全文获取类型
收费全文 | 737篇 |
免费 | 27篇 |
国内免费 | 3篇 |
专业分类
化学 | 369篇 |
晶体学 | 23篇 |
力学 | 25篇 |
数学 | 68篇 |
物理学 | 282篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 25篇 |
2014年 | 24篇 |
2013年 | 67篇 |
2012年 | 51篇 |
2011年 | 48篇 |
2010年 | 39篇 |
2009年 | 37篇 |
2008年 | 48篇 |
2007年 | 36篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 24篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1937年 | 2篇 |
1930年 | 10篇 |
1929年 | 4篇 |
1906年 | 2篇 |
排序方式: 共有767条查询结果,搜索用时 15 毫秒
151.
152.
153.
Peterka P. Faure B. Blanc W. Karásek M. Dussardier B. 《Optical and Quantum Electronics》2004,36(1-3):201-212
A comprehensive numerical model of a thulium-doped silica-based fibre amplifiers is presented. The model is spectrally and spatially resolved and is general in terms of pumping scheme used. The application of the model for predicting the S-band amplifier performance and for optimization of amplifier parameters is shown. For optimized Tm-doped fibre with 3H4 level lifetime of 45 μs, which is the maximum value in the Tm-doped silica fibres prepared by the authors, above 20 dB of gain with 2000 mW pump power at the 1050 nm pump band can be expected according to the simulations. 相似文献
154.
155.
156.
Lee Kar Wei Nor Hisam Zamakshshari Siau Hui Mah Siti Mariam Mohd Nor 《Natural product research》2018,32(18):2147-2151
Two naturally occurring xanthones, ananixanthone (1) and β-mangostin (2), were isolated using column chromatographic method from the n-hexane and methanol extracts of Calophyllum teysmannii, respectively. The major constituent, ananixanthone (1), was subjected to structural modifications via acetylation, methylation and benzylation yielding four new xanthone derivatives, ananixanthone monoacetate (3), ananixanthone diacetate (4), 5-methoxyananixanthone (5) and 5-O-benzylananixanthone (6). Compound 1 together with its four new derivatives were subjected to MTT assay against three cancer cell lines; SNU-1, K562 and LS174T. The results indicated that the parent compound has greater cytotoxicity capabilities against SNU-1 and K562 cell lines with IC50 values of 8.97 ± 0.11 and 2.96 ± 0.06 μg/mL, respectively. Compound 5 on the other hand exhibited better cytotoxicity against LS174T cell line with an IC50 value of 5.76 ± 1.07 μg/mL. 相似文献
157.
Rafael Doležal Natálie Karásková Karel Musil Martin Novák Nadezhda V. Maltsevskaya Dávid Maliňák 《Analytical letters》2018,51(15):2401-2414
The biological activity of drugs on organisms is associated with the pharmacokinetic properties, such as the ability to penetrate through environments of varying polarity such as cellular organelles. In this area, particular attention is turned to the physicochemical properties that determine the potential of drugs to pass across the blood–brain barrier and thus to act on the central nervous system. In this study, special effort has been devoted to the simulation of passive diffusion of seven drugs (propranolol, ibuprofen, atenolol, promazine, chlorpromazine, imipramine, and desipramine) through the blood–brain barrier by high-performance liquid chromatography (HPLC) using a column with an immobilized artificial membrane. Gradient reverse elution was used to develop a linear correlation model for the capacity factors kIAM and the in vivo logarithmic values of brain-to-blood drug concentration ratios (log BB) with R of 0.9851. Eleven additional pharmaceuticals were determined by the same method to predict their potential to penetrate the blood–brain barrier. The reported analytical method represents an alternative tool for rapid and noninvasive assessment of the absorption properties of chemicals, especially for the development of novel drugs. The retention of the studied compounds on the immobilized artificial membrane column was also compared with three other C18-based stationary phases. Herein, the results of the HPLC determination of drugs using an immobilized artificial membrane are briefly discussed with respect to a general application of the method for evaluating a broader spectrum of pharmaceutical compounds. 相似文献
158.
159.
Zusammenfassung Natürlich vorkommende Montmorillonite sind als Objekt von Strukturuntersuchungen wenig geeignet, da deren Zusammensetzung sehr veränderlich ist. Es wurden daher hydrothermal Mg- und Na-Montmorillonite dargestellt, deren chemischer Aufbau innerhalb weiter Grenzen variiert werden konnte. An solchen definierten Montmorilloniten wurden die Austauschkapazitäten, die Röntgenstruktur, das thermische Verhalten und die Menge des tetraedrisch koordinierten Aluminiums bestimmt. Die experimentell erhaltenen Resultate stimmen mit der nachC. S. Ross undS. B. Hendricks berechnetenHofmann-Endell-Wilm-Struktur der Montmorillonite gut überein.Mit 13 Abbildungen.In gekürzter Form vorgetragen anläßlich des XIII. Internat. Kongresses für Chemie in Stockholm, 1953. 相似文献
160.
Somnath Roy Tarak Nath Mandal Anil Kumar Barik Sachindranath Pal Samik Gupta Arijit Hazra Ray J. Butcher Allen D. Hunter Matthias Zeller Susanta Kumar Kar 《Polyhedron》2007
Two new pyrimidine based NNS tridentate Schiff base ligands S-methyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL1] and S-benzyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL2] have been synthesised by the 1:1 condensation of 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde and S-methyl/S-benzyl dithiocarbazate. A Ni(II) complex of HL1 and Co(III) and Fe(III) complexes of HL2 have been prepared and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and spectroscopic studies. All the bis-chelate complexes have a distorted octahedral arrangement with an N4S2 chromophore around the central metal ion. Each ligand molecule binds the metal ion using the pyrimidyl and azomethine nitrogen and thiolato sulfur atoms (except in the nickel complex, one ligand molecule uses the thione sulfur in lieu of thiolato sulfur atom). In the Ni(II) complex, one of the ligand molecules behaves as a neutral tridentate and the other molecule functions as a uninegative tridentate, whereas in the Co(III) and Fe(III) complexes, the ligand molecules behave as monoanionic tridentate. All the complexes were analyzed by single crystal X-ray diffraction and significant differences concerning the distortion from an octahedral geometry of the coordination environment were observed. 相似文献