全文获取类型
收费全文 | 1925篇 |
免费 | 42篇 |
国内免费 | 12篇 |
专业分类
化学 | 1154篇 |
晶体学 | 24篇 |
力学 | 58篇 |
数学 | 187篇 |
物理学 | 556篇 |
出版年
2022年 | 24篇 |
2021年 | 42篇 |
2020年 | 44篇 |
2019年 | 59篇 |
2018年 | 47篇 |
2017年 | 41篇 |
2016年 | 57篇 |
2015年 | 41篇 |
2014年 | 67篇 |
2013年 | 120篇 |
2012年 | 108篇 |
2011年 | 109篇 |
2010年 | 91篇 |
2009年 | 74篇 |
2008年 | 97篇 |
2007年 | 75篇 |
2006年 | 76篇 |
2005年 | 57篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 40篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 22篇 |
1977年 | 38篇 |
1976年 | 31篇 |
1975年 | 16篇 |
1974年 | 17篇 |
1973年 | 25篇 |
1972年 | 11篇 |
1963年 | 15篇 |
排序方式: 共有1979条查询结果,搜索用时 312 毫秒
71.
72.
73.
74.
75.
76.
BaSeO3·2·5H2O(I), PbSeO3· 2H2O(II) and CdSeO3·3.5H2O(III) were prepared and analysed. Their hygroscopicity and solubility was investigated. These compounds have high thermal Stability, as shown by their TG and DTA data. IR spectra show multi-dentate coordination of selenite to cations, due to considerable splitting of the asymmetric v3 and v4 bands of SeO
3
2
– in the 780-730 cm–1 and 420-325 cm–1 region.Tentative structures have been proposed involving bridging oxygen atoms.
Zusammenfassung BaSeO3-2.5H2O(I), PbSeO3 · 2H2O(II) und CdSeO3· 3.5H2O(III) wurden hergestellt, analysiert sowie deren Hygroskopizität und Löslichkeit untersucht. TG- und DTA-Untersuchungen erweisen die hohe thermische Stabilität dieser Verbindungen. Die IR-Spektren zeigen mehrzählige Koordination von Selenit zu Kationen, was aus einer beträchtlichen Aufspaltung der antisymmetrischenv 3 undv 4 Banden von SeO 3 2 – im Bereich 780-730cm–1 bzw. 420-325 cm–1 hervorgeht. Es wurden versuchsweise Strukturen mit überbrückenden Sauerstoffatomen vorgeschlagen.
BaSeO3· 2,5H2O, PbSeO3 · 2H2O CdSeO3 · 3,5H2O . . - , v 3 v 4 SeO 3 2 }- 780-730 420-325 –1. , .相似文献
77.
A polystyrenedivinylbenzene-based macroreticular resin was functionalised with bis-(N,N'-salicylidene)1,3-propanediamine ligands and its analytical properties have been investigated. The pH dependence of metal resin chelation has been determined for Cu(II), Ni(II), Co(II), Zn(II), Fe(II), Mn(II), Pb(II), Cd(II) and Cr(III). Trace amounts of these metal ions were quantitatively retained on the resin at neutral pH and easily recovered by elution with 1 N hydrochloric acid. The resin exhibits good chemical stability and fast equilibration with the metal ion making it useful for rapid concentration of trace amounts of metal ions on the resin columns. 相似文献
78.
Procedures are described for the determination of organic compounds with iodine trichloride under Andrews's titration conditions. Samples are directly titrated with iodine trichloride or first reacted with an excess of iodine monochloride, with subsequent titration of the iodine formed. The direct titration is done initially in feebly acid medium, then the acidity is raised (biotin, methionine, cystine and thiomersal). Pre-oxidation with iodine monochloride is used if the organic compound reacts slowly [tryptophan and arsenic(III) compounds] or is determined in bicarbonate medium (hydroxylamine and thiosemicarbazide). The ferrocyanide formed by the reduction of ferricyanide (by thiourea and allylthiourea) can also be titrated. Arsenic(V) compounds are determined after reduction to arsenic(III), and iodine in organic compounds is converted into iodide by alkaline fusion into iodide and the iodide titrated. 相似文献
79.
S. B. Manohar S. K. Aggarwal S. M. Deshmukh A. R. Parab P. P. Burte H. C. Jain Satya Prakash 《Journal of Radioanalytical and Nuclear Chemistry》1981,63(1):145-153
A gamma-spectrometric method using an intrinsic high resolution germanium detector has been developed for the determination
of isotope ratios of plutonium from samples in solution form. The method is based on the assay of low energy gamma-rays of238Pu,239Pu,240Pu and241Pu and does not require the use of branching intensities or the knowledge of detection efficiencies for different gamma rays.
Since low energy gamma-rays are used, the effect of241Am has also been studied. It is found that results are not affected up to 0.5 wt% of241Am in plutonium samples. An accuracy of 3% is achievable in the determination of240Pu/239Pu and241Pu/239Pu atom ratios as demonstrated by carrying out measurements on isotopic standards of plutonium. 相似文献
80.
Aromatic primary amines are determined by injection into dilute hydrochloric acid carrier which merges sequentially with 4-N-methylaminophenol and dichromate. The purple-red color formed by oxidative coupling of amines with 4-N-methylaminophenol is measured at 530 nm. In contrast to the manual procedure, the flow-injection procedure avoided errors arising from the instability of the coupling intermediate, oxidation of the amine, and too great an excess of the oxidant. The method improves the selectivity for certain amines in the presence of those which are sterically hindered or have an electron-deficient aromatic nucleus. Nitrite is determined by diazotization of sulfanilamide and quantifying the residual sulfanilamide by oxidative coupling. The sample thourghout for the assay of amines (0.05–20 μg ml?1 NH2-N) and nitrite (1–10 μg ml?1 NO2--N) was 120 h?1. A system for the consecutive determination of aromatic primary amines and nitrite is decribed. 相似文献