全文获取类型
收费全文 | 414篇 |
免费 | 9篇 |
专业分类
化学 | 218篇 |
晶体学 | 1篇 |
力学 | 20篇 |
数学 | 76篇 |
物理学 | 108篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 34篇 |
2012年 | 17篇 |
2011年 | 23篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 24篇 |
2007年 | 17篇 |
2006年 | 20篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 3篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1973年 | 2篇 |
1939年 | 3篇 |
1911年 | 2篇 |
1908年 | 2篇 |
1905年 | 1篇 |
1893年 | 1篇 |
1891年 | 1篇 |
1889年 | 1篇 |
1882年 | 1篇 |
排序方式: 共有423条查询结果,搜索用时 31 毫秒
141.
Guido Barone Giuseppina Castronuovo Vittorio Elia Vito Savino 《Journal of solution chemistry》1984,13(3):209-219
The excess Gibbs free energies of four -methyl-D-aldopyranosides in water were determined at 25°C from isopiestic measurements. The excess entropies were obtained by subtracting the free energy values from the enthalpy data. The results show a remarkable enthalpy-entropy compensation. The positive sign of the excess free energies is interpreted as due to the favorable solute-solvent interactions that prevent the favorable solute-solute interaction. The signs and magnitudes of the pair interaction coefficients are attributed to the release of water from the hydration cospheres during the concentration process. The excess properties seem to depend, however, on the stereochemistry of the solutes. This effect is discussed and attributed to the different specific stabilities of the hydration shells. 相似文献
142.
Giuseppina Castronuovo Vittorio Elia Marcella Niccoli Filomena Velleca 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):229-234
The formation of complexes of -cyclodextrin with 1,2-alkanediols, ,-alkanediols and some cycloalkanols has been studied calorimetrically at 25 °C in water, in 7 mol kg-1 aqueous urea and in 3 mol kg-1 aqueous glucose. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained. The effect of the variation of the aqueous medium on the hydration of the interacting substances and the consequent changes in the association parameters have been investigated. As respect to water, complexes are less stable in urea and more stable in glucose. The analysis of the data shows that this is the result of a different enthalpy-entropy balance in the two solvent media. Deaquation of the interacting substances plays a major role in determining the stability of the inclusion complexes. 相似文献
143.
144.
Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Mariya V. Shamzhy Dr. Pavla Eliašová Dr. Dana Vitvarová Dr. Maksym V. Opanasenko Daniel S. Firth Prof. Russell E. Morris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17377-17386
Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited. 相似文献
145.
Dorina Mitrea Irina Mitrea Marius Mitrea Elia Ziadé 《Journal of Functional Analysis》2012,262(11):4766-4830
We are concerned with establishing completeness and separability criteria for large classes of topological vector spaces which are typically non-locally convex, including Lebesgue-like spaces, Lorentz spaces, Orlicz spaces, mixed-normed spaces, tent spaces, and discrete Triebel–Lizorkin and Besov spaces. For vector spaces of measurable functions we also derive pointwise convergence results. Our approach relies on abstract capacitary estimates and works in certain cases of interest even in the absence of a background measure space and/or of a vector space structure. 相似文献
146.
147.
Time‐of‐flight secondary ion mass spectrometry imaging of biological samples with delayed extraction for high mass and high spatial resolutions
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
148.
An Acoustic Black Hole (ABH) effect is a passive vibration reduction technique which takes advantage of properties of wave propagation in thin structures of varying thickness. A practical implementation of ABH on a uniform beam consists in an extremity whose thickness follows a power-law profile covered by a very thin layer of additional damping material. A modal analysis based on a High Resolution technique shows that the ABH significantly increases the Modal Overlap Factor (MOF) of the beam, thus reducing the resonant behaviour of the structure. Further investigations, including a two-dimensional numerical model of the structure based on the finite difference method, show that this MOF can be explained by an increase of the modal density and a high damping of a number of modes of the structure due to the ABH. 相似文献
149.
C. J. J. Elie R. Verduyn C. E. Dreef G. A. van der Marel J. H. van Boom 《Journal of carbohydrate chemistry》2013,32(6):715-739
Abstract Iodonium ion-mediated glycosylation of 1-O-allyl-3,4,5-tri-O-benzyl-6-O-para-methoxybenzyl-D/L-myo-inositol by ethyl 2-O-benzoyl-3,4,6-tri-O-benzyl-l-thio-α-D-mannopyranoside gave, after removal of the para-methoxybenzyl group and column chromatography, an α/β-mixture of the individual diastereoisomeric disaccharides. Subsequent stereospecific glycosylation of the α(1-2) linked mannopyranosyl-D-myo-inositol enantiomorph by the same ethyl 1-thiomannopyranoside donor afforded, after debenzoylarion, benzylation and subsequent deallylation the partially benzylated 2,6-dimannopyranosyl-D-myo-inositol derivative, the HO-1 position of which was phosphorylated, via the H-phosphonate method, with 1,2-dipalmitoyl-sn-glycerol. Oxidation of the intermediate phosphonate diester, and subsequent hydrogenolysis of the O-benzyl groups, furnished the target compound 1-O-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)-2,6-di-O-α-D-mannopyranosyl-D-myo-inositol. 相似文献
150.
Nanoscale Confinement Controls the Crystallization of Calcium Phosphate: Relevance to Bone Formation
Bram Cantaert Dr. Elia Beniash Prof. Fiona C. Meldrum 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14918-14924
A key feature of biomineralization processes is that they take place within confined volumes, in which the local environment can have significant effects on mineral formation. Herein, we investigate the influence of confinement on the formation mechanism and structure of calcium phosphate (CaP). This is of particular relevance to the formation of dentine and bone, structures of which are based on highly mineralized collagen fibrils. CaP was precipitated within 25–300 nm diameter, cylindrical pores of track etched and anodised alumina membranes under physiological conditions, in which this system enables systematic study of the effects of the pore size in the absence of a structural match between the matrix and the growing crystals. Our results show that the main products were polycrystalline hydroxapatite (HAP) rods, together with some single crystal octacalcium phosphate (OCP) rods. Notably, we demonstrate that these were generated though an intermediate amorphous calcium phosphate (ACP) phase, and that ACP is significantly stabilised in confinement. This effect may have significance to the mineralization of bone, which can occur through a transient ACP phase. We also show that orientation of the HAP comparable, or even superior to that seen in bone can be achieved through confinement effects alone. Although this simple experimental system cannot be considered, a direct mimic of the in vivo formation of ultrathin HAP platelets within collagen fibrils, our results show that the effects of physical confinement should not be neglected when considering the mechanisms of formation of structures, such as bones and teeth. 相似文献