全文获取类型
收费全文 | 660篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
化学 | 570篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 19篇 |
物理学 | 111篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 23篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 37篇 |
2012年 | 37篇 |
2011年 | 61篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 34篇 |
2007年 | 41篇 |
2006年 | 33篇 |
2005年 | 43篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 18篇 |
2000年 | 22篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 13篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1968年 | 3篇 |
1966年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有705条查询结果,搜索用时 15 毫秒
701.
Yamamoto K Nakatsuji T Yaoi Y Yamato Y Yanagitani T Matsukawa M Yamazaki K Matsuyama Y 《Ultrasonics》2012,52(3):377-386
Quantitative ultrasound (QUS) is now widely used for evaluating bone in vivo, because obtained ultrasonic wave properties directly reflect the visco-elasticity. Bone tissue is composed of minerals like hydroxyapatite (HAp) and a collagen matrix. HAp crystallites orientation is thus one parameter of bone elasticity. In this study, we experimentally investigated the anisotropy of ultrasonic wave velocity and the HAp crystallites orientation in the axial-radial and axial-tangential planes in detail, using cylindrical specimens obtained from the cortical bone of three bovine femurs. Longitudinal bulk wave propagation was investigated by using a conventional ultrasonic pulse system. We used the one cycle of sinusoidal pulse which was emitted from wide band transmitter. The nominal frequency of the pulse was 1 MHz. First, we investigated the anisotropy of longitudinal wave velocity, measuring the anisotropy of velocity in two planes using cylindrical specimens obtained from identical bone areas. The wave velocity changed due to the rotation angle, showing the maximum value in the direction a little off the bone axis. Moreover, X-ray pole figure measurements also indicated that there were small tilts in the HAp crystallites orientation from the bone axis. The tilt angles were similar to those of the highest velocity direction. There were good correlations between velocity and HAp crystallites orientation obtained in different directions. However, a comparatively low correlation was found in posterior bone areas, which shows the stronger effects of bone microstructure. In the radial-tangential plane, where the HAp crystallites hardly ever align, weak anisotropy of velocity was found which seemed to depend on the bone microstructure. 相似文献
702.
Ezoe Y Moriyama T Ogawa T Kakiuchi T Mitsuishi I Mitsuda K Aoki T Morishita K Nakajima K 《Optics letters》2012,37(5):779-781
Large-aperture focusing of Al K(α) 1.49 keV x-ray photons using micropore optics made from a dry-etched 4 in. (100 mm) silicon wafer is demonstrated. Sidewalls of the micropores are smoothed with high-temperature annealing to work as x-ray mirrors. The wafer is bent to a spherical shape to collect parallel x rays into a focus. Our result supports that this new type of optics allows for the manufacturing of ultralight-weight and high-performance x-ray imaging optics with large apertures at low cost. 相似文献
703.
Dr. Kazuto Suzuki Dr. Joshua Kyle Stanfield Dr. Keita Omura Dr. Yuma Shisaka Dr. Shinya Ariyasu Chie Kasai Dr. Yuichiro Aiba Dr. Hiroshi Sugimoto Prof. Dr. Osami Shoji 《Angewandte Chemie (International ed. in English)》2023,62(13):e202215706
Catching the structure of cytochrome P450 enzymes in flagrante is crucial for the development of P450 biocatalysts, as most structures collected are found trapped in a precatalytic conformation. At the heart of P450 catalysis lies Cpd I, a short-lived, highly reactive intermediate, whose recalcitrant nature has thwarted most attempts at capturing catalytically relevant poses of P450s. We report the crystal structure of P450BM3 mimicking the state in the precise moment preceding epoxidation, which is in perfect agreement with the experimentally observed stereoselectivity. This structure was attained by incorporation of the stable Cpd I mimic oxomolybdenum mesoporphyrin IX into P450BM3 in the presence of styrene. The orientation of styrene to the Mo-oxo species in the crystal structures sheds light onto the dynamics involved in the rotation of styrene to present its vinyl group to Cpd I. This method serves as a powerful tool for predicting and modelling the stereoselectivity of P450 reactions. 相似文献
704.
Jing‐Ji Jin Yuichiro Haramoto Masato Nanasawa 《Macromolecular rapid communications》1999,20(3):135-138
A ferric bipyridine complex linked viologen unit was synthesized and its photoinduced coloration properties were investigated in a thin poly(vinyl alcohol) film. The colorless‐to‐color change of the film occurs upon irradiation, associated with the intramolecular electron transfer from the photoreduced viologen to the colorless ferric bipyridine complex. 相似文献
705.
Dr. Yuichiro Kawamoto Naoki Noguchi Dr. Toyoharu Kobayashi Prof. Hisanaka Ito 《Angewandte Chemie (International ed. in English)》2023,62(24):e202304132
The total synthesis of lucidumone ( 1 ), a Ganoderma meroterpenoid, was accomplished in racemic form from easily prepared 6 and 7 in 10 steps as the longest linear sequence. The synthesis was completed through one-pot preparation of the tetracyclic core skeleton by Claisen rearrangement followed by an intramolecular aldol reaction. The intramolecular aldol reaction allowed for the stereocontrolled construction of the bicyclo [2.2.2] octane skeleton fused to an indanone structure. The enantioselective total synthesis of 1 was also described via a chiral transfer strategy in the Claisen rearrangement. 相似文献