全文获取类型
收费全文 | 5078篇 |
免费 | 247篇 |
国内免费 | 28篇 |
专业分类
化学 | 3904篇 |
晶体学 | 46篇 |
力学 | 71篇 |
数学 | 400篇 |
物理学 | 932篇 |
出版年
2023年 | 32篇 |
2022年 | 47篇 |
2021年 | 109篇 |
2020年 | 89篇 |
2019年 | 95篇 |
2018年 | 74篇 |
2017年 | 71篇 |
2016年 | 177篇 |
2015年 | 144篇 |
2014年 | 179篇 |
2013年 | 314篇 |
2012年 | 360篇 |
2011年 | 442篇 |
2010年 | 256篇 |
2009年 | 249篇 |
2008年 | 354篇 |
2007年 | 289篇 |
2006年 | 295篇 |
2005年 | 227篇 |
2004年 | 207篇 |
2003年 | 179篇 |
2002年 | 213篇 |
2001年 | 102篇 |
2000年 | 106篇 |
1999年 | 61篇 |
1998年 | 39篇 |
1997年 | 51篇 |
1996年 | 46篇 |
1995年 | 35篇 |
1994年 | 27篇 |
1993年 | 32篇 |
1992年 | 39篇 |
1991年 | 23篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1970年 | 17篇 |
排序方式: 共有5353条查询结果,搜索用时 187 毫秒
901.
Several nucleic acid analogues as shown in Scheme 1 were synthesized by alternating copolymerization of nucleoside analogues with maleic anhydride or acrylic anhydride. These polymers showed similar physicochemical properties to those of the natural polymers, such as base-pairing and base-stacking. Polymer 3U, for example, formed 1:1 complex with poly(adenylic acid) by base-pairing. Polymer 4A showed 33% of hypochromicity compared with the UV-absorption of adenosine due to the base-stacking. Polymer 5 catalyzed the cleavage of DNA and the hydrolysis of phosphodiester with a rate acceleration of 103 compared with the uncatalyzed reaction. 相似文献
902.
Miscibility behavior and rheological properties with mechanical spectroscopy study of both poly(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) and biodegradable synthetic aliphatic polyester (BDP)/linear low density polyethylene (LLDPE) were investigated. Blends of BDP with LLDPE were immiscible, showing two separate Tg values in all compositions; whereas blends of PHB with PEO were miscible, showing a single Tg in the whole range of compositions. However, the shear viscosities of both synthetic and biosynthetic blend systems decrease with increasing shear rate. When a modified Cole-Cole plot of the blend system is further considered, the logG′-logG” plot shows little sensitivity to a variation in both LLDPE composition for synthetic BDP and PEO composition for biosynthetic PHB. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) random copolymers were also investigated. 相似文献
903.
904.
905.
906.
907.
Peddaboodi Gopikrishna Huijeong Choi Do Hui Kim Jun Ho Hwang Youngwan Lee Hyeonwoo Jung Gyeonghwa Yu Telugu Bhim Raju Eunji Lee Youngu Lee Shinuk Cho BongSoo Kim 《Chemical science》2021,12(42):14083
The concurrent enhancement of short-circuit current (JSC) and open-circuit voltage (VOC) is a key problem in the preparation of efficient organic solar cells (OSCs). In this paper, we report efficient and stable OSCs based on an asymmetric non-fullerene acceptor (NFA) IPC-BEH-IC2F. The NFA consists of a weak electron-donor core dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (BEH) and two kinds of strong electron-acceptor (A) units [9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) with a tricyclic fused system and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC2F)]. For comparison, the symmetric NFAs IPC-BEH-IPC and IC2F-BEH-IC2F were characterised. The kind of flanking A unit significantly affects the light absorption features and electronic structures of the NFAs. The asymmetric IPC-BEH-IC2F has the highest extinction coefficient among the three NFAs owing to its strong dipole moment and highly crystalline feature. Its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels lie between those of the IPC-BEH-IPC and IC2F-BEH-IC2F molecules. The IPC group also promotes molecular packing through the tricyclic π-conjugated system and achieves increased crystallinity compared to that of the IC2F group. Inverted-type photovoltaic devices based on p-type polymer:NFA blends with PBDB-T and PM6 polymers as p-type polymers were fabricated. Among all these devices, the PBDB-T:IPC-BEH-IC2F blend device displayed the best photovoltaic properties because the IPC unit provides balanced electronic and morphological characteristics. More importantly, the PBDB-T:IPC-BEH-IC2F-based device exhibited the best long-term stability owing to the strongly interacting IPC moiety and the densely packed PBDB-T:IPC-BEH-IC2F film. These results demonstrate that asymmetric structural modifications of NFAs are an effective way for simultaneously improving the photovoltaic performance and stability of OSCs.A 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) moiety in asymmetric non-fullerene acceptors promotes the formation of a densely packed crystalline structure, enabling efficient and long-term stable organic solar cells. 相似文献
908.
909.
910.