全文获取类型
收费全文 | 498篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 312篇 |
晶体学 | 9篇 |
力学 | 26篇 |
综合类 | 1篇 |
数学 | 23篇 |
物理学 | 141篇 |
出版年
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 18篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 38篇 |
2012年 | 29篇 |
2011年 | 43篇 |
2010年 | 12篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 19篇 |
2006年 | 24篇 |
2005年 | 21篇 |
2004年 | 23篇 |
2003年 | 13篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 13篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1968年 | 3篇 |
1966年 | 1篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1935年 | 1篇 |
1934年 | 3篇 |
1933年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有512条查询结果,搜索用时 31 毫秒
461.
462.
G. R. Mahajan V. K. Rao P. R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》1989,137(3):219-227
The stability constants of the complex of Pu/III/ with a humic acid at pH 2.9 and 5.0 were measured using solvent-extraction technique. The organic extractant was dinonyl naphthalene sulphonic acid in sodium form /NaD/ in benzene while the humate aqueous phase had a constant ionic strength of 0.5M /NaClO4/. The total carboxylate capacity of the humic acid was determined by direct potentiometric titration to be 6.201 Meq g–1. The apparent pKa increased as the degree of ionization // increased. The 1g 1 values of the complex of Pu/III/ with humic acid have been determined to be 2.8 and 3.11 at pH 2.9 and 5.0, respectively. 相似文献
463.
Suryanarayan MV Shrivastava RK Pandey D Vaidyanathaswamy R Mahajan S Bhoumik D 《Journal of chromatography. A》2001,907(1-2):229-234
A simple air-monitoring method was developed and validated for vesicant sulfur mustard (HD) in the work place at time weighted average levels. XAD-2 adsorbent was used for the collection of HD vapours for 8 h followed by liquid desorption with carbon tetrachloride. The trace level analysis was carried out by gas chromatography-photoionization detection and was confirmed by gas chromatography-mass spectrometric detection in the selected ion mode. 相似文献
464.
465.
1-Methyl-1,2,3,4,5-pentaphenyl-1-silacyclopentadiene on treatment with perbenzoic acid afforded a mixture of products consisting of tetraphenylfuran, cis-dibenzoylstilbene, cis-dibenzoylstilbene epoxide, 2,5-dihydro-2,3,4,5-tetraphenylfuran, 1,2,3-triphenyl-1,3-propanedione, 1-methylphenylhydroxysilyl-1,2,3,4-tetraphenyl-1,3-butadiene and cis, cis-1,2,3,4-tetraphenyl-1,3-butadiene. Similarly, hexaphenylsilacyclopentadiene reacted with perbenzoic acid to give a mixture comprising tetraphenylfuran and cis-dibenzoylstilbene. Photooxygenation of 1-methyl-1-vinyl-2,3,4,5-tetraphenyl-1-silacyclopentadiene has been found to give a mixture of products including cis-dibenzoylstilbene, trans-dibenzoylstilbene and isodidesyl. Possible mechanistic pathways for these reactions have been suggested. 相似文献
466.
Aman Bhalla 《Tetrahedron》2007,63(15):3195-3204
An efficient protocol for the synthesis of novel seleno-β-lactams using operationally simple strategies is presented. 3-Phenyl/benzylseleno-β-lactams, obtained from 2-phenyl/benzylselenoethanoic acids, are transformed to cis-3-chloro-3-phenyl/benzylseleno-β-lactams, which undergo reaction with various active aliphatic and aromatic substrates catalyzed by Lewis acid to produce cis-3-alkoxy-3-phenyl/benzylseleno-β-lactams and C-3 monosubstituted seleno-β-lactams. Halogen mediated intraselenyl cyclization of cis-3-(prop-2-ynyloxy)-3-benzylseleno-β-lactams affords novel spiro seleno-β-lactams. 相似文献
467.
Osamu Shimomura Byoung Se Lee Sergio Meth Suresh Mahajan Kim D. Janda 《Tetrahedron》2005,61(51):12160-12167
Cross-linked polystyrene (PS) with polytetrahydrofuran (PTHF) chains were prepared for use in solid phase organic synthesis (SPOS). The resins were prepared from styrene, styrene-PTHF macromonomers and cross-linkers 1,4-bis[4-vinylphenoxy]butane or divinylbenzene by suspension polymerization. The styrene-PTHF macromonomers were prepared by cationic polymerization of 4-vinylbenzyl bromide and 4-(4-vinylphenoxy)butyl iodide activated by silver hexafluoroantimonate and 4-(5-hydroxypentyl)styrene activated by triflic anhydride. Alternatively, polytetrahydrofuran-grafted polystyrene (PS-PTHF) resins could also be directly prepared from 5-hydroxypentyl JandaJel by cationic polymerization using triflic anhydride as the initiator. These PS-PTHF resins exhibited good swelling characteristics across a wide spectrum of polar and non-polar solvents. These resins were used in the synthesis of 3-methyl-1-phenyl-2-pyrazolin-5-one, which requires β-ketoester formation at low temperature (−78 °C), resulting in good yield and product purity; whereas the same synthesis carried out on PEG-grafted PS (PS-PEG) resin resulted in incomplete synthesis. 相似文献
468.
Several examples of the photochemical Myers-Saito and C2-C6 cyclization of enyne-allenes are described. The presence of a triplet sensitizing unit at the allene terminus and laser flash photolysis results suggest that the cyclization proceeds along the triplet manifold. An intermediate with tau = 33 +/- 5 mus was tentatively assigned to a singlet biradical. 相似文献
469.
Flarakos J Luo W Aman M Svinarov D Gerber N Vouros P 《Journal of chromatography. A》2004,1026(1-2):175-183
A robust and validated LC-MS-MS quantitative method, using column switching and mutiple reaction monitoring was developed for the analysis of risperidone (RIS) and 9-hydroxyrisperidone in human plasma and saliva. The analytical range was 1-100 ng/ml. The method used 25 microl of sample precipitated with 75 microl of acetonitrile containing internal standard (R068808). Analyses were conducted on a PE Sciex API-III + triple quadrupole mass spectrometer fitted with a Turbo IonSpray source. The method was validated for human plasma using EDTA as the anticoagulant and cross-validated to heparinized human plasma and saliva. The recoveries of risperidone and 9-hydroxyrisperidone were 90-93 and 89-93%, respectively. The validated method was applied to clinical samples to study risperidone and 9-hydroxyrisperidone concentrations in plasma and saliva. Risperidone and 9-hydroxyrisperidone appear in the saliva of patients treated with risperidone. Their detection/quantification in saliva provides evidence for recent adherence with therapy. 相似文献
470.
R. M. Sawant M. A. Mahajan N. K. Chaudhuri S. K. Patil 《Journal of Radioanalytical and Nuclear Chemistry》1993,170(1):197-205
Stability constants of the fluoride complexes of Pu(III), Sm(III) and Bi(III) in 1.0M NaClO4/HClO4 medium at 23±1°C have been determined by potentiometry using a fluoride ion-selective electrode. Plutonium was reduced to the trivalent state using quinhydrone with an excess to serve as holding reductant. The log values of concentration stability constants log 1, log 2, and log 3 are 3.58, 6.40 and 12.61 for Pu(III), 3.23, 5.81 and 10.54 for Sm(III) and 3.69, 6.13 and 11.04 for Bi(III), respectively. The log 2 values in all these cases have very large deviation and may be taken only as rough estimates. 相似文献