全文获取类型
收费全文 | 1311篇 |
免费 | 22篇 |
国内免费 | 7篇 |
专业分类
化学 | 1039篇 |
晶体学 | 23篇 |
力学 | 8篇 |
数学 | 142篇 |
物理学 | 128篇 |
出版年
2023年 | 17篇 |
2022年 | 32篇 |
2021年 | 57篇 |
2020年 | 33篇 |
2019年 | 23篇 |
2018年 | 26篇 |
2017年 | 20篇 |
2016年 | 23篇 |
2015年 | 35篇 |
2014年 | 30篇 |
2013年 | 72篇 |
2012年 | 64篇 |
2011年 | 83篇 |
2010年 | 58篇 |
2009年 | 48篇 |
2008年 | 81篇 |
2007年 | 76篇 |
2006年 | 84篇 |
2005年 | 65篇 |
2004年 | 58篇 |
2003年 | 61篇 |
2002年 | 49篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1959年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有1340条查询结果,搜索用时 234 毫秒
91.
Valentina Laghezza Masci Anna‐Rita Taddei Thomas Courant Ozgül Tezgel Fabrice Navarro Franco Giorgi Denis Mariolle Anna‐Maria Fausto Isabelle Texier 《Macromolecular bioscience》2019,19(5)
Curcumin‐loaded collagen cryostructurates have been devised for wound healing applications. Curcumin displays strong antioxidant, antiseptic, and anti‐inflammatory properties, while collagen is acknowledged for promoting cell adhesion, migration and differentiation. However, when curcumin is loaded directly into collagen hydrogels, it forms large molecular aggregates and clogs the matrix pores. A double‐encapsulation strategy is therefore developed by loading curcumin into lipid nanoparticles (LNP), and embedding these particles inside collagen scaffolds. The resulting collagen/LNP cryostructurates have an optimal fibrous structure with ≈100 µm average pore size for sustaining cell migration. Results show that collagen is structurally unaltered and that nanoparticles are homogeneously distributed amidst collagen fibers. Hydrogels soaked in saline buffer release about 20 to 30% of their nanoparticles content within 24 h, while achieved 100% release after 25 days. When exposed to NIH 3T3 fibroblasts, these hydrogels provide a satisfactory scaffold for cell interaction as early as 4 h after seeding, with no cytotoxic counter effect. These positive features make the collagen/lipid cryostructurates a promising material for further use in wound healing. 相似文献
92.
A variety of arylhydrazonopyridinones were prepared via heating cyanoacetamides with ethyl acetoacetate in absence of solvent under reflux conventionally or ultrasound irradiation or in a microwave oven. The formed products 5 and 6 could be readily converted to thienopyridones. Attempted addition of the latter to electron poor olefins afforded only arylhydrazonopyridinones. 相似文献
93.
94.
Alejandro M. Fracaroli O. Fernando Silva Alejandro M. Granados Rita H. de Rossi 《Journal of Physical Organic Chemistry》2008,21(11):1007-1013
The UV–Vis spectrum of 5‐(1‐butylthio)‐3H‐1,2‐dithiole‐3‐thione (1a) and that of the chromium pentacarbonyl complex of 5‐methyl‐3H‐1,2‐dithiole‐3‐thione (3) present significant changes with the solvent polarity. The two absorption bands shown by the compounds in the region above 300 nm were identified by theoretical calculations. For Compound 1a these are n→π* and →π* transitions and for Compound 3 the longest wavelength absorption corresponds to a charge transfer band and shows a remarkably negative solvatochromism. Not only has the wavelength of maximum absorption changed with the solvent but also the ratio of the absorbances at the two wavelengths. The effect of solvents was correlated with solvatochromic parameters such as π* and α. The spectrum of 5‐(1‐butylthio)‐3H‐1,2‐dithiole‐3‐one ( 2 ) was also measured in different solvents but in this case the changes observed are less significant than for the other two compounds. The spectra of 1a and 3 were also determined in the presence of anionic (SDS), cationic (CTAB), and neutral surfactants (Brig‐35) and it is shown that these compounds can be used as probes for the polarity of the binding sites of organized assemblies. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
95.
We report the results of Monte Carlo simulation of the phase diagram and oxygen ordering in YBa2Cu3O6+x
for low intra-sublattice repulsion. At low temperatures, apart from tetragonal (T), orthorhombic (OI) and ‘double cell’ ortho II phases, there is evidence for two additional orthorhombic phases labelled here asOI andOIII. At high temperatures, there was no evidence for the decomposition of theOI phase into theT andOI phases. We find qualitative agreement with experimental observations and cluster-variation method results. 相似文献
96.
97.
Rita Menicagli Corrado Malanga Luciano Lardicci Laura Tinucci 《Tetrahedron letters》1980,21(47):4525-4528
2-Ethoxy-5-alkyl-3,4-dihydro-2H-pyrans react with Albui3 and through a regioselective hydride addition provide substituted cyclobutylmethanols in very good yields. 相似文献
98.
Experimentally observed phonon softening of the 520 cm-1 Raman line in ultra-heavily doped n-Si is attributed to the electron-phonon self-energy effects as well as change in lattice force constants of the alloy system. 相似文献
99.
100.
Wahl U Rita E Correia JG Marques AC Alves E Soares JC;ISOLIDE Collaboration 《Physical review letters》2005,95(21):215503
Arsenic has been reported in the literature as one of the few p-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the p-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined the lattice location of implanted As in ZnO by means of conversion-electron emission channeling from radioactive (73)As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites but in its large majority substitutional Zn sites. Arsenic in ZnO (and probably also in GaN) is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. 相似文献