全文获取类型
收费全文 | 2026篇 |
免费 | 57篇 |
国内免费 | 8篇 |
专业分类
化学 | 1597篇 |
晶体学 | 33篇 |
力学 | 31篇 |
数学 | 63篇 |
物理学 | 367篇 |
出版年
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 24篇 |
2019年 | 25篇 |
2018年 | 19篇 |
2016年 | 30篇 |
2015年 | 33篇 |
2014年 | 40篇 |
2013年 | 121篇 |
2012年 | 94篇 |
2011年 | 109篇 |
2010年 | 80篇 |
2009年 | 79篇 |
2008年 | 124篇 |
2007年 | 98篇 |
2006年 | 117篇 |
2005年 | 104篇 |
2004年 | 91篇 |
2003年 | 94篇 |
2002年 | 112篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 33篇 |
1998年 | 18篇 |
1997年 | 25篇 |
1996年 | 30篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 29篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 37篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 8篇 |
1973年 | 15篇 |
1972年 | 8篇 |
排序方式: 共有2091条查询结果,搜索用时 531 毫秒
31.
Yasuyuki Kurita Chiyozo Takayama Shizuya Tanaka 《Journal of computational chemistry》1994,15(9):1013-1018
Although there is a similarity in the orbital interaction scheme between quinhydrone and N,N,N′,N′-tetramethyl-p-diaminobenzene-chloranil complex, the stacking conformations are different from each other. The former prefers the half-stacked conformation, whereas the latter prefers the completely stacked conformation. We have done ab initio molecular orbital calculations and decomposition analyses of the intermolecular interaction energies to clarify the origin of the different stacking conformations. It was concluded that the main origin is the difference in the steric part of the interaction energies. © 1994 by John Wiley & Sons, Inc. 相似文献
32.
Yoshimoto S Honda Y Murata Y Murata M Komatsu K Ito O Itaya K 《The journal of physical chemistry. B》2005,109(18):8547-8550
Adlayers of ZnOEP were prepared on reconstructed Au(100)-(hex) and unreconstructed Au(100)-(1 x 1) surfaces by immersing into a benzene solution containing ZnOEP molecules, and the adlayer structures were characterized by scanning tunneling microscopy (STM). A hexagonally arranged ZnOEP array was formed on an Au(100)-(hex) surface, whereas a rectangularly arranged ZnOEP array was found on an Au(100)-(1 x 1) surface. The adlayer structure of ZnOEP was dependent upon the underlying Au atomic arrangements. Furthermore, an investigation of the spuramolecular assembly for these modified surfaces was carried out by using an open-cage C(60) derivative (opened C(60)). A supramolecular assembled adlayer with a 1:1 composition of opened C(60)/ZnOEP was formed on Au(100)-(hex), whereas aggregates of opened C(60) were found on the ZnOEP-modified Au(100)-(1 x 1) surface. Electrochemical responses of opened C(60) were significantly influenced by underlying ZnOEP arrays. This finding suggests that precise control of underlying ZnOEP adlayers with the Au atomic structure is important to recognize the opened C(60) on them. 相似文献
33.
The hydronaphthalene moieties of mevinic acids are synthesized enantioselectively by using the asymmetric intramolecular Diels-Alder reaction catalyzed by a chiral titanium reagent. 相似文献
34.
Highly selective asymmetric induction can be achieved in the reduction of acyclic β-hydroxyketones via boron chelates. Treatment of β-hydroxyketones (1) with tributyl or tri-isobutylborane and successively with sodium borohydride afforded syn-1,3-diols (3) in highly stereo-selective manner, Syn -α-substituted-β -hydroxyketones (8) were also reduced to give syn, syn-1,3-diols (9) exclusively. The reaction was further applied to the convenient preparation of 3-deoxy-hexoses. 相似文献
35.
Shuzi Hayase Yasunobu Onishi Shuichi Suzuki Moriyasu Wada Atushi Kurita 《Journal of polymer science. Part A, Polymer chemistry》1987,25(3):753-763
o-Nitrobenzyl triphenylsilyl ehther/aluminum compound has been previously shown by the authors to act as catalyst in the photopolymerization of epoxides. The dependence of the structure of the silyl ether on the catalyst activity was examined. There were two steps in the photopolymerization. The first step (“Step 1”) is photodecomposition of the silyl ether to silanol. The second step (“Step 2”) is the initiation of polymerization by silanol and the aluminum compound. The introduction of an electron withdrawing group, Cl, CF3, on the benzene ring bonded to Si made the quantum yield of Step 1 low, however, the rate of Step 2 was increased. The low quantum yield of Step 1 was explained in terms of the rate of electron transfer that is controlled by the relative electron density between the CH2 and NO2 in the o-nitrobenzyl group. The acceleration of Step 2 was explained in terms of an increase in silanol acidity that was promoted by the introduction of an electron withdrawing group. The overall rate of the photopolymerizatiol depends to a greater degree on the rate of Step 2 than on that of Step 1. 相似文献
36.
X-ray analysis of the title complex revealed hydrogen-bonded chains comprising two crystallographically independent types of -9,10-dihydroxy-9,10-diphenyl-9,10-dihydroanthracene molecules, in which the central 1,4-cyclohexadiene rings are respectively flat and very slightly puckered, with the ethanol molecules attached exclusively to the latter type. 相似文献
37.
Israel Goldberg Zafra Stein Koichi Tanaka Fumio Toda 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):97-107
The crystal structures of the 2,2-di(p-hydroxyphenyl)propane host and its 1:1 adducts withm-andp-cresol guests have been studied. The preferential complexation of this host withp-cresol overm-cresol is related to the opposite trend exhibited by 1,1-di(p-hydroxyphenyl)cyclohexane; both hosts can separate effectively the two cresols from their liquid mixture by crystalline inclusion. A plausible explanation of the different inclusion features is provided by examining the intermolecular association in the corresponding solids. The analysed structures are stabilized by strong and continuous H-bonding between the constituent entities along two dimensions, and by weak van der Waals forces along the third axis. The p-cresol complex of the title host reveals a unique arrangement within and a more efficient packing of the layered structure, and thus represents a more stable and less soluble crystal lattice than itsm-cresol analog.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82099 (8 pages). 相似文献
38.
Koichi Kikuta Koji Noda Shin Okumura Toshiaki Yamaguchi Shin-ichi Hirano 《Journal of Sol-Gel Science and Technology》2007,42(3):381-387
Orientation control of perovskite compounds was investigated by the application of a seed layer prepared from oxide nanosheets.
An aqueous suspension of oxide nanosheets was prepared by the exfoliation of a layered compound of KCa2Nb3O10 oxide grains. A seed layer composed of (TBA)Ca2Nb3O10 nanosheets (TBA = tetrabutylammonium) was formed on a glass substrate by simply dip coating it in the suspension. Two kinds
of perovskite compounds, LaNiO3 (LNO) and Pb(Zr,Ti)O3 (PZT) with a preferred orientation of (00l) were successfully grown on this seeded glass substrate. In this study, the relation between lattice mismatch and electrical
properties is investigated. A large, oriented PZT film with a size of 5 ×4 cm shows an improved P-E hysteresis behavior by
use of this orientation control. 相似文献
39.
40.