全文获取类型
收费全文 | 7089篇 |
免费 | 192篇 |
国内免费 | 1480篇 |
专业分类
化学 | 6296篇 |
晶体学 | 129篇 |
力学 | 150篇 |
综合类 | 6篇 |
数学 | 64篇 |
物理学 | 2116篇 |
出版年
2024年 | 28篇 |
2023年 | 313篇 |
2022年 | 238篇 |
2021年 | 200篇 |
2020年 | 202篇 |
2019年 | 261篇 |
2018年 | 175篇 |
2017年 | 219篇 |
2016年 | 223篇 |
2015年 | 193篇 |
2014年 | 217篇 |
2013年 | 484篇 |
2012年 | 355篇 |
2011年 | 404篇 |
2010年 | 338篇 |
2009年 | 518篇 |
2008年 | 491篇 |
2007年 | 498篇 |
2006年 | 474篇 |
2005年 | 367篇 |
2004年 | 336篇 |
2003年 | 238篇 |
2002年 | 211篇 |
2001年 | 189篇 |
2000年 | 199篇 |
1999年 | 162篇 |
1998年 | 181篇 |
1997年 | 128篇 |
1996年 | 124篇 |
1995年 | 105篇 |
1994年 | 93篇 |
1993年 | 86篇 |
1992年 | 76篇 |
1991年 | 74篇 |
1990年 | 59篇 |
1989年 | 45篇 |
1988年 | 54篇 |
1987年 | 37篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 7篇 |
排序方式: 共有8761条查询结果,搜索用时 0 毫秒
41.
脑神经退行性疾病中的有机化学-朊病毒(疯牛病)中的蛋白物理有机化学和自由基化学 总被引:5,自引:0,他引:5
杨池明 《高等学校化学学报》2002,23(2):243-250
通过关于“普里昂”蛋白病毒疾病的已有临床、医学生理、免疫和化学等方面的现象,讨论了朊病毒当中的部分蛋白氧化损伤和蛋白自由基化学本质。 相似文献
42.
Svein G. Dahl Peter A. Kollman Shashidhar N. Rao U. Chandra Singh 《Journal of computer-aided molecular design》1992,6(3):207-222
Summary The side-chain conformations of psychoactive phenothiazine drugs in crystals are different from those of biologically inactive ring sulfoxide metabolites. This study examines the potential energies, molecular conformations and electrostatic potentials in chlorpromazine, levomepromazine (methotrimeprazine), their sulfoxide metabolites and methoxypromazine. The purpose of the study was to examine the significance of the different crystal conformations of active and inactive phenothiazine derivatives, and to determine why phenothiazine drugs lose most of their biological activity by sulfoxidation. Quantum mechanics and molecular mechanics calculations demonstrated that conformations with the side chain folded over the ring structure had lowest potential energy in vacuo, both in the drugs and in the sulfoxide metabolites. In the sulfoxides, side chain conformations corresponding to the crystal structure of chlorpromazine sulfoxide were characterized by stronger negative electrostatic potentials around the ring system than in the parent drugs. This may weaken the electrostatic interaction of sulfoxide metabolites with negatively charged domains in dopamine receptors, and cause the sulfoxides to be virtually inactive in dopamine receptor binding and related pharmacological tests. 相似文献
43.
Summary The capillary gas chromatographic retention behavior of -pinene and tricyclene has been investigated on stationary phases of different polarities. On all but one of the columns employed, tricyclene eluted before -pinene; only permethylated -cyclodextrins dissolved in moderately polar polisiloxanes gave a reversed elution order. The intermolecular interactions which caused the unexpected retention behavior were investigated in detail, applying methods of computer simulation. To achieve this, we have developed a calculation algorithm on the basis of molecular mechanical optimizations and programmed it in a macro. This makes it possible to systematically investigate a given configuration space in which all the possible interactions can take place. It was shown that permethylated -cyclodextrin as host molecule for both guest molecules offers an optimum cavity size. As a result the number of energetically favorable contacts between host and guest molecules as well as the strength of the interactions in this stationary phase were larger. As a consequence the elution order, normally only influenced by the vapor pressure of the compounds at a given temperature, was changed. Nonspecific interactions played an especially important role for these kinds of substances. 相似文献
44.
The recent progress of wide bandgap (WBG) donor polymers for non-fullerene polymer solar cells (NF-PSCs) were reviewed in detail, which was classified by D-type and D-A type molecular backbones to discuss the related structure-property correlations and put forward an outlook for future innovations. 相似文献
45.
L.L. Carvalho 《European Polymer Journal》2006,42(10):2589-2595
Samples of a methacrylic side-chain azopolymer were synthesized by a radical copolymerization of methyl-methacrylate with the methacrylic derivative of the commercial dye Disperse Red-13 (DR13). Copolymers with different molecular weight were obtained by varying the reaction time and the concentration of initiator. Samples with molecular weight averages (Mw) from 3 to 8 × 104 g/mol and 1.4-1.7 polydispersity were obtained. The glass transition temperature of the samples increased linearly from the lower to the highest molecular weight. Optical quality cast films were prepared for all samples and photoinduced birefringence was successfully carried out in all samples as well as surface relief gratings could be inscribed in the cast films. 相似文献
46.
合成了甘氨酸 (Gly) 天冬氨酸 (Asp)组成的肽链Gly Asp、Gly Asp Gly Asp、Gly Asp (Gly Asp) 2 .分别将天冬氨酸及上述合成的肽链引入到聚酰胺 胺型树枝状化合物 (PAMAM)的表面 .对所得化合物进行了分子模拟 ,结果表明Gly Asp (Gly Asp) 2 肽链在PAMAM表面可形成接近于 β sheet的构象 .由实验得知 ,经Asp、Gly Asp、Gly Asp Gly Asp、Gly Asp (Gly Asp) 2 修饰的PAMAM树枝状化合物对抗坏血酸还原FeⅢ 细胞色素C(cytc)的反应有干扰作用 ,导致该反应速率下降 .这说明所合成的化合物与cytc有较好的结合能力 .特别是Gly Asp (Gly Asp) 2 修饰的PAMAM ,其与cytc的结合常数为 1 6ⅹ 1 0 5. 相似文献
47.
48.
Shiling Yuan Yijian Chen Guiying Xu 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,280(1-3):108-115
Molecular dynamics simulations on surfactant octadecylammonium chloride at the air/liquid interface were performed. It was found that the alkyl chains of octadecylammonium would change to order with increasing the concentration of octadecylammonium at the air/liquid interface. Some functions, such as the concentration distributions, the radial distribution function and the mean squared displacement (MSD) were evaluated to investigate the structural properties of interface. We found that the salts can affect octadecylammonium aggregate at the interface: (1) univalent ions, such as chloride and sodium ions, affect slightly the structure of monolayer and (2) bivalent ions, such as sulfate or calcium ions, affect greatly, especially for the bivalent negative ions. 相似文献
49.
50.
D. J. Subach 《Chromatographia》1981,14(6):371-373
Summary A series of thirty s-triazine compounds have been separated using reversed-phase high-pressure liquid chromatography. A relationship between substituent activity and retention time was developed to predict molecular structure.Work partially completed at the CIBA-GEIGY Corp., McIntosh, Ala., USA. 相似文献