全文获取类型
收费全文 | 241篇 |
免费 | 8篇 |
专业分类
化学 | 178篇 |
晶体学 | 5篇 |
力学 | 5篇 |
数学 | 12篇 |
物理学 | 49篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 1篇 |
2008年 | 19篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 15 毫秒
61.
62.
Dispersion behavior of aqueous solutions containing oleic acid (RH), sodium oleate (R-Na+), and NaCl was investigated by turbidity and dynamic light-scattering measurements. Changes of the size of scattering particles
in solution composed of 1 mM oleic acid and 100 mM NaCl were traced as a function of the degree of ionization α, in terms
of radius of the equivalent hydrodynamic sphere. Large associated micelles with a radius of 30 nm appeared by a slight decline
of α and existed at α higher than 0.75. They were responsible for the three-phase equilibrium (solution, micelle and aggregated
micelle, and acid–soap, (R-Na+)3RH) characterized by a constant pH of 9.75. The appearance of a new phase, (R-Na+)3RH, contributed to increase both the turbidity and averaged scattering particle size. As the breakdown of the three-phase
equilibrium, radius of scattering particles increased significantly. Finally, oleic acid oil droplets were separated from
aqueous phase at low α. When the system was buffered by tris(hydroxymethyl)aminomethane (Tris), scattering particles with
a weight-averaged hydrodynamic radius of 75 nm existed in a wide range of α from 0.85 to 0.65. In Tris buffered solution,
turbidity formation was induced by the increase in the number of aggregated particles.
Received: 12 November 1996 Accepted: 4 April 1997 相似文献
63.
A crucial enzyme in the biosynthesis of the 2-deoxystreptamine aglycon of clinically important aminocyclitol antibiotics is 2-deoxy-scyllo-inosose synthase (DOIS), which converts ubiquitous D-glucose 6-phosphate (G-6-P) into the specific carbocycle 2-deoxy-scyllo-inosose. Among all the oxygenated carbons of the substrate, C-1, -4, -5, and -6 are directly involved in the chemical transformation. To get insight into the roles of C-2 and C-3 hydroxy groups, 2-deoxy-2-fluoro-, 3-deoxy-3-fluoro-, 2-amino-2-deoxy-, and 3-amino-3-deoxy-D-glucose 6-phosphates (2-F-G-6-P, 3-F-G-6-P, 2-NH(2)-G-6-P, and 3-NH(2)-G-6-P, respectively) were subjected to the DOIS reaction as probe, since a fluorine substituent generally acts as a hydrogen-bond acceptor, and an ammonium functionality derived physiologically from an amino group as a hydrogen-bond donor. Among those tested, 2-F-G-6-P and 3-NH(2)-G-6-P were used as substrates by DOIS and were converted into the corresponding deoxyfluoro- and aminodeoxy-scyllo-inososes, respectively. In contrast, 3-F-G-6-P and 2-NH(2)-G-6-P were inactive in the cyclization reaction. Clearly, DOIS recognizes the G-6-P substrate through specific hydrogen-bonding interactions, i.e., through a hydrogen-donating group for C-2 and an accepting group for C-3 of the substrate. Modeling of DOIS based on the structure of evolutionary-related dehydroquinate synthase is also described. 相似文献
64.
Ryosuke Matsubara Yuki Katsuragi Takaya Sakaguchi Shuhei Eguchi Masahiko Hayashi Akihiro Ando 《Tetrahedron》2018,74(27):3642-3651
Furoxans are distinctive heteroaromatic compounds in that they are potentially capable of releasing nitric oxide under physiological conditions. In order to utilize the furoxan scaffold for the development of functional molecules, synthetically relevant functional groups are required for access to diverse furoxans. In this report, a facile route to furoxans with sulfonyloxy groups, which are halide surrogates, has been developed. The key features of this strategy include the synthesis and utilization of bench-stable hydroxyfuroxan salts, the use of sulfonyl anhydrides in the sulfonylation step instead of sulfonyl chlorides, and the photochemical isomerization of one regioisomer to another in order to gain access to both. 相似文献
65.
In addition to our previous paper on the photochemical behaviors of chrysanthemic acid,2 we wish to report preliminary results on its photosensitized oxygenation, in which a marked reactivity difference has been observed between the cis- and trans isomers. 相似文献
66.
Motoki Kaneno Shunro Yamaguchi Hirokazu Nakayam Keisuke Miyakubo Takahiro Ueda Taro Eguchi 《Molecular Crystals and Liquid Crystals》2013,570(2):561-566
Abstract The intercalation compound between α-zirconium phosphate and N,N′-bis-(3-aminopropyl)-1, 3-propanediamine has two different modifications with respect to the conformation of the guest amine molecules: one is “bent form” and the other “straight form”. Reactivity of each phase with a series of aldehydes was examined. 13C CP/MAS NMR indicated that the tetraamine reacts stereoselectively with aldehydes to form cis-imine in the interlayer spacing. Depending on the molecular size of aldehyde, it is found that a significant difference can be recognized in the yields of the imine products for the two phases of intercalation compounds. It is also noted that residual water molecules in the interlayer spacing play an important role in the imine formation reaction. 相似文献
67.
68.
We use the representation theory of \({\mathcal{N}=2}\) superconformal algebra to study the elliptic genera of Calabi–Yau (CY) D-folds. We compute the entropy of CY manifolds from the growth rate of multiplicities of the massive (non-BPS) representations in the decomposition of their elliptic genera. We find that the entropy of CY manifolds of complex dimension D behaves differently depending on whether D is even or odd. When D is odd, CY entropy coincides with the entropy of the corresponding hyperKähler (D ? 3)-folds due to a structural theorem on Jacobi forms. In particular, we find that the Calabi–Yau 3-fold has a vanishing entropy. At D > 3, using our previous results on hyperKähler manifolds, we find \({S_{CY_D}\sim 2\pi \sqrt{\frac{(D-3)^2}{2(D-1)}n}}\). When D is even, we find the behavior of CY entropy behaving as \({S_{CY_D}\sim 2 \pi\sqrt{\frac{D-1}{2}n}}\). These agree with Cardy’s formula at large D. 相似文献
69.
70.
Denticulatolide, an ichthyotoxic cembranoid diterpene bearing acetoxy, α-methylene γ-lactone, and cyclic peroxide functions, has been isolated from the soft coral Lobophytum denticulatum. The structure (1) has been determined by spectral and chemical evidence and X-ray crystallographic method. 相似文献