全文获取类型
收费全文 | 2358篇 |
免费 | 81篇 |
国内免费 | 9篇 |
专业分类
化学 | 1963篇 |
晶体学 | 12篇 |
力学 | 25篇 |
数学 | 221篇 |
物理学 | 227篇 |
出版年
2023年 | 24篇 |
2022年 | 45篇 |
2021年 | 68篇 |
2020年 | 48篇 |
2019年 | 59篇 |
2018年 | 40篇 |
2017年 | 37篇 |
2016年 | 81篇 |
2015年 | 85篇 |
2014年 | 82篇 |
2013年 | 116篇 |
2012年 | 150篇 |
2011年 | 201篇 |
2010年 | 119篇 |
2009年 | 109篇 |
2008年 | 152篇 |
2007年 | 153篇 |
2006年 | 115篇 |
2005年 | 121篇 |
2004年 | 101篇 |
2003年 | 93篇 |
2002年 | 74篇 |
2001年 | 37篇 |
2000年 | 20篇 |
1999年 | 34篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1970年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有2448条查询结果,搜索用时 15 毫秒
991.
Alain Guinault Cyrille Sollogoub Violette Ducruet Sandra Domenek 《European Polymer Journal》2012,48(4):779-788
The helium and oxygen gas barrier properties of poly(lactide) were investigated as a function of stereochemistry and crystallinity degree. Poly(l-lactide) and poly(d,l-lactide) films were obtained by extrusion and thermally cold crystallized in either α′- or α-crystalline form with increasing crystallinity degree. Annealing of the films at low temperatures yielded to α′-crystals as well as the creation of a rigid amorphous fraction in the amorphous phase. Unexpectedly, the quantity of the rigid amorphous fraction was highest in poly(l-lactide) crystallized under α′-form. Unexpectedly, the gas permeability increased with increasing quantity of α′-crystals in poly(l-lactide) and remained constant with increasing quantity of α′-crystals in poly(d,l-lactide). A gain in gas barrier properties was obtained upon crystallization at higher temperatures yielding α-crystals. The analysis of the oxygen transport parameters, in particular the diffusion and the solubility coefficient showed that the diffusion was accelerated upon crystallization, while the solubility coefficient decreased in an expected manner which led to conclude that it remained constant in the amorphous phase. The acceleration of the diffusion seems to be correlated to the occurrence of the rigid amorphous fraction, which holds larger free volume. To conclude, for optimization of poly(lactide) gas barrier properties by focussing on the decrease of the diffusion coefficient it can be suggested to work with poly(d,l-lactide) and to aim a crystallization in α-form avoiding the formation of a rigid amorphous fraction. 相似文献
992.
Nelson Libardi Junior Regina Maria Miranda Gern Sandra Aparecida Furlan Dietmar Schlosser 《Applied biochemistry and biotechnology》2012,167(5):1144-1156
This work aimed to study the production of laccase from Pleurotus ostreatus DSM 1833 and Phoma sp. UHH 5-1-03 using banana peels as alternative carbon source, the subsequent partial purification and characterization of the enzyme, as well the applicability to degrade endocrine disruptors. The laccase stability with pH and temperature, the optimum pH, the K m and V max parameters, and the molar mass were determined. Tests were conducted for assessing the ability of degradation of the endocrine disruptors t-nonylphenol, bisphenol A, and 17??-ethinylestradiol. Laccase production of 752 and 1,117?U?L?1 was obtained for Phoma sp. and P. ostreatus, respectively. Phoma sp. laccase showed higher stability with temperature and pH. The laccase from both species showed higher affinity by syringaldazine. The culture broth with banana peels induced the production of two isoforms of P. ostreatus (58.7 and 21?kDa) and one of Phoma sp. laccase (72?kDa). In the first day of incubation, the concentrations of bisphenol A and 17??-ethinylestradiol were reduced to values close to zero and after 3?days the concentration of t-nonylphenol was reduced in 90% by the P. ostreatus laccase, but there was no reduction in its concentration by the Phoma sp. laccase. 相似文献
993.
994.
Selective removal of nitrate by using a novel macroporous acrylic anion exchange resin 总被引:1,自引:0,他引:1
Sandra Mueller 《中国化学快报》2012,23(5):603-606
An anion exchange resin NDP-5 has been prepared successfully and applied on the selective removal of nitrate from SO42-/ NO3- binary co-existence system.The composition and morphology of NDP-5 were confirmed by FT-IR and SEM.The NDP-5 resin exhibits the completely different behavior on the adsorption capacity,adsorption kinetic and the effect of the completing anion in the absence or presence of sulfate,compared to D213.And,the resultants of kinetic are well fitted by the pseudo-first-order and pseudo-second-order models.These results are very important to develop novel resins with great features. 相似文献
995.
Ivone Peres Sandra Rocha Joana A. Loureiro Maria do Carmo Pereira Galya Ivanova Manuel Coelho 《Journal of nanoparticle research》2012,14(9):1-11
We report a simple and effective supercritical fluid route to uniformly load ultrafine metal nanoparticles on the hydrophobic surfaces of graphene sheets. In the presence of supercritical carbon dioxide, PtRu alloy nanoparticles are decorated evenly on functionalized graphene sheets (FGSs) upon the reduction of organic platinum (II) and ruthenium (III) precursors, and its application as an electrocatalyst for methanol oxidation is studied. Transmission electron microscopy observation shows that highly dispersed PtRu metallic nanoparticles with an average size of about 3.11?nm are uniformly and densely distributed on the hydrophobic surface of FGSs. X-ray diffraction patterns demonstrate that the particles had a face-centered cubic crystal structure, and X-ray photoelectron spectroscopy analysis indicates the existence of zero-valence metals. Compared with the widely used Vulcan XC-72 carbon black, the PtRu/FGS composites exhibit superior catalytic activity and stability for methanol oxidation. The huge surface area of graphene and uniform distribution of nanosized metal particles are two critical factors for the significantly enhanced electrocatalytic efficiency. The findings suggest that the supercritical fluid method is highly efficient in preparing graphene-supported metallic catalysts, and FGSs serve as a favorable electrocatalytic carrier for direct methanol fuel cells. 相似文献
996.
We present a dynamic approach for measuring the interstitial iron concentration in boron‐doped crystalline silicon using photoluminescence (PL) imaging. This camera‐based technique utilizes the characteristic dependence of the dissociation rate of iron–boron pairs on the interstitial iron concentration. We determine the dissociation rate by measuring the time‐dependent PL signal after complete association of iron–boron pairs in the sample. Since we are only interested in the time dependence of the PL signal, we are able to generate images of the interstitial iron concentration in absolute units without any calibration and without knowing the recombination properties of the interstitial iron or iron–boron pairs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
997.
998.
999.
1000.
A simple, rapid, reproducible and effective one-step procedure for biosensor construction, based on casting mixed poly(ester-sulfonic acid)-glucose oxidase solutions onto solid electrodes is described. The cation exchanger simultaneously performs the entrapment, charge permselectivity and antifouling functions. The discrimination against potential interferences is accompanied with a fast and sensitive response to glucose. With flow injection operation, 180 samples can be processed per hour, with a detection limit of 3 × 10?6 M. The effects of numerous experimental variables are explored. These properties of poly(ester-sulfonic acid) ionomers, coupled with their availability as aqueous dispersions, make them attractive and versatile for biosensor work. 相似文献