全文获取类型
收费全文 | 849篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 698篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 70篇 |
物理学 | 100篇 |
出版年
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 33篇 |
2012年 | 44篇 |
2011年 | 59篇 |
2010年 | 31篇 |
2009年 | 29篇 |
2008年 | 48篇 |
2007年 | 64篇 |
2006年 | 61篇 |
2005年 | 39篇 |
2004年 | 48篇 |
2003年 | 46篇 |
2002年 | 47篇 |
2001年 | 7篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 18篇 |
1995年 | 4篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有877条查询结果,搜索用时 31 毫秒
161.
We investigated the simultaneous chiral separation of nine amphetamine type stimulants (dl-norephedrine, dl-norpseudoephedrine, dl-ephedrine, dl-pseudoephedrine, dl-amphetamine, dl-methamphetamine, dl-methylenedioxyamphetamine (MDA), dl-methylenedioxymethamphetamine (MDMA), and dl-methylenedioxyethylamphetamine (MDEA)) by capillary electrophoresis using highly sulfated gamma-cyclodextrin (SU(XIII)-gamma-CD) as a chiral selector. Three different approaches using SU(XIII)-gamma-CD with 50 mM phosphate background electrolyte were designed; (I) high CD concentration (10 mM SU(XIII)-gamma-CD) at neutral pH (pH 7.0) in the normal polarity mode, (II) low CD concentration (1.0 mM) at low pH (pH 2.6) in the normal polarity mode and (III) high CD concentration at low pH (pH 2.6) in the reversed-polarity mode. In mode (II), the effects of adding three neutral CDs (beta-CD, dimethyl-beta-CD and hydroxypropyl-beta-CD) were also investigated. The best separation was obtained after optimizing mode (III) as follows: run buffer of 10 mM SU(XIII)-gamma-CD with 50 mM phosphate background electrolyte at pH 2.6, applied voltage of -12 kV and capillary temperature of 15 degrees C. 相似文献
162.
Takushi Nagata Kiyoaki D. Sugi Kiyotaka Yorozu Tohru Yamada Teruaki Mukaiyama 《Catalysis Surveys from Japan》1998,2(1):47-57
Optically active aldiminato cobalt(II) complexes have been found to catalyze the enantioselective reduction of ketones with sodium borohydride affording the corresponding optically active secondary alcohols in high chemical yields with high enantioselectivities. The enantioselective borohydride reduction is also applicable to not only C=O bonds in aromatic ketones but also to C=N bonds in aromatic imines. 相似文献
163.
A sensitive and selective column adsorption method is proposed for the off-line preconcentration and determination of phthalic acid esters (PAEs), namely benzyl-butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di-cyclohexyl phthalate (DCHP). The PAEs was preconcentrated on Saccharomyces cerevisiae immobilized on silica gel and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analytes were investigated. Recoveries of BBP, DBP and DCHP were 100±2, 98±2 and 98±3%, respectively, at 95% confidence level under optimum conditions. The detection limits (3S/N) of BBP, DBP and DCHP were 3.2, 6.3 and 3.1 μg l−1, respectively. The capacity of the adsorbent was also examined and found to be 1.4 mg g−1 for BBP and DBP, and 3.6 mg g−1 for DCHP. S. cerevisiae immobilized on silica gel is suitable for repeated use without decreasing recovery up to about 25 adsorption-elution cycles. The proposed method was successfully applied to the determination of PAEs in river water with high precision and accuracy. 相似文献
164.
Syntheses and pH dependent electrochemical properties of aqua-ruthenium(II) complexes, [Ru(trpy)(PDA-N,N')(OH2)](ClO4)2 ([1](ClO4)2) and [Ru(trpy)(PD-N,N')(OH2)](ClO4)2 ([2](ClO4)2) (trpy = 2,2':6',2'-terpyridine, PDA = 6-acetonyl-6-hydroxy-1,10-phenanthroline-5-one, PD = 1,10-phenanthroline-5,6-dione) are presented. Treatment of [Ru(trpy)(PD-N,N')Cl](PF6) with AgClO4 in a mixed solvent of acetone and H2O selectively produced the acetonyl-PD complex [1](ClO4)2, and the similar treatment in a mixed solvent of 2-methoxyethanol and H2O gave the PD complex [2](ClO4)2. The molecular structures of both complexes were determined by X-ray structural analysis. The proton dissociation constants of various oxidations state of [1]2+ and [2]2+ were evaluated by simulation of E(1/2) values of those redox potentials depending on pH. The simulation revealed that the acetonyl-PD complex [1]2+ underwent successive Ru(II)/Ru(III) and Ru(III)/Ru(IV) redox couples though the two redox reactions were not separated in the cyclic voltammograms. The redox behavior of [2]2+ in H2O is reasonably explained by not only the similar successive metal-centered redox reactions but also simultaneous two-electron quinone/catechol redox couple of the PD ligand including the contribution of hydration on a carbonyl carbon. 相似文献
165.
Chizuko Shichijo Tohru Hamada Christopher B. Johnson Tohru Hashimoto † 《Photochemistry and photobiology》1996,63(3):328-335
Abstract— Effects on phytochrome-mediated anthocyanin synthesis of moderately low temperature (MLT) given during the preirradiation culture period were studied with seedlings of broom sorghum ( Sorghum bicolor Moench, cvs. Acme Broomcorn and Sekishokuzairai-Fukuyama). Seedlings were grown in the dark at 20°C (MLT) and 24°C (control). The MLT treatment strikingly enhanced the action induced by a red light (R) pulse above ca 200 μmol m−2 and suppressed the action induced by an R pulse below ca 30 μmol m−2 and by a far-red light (FR) pulse alone. We refer to these MLT-affected distinct responses as "high-Pfr/Ptot response" and "low-Pfr/Ptot response," as they have features different from the high-irradiance and very-low-fluence responses, respectively. The destruction rate of spectroscopically detectable phytochrome (phyA) and the time course of escape of anthocyanin synthesis from FR reversibility did not match, and hence the possibility of phyA being involved in high-Pfr/Ptot response was rejected, although it might be involved in low-Pfr/Ptot response. Possible mechanisms for the two distinct phytochrome responses are discussed. 相似文献
166.
[reaction: see text] The optically active beta-ketoiminato cationic cobalt(III) complexes were employed as efficient Lewis acid catalysts for the enantioselective 1,3-dipolar cycloaddition reaction of alpha,beta-unsaturated aldehydes with nitrones. Excellent endo selectivities and high enantioselectivities were achieved in the cycloaddition reaction of 1-cyclopentene-1-carbaldehyde and the nitrones derived from 2-halobenzaldehyde. 相似文献
167.
[structure: see text] An enantioselective total synthesis of aspidophytine is described. The indole fragment bearing a cis-alkene substituent was efficiently prepared through radical cyclization of a 2-alkenylphenylisocyanide followed by Sonogashira coupling of the generated 2-iodoindole derivative with a functionalized acetylene unit. After formation of the 11-membered cyclic amine, the aspidosperma skeleton and lactone ring were constructed to complete the total synthesis. 相似文献
168.
Tohru Sakakibara Kiyotaka SuzukiAkiko Sakai Miwa ShindoChihiro Nagano Shinya NarumiYasuhiro Kajihara Katsura Mochizuki 《Tetrahedron letters》2003,44(30):5711-5714
Methyl 4,6-O-benzylidene-2,3-dideoxy-3-C-p-tolylsulfonyl-2-C-p-tolylthio-β-d-glucopyranoside and its 5a-carba-dl-analog exit mainly in a non-chair conformation in solutions, but the latter occupies a chair conformation in a solid state. 相似文献
169.
Tohru Kanno Yukitoshi Tatsumoto Masayoshi Kobayashi 《Reaction Kinetics and Catalysis Letters》1991,43(1):237-241
Ethylene hydroformylation over a Nafion-supported rhodium catalyst has been studied under atmospheric pressure in the temperature range of 100–135 °C, using the transient response method.
, , 100–135°C, .相似文献
170.
Kinoshita E Takahashi M Takeda H Shiro M Koike T 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1189-1193
Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex (Zn2L3+) has been studied (L = alkoxide species of 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol). Potentiometric pH titration study disclosed a 1 : 1 phenyl phosphate complexation with Zn2L3+ in aqueous solution. The dissociation constant (= [Zn2L3+][PhOPO3(2-)]/[Zn2L3+-PhOPO3(2-)]) is an extremely small value of 2.5 x 10(-8) mol dm(-3) at 25 degrees C with I = 0.10 (NaNO3). The X-ray crystal analysis of the dizinc(II) complex with p-nitrophenyl phosphate showed that the phosphate dianion binds as a bridging ligand to the two zinc(II) ions. 相似文献