首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   907篇
  免费   46篇
化学   748篇
晶体学   15篇
力学   15篇
数学   68篇
物理学   107篇
  2024年   4篇
  2023年   5篇
  2022年   14篇
  2021年   23篇
  2020年   28篇
  2019年   19篇
  2018年   16篇
  2017年   24篇
  2016年   31篇
  2015年   27篇
  2014年   37篇
  2013年   62篇
  2012年   66篇
  2011年   54篇
  2010年   39篇
  2009年   50篇
  2008年   57篇
  2007年   44篇
  2006年   61篇
  2005年   43篇
  2004年   40篇
  2003年   36篇
  2002年   20篇
  2001年   7篇
  2000年   7篇
  1999年   2篇
  1998年   3篇
  1997年   7篇
  1996年   6篇
  1995年   8篇
  1994年   10篇
  1993年   11篇
  1992年   7篇
  1991年   9篇
  1990年   10篇
  1989年   9篇
  1988年   7篇
  1987年   4篇
  1986年   7篇
  1985年   5篇
  1984年   8篇
  1983年   3篇
  1982年   6篇
  1981年   5篇
  1977年   2篇
  1976年   2篇
  1973年   1篇
  1972年   3篇
  1971年   1篇
  1968年   1篇
排序方式: 共有953条查询结果,搜索用时 15 毫秒
121.

Tritium concentration was monitored in different water sources collected around Kaiga Nuclear Power plant, India. The concentration was in the ranges?<?1.9–27.4 Bq L?1 (GM?=?4.0 Bq L?1) for groundwater,?<?1.9–42.1 Bq L?1 (GM?=?3.5 Bq L?1) for surface water and in 12.4–42.0 Bq L?1 (GM?=?24.07 Bq L?1) for reservoir water. The concentration values observed in this study are similar to those reported for other PHWR stations of the world. The radiation dose to the public due to ingestion of Tritium through groundwater was computed to be 0.08 μSvy?1.

  相似文献   
122.
Russian Journal of General Chemistry - A series of novel 1,2,4-oxadiazole-isoxazole linked quinazoline compounds is designed, synthesized and screened for anticancer activity on four human cancer...  相似文献   
123.
124.
The influence of Mm (Mm=mischmetal) substitution and hydrogen absorption on the magnetic properties of Ho1−xMmxCo2 (x=0, 0.1, 0.2, 0.3 and 0.4) alloys have been determined through the temperature dependence of ac susceptibility and thermopower measurements. The changes in magnetic-ordering temperature of Ho1−xMmxCo2 alloys have been explained based on the dilution of the magnetic ions and weakening of 4f3d exchange interactions. The gradual disappearance of the magnetic transition temperature upon increasing hydrogen concentration (y) has been interpreted by the lattice expansion and charge transfer between absorbed hydrogen and 3d-band of Ho1−xMmxCo2.  相似文献   
125.
We developed and validated a simple, sensitive, selective, and reliable LC–MS/MS–ESI method for the direct quantitation of lumefantrine (LFN) enantiomers [(−)-LFN and (+)-LFN] in mice plasma as per regulatory guideline. LFN enantiomers and carbamazepine (internal standard) were extracted from mice plasma using Strata X SPE (solid-phase extraction) cartridges. Good resolution between enantiomers was achieved on a Chiralpak IA-3 column using an isocratic mobile phase (0.1% of diethyl amine in methanol), which was delivered at a flow rate of 0.8 mL/min. Detection and quantitation were performed using multiple reaction monitoring mode following the transitions m/z 530.27 → 512.30 and 237.00 → 194.00 for LFN enantiomers and the internal standard, respectively, in the positive-ionization mode. The proposed method provided accurate and reproducible results over the linearity range of 2.39–895 ng/mL for each enantiomer. The intra- and inter-day precisions were in the range of 1.03–6.14 and 6.36–8.70 and 2.03–4.88 and 5.82–11.5 for (−)-LFN and (+)-LFN, respectively. Both (−)-LFN and (+)-LFN were found to be stable under different stability conditions. The method was successfully used to delineate stereoselective pharmacokinetics of LFN enantiomers in mice after an oral administration of rac-LFN (20 mg/kg). The pharmacokinetic results indicated that the disposition of LFN enantiomers was stereoselective in mice.  相似文献   
126.
A selective, sensitive and rapid LC–MS/MS method has been developed and validated as per US Food and Drug Administration regulatory guidelines for the simultaneous quantitation of colchicine and febuxostat in rat plasma. Colchicine and febuxostat were extracted from the rat plasma using 10% tert-butyl methyl ether in ethyl acetate using colchicine-d6 as an internal standard (IS). The chromatographic separation of colchicine, febuxostat and the IS was achieved using a mobile phase comprising 5 mm ammonium formate and 0.025% formic acid in acetonitrile (20:80, v/v) in isocratic mode on an Eclipse XDB-C18 column. The injection volume and flow rate were 5.0 μl and 0.9 ml/min, respectively. Colchicine and febuxostat were detected by positive electrospray ionization in multiple reaction monitoring mode using transition pairs (Q1 → Q3) of m/z 400.10 → 358.10 and 317.05 → 261.00, respectively. The assay was linear in the ranges of 0.25–254 and 2.60–622 ng/ml for colchicine and febuxostat, respectively. The inter- and intra-day precision values were 0.58–13.0 and 1.03–4.88% for colchicine and febuxostat, respectively. No matrix or carryover effects were observed during the validation. Both analytes were stable on the bench-top, in the autosampler and in storage (freeze–thaw cycles and long-term storage at −80 ° C). A pharmacokinetic study in rats was performed to show the applicability of the validated method.  相似文献   
127.
Russian Journal of Organic Chemistry - tert-Butyl 4-[(E)-but-1-en-3-yn-1-yl]-3-{[tert-butyl(dimethyl)silyl]oxy}-1H-indole-1-carboxylate has been synthesized with a good yield and selectivity...  相似文献   
128.
Russian Journal of General Chemistry - A thiophene contained imidazo phenanthroline ligand TIP {TIP = 2-(thiophen-2-yl)-1H-imidazo-[4,5-f][1,10]phenanthroline{ and its mononuclear Ru(II)...  相似文献   
129.
Three spectrophotometric methods (A-C) for the assay of cisapride (CPD) in pure and dosage forms are described. Method A is based on the oxidative coupling reaction of CPD with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of ferric chloride to form a coloured species (max; 565 nm.) Method B is based on the oxidation of CPD with Fe (III) and subsequent chelation of Fe(II) to form a coloured complex with 1,10-phenanthroline (max: 520 nm). Method C is based on the formation of a coloured charge-transfer complex between CPD and chloranilic acid (max; 555 nm). Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 2.0–32.0, 0.4–6.4 and 25.0–450.0 g/ml for methods A,B and C, respectively. The validity of the proposed methods was tested by analysing pharmaceutical dosage forms containing CPD and the relative standard deviations were within 1.0%  相似文献   
130.
Ordered, mesoporous SBA-15 functionalized with organic and inorganic moieties exhibits efficient catalytic activity in a variety of organic transformations. In this account, reviewing our own work, three-sets of surface-modified SBA-15 materials have been investigated. The first-set of materials consists of SBA-15 modified with organo-acidic (propyl thiol and propyl sulfonic acid) and basic (propyl amine and propyl adenine) moieties. The second-set of materials was prepared by grafting Mn complexes to the organo-functionalized SBA-15. The third-set composes of nanocrystalline metal oxides supported on SBA-15. All these catalysts have been characterized by structural and spectroscopic techniques. Catalytic activities of the first-set of solid materials have been investigated in acid/base-catalyzed reactions viz., ring-opening of epoxides with amines (producing β-amino alcohols), esterification, three-component-Mannich reactions and cycloaddition of CO2 to epoxides. The Mn complexes grafted on organofunctionalized SBA-15 are efficient catalysts for the chemo-, regio- and stereoselective aerial oxidation of monoterpenes at ambient conditions. TiOx, VOx, MoOx and WOx supported on SBA-15 catalyzed biomimetic oxyhalogenation of aromatic compounds. In all these reactions, the functionalized SBA-15 showed high selectivity.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号