全文获取类型
收费全文 | 175篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
化学 | 133篇 |
力学 | 2篇 |
数学 | 35篇 |
物理学 | 9篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 19篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有179条查询结果,搜索用时 0 毫秒
1.
Virve A. Karttunen Mikko Linnolahti Tapani A. Pakkanen Janne Maaranen Päivi Pitkänen 《Theoretical chemistry accounts》2007,118(5-6):899-913
The performance of quantum chemical methods for geometry prediction of hafnocenes was evaluated. HF, B3LYP and MP2 in combination
with nonrelativistic (MHF) and relativistic (MWB and LANL2DZ) basis sets for hafnium together with standard basis sets 3-21G*,
6-31G* and 6-311G** for other elements were applied. Five basic structural parameters of the optimized structures of the hafnocenes
were compared with experimental crystal structures obtained from the Cambridge structural database. Altogether 80 hafnocenes
were included in the analysis. The results show that relativistic corrections are necessary for Hf atom. However, even the
Hartree–Fock (HF) method, when combined with relativistic pseudopotentials, reproduces the experimental crystal structures
with significant accuracy. The good performance of the HF method can be understood to originate from the absence of significant
near-degeneracy correlations for hafnium. On average, the B3LYP and MP2 methods provide structural parameters somewhat closer
to the experimental ones. 相似文献
2.
Puukilainen E Rasilainen T Suvanto M Pakkanen TA 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):7263-7268
Superhydrophobic polyolefin surfaces were prepared by simultaneous micro- and nanostructuring. Electropolished aluminum foil was microstructured with a micro working robot and then anodized in polyprotic acid. The surface microstructure can be tailored by adjusting the settings of the micro working robot and the nanostructure by adjusting the parameters of the anodization procedure. Surface structuring was done by injection molding where a microstructured anodized aluminum oxide mold insert was used to pattern the surfaces. Structuring had a marked effect on the contact angle between the injection-molded polyolefins and water. When the optimized microstructure was covered with nanostructure, the static contact angle between polypropylene and water obtained a value of about 165 degrees and the sliding angle decreased to about 2.5 degrees. The superhydrophobic state was achieved. 相似文献
3.
4.
Based on Crapo's theory of one point extensions of combinatorial geometries, we find various classes of geometric lattices that behave very well from the point of view of stability theory. One of them, , is ω-stable, it has a monster model and an independence calculus that satisfies all the usual properties of non-forking. On the other hand, these classes are rather unusual, e.g. in the Smoothness Axiom fails, and so is not an AEC. 相似文献
5.
Quantitative assessment of the enzymatic degradation of amorphous cellulose by using a quartz crystal microbalance with dissipation monitoring 总被引:1,自引:0,他引:1
Suchy M Linder MB Tammelin T Campbell JM Vuorinen T Kontturi E 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8819-8828
The systematic evaluation of the degradation of an amorphous cellulose film by a monocomponent endoglucanase (EG I) by using a quartz crystal microbalance with dissipation monitoring (QCM-D) identified several important aspects relevant to the study the kinetics of cellulose degradation by enzymes. It was demonstrated that, to properly evaluate the mechanism of action, steady state conditions in the experimental set up need to be reached. Rinsing or diluting the enzyme, as well as concentration of the enzyme, can have a pronounced effect on the hydrolysis. Quantification of the actual hydrolysis was carried out by measuring the film thickness reduction by atomic force microscopy after the enzymatic treatment. The values correlated well with the frequency data obtained by QCM-D measurement for corresponding films. This demonstrated that the evaluation of hydrolysis by QCM-D can be done quantitatively. Tuning of the initial thickness of films enabled variation of the volume of substrate available for hydrolysis which was then utilized in establishing a correlation between substrate volume and hydrolytic activity of EG I as measured by QCM-D. It was shown that, although the amount of substrate affects the absolute rate of hydrolysis, the relative rate of hydrolysis does not depend on the initial amount of substrate in steady state system. With this experimental setup it was also possible to demonstrate the impact of concentration on crowding of enzyme and subsequent hydrolysis efficiency. This effort also shows the action of EG I on a fully amorphous substrate as observed by QCM-D. The enzyme was shown to work uniformly within the whole volume of swollen film, however being unable to fully degrade the amorphous film. 相似文献
6.
Ligand substitution of the mixed-metal clusters FeRu2(CO)12 and Fe2Ru(CO)12 with triphenylphosphine and trimethylphosphite has been studied. Mono- and di-substituted derivatives have been synthesized and characterized structurally. The following crystal and molecular structures are reported: Fe2Ru(CO)11PPh3: triclinic, space group P, a 9.203(2), b 11.903(3), c 15.117(4) Å, α 81.54(2), β 87.28(2), γ 66.72(2)°, Z = 2; Fe2Ru(CO)11P(OMe)3: orthorhombic, space group Pna21, a 17.220(5), b 14.572(4), c 8.708(6) Å, Z = 4, FeRu2(CO)11PPh3: monoclinic, space group P21/n, a 11.435(3), b 16.034(5), c 16.642(4) Å, β 93.35(2)°, Z = 4; FeRu2(CO)10(PPh3)2: orthorhombic, space group Pccm, a 14.854(4), b 17.180(7), c 16.786(12) Å, Z = 4.Ligand substitution is found to occur preferentially at the ruthenium centers of the FeRu2 and Fe2Ru clusters. Monosubstitution causes expansion of both of the clusters while the overall geometry is practically unchanged. Disubstitution of FeRu2(CO)12 causes contraction of the cluster and leads to a formation of carbonyl bridges. The structural trends have been interpreted in terms of electronic and packing effects of ligand substitution. The X-ray structures of Fe2Ru(CO)12 and FeRu2(CO)12 are not known; the ligand substitution studies indicate that Fe2Ru(CO)12 has the same structure as Fe3(CO)12, and that FeRu3(CO)12 does not have a Ru3(CO)12 structure as postulated previously from the IR studies. 相似文献
7.
Tuula T. Pakkanen Tapani A. Pakkanen Kimmo Smolander 《Journal of Molecular Structure》1987,162(3-4):313-320
The structures of two glycinohydroxamoto (GHA) complexes of Ni(II) and Co(III) have been determined by single-crystal X-ray diffraction methods. The crystals of Ni(GHA)2 are monoclinic with a = 5.360(1), b = 7.315(4), c = 10.194(4) Å, β = 96.57(3), Z = 2, and space group P21/c. The crystals of Co(GHA)3•1/2 H2O are monoclinic with a = 22.467(19), b = 8.041(4), c = 13.700(11) Å, β = 116.01(7), Z = 8, and space group C2/c. The values of the final residuals R for Ni(GHA)2 and Co(GHA)3•1/2 H2O are 0.0275 and 0.032, respectvely. The molecular structures of Ni(GHA)2 and Co(GHA)3 consist of a square planar and an octahedral coordination, respectively, with the glycinohydroxamato (NH2CH2CONOH−) ligands coordinating to the metal ion via the N (amino) and the N (NOH−). These two complexes are the first well-established cases of coordination of the NHO− group of a hydroxamic acid to a transition metal via the nitrogen atom. 相似文献
8.
Tapani Hyttinen Saharon Shelah 《Proceedings of the American Mathematical Society》2002,130(10):2837-2843
For suitable groups we will show that one can add a Boolean algebra by forcing in such a way that is almost isomorphic to . In particular, we will give a positive answer to the following question due to J. Roitman: Is a possible number of automorphisms of a rich Boolean algebra?
9.
Anders Lindfors Anu Heikkilä Jussi Kaurola Tapani Koskela Kaisa Lakkala 《Photochemistry and photobiology》2009,85(5):1233-1239
UV radiation exerts several effects concerning life on Earth, and spectral information on the prevailing UV radiation conditions is needed in order to study each of these effects. In this paper, we present a method for reconstruction of solar spectral UV irradiances at the Earth's surface. The method, which is a further development of an earlier published method for reconstruction of erythemally weighted UV, relies on radiative transfer simulations, and takes as input (1) the effective cloud optical depth as inferred from pyranometer measurements of global radiation (300–3000 nm); (2) the total ozone column; (3) the surface albedo as estimated from measurements of snow depth; (4) the total water vapor column; and (5) the altitude of the location. Reconstructed daily cumulative spectral irradiances at Jokioinen and Sodankylä in Finland are, in general, in good agreement with measurements. The mean percentage difference, for instance, is mostly within ±8%, and the root mean square of the percentage difference is around 10% or below for wavelengths over 310 nm and daily minimum solar zenith angles (SZA) less than 70°. In this study, we used pseudospherical radiative transfer simulations, which were shown to improve the performance of our method under large SZA (low Sun). 相似文献
10.
Summary Translational symmetry has been shown to be useful in the calculation of electronic structures of large lattice models. The number of unique integrals has been derived for cases of different dimensionality. For the unique integrals zero screening and approximation methods are described. The method has been applied to arrays of hydrogen atoms and to a zincblende surface model. When the size of the system is increased the translationally unique integrals are shown to become either zero or they can be calculated by simple coulombic approximations. 相似文献