全文获取类型
收费全文 | 4935篇 |
免费 | 195篇 |
国内免费 | 12篇 |
专业分类
化学 | 3804篇 |
晶体学 | 20篇 |
力学 | 55篇 |
数学 | 515篇 |
物理学 | 748篇 |
出版年
2022年 | 37篇 |
2021年 | 45篇 |
2020年 | 70篇 |
2019年 | 62篇 |
2018年 | 42篇 |
2016年 | 140篇 |
2015年 | 133篇 |
2014年 | 114篇 |
2013年 | 209篇 |
2012年 | 264篇 |
2011年 | 309篇 |
2010年 | 182篇 |
2009年 | 129篇 |
2008年 | 253篇 |
2007年 | 228篇 |
2006年 | 219篇 |
2005年 | 216篇 |
2004年 | 202篇 |
2003年 | 168篇 |
2002年 | 152篇 |
2001年 | 114篇 |
2000年 | 93篇 |
1999年 | 60篇 |
1998年 | 55篇 |
1997年 | 47篇 |
1996年 | 73篇 |
1995年 | 83篇 |
1994年 | 49篇 |
1993年 | 66篇 |
1992年 | 64篇 |
1991年 | 43篇 |
1990年 | 53篇 |
1989年 | 46篇 |
1988年 | 49篇 |
1987年 | 43篇 |
1986年 | 37篇 |
1984年 | 51篇 |
1982年 | 43篇 |
1981年 | 56篇 |
1980年 | 34篇 |
1979年 | 41篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 35篇 |
1974年 | 41篇 |
1973年 | 33篇 |
1967年 | 35篇 |
1966年 | 43篇 |
1964年 | 40篇 |
1963年 | 36篇 |
排序方式: 共有5142条查询结果,搜索用时 31 毫秒
31.
32.
K. Jungmann P. E. G. Baird J. R. M. Barr C. Bressler P. F. Curley R. Dixson G. H. Eaton A. I. Ferguson H. Geerds V. W. Hughes J. Kenntner S. N. Lea F. Maas M. A. Persaud G. zu Putlitz P. G. H. Sandars W. Schwarz W. T. Toner M. Towrie G. Woodman L. Zhang Z. Zhang 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,21(3):241-243
The 12 S 1/2(F=1)?22 S 1/2(F=1) energy interval in muonium has been investigated by Doppler-free two-photon laser spectroscopy. The transition was observed by uniquely identifying and counting the muons released after the photoionization of the 2S state by the same laser field. The measured transition frequency of 2455 528016(58)(43) MHz is in good agreement with QED calculations. The experiment can be interpreted as a test of the Lamb shift contributions at the 1% level. The method is also well suited for a precise determination of the mass of the positive muon in a muoniumhydrogen isotope shift measurement. 相似文献
33.
By investigation of isomeric 2H- and 13C-labelled C9H11 Cl-compounds it has been shown that the ion [M ? Cl]+ is transformed mainly to the ion [C7H7]+ via C2H4-elimination from alkyl-substituted tropylium-ions. Phenyl-cyclopropane-cations play only a small part, if at all, in this fragmentation process. 相似文献
34.
35.
36.
37.
A radical cascade involving a 5-exo-dig cyclization followed by a 6-endo-trig radical trapping transforms ynamides into heterogeneous polycyclic compounds in good yields. This leads interestingly to the formation of isoindols, isoindolinones, and pyridoisoindolones. [reaction: see text] 相似文献
38.
"Bare" CeO(2)(+) ions can be prepared in the gas phase by consecutive oxidation of Ce(+) with O(2) and NO(2). The ability to activate saturated and unsaturated hydrocarbons is investigated by use of Fourier-transform ion cyclotron resonance mass spectrometry. In the reactions of CeO(2)(+) with linear and branched alkanes C-H bond activation is observed almost exclusively. In contrast, both oxygen-atom transfer and C-H bond activation processes occur when thermalized CeO(2)(+) cations react with simple alkenes and aromatic compounds. C-C bond activation is not observed at all. Insight into the structural and electronic properties of neutral CeO(2) and cationic CeO(2)(+) is provided by means of quasirelativistic density-functional and ab initio pseudopotential calculations. They reveal a (2)Sigma(u)(+) ground state for CeO(2)(+) which is best described as a linear cerium dioxide with a resonating pi bond. Finally, we discuss the influence of oxo ligands on the chemistry of the cationic CeO(n)()(+) (n = 0-2) species toward hydrocarbons. 相似文献
39.
40.
Benítez IO Bujoli B Camus LJ Lee CM Odobel F Talham DR 《Journal of the American Chemical Society》2002,124(16):4363-4370
Organized monolayer films of a manganese tetraphenylporphyrin have been prepared and used as supported oxidation catalysts. Manganese 5,10,15,20-tetrakis(tetrafluorophenyl-4'-octadecyloxyphosphonic acid) porphyrin (1) has been immobilized as a monolayer film by a combination of Langmuir-Blodgett (LB) and self-assembled monolayer techniques that use zirconium phosphonate linkages to bind the molecule to the surface. Analysis by FTIR, XPS, UV-vis and polarized optical spectroscopy show that the films consist of noninteracting molecules effectively anchored and oriented nearly parallel to the surface. The monolayer films are stable to the solvent and temperature conditions needed to explore organic oxidations. The activity of films of 1 toward the epoxidation of cyclooctene using iodosylbenzene as the oxidant was compared to that of Manganese 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin (2) and 1 under equivalent homogeneous conditions. The immobilized porphyrin 1 shows an enhanced activity relative to either homogeneous reaction. The main difference between 1 and 2 is the four alkyl phosphonate arms in 1 designed to incorporate the porphyrin within the films. The increased activity of immobilized 1 is a combination of the porphyrin structure, which prohibits the formation of mu-oxo dimers even in solution, and a change in conformation when anchored to the surface. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems. 相似文献