全文获取类型
收费全文 | 436篇 |
免费 | 13篇 |
专业分类
化学 | 235篇 |
力学 | 12篇 |
数学 | 93篇 |
物理学 | 109篇 |
出版年
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 17篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 22篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 22篇 |
2012年 | 24篇 |
2011年 | 35篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 24篇 |
2007年 | 22篇 |
2006年 | 18篇 |
2005年 | 28篇 |
2004年 | 16篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有449条查询结果,搜索用时 15 毫秒
61.
Nonexistence results for a class of two‐times differential equations with fractional derivatives of orders between zero and one are presented. Furthermore, the result is extended to a two‐times system of two differential equations with fractional derivatives of orders between zero and one. 相似文献
62.
63.
Dalila Hammiche Amar Boukerrou Bettache Azzeddine Noamen Guermazi Tatiana Budtova 《International Journal of Polymer Analysis and Characterization》2019,24(3):236-244
The growing interest in the preservation of our environment is pushing for solutions to develop less impacting materials. Thus, the development of biocomposites and is recyclable and compostable end-of-life resources seem an interesting alternative. In this study, the characterization of Polylactic acid (PLA) reinforced with treated and untreated Olive husk flour (OHF) were investigated. More then, their biodegradation with a Bacillus sp. has been evaluated. The main results show that the bacteria degraded both the PLA and the composite. This degradation was confirmed by the release of reducing sugars as well as increasing weight loss of PLA matrix and composites. 相似文献
64.
A new aporphine glycoside, (-)-anolobine-9-O-β-D-glucopyranoside was isolated from the twigs of pawpaw (Asimina triloba) along with 7 known alkaloids including five aporphine alkaloids (anolobine, nornuciferine, norushinsunine, liriodenine, and lysicamine), a proaporhine alkaloid (stepharine), and a tetrahydrobenzylisoquinoline alkaloid (coclaurine). Among these compounds, nornuciferine, lysicamine, stepharine, and coclaurine are reported for the first time from this plant. The structure of the new compound was elucidated by spectroscopic methods, including 1?D, 2?D NMR, and HRESI-MS. The absolute configuration of compounds 1, 2, 7 and 8 was determined by CD experiment. 相似文献
65.
C.E. Satheesh Pushpanathan N. Sathish Kumar P. Raghavendra Kumara Ramasamy Karvembu Amar Hosamani M. Nethaji 《应用有机金属化学》2019,33(10)
Two new half‐sandwich Ru (II)(p‐cymene) complexes ( 1 and 2 ) containing dopamine‐based (N, O) Schiff base ligands ( L 1 H and L 2 H ) were synthesized and characterized by FT‐IR, UV–Visible and 1H & 13C NMR spectral techniques, and elemental analyses. The spectroscopic and analytical data revealed monobasic bidentate coordination of the ligands with Ru ion. The molecular structures of L 1 H , L 2 H and 2 were further confirmed by single crystal X‐ray diffraction study. Complexes 1 and 2 have been employed as catalysts in the transfer hydrogenation of ketones using 2‐propanol as a hydrogen source at 85 °C under base‐free condition. Good to the excellent yield of secondary alcohols, gram scale synthesis, and high TON and TOF made this catalytic system interesting. 相似文献
66.
67.
Theoretical study of selenium and tellurium impurities in (ZnO)6 clusters using DFT and TDDFT
下载免费PDF全文
![点击此处可从《International journal of quantum chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nour El Houda Bensiradj Amar Saal Azeddine Dekhira Ourida Ouamerali 《International journal of quantum chemistry》2016,116(24):1862-1871
Zinc oxide (ZnO) nanostructures have attracted much interest due to their potential applications in various fields including optoelectronics, glass industries, and solar cells. These compounds hold the promise of creating new materials that can advance energy technologies. In this work, a series of (ZnO)6 clusters with selenium and tellurium applied as substitutional impurities has been studied. The investigated structures have been produced through the doping of (ZnO)6 clusters by replacing an oxygen atom with a selenium or a tellurium atom at each time. The ground state geometric parameters of (ZnO)6 structures, containing selenium or tellurium atoms as substitutional impurities, were calculated using density functional theory (DFT) with B3LYP and LanL2DZ basis set. Excited state energies and absorption wavelengths were computed using time‐dependent‐DFT (TDDFT). For the calculation of emission wavelengths, Hartree–Fock configuration interaction singles (HF/CIS) has been used in order to perform the excited state geometry optimization. This work led to some important results that can be helpful for developing novel THz sensitive materials and imaging detectors that may be an alternative to x‐rays detectors for radiology as well as for the development of solar cells and electroluminescent diodes. Zinc oxide (ZnO) nanostructures have attracted growing interest due to their potential applications in many technological fields, including optoelectronics, the glass industry, and energy. The presence of impurities, in particular selenium and tellurium, in ZnO‐based clusters can affect their structural and spectroscopic properties. Some of these doped nanostructures have favorable Terahertz emission characteristics that make them good candidates for applications in biology and medicine. 相似文献
68.
Micol Amar Daniele Andreucci Roberto Gianni 《NoDEA : Nonlinear Differential Equations and Applications》2016,23(4):48
We consider a nonlinear model for electrical conduction in biological tissues. The nonlinearity appears in the interface condition prescribed on the cell membrane. The purpose of this paper is proving asymptotic convergence for large times to a periodic solution when time-periodic boundary data are assigned. The novelty here is that we allow the nonlinearity to be noncoercive. We consider both the homogenized and the non-homogenized version of the problem. 相似文献
69.
Si?Amar?DahoumaneEmail author Claude?Yéprémian Chakib?Djédiat Alain?Couté Fernand?Fiévet Thibaud?Coradin Roberta?Brayner 《Journal of nanoparticle research》2016,18(3):79
Recent years have witnessed a boom in the biosynthesis of a large variety of nanomaterials using different biological resources among which algae-based entities have been gaining much more attention within the community of material scientists worldwide. In our previously published findings, we explored some factors that governed the biofabrication of gold nanoparticles using living cultures of microalgae, such as the utilized microalgal genera, the phylum they belong to, and the impact of tetrachloroauric acid concentrations on the ability of these strains to perform the biosynthesis of gold nanoparticles once in contact with these cations. As a follow-up, we present in this paper an improvement of the features of bioproduced gold colloids using living cells of Euglena gracilis microalga when this species is grown under either mixotrophic or autotrophic conditions, i.e., exposed to light and grown in an organic carbon-enriched culture medium versus under autotrophic conditions. As an outcome to this alteration, the growth rate of this photosynthetic microorganism is multiplied 7–8 times when grown under mixotrophic conditions compared to autotrophic ones. Therefore, the yield, the kinetics, and the colloidal stability of the biosynthesized gold nanoparticles are dramatically enhanced. Moreover, the shape and the size of the as-produced nano-objects via this biological method are affected. In addition to round-shaped gold nanoparticles, particular shapes, such as triangles and hexagons, appear. These findings add up to the amassed knowledge toward the design of photobioreactors for the scalable and sustainable production of interesting nanomaterials. 相似文献
70.