全文获取类型
收费全文 | 1465篇 |
免费 | 221篇 |
国内免费 | 390篇 |
专业分类
化学 | 1875篇 |
晶体学 | 32篇 |
力学 | 5篇 |
综合类 | 17篇 |
物理学 | 147篇 |
出版年
2023年 | 28篇 |
2022年 | 17篇 |
2021年 | 45篇 |
2020年 | 75篇 |
2019年 | 35篇 |
2018年 | 52篇 |
2017年 | 46篇 |
2016年 | 74篇 |
2015年 | 76篇 |
2014年 | 86篇 |
2013年 | 149篇 |
2012年 | 124篇 |
2011年 | 131篇 |
2010年 | 91篇 |
2009年 | 75篇 |
2008年 | 101篇 |
2007年 | 104篇 |
2006年 | 107篇 |
2005年 | 81篇 |
2004年 | 97篇 |
2003年 | 79篇 |
2002年 | 71篇 |
2001年 | 30篇 |
2000年 | 36篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 32篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 11篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有2076条查询结果,搜索用时 15 毫秒
71.
A. R. Crosland S. P. McGrath P. W. Lane 《International journal of environmental analytical chemistry》2013,93(1-4):153-160
Abstract A standardised EDTA extraction procedure was tested collaboratively by six laboratories using two in-house reference soils identified as soil A and soil B. The extracts were analysed for Zn, Cu, Pb and Mn by Inductively Coupled Plasma Spectrometry. Concentrations of extractable elements in soil A were generally much lower than those found in soil B. All laboratories produced some extreme outlying results, most of these were produced in soil B. Results for Mn were the most variable, with a range of 63.4–100.3 μg g?1 in soil A and 226.4–415.3 μg g?1 in soil B. In both soils, one laboratory reported high values for Zn and Mn and, one laboratory, for soil B, produced values for all four elements which were consistently low. If outlying results are ignored, the results from most laboratories were in reasonable agreement for all elements except Mn. 相似文献
72.
Daniela Schiavo 《光谱学快报》2013,46(7):354-360
ABSTRACT The effects caused by concomitants [Na(I), K(I), Ca(II), and Mg(II)] on the atomization of cobalt and manganese by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) were here studied. The main concomitants were chosen according to typical major elements found in foods and beverages. Severe interference effects were caused by all concomitants. The interferences varied from ?101.0% to +360.0% and ?117.5% to +175.5% for Co and Mn, respectively. These data demonstrated a frequently paradoxical situation in spectrochemical analysis, that is, efforts are directed toward the introduction of a higher amount of sample, however, when this condition is attained, there is the manifestation of severe processes of interferences. These interference processes require the application of either previous separation steps or special strategies of calibration. 相似文献
73.
Rolf Appel Nikolaos Siabalis 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):273-274
Abstract Reactions of carbonyl cyclopentadienyl hydrides from molybdenum and tungsten with 1,4-diphosphabuta-1,3-diene yield metalla-diphospha-pentadiene with a metal-phosphorus-double bond. Metalla-diphosphapentadiene mit einer Metall-Phosphor-Doppelbindung werden durch Umsetzung von Carbonylcyclopentadienylhydriden des Molybdäns und Wolframs mit einem 1,4-Diphospha-buta-1,3-dien erhalten. 相似文献
74.
Bojan Šoptrajanov Gligor Jovanovski Viktor Stefov Igor Kuzmanovski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract The infrared (IR) and Raman spectra of MgHPO4. 3H2O and of a series of partially deuterated analogues as well as the IR spectra of MnHPO4. 3H2O have been recorded and interpreted. The analysis of the IR spectra in the HOD bending region rules out the possibility of existence of H3OC+ ions in the structure. 相似文献
75.
《Analytical letters》2012,45(1):57-61
Abstract A new method for the determination of the titre of ascorbic acid standard solutions employing potassium dichromate as a primary standard has been developed. In a pyrophosphate medium, the pyrophosphate complex of divalent manganese is oxidized by dichromate to the pyrophosphate complex of tervalent manganese; the latter oxidizes o-tolidine reversibly with formation of the corresponding quinonediimine, which is visually titrated by the ascorbic acid standard solution. 相似文献
76.
Dr. Qingquan Lu Steffen Greßies Felix J. R. Klauck Prof. Dr. Frank Glorius 《Angewandte Chemie (International ed. in English)》2017,56(23):6660-6664
A MnI-catalyzed regioselective C−H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93 % ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by MnI-catalyzed C−H activation. Mechanistic investigations revealed that the precoordination of the oxygen atom to the manganese center as well as the congested tertiary carbon atom in the propargylic carbonates play a crucial role. 相似文献
77.
Dr. Shiyong Zuo Dr. Xijun Xu Prof. Shaomin Ji Zhuosen Wang Dr. Zhengbo Liu Prof. Jun Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):830-860
As concerns about the safety of lithium-ions batteries (LIBs) increases, aqueous zinc-ion batteries (ZIBs) with a lower cost, higher safety, and higher co-efficiency have attracted more and more interest. However, finding suitable cathode materials is still an urgent problem in ZIBs. In recent years, a lot of significant works have been reported, including manganese-based cathodes, vanadium-based cathodes, Prussian blue analog-based materials, and sustainable quinone cathodes. In this review, some typical cathode materials are introduced. The detailed storage mechanisms and methods for improving the reaction kinetics of the zinc ions are summarized. Finally, the issues, challenges, and the research directions are provided. 相似文献
78.
79.
《Journal of Coordination Chemistry》2012,65(1-3):17-23
The DNA cleavage properties of two cationic manganese porphyrins possessing different peripheral substituents were compared. The identical nature of the strand scission patterns of the porphyrins on a 139 base pair restriction fragment of pBR-322 DNA, along with other evidence, suggests that the porphyrin is end-on bound via the minor groove in a melted or partially melted region of DNA. This unusual binding mode underscores the potential of outisde binding cationic metalloporphyrins as probes for low melting regions of DNA 相似文献
80.
《Analytical letters》2012,45(6):427-438
Abstract Mercury(II) ion accelerates the complex formation reaction of manganese(II) with α, β, γ δ-tetraphenylporohinesulfonate (TPPS). Mercury(II) concentrations as low as 10?8 mol dm?3 can be determined from the decrease in absorbance at 413 nm (Λmax of TPPS) at a fixed time after the initiation of the reaction of rnanganese(II) with TPPS. Sandell's sensitivity calculated from the calibration curve at 30 min after the start of the reaction is 3.8 × 10?2 ng cm?2. After the separation of metallic mercury by distillation at room temperature, the method is highly selective and is free from interference of most substances usually encountered. 相似文献