全文获取类型
收费全文 | 1503篇 |
免费 | 85篇 |
国内免费 | 31篇 |
专业分类
化学 | 1055篇 |
晶体学 | 14篇 |
力学 | 65篇 |
综合类 | 1篇 |
数学 | 100篇 |
物理学 | 384篇 |
出版年
2023年 | 11篇 |
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 46篇 |
2013年 | 61篇 |
2012年 | 111篇 |
2011年 | 138篇 |
2010年 | 70篇 |
2009年 | 67篇 |
2008年 | 108篇 |
2007年 | 76篇 |
2006年 | 68篇 |
2005年 | 91篇 |
2004年 | 64篇 |
2003年 | 50篇 |
2002年 | 42篇 |
2001年 | 42篇 |
2000年 | 29篇 |
1999年 | 18篇 |
1998年 | 10篇 |
1997年 | 19篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 24篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 3篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1965年 | 2篇 |
1939年 | 2篇 |
排序方式: 共有1619条查询结果,搜索用时 31 毫秒
991.
Solid oxide fuel cell (SOFC) unit was constructed with Ni–GDC (gadolinia-doped ceria) as the anode, YSZ as the electrolyte, and Cu-added La0.58Sr0.4Co0.2Fe0.8O3–δ–GDC as the cathode. Electrochemical CO2 reduction occurs. The CO formation rate, the CO2 conversion and the generated current density increase with increasing CO2 concentration and temperature. The CO2 conversion rate equals exactly the CO formation rate. No carbon deposition occurs. The activation energy is 2.72 kcal mol?1. The electrochemical CO2 reduction (dissociation) can have much lower activation barrier than the catalytic one. Simultaneous CO2 reduction with power generation in SOFCs can be feasible. 相似文献
992.
Experimental studies on drag reduction and rheology of mixed cationic surfactants with different alkyl chain lengths 总被引:2,自引:0,他引:2
Zhiging Lin Lu Chou Bin Lu Yi Zheng H. Ted Davis L. E. Scriven Y. Talmon Jacques L. Zakin 《Rheologica Acta》2000,39(4):354-359
Experimental studies of the effects of mixtures of cationic surfactants on their drag reduction and rheological behaviors
are reported. Cationic alkyl trimethyl quaternary ammonium surfactants with alkyl chain lengths of C12 and C22 were mixed at different molar ratios (total surfactant concentrations were kept at 5 mM with 12.5 mM sodium salicylate (NaSal)
as counterion). Drag reduction tests showed that by adding 10% (mol) of C12, the effective drag reduction range expanded to 4–120 °C, compared with 80–130 °C with only the C22 surfactant. Thus mixing cationic surfactants with different alkyl chain lengths is an effective way of tuning the drag reduction
temperature range. Cryo-TEM micrographs revealed thread-like micellar networks for surfactant solutions in the drag reducing
temperature range, while vesicles were the dominant microstructures at non-drag reducing temperatures. High extensional viscosity
was the main rheological feature for all solutions except 50% C12 (mol) solution, which also does not show strong viscoelasticity. It is not clear why this low extensional viscosity solution
with relatively weak viscoelasticity is a good drag reducer.
Received: 3 November 1999/Accepted: 5 January 2000 相似文献
993.
Linbo Shang I‐Ming Chou R. C. Burruss Ruizhong Hu Xianwu Bi 《Journal of Raman spectroscopy : JRS》2014,45(8):696-702
The positions of the CH4 Raman ν1 symmetric stretching bands were measured in a wide range of temperature (from −180 °C to 350 °C) and density (up to 0.45 g/cm3) using high‐pressure optical cell and fused silica capillary capsule. The results show that the Raman band shift is a function of both methane density and temperature; the band shifts to lower wavenumbers as the density increases and the temperature decreases. An equation representing the observed relationship among the CH4 ν1 band position, temperature, and density can be used to calculate the density in natural or synthetic CH4‐bearing inclusions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
994.
995.
Growth processes and interface fluctuations can be studied through the properties of global quantities. We here discuss a global quantity that not only captures better the roughness of an interface than the widely studied surface width, but that is also directly conjugate to an experimentally accessible parameter, thereby allowing us to study in a consistent way the global response of the system to a global change of external conditions. Exploiting the full analyticity of the linear Edwards–Wilkinson and Mullins–Herring equations, we study in detail various two-time functions related to that quantity. This quantity fulfills the fluctuation–dissipation theorem when considering steady-state equilibrium fluctuations. 相似文献
996.
997.
998.
999.
During the course of investigating the anticancer activities of new compounds, we have synthesized a series of novel cyclic N-hydroxyurea derivatives and several carbamate intermediates1–3. Infrared absorption, nuclear magnetic resonance, and electronic absorption spectra were examined in order to confirm the identities and to study the molecular structure of these compounds. 相似文献
1000.
Hole‐buffer polymer composed of alternating p‐terphenyl and tetraethylene glycol ether moieties: Synthesis and application in polymer light‐emitting diodes 下载免费PDF全文
Carrier balance is essential to obtain efficient emission in polymer light‐emitting diodes (PLEDs). A new polymer 3P5O composed of alternating p‐terphenyl and tetraethylene glycol ether segments is designed and synthesized by the Suzuki coupling reaction and successfully employed as hole‐buffer layer to improve carrier balance. Multilayer PLEDs [ITO/PEDOT:PSS/ 3P5O /SY/LiF/Al], with Super Yellow (SY) as the emitting layer and 3P5O as the hole‐buffer layer, reveal maximum luminance (17,050 cd/m2) and maximum current efficiency (6.6 cd/A) superior to that without the hole‐buffer layer (10,017 cd/m2, 3.0 cd/A). Moreover, it also shows better performance than that using conventional BCP as hole‐blocking layer [ITO/PEDOT:PSS/SY/BCP/LiF/Al (80 nm): 13,639 cd/m2, 4.1 cd/A]. The performance enhancement has been attributed to hole‐buffering characteristics of 3P5O that results in improved carrier recombination ratio and wider carrier recombination region. Current results indicate that the 3P5O is a promising hole‐buffer polymer to enhance the performance of optoelectronic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 785–794 相似文献