全文获取类型
收费全文 | 2698篇 |
免费 | 84篇 |
国内免费 | 17篇 |
专业分类
化学 | 1544篇 |
晶体学 | 27篇 |
力学 | 151篇 |
数学 | 327篇 |
物理学 | 750篇 |
出版年
2023年 | 8篇 |
2022年 | 43篇 |
2021年 | 54篇 |
2020年 | 41篇 |
2019年 | 45篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 51篇 |
2015年 | 67篇 |
2014年 | 90篇 |
2013年 | 139篇 |
2012年 | 175篇 |
2011年 | 201篇 |
2010年 | 125篇 |
2009年 | 112篇 |
2008年 | 197篇 |
2007年 | 137篇 |
2006年 | 152篇 |
2005年 | 131篇 |
2004年 | 108篇 |
2003年 | 84篇 |
2002年 | 91篇 |
2001年 | 66篇 |
2000年 | 66篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 22篇 |
1996年 | 44篇 |
1995年 | 36篇 |
1994年 | 36篇 |
1993年 | 41篇 |
1992年 | 30篇 |
1991年 | 36篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有2799条查询结果,搜索用时 15 毫秒
31.
The acylation of 2-methoxynaphthalene with acetic anhydride was carried out over zeolite beta catalysts having various Si/Al
ratios. It was found that the reaction performance is strongly dependent on the Si/Al ratio of the catalyst. The catalytic
reaction features were elucidated in terms of the acidic properties of the catalysts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
32.
5-Substituted-1,3,4-oxadiazolin-2-ones 2 were synthesized by the oxidation of carbo-t-butoxyhydrazones 1 of aromatic aldehydes with lead tetraacetate or, preferably, iodosobenzene diacetate. In some instances 5-acetoxy-1,3,4-oxadiazoles 3 were obtained along with 2 . The oxidation of carboethoxyhydrazones 4 gave 2-ethoxy-1,3,4-oxadiazoles 5 . 相似文献
33.
Depigmenting activity and low cytotoxicity of alkoxy benzoates or alkoxy cinnamte in cultured melanocytes 总被引:2,自引:0,他引:2
To obtain effective and safe topical depigmenting agents, we synthesized hydroxybenzoates, alkoxybenzoates, and 3,4,5-trimethoxycinnamate containing a thymol moiety and screened then for high-level inhibitory activity against melanin synthesis in cultured melanocytes. Eight compounds were tested for their depigmenting effect and cytotoxicity using a murine melanocyte cell line. We found that 3,4,5-trialkoxybenzoates and 3,4,5-trimethoxycinnamate, synthesized by conjugating 3,4,5-trialkoxybenzoic acids and 3,4,5-trimethoxycinnmic acid with thymol, showed a potent depigmenting effect and low cytotoxicity. Compound 4h, 5-methyl-2-(methylethyl)phenyl (2E)-3-(3,4,5-trimethoxyphenyl)prop-2-enoate, showed the most potent depigmenting effect (IC50=10 microM) with low cytotoxicity (IC50=200 microM). 相似文献
34.
Integrins are heterodimeric glycoproteins that have been found to undergo dynamic temporal and spatial changes in the endometrium during the menstrual cycle and in early pregnancy. Specificity of integrins is known to be different in human endometrial stromal cells and decidual cells. These shifts of integrins suggested to play an important role in embryo implantation and can be modulated by progesterone, cAMP derivatives, and cytokines. The mechanisms of decidualization and its precise physiological role are still not clearly understood and in vitro systems could provide an alternative that overcomes limitations of studying such complex biological phenomena in vivo at the time of implantation. This study was undertaken to establish an in vitro model system for human decidualization using 8-bromo-cAMP and to investigate the characteristics of stromal integrin expression in vitro by 8-Br-cAMP. Endometrial stromal cells were isolated and cultured, and then were induced to decidualize by 0.5 mM 8-Br-cAMP for 15 days. Immunofluorescence staining and flow cytometric analyses of the integrin subunits (alpha1, alpha4, alpha5, alpha6, beta1 and alphavbeta3) were performed at day 9. In the presence of 8-Br-cAMP, the staining intensity of alphavbeta3 was significantly higher than control and measurements for alpha1, alpha4, alpha5, alpha6, and beta1 were similar. Immunofluorescent localization of the integrins reflected the differences obtained from the flow cytometric analyses described above. In summary, the expression of alphavbeta3 integrin increased in stromal cells in vitro decidualized by 8-Br-cAMP and this up-regulation of alphavbeta3 integrin expression during decidualization might influence on human implantation. 相似文献
35.
The fluid motion of an assemblage of cohesionless granules is governed by the balance laws of mass, momentum and energy and is special because due to the variability of the mean free path of the particles the density is not preserved and the particle fluctuation energy (= granular temperature) is determined together with the mean fields. Constitutive equations are postulated for the dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate in terms of the mean free path length, the time of encounter between two collisions and geometric and dynamic quantities via dimensional arguments. The model defines the time of encounter to consist of the free flying time between collisions plus the contact duration. The inclusion of the latter brings in the elasticity of the particles and introduces a relaxation mechanism that explains the typical behaviour of shear and fluidized layers better than has been done by previous models. 相似文献
36.
37.
38.
39.
40.