全文获取类型
收费全文 | 1746篇 |
免费 | 28篇 |
国内免费 | 4篇 |
专业分类
化学 | 1261篇 |
晶体学 | 11篇 |
力学 | 14篇 |
数学 | 127篇 |
物理学 | 365篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 23篇 |
2017年 | 14篇 |
2016年 | 20篇 |
2015年 | 22篇 |
2014年 | 19篇 |
2013年 | 62篇 |
2012年 | 59篇 |
2011年 | 94篇 |
2010年 | 58篇 |
2009年 | 52篇 |
2008年 | 80篇 |
2007年 | 91篇 |
2006年 | 98篇 |
2005年 | 79篇 |
2004年 | 74篇 |
2003年 | 80篇 |
2002年 | 56篇 |
2001年 | 40篇 |
2000年 | 28篇 |
1999年 | 24篇 |
1998年 | 19篇 |
1997年 | 37篇 |
1996年 | 26篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 31篇 |
1979年 | 35篇 |
1978年 | 27篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1974年 | 17篇 |
1972年 | 11篇 |
排序方式: 共有1778条查询结果,搜索用时 15 毫秒
21.
22.
A chiral HWE reagent reacted with an alternative carbonyl group of meso-α-diketones of bicyclo[2.2.1] system to give non-racemic (Z)- and (E)-olefins, respectively. 相似文献
23.
Isomers of O-alpha-D-glucopyranosyl-(1----6)-O-beta-D-glucopyranosyl- (1----6)-N-[L-aspart-1-oyl-(L-proline)-4-oyl]-alpha-D-glucopyranos ylamine have been prepared, as models for a derivative possibly present in the glomerular basement membrane of rats, by condensation of the corresponding dipeptide derivative (5) with triglycosylamine (4) in the presence of O,O-diethylcyanophosphonate, followed by deprotection of the trisaccharide-dipeptide derivative. During the deprotection process, cis- and trans-isomers containing proline were separated by silica gel column chromatography and also reversed-phase high performance liquid chromatography. 相似文献
24.
Relative concentrations of nine isomers of Ca at C82 derived from the C82 isolated-pentagon-rule satisfying cages are computed in a wide temperature interval. The computations are based on the Gibbs energy constructed from partition functions supplied with molecular parameters from density functional theory calculations. Five structures show significant populations at higher temperatures: C2v > Cs > C2 > C3v > Cs. The computed relative stabilities agree well with available observations. 相似文献
25.
26.
One step syntheses of 3-substituted furans by the reactions of a new reagent, lithium di(3-furyl)cuprate , with various substrates and the application of to a total synthesis of dendrolasin are described. 相似文献
27.
Vanadiuin(V) com: with an acidic hydroxy group attached to the metal form the crorrresponding.; with alcohols. These esters show a characteristic absorption at 445–480 that alcoholic hydroxy groups can be determined photometrically. The formation constant of the n-butanol esters of vanadium maltolate and 2-methyl-.S-hydroxyquinolinate Were determined in benzene or benzenechloroform (1:1). Simple methods are determined for the determination of alcohol in the concentration range 10-1–10-4M. 相似文献
28.
Kojima Kunihiko Miyazaki Mitsuharu Mizukami Fujio Maeda Kazuyuki 《Journal of Sol-Gel Science and Technology》1997,8(1-3):77-81
The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic
polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate
nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe2O3 with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the
calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one
mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe2O3 with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe2O3 appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in
thin films. Thus, a transparent magnetic film composed of γ-Fe2O3 could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz
and calcining the gel film at 350°C. 相似文献
29.
A novel oligothiophene derivative containing the triphenylamine moiety with high glass transition temperature (Tg; 135 °C), 5,5′‐{bis[4‐di(4‐thiophenyl)amino]phenyl}‐2,2′‐bithiophene (TTPA‐dimer) was synthesized by the dimerization of tris[4‐(2‐thienyl)phenyl]amine (TTPA) with a palladium catalysis. Some types of electroluminescent (EL) devices that use the amorphous material for a hole‐ and an electron‐transporting with an emitting layer were fabricated. These devices emitted a bright green‐yellowish light (λemi; around 510 nm) with a small full width at half maximum (FWHM) rather than that of Alq3. The single layer EL device showed a maximum luminance of 221 cd/m2 at 8 V (0.06 lm/W at 100 cd/m2). On the other hand, the double layer (TTPA‐dimer/Alq3) EL device that used Alq3 as the electron transport material was increased up to 10830 cd/m2 at 12 V (0.89 lm/W at 300 cd/m2) and with a lower turn‐on voltage (3.2 V at 0.1 cd/m2) than other types of EL devices. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
30.
Manabu Tanaka Kaoru Hatta Tomohiko Edura Ken Tsutsui Yasuo Wada Hiroyuki Nishide 《先进技术聚合物》2007,18(11):925-931
The electric conductivity of π‐conjugated and radical‐bearing polymers, i.e., polythiophenes bearing pendant galvinoxyl and phenoxyl radical groups, was measured using a microcomb‐shaped electrode. The electric conductivity was found to be enhanced by the radical content in the polymer. The infrared (IR) and Raman spectroscopies suggested a structural change from an aromatic form to a quinoid one in the polythiophene backbone by the phenoxyl radical generation. The effect of the pendant galvinoxyl radical's unpaired electron on the electric conductivity of the polythiophene was discussed by comparing the conductivity of a radical‐bearing polystyrene and a polythiophene mixed with low‐molecular radical molecules. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献