全文获取类型
收费全文 | 1355篇 |
免费 | 95篇 |
国内免费 | 41篇 |
专业分类
化学 | 895篇 |
晶体学 | 13篇 |
力学 | 12篇 |
综合类 | 3篇 |
数学 | 167篇 |
物理学 | 401篇 |
出版年
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 26篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 34篇 |
2015年 | 47篇 |
2014年 | 36篇 |
2013年 | 95篇 |
2012年 | 87篇 |
2011年 | 81篇 |
2010年 | 65篇 |
2009年 | 72篇 |
2008年 | 99篇 |
2007年 | 89篇 |
2006年 | 84篇 |
2005年 | 89篇 |
2004年 | 56篇 |
2003年 | 43篇 |
2002年 | 44篇 |
2001年 | 43篇 |
2000年 | 45篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有1491条查询结果,搜索用时 0 毫秒
21.
22.
J. Nilsen J. C. Moreno B. J. MacGowan J. A. Koch 《Applied physics. B, Lasers and optics》1993,57(5):309-311
We report lasing for the first time in nickel on the neon-like J=01, 3p3s transition at 231 Å as well as several weaker transitions including the J=2»1 lines at 298 Å and 304 Å. Amplification is seen only when the prepulse technique of using a low intensity prepulse before the main optical drive pulse is used to illuminate the nickel target. The prepulse technique is also shown to produce lasing in copper and dramatically improve the output of the germanium laser. 相似文献
23.
24.
A simple and very sensitive spectrophotometric method for the direct determination of copper ions 总被引:1,自引:0,他引:1
A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%. 相似文献
25.
高效液相色谱氮杂冠醚键合固定相的合成及性能研究 总被引:2,自引:0,他引:2
我们曾用γ-氯丙基键合硅胶(CPS),在氢化钠(NaH)作用下合成了3-(氮杂-18-冠-6)丙基键合固定相(BCP)[1].该固定相对碱基、核苷酸、硝基苯酚等有较好的分离选择性,但由于NaH对硅胶基质腐蚀作用较大,导致BCP柱效及渗透性较低.本文采... 相似文献
26.
Moreno M. M. Torres Santos R. H. A. Gambardella M. T. P. Camargo A. J. da Silva A. B. F. Trsic M. 《Structural chemistry》1998,9(5):365-373
The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, l-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitroindoline, and l-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species. 相似文献
27.
Pérez Pavón JL Guerrero Peña A García Pinto C Moreno Cordero B 《Journal of chromatography. A》2004,1047(1):101-109
The direct coupling of a headspace sampler with a mass spectrometer is proposed as a screening tool for the rapid detection of soil pollution by hydrocarbons from petroleum and derivatives. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of the sample analysed. Suitable treatment of the signal by chemometric techniques allows unequivocal characterisation of the different types of sample. The use of fast gas chromatography with a mass spectrometer detector coupled to the headspace sampler allows identification of the major hydrocarbons present in the mineral and organic polluted samples, interpretation of the results obtained, and demonstrates the analytical potential of headspace-mass spectrometry coupling. 相似文献
28.
Luís J. Moreno López Manuel Callejón Mochón Juán C. Jiménez Sánchez Alfonso Guiraúm Pérez 《Mikrochimica acta》1996,124(3-4):187-194
A method for the determination of salicylaldehyde (2 × 10–6–10–4
M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10–5
M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid. 相似文献
29.
Juan Manuel Ortiz-Sánchez Ricard Gelabert Miquel Moreno José M Lluch 《Chemphyschem》2007,8(8):1199-1206
The two isoelectronic bipyridyl derivatives, [2,2'-bipyridyl]-3,3'-diamine and [2,2'-bipyridyl]-3,3'-diol, are experimentally known to undergo very different excited-state double-proton-transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. Herein, density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations are used to study the double-proton-transfer processes in the ground and first singlet pi-->pi* excited state. The quantum-chemistry calculations indicate 1) the existence of only one energy minimum in the ground electronic state corresponding to reactants (thus avoiding the possibility of a fast fluorescent relaxation process from the photoproducts region), 2) an endoergic process of the complete double proton transfer, and 3) the presence of a conical intersection in the excited intermediate region of [2,2'-bipyridyl]-3,3'-diamine. These facts explain the very low fluorescence quantum yield in [2,2'-bipyridyl]-3,3'-diamine compared to [2,2'-bipyridyl]-3,3'-diol. 相似文献
30.
Avelina Arnanz Consuelo Moreno Allan J. Lough Salomé Delgado 《Journal of organometallic chemistry》2004,689(20):3218-3231
The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co2(CO)8 or Co2(CO)6(X), (X = dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co2(CO)6 or Co2(CO)4(X) units, 2-[Co2(CO)4(X){μ2-η2-(SiMe3)C2}]-5-(Me3SiCC)C4H2S (X = 2CO (1), dppa (3) or dppm (4)) and 2,5-[Co2(CO)4(X){μ2-η2-SiMe3C2}]2C4H2S (X = 2CO (2), dppa (5) or dppm (6)). Desilylation of the non-metallated and metallated alkynes in 3, 4 and 6 occurred on treatment with KOH and tetrabutylammonium fluoride to give 2-[Co2(CO)4(μ-X){μ2-η2-SiMe3C2}]-5-(CCH)C4H2S (X = dppa (7), dppm (8)) and 2,5-[Co2(CO)4(μ-dppm){μ2-η2-HC2}]2C4H2S (9), respectively. Crystals of 6 suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed. A comparative electrochemical study of all these complexes is presented by means of the cyclic and square-wave voltammetry techniques. 相似文献