全文获取类型
收费全文 | 161篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
化学 | 92篇 |
力学 | 4篇 |
数学 | 14篇 |
物理学 | 55篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 29篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有165条查询结果,搜索用时 15 毫秒
111.
The polarographic determination of aluminium as its complex with alizarin in the pH range 9.2-10.1, with the cathode ray polarograph, is described. A solvent extraction procedure is used to eliminate interferences from many other metals. 相似文献
112.
Synthetic exploration of K/Cu/Th/S quaternary phase space has yielded three new compounds: KCuThS3 (I), K2Cu2ThS4 (II), and K3Cu3Th2S7 (III). All three phases are semiconductors with optical band gaps of 2.95, 2.17, and 2.49 eV(I-III). Compound I crystallizes in the orthorhombic space group Cmcm with a = 4.076(1) A, b = 13.864(4) A, and c = 10.541(3) A. Compound II crystallizes in the monoclinic space group C2/m with a = 14.522(1) A, b = 4.026(3) A, and c = 7.566(6) A; beta = 109.949(1) degrees . Compound III crystallizes in orthorhombic space group Pbcn with a = 4.051(2) A, b = 14.023(8) A, and c = 24.633(13) A. The compounds are all layered materials, with each layer composed of threads of edge-sharing ThS6 octahedra bridged by CuS4 tetrahedral threads of varying dimension. The layers are separated by well-ordered potassium ions. The relatively wide range of optical band gaps is attributed to the extent of the CuS4 motifs. As the dimension of the CuS4 chains increases, band gaps decrease in the series. All materials were characterized by single-crystal X-ray diffraction, microprobe chemical analysis, and diffuse reflectance spectroscopy (NIR-UV). 相似文献
113.
[structure: see text] Triamino-s-triazine derivatives 3a, 4, and 5 have been prepared, and their cationic states have been analyzed electrochemically. At 298 K, 3a+ has a limited lifetime in CH2Cl2 solution. However, 4+ and 5+ are long-lived under such conditions, and quartet states of 4(3+) and 5(3+) are observed by ESR spectroscopy. Variable-temperature ESR analysis and NMR shift susceptibility measurements indicate that 5(3+) is a doublet ground state with a populated quartet state. 相似文献
114.
A nearlattice S is a meet semilattice together with the property that any two elements possessing a common upper bound have a supremum. Here the authors have introduced the notion of sectionally semicomplemented distributive nearlattices and given several characterizations of them. The skeleton SCon(S) of Con(S), the congruence lattice, consists of all those nearlattice congruences which are the pseudocomplements of members of Con(S). The relationship between skeletal congruences and kernel of skeletal congruences leads to numerous characterizations of sectionally semicomplemented distributive nearlattices and semiboolean algebras. For example we prove, for a distributive nearlattice S with 0, the following conditions are equivalent:
AMS Subject Classifications (1991): 06A12, 06A99, 06B10. 相似文献
(i) | S is sectionally semicomplemented |
(ii) | The map Θ Θ ̸ker Θ of SCon(S) onto KSCon(S) is one-to-one. |
(iii) | The map Θ Θ ̸ker Θ of SCon(S) onto KSCon(S) preserves finite joins. |
(iv) | The map Θ Θ ker ̸Θ is a lattice isomorphism of SCon(S) onto KSCon(S), whose inverse is the map J ̸ Θ(J)**. |
115.
116.
The dose-response relationship for photomutation (i.e. photosensitized mutation) by a shale-derived oil was examined. The Ames' Salmonella typhimurium tester strain TA98 was exposed to several concentrations of an Eastern shale oil and UV-visible radiation from illumination-type fluorescent lamps. Reversion to histidine prototrophy and survival were assayed following various radiation doses. Reciprocity of shale oil concentration and radiation exposure over approximately 10-fold ranges of oil concentrations and radiation doses was observed with revertant numbers per plate, percent survival, and the induced frequency of revertants (revertants per survivor). The relationship between mutation frequency and the product (shale oil concentration times radiation exposure) fit well with either a linear model or a power law model in which the frequency of induced mutations was described by the product dose raised to the 1.26th power. Similar dose-response relationships provide potential criteria for comparing potency of photomutagenic substances, comparisons that may be valuable towards assessing, and perhaps modifying, risks imposed by human exposure to synthetic fuels. 相似文献
117.
A magnetized Iron CALorimeter (ICAL) detector at the India-based neutrino observatory (INO) is used to study neutrino oscillation sensitivity using atmospheric muon neutrino source. The ICAL detector will be able to detect muon tracks and hadron showers produced by neutrino interactions with the iron target. We have performed precision measurement analysis for the atmospheric neutrino oscillation parameters with the muon neutrino events, generated by Monte Carlo NUANCE event generator. A marginalized χ2 analysis based on reconstructed neutrino energy and muon zenith angle binning scheme has been performed to determine the sensitivity for the atmospheric neutrino mixing parameters, \(\sin ^{2}\theta _{23}\) and \(| {\Delta } m^{2}_{23}|\). 相似文献
118.
Nitrosation of hydrazino substituted thiazole-4-acetates has been shown to occur on the ring, rather than the α-methylene carbon, as previously reported. Thus nitrosation of ethyl 2-isopropylidenehydrazono-, 2-benzylidenehydrazono-, 2-(2-benzoylhydrazino)-, and 2-(2-acetylhydrazino)thiazole-4-acetates yielded the corresponding 2-hydrazino-4-carbethoxymethylidene-4,5-dihydrothiazoline-5-oximes. Basic hydrolysis of the thiazoline-5-oxime esters, followed by decarboxylation gave tautomeric mixtures of the 2-hydrazino-4-methyl-2,5-dihydrothiazoline-5-oxime and 2-hydrazino-4-methyl-5-nitrosothiazol derivatives. These tautomeric mixtures were also prepared by nitrosating the 2-hydrazino-4-methylthiazoles. The α,β-unsaturated acids, 2-isopropylidenehydrazono-, 2-benzylidenehydrazono-, and 2-(2-benzoyl-hydrazino)-4-carboxymethylidene-4,5-dihydrothiazoline, were isolated after basic hydrolysis of the corresponding 2-hydrazinothiazole-4-acetic esters. Dinitrosation of the 2-isopropylidenehydrazono-4-carboxy-methylidene-4,5-dihydrothiazoline, followed by decarboxylation, generated 2-isopropylidenehydrazono-5-nitrosothiazole-4-formyloxime. 相似文献
119.
120.