全文获取类型
收费全文 | 426篇 |
免费 | 16篇 |
专业分类
化学 | 355篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 11篇 |
物理学 | 71篇 |
出版年
2023年 | 2篇 |
2020年 | 4篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 16篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 7篇 |
2008年 | 19篇 |
2007年 | 26篇 |
2006年 | 17篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 9篇 |
1969年 | 2篇 |
1967年 | 5篇 |
1966年 | 2篇 |
1907年 | 3篇 |
1898年 | 1篇 |
排序方式: 共有442条查询结果,搜索用时 521 毫秒
121.
122.
123.
124.
Chiang Y Gaplovsky M Kresge AJ Leung KH Ley C Mac M Persy G Phillips DL Popik VV Rödig C Wirz J Zhu Y 《Journal of the American Chemical Society》2003,125(42):12872-12880
Light-induced deazotization of 3-diazo-3H-benzofuran-2-one (1) in solution is accompanied by facile (CO)-O bond cleavage yielding 6-(oxoethenylidene)-2,4-cyclohexadien-1-one (3), which appears with a rise time of 28 ps. The expected Wolff-rearrangement product, 7-oxabicyclo[4.2.0]octa-1,3,5-trien-8-ylidenemethanone (4), is not formed. The efficient light-induced formation of the quinonoid cumulenone 3 opens the way to determine the reactivity of a cumulenone in solution. The reaction kinetics of 3 were monitored by nanosecond flash photolysis with optical (lambda(max) approximately 460 nm) as well as Raman (1526 cm(-1)) and IR detection (2050 cm(-)(1)). Remarkably, the reactivity of 3 is that expected from its valence isomer, the cyclic carbene 3H-benzofuran-2-one-3-ylidene, 2. In aqueous solution, acid-catalyzed addition of water forms the lactone 3-hydroxy-3H-benzofuran-2-one (5). The reaction is initiated by protonation of the cumulenone on its beta-carbon atom. In hexane, cumulenone 3 dimerizes to isoxindigo ((E)-[3,3']bibenzofuranylidene-2,2'-dione, 7), coumestan (6H-benzofuro[3,2-c][1]benzopyran-6-one, 8), and a small amount of dibenzonaphthyrone ([1]benzopyrano[4,3-][1]benzopyran-5,11-dione, 9) at a nearly diffusion-controlled rate. Ab initio calculations (G3) are consistent with the observed data. Carbene 2 is predicted to have a singlet ground state, which undergoes very facile, strongly exothermic (irreversible) ring opening to the cumulenone 3. The calculated barrier to formation of 4 (Wolff-rearrangement) is prohibitive. DFT calculations indicate that protonation of 3 on the beta-carbon is accompanied by cyclization to the protonated carbene 2H(+), and that dimerization of 3 to 7 and 9 takes place in a single step with negligible activation energy. 相似文献
125.
Dettlaff-Weglikowska U Skákalová V Graupner R Jhang SH Kim BH Lee HJ Ley L Park YW Berber S Tománek D Roth S 《Journal of the American Chemical Society》2005,127(14):5125-5131
Chemical modification by SOCl2 of an entangled network of purified single-wall carbon nanotubes, also known as 'bucky paper', is reported to profoundly change the electrical and mechanical properties of this system. Four-probe measurements indicate a conductivity increase by up to a factor of 5 at room temperature and an even more pronounced increase at lower temperatures. This chemical modification also improves the mechanical properties of SWNT networks. Whereas the pristine sample shows an overall semiconducting character, the modified material behaves as a metal. The effect of SOCl2 is studied in terms of chemical doping of the nanotube network. We identified the microscopic origin of these changes using SEM, XPS, NEXAFS, EDX, and Raman spectroscopy measurements and ab initio calculations. We interpret the SOCl2-induced conductivity increase by p-type doping of the pristine material. This conclusion is reached by electronic structure calculations, which indicate a Fermi level shift into the valence band, and is consistent with the temperature dependence of the thermopower. 相似文献
126.
127.
128.
P. H. Liang C. J. Fang D. S. Jiang P. Wagner L. Ley 《Applied Physics A: Materials Science & Processing》1981,26(1):39-43
Crystallization of hydrogenated amorphous silicon (a-SI:H) has been initiated using ultrashort laser-pulse train annealing. Optical microscopy, infrared absorption, Raman spectroscopy and photoluminescence measurements show that in our experiment the crystallized layer is localized on the surface and is non-epitaxial. The depth of the crystalline layer and its surface morphology are discussed. A sharp luminescence band at 0.970 eV with fine structure is found after laser annealing and is identified as a recombination center similar to irradiation induced defects in crystalline Si. 相似文献
129.
Elena Díez DarrenJ. Dixon StevenV. Ley Alessandra Polara Felix Rodríguez 《Helvetica chimica acta》2003,86(11):3717-3729
The total synthesis of phytotoxic nonenolide herbarumin II ( 1 ) has been achieved by implementation of butane diacetal (BDA)‐desymmetrised glycolate building blocks. Three of the four stereogenic centres present in the key coupling fragments were generated from both enantiomeric forms of the BDA building block in highly diastereoselective alkylation and aldol reactions. 相似文献
130.