全文获取类型
收费全文 | 811篇 |
免费 | 23篇 |
国内免费 | 6篇 |
专业分类
化学 | 629篇 |
晶体学 | 14篇 |
力学 | 18篇 |
数学 | 61篇 |
物理学 | 118篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 18篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 42篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 40篇 |
2004年 | 27篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1972年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有840条查询结果,搜索用时 31 毫秒
41.
42.
The formation of a pink-coloured product when rhodamine 6G is treated with tetraiodomercurate(II) is used to determine mercury (5–25 μg) in a final volume of 25 ml. The reaction occurs immediately over the pH range 1–7 and, when the system is stabilized with gelatin, the absorbance remains unchanged at 575 nm for at least 24 h. The few interfering ions can be masked by the addition of appropriate reagent solutions. The method is simple and reliable and provides a molar absorptivity of 7.0·104 l mole-1 cm-1. 相似文献
43.
B. N. Lakshminarayana C. R. Gnanendra T. N. Mahadeva Prasad M. A. Sridhar Nagaraja Naik D. Chenne Gowda J. Shashidhara Prasad 《Journal of chemical crystallography》2010,40(8):686-690
Abstract
The novel 3-methyl-2,6-dip-toylpiperidine-4-one was acylated by 3-chloropropanoychloride and subjected for dehydrohalogenation. The synthesized compound was characterized by spectroscopic techniques and finally confirmed by X-ray diffraction studies. The molecule crystallizes in the monoclinic crystal class in the space group C 2/c with cell parameters a = 18.538(2) ?, b = 9.9050(1) ?, c = 22.954(2) ?, β = 94.486(8)° and Z = 8. The piperidine ring adopts a twist boat conformation. 相似文献44.
Dihalobridged binuclear complexes [Rh(diolefin)(μ-X)]2 {diolefin = 1,5-cyclooctadiene (cod), X = Cl or Br; diolefin = norbornadiene (nbd), X = Cl}, undergo halide bridge cleavage reactions with multidentate N,N-heterocycles 1,3,5-tris(benzimidazolyl)benzene (L1H3), 1,3,5-tris(N-methylbenzimidazolyl)benzene (L2H3) and N,S-heterocycle 1,3,5-tris(benzothiazolyl)benzene (L3H3) to yield trinuclear heterocycle bridged complexes [{RhX(cod)}3(μ-LH3)] and [{RhCl(nbd)}3(μ-LH3)] (LH3 = L1H3, L2H3, L3H3). 1H NMR exchange measurements have shown resonances for olefinic protons 1″, 2″, 5″ and 6″ of cod at different chemical shifts, perhaps due to restricted Rh–N bond rotation. The olefinic and aliphatic protons would undergo exchange with each other and also with intermediate species. The exchange mechanism may be visualized to involve Rh–N bond breaking, rotation of the cod ligand of the T-shaped (three-coordinate) intermediate species followed by recomplexation. An alternate mechanism may be Rh–cod bond breaking at olefin positions 5″ and 6″, isomerisation of the T-complex such that 5″/6″ moves trans to X coupled with rotation of the heterocycle about the Rh–N bond (made easier by the reduced coordination number of the intermediate), followed by recoordination of 1″/2″ trans to N, followed by recomplexation. NMR signals from the intermediate species in one dimensional 1H, 13C and 2D NMR spectra have supported the exchange of protons. 相似文献
45.
Promethazine hydrochloride forms a red colored species with vanadium(V) in 6.0–7.5 M phosphoric acid. A 16-fold molar excess of the reagent is necessary for full development of color intensity. Beer's law is valid over the concentration range of 0.1–7.0 ppm. The optimum concentration range as evaluated by Ringbom's method is 0.5–7.0 ppm. The sensitivity of the reaction is 0.005 μg cm?2 and the molar absorptivity is 9.60 × 103 liter mol?1 cm?1 at 517 nm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions were reported. Vanadium in vanadium steel containing chromium, molybdenum, manganese, and nickel was determined. 相似文献
46.
47.
P. Prathap N. Revathi Y.P.V. Subbaiah K.T. Ramakrishna Reddy R.W. Miles 《Solid State Sciences》2009,11(1):224-232
Al-doped ZnS films were deposited using close-spaced evaporation of the powders synthesized by chemical precipitation method. The films were prepared for different Al concentrations in the range 0–10 at.% on glass substrates kept at 300 °C. The effect of Al-doping on ZnS composition, microstructure and optoelectronic properties of as-grown ZnS layers was determined using appropriate techniques. The films were polycrystalline and showed (111) preferred orientation for all the doping concentrations in spite of an additional phase of Al2S3 observed at higher dopant levels. The surface morphological studies indicated that the Al incorporation had a considerable effect on the surface roughness of the films. The optical measurements indicated that the optical energy band gap decreased slightly with the increase of dopant concentration without affecting the optical transmittance characteristics significantly. The electrical analysis indicated that the resistivity of the layers changed significantly with the doping concentration in the layers. The change of photoluminescence behaviour of the as-grown ZnS:Al films with dopant concentration was also studied. 相似文献
48.
49.
Ramakrishna Katakam Rajender Anugula Lingamurthy Macha Venkateswara Rao Batchu 《Tetrahedron letters》2017,58(6):559-562
A short and stereoselective synthesis of conduramine F-1 and ent-conduramine E-1 derivatives have been achieved starting from d-mannitol using nucleophilic vinylation on imine. A concise sequence of vinylation at both ends of d-mannitol and followed by RCM allowed us to prepare target compound. 相似文献