全文获取类型
收费全文 | 876篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
化学 | 671篇 |
晶体学 | 4篇 |
力学 | 21篇 |
数学 | 104篇 |
物理学 | 112篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 39篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 33篇 |
2012年 | 63篇 |
2011年 | 78篇 |
2010年 | 42篇 |
2009年 | 41篇 |
2008年 | 57篇 |
2007年 | 55篇 |
2006年 | 60篇 |
2005年 | 56篇 |
2004年 | 52篇 |
2003年 | 35篇 |
2002年 | 29篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有912条查询结果,搜索用时 156 毫秒
71.
72.
73.
Jamila Ghamri Herv Baussart Michel le Bras Jean-Marie Leroy 《Journal of Physics and Chemistry of Solids》1989,50(12):1237-1244
The mixed oxides BixEu1−xVO4 and BiyGd1−yVO4 crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s2 of Bi3+ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the BixEu1−xVO4 spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu3+ ion. The broad absorption shift in BiLnVO4 (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO4 lattice, is ascribed to charge transfer processes in a Bi-VO4 center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi3+. The concept of an internal pressure of Bi3+ ions is also used to explain the broad A-band shifts. 相似文献
74.
75.
Wim Couwenberg Gert Heckman Eduard Looijenga 《Publications Mathématiques de L'IHéS》2005,101(1):69-161
Consider a complex projective space with its Fubini-Study metric. We study certain one parameter deformations of this metric on the complement of an arrangement (= finite union of hyperplanes) whose Levi-Civita connection is of Dunkl type. Interesting examples are obtained from the arrangements defined by finite complex reflection groups. We determine a parameter interval for which the metric is locally of Fubini-Study type, flat, or complex-hyperbolic. We find a finite subset of this interval for which we get a complete orbifold or at least a Zariski open subset thereof, and we analyze these cases in some detail (e.g., we determine their orbifold fundamental group).In this set-up, the principal results of Deligne-Mostow on the Lauricella hypergeometric differential equation and work of Barthel-Hirzebruch-Höfer on arrangements in a projective plane appear as special cases. Along the way we produce in a geometric manner all the pairs of complex reflection groups with isomorphic discriminants, thus providing a uniform approach to work of Orlik-Solomon. 相似文献
76.
Frederik Detobel Veronika Fekete Wim De Malsche Selm De Bruyne Han Gardeniers Gert Desmet 《Analytical and bioanalytical chemistry》2009,394(2):399-411
The present paper provides a detailed analysis of the analyte-wall adsorption effects in nanochannels, including a random
walk study of the analyte-wall collision frequency, and uses these insights to estimate wall desorption times from chromatographic
experiments in nanochannels. Using coumarin dye analytes and using a methanol/water mixture buffered at pH 3 in 120-nm deep
channels, the surface desorption times on naked fused-silica glass were found to be maximally of the order of 60 to 150 μs,
while they were found to be on the order of 100 to 500 μs on a hydrophobically coated wall. These nonzero adsorption and desorption
times lead to an additional band broadening when conducting chromatographic separations. Shear-driven flows, requiring a noncoated
moving wall and a stationary coated wall, intrinsically turn out to be more prone to this effect than pressure-driven or electro-driven
flows for example. The present study also shows that, interestingly, the number of analyte-wall collisions increases with
the inverse of the channel depth and not with its second power, as would be expected from the Einstein–Smoluchowski relationship
for molecular diffusion. 相似文献
77.
78.
Anne Vuorema Mika Sillanpää Liza Rassaei Matthew J. Wasbrough Karen J. Edler Wim Thielemans Sara E. C. Dale Simon Bending Daniel Wolverson Frank Marken 《Electroanalysis》2010,22(6):619-624
A novel way to produce ultrathin transparent carbon layers on tin‐doped indium oxide (ITO) substrates is developed. The ITO surface is coated with cellulose nanofibrils (from sisal) via layer‐by‐layer electrostatic binding with poly(diallyldimethylammonium chloride) or PDDAC acting as the binder. The cellulose nanofibril‐PDDAC composite film is then vacuum‐carbonised at 500 °C. The resulting carbon films are characterised by atomic force microscopy (AFM), small angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS), and Raman methods. Smooth carbon films with good adhesion to the ITO substrate are formed. The electrochemical characterisation of the carbon films is based on the oxidation of hydroquinone and the reduction of benzoquinone in aqueous phosphate buffer media. A modest effect of the cellulose nanofibril‐PDDAC film on the rate of electron transfer is observed. The effect of the film on the rate of electron transfer after carbonisation is more dramatic. For a 40‐layer cellulose nanofibril‐PDDAC film after carbonisation a two‐order of magnitude change in the rate of electron transfer occurs presumably due to a better interaction of the hydroquinone/benzoquinone system with the electrode surface. 相似文献
79.
An oxacalix[2]arene[2]pyrimidine-bis(ZnII-porphyrin) conjugate was readily prepared via nucleophilic aromatic substitution of a phenolic AB3-Zn-porphyrin on the upper rim of a (1,3-alternate) 5,17-bis(methylsulfonyl)oxacalix[4]arene precursor. Efficient 1:1 complex formation between the ‘jaws’ bisporphyrin tweezer and fullerene C70 was evidenced by 1H NMR titrations (K = 3.0 × 104 M−1), while no detectable complexation could be observed with C60. On the other hand, an analogous oxacalix[4]arene-bis(Cu-corrole) conjugate did not show any measurable (C60 or C70) fullerene binding. 相似文献
80.
Vermonden T Jena SS Barriet D Censi R van der Gucht J Hennink WE Siegel RA 《Macromolecules》2010,43(2):782-789
Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A blocks (~22 kDA) but differing PEG-midblock lengths (2, 4 and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDA). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery. 相似文献