全文获取类型
收费全文 | 1086篇 |
免费 | 53篇 |
国内免费 | 13篇 |
专业分类
化学 | 695篇 |
力学 | 13篇 |
数学 | 263篇 |
物理学 | 181篇 |
出版年
2023年 | 12篇 |
2022年 | 4篇 |
2021年 | 17篇 |
2020年 | 23篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 18篇 |
2016年 | 43篇 |
2015年 | 26篇 |
2014年 | 44篇 |
2013年 | 67篇 |
2012年 | 84篇 |
2011年 | 84篇 |
2010年 | 63篇 |
2009年 | 55篇 |
2008年 | 73篇 |
2007年 | 73篇 |
2006年 | 59篇 |
2005年 | 73篇 |
2004年 | 57篇 |
2003年 | 33篇 |
2002年 | 44篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 15篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1931年 | 1篇 |
1930年 | 1篇 |
1926年 | 1篇 |
1922年 | 1篇 |
排序方式: 共有1152条查询结果,搜索用时 15 毫秒
1.
Beatriz Pelado Dr. Fawzi Abou‐Chahine Joaquín Calbo Dr. Rubén Caballero Dr. Pilar de la Cruz Dr. José M. Junquera‐Hernández Prof. Enrique Ortí Prof. Nikolai V. Tkachenko Prof. Fernando Langa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5814-5825
The role of π‐conjugated molecular bridges in through‐space and through‐bond electron transfer is studied by comparing two porphyrin–fullerene donor–acceptor (D–A) dyads. One dyad, ZnP–Ph–C60 (ZnP=zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP–EDOTV–C60, introduces an additional 3,4‐ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge‐separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP–Ph–C60 dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D–A bridge. 相似文献
2.
3.
4.
5.
6.
7.
π‐Expanded α,β‐Unsaturated Ketones: Synthesis,Optical Properties,and Two‐Photon‐Induced Polymerization 下载免费PDF全文
Rashid Nazir Dr. Florent Bourquard Evaldas Balčiūnas Dr. Sabina Smoleń Dr. David Gray Prof. Dr. Nikolai V. Tkachenko Dr. Maria Farsari Prof. Dr. Daniel T. Gryko 《Chemphyschem》2015,16(3):682-690
A library of π‐expanded α,β‐unsaturated ketones was designed and synthesized. They were prepared by a combination of Wittig reaction, Sonogashira reaction, and aldol condensation. It was further demonstrated that the double aldol condensation can be performed effectively for highly polarized styrene‐ and diphenylacetylene‐derived aldehydes. The strategic placement of two dialkylamino groups at the periphery of D ‐π‐A‐π‐D molecules resulted in dyes with excellent solubility. These ketones absorb light in the region 400–550 nm. Many of them display strong solvatochromism so that the emission ranges from 530–580 nm in toluene to the near‐IR region in benzonitrile. Ketones based on cyclobutanone as central moieties display very high fluorescence quantum yields in nonpolar solvents, which decrease drastically in polar media. Photophysical studies of these new functional dyes revealed that they possess an enhanced two‐photon absorption cross section when compared with simpler ketone derivatives. Due to strong polarization of the resulting dyes, values of two‐photon absorption cross sections on the level of 200–300 GM at 800 nm were achieved, and thanks to that as well as the presence of the keto group, these new two‐photon initiators display excellent performance so that the operating region is 5–75 mW in some cases. 相似文献
8.
The authors show that for any e ∈]0,1[,there exists an analytic outside zero solution to a uniformly elliptic conformal Hessian equation in a ball B C R5 which belongs to C1'ε(B) \ C1'ε+(B). 相似文献
9.
Alexander?Fabricant Nikolai?Kutev Tsviatko?RangelovEmail author 《Mediterranean Journal of Mathematics》2017,14(1):21
Improved Hardy inequality with double singular kernel in bounded, star-shaped domains \(\Omega \subset R^n\) is proved. The case of singularity at an interior point and on the boundary of the domain is considered. The Hardy constant is optimal and the inequality is sharp due to the additional term. 相似文献
10.
Jarno Riefer Ludwig Zapf Dr. Raphael Wirthensohn Dr. Philipp T. Hennig Dr. Tatjana Ribbeck Dr. Jan A. P. Sprenger Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《European journal of organic chemistry》2023,26(17):e202300031
Cyanoborane adducts of the Lewis acids B(CN)3, BF(CN)2, and BH(CN)2 with pyridine and 4-cyanopyridine have been obtained in high yields. The syntheses were accomplished by oxidation of the readily available potassium salts of the cyano(hydrido)borate anions [BH(CN)3]− ( MHB ), [BFH(CN)2]− ( FHB ), and [BH2(CN)2]− ( DHB ) with bromine in the presence of the respective pyridine derivative C5H5N or 4-CN-C5H4N as starting material. All six cyanoborane adducts have been characterized by NMR and vibrational spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The reduction of the cyanoborane adducts has been investigated by cyclic voltammetry and the Lewis acidity of the different cyanoboranes has been assessed using the Gutmann-Beckett method. Selected experimental data and trends are compared to theoretical ones, for example fluoride ion affinities (FIAs). 相似文献