全文获取类型
收费全文 | 617篇 |
免费 | 29篇 |
专业分类
化学 | 497篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 68篇 |
物理学 | 72篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 26篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 23篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 44篇 |
2012年 | 49篇 |
2011年 | 43篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 32篇 |
2005年 | 24篇 |
2004年 | 28篇 |
2003年 | 25篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有646条查询结果,搜索用时 46 毫秒
41.
We present a two-photon fluorescence microscope based on a three-port single-mode optical fiber coupler. It is found that the coupler behaves as a low-pass filter that can deliver an ultrashort-pulsed laser beam of as much as 150 mW of power in the wavelength range from 770 to 870 nm as well as collect a two-photon fluorescence signal in the visible range. As a result of using the fiber coupler, the new two-photon imaging system exhibts a number of advantages, including a compact arrangement, freedom from vibration from lasers and electronic devices, self-alignment, reduction of multiple scattering, and an enhanced optical sectioning effect. The effectiveness of the new instrument is demonstrated with a set of three-dimensional images of biological samples. This instrument may make two-photon fluorescence endoscopy possible for in vivo medical applications. 相似文献
42.
43.
44.
45.
A theorem of Green, Lazarsfeld and Simpson (formerly a conjecture of Beauville and Catanese) states that certain naturally defined subvarieties of the Picard variety of a smooth projective complex variety are unions of translates of abelian subvarieties by torsion points. Their proof uses analytic methods. We refine and give a completely new proof of their result. Our proof combines galois-theoretic methods and algebraic geometry in positive characteristic. When the variety has a model over a function field and its Picard variety has no isotrivial factors, we show how to replace the galois-theoretic results we need by results from model theory (mathematical logic). Furthermore, we prove partial analogs of the conjecture of Beauville and Catanese in positive characteristic. 相似文献
46.
The inelastic neutron scattering (INS) and periodic density functional theory (DFT) vibrational spectra of H3B:NH3 are reported to 1600 cm-1. The H3B:NH3 structural and INS features, specifically the reduced solid-state B:N dative bond length and the altered B:N stretching frequency, are reproduced by the periodic DFT calculations, placing the B:N stretching mode at 800 cm-1, in excellent agreement with experiment relative to previous nonperiodic theoretical treatments of this molecule. 相似文献
47.
48.
Wongi Park Minyong Yang Hyewon Park Dr. Joanna M. Wolska Dr. Hyungju Ahn Prof. Dr. Tae Joo Shin Prof. Dr. Damian Pociecha Prof. Dr. Ewa Gorecka Prof. Dr. Dong Ki Yoon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(24):7108-7113
Herein, it is reported that the polymorphism in the helical nanofilament (HNF, B4) liquid-crystalline phase depends on the fabrication methods, that is, UV-driven formation and template-assisted self-assembly in the nanoconfined geometry. As a result, uniaxially oriented HNFs with different helical structures were obtained, in which generation of the twisted-ribbon and cylindrical-ribbon polymorphs showed that even the molecular lattice has a different orientation. The detailed structures were directly observed by SEM and grazing-incidence X-ray diffraction with synchrotron radiation. The resultant polymorphs could be used in chiro-optical applications due to the capability for fine control of the helical structures. 相似文献
49.