全文获取类型
收费全文 | 2088篇 |
免费 | 63篇 |
国内免费 | 4篇 |
专业分类
化学 | 1560篇 |
晶体学 | 22篇 |
力学 | 32篇 |
数学 | 49篇 |
物理学 | 492篇 |
出版年
2023年 | 10篇 |
2021年 | 22篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 29篇 |
2016年 | 29篇 |
2015年 | 42篇 |
2014年 | 43篇 |
2013年 | 78篇 |
2012年 | 96篇 |
2011年 | 114篇 |
2010年 | 67篇 |
2009年 | 76篇 |
2008年 | 116篇 |
2007年 | 105篇 |
2006年 | 110篇 |
2005年 | 101篇 |
2004年 | 109篇 |
2003年 | 115篇 |
2002年 | 96篇 |
2001年 | 56篇 |
2000年 | 54篇 |
1999年 | 24篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 25篇 |
1994年 | 29篇 |
1993年 | 22篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 30篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1976年 | 24篇 |
1975年 | 21篇 |
1974年 | 11篇 |
1968年 | 7篇 |
排序方式: 共有2155条查询结果,搜索用时 125 毫秒
41.
42.
We apply the singular value decomposition to compress the degrees of freedom of T3 amplitude for the CCSDT-1 method (compressed CCSDT-1). This method enables us to make the number of the T3 amplitudes less than that of the T2 amplitudes, making CCSDT-1 calculations much less expensive without losing accuracy. We perform test calculations on some atoms and molecules to investigate the applicability of this method. Computational results for the electronic energies as well as timings of these calculations are presented. 相似文献
43.
44.
Ueda J Takeshita K Matsumoto S Yazaki K Kawaguchi M Ozawa T 《Photochemistry and photobiology》2003,77(2):165-170
The reaction of singlet oxygen (1O2) generated by ultraviolet-A (UVA)-visible light (lambda > 330 nm) irradiation of air-saturated solutions of hematoporphyrin with phenolic compounds in the presence of a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), gave an electron spin resonance (ESR) spectrum characteristic of the DMPO-hydroxyl radical spin adduct (DMPO-*OH). In contrast, the ESR signal of 5,5-dimethyl-2-pyrrolidone-N-oxyl, an oxidative product of DMPO, was observed in the absence of phenolic compounds. The ESR signal of DMPO-*OH decreased in the presence of either a *OH scavenger or a quencher of *O2 and under anaerobic conditions, whereas it increased depending on the concentration of DMPO. These results indicate both 1O2- and DMPO-mediated formation of free *OH during the reaction. When DMPO was replaced with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), no DEPMPO adduct of oxygen radical species was obtained. This suggests that 1O2, as an oxidizing agent, reacts little with DEPMPO, in which a strong electron-withdrawing phosphoryl group increases the oxidation potential of DEPMPO compared with DMPO. A linear correlation between the amounts of DMPO-*OH generated and the oxidation potentials of phenolic compounds was observed, suggesting that the electron-donating properties of phenolic compounds contribute to the appearance of *OH. These observations indicate that 1O2 reacts first with DMPO, and the resulting DMPO-1O2 intermediate is immediately decomposed/reduced to give *OH. Phenolic compounds would participate in this reaction as electron donors but would not contribute to the direct conversion of 1O2 to *OH. Furthermore, DEPMPO did not cause the spin-trapping agent-mediated generation of *OH like DMPO did. 相似文献
45.
Tomoko Nii Akira Takamura Kiminori Mohri Fumiyoshi Ishii 《Colloids and surfaces. B, Biointerfaces》2003,27(4):436-332
We examined hydrogenated purified egg yolk lecithins, having practical advantages over non-hydrogenated ones, as liposomal membrane materials. Liposomes were prepared by the microencapsulation vesicle (MCV) method in which liposomes are formed through two-step emulsification and dispersion. Three types of purified egg yolk lecithins with different iodine values were examined after being dissolved in one of three lipid solvents. The liposome size increased as the temperature during the second emulsification increased, being closer to the boiling temperature of the solvent. The preparation temperature in relation to the transition temperature of each lecithin was also a factor affecting liposome sizes. As for the encapsulation efficiencies of the model compound calcein in liposomes, they differed mainly depending on the solubility of each lecithin in a lipid solvent and it was more obvious in hydrogenated lecithins. A high preparation temperature resulted in lower encapsulation efficiencies, suggesting that leakage of encapsulated calcein was facilitated at high temperature in the MCV methods. There was a significant correlation between liposome sizes and encapsulation efficiencies in non-hydrogenated purified egg yolk lecithin but not in hydrogenated ones. When using hydrogenated purified egg yolk lecithins as liposomal membrane materials, it was suggested that a lipid solvent should be chosen so that a lecithin completely dissolves under the preparation condition in order to achieve a higher encapsulation efficiency. Smaller liposome particles were obtained when the second emulsification was performed at a lower temperature compared with the boiling point of the lipid solvent. These findings can be applied to control encapsulation efficiencies and particle sizes in each particular liposome preparation enclosing therapeutic agents. 相似文献
46.
[structure: see text]. A fast, inexpensive, and highly efficient synthesis of aromatic polyamide dendrimers without the need for protection and deprotection steps has been developed. Dendrons and third-generation polyamide dendrimers were easily prepared by a convergent approach involving activation of a focal point with thionyl chloride, followed by condensation with unprotected AB2 building blocks. 相似文献
47.
Hitoshi?MatsukiEmail author Michio?Yamanaka Hiroshi?Kamaya Shoji?Kaneshina Issaku?Ueda 《Colloid and polymer science》2005,283(5):512-520
The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH+) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality mt at 0X20.5, where X2 is the mole fraction of LC in the mixture, while they decreased rapidly with increasing mt at 0.5<X21. It was shown from the pH measurements that almost all LC molecules were changed into LCH+ ions by protonation at 0X20.5 and both forms coexisted only at 0.5<X21. The quantities of the respective LC and LCH+ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH+ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH+ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH+ in the region at 0X20.5, (2) preferential partitioning of LC at 0.5<X2<around 0.7, and (3) negative partitioning of LCH+ at around 0.7X21. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones. 相似文献
48.
49.
50.
Miyabe H Nishimura A Ueda M Naito T 《Chemical communications (Cambridge, England)》2002,(14):1454-1455
The indium-mediated allylation and alkylation reactions of the Oppolzer camphorsultam derivative of glyoxylic oxime ether proceeded with excellent diastereoselectivity in aqueous media, providing a variety of enantiomerically pure alpha-amino acids. 相似文献