全文获取类型
收费全文 | 763篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 418篇 |
晶体学 | 6篇 |
力学 | 2篇 |
数学 | 92篇 |
物理学 | 253篇 |
出版年
2022年 | 4篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 31篇 |
2010年 | 21篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 39篇 |
2006年 | 43篇 |
2005年 | 41篇 |
2004年 | 31篇 |
2003年 | 22篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 16篇 |
1999年 | 7篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1974年 | 12篇 |
1973年 | 5篇 |
1943年 | 3篇 |
1933年 | 3篇 |
1928年 | 5篇 |
1926年 | 6篇 |
1925年 | 5篇 |
1923年 | 4篇 |
1922年 | 4篇 |
排序方式: 共有771条查询结果,搜索用时 31 毫秒
41.
Special aspects of ion-selective electrodes relevant to applications in flow-through systems are discussed. The predominant role of the dynamic response characteristics of the sensor, especially in flow-injection analysis, is emphasized. Indirectly, these characteristics can affect the linear response range, the detection limit and the selectivity properties of the sensors. As examples, flow-injection methods are described for the determination of fluoride in rain-water samples and of potassium ion activity in blood sera. 相似文献
42.
E. Krös L. Ladányi V. Friedrich Zs. Nagy Á. Kis 《Reaction Kinetics and Catalysis Letters》1974,1(4):455-460
The Ru(dipy)
3
2+
-bromate-malonic acid oscillating system was in vestigated. It has been established that at early stages of the reaction the period of oscillation is about 20 sec and the potential change is about 170 mV; chloride at concentrations hiherg than 10–3M is an inhibitor. The rates of both heat evolution and formation of bromomalonic acid are periodic. The activation energy of the oscillating (E) is 16.2 kcal mol–1. Ru(dipy)
3
2+
-- . , 20 , 170 ; , - 10–3 M, . . (E) 16,2 /. 相似文献
43.
A chelate-forming cellulose, iminodiacetic acid/ethylcellulose (IDAEC), is applied to the collection of metals from ammonium citrate and acetate solutions. A method is devised for the i.c.p./a.e.s. determination of metal contaminants in magnesium by separation and preconcentration of the metals with IDAEC. 相似文献
44.
The fragmentation patterns of selected glycosidic linkage containing non-reducing (methylmannoside, methylgalactoside, lactitol, sucrose, trehalose, raffinose, erlose, melezitose) and reducing saccharides (maltose, cellobiose, lactose, melibiose, palatinose, primeverose, rutinose) have been compared as their trimethylsilyl and as their trimethylsilyl-oxime derivatives. Fragmentation characteristics of the glycosidic linkage containing trimethylsilyl-oxime derivatives have been investigated at the first time: these spectra are not available in the official libraries (NIST, Wiley). Applying gas chromatography-ion trap mass spectrometry, informative fragments of high masses with high intensities have been obtained. Results confirmed characteristic differences between the simple trimethylsilyl derivative providing non-reducing glycosides and the trimethylsilyl, syn and antioxime species. Fragmentation starts at the glycosidic linkage resulting in the case of the non-reducing di- and trisaccharides in two, identical fragments of ring structure, with the abundant selective fragment ion at m/z=361. In the case of reducing disaccharides fragmentation provides two different moieties: one moiety of ring structure at m/z=361, and one of the open chain trimethylsilyl-oxime moiety with two special fragment ions at m/z=361 and at m/z=538. These fragmentation patterns proved to be independent on the position of the glycosidic linkage. Distribution of the selective fragment ions, obtained from their total ion current elutions, was evaluated on a quantitative basis, expressed in percentages of the total of ions formed. Reproducibility in the formation of these selective fragment ions, depending on their amount to be fragmented, proved to be proper for identification and quantitation purposes, equally. On this basis, in addition to the authentic ones, also two reducing disaccharides (primeverose and rutinose), as authentic compounds not available on the market, were identified and quantified in natural matrices. 相似文献
45.
Wipf P Coleman CM Janjic JM Iyer PS Fodor MD Shafer YA Stephenson CR Kendall C Day BW 《Journal of combinatorial chemistry》2005,7(2):322-330
Cascade reactions of internal and terminal alkynes, zirconocene hydrochloride, dimethylzinc, and phosphinoyl imines (prepared in one step from aldehydes and diphenylphosphinoyl amide) lead to allylic phosphinoyl amides after aqueous workup. Microwave acceleration allows the completion of this one-pot reaction sequence in 10 min. These allylic amides can be converted into a variety of derivatives, including carbamates and sulfonamides, or reacted prior to workup with diiodomethane to give novel C-cyclopropylalkylamides. A solution-phase "libraries from libraries" approach was used to generate an intermediate 20-member library which was subsequently expanded to a 100-member library by a series of N-functionalizations. The biological activity was evaluated in an assay for competitive binding to the estrogen receptor (ERalpha), revealing three potent lead compounds of a new structural type. 相似文献
46.
The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation
behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was
used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh4). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min.
The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation
was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte
loss was observed for EtHg after 2 minutes at 40 W of microwave power.
Awarded a Poster Prize on the occasion of the European Winter Conference on Plasma Spectrochemistry, February 2005, Budapest,
Hungary 相似文献
47.
Abstract Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl4/methylcyclohexane:methyl chloride (60:40 v:v)/ ?80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the Mn of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the Mn of the PSt segment reaches ~ 5,000, and it is complete when the Mn reaches ~ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization. 相似文献
48.
I. Lukovits J. Fodor Á. Gömöry K. István G. Keresztury L. Kótai 《SAR and QSAR in environmental research》2013,24(3):323-335
The presence and absence of alkane isomers in petroleum and petroleum derivatives depend on the complexity of these structures. It was assumed that the more complex the structure is the less probable it is that that the molecule can be detected in any petroleum derivative. Complexity is a vague concept, which has not been defined in quantitative terms yet, and therefore there is no experimental method, which could be used to determine ‘complexity’. Mass spectrometry and infrared spectroscopy in combination with gas chromatography were used to identify the various structural isomers of alkanes in petroleum ether. The isomers were categorised in quantitative terms by using topological indices and linear discriminant analysis. It was found that alkanes possessing a more complex, highly branched structure are less probable to be detected in petroleum ether than isomers with a simpler backbone structure. It was proposed that the experimental ‘measure’ of the complexity of isomeri should be proportional to 1/Ci , where Ci , denotes the concentration of isomeri in a (primary) petroleum derivative. 相似文献
49.
I. Petneházy Zs. M. Jászay Gy. Keglevich L. Toke 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract Reaction of trialkyl phosphites 1 with α,β-unsaturated oxo-compounds 2 gives oxaphospholenes 3 or/and two types of Arbuzov products, γ-keto-phosphonates 4 and alkyl-enol-ethers 5. 相似文献
50.
Zs. Sándor S. Tölgyesi I. Gresits M. Káplán-Juhász 《Journal of Radioanalytical and Nuclear Chemistry》2000,246(2):385-389
Energy-dispersive X-ray fluorescence spectrometry was applied for the analysis of historical silver coins to determine the elemental composition in a fast and non-destructive way. Ag, Cu and trace elements (V, Cr, Mn, Fe, Co, Ni, Hg, Pd, Zr, Mo, Rh, Ru) were determined in coins of King Mathias (Hungary, 1458–1490). A new data evaluation technique was used to avoid the problems arising from the different sizes, surfaces and geometries. The appropriateness of this method was confirmed by analysing certified silver/copper standard alloys. 相似文献