全文获取类型
收费全文 | 672篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 592篇 |
晶体学 | 4篇 |
力学 | 3篇 |
数学 | 29篇 |
物理学 | 66篇 |
出版年
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 33篇 |
2012年 | 28篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 20篇 |
2008年 | 42篇 |
2007年 | 56篇 |
2006年 | 40篇 |
2005年 | 47篇 |
2004年 | 45篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 4篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1967年 | 1篇 |
1941年 | 1篇 |
1929年 | 1篇 |
1905年 | 2篇 |
排序方式: 共有694条查询结果,搜索用时 15 毫秒
1.
Mineo Hashizume Hiroaki Inoue Kiyofumi Katagiri Atsushi Ikeda Jun-Ichi Kikuchi 《Journal of Sol-Gel Science and Technology》2004,31(1-3):99-102
Morphological characterization of the organic-inorganic vesicular nanohybrids, Cerasomes, was performed in aqueous media from two aspects. Firstly, a novel Cerasome-forming lipid having two triethoxysilyl groups in the head moiety was synthesized and the physical property of the Cerasome was investigated. While the morphological stability of the Cerasomes, as evaluated from the vesicular collapse behavior against a micelle-forming nonionic surfactant, Triton-X 100, was extremely higher than that of the conventional phospholipid liposome, the stabilities were comparable to each other for the Cerasomes derived from the dual- and single-head lipids. On the other hand, the surface property of the Cerasome formed with the dual-head lipid more closely resembled the colloidal silica particles rather than that derived from the single-head lipid, as suggested by zeta-potential measurements. Secondly, the effect of the media pH on the morphological stability of the Cerasome formed with the single-head lipid was evaluated and appeared as a time difference in obtaining the morphological stability of the Cerasome. These morphological characteristics of the Cerasomes could be mainly owing to the development of the siloxane network on the vesicular surface. 相似文献
2.
Yan Yin Otoo Yamada Shunsuke Hayashi Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3751-3762
A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm?1 at 50% relative humidity. In a single H2/O2 fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006 相似文献
3.
4.
Dehydration of zinc biladienone was catalyzed by zinc acetate, while the reverse reaction was catalyzed by triethylamine. The transformation can be performed thermally without catalyst, and the ratio of the hydrated form to the dehydrated form depended on the solvents: the dehydrated form is favored in CHCl3 and CH2Cl2, while the hydrated form is favored in hexane, pyridine, and DMF. Kinetic studies on the thermal transformation of zinc biladienone from its hydrated blue form to the dehydrated yellow-brown form were performed in toluene and THF. The rate law was half order with respect to the zinc biladienone concentration in toluene, while first order in THF, leading to a slow transformation in concentrated solution in toluene. 相似文献
5.
Novel catalytic asymmetric sulfoxidation in water using the hypervalent iodine reagent iodoxybenzene
Tohma H Takizawa S Morioka H Maegawa T Kita Y 《Chemical & pharmaceutical bulletin》2000,48(3):445-446
A new catalytic asymmetric oxidation of sulfides to sulfoxides in water using the hypervalent iodine(V) reagent iodoxybenzene (PhIO2) has been developed. This methodology is distinctly different from the previously reported use of cyclodextrins or biological catalysts and provides a new route to asymmetric sulfoxidation in water. 相似文献
6.
Jun-Ichi Anzai Yoko Sakata Yasuhiro Suzuki Akihiko Ueno Tetsuo Osa 《Journal of polymer science. Part A, Polymer chemistry》1983,21(3):855-864
Crown ether-modified polyethylenimines (PEI-CR) were prepared to elucidate their cation binding efficiency and selectivity by liquid-liquid and solid-liquid extraction methods. With alkali metal cations it was found that polyethylenimines containing benzo-15-crown-5 moieties (Ia and Ib) extracted all cations examined more efficiently than their monomeric analogs, especially in the cases of K+ and Rb+ cations. The solid-liquid extraction revealed clearly that the polymers complexed with K+ and Rb+ cations according to a 1:2 cation-to-crown stoichiometry. The high selectivities of the polymers for K+ and Rb+ were interpreted in terms of the favourable conformation of the polymer chain for the formation of intramolecular 1:2 complexes. On the contrary, these polymers bound alkali earth cations less effectively with low selectivities. 相似文献
7.
Determination of molecular weight of native proteins by polyacrylamide gradient gel electrophoresis 总被引:1,自引:0,他引:1
An improved method for the estimation of molecular weights of native proteins by polyacrylamide gel electrophoresis, in 9 cm x 9 cm x 0.05 mm 4-20% T fabric reinforced gradient gels, is described. Plotting the logarithm of the relative mobilities of proteins versus gel concentrations produces lines whose slopes are related to molecular weights. 相似文献
8.
The separation of diastereomeric esters derived from (±)-pyridylethanols and 3β-acetoxyetienic acid were achieved by an extraction technique using diethyl ether and aqueous hydrochloric acid. A formal total synthesis of PNU-142721 was effectively carried out to prepare the chiral, non-racemic synthon 1-furo[2,3-c]pyridin-5-yl-ethanol (1) by means of this technique. The structure optimized using MOPAC calculations on each diastereomer suggested the presence of intramolecular CH/π interaction in only the (S)-isomer of the diastereomers. 相似文献
9.
Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption. 相似文献
10.
Aquation of [Cr(pic)3]0 and [Cr(pic)2(OH)]2
0 in aqueous HClO4 solutions leads to formation of the common product – [Cr(pic)2(H2O)2]+. The first, reversible stage, the ring opening via Cr—N bond breaking in [Cr(pic)3]0 is followed by the second, rate-determining step – one-end bonded pic ligand liberation. In the case of the [Cr(pic)2(OH)]2
0 complex, the first faster stage produces the singly bridged dimer, which undergoes cleavage into the parent monomers in the second, much slower step. The subsequent aquation of [Cr(pic)2(H2O)2]+ is extremely slow and leads to [Cr(pic)(H2O)4]2+ formation, which practically does not undergo further ligand substitution under the conditions applied. Kinetics of the first aquation stage for [Cr(pic)3]0 and of the second step for [Cr(pic)2(OH)]2
0 were studied spectrophotometrically in the 0.1–1.0 M HClO4 range at I = 1.0 M. The observed pseudo-first order rate constant for [Cr(pic)3]0 decreases with [H+] increase according to the rate law: k
obs = k
1 + k
–1
Q
1/[H+], where k
1 and k
–1 are the rate constants of the forward and the reverse processes in the unprotonated substrate and Q
1 is the protonation constant of the pyridine nitrogen atom. In the case of the [Cr(pic)2(OH)]2
0 complex, the rate for the singly bridged dimer cleavage does not depend on [H+]. The activation parameters for the chelate-ring opening in [Cr(pic)3]0 and for the singly bridged dimer cleavage have been determined and discussed. Some kinetic data of the slow, second aquation stage for the [Cr(pic)3]0 complex and of the fast, first aquation stage for the doubly bridged dimer have been studied; for both reactions the rate increases linearly with the increase in [H+]. 相似文献