全文获取类型
收费全文 | 6400篇 |
免费 | 273篇 |
国内免费 | 1523篇 |
专业分类
化学 | 3751篇 |
晶体学 | 6篇 |
力学 | 446篇 |
综合类 | 62篇 |
数学 | 1060篇 |
物理学 | 2871篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 23篇 |
2014年 | 16篇 |
2013年 | 62篇 |
2012年 | 76篇 |
2011年 | 1123篇 |
2010年 | 571篇 |
2009年 | 583篇 |
2008年 | 91篇 |
2007年 | 102篇 |
2006年 | 149篇 |
2005年 | 289篇 |
2004年 | 1064篇 |
2003年 | 636篇 |
2002年 | 476篇 |
2001年 | 369篇 |
2000年 | 131篇 |
1999年 | 155篇 |
1998年 | 199篇 |
1997年 | 141篇 |
1996年 | 71篇 |
1995年 | 94篇 |
1994年 | 66篇 |
1993年 | 358篇 |
1992年 | 409篇 |
1991年 | 252篇 |
1990年 | 258篇 |
1989年 | 255篇 |
1988年 | 55篇 |
1987年 | 12篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1908年 | 1篇 |
排序方式: 共有8196条查询结果,搜索用时 31 毫秒
991.
992.
目前有大量关于全程电荷匹配设计肽的应用的研究,但是关于半程电荷匹配设计肽作为药物的应用研究却未见报道.本文对新型设计的半程电荷匹配肽P9(AC-Pro-Ser-Phe-Asn-Phe-Lys-Phe-Glu-Pro-NH2)的研究发现,P9可以成功地将作为疏水药物模型的芘稳定悬浮于水溶液中.大豆卵磷脂微囊被用以模拟细胞膜.荧光数据显示芘可以借助P9的包埋作用以晶体状态存在于水溶液中.并且当包埋体加入到脂质体微囊体系中时,芘可以从P9的包埋体系中以分子形态释放到膜的脂质层内.实验发现当包埋于芘上的P9较多,包埋壁较厚,芘的释放速度相对变缓.我们可以利用这一特性,通过调节加入的P9的浓度来控制包埋于芘上P9的厚度,从而控制芘的释放速率.研究表明,具有半程电荷匹配性质的P9肽可以作为运载疏水药物的载体. 相似文献
993.
反相液相色谱中离子抑制剂的有机调节剂作用 总被引:1,自引:0,他引:1
系统地研究了在反相液相色谱(RPLC)流动相中作为离子抑制剂的酸、碱及缓冲溶液对中性化合物保留行为的影响,着重探讨了有机酸、有机碱离子抑制剂的有机调节剂作用,定量地考察了甲醇和乙腈、甲醇和乙酸、甲醇和三乙胺、乙腈和乙酸、乙腈和三乙胺在十八烷基硅烷键合相上洗脱强度之间的关系,为RPLC中有机调节剂的洗脱强度排序提供一种评判方法.另外,讨论了乙酸和三乙胺作为有机调节剂时不同的作用机理.本实验结果对于RPLC分离方法的快速建立和准确优化都具有一定的借鉴意义. 相似文献
994.
Ke Xin Huang Yu Bing Feng Wei Yao Lei Xiang Yang Feng Wang Hai Bo Li Su Zeng Jing Xu Gong Ming Hui Hu Yu Zhao Xiu Mei Wu Xiao Kun Li Jia Qu 《中国化学快报》2009,20(10):1187-1190
Four naturally rare 5,6,7-trimethoxy-2,3-cis-dihydroflavonols(3-6) and two 5,6,7-trimethoxy-2,3-trans-dihydroflavonols(7-8) were designed and synthesized.Their antioxidative properties were evaluated by way of examining their scavenging capacities towards DPPH and O_2~(·-) free radicals,as well as by measuring their inhibitory ability against LPO.Both the 2,3-trans and the 2,3- cis conformers exhibited certain quenching abilities to DPPH and O_2~(·-) radicals,while most of the synthetic dihydroflavonols ... 相似文献
995.
Preparation of an amphiphilic graft copolymer having poly(phthalazinone ether sulfone ketone)(PPESK) as main chains was carried out by atom transfer radical polymerization(ATRP).The precursor,chloromethylated PPESK (CMPPESK),was prepared by using chioromethylether as chloromethylation agent.Then,poly(ethylene glycol) methyl ether methacrylate(PEGMA) was used as monomer to synthesize PPESK-g-P(PEGMA) by ATRP method under the catalysis of a cuprous chloride/2,2'-bipyridyl system.PPESK/PPESK-g-P(PEGMA) blen... 相似文献
996.
Yu Lu Chen Yi Bo Niea Ming Wu Ding a Key Laboratory of Pesticide & Chemical Biology of Ministry of Education Central China Normal University Wuhan China b 《中国化学快报》2009,(9)
5,6-Dihydrothieno[3′,2′:4,5]thieno[2,3-d]pyrimidin-4(3H)-ones 6 were synthesized in yields of 71-87%by a consecutive method,which includes aza-Wittig reaction of iminophosphorane 3 with aromatic isocynate to give carbodiimide 4 and subsequent reaction of 4 with various amines,phenols or alcohols in the presence of catalytic amount of sodium ethoxide or solid potassium carbonate. 相似文献
997.
Ying Peng Huo Xu Qiu Wei Yan Shao Lin Kun An Xian Zhang Bu Lian Quan Gu 《中国化学快报》2009,20(11):1291-1295
Series of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives were synthesized in acceptable to good yields by treatment of the curcuminoids with aqueous ammonia,the mechanism was proposed.By modification of the primary products,total 13 new compounds were obtained.The structures of all products were elucidated by spectroscopy analysis including HR-MS,~1H NMR and ~(13)C NMR. 相似文献
998.
Click chemistry was applied to immobilize L-proline derivative onto azide-modified silica gel to give a novel chiral stationary phase(denoted as click-CSP) for ligand exchange chromatography.The developed protocol combines the benefits of operational simplicity,exceptionally mild conditions and high surface loadings.The enantioselectivityαof some DL-amino acids on the click-CSP were found to be in the range from 1.13 to 3.46.The chromatographic resolutions of some DL-amino acids and the stability study f... 相似文献
999.
HUANG HuoQiang PAN XuLin JI ChangJiu ZENG GuangZhi JIANG LiHua FU Xiang LIU JiKai HAO XiaoJiang ZHANG YingJun & TAN NingHua State Key Laboratory of Phytochemistry Plant Resources in West China Kunming Institute of Botany Chinese Academy of Sciences Kunming China Graduate University of the Chinese Academy of Sciences Beijing 《中国科学B辑(英文版)》2009,(3)
Carbonic anhydrase Ⅱ (CAⅡ) is an important enzyme complex with Zn2+,which is involved in many physiological and pathological processes, such as calcification, glaucoma and tumorigenicity. In order to search for novel inhibitors of CAⅡ, inhibition assay of carbonic anhydrase Ⅱ was performed, by which seven natural phenolic compounds, including four phenolics (grifolin, 4-O-methyl-grifolic acid, grifolic acid, and isovanillic acid) and three flavones (eriodictyol, quercetin and puerin A), showed in-hibitory a... 相似文献
1000.
ZENG Xi WU Chong DONG Lei MU Lan XUE SaiFeng & TAO Zhu College of Chemistry Chemical Engineering Guizhou University Guiyang China Key Laboratory of Macrocyclic Supramolecular Chemistry of Guizhou Province Guiyang 《中国科学B辑(英文版)》2009,(4)
A new tripodal rhodamine B derivative 2 was designed and synthesized by tripodal trialdehyde and rhodamine B hydrazide for the first time. This derivative could be used as a fluorescent chemosensor for the selective and sensitive determination of copper(II) in Tris-HCl buffer and ethanol aqueous mixed media. Under the optimum conditions described herein,fluorescence enhancement at 557/577 nm was linearly related to the concentration of copper(II) in the range of 0.10 to 10.00×10-5 mol·L-1,with a corre-latio... 相似文献