全文获取类型
收费全文 | 786篇 |
免费 | 36篇 |
专业分类
化学 | 457篇 |
晶体学 | 17篇 |
力学 | 36篇 |
数学 | 52篇 |
物理学 | 260篇 |
出版年
2023年 | 11篇 |
2022年 | 29篇 |
2021年 | 22篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 23篇 |
2017年 | 29篇 |
2016年 | 30篇 |
2015年 | 17篇 |
2014年 | 38篇 |
2013年 | 86篇 |
2012年 | 65篇 |
2011年 | 52篇 |
2010年 | 47篇 |
2009年 | 40篇 |
2008年 | 34篇 |
2007年 | 39篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2002年 | 8篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1967年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有822条查询结果,搜索用时 0 毫秒
251.
Brijesh Pandey Veda P. Pandey A. K. Shasany U. N. Dwivedi 《Applied biochemistry and biotechnology》2014,172(7):3414-3423
A cinnamyl alcohol dehydrogenase (CAD) from the secondary xylem of Leucaena leucocephala has been purified to homogeneity through successive steps of ammonium sulfate fractionation, DEAE cellulose, Sephadex G-75, and Blue Sepharose CL-6B affinity column chromatographies. CAD was purified to 514.2 folds with overall recovery of 13 % and specific activity of 812. 5 nkat/mg. Native and subunit molecular masses of the purified enzyme were found to be ~76 and ~38 kDa, respectively, suggesting it to be a homodimer. The enzyme exhibited highest catalytic efficiency (Kcat/Km 3.75 μM?1 s?1) with cinnamyl aldehyde among all the substrates investigated. The pH and temperature optima of the purified CAD were pH 8.8 and 40 °C, respectively. The enzyme activity was enhanced in the presence of 2.0 mM Mg2+, while Zn2+ at the same concentration exerted an inhibitory effect. The inclusion of 2.0 mM EDTA in the assay system activated the enzyme. The enzyme was inhibited with caffeic acid and ferulic acid in a concentration-dependent manner, while no inhibition was observed with salicylic acid. Peptide mass analysis of the purified CAD by MALDI-TOF showed a significant homology to alcohol dehydrogenases of MDR superfamily. 相似文献
252.
253.
Tiwari R Toppino A Agarwal HK Huo T Byun Y Gallucci J Hasabelnaby S Khalil A Goudah A Baiocchi RA Darby MV Barth RF Tjarks W 《Inorganic chemistry》2012,51(1):629-639
The synthesis and initial biological evaluation of 3-carboranylthymidine analogues (3CTAs) that are (radio)halogenated at the closo-carborane cluster are described. Radiohalogenated 3CTAs have the potential to be used in the radiotherapy and imaging of cancer because they may be selectively entrapped in tumor cells through monophosphorylation by human thymidine kinase 1 (hTK1). Two strategies for the synthesis of a (127)I-labeled form of a specific 3CTA, previously designated as N5, are described: (1) direct iodination of N5 with iodine monochloride and aluminum chloride to obtain N5-(127)I and (2) initial monoiodination of o-carborane to 9-iodo-o-carborane followed by its functionalization to N5-(127)I. The former strategy produced N5-(127)I in low yields along with di-, tri-, and tetraiodinated N5 as well as decomposition products, whereas the latter method produced only N5-(127)I in high yields. N5-(127)I was subjected to nucleophilic halogen- and isotope-exchange reactions using Na(79/81)Br and Na(125)I, respectively, in the presence of Herrmann's catalyst to obtain N5-(79/81)Br and N5-(125)I, respectively. Two intermediate products formed using the second strategy, 1-(tert-butyldimethylsilyl)-9-iodo-o-carborane and 1-(tert-butyldimethylsilyl)-12-iodo-o-carborane, were subjected to X-ray diffraction studies to confirm that substitution at a single carbon atom of 9-iodo-o-carborane resulted in the formation of two structural isomers. To the best of our knowledge, this is the first report of halogen- and isotope-exchange reactions of B-halocarboranes that have been conjugated to a complex biomolecule. Human TK1 phosphorylation rates of N5, N5-(127)I, and N5-(79/81)Br ranged from 38.0% to 29.6% relative to that of thymidine, the endogenous hTK1 substrate. The in vitro uptake of N5, N5-(127)I, and N5-(79/81)Br in L929 TK1(+) cells was 2.0, 1.8, and 1.4 times greater than that in L929 TK1(-) cells. 相似文献
254.
255.
Kapil Upadhyaya Arya Ajay Rohit Mahar Renu Pandey Brijesh Kumar Sanjeev K. Shukla Rama Pati Tripathi 《Tetrahedron》2013
Fused triazoloquinolines have been prepared starting from (E)-3-(2-nitrophenyl)-1-aryl-prop-2-en-1-ones and sugar or benzyl azides in a sequential [3+2] cycloaddition reaction, followed by one pot Pd–C assisted reduction, cyclization and aromatization. The triazolyl fused quinolines with N1-glycosyl substituents as unnatural nucleosides have inherent potential to generate a library of compounds for bioevaluations. 相似文献
256.
In this paper, first-order optimality conditions for certain type of multi-objective optimisation problems are discussed under
univexity concept. A number of duality results corresponding to this sort of multi-objective problems are also shown. 相似文献
257.
Ashutosh Gupta R. P. Singh V. B. Singh Brijesh Kumar Mishra N. Sathyamurthy 《Journal of Chemical Sciences》2007,119(5):457-465
The reaction of ground-state atomic oxygen [O(3
P
2)] with methyl, ethyl, n-propyl and isopropyl radicals has been studied using the density functional method and the complete basis set model. The
energies of the reactants, products, reaction intermediates and various transition states as well as the reaction enthalpies
have been computed. The possible product channels and the reaction pathways are identified in each case. In the case of methyl
radical the minimum energy reaction pathway leads to the products CO + H2 + H. In the case of ethyl radical the most facile pathway leads to the products, methanal + CH3 radical. For propyl radical (n- and iso-), the minimum energy reaction pathways would lead to the channel containing ethanal + methyl radical. 相似文献
258.
A simple and rapid method has been developed for the determination of milligram amounts of aromatic amines and phenols. An aliquot containing 2-4 mg of sample is dissolved in a mixture of hydrochloric and acetic acids and allowed to react with N-bromo-succinimide, the excess of which is determined iodometrically after the reaction is over. The reaction time varies from 1-10 min and the absolute error generally is negative, ranging from -1 to -4%. 相似文献
259.
A new germacrane derivative, care none (1) was isolated from the stems of a well-known medicinal plant, Carissa spinarum L. together with a new ester, 3'-(4'-methoxyphenyl)-3-oxo-ropionyl hexadecanoate (2). Their structures were established using 1D, 2D NMR spectroscopic and synthetic methods. The chloroform extract of the plant displayed strong antioxidant (DPPH) activity. Several other known compounds were also isolated for the first time from this active extract. The antioxidant activity of major lignans was studied. 相似文献
260.
Reactions of 6-(1′-phenylvinyl)-1,2,4-trioxanes 2-5, with FeCl2·4H2O, FeBr2, and a combination of hemin (bovine) and reduced glutathione (GSH) under various conditions have been studied. 相似文献