全文获取类型
收费全文 | 199篇 |
免费 | 1篇 |
专业分类
化学 | 115篇 |
力学 | 6篇 |
数学 | 22篇 |
物理学 | 35篇 |
综合类 | 22篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 16篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有200条查询结果,搜索用时 187 毫秒
191.
Leonard JP Jensen P McCabe T O'Brien JE Peacock RD Kruger PE Gunnlaugsson T 《Journal of the American Chemical Society》2007,129(36):10986-10987
192.
La Spina G Clérac R Collins ES McCabe T Venkatesan M Ichinose I Schmitt W 《Dalton transactions (Cambridge, England : 2003)》2007,(45):5248-5252
Hybrid organic-inorganic coordination assemblies are synthesized using modified aminocarboxylic acid ligands as the structure-directing agents. The synthetic approach results in two novel dinuclear copper(II) complexes, K2[CuII(hnida)]2.2H2O (1) and K4[CuII(chnida)]2.4H2O.4MeOH (2) that assemble in the presence of suitable counterions into a densely packed hexagonal array or an open-framework structure. The functionality of the aminocarboxylic acid ligands provides a tool to control the supramolecular structure. The materials combine promising thermal stabilities with the necessary flexibility to withstand structural changes induced by calcinations or the uptake and release of guest molecules. The structural and physicochemical properties of the complexes were investigated using X-ray diffraction, magnetic measurements, thermogravimetric analysis and spectroscopy. 相似文献
193.
Morgado P Zhao H Blas FJ McCabe C Rebelo LP Filipe EJ 《The journal of physical chemistry. B》2007,111(11):2856-2863
We have performed a combined experimental and theoretical study of the thermodynamic properties of semifluorinated alkanes. In particular, the liquid density of perfluorohexylhexane (F6H6) and perfluorohexyloctane (F6H8) has been measured as a function of temperature from 273.15 to 353.15 K and at four temperatures as a function of pressure up to 600 bar. The results were interpreted using the SAFT-VR equation of state. The perfluoroalkylalkanes were modeled as heterosegmented diblock chains using parameters for the alkyl and perfluoroalkyl segments developed in earlier work. Through this simple approach, we are able to predict the thermodynamic behavior of the perfluoroalkylalkanes studied without fitting to any experimental data for the systems being studied. 相似文献
194.
The ability to detect and isolate rare target cells from heterogeneous samples is in high demand in cell biology research, immunology, tissue engineering and medicine. Techniques allowing label-free cell enrichment or detection are especially important to reduce the complexity and costs towards clinical applications. Single-cell deformability has recently been recognized as a unique label-free biomarker for cell phenotype with implications for assessment of cancer invasiveness. Using a unique combination of fluid dynamic effects in a microfluidic system, we demonstrate high-throughput continuous label-free cell classification and enrichment based on cell size and deformability. The system takes advantage of a balance between deformability-induced and inertial lift forces as cells travel in a microchannel flow. Particles and droplets with varied elasticity and viscosity were found to have separate lateral dynamic equilibrium positions due to this balance of forces. We applied this system to successfully classify various cell types using cell size and deformability as distinguishing markers. Furthermore, using differences in dynamic equilibrium positions, we adapted the system to conduct passive, label-free and continuous cell enrichment based on these markers, enabling off-chip sample collection without significant gene expression changes. The presented method has practical potential for high-throughput deformability measurements and cost-effective cell separation to obtain viable target cells of interest in cancer research, immunology, and regenerative medicine. 相似文献
195.
Bradley SA Bresnan BJ Draper SM Geraghty NW Jeffares M McCabe T McMurry TB O'Brien JE 《Organic & biomolecular chemistry》2011,9(8):2959-2968
A series of 6-alkenyl-3-phenylcyclohex-2-enones has been synthesised and the structures of the products obtained from them on irradiation have been determined. The 6-propenyl compounds afforded a tricyclic 'parallel' [2 + 2] cycloaddition product and a bicyclic enone resulting from hydrogen abstraction in the biradical intermediate. The 6-butenyl and 6-pentenyl analogues gave 'crossed' cycloaddition products only. Although the regiochemistry of these cycloaddition reactions cannot be explained in terms of the 'rule of five', it is compatible with the concept of 'biradical conformation control' which is based on a consideration of the energy and structure of the possible 1,4-biradical intermediates. 相似文献
196.
Kelly B O'Donovan DH O'Brien J McCabe T Blanco F Rozas I 《The Journal of organic chemistry》2011,76(22):9216-9227
The synthesis and conformational analysis of a series of pyridin-2-yl guanidine derivatives using NMR, X-ray crystallography, and B3LYP/6-31+G** theoretical studies are reported. A remarkable difference was observed in the (1)H NMR spectra of the guanidinium salts as compared with their N,N'-di-Boc protected and neutral analogues. This difference corresponds to a 180° change in the dihedral angle between the guanidine/ium moiety and the pyridine ring in the salts as compared to the Boc-protected derivatives, a conclusion that was supported by theoretical studies, X-ray data, and NMR analysis. Moreover, our data sustain the existence of two intramolecular hydrogen-bonding systems: (i) between the pyridine N1 atom and the guanidinium protons in the salts and (ii) within the tert-butyl carbamate groups of the Boc-protected derivatives. To verify that the observed conformational control arises from these intramolecular interactions, a new series of N-Boc-N'-propyl-substituted pyridin-2-yl guanidines were also prepared and studied. 相似文献
197.
In this communication we report the synthesis, structural and preliminary physical characterisation of a new layered oxyselenide Ce(2)O(2)FeSe(2). This material, containing a 1D portion of the structure of the layered FeSe-related superconductors, is a semiconductor with a band gap of around 0.64 eV and orders antiferromagnetically at low temperatures. 相似文献
198.
Helane?MS?Costa Augusto?CV?Freitas Júnior Ian?PG?Amaral Izaura?Y?Hirata Patrícia?MG?Paiva Luiz?B?CarvalhoJr Vitor?Oliveira Ranilson?S?BezerraEmail author 《Chemistry Central journal》2013,7(1):166
Background
Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.Results
A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K m , kcat, and k cat /K m values using BApNA as substrate were 0.689 mM, 6.9 s-1, and 10 s-1 mM-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd2+, Al3+, Zn2+, Cu2+, Pb2+, and Hg2+ at 1 mM, revealing high sensitivity of the enzyme to metal ions.Conclusions
Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.199.
A. Shigapov A. Dubkov R. Ukropec B. Carberry G. Graham W. Chun R. McCabe 《Kinetics and Catalysis》2008,49(5):756-764
The activity of Ag-based catalysts in soot oxidation using NO2 and oxygen as oxidants has been characterized in laboratory tests (TGA) and under real conditions on an engine dynamometer. Under low-temperature NO2-assisted and high-temperature O2-assisted soot oxidation conditions, the activity of Ag-based catalysts was found to be comparable or higher than that of commercial Pt-catalysts. In addition, Ag-based compositions also revealed noticeable NO x storage, some passive NO x reduction ability, and activity in NO oxidation. Ag-catalysts characterized in the present paper may be promising for the retrofit applications and high-temperature periodical regenerations with air for diesel passenger cars. 相似文献
200.
L. Tandon E. Hastings J. Banar J. Barnes D. Beddingfield D. Decker J. Dyke D. Farr J. FitzPatrick D. Gallimore S. Garner R. Gritzo T. Hahn G. Havrilla B. Johnson K. Kuhn S. LaMont D. Langner C. Lewis V. Majidi P. Martinez R. McCabe S. Mecklenburg D. Mercer S. Meyers V. Montoya B. Patterson R. A. Pereyra D. Porterfield J. Poths D. Rademacher C. Ruggiero D. Schwartz M. Scott K. Spencer R. Steiner R. Villarreal H. Volz L. Walker A. Wong C. Worley 《Journal of Radioanalytical and Nuclear Chemistry》2008,276(2):467-473
The goal of nuclear forensics is to establish an unambiguous link between illicitly trafficked nuclear material and its origin.
The Los Alamos National Laboratory (LANL) Nuclear Materials Signatures Program has implemented a graded “conduct of operations”
type analysis flow path approach for determining the key nuclear, chemical, and physical signatures needed to identify the
manufacturing process, intended use, and origin of interdicted nuclear material. This analysis flow path includes both destructive
and non-destructive characterization techniques and has been exercized against different nuclear materials from LANL’s special
nuclear materials archive. Results obtained from the case study will be presented to highlight analytical techniques that
offer the critical attribution information. 相似文献