全文获取类型
收费全文 | 394篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 252篇 |
晶体学 | 6篇 |
力学 | 11篇 |
数学 | 39篇 |
物理学 | 96篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 6篇 |
2013年 | 23篇 |
2012年 | 17篇 |
2011年 | 40篇 |
2010年 | 11篇 |
2009年 | 14篇 |
2008年 | 20篇 |
2007年 | 21篇 |
2006年 | 21篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 15 毫秒
201.
Spontaneous two-photon emission from a solid-state single quantum emitter is observed. We investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high Q photonic crystal nanocavity. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity inspires the biexciton to simultaneously emit two photons into the mode, resulting in clear emission enhancement of the mode. Meanwhile, the suppression of other single photon emission from the biexciton was observed, as the two-photon emission process becomes faster than the others at the resonance. 相似文献
202.
T. R. Ravindran A. K. Arora M. Singh S. B. Ota 《Journal of Raman spectroscopy : JRS》2013,44(1):108-113
Rock‐shelter paintings of Bhimbetka world‐heritage site near Bhopal, India have been investigated using a portable Raman spectrometer. These paintings in the rock shelters belong to periods starting from pre‐historic to the 19th century AD (Gond period). In addition, tiny fragments of pigments (100–200 µm in size) extracted from some of the artworks were also studied in laboratory using a micro‐Raman spectrometer and analyzed using energy‐dispersive X‐ray analysis for elemental composition. Based on the Raman spectra and the elemental analysis mineral‐based pigments such as calcite, gypsum, hematite, whewellite, and goethite could be identified. A comparison of the spectra recorded on‐site using a light‐weight portable spectrometer with those using laboratory equipment is also made and discussed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
203.
Let ${\mathcal{F}}$ be a family of connected graphs. A graph G is said to be ${\mathcal{F}}$ -free if G is H-free for every graph H in ${\mathcal{F}}$ . We study the problem of characterizing the families of graphs ${\mathcal{F}}$ such that every large enough connected ${\mathcal{F}}$ -free graph of even order has a perfect matching. This problems was previously studied in Plummer and Saito (J Graph Theory 50(1):1–12, 2005), Fujita et al. (J Combin Theory Ser B 96(3):315–324, 2006) and Ota et al. (J Graph Theory, 67(3):250–259, 2011), where the authors were able to characterize such graph families ${\mathcal{F}}$ restricted to the cases ${|\mathcal{F}|\leq 1, |\mathcal{F}| \leq 2}$ and ${|\mathcal{F}| \leq 3}$ , respectively. In this paper, we complete the characterization of all the families that satisfy the above mentioned property. Additionally, we show the families that one gets when adding the condition ${|\mathcal{F}| \leq k}$ for some k ≥ 4. 相似文献
204.
Dr. Jun Kikuchi Kyohei Takano Dr. Yusuke Ota Dr. Shigenobu Umemiya Prof. Dr. Masahiro Terada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11124-11128
Despite the significant progress of the enantioselective reaction using chiral catalysts, the enantioselective nucleophilic substitution reaction at the chiral sp3-hybridized carbon atom of a racemic electrophile has not been largely explored. Herein, we report the enantioconvergent propargylic substitution reaction of racemic propargylic alcohols with thiols using chiral bis-phosphoric acid as the chiral Brønsted acid catalyst. The substitution products were formed in high yields with high enantioselectivities in most cases. The cation-stabilizing effect of the sulfur functional group introduced at the alkynyl terminus is the key to achieving the efficient enantioconvergent process, in which chiral information originating from not only the racemic stereogenic center but also the formed contact ion pair is completely eliminated from the present system. 相似文献
205.
206.
Optical Review - Sound evokes sub-nanoscale vibration within the sensory epithelium. The epithelium contains not only immotile cells but also contractile outer hair cells (OHCs) that actively... 相似文献
207.
208.
Liquid chromatography/tandem mass spectrometry for simultaneous determination of undeclared corticosteroids in cosmetic creams 下载免费PDF全文
209.
M. Niikura E. Ideguchi N. Aoi H. Baba T. Fukuchi Y. Ichikawa H. Iwasaki T. Kubo M. Kurokawa M. Liu S. Michimasa T. Ohnishi T. K. Onishi S. Ota S. Shimoura H. Suzuki D. Suzuki Y. Wakabayashi K. Yoshida Y. Zheng 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):471-475
In-beam $ \gamma$ -ray spectroscopy of high-spin states in 49-51Ti was performed via the fusion-evaporation reaction using a radioactive beam. By excitation function and $ \gamma$ - $ \gamma$ coincidence analysis, yrast high-spin levels up to I = (21/2-),(11+),(17/2-) in 49-51Ti were determined. The levels were compared with full-pf -shell model calculation. The level structure indicates the persistency of the N = 28 shell gap at yrast states in 49-51Ti . 相似文献
210.
H. J. Ong N. Imai D. Suzuki H. Iwasaki H. Sakurai T. K. Onishi M. K. Suzuki S. Ota S. Takeuchi T. Nakao Y. Togano Y. Kondo N. Aoi H. Baba S. Bishop Y. Ichikawa M. Ishihara T. Kubo K. Kurita T. Motobayashi T. Nakamura T. Okumura Y. Yanagisawa 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):393-396
We have measured the lifetime of the first excited 2+ state in 18C using an upgraded recoil shadow method to determine the electric quadrupole transition. The measured mean lifetime is 18.9±0.9 (stat)±4.4 (syst) ps, corresponding to B(E2;21 + $ \rightarrow$ 0+ gs) = 4.3±0.2±1.0e 2 fm^4, or about 1.5 Weisskopf units. The mean lifetime of the first 2+ state in 16C was remeasured to be 18.3±1.4±4.8 ps, about four times shorter than the value reported previously. The discrepancy is explained by incorporating the $ \gamma$ -ray angular distribution obtained in this work into the previous measurement. The observed transition strengths in 16, 18C are hindered compared to the empirical values, indicating that the anomalous E2 strength observed in 16C persists in 18C . 相似文献