全文获取类型
收费全文 | 7994篇 |
免费 | 336篇 |
国内免费 | 76篇 |
专业分类
化学 | 5915篇 |
晶体学 | 70篇 |
力学 | 327篇 |
综合类 | 3篇 |
数学 | 1049篇 |
物理学 | 1042篇 |
出版年
2024年 | 16篇 |
2023年 | 57篇 |
2022年 | 285篇 |
2021年 | 406篇 |
2020年 | 266篇 |
2019年 | 308篇 |
2018年 | 297篇 |
2017年 | 239篇 |
2016年 | 393篇 |
2015年 | 272篇 |
2014年 | 294篇 |
2013年 | 729篇 |
2012年 | 509篇 |
2011年 | 554篇 |
2010年 | 335篇 |
2009年 | 292篇 |
2008年 | 340篇 |
2007年 | 350篇 |
2006年 | 282篇 |
2005年 | 242篇 |
2004年 | 218篇 |
2003年 | 196篇 |
2002年 | 212篇 |
2001年 | 94篇 |
2000年 | 113篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 53篇 |
1994年 | 58篇 |
1993年 | 43篇 |
1992年 | 45篇 |
1991年 | 47篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 41篇 |
1986年 | 38篇 |
1985年 | 50篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 42篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 12篇 |
1975年 | 15篇 |
排序方式: 共有8406条查询结果,搜索用时 15 毫秒
951.
Mohamed Rifaat Hamza Elmoghayar Abdel-Ghani Ali El-Agamey Mohamed Yousri Abdel-Samad Nasr Mohamed Mohamed Mohamed Sallam 《Journal of heterocyclic chemistry》1984,21(6):1885-1887
The reaction of 2-cyanoethanoic acid hydrazide and arylidenemalononitrile was studied as a new route for the synthesis of N-amino-2-pyridones. Pyrano[2,3-c]pyrazole and thiazolo[2,3-a]pyridine could be prepared from the reaction of arylideneazolones with the same reagent. 相似文献
952.
An idea to design a new converging collimator for cold neutron time-of-flight measurements is presented. Using this new facility in combination with a neutron time-of-flight spectrometer, we may have neutron intensity gain factors about three times that obtained using the conventional straight slit collimators. Expressions for calculating the collimators dimensions as well as the intensity gain and the time resolution broading were presented. 相似文献
953.
Sanaa O. Abd Allah Mohamed R. Elmoghayar Sadek E. Abdou 《Journal of heterocyclic chemistry》1984,21(1):253-256
The 4-arylhydrazono-3-phenyl-2-isoxazoline-5-thiones 2 react with hydrazines to yield the 5-hydrazones 3 and 5 . The reaction of 2 with Grignard reagent resulted in addition of the reagent to the thiocarbonyl group to yield 7 . Treatment of 2 with diazomethane effected S - and N -methylation beside 1,2,3-triazole derivative 11 obtained through isomerisation. The potassium salt of 2 react with alkyl halides to yield the S-alkyl derivatives 12 . 相似文献
954.
M. M. Eid M. A. Badawy M. A. H. Ghazala Yehia A. Ibrahim 《Journal of heterocyclic chemistry》1983,20(6):1709-1711
Synthesis of several derivatives of thieno[2,3-e]-1,2,4-triazines has been achieved via the action of phosphorus pentasulfide on 6-vinyl- or 6-acylmethyl-5-oxo-1,2,4-triazine derivatives. During these investigations interesting synthetically useful functions for phosphorus pentasulfide in pyridine were observed, among which the deamination of certain N-amino heterocycles is unprecedented. 相似文献
955.
Ibrahim A. Ahmad 《Annals of the Institute of Statistical Mathematics》1982,34(1):339-350
Summary The rates at which integrated mean square and mean squre errors of nonparametric density estimation by orthogonal series method
for sequences of strictly stationary strong mixing random variables are obtained. These rates are better than those known
to hold for the independent case and they are shown to hold for Markov processes. In fact our results when specialized to
the independent case are improvements over previously known results of Schwartz (1967,Ann. Math. Statist.,38, 1262–1265). An extension of the results to estimation of the bivariate density is also given.
Research supported by a faculty summer research grant MS-STAT-42 from the University of Petroleum and Minerals. 相似文献
956.
Zusammenfassung Es wird ein zweites graphisches Verfahren dargestellt, welches gestattet, die Viskosität zäher Flüssigkeiten zu ermitteln. 相似文献
957.
Relative rates of heavy-atom-enhanced photosensitized 1O2-reactions may be used to determine φoT of sensitizers in heavy-atom-free solutions. φoT = 0.12 ± 0.02 is obtained for a 5·10?5 M methanolic solution of Rhodamine B . 相似文献
958.
The kinetics and mechanism of zinc ferrite formation are studied for pure oxide mixtures at temperatures up to 1000°C by X-ray analysis, DTA and chemical analysis. Formation of ferrite obeys a random nucleation equation with an activation energy of 29.4 kcal mole?1 in the temperature range 635–780°C. The nucleation process is followed by formation of spinel in an ordered lattice at temperatures /s> 800°C. The possibility of ZnO dissolution in the ferrite is also considered for ZnO at ratios higher than equimolecular. 相似文献
959.
Mohamed AM 《Talanta》1988,35(8):621-624
A new spectrophotometric method for the determination of some benzothiadiazine drugs is presented, based on reaction with 7,7,8,8-tetracyanoquinodimethane in sodium acetate medium and measurement at 578 nm. Beer's law is obeyed in the concentration range 0.7-6.0 mug/ml for all eight drugs tested. 相似文献
960.
Summary The closed-flask combustion products of some nitrogen compounds were studied. The percentage of nitrogen oxides formed (expressed as nitrate-nitrogen) was determined. Combustion of these samples, after mixing with inorganic oxidants, in a stream of oxygen was also investigated. Trials for the application of the oxygen-flask method for the microdetermination and detection of nitrogen in many organic compounds are reported.
Zusammenfassung Die aus einigen Stickstoffverbindungen bei der Verbrennung im sauerstoffgefüllten Kolben entstehenden Produkte wurden untersucht. Der Anteil an Stickstoffoxiden (ausgedrückt als Nitratstickstoff) wurde bestimmt. Ebenso wurde auch die Verbrennung dieser Substanzen im Sauerstoffstrom bei Gegenwart anorganischer Oxydantien untersucht. Über Versuche, die Kolbenmethode zum Nachweis und zur Bestimmung des Stickstoffs in vielen organischen Verbindungen anzuwenden, wurde berichtet.相似文献