全文获取类型
收费全文 | 1858篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
化学 | 1444篇 |
晶体学 | 25篇 |
力学 | 36篇 |
数学 | 63篇 |
物理学 | 334篇 |
出版年
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 34篇 |
2014年 | 34篇 |
2013年 | 79篇 |
2012年 | 77篇 |
2011年 | 97篇 |
2010年 | 47篇 |
2009年 | 57篇 |
2008年 | 108篇 |
2007年 | 97篇 |
2006年 | 105篇 |
2005年 | 88篇 |
2004年 | 88篇 |
2003年 | 85篇 |
2002年 | 66篇 |
2001年 | 41篇 |
2000年 | 33篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 29篇 |
1987年 | 29篇 |
1986年 | 18篇 |
1985年 | 41篇 |
1984年 | 36篇 |
1983年 | 14篇 |
1982年 | 37篇 |
1981年 | 33篇 |
1980年 | 20篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 30篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 17篇 |
1973年 | 10篇 |
1967年 | 8篇 |
排序方式: 共有1902条查询结果,搜索用时 10 毫秒
101.
Petronela Drambei Yumiko Nakano Yuezhen Bin Tsumuko Okuno Masaru Matsuo 《Macromolecular Symposia》2006,242(1):146-156
Uniplaner orientation of a particular crystal plane along the surface of a film was investigated for poly (vinyl alcohol) (PVA) film prepared by a coagulation bath with concentrated aqueous solution containing 100 ∼ 300g of Na2SO4 against 1 ℓ of water. The orientation distribution functions of the three crystallographic principal axes of the dried films were obtained by the X-ray diffraction technique. The same treatment was carried out for the films prepared by stretching biaxially of the fresh gel and then by drying the resultant fresh gel. The very high preferential orientation of the crystal chain axes and amorphous chain segments could be realized by the biaxially elongation. Accordingly, the techniques were applied to the biaxially stretching of chitosan and PVA blend films with high Young's modulus. The planer orientation of the chain axes of chitosan and PVA crystallites could be confirmed. The morphology of the film surface was estimated by measurements of contact angle and electron spectroscopy for chemical analysis. The results suggested that the admixture of chitosan decreases wet ability of the specimen and this tendency was slightly enhanced by the biaxially elongation. 相似文献
102.
103.
Time-resolved magneto photoluminescence in a diluted magnetic semiconductor Cd 0.9 Mn 0.1 Te has been carried out with varying exciton density from 10 14 to 10 19 cm m 3 . The reduction of the Zeeman shift and that of the magnetic polaron energy was found under strong photoexcitation. The spectral feature is interpreted in terms of the heating of the manganese spin subsystem. Polarization dependence of the spin heating is observed for the first time, revealing the contribution of the spin flip between excitons and magnetic ions to the heating process. 相似文献
104.
105.
106.
Abstract Three cases are described where chirality is recognized by achiral molecules, where chirality is induced into achiral compounds through interactions with chiral compounds, and lastly where induced chirality in the solid-state is utilized for an enantio-selective photoreaction. In the first instance, the thermodynamically and kinetically preferred diastereoisomer of an optically labile chromium complex depended on the nature of the achiral solvent. In the second case, for the first time 1,2-chloroethane was trapped and observed in a chiral near-eclipsed form and 1-chloropropane in the truly eclipsed form at room temperature in a 1:1 inclusion complex with an optically active host molecule. Finally, induced chirality in a prochiral compound in the solid-state was successfully employed in an enantio-selective photoreaction. In the two cases, solid-state CD provided valuable information. 相似文献
107.
Mitsunori Oda Takanori Kajioka Kazuya Ikeshima Ryuta Miyatake Shigeyasu Kuroda 《合成通讯》2013,43(13):2335-2343
The trimethylsilyl enol ether of l-acetylcyclohepta-1,3,5-triene was transformed to 3,3-dialkyl-1,2,3,8-tetrahydroazulen-1-one by a two-step sequence involving the Mukaiyama aldol reaction with ketones and the subsequent Nazarov cyclization. 相似文献
108.
109.
Dr. Emi Uchida Dr. Kouji Sakaki Dr. Yumiko Nakamura Dr. Reiko Azumi Dr. Yuki Hirai Dr. Haruhisa Akiyama Dr. Masaru Yoshida Dr. Yasuo Norikane 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(51):17391-17397
Photoinduced phase transitions caused by photochromic reactions bring about a change in the state of matter at constant temperature. Herein, we report the photoinduced phase transitions of crystals of a photoresponsive macrocyclic compound bearing two azobenzene groups ( 1 ) at room temperature on irradiation with UV (365 nm) and visible (436 nm) light. The trans/trans isomer undergoes photoinduced phase transitions (crystal–isotropic phase–crystal) on UV light irradiation. The photochemically generated crystal exhibited reversible phase transitions between the crystal and the mesophase on UV and visible light irradiation. The molecular order of the randomly oriented crystals could be increased by irradiating with linearly polarized visible light, and the value of the order parameter was determined to be ?0.84. Heating enhances the thermal cis‐to‐trans isomerization and subsequent cooling returned crystals of the trans/trans isomer. 相似文献
110.
Based on the fact that anthracene (Anth) possesses much higher similarity in electron-releasing ability to porphyrin nucleus than the other polyacenes, the dimeric octaethylporphyrin (OEP) derivatives 4 and 5 (OEP–Anth–OEP) were synthesized and their structure–property relationships were examined, as compared with related OEP dimers 1–3. Among them, the derivative 4 showed enormously high electronic communication between two terminal OEP rings, potentially providing a suitable unit of the electronic structure for molecular design of the OEP devices operating with less energy and with higher sensitivity to outside stimuli. 相似文献