全文获取类型
收费全文 | 1956篇 |
免费 | 63篇 |
国内免费 | 26篇 |
专业分类
化学 | 1516篇 |
晶体学 | 27篇 |
力学 | 43篇 |
数学 | 70篇 |
物理学 | 389篇 |
出版年
2022年 | 14篇 |
2020年 | 13篇 |
2019年 | 25篇 |
2018年 | 16篇 |
2017年 | 20篇 |
2016年 | 25篇 |
2015年 | 45篇 |
2014年 | 32篇 |
2013年 | 89篇 |
2012年 | 88篇 |
2011年 | 93篇 |
2010年 | 46篇 |
2009年 | 49篇 |
2008年 | 130篇 |
2007年 | 102篇 |
2006年 | 128篇 |
2005年 | 108篇 |
2004年 | 102篇 |
2003年 | 71篇 |
2002年 | 81篇 |
2001年 | 51篇 |
2000年 | 46篇 |
1999年 | 35篇 |
1998年 | 21篇 |
1997年 | 26篇 |
1996年 | 28篇 |
1995年 | 18篇 |
1994年 | 30篇 |
1993年 | 17篇 |
1992年 | 31篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 36篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 26篇 |
1975年 | 18篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1971年 | 15篇 |
1968年 | 11篇 |
排序方式: 共有2045条查询结果,搜索用时 15 毫秒
51.
Control of viscoelasticity using redox reaction 总被引:1,自引:0,他引:1
Tsuchiya K Orihara Y Kondo Y Yoshino N Ohkubo T Sakai H Abe M 《Journal of the American Chemical Society》2004,126(39):12282-12283
The viscoelasticity of a fluid was tuned with the Faradaic reaction of (11-ferrocenylundecyl)trimethylammonium bromide (FTMA), a "redox-switchable" surfactant. An aqueous solution of the reduced form of FTMA exhibited a remarkable viscoelasticity in the presence of sodium salicylate (NaSal) because of the formation of three-dimensional entanglement of wormlike micelles. Electrolytic oxidation of FTMA caused the viscosity of the system to dramatically decrease and the elasticity to disappear. This drastic decrease in viscoelasticity arose from the disruption of wormlike micelles. This novel electrorheological phenomenon is expected to be applicable to ink for inkjet printers, the electrochemically controlled release of substances entrapped in wormlike micelles of FTMA, and fluid flow rate control using electric signals. 相似文献
52.
Naoki KakusawaYoshinori Tobiyasu Shuji YasuikeKentaro Yamaguchi Hiroko SekiJyoji Kurita 《Tetrahedron letters》2003,44(47):8589-8592
The reaction of 12-arylethynyl-6-methyl-5,6,7,12-tetrahydrodibenzo[c,f][1,5]-azastibocines with organic halides such as acyl halides and aryl halides in the presence of PdCl2(PPh3)2 as a catalyst led to the formation of cross-coupling products, alkynyl ketones and diaryl acetylenes, in good yields. The reactivity of the ethynyl group on the 1,5-azastibocines was far superior to that on diphenyl(phenylethynyl)stibane, which brought about marked improvement in the reaction conditions (lower temperature and shorter reaction time) and in the yields of the cross-coupling products. Single-crystal X-ray analysis of the ethynyl-1,5-azastibocine showed the presence of intramolecular Sb?N interaction which should be responsible for the remarkable reactivity enhancement of the 1,5-azastibocines for this type of reaction. 相似文献
53.
Y. Kondo M. Matsumura M. Kubota 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(2):311-320
The acidity change and solid formation in a simulated high level liquid waste (HLLW) containing precipitate were experimentally examined, when the acidity was reduced from 2M to 0.5M by denitration or simple dilution. The acidity of the simulated HLLW containing precipitate could be adjusted from 2M to around 0.5M by means of denitration or dilution, as well as the case of simulated HLLW without precipitate. The precipitation fractions of Zr, Mo and Te during denitration decreased with increasing amount of the precipitate already contained in the simulated HLLW. The amount of solid formed in the dilute simulated HLLW also decreased with increasing amount of precipitate in the simulated HLLW. Two process flow sheets for preparing HLLW for transuranic elements extraction were developed. One was a denitration process and the other a dilution process. 相似文献
54.
Shuji Saito 《Colloid and polymer science》1982,260(6):613-615
Zusammenfassung Das Vorkommen der Ausfällung zwischen Polykarbonsäuren und nichtionischen Polymeren im Wasser wurde durch Zufügung der Tenside (anionisch, kationisch und nichtionisch) beeinflußt. Die Grenzkonzentrationen der Tenside für Auflösung wasserunlöslicher Komplexe von Polymersäuren (Polyakryl- und Polymethakrylsäure) und Polyvinylpyrrolidon (PVP) wurden bestimmt und in Bezug auf die Wechselwirkungen zwischen je zwei Komponenten im ternären System, d. i., Tensid-Polymersäure, Tensid-PVP, und Polymersäure-PVP, erläutert.
The precipitation formation between polycarboxylic acids and nonionic polymers in water was suppressed by addition of surfactants (anionic, cationic and nonionic). The critical surfactant concentrations needed for dissolving the precipitates were determined about the water-insoluble complexes of polymeric: acids (polyacrylic and polymethacrylic acids) with polyvinylpyrrolidone (PVP). The results were discussed with regard to each two component interaction in the ternary system, i. e., surfactant-polymeric acid, surfactant-PVP, and polymeric acid-PVP.相似文献
55.
A number of nitrato complexes of metals have been found to be adsorbed on DEAE-cellulose from mixed acetic acid-nitric acid media, although none can be adsorbed from aqueous nitric acid solutions. The distribution coefficients of Sc, Mo, La, Sm, W, Re, Bi, Th and U are given as functions of acetic acid and nitric acid concentrations (sometimes in the presence of hydrogen peroxide to prevent hydrolytic precipitation). For 25 other metals column adsorption behaviour is described for a 90% acetic acid-10% 7.6M nitric acid mixture. Favourable differences in the distribution coefficients allow useful separations such as FeMoW and USmMoBiTh, to be achieved. 相似文献
56.
A. Fukumi I. Endo T. Horiguchi Y. Ishida T. Kondo T. Kuwamoto H. Matsuzaki T. Nakamura T. Takahashi 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,42(4):243-249
Systematic study of hyperfine structures, Zeeman and Stark effects in Sm I is performed for the lowest 7G1-6 levels belonging to the configuration 4f 66s6p by atomic-beam laser spectroscopy with fluorescence detection. The hyperfine coupling constants of 7G2-6 levels are determined. From the Zeeman splittings for the 4f 66s 2 7F2-6 ? 4f 66s6p 7G2-6 transitions, g-values are determined for the 7G2.6 levels and the precision is improved by several orders of magnitude. From the Stark splittings for the 7F0-3 ? 7G1-3 transitions, tensor polarizabilities α 2(J) are determined for the upper 7G1-3 levels. Particularly for the 7G1 level (15 650.55 cm?1) which has close-lying opposite-parity level, the isotope dependence of α 2(J) is clearly observed for the first time. 相似文献
57.
乙醇羰化反应负载型催化剂的研究 总被引:9,自引:0,他引:9
本文由七种负载型催化剂中选出两种比较好的乙醇羰化催化剂,研究了影响反应转化率和选择性的因素,考察了活性组份的价态和载体的酸性。此外,还对催化剂进行了能量色散X射线分析。从其结果看,谱图上只有活性中心铑的谱峰而没有氯的谱峰,说明铑是以离子形式进入载体,而不是以化合物形式被吸附于载体上。 相似文献
58.
Tsujita H Ura Y Wada K Kondo T Mitsudo TA 《Chemical communications (Cambridge, England)》2005,(40):5100-5102
2-(1-Alkoxycarbonyl)alkylidenetetrahydrofurans were readily synthesized by the codimerization of 2,3- or 2,5-dihydrofurans with alpha,beta-unsaturated esters using a zerovalent Ru catalyst, Ru(cod)(cot), with high regio- and stereoselectivity. 相似文献
59.
Ishikawa A Takata T Kondo JN Hara M Kobayashi H Domen K 《Journal of the American Chemical Society》2002,124(45):13547-13553
A Ti-based oxysulfide, Sm(2)Ti(2)S(2)O(5), was studied as a visible light-driven photocatalyst. Under visible light (440 nm < or = lambda < or = 650 nm) irradiation, Sm(2)Ti(2)S(2)O(5) with a band gap of approximately 2 eV evolved H(2) or O(2) from aqueous solutions containing a sacrificial electron donor (Na(2)S-Na(2)SO(3) or methanol) or acceptor (Ag(+)) without any noticeable degradation. This oxysulfide is, therefore, a stable photocatalyst with strong reduction and oxidation abilities under visible-light irradiation. The electronic band structure of Sm(2)Ti(2)S(2)O(5) was calculated using the plane-wave-based density functional theory (DFT) program. It was elucidated that the S3p orbitals constitute the upper part of the valence band and these orbitals make an essential contribution to the small band gap energy. The conduction and valence bands' positions of Sm(2)Ti(2)S(2)O(5) were also determined by electrochemical measurements. It indicated that conduction and valence bands were found to have satisfactory potentials for the reduction of H(+) to H(2) and the oxidation of H(2)O to O(2) at pH = 8. This is consistent with the results of the photocatalytic reactions. 相似文献