全文获取类型
收费全文 | 494篇 |
免费 | 15篇 |
专业分类
化学 | 333篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 45篇 |
物理学 | 117篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 40篇 |
2011年 | 38篇 |
2010年 | 26篇 |
2009年 | 21篇 |
2008年 | 33篇 |
2007年 | 32篇 |
2006年 | 27篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 10篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有509条查询结果,搜索用时 15 毫秒
91.
92.
Ercules E.S. Teotonio Hermi F. Brito Hans Viertler Wagner M. Faustino Oscar L. Malta Gilberto F. de S Maria Cludia F.C. Felinto Regina H.A. Santos Marco Cremona 《Polyhedron》2006,25(18):3488-3494
Europium complexes presenting general formulas [Eu(ACIND)3(H2O)2] and [Eu(ACIND)3(TPPO)2] have been synthesized and characterized. In these formulas ACIND is stands for the ligands 2-acetyl-1,3-indandionate (AIND), 2-isovaleryl-1,3-indandionate (ISOVIND) or 2-benzyl-1,3-indandionate (BIND). The [Eu(ISOVIND)3(H2O)(EtOH)] complex was also prepared and its structure determined by single crystal X-ray analysis, showing that this complex crystallize in a monoclinic space group P21/n with the water molecules bridging through the hydrogen bond. The Eu(III) ion is eight-coordinate in a bicapped trigonal prismatic geometry defined by the oxygen donor atoms with a site of symmetry close to C2ν. Isovaleryl groups in the ISOVIND molecules in the structure are disordered over two positions of the europium complex. Carbon atoms in ethanol molecule are disordered by the thermal vibration. Photoluminescence properties of these complexes in solid state were investigated both experimentally and theoretically, suggesting an efficient ligand-to-metal intramolecular energy transfer process. 相似文献
93.
Ivn Brito Aldo Mundaca Alejandro Crdenas Matías Lpez‐Rodríguez 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o606-o608
In the title disulfide, C12H8N6O2S2, all bond lengths and angles are within normal ranges, and the molecules are linked into centrosymmetric R22(20) dimers by simple C—H...N interactions. Weak intermolecular C—H...π(arene) and π–π interactions, involving the benzene CH groups and the benzene rings, and the pyridine rings, respectively, further stabilize and reinforce the crystal structure. 相似文献
94.
J. -C. Diels J. J. Fontaine J. C. McMichael C. Y. Wang A. Andreoni R. Cubeddu S. Cova A. Longoni W. Knox G. Mourou T. M. Nordlund C. H. Brito Cruz F. De Martini P. Mataloni E. Palange J. M. Catherall P. M. Radmore G. H. C. New A. Müller F. P. Schäler Zs. Bor B. Rácz D. Relser A. Laubereau B. Pouligny J. R. Lalanne B. Couilaud A. Ducasse C. Vaucamps D. Schubert J. Schwarz H. Wabnitz B. Wilhelmi 《Applied physics. B, Lasers and optics》1982,28(2-3):172-179
95.
Anne-Sylvie Fabiano David Allouche Yves-Henri Sanejouand Nicole Paillous 《Photochemistry and photobiology》1997,66(3):336-345
Abstract— A new water-soluble cationic pyropheophorbide was prepared from pyropheophorbide a by a Curtius rearrangement. The self-aggregation process of this chlorhydrate of aminopyropheophorbide was investigated from the changes observed in its spectroscopic properties when passing from ethanol to aqueous solutions. The formation of aggregates was characterized in the absorption spectrum by a broadening of the Qy band, which is slightly shifted to the red, a significant increase in signals of circular dichroism and a drastic quenching of the fluorescence intensity at 674 nm. Analysis of the nonlinear variation of the fluorescence intensity with the dye concentration in Tris-buffered solutions shows that dimerization is the dominant aggregation process. The dimerization equilibrium constant(at 25Ao C, pH 7.5 in 5 m M Tris buffer, 10 m M NaCl) was determined to be 3.106 M -l . NMR measurements performed in DMSO at various dye concentrations showed that only the chemical shifts of some atoms are affected by these changes, indicating the part of the ring involved in the overlap of the two molecules in the dimer.A molecular modeling study of the packing arrangement of the aminopyropheophorbide molecules in aggregates performed by both semi-empirical quantum chemical PM3 and force field MM2 methods provided a structure consistent with these spectroscopic data. 相似文献
96.
97.
The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling
of star interiors possessing elastic properties such as the ones expected in neutron stars. Emphasis is placed on generality
in the main sections of the paper, and the results are then applied to specific examples. Along the way, a few general results
for spacetimes admitting isometries are reviewed, and their consequences are fully exploited in the case of spherical symmetry
relating them next to the the case in which the material content of the spacetime is some elastic material. Specific examples
are provided satisfying the dominant energy condition and admitting a constitutive equation, including a static two-layer
star ‘toy model’ consisting of an elastic core surrounded by a perfect fluid corresponding to the interior Schwarzschild solution
matched to the vacuum Schwarzschild solution. This paper extends and generalizes the pioneering work by Magli and Kijowski
(Gen Relat Gravit 24:139, 1992), Magli (Gen Relat Gravit 25:1277, 1993; 25:441, 1993), and complements, in a sense, that by
Karlovini and Samuelsson in their interesting series of papers (Karlovini and Samuelsson in Class Quantum Grav 20:363, 2003;
21:1559, 21:4531, 2004). 相似文献
98.
99.
Rodrigo Barcellos Hoff Fabiano Barreto Tarso B. Ledur Kist 《Journal of chromatography. A》2009,1216(46):8254-8261
A multiresidue method is described for determining six sulfonamides (SAs) (sulfadiazine, sulfathiazole, sulfamethazine, sulfamethoxazole, sulfaquinoxaline and sulfadimethoxine) in liver by a capillary electrophoresis screening method and a liquid chromatography coupled to tandem mass spectrometry confirmatory assay. Samples were prepared by homogenizing the tissue, with sodium hydroxide and acetonitrile. After evaporation, extracts were injected in the capillary electrophoresis system or mass spectrometry system for confirmatory analysis. The detection of analytes was achieved by laser-induced fluorescence in capillary electrophoresis. Procedures were validated according to the European Union regulation 2002/657/EC determining specificity, selectivity and detection capability for screening method and decision limit, detection capability, specificity, selectivity, trueness and precision for confirmation method. The results of validation process demonstrate that the method is suitable for application in Brazilian statutory veterinary drug residue surveillance programs. Capillary electrophoresis was proved to be a fast, robust method with low time and reagents consumption. 相似文献
100.
Rodrigo Brito Santos Railmara Pereira da Silva Felipe Akihiro Melo Otsuka Danielle de Jesus Trindade Aline Costa Santos Humberto Reis Matos 《Biomedical chromatography : BMC》2019,33(4)
Hexokinases play a critical role in the cellular uptake and utilization of glucose. As such, they are of fundamental importance to all cells. By catalyzing glucose to produce glucose‐6‐phosphate, hexokinases control the first irreversible step of glucose metabolism and initiate all major pathways of glucose consumption. Our objective was to develop and validate highly sensitive and selective high‐performance liquid chromatography with photodiode array detector (HPLC‐PDA) assays allowing the determination of adenosine diphosphate, which was used for the determination of hexokinase activity. Samples were analyzed by HPLC‐PDA using a C18 analytical column (250 × 4.6 mm) for chromatographic separation. Optimal detection was achieved based on isocratic elution with a mobile phase consisting of a mixture of sodium phosphate monobasic buffer and methanol. This method met all of the requirements of specificity, sensitivity, linearity, precision, accuracy and stability generally accepted in bioanalytical chemistry and was successfully applied to a study of hexokinase activity in an alloxan‐induced diabetic rat model. Determination of hexokinase activity will permit characterization of cellular metabolic state in many diseases, such as cancer and diabetes. 相似文献