全文获取类型
收费全文 | 874篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
化学 | 581篇 |
晶体学 | 2篇 |
力学 | 28篇 |
数学 | 64篇 |
物理学 | 209篇 |
出版年
2020年 | 6篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 118篇 |
2012年 | 32篇 |
2011年 | 26篇 |
2010年 | 34篇 |
2009年 | 21篇 |
2008年 | 42篇 |
2007年 | 36篇 |
2006年 | 25篇 |
2005年 | 41篇 |
2004年 | 29篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1967年 | 8篇 |
1966年 | 6篇 |
1964年 | 8篇 |
排序方式: 共有884条查询结果,搜索用时 93 毫秒
1.
Chris H. Hill Agnete H. Viuff Samantha J. Spratley Stéphane Salamone Stig H. Christensen Randy J. Read Nigel W. Moriarty Henrik H. Jensen Janet E. Deane 《Chemical science》2015,6(5):3075-3086
Krabbe disease is a devastating neurodegenerative disorder characterized by rapid demyelination of nerve fibers. This disease is caused by defects in the lysosomal enzyme β-galactocerebrosidase (GALC), which hydrolyzes the terminal galactose from glycosphingolipids. These lipids are essential components of eukaryotic cell membranes: substrates of GALC include galactocerebroside, the primary lipid component of myelin, and psychosine, a cytotoxic metabolite. Mutations of GALC that cause misfolding of the protein may be responsive to pharmacological chaperone therapy (PCT), whereby small molecules are used to stabilize these mutant proteins, thus correcting trafficking defects and increasing residual catabolic activity in cells. Here we describe a new approach for the synthesis of galacto-configured azasugars and the characterization of their interaction with GALC using biophysical, biochemical and crystallographic methods. We identify that the global stabilization of GALC conferred by azasugar derivatives, measured by fluorescence-based thermal shift assays, is directly related to their binding affinity, measured by enzyme inhibition. X-ray crystal structures of these molecules bound in the GALC active site reveal which residues participate in stabilizing interactions, show how potency is achieved and illustrate the penalties of aza/iminosugar ring distortion. The structure–activity relationships described here identify the key physical properties required of pharmacological chaperones for Krabbe disease and highlight the potential of azasugars as stabilizing agents for future enzyme replacement therapies. This work lays the foundation for new drug-based treatments of Krabbe disease. 相似文献
2.
E. S. Moskalenko M. Larsson K. F. Karlsson P. O. Holtz B. Monemar W. V. Schoenfeld P. M. Petroff 《Physics of the Solid State》2007,49(10):1995-1998
We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral
external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external
and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially
faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed
effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity
measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications.
The text was submitted by the authors in English. 相似文献
3.
4.
The gas phase reaction between CO2 and lanthanide atoms. A test of a model for the isokinetic effect
Summary Co3O4, NiCo2O4 and LaCo2O4catalysts were synthesizedby the citric acid-ligated method. These catalysts containing Co-oxide active components can largely
lower the temperature of soot combustion under tight contact conditions. Under the conditions of loose contact NiCo2O4 cannot promote soot combustion, but LaCo2O4 can effectively promote soot combustion because the nanometric perovskite-type catalyst LaCoO3produced in the LaCo2O4sample.</o:p> 相似文献
5.
Torabi F Ramanathan K Larsson PO Gorton L Svanberg K Okamoto Y Danielsson B Khayyami M 《Talanta》1999,50(4):787-797
An electrochemical method for the measurement of NAD(+) and NADH in normal and cancer tissues using flow injection analysis (FIA) is reported. Reticulated vitreous carbon (RVC) electrodes with entrapped l-lactate dehydrogenase (LDH) and a new redox polymer containing covalently bound toluidine blue O (TBO) were employed for this purpose. Both NAD(+) and NADH were estimated coulometrically based on their reaction with LDH. The latter was immobilized on controlled pore glass (CPG) by cross-linking with glutaraldehyde and packed within the RVC. The concentrations of NAD(+) and NADH in the tissues, estimated using different electron mediators such as ferricyanide (FCN), meldola blue (MB) and TBO have also been compared. The effects of flow rate, pH, applied potential (versus Ag/AgCl reference) and adsorption of the mediators have also been investigated. Based on the measurements of NAD(+) and NADH in normal and cancer tissues it has been concluded that the NADH concentration is lower, while the NAD(+) concentration is higher in cancer tissues. Amongst the electron mediators TBO was found to be a more stable mediator for such measurements. 相似文献
6.
Philip Wormald Kristina Wickholm Per Tomas Larsson Tommy Iversen 《Cellulose (London, England)》1996,3(1):141-152
An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by13C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the13C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions. 相似文献
7.
Brett Ammundsen Gary R. Burns Ali Amran Stig E. Friberg 《Journal of Sol-Gel Science and Technology》1995,4(1):23-29
The effects of thermal treatment on composite materials prepared by the gelation of sols comprising large concentrations of metal oxide precursor salts have been investigated, in order to determine the compositional and thermal requirements for forming spinel magnesium manganates in such systems. The preparative technique has been found to give rise to derived gel materials in which the metal oxide phase, in the form of regular spherical particles, is dispersed throughout a continuous silica matrix. Silica-supported mixed magnesium and manganese spinel oxide phases were obtained for systems comprising at least 30 wt% metal nitrate after heating to temperatures between 700 and 850°C, but not without concomitant formation of Mn2O3 and modification of the silica network by magnesium. 相似文献
8.
Jan-Olov Willerström Bertil Carlsson Stig Rundqvist 《Journal of solid state chemistry》1980,31(2):227-232
Hf3As has a monoclinic unit cell of dimensions a = 15.3898(14) Å, b = 5.3795(5) Å, c = 15.330(14) Å, β = 90.291(6)°. A structure proposal based on space group (No. 15) has been refined by the least-squares method using a Rietveld-type fullprofile analysis of Guinier-Hägg X-ray powder film intensity data. The Hf3As structure is an intermediate between the Fe3P and the Ti3P types. The atomic coordination follows rules formulated earlier for representatives of the Fe3PTi3PV3S family of structures. 相似文献
9.
Stig Veibel 《Fresenius' Journal of Analytical Chemistry》1964,205(1):94-109
Zusammenfassung Der grundsätzliche Unterschied zwischen anorganischer und organischer Analyse wird diskutiert, wobei dargelegt wird, daß die Gruppenreaktionen der funktioneilen Gruppen in der organischen Analyse die Funktionen der Ionenreaktionen der anorganischen Analyse übernommen haben.Als Beispiele werden sowohl chemische Reaktionen als auch instrumentelle Methoden zur Identifikation von Hydroxylverbindungen, Carboxylsäuren, Carbonylverbindungen, Aminen, einschließlich Aminosäuren, N-Oxiden, schwefelhaltige Verbindungen, Alkoxyverbindungen und Kohlenwasserstoffen erwähnt.Es wird betont, daß sich die endgültige Identifikation einer organischen Verbindung nur durch Konbination qualitativer und quantitativer Methoden durchführen läßt.
Summary The fundamental difference between inorganic and organic analysis is discussed, and it is shown how group reactions in organic analysis have assumed the function of ionic reactions in inorganic analysis.Chemical reactions and instrumental methods for the identification of the following compounds are mentioned hydroxy compounds, carboxylic acids, carbonyl compounds, amines, including amino-acids, N-oxides, sulphur containing compounds, alkoxy compounds and hydrocarbons. It is emphasized that a combination of qualitative and quantitative methods is necessary for obtaining a final identification.相似文献
10.
Dissociative recombination of the weakly bound NO-dimer cation: cross sections and three-body dynamics 总被引:1,自引:0,他引:1
Petrignani A Andersson PU Pettersson JB Thomas RD Hellberg F Ehlerding A Larsson M van der Zande WJ 《The Journal of chemical physics》2005,123(19):194306
Dissociative recombination (DR) of the dimer ion (NO)(2) (+) has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69+/-0.02. The second most important channel yields NO+NO fragments with a probability of 0.23+/-0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(upsilon=0)+N((4)S)+O((3)P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer. 相似文献