全文获取类型
收费全文 | 764篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
化学 | 434篇 |
晶体学 | 4篇 |
力学 | 33篇 |
数学 | 83篇 |
物理学 | 222篇 |
出版年
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 16篇 |
2013年 | 33篇 |
2012年 | 35篇 |
2011年 | 53篇 |
2010年 | 23篇 |
2009年 | 18篇 |
2008年 | 35篇 |
2007年 | 29篇 |
2006年 | 29篇 |
2005年 | 25篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 20篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1977年 | 5篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1970年 | 5篇 |
1968年 | 7篇 |
1966年 | 4篇 |
排序方式: 共有776条查询结果,搜索用时 46 毫秒
771.
Barin G Coskun A Friedman DC Olson MA Colvin MT Carmielli R Dey SK Bozdemir OA Wasielewski MR Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):213-222
Rotacatenanes are exotic molecular compounds that can be visualized as a unique combination of a [2]catenane and a [2]rotaxane, thereby combining both the circumrotation of the ring component (rotary motion) and the shuttling of the dumbbell component (translational motion) in one structure. Herein, we describe a strategy for the synthesis of a new switchable [3]rotacatenane and the investigation of its switching properties, which rely on the formation of tetrathiafulvalene (TTF) radical π-dimer interactions-namely, the mixed-valence state (TTF(2) )(+.) and the radical-cation dimer state (TTF(+.) )(2) -under ambient conditions. A template-directed approach, based on donor-acceptor interactions, has been developed, resulting in an improved yield of the key precursor [2]catenane, prior to rotacatenation. The nature of the binding between the [2]catenane and selected π-electron-rich templates has been elucidated by using X-ray crystallography and UV/Vis spectroscopy as well as isothermal titration microcalorimetry. The multistate switching mechanism of the [3]rotacatenane has been demonstrated by cyclic voltammetry and EPR spectroscopy. Most notably, the radical-cation dimer state (TTF(+.) )(2) has been shown to enter into an equilibrium by forming the co-conformation in which the two 1,5-dioxynaphthalene (DNP) units co-occupy the cavity of tetracationic cyclophane, thus enforcing the separation of TTF radical-cation dimer (TTF(+.) )(2) . The population ratio of this equilibrium state was found to be 1:1. We believe that this research demonstrates the power of constructing complex molecular machines using template-directed protocols, enabling us to make the transition from simple molecular switches to their multistate variants for enhancing information storage in molecular electronic devices. 相似文献
772.
As a result of the cochlea's nonlinear mechanics, stimulation by two tones results in the generation of distortion products (DPs) at frequencies flanking the primary tones. DPs are measurable in the ear canal as oto-acoustic emissions, and are used to noninvasively explore cochlear mechanics and diagnose hearing loss. Theories of DP emissions generally include both forward and reverse cochlear traveling waves. However, a recent experiment failed to detect the reverse-traveling wave and concluded that the dominant emission path was directly through the fluid as a compression pressure [Ren, 2004, Nat. Neurosc.7, 333-334]. To explore this further, we measured intracochlear DPs simultaneously with emissions over a wide frequency range, both close to and remote from the basilar membrane. Our results support the existence of the reverse-traveling wave: (1) They show spatial variation in DPs that is at odds with a compression pressure. (2) Although they confirm a forward-traveling character of intraocochlear DPs in a broad frequency region of the best frequency, this behavior does not refute the existence of reverse-traveling waves. (3) Finally, the results show that, in cases in which it can be expected, the DP emission is delayed relative to the DP in a way that supports reverse-traveling-wave theory. 相似文献
773.
Main observation and conclusion
A catalytic two-component three-centered(2C3C)Ugi-type reaction was developed for the synthesis of L-1-deoxynojirimycin(DNJ)isom... 相似文献
774.
Lorraine A. Malaspina Nils Frerichs Christian Adler Marc Schmidtmann Rüdiger Beckhaus Simon Grabowsky 《Helvetica chimica acta》2023,106(6):e202300012
Agostic interactions involving titanium are textbook examples for C−H bond activation. Therefore, it is surprising that there is no study in the literature in which the hydrogen atom in the C−H⋅⋅⋅Ti interaction has been determined reliably, although nearly all the criteria for assessing the strength and character of the agostic interaction depend on the hydrogen atom and its position. Here, we demonstrate with quantum crystallographic techniques how hydrogen atoms in a series of three titanium amides can indeed be localized accurately and precisely based on routine single-crystal X-ray diffraction data. Once the hydrogen positions have been established, theoretical and experimentally fitted bonding analyses reveal that the C−H⋅⋅⋅Ti interaction becomes stronger with increasing inter-ligand London dispersion stabilization of bulky alkyl groups. 相似文献
775.
776.