全文获取类型
收费全文 | 771篇 |
免费 | 20篇 |
国内免费 | 3篇 |
专业分类
化学 | 623篇 |
晶体学 | 9篇 |
力学 | 6篇 |
数学 | 28篇 |
物理学 | 128篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 47篇 |
2012年 | 31篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 25篇 |
2008年 | 34篇 |
2007年 | 45篇 |
2006年 | 38篇 |
2005年 | 37篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 35篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1989年 | 5篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1970年 | 6篇 |
1967年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有794条查询结果,搜索用时 15 毫秒
1.
I Kitagawa A Matsuda T Nishimura S Hirai I Yoshioka 《Chemical & pharmaceutical bulletin》1967,15(9):1435-1437
2.
3.
Katsuma Hiraki Takeo Inoue Hidefumi Hirai 《Journal of polymer science. Part A, Polymer chemistry》1970,8(9):2543-2554
ESR spectra of homogeneous catalyst derived from tris(acetylacetonato)titanium(III) and triethylaluminum were observed at several temperatures from ?78°C, to +25°C, at molar ratios of aluminum to titanium of 1–108. At ?78°C, this catalyst yields a violet complex which shows an ESR signal with a g value of 1.959 and is associated with the first intermediate. At ?40°C to ?30°C, this signal decreases, and two signals with g values of 1.947 and 1.960 are observed. The latter two signals diminish at ?5°C to +10°C, while two kinds of new signals with g values of 1.965 and 1.969 appear overlapping each other. The structures of the species corresponding to these five signals are discussed on the basis of the ESR spectra, the intensity change, and the unpaired spin distribution. A new signal with a g value of 1.978 is found in the presence of butadiene at 25°C at Al/Ti > 8 and is assigned to a growing end of polybutadiene with this catalyst. The polymer yield increases remarkedly at Al/Ti molar ratios greater than 10. The microstructure of the resulting polymer consists almost completely of 1,2 units. The structure of the growing end is proposed to be a titanium (III) species containing two 1-substituted allyl groups, by comparison with the structure ascribed to the growing end of polybutadiene with n-butyl titanate-triethylaluminum catalyst. 相似文献
4.
Katsuma Hiraki Shigeru Ikeda Shoichi Kaneko Hidefumi Hirai 《Journal of polymer science. Part A, Polymer chemistry》1979,17(8):2363-2369
n-Butyl titanate(IV)–triethylaluminum catalyst at Al/Ti molar ratios greater than 6 polymerizes methyl and n-butyl acrylates at ?78°C. The polymerization system which includes methyl acrylate at ?78°C, gives two ESR signals with g factors of 1.958 and 1.961 that overlap each other. The absorption intensity of the latter signal is approximately proportional to the polymer chain concentration calculated from polymer yield and the molecular weight. The polymerization system at Al/Ti ratios smaller than 3 has no catalytic activity on the polymerization and shows only the ESR signal with the g factor of 1.958. On the basis of these facts the ESR signal with the g factor of 1.961 is attributed to the active growing end of poly(methyl acrylate) with this catalyst. The character of this active growing end is discussed. 相似文献
5.
Sadao Hayashi Toshihiro Hirai Sonoko Shimomichi Nobumasa Hojo 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):839-846
Polyiodide formed by complexation of poly(vinyl acetate) (PVAc) with iodine in the presence of iodide has been investigated by chemical analysis and resonance Raman spectrophotometry. When PVAc films were immersed in iodide-iodine aqueous solutions which had different ratios of iodide to iodine concentration [I?]/[I2], the complex films exhibited tremendous variations of swelling degree, despite the relatively small change in the amount of bound iodine. From a quantitative chemical analysis, the composition of polyiodide bound to PVAc was found to be 1.01 ± 0.035 in the molar ratio of iodide to iodine irrespective of the composition of the iodide-iodine aqueous solution ([I?]/[I2] = 2–500). The polyiodide formed in PVAc-iodine-iodide complex was therefore inferred to be (I3?)n. Resonance Raman spectra obtained on PVAc-iodine-iodide complexes were also identical to those of the benzamide-iodine complex, in which the polyiodide consists of (I3?)n, consistent with the result from chemical analysis. 相似文献
6.
The reaction of 2-dialkylamino-5-phenyl-1,3-oxathiolium cation 1 with sulphur ylides 2 was investigated. The behavior of 1 was solvent-dependent. In CH2Cl2, carbamate ester 3 was obtained: in CH3CN, the intermediate sulphonium salt 5, which on hydrolysis gave 3, was isolated. On the other hand, reaction in MeOH gave the diphenacyl derivative 6. The reaction mechanism is discussed. 相似文献
7.
The reaction of alpha,beta-unsaturated imines with CO and alkenes in the presence of Ru(3)(CO)(12) as a catalyst results in a three-component coupling reaction that gives alpha,alpha-disubstituted beta,gamma-unsaturated gamma-butyrolactams. The reaction proceeds via a two-step sequence involving the initial formation of ketone derivatives by catalytic carbonylation at the beta-olefinic C-H bonds of alpha,beta-unsaturated imines, followed by the (uncatalyzed) intramolecular nucleophilic attack of the imine nitrogen on the ketonic carbon to generate a tetrahedral intermediate, which then undergoes a 1,2-ethyl migration. The reaction of a cyclic unsaturated imine, derived from the reaction of (1R)-(-)-myrtenal with tert-butylamine, gives a beta-aminocyclopentene derivative, which is formed by an aldol-type condensation of the initially formed ketone, indicating the initial formation of ethyl ketone. 相似文献
8.
9.
Anionic surfactants are preconcentrated from 5-ml samples by extraction as the ion-pair with ethyl violet into toluene. The absorbance of aliquots of the toluene phase is measured at 610 nm in a flow-injection system. A phase converter is located prior to the injection valve to convert a water stream to, pumped with ordinary pump tubing, to a toluene stream. The working range was 0.01–1.0 mg l?1 and the reproductibility (r.s.d, n = 10) was 2% for 0.4 mg l?1 sodium dodecyl sulphate. The non-aqueous flow-injection system serves to miniaturize the extraction from separatory funnel (200 ml) to test tube (10 ml) scale without loss of precision or validity. 相似文献
10.
N-Acyl-α-amino acids are synthesized by the amidocarbonylation of allylic alcohols catalyzed by homogeneous binary systems which consist of cobalt carbonyl and rhodium (or iron or palladium) complexes. 相似文献