全文获取类型
收费全文 | 17888篇 |
免费 | 496篇 |
国内免费 | 90篇 |
专业分类
化学 | 11286篇 |
晶体学 | 278篇 |
力学 | 420篇 |
综合类 | 1篇 |
数学 | 2856篇 |
物理学 | 3633篇 |
出版年
2023年 | 112篇 |
2022年 | 233篇 |
2021年 | 318篇 |
2020年 | 303篇 |
2019年 | 390篇 |
2018年 | 292篇 |
2017年 | 293篇 |
2016年 | 604篇 |
2015年 | 466篇 |
2014年 | 560篇 |
2013年 | 1177篇 |
2012年 | 954篇 |
2011年 | 1061篇 |
2010年 | 786篇 |
2009年 | 707篇 |
2008年 | 927篇 |
2007年 | 957篇 |
2006年 | 778篇 |
2005年 | 787篇 |
2004年 | 663篇 |
2003年 | 581篇 |
2002年 | 513篇 |
2001年 | 316篇 |
2000年 | 282篇 |
1999年 | 199篇 |
1998年 | 214篇 |
1997年 | 193篇 |
1996年 | 193篇 |
1995年 | 207篇 |
1994年 | 149篇 |
1993年 | 153篇 |
1992年 | 149篇 |
1991年 | 125篇 |
1990年 | 146篇 |
1989年 | 127篇 |
1988年 | 116篇 |
1987年 | 113篇 |
1986年 | 137篇 |
1985年 | 203篇 |
1984年 | 216篇 |
1983年 | 148篇 |
1982年 | 135篇 |
1981年 | 149篇 |
1980年 | 152篇 |
1979年 | 119篇 |
1978年 | 130篇 |
1977年 | 111篇 |
1976年 | 101篇 |
1975年 | 104篇 |
1974年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Jan Blomberg Peter J. Schoenmakers Jan Beens Robert Tijssen 《Journal of separation science》1997,20(10):539-544
In general, petrochemical products contain only a limited number of chemical classes of compounds (sample dimensionality). The enormous number of individual components within these classes, however, soon puts limitations upon a single chromatographic technique when it comes to adequate characterization of these products. Comprehensive two-dimensional gas chromatography (GC×GC) clearly opens the possibility of estimating the composition of hydrocarbon mixtures in a far more detailed fashion than hitherto possible. Although the emphasis of papers of GCxGC thus far almost exclusively applies to the unsurpassed peak-capacity, in the oil industry there is a need for characterization, rather than for analyzing all the individual compounds. In principle a GCxGC system can provide an almost perfect match between its intrinsic properties and the dimensionality of oil samples. To establish the applicability of GCxGC towards petrochemical analytical challenges, a commercially aavailable prototype instrument was subjected to an exhaustive characterization of a typical hydrocarbon precess stream and a fast characterization of a light gas oil. Although there are no fundamental limitations towards the quantitative aspects of a GCxGC system, this paper confines itself to qualitative results only. Quantitative aspects of GCxGC will be published in a forthcoming paper. 相似文献
82.
Selected triphenylmethane dyes were used as new visualizing agents in thin-layer chromatography of higher fatty acids, higher fatty alcohols, and higher aliphatic amines. 相似文献
83.
Jan de Jong Aalt Bast Wim J.F. van der Vijgh 《Trends in analytical chemistry : TRAC》1993,12(10):422-428
Anthracyclines, with doxorubicin as the major representative, are amongst the most important chemotherapeutic agents used in cancer therapy. In order to reduce the severe side effects associated with their use, and to increase therapeutic efficacy, analogue development still continues, and analytical requirements change concomitantly. The available methods for bioanalysis of anthracyclines are summarized, with emphasis on high-performance liquid chromatography. Attention is paid to sample pretreatment, the possibilities of liquid—liquid and solid-phase extraction, and the chromatographic behaviour of the anthracyclines. 相似文献
84.
85.
K. Jerie A. Baranowski J. Gliński J. Przybylski 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(3):645-649
Experimental results of positron annihilation experiments in solutions of n-butanol in three diols are compared to those of
ultrasonic velocity and absorption. Variations of the annihilation parameters with composition show that the effect of the
hydrophobic solute on the original diol structure is rather limited and occurs only in the system where ethylene glycol is
the solvent. Subtle similarities were found when compared it to the respective results for similar aqueous systems, suggesting
that crystalline-like solvates are forming in ethylene glycol. However, no such evidences were found for the systems where
butanediols are the solvents. Ultrasonic investigations do not confirm formation of any specific structures. This is caused,
most possibly, by the fact that compressibility of solvates is close to those of the pure components and/or that of unstructured
medium (regular solution). 相似文献
86.
Jan Vorlíek Milan Fara Frantiek Vydra 《Fresenius' Journal of Analytical Chemistry》1968,241(5):314-318
Summary Conditions for the magnesium determination in alkaline solution by EDTA titration with biamperometric indication were examined. The most preferable pH range was found to be above 9.6. A reliable determination can be carried out in the presence of Ca, Ni, Cu and Co up to the ratio of 11. In the case of higher concentrations of Cu and Ni masking with potassium cyanide can be used. In this case, however, a change of the titration curves occurs.A new method for the determination of water-hardness by biamperometric indication is proposed. It is rapid and accurate and meets the requirements of routine and research work (error: ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
Zusammenfassung Die Bedingungen für die Magnesiumbestimmung in alkalischer Lösung durch Titration mit ÄDTA bei biamperometrischer Endpunktsanzeige wurden untersucht. Der günstigste pH-Bereich liegt über 9,6. Zuverlässige Bestimmungen können in Gegenwart von Ca, Ni, Cu und Co bis zum Verhältnis 11 ausgeführt werden. Höhere Konzentrationen an Cu oder Ni können mit KCN maskiert werden, wobei allerdings eine Umkehrung der Kurven auftritt.Ein Verfahren zur Wasserhärtebestimmung mit biamperometrischer Indikation wird vorgeschlagen, das schnell durchzuführen ist und genaue Werte liefert (Fehler ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
87.
A mixture of both geometrical isomers of hydrazones 3a‐3e was obtained by the coupling reactions of pyrazole‐3‐diazonium salts 2a‐2d and benzenediazonium chloride 2e with 2‐pyridylacetonitrile 1 . Hydrazones 3a‐3d were cyclized to the corresponding 4‐amino‐3‐(2‐pyridyl)pyrazolo[5,1‐c][1,2,4]triazines 4a‐4d. 相似文献
88.
The electrode kinetic parameters of the In(III)/In(I) couple in acidic 4M bromide solution have been determined by means of the rotating disc electrode technique.
Die elektrochemisch-kinetischen Parameter des In(III)/In(I)-Redoxsystems in Bromidlösung (Kurze Mitteilung)
Zusammenfassung Die elektrochemisch-kinetischen Parameter am In(III)/In(I)-Redoxsystem wurden in saurer 4-M-Bromidlösung mittels der rotierenden Scheibenelektrode bestimmt.相似文献
89.
Summary Experimental results are presented on the application of Carbosieve S (Supelco) and Spherocarb (Analabs) spherical carbon molecular sieves for the gas chromatographic separation of mixtures of permanent gases and C1–C3 hydrocarbons using a single column or two columns in series. At a programmed temperature of 35–300°C, good separation of the sample components was obtained when using helium as the carrier gas. When hydrogen was used as the carrier gas and the analysis was carried out under isothermal conditions the elution sequence of oxygen and nitrogen reversed as the temperature was increased. This behaviour was observed within a temperature range of 35–225°C for Carbosieve S, and within a temperature range of 35–300°C for Spherocarb. 相似文献
90.
The synthesis and characterization of CuX2L; (X = CH3CH2COO?, ClCH2CH2COO?, CH3CHClCOO? or CH3CCl2COO?; and L = 4-acetylpyridine N-oxide) is reported. The characterization of these compounds was based on electronic, infrared and EPR spectra, as well as magnetic measurements over the temperature range. Several correlations between the spectral and magnetic data as well as pKa values of the respective acids were found and discussed. On the basis of spectral and magnetic data the structures of the compounds are discussed. 相似文献