全文获取类型
收费全文 | 7521篇 |
免费 | 286篇 |
国内免费 | 2篇 |
专业分类
化学 | 3995篇 |
晶体学 | 46篇 |
力学 | 139篇 |
数学 | 1648篇 |
物理学 | 1981篇 |
出版年
2021年 | 100篇 |
2020年 | 123篇 |
2019年 | 95篇 |
2018年 | 169篇 |
2017年 | 178篇 |
2016年 | 412篇 |
2015年 | 265篇 |
2014年 | 302篇 |
2013年 | 683篇 |
2012年 | 367篇 |
2011年 | 471篇 |
2010年 | 271篇 |
2009年 | 228篇 |
2008年 | 239篇 |
2007年 | 181篇 |
2006年 | 141篇 |
2005年 | 92篇 |
2004年 | 96篇 |
2003年 | 104篇 |
2002年 | 118篇 |
2001年 | 104篇 |
2000年 | 80篇 |
1999年 | 90篇 |
1998年 | 89篇 |
1997年 | 89篇 |
1996年 | 84篇 |
1995年 | 81篇 |
1994年 | 74篇 |
1993年 | 70篇 |
1992年 | 71篇 |
1991年 | 64篇 |
1990年 | 59篇 |
1989年 | 62篇 |
1988年 | 67篇 |
1987年 | 72篇 |
1986年 | 66篇 |
1985年 | 89篇 |
1984年 | 83篇 |
1983年 | 76篇 |
1982年 | 69篇 |
1981年 | 72篇 |
1980年 | 84篇 |
1979年 | 76篇 |
1978年 | 80篇 |
1977年 | 84篇 |
1976年 | 64篇 |
1974年 | 69篇 |
1973年 | 75篇 |
1966年 | 64篇 |
1965年 | 66篇 |
排序方式: 共有7809条查询结果,搜索用时 15 毫秒
181.
Thermoanalytical techniques (TG, DTG, DTA and EGA) can be helpful in studying gel compositions and relating the chemical history and the role of the precipitant to the chemical properties of gels. The objective of our work was to determine the influence of the initial conditions in the reaction mixture on the product characteristics. Zirconia gels were prepared by the gelprecipitation method by the hydrolysis of zirconium tetrachloride dissolved in methanol. The substitution of water by methanol was chosen in order to obtain a reaction medium in which better control of the hydrolysis and condensation reactions of the zirconium precursor were achieved and thus also better control of the final properties of the dried zirconia gel-precipitates could be obtained. The nature of the hydrated zirconia gels obtained during the gelation process is strongly influenced by the conditions of the reaction mixture, e.g. concentration of the zirconium precursor, the mixing rate and particularly by the amount of water added. To distinguish between various types of water in the gel-precipitates, the furnace atmosphere and the partial water pressure were altered appropriately. It was shown that initial zirconium to water molar ratio has a significant effect on the properties of the final products. It was assumed that, according to the preparation conditions, three different types of water are present in the formed zirconia gel-precipitates. Modification of the dehydration processes of zirconia gel-precipitates enables control of the final microstructural and surface properties of the dried gels which are suitable for further catalysts support as well as mixed oxide preparation. 相似文献
182.
183.
B. V. Pomorišac 《International Journal of Theoretical Physics》1984,23(6):575-583
We speculate on a generalized dynamics described by an integral over action functionals that is a generalization of the standard functional integral. In a simple Gaussian case we obtain a certain differential equation for the measure of Feynman integral. We prove that the equation is satisfied for the spin zero field in one space-time dimension. 相似文献
184.
Djordje Vlaović Gordana Ćetković Ivan Juranić Jelica Balaž Stevan Lajšić Dejan Djoković 《Monatshefte für Chemie / Chemical Monthly》1990,121(11):931-939
Summary The syntheses andin vitro antibacterial and antifungal evaluation of certain (5-nitro-2-furyl)azomethines with different heterocyclic nuclei are described.
Die Anwendung von Lävulinsäure und 5-Nitro-2-furylmethylendiacetat in der Totalsynthese einiger neuer biologisch aktiver (5-Nitro-2-furyl)azomethine
Zusammenfassung Es wird die Synthese und diein-vitro-antibakterielle und antifungale Wirksamkeit für bestimmte (5-Nitro-2-furyl)azomethine mit verschiedenen heterocyclischen Kernen beschrieben.相似文献
185.
Štefan Marchalín Dušan Ilavský Milan Bruncko 《Monatshefte für Chemie / Chemical Monthly》1989,120(12):1101-1105
Summary Good yields of substituted 5-(5R-2-furyl)-4H-pyrano[2,3-d]pyrimidines4 were obtained in the reaction of 2-ethoxymethyleneamino-3-cyano-4H-pyranes2 with ammonia. Compounds2 were prepared by the condensation of the starting 2-amino-5-acetyl-3-cyano-6-methyl-4H-pyranes1 with ethyl orthoformate. Spectral properties of the bicyclic system4 in relation to compounds3 are discussed. 相似文献
186.
Summary The formation of V2O5 fibrous microcrystals in the V2O5-NH3-H2O system has been investigated by electron microscopy. The morphology of these microcrystals is dependent on the concentration of the particular components in the colloidal system and on the time of aging. In some colloid systems the orientation of V2O5 fibrous crystals with their long axes parallel to one another is also possible. The microcrystal growth in these systems can be attributed to very effective conditions for the recrystallization of vanadium pentoxide crystals in equilibrium with ammonium vanadate in solution.With 3 figures 相似文献
187.
Maleš Željan Plazibat Miško Vundać Vjera Bilušić Žuntar Irena Pilepić Kroata Hazier 《平面色谱法杂志一现代薄层色谱法》2004,17(4):280-285
JPC – Journal of Planar Chromatography – Modern TLC - The flowering tops of Hypericum hirsutum, H. montanum, H. perforatum subsp. angustifolium, H. perforatum subsp. perforatum, and H.... 相似文献
188.
The method is based on the oxidation of ethanol in the presence of alcohol oxidase, followed by oxidation of 2,2'-azino-di(3-ethylbenzthiazoline-6-sulfonate) in the presence of peroxidase. 相似文献
189.
190.
The present paper deals with the application of direct injection enthalpimetry (DIE) in the study of the kinetics of azo coupling reactions. On the example of the coupling of diazotized aniline-4-sulphonic acid with 1,8-dihydroxynaphthalene-3,6-disulphonic acid, it was verified that the rate constants determined using DIE are comparable with those determined using spectrophotometry. Advantages result from the application of DIE in the study of the kinetics of azo coupling reactions. 相似文献