全文获取类型
收费全文 | 298篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 225篇 |
晶体学 | 6篇 |
力学 | 3篇 |
数学 | 17篇 |
物理学 | 58篇 |
出版年
2023年 | 2篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 24篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有309条查询结果,搜索用时 46 毫秒
291.
Ten varieties of liquid-crystalline side chain polymers, poly(cholesteryl-ω-(methacryloyloxy)alkanoates) (pChMO-n, n = 1, 2, 3, 4, 5, 7, 9, 10, 11 and 15; the carbon number of the alkyl chain), were studied by differential scanning calorimetry and small angle X-ray scattering. On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. X-ray investigations showed that pChMO-n with short spacers (n = 1-7) has a two layer (bilayer) SA packing structure, and pChMO-n with a longer spacer (n= 15) has a single layer (monolayer) SA packing structure. However, these two types of packing structure appear simultaneously in pChMO-n (n = 9s-11) below their phase transition temperature. To clarify the manner of the coexistence of the two different structures the smectic layer spacing and X-ray diffraction patterns were examined by small angle X-ray scattering at various temperatures. 相似文献
292.
Kise N Ohya K Arimoto K Yamashita Y Hirano Y Ono T Ueda N 《The Journal of organic chemistry》2004,69(22):7710-7719
The electroreduction of aromatic beta- and gamma-imino esters prepared from beta-alanine and GABA in the presence of chlorotrimethylsilane and subsequent N-alkoxycarbonylation of the resulting five- and six-membered cyclized amines gave mixed ketals of N-alkoxycarbonyl-2-arylpyrrolidin-3-ones and 2-arylpiperidin-3-ones, respectively. The best result of the electroreductive intramolecular coupling was achieved using Bu(4)NClO(4) as a supporting electrolyte and a Pb cathode in THF. Acid hydrolysis of the mixed ketals afforded N-alkoxycarbonyl-2-arylpyrrolidin-3-ones and 2-arylpiperidin-3-ones in good yields. The reduction of these ketones with NaBH(4) in methanol afforded the corresponding N-alkoxycarbonyl-cis-2-arylpyrrolidin-3-ols and cis-2-arylpiperidin-3-ols diastereospecifically. 相似文献
293.
Jing Chen Yeong-Eun Lee Masahiro Ueda Keiji Taniguchi Katsuhiko Asada 《Optics and Lasers in Engineering》1998,29(1):67
An optical method for measuring glass wool fiber diameter has been proposed and discussed from the viewpoint of practical use. The method is based on both light scattering and light reflection on the glass wool. The method can measure the mean fiber diameter, d, in the area illuminated by laser light in realtime. The accuracy of the method, i.e., the dimensional resolution, was found to be about 0·7 μm within the diameter range of d7·0 μm. 相似文献
294.
Jun-ichi Yoshida Shinji Yano Tadahiro Ozawa Nariyoshi Kawabata 《Tetrahedron letters》1984,25(26):2817-2820
2,2-Dibromo-1,3-diketones reacted with copper powder and olefin to give 4,5-dihydrofuran derivatives in a highly regioselective fashion. 相似文献
295.
Jun'ichi Katakawa Tadahiro Tetsumi Tadamasa Terai Masaaki Katai Ken-ichi Sakaguchi Mamoru Sato 《Journal of chemical crystallography》2000,30(2):139-141
The crystal and molecular structure of a grayanotoxin derivative, iso-grayanotoxin II, is presented. The crystal is orthorhombic, space group
. The molecule is based on a tetracyclic structure consisting of two five-membered, one six-membered, and one seven-membered rings with various conformations. 相似文献
296.
Toshio Asada Kenichi Ohta Takeshi Matsushita Shiro Koseki 《Theoretical chemistry accounts》2011,130(2-3):439-448
The mechanism of charge transfer among tris(8-hydroxyquinolinate)aluminum (Alq3) molecules in the electron-transporting layer (ETL) under amorphous conditions was theoretically investigated using both quantum mechanical/molecular mechanical (QM/MM) calculations and molecular dynamics (MD) simulations. The rate constant of the electron transfer was estimated for the equilibrated structure taken from the QM/MM MD simulations, based on the hopping model and Marcus theory. It was found that the coordination of a (LiF)4 cluster in ETL drastically lowers the energy of the lowest unoccupied molecular orbital in the Alq3 molecule. The small rate constant, namely the slow charge mobility, in ETL is believed to be causally related to the low-lying delocalized unoccupied molecular orbital of Alq3 coordinated by the (LiF)4 cluster. The results suggest that their interaction has a considerable influence on efficiency and is attributed in part to ETL degradation in organic light-emitting diodes. 相似文献
297.
298.
Hydrated nitrosonium ion clusters NO(+)(H(2)O)(n) (n = 4 and 5) were investigated by using MP2/aug-cc-pVTZ level of theory to clarify isomeric reaction pathways for formation of HONO and fully hydrated hydride ions. We found some new isomers and transition state structures in each hydration number, whose lowest activation energies of the intracluster reactions were found to be 4.1 and 3.4 kcal mol(-1) for n = 4 and n = 5, respectively. These thermodynamic properties and full quantum mechanical molecular dynamics simulation suggest that product isomers with HONO and fully hydrated hydride ions can be obtained at n = 4 and n = 5 in terms of excess hydration binding energies which can overcome these activation barriers. 相似文献
299.
Okamoto T Yamada K Koyano Y Asada T Koga N Nagaoka M 《Journal of computational chemistry》2011,32(5):932-942
For applying to a number of theoretical methodologies based on an ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics method connecting AMBER9 with GAUSSIAN03, we have developed an AMBER-GAUSSIAN interface (AG-IF), which can be one of the simplest architectures. In the AG-IF, only a few subroutines addition is necessary to retrieve the QM/MM energy and forces, obtained by GAUSSIAN, for solving a set of Newtonian equations of motion in AMBER. It is, therefore, easy to be modified for individual applications since AG-IF utilizes most of those functions originally equipped not only in AMBER but also in GAUSSIAN. In the present minimal implementation, only AMBER is modified, whereas GAUSSIAN is left unchanged. Moreover, a different method of calculating electrostatic forces of MM atoms interacting with QM region is proposed. Using the AG-IF, we also demonstrate three examples of application: (i) the QM versus MM comparison in the radial distribution function, (ii) the free energy gradient method, and (iii) the charge from interaction energy and forces. 相似文献
300.
Sasaki T Li W Morimura H Li S Li Q Asada Y Koike K 《Chemical & pharmaceutical bulletin》2011,59(11):1396-1399
The MeOH extract from the whole plants of Sambucus adnata has shown significant protein-tyrosine phosphatase 1B (PTP1B) inhibitory activity. Chemical study on the extract resulted in the isolation of thirteen compounds, including a novel triterpene (1). The structure of 1 was determined to be 1α,3β-dihydroxy-urs-12-en-11-one-3-yl palmitate on the basis of extensive spectroscopic analyses. Among the isolated compounds, ursolic acid, oleanolic acid and (±)-boehmenan showed the most potent PTP1B inhibitory activity in vitro with the IC(50) values of 4.1, 14.4 and 43.5 μm, respectively. The kinetic analysis indicated that (±)-boehmenan inhibits PTP1B activity in a competitive manner. 相似文献