全文获取类型
收费全文 | 622篇 |
免费 | 14篇 |
国内免费 | 45篇 |
专业分类
系统科学 | 3篇 |
丛书文集 | 20篇 |
教育与普及 | 4篇 |
现状及发展 | 30篇 |
综合类 | 624篇 |
出版年
2024年 | 1篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 9篇 |
2012年 | 22篇 |
2011年 | 25篇 |
2010年 | 14篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 34篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 27篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有681条查询结果,搜索用时 31 毫秒
81.
新型抗癌药——硒化多烯脂肪酸多相脂质体的研究 总被引:1,自引:0,他引:1
用作者首次合成的几种硒化多烯脂肪酸,分别制成乳剂和多相脂质体,进行动物体内抗癌活性实验,结果表明,硒化亚油酸乳剂(62)在200mg/(kg·d)的剂量下对S_(180)。实体瘤的抑制率为28.7%,而其多相脂质体(118)在相同剂量下对肿瘤的抑制率为45.1%;硒化蓖酸乳剂(92)在200mg/(kg·d)的剂量下对肿瘤的抑制率为33.3%,而其多相脂质体(114)在400mg/(kg·d)剂量下的抑瘤率则达61.4%,说明当将药物包封于脂质体后,可使其毒性下降,抗癌活性明显升高。 相似文献
82.
在芽殖酵母中构建CDC10-mCherry和SPC42-mCherry荧光蛋白, 作为酵母细胞周期不同时期的报告系统。根据酵母细胞中芽环(CDC10-mCherry)的产生和消失以及纺锤体极体(SPC42-mCherry)的复制和分离,可以测量细胞周期中 G1期、S期、Early M期和Late M期的时间长度。在此报告系统的基础上, 分别构建S期细胞周期蛋白CLB5-GFP和M 期细胞周期蛋白CLB2-GFP菌株, 实现单细胞观测, 检验报告系统工作的稳定性和准确性。该报告系统可作为研究酵母细胞周期不同时期时间长度等定量生物学问题的背景菌株。 相似文献
83.
84.
85.
Jing Li XiaoMan Liu YueTong Ji ZhenHui Qi Yan Ge JiaYun Xu JunQiu Liu GuiMin Luo JiaCong Shen 《科学通报(英文版)》2008,53(16):2454-2461
Glutathione peroxidase (GPx, EC1.11.1.9), an important anti-oxidative selenoenzyme, can catalyze the reduction of harmful hydroperoxides with concomitant glutathione, thereby protecting cells and other biological issues against oxidative damage. It captures considerable interest in redesign of its function for either the mechanism study or the pharmacological development as an antioxidant. In order to develop a general strategy for specifically targeting and operating selenium in active sites of enzymes, the catalytically essential residue selenocysteine (Sec) was first successfully bioincorporated into the catalytic center of subtilisin by using an auxotrophic expression system. The studies of the catalytic activity and the steady-state kinetics demonstrated that selenosubtilisin is an excellent GPx-like biocatalyst. In comparison with the chemically modified method, biosynthesis exhibits obvious advantages: Sec could be site-directly incorporated into active sites of enzymes to overcome the non-specificity generated by chemical modification. This study provides an important strategy for specifically targeting and operating selenium in the active site of an enzyme. 相似文献
86.
S. Ruggieri L. Gregori P. Natalmi A. Vita G. Magni 《Cellular and molecular life sciences : CMLS》1988,44(1):27-29
Summary A homogeneous preparation of yeast NMN adenylyltransferase (EC 2.7.7.1) showed microheterogeneity, which was revealed by FPLC (Fast Protein Liquid Chromatography) ion exchange chromatography. The resolved components have been characterized with respect to electrophoretic behavior and adenine content. The results led to a hypothesis about a possible role of poly(ADP-ribosylation) in modulating the enzyme activity. 相似文献
87.
CHENSanfeng GUANYu TURan SUNWengai LIJilun 《科学通报(英文版)》2005,50(7):641-646
NifA in AzospiriUum brasilense plays a key role in regulating the synthesis and activity of nitrogenase in response to ammonia and oxygen available. In this work we used the yeast two-hybrid system to identify the proteins that interact with NifA. The nifA gene was fused to the yeast two-hybrid vector pGBD-C2, and three A. brasilense Sp7 genomic libraries for use in yeast two-hybrid studies were constructed. Screening of the libraries identified four clones encoding proteins that interact with NifA. The confirmation of the interactions of each gene product of the four clones and NifA were carried out by exchanging the vectors for nifA and the four clones and by mutageneses of the four clones with shift reading frame experiments in yeast two-hybrid studies. DNA sequence analyses showed that two clones encode proteins containing PAS domains that play an important role in signal transduction. One clone has high similarity with the fhuE gene of Escherichia coli, whose gene product is involved in iron uptake and transportation, and the other clone encodes an unknown protein. 相似文献
88.
本文以4,6-二溴代苤硒脑为活性物质,邻苯二甲酸二丁酯为增塑剂,PVC为支持体研制了亚硒酸根离子选择性电极.电极对硒(Ⅳ)的响应范围为3.2×10~(-6)~1.0×10~(-1)mol硒(Ⅳ)/L,斜率为-23.6mV(21℃),检测限为1.0×10~(-6)mol硒(Ⅳ)/L. 相似文献
89.
90.
为实现RNA和β(1,3)-D-葡聚糖的综合提取,通过碱-酶提取法和优化稀碱提取条件,研究了温度、NaOH质量分数对RNA提取的影响.结果表明:温度为100℃,NaOH质量分数为4%时,提取率为7.65%,纯度为70.24%.进一步比较中性蛋白酶和碱性蛋白酶对β-(1,3)-D-葡聚糖提取的影响,发现中性蛋白酶得到的产物较多,纯度较高,实验结果为进一步的工业化生产奠定了基础. 相似文献