全文获取类型
收费全文 | 517篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
化学 | 396篇 |
晶体学 | 9篇 |
力学 | 4篇 |
数学 | 52篇 |
物理学 | 92篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 21篇 |
2013年 | 26篇 |
2012年 | 45篇 |
2011年 | 47篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 45篇 |
2007年 | 32篇 |
2006年 | 37篇 |
2005年 | 25篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 263 毫秒
61.
A new chelating reagent, bis(8-hydroxy-2-methyl-5-quinolyl) methane, has been prepared and characterized. It does not react with aluminum but does chelate with many other metals. Analytical data did not permit a decision on the possibility that some of these chelates arc polymeric. 相似文献
62.
63.
H. N. Rutt D. N. Travis K. C. Hawkins 《International Journal of Infrared and Millimeter Waves》1984,5(9):1201-1219
An extensive study of the propyne optically pumped laser is presented. 32 new far infrared and 8 new mid infrared outputs are reported, together with pump frequency offset data. Complete assignments of some far infrared transitions and partial assignments of the mid infrared outputs are given. Very strong interactions occur between the mid and far infrared laser transitions. These interactions are of vital importance in obtaining high output energies. 相似文献
64.
65.
This paper describes the synthesis of mixed Rh(2)(II) complexes containing bridging acetate and R,R-diphenyl-N-triflylimidazolidinone (DPTI) ligands (1, 2, and 9-19), and their function as enantioselective catalysts for the conversion of ethyl diazoacetate and terminal acetylenes to chiral cyclopropenes. Of these catalysts, 1 and 10 functioned with the highest enantioselectivity, in accord with a mechanistic model in which one of the ligand bridges is broken in the intermediate Rh-carbene complex. The synthetic results allow conclusions with regard to kinetically and thermodynamically favored pathways for the synthesis of mixed acetate-DPTI complexes. A new C(2)-symmetric complex having only two anti-DTBTI bridges (23) is shown to be a highly effective chiral catalyst, as expected from the model. 相似文献
66.
67.
Alexander Scheeline John A. Norris J.C. Travis J.R. Devoe John P. Walters 《Spectrochimica Acta Part B: Atomic Spectroscopy》1981,36(4):373-383
Light scattering was used to demonstrate the presence of small (?1 μm) particles in the immediate surroundings of a stable spark discharge. Several parameters, including electrode composition and surface condition, which are of importance in emission spectrochemical analysis, were found to be of importance in affecting the scattering signal. Electron micrographs of the heaviest particles revealed two distinct types of particles. Analytical implications are discussed. 相似文献
68.
Fridgen TD Macaleese L McMahon TB Lemaire J Maitre P 《Physical chemistry chemical physics : PCCP》2006,8(8):955-966
The infrared multiphoton dissociation (IRMPD) spectra of three homogenous proton-bound dimers are presented and the major features are assigned based on comparisons with the neutral alcohol and with density functional theory calculations. As well, the IRMPD spectra of protonated propanol and the propanol/water proton-bound dimer (or singly hydrated protonated propanol) are presented and analysed. Two primary IRMPD photoproducts were observed for each of the alcohol proton bound dimers and were found to vary with the frequency of the radiation impinging upon the ions. For example, when the proton-bound dimer absorbs weakly a larger amount of S(N)2 product, protonated ether and water, are observed. When the proton-bound dimer absorbs more strongly, an increase in the simple dissociation product, protonated alcohol and neutral alcohol, is observed. With the aid of RRKM calculations this frequency dependence of the branching ratio is explained by assuming that photon absorption is faster than dissociation for these species and that only a few photons extra are necessary to make the higher-energy dissociation channel (simple cleavage) competitive with the lower energy (S(N)2) reaction channel. 相似文献
69.
Tam-Chang SW Helbley J Carson TD Seo W Iverson IK 《Chemical communications (Cambridge, England)》2006,(5):503-505
We have developed an approach to generate micropatterns of anisotropic organic materials which exploits the self-organization, driven by pi-stacking and hydrophobic interactions, of an ionic perylenebis(dicarboximide) in aqueous solutions. 相似文献
70.
Enolate additions to chiral N-sulfonyloxaziridines providing enantiomerically enriched α-hydroxy carbonyl compounds is a reaction of importance, yet a clear understanding of the factors governing stereoinduction in these transformations remains ambiguous. This is despite, previous computational studies, one by Bach et al. employing truncated model systems exploring oxygen atom transfer to an unsubstituted lithium enolate and another by our own group. In clarifying this reactivity we report here a computational study examining oxygen atom transfer from 1-S-(+)-(10-camphorsulfonyl)oxaziridine, viz., archetypal Davis chiral oxaziridine to substituted Li, Na, K enolates offering improved mechanistic understanding. From this investigation, a revised model is offered revealing the metal cation, chelation effects and sterics as decisive stereocontrolling factors in enolate additions to chiral N-sulfonyloxaziridines affording enantiomerically enriched α-hydroxy carbonyl compounds. 相似文献