSTRACT A new density functional for the study of associating inhomogeneous fluids based on Wertheim's first-order thermodynamic perturbation theory is presented and compared to the most currently used associating density functionals. This functional is developed using the weighted density approximation in the range of association of hard spheres. We implement this functional within the framework of classical density functional theory together with modified fundamental measure theory to account for volume exclusion of hard spheres. This approach is tested against molecular simulations from literature of pure associating hard spheres and mixtures of non-associationg and associating hard spheres with different number of bonding sites close to a hard uniform wall. Furthermore, we compare and review our results with the performance of associating functionals from literature, one based on fundamental measure theory and the inhomogeneous version of Wertheim's perturbation theory. Results obtained with classical DFT and the three functionals show excellent agreement with molecular simulations in systems with one hard wall. For the cases of small pores where only one or two layers of fluid are allowed discrepancies between results with classical DFT and molecular simulations were found. 相似文献
155.
156.
Journal of Structural Chemistry - Thermodynamic characteristics are calculated for aqueous alkanolamine solutions that are obtained by substituting alkyl radicals for the protons in the amino group... 相似文献
157.
158.
Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery,density, and oxygen transport considerations
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Steven K. Burgess Christopher R. Mubarak Robert M. Kriegel William J. Koros 《Journal of Polymer Science.Polymer Physics》2015,53(6):389-399
The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399 相似文献
159.
Gelikonov G. V. Ksenofontov S. Yu. Shilyagin P. A. Gelikonov V. M. 《Radiophysics and Quantum Electronics》2019,62(3):228-236
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in... 相似文献
160.
Yamshchikov V. M. Rogachev V. G. Kudryashov E. A. Kachalin G. N. 《Optics and Spectroscopy》2020,128(8):1182-1186
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical... 相似文献