全文获取类型
收费全文 | 393篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 332篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 42篇 |
物理学 | 21篇 |
出版年
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 11篇 |
2013年 | 19篇 |
2012年 | 27篇 |
2011年 | 30篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 32篇 |
2007年 | 36篇 |
2006年 | 28篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有407条查询结果,搜索用时 15 毫秒
191.
We present here a new model for the imidazolium-based ionic liquids (ILs) with the bis(trifluoromethylsulfonyl)imide anion [Tf(2)N](-) in the context of the soft-SAFT EoS. The model is used to predict the solubility of several compounds in these ILs, and results are compared to available experimental data. Since in the soft-SAFT EoS an associating site is used to represent a short-range and highly directional attractive force among molecules, we have used this feature to mimic the main interactions between the anion and the cation for the alkylimidazolium-[Tf(2)N] ILs. The members of the alkylimidazolium-[Tf(2)N] family are modeled as Lennard-Jones chains with three associating sites in each molecule (one "A" site and two "B" sites). An "A" site represents the nitrogen atom interactions with the cation, and a "B" site represents the delocalized charge due the oxygen molecules on the anion. Each type of associating site is identically defined, but only AB interactions between different IL molecules are allowed. Model parameters for the ionic liquids were estimated with experimental density data from different authors, following a similar approach taken in our previous work [Andreu and Vega, J. Phys. Chem. C 2007, 111, 16028]. The new set of parameters was used to study the solubility behavior of hydrogen, carbon dioxide, and xenon in these ILs over a wide range of temperature and pressure. It has been observed that no binary parameters are needed to correlate the solubility of hydrogen in [C(6)-mim][Tf(2)N] at different temperatures, and predictions up to 100 MPa are presented here. The model is able to correlate with very good agreement the experimental data for the systems [C(n)-mim][Tf(2)N] + CO(2) with only one temperature-independent mixture parameter, while two temperature-independent mixture parameters are needed to correlate the experimental solubility data for the systems IL + Xe, attaining an excellent agreement in a wide range of temperatures. The work presented here reinforces previous results, proving that a reasonable simple model for the IL within the framework of soft-SAFT is able to describe the physical absorption of different gases in ILs with good accuracy, in spite of the most complex nature of the anion, without the need of further parameters or terms. In addition, since these parameters do not depend on the particular conditions at which they were fitted, soft-SAFT is used then to analyze the solubility dependence of these gases in ILs, according to the anion nature and the alkyl chain length of the imidazolium cation by the use of the models developed within this approach. 相似文献
192.
Jorge J. Betancor Juan C. Fariña Teresa Martinez Lourdes Rodríguez-Mesa 《Arkiv f?r Matematik》2008,46(2):219-250
In this paper we investigate Riesz transforms R
μ
(k) of order k≥1 related to the Bessel operator Δμ
f(x)=-f”(x)-((2μ+1)/x)f’(x) and extend the results of Muckenhoupt and Stein for the conjugate Hankel transform (a Riesz transform of order one). We
obtain that for every k≥1, R
μ
(k) is a principal value operator of strong type (p,p), p∈(1,∞), and weak type (1,1) with respect to the measure dλ(x)=x
2μ+1
dx in (0,∞). We also characterize the class of weights ω on (0,∞) for which R
μ
(k) maps L
p
(ω) into itself and L
1(ω) into L
1,∞(ω) boundedly. This class of weights is wider than the Muckenhoupt class of weights for the doubling measure dλ. These weighted results extend the ones obtained by Andersen and Kerman. 相似文献
193.
Water oligomers in crystal hydrates--what's news and what isn't? 总被引:1,自引:0,他引:1
194.
Lourdes Urpí Alfonso Rodríguez-Galán Jordi Puiggalí 《Journal of chemical crystallography》1998,28(8):605-610
The conformation of 1,6-bis-O-(N-propionyl-L-alanyl)-1,6-hexanediol (PrAHAPr) has been investigated in the crystalline state by X-ray analysis. PrAHAPr crystallizes in the monoclinic system, space group P21 with a = 4.861(4), b = 26.24 (1), c = 8.716 (3) Å and = 105.25 (1)°. In the crystal, the molecules are hydrogen bonded in a single direction that runs parallel to the a crystallographic axis. In spite of its chemical symmetry the molecule adopts an asymmetric conformation, where one of the alanine residues takes a folded conformation. PrAHAPr belongs to a series of model compounds for poly(ester amide)s derived from amino acids that we are presently investigating. 相似文献
195.
Lourdes Urpí Meritxell Martínez‐Palau Merc Font‐Bardia Jordi Puiggalí 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(12):o847-o849
The title compound, C8H12Cl2O4, lies about an inversion centre. The molecular conformation is characterized by a conformation for the butanedioxy moiety and a trans conformation for the ClCH2—C(=O)O bond. The molecular packing is stabilized by a network of weak CH2⋯O=C intermolecular hydrogen bonds, where each molecule interacts with its four closest neighbours. 相似文献
196.
Jorge J. Betancor Sandra M. Molina Lourdes Rodríguez–Mesa 《Mathematische Nachrichten》2009,282(6):800-819
In this paper we investigate Dunkl transforms and Dunkl convolutions on R in some spaces of functions and distributions with exponential growth introduced by Hasumi [12] (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
197.
Iaralice Medeiros de Souza Milton Neto da Silva Elza Scott Figueira Maria de Lourdes Leal Ellen Jessouroun Shirley de Mello Pereira Abrantes Ivna Alana Freitas Brasileiro da Silveira 《Electrophoresis》2013,34(22-23):3221-3226
Neisseria meningitidis group C is an encapsulated bacterium that causes several diseases and is associated with high mortality rates, thereby constituting a serious public health problem. Bio‐Manguinhos/Fiocruz is developing a conjugate vaccine by covalent attachment of capsular polysaccharide to hydrazide‐activated tetanus toxoid through reductive amination. It is necessary to quantify free components as a quality control process to prevent exacerbated adverse reactions and/or attenuation of vaccine immunogenicity. Thus, this study aimed to develop and validate a quality control method appropriate for the separation and quantification of free polysaccharide present in this conjugate N. meningitidis group C vaccine using CE. CZE was used to remove unbound polysaccharide, and the electrophoretic conditions were varied to optimize resolution. We were able to develop and validate the proposed method, which was linear and showed a matrix effect. Repeatability and partial reproducibility of the method were also evaluated. The robustness results showed that control of temperature is required for reliable results. The validated method will be used to evaluate the conjugate batches submitted for Phase III clinical studies and for routine quality control of the conjugate vaccine. 相似文献
198.
Elaine Armelin Lourdes Urpí Xavier Solans Jordi Puiggalí 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):932-933
The title compound, dimethyl 2,2′‐(oxalyldiimino)diethanoate, C8H12N2O6, exhibits a network of hydrogen bonds between amide and ester groups. Molecules lie on inversion centres and show a planar conformation for both the oxalamide and ester groups. The glycine residues adopt a conformation close to the polyglycine II structure. 相似文献
199.
Abstract Based on a previous model describing the behavior of a holocoupler/fiber optic device, we develop a new model for a holocoupler/GRIN lens system and analyze the conditions for the coupling to hold and the requirements of the coupled signal. 相似文献
200.
Lourdes Mendoza Willy Verstraete Marta Carballa 《Applied biochemistry and biotechnology》2010,160(6):1822-1832
Sanitary landfill leachates are a major environmental problem in South American countries where sanitary landfills are still
constructed and appropriate designs for the treatment of these leachates remain problematic. The performance of a lab-scale
Gradual Concentric Chamber (GCC) reactor for leachates treatment is presented in this study. Two types of sanitary landfill
residuals were evaluated, one directly collected from the garbage trucks (JGL), with high organic strength (84 g COD/l) and
the second one, a 6-month-generated leachate (YL) collected from the lagoon of the sanitary landfill in Quito, Ecuador, with
an organic strength of 66 g COD/l. Different operational parameters, such as organic loading rate (OLR), temperature, recycling
and aeration, were tested. The GCC reactor was found to be a robust technology to treat these high-strength streams with organic
matter removal efficiencies higher than 65%. The best performance of the reactors (COD removal efficiencies of 75–80%) was
obtained at a Hydraulic Retention Time (HRT) of around 20 h and at 35 °C, with an applied OLR up to 70 and 100 g COD/l per
day. Overall, the GCC reactor concept appears worth to be further developed for the treatment of leachates in low-income countries. 相似文献