全文获取类型
收费全文 | 4004篇 |
免费 | 241篇 |
国内免费 | 206篇 |
出版年
2023年 | 67篇 |
2022年 | 81篇 |
2021年 | 89篇 |
2020年 | 91篇 |
2019年 | 146篇 |
2018年 | 160篇 |
2017年 | 104篇 |
2016年 | 110篇 |
2015年 | 137篇 |
2014年 | 196篇 |
2013年 | 377篇 |
2012年 | 172篇 |
2011年 | 166篇 |
2010年 | 184篇 |
2009年 | 165篇 |
2008年 | 189篇 |
2007年 | 242篇 |
2006年 | 195篇 |
2005年 | 173篇 |
2004年 | 111篇 |
2003年 | 110篇 |
2002年 | 114篇 |
2001年 | 87篇 |
2000年 | 70篇 |
1999年 | 62篇 |
1998年 | 49篇 |
1997年 | 45篇 |
1996年 | 51篇 |
1995年 | 36篇 |
1994年 | 41篇 |
1993年 | 33篇 |
1992年 | 51篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 38篇 |
1988年 | 36篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 63篇 |
1983年 | 38篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 32篇 |
1979年 | 34篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有4451条查询结果,搜索用时 984 毫秒
1.
The interrelation was studied between the phototransient absorbing maximally at 412 nm (M412) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M412 was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M412 which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M412 was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M412 without affecting the level of M412 which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca2+ and their antagonists La3+ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed. 相似文献
2.
3.
Yitao Luo Chengqiang Zhang Li Ma Yuxiao Zhang Zhengyuan Liu Li Chen Rui Wang Yujing Luan Yulan Rao 《Journal of lipid research》2022,63(6):100228
7-dehydrocholesterol (7-DHC) and cholesterol (CHOL) are biomarkers of Smith-Lemli-Opitz Syndrome (SLOS), a congenital autosomal recessive disorder characterized by elevated 7-DHC level in patients. Hair samples have been shown to have great diagnostic and research value, which has long been neglected in the SLOS field. In this study, we sought to investigate the feasibility of using hair for SLOS diagnosis. In the presence of antioxidants (2,6-ditert-butyl-4-methylphenol and triphenylphosphine), hair samples were completely pulverized and extracted by micro-pulverized extraction in alkaline solution or in n-hexane. After microwave-assisted derivatization with N,O-Bis(trimethylsilyl)trifluoroacetamide, the analytes were measured by GC-MS. We found that the limits of determination for 7-DHC and CHOL were 10 ng/mg and 8 ng/mg, respectively. In addition, good linearity was obtained in the range of 50–4000 ng/mg and 30–6000 ng/mg for 7-DHC and CHOL, respectively, which fully meets the requirement for SLOS diagnosis and related research. Finally, by applying the proposed method to real hair samples collected from 14 healthy infants and two suspected SLOS patients, we confirmed the feasibility of hair analysis as a diagnostic tool for SLOS. In conclusion, we present an optimized and validated analytical method for the simultaneous determination of two SLOS biomarkers using human hair. 相似文献
4.
I. J. Pickering Graham N. George Verena Van Fleet-Stalder Thomas G. Chasteen Roger C. Prince 《Journal of biological inorganic chemistry》1999,4(6):791-794
Received: 2 April 1999 / Accepted: 17 September 1999 相似文献
5.
6.
7.
8.
Kiyohiko Sugano 《化学与生物多样性》2009,6(11):2014-2029
Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed. 相似文献
9.
10.