全文获取类型
收费全文 | 805篇 |
免费 | 27篇 |
国内免费 | 9篇 |
专业分类
化学 | 498篇 |
晶体学 | 13篇 |
力学 | 25篇 |
数学 | 143篇 |
物理学 | 162篇 |
出版年
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 9篇 |
2013年 | 33篇 |
2012年 | 33篇 |
2011年 | 60篇 |
2010年 | 34篇 |
2009年 | 21篇 |
2008年 | 40篇 |
2007年 | 39篇 |
2006年 | 36篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 14篇 |
1973年 | 12篇 |
1972年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有841条查询结果,搜索用时 15 毫秒
21.
22.
Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1993,70(6):722-725
23.
The mass spectra of 1,1′-diacetylferrocene, 1,1′-dipropionyl ferrocene and their deuterium and Fe57 isotope labeled analogs are herein reported and discussed. Fragmentation pathways are established and evidence is presented that in the process of fragmentation there is extensive interaction between substituents on the two ferrocene rings. This process apparently has little precedent in the mass spectrometry of ferrocene derivatives. Specifically, the experimental results suggest the simultaneous elimination of two molecules of carbon monoxide, or in another case, of carbon monoxide and ethylene from ions produced in the mass spectrometry of the above compounds. 相似文献
24.
The mechanism of base catalyzed proton exchange at the 5-position of uracil and its N-methylated derivatives has been studied. These reactions proceed by addition — elimination across the 5,6-double bond when the 1-nitrogen is substituted with a methyl group, or with anchimeric assistance of the N-1 anion if the 1-position is unsubstituted. The base catalyzed hydrolyses of 1,3-dimethyluracil and 3-methyluracil also appear to proceed through hydrated intermediates. A facile method for an acid catalyzed preparation of 5-deuterated uracils is described as well as a simple and accurate method for analysis of deuterium content. 相似文献
25.
26.
Zinc ions react with the surfactant ethylhexadecyldimethylammonium bromide (EHDABr) to form a surface active sublate which can be removed from aqueous chloride solutions by ion flotation. A typical ion flotation procedure involves passing air through a 235-ml solution containing 5 ppm Zn2+, 2.0 M HCl, and 2.5 × 10?3M EHDABr at a flow rate of 40 ml/min for 150 min. The procedure is simple and rapid. Cadmium, copper, lead, and nickel ions cause reductions of zinc flotation efficiencies of less than 2.5% under the experimental conditions. 相似文献
27.
J. M. Curtis R. K. Boyd B. Shushan T. G. Morgan J. H. Beynon 《Journal of mass spectrometry : JMS》1984,19(5):207-216
A mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes. 相似文献
28.
Aaron Goldman Frank J. Murcray Frank H. Murcray David G. Murcray Curtis P. Rinsland 《Mikrochimica acta》1988,95(1-6):409-415
Simultaneous total column amounts of a number of minor and trace atmospheric gases above the South Pole in December 1980 and December 1986 have been deduced from analysis of high resolution solar absorption spectra recorded (by F. J. M. and F. H. M.) from Amundsen-Scott South Pole Station. These spectra also contain some limited information on the vertical profiles of the observed atmospheric gases.The data sets were recorded with a Bomem Michelson-type interferometer and analyzed with a spectral least-squares fitting procedure, utilizing the best available spectroscopic line parameters and absorption cross sections. Because the same instrument, line parameters, and analysis method have been used in analyzing the December 1980 and December 1986 data sets, the precision in comparing the column amounts from these two dates is rather high, about 10–20% for the stronger absorbing gases. For this reason, it has been possible to quantify or determine upper limits for differences between the December 1980 and December 1986 total column amounts, of a number of atmospheric gases including O3, N2O, HNO3, CO2, CH4, and CF2C1
2 (CFC 12). In addition, vertical column amounts for a number of atmospheric gases covered only in the December 1986 observations have been derived, including HC1, NO, NO2, and C2H6. Some of these results will be discussed here. The HC1 measurements are especially interesting since the observed amounts are higher than expected from observations made at lower latitudes in the northern and southern hemispheres. 相似文献
29.
30.
Summary A study has been undertaken to develop a solvent extraction system for mercury using Alamine 304 in aqueous chloride medium. The parameters investigated included reagent concentration, acid concentration, pH, aqueous to organic phase ratio, and rate of extraction and stripping. The study shows that mercury can be extracted rapidly and efficiently from aqueous chloride solutions. A number of aqueous stripping reagents removed more than 90% of the mercury from the organic phase with only one equilibrium. These include HNO3, NaOH and EDTA.
Extraktion von Quecksilber mit Alamin 304
Zusammenfassung Die Extraktion von Quecksilber aus der wäßrigen Lösung des Chlorids mit Alamin 304 wurde untersucht. Die Konzentration des Reagens, der Säure, das pH, das Verhältnis der wäßrigen zur organischen Phase sowie das Extraktionsverhältnis wurden geprüft. Die Extraktion verläuft rasch und wirkungsvoll. Eine Reihe wäßriger Reagenzien entzieht mehr als 90% des Quecksilbers aus der organischen Phase. Dazu gehören Salpetersäure, Natronlauge und EDTA.相似文献