全文获取类型
收费全文 | 1276898篇 |
免费 | 31275篇 |
国内免费 | 10296篇 |
专业分类
化学 | 630967篇 |
晶体学 | 20204篇 |
力学 | 74370篇 |
综合类 | 323篇 |
数学 | 238470篇 |
物理学 | 354135篇 |
出版年
2021年 | 13899篇 |
2020年 | 16279篇 |
2019年 | 16509篇 |
2016年 | 27488篇 |
2015年 | 21148篇 |
2014年 | 31034篇 |
2013年 | 75083篇 |
2012年 | 35134篇 |
2011年 | 28917篇 |
2010年 | 35548篇 |
2009年 | 38635篇 |
2008年 | 29239篇 |
2007年 | 23901篇 |
2006年 | 32372篇 |
2005年 | 23432篇 |
2004年 | 26016篇 |
2003年 | 25309篇 |
2002年 | 27053篇 |
2001年 | 24698篇 |
2000年 | 22533篇 |
1999年 | 21601篇 |
1998年 | 20758篇 |
1997年 | 20738篇 |
1996年 | 21003篇 |
1995年 | 19131篇 |
1994年 | 18516篇 |
1993年 | 18044篇 |
1992年 | 17506篇 |
1991年 | 17851篇 |
1990年 | 17081篇 |
1989年 | 17183篇 |
1988年 | 16706篇 |
1987年 | 16756篇 |
1986年 | 15635篇 |
1985年 | 22112篇 |
1984年 | 23486篇 |
1983年 | 19756篇 |
1982年 | 21500篇 |
1981年 | 20754篇 |
1980年 | 20082篇 |
1979年 | 20089篇 |
1978年 | 21507篇 |
1977年 | 21056篇 |
1976年 | 20715篇 |
1975年 | 19383篇 |
1974年 | 19011篇 |
1973年 | 19489篇 |
1972年 | 14014篇 |
1968年 | 11889篇 |
1967年 | 12269篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
212.
213.
Effect of additive length and chemistry on the morphology of blends of conjugated thiophenes and fullerene derivative acceptor molecules 下载免费PDF全文
Small molecule additives have been shown to increase the device efficiency of conjugated polymer (donor) and fullerene derivative (acceptor) based organic solar cells by modifying the morphology of the device active layer. In this paper we conduct a systematic study of how additives affect the donor‐acceptor morphology using molecular dynamics simulations of blends of thiophene‐based oligomers, mimicking poly(3‐dodecylthiophene) (P3DDT) or poly(2,2′:5′,2”‐3,3”‐didocyl‐terthiophene) (PTTT), and fullerene derivatives with additives of varying length and chemical functionalization, mimicking experimentally used additives like methyl ester additives, diiodooctane, and alkanedithiols. We find that functionalization of additives with end groups that are attracted to acceptor molecules are necessary to induce increased donor‐acceptor macrophase separation. In blends where acceptors intercalate between oligomer alkyl side chains, functionalized additives decrease acceptor intercalation. Functionalized additives with shorter alkyl segments increase acceptor macrophase separation more than additives with same chemical functionalization but longer alkyl segments. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1046–1057 相似文献
214.
215.
216.
Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8047-8051
A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups. 相似文献
217.
D3h‐Symmetric Porphyrin‐Based Rigid Macrocyclic Ligands for Multicofacial Multinuclear Complexes in a One‐Nanometer‐Sized Cavity 下载免费PDF全文
Yohei Ohkoda Akane Asaishi Tomoya Namiki Tomoaki Hashimoto Midori Yamada Koichiro Shirai Yuta Katagami Dr. Tomoaki Sugaya Prof. Makoto Tadokoro Prof. Akiharu Satake 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11745-11756
The one‐step synthesis of D3h‐symmetric cyclic porphyrin trimers 1 composed of three 2,2′‐[4,4′‐bis(methoxycarbonyl)]bipyridyl moieties and three porphyrinatozinc moieties was achieved from a nickel‐mediated reductive coupling of meso‐5,15‐bis(6‐chloro‐4‐methoxycarbonylpyrid‐2‐yl)porphyrinatozinc. Although cyclic trimers 1 were obtained as a mixture that included other cyclic and acyclic porphyrin oligomers, an extremely specific separation was observed only for cyclic trimers 1 when using columns of silica gel modified with pyrenylethyl, cyanopropyl, and other groups. Structural analysis of cyclic trimers 1 was carried out by means of NMR spectroscopy and X‐ray crystallography. Treatment of an η3‐allylpalladium complex with a cyclic trimer gave a tris(palladium) complex containing three η3‐allylpalladium groups inside the space, which indicated that the bipyridyl moieties inside the ring could work as bidentate metalloligands. 相似文献
218.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
219.
220.