全文获取类型
收费全文 | 1085篇 |
免费 | 9篇 |
国内免费 | 12篇 |
专业分类
化学 | 594篇 |
晶体学 | 5篇 |
力学 | 35篇 |
数学 | 331篇 |
物理学 | 141篇 |
出版年
2019年 | 6篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 31篇 |
2012年 | 24篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 23篇 |
2008年 | 39篇 |
2007年 | 50篇 |
2006年 | 35篇 |
2005年 | 41篇 |
2004年 | 39篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 23篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 21篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 33篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1978年 | 22篇 |
1977年 | 10篇 |
1976年 | 19篇 |
1975年 | 19篇 |
1974年 | 26篇 |
1973年 | 20篇 |
1972年 | 15篇 |
1971年 | 14篇 |
1970年 | 13篇 |
1969年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有1106条查询结果,搜索用时 828 毫秒
71.
In this paper we investigate linear operators between arbitrary BK spaces X and spaces Y of sequences that are
summable or bounded. We give necessary and sufficient conditions for infinite matrices A to map X into Y. Further, the Hausdorff measure of noncompactness is applied to give necessary and sufficient conditions for A to be a compact operator. 相似文献
72.
Vocal vibrato is regarded as one of the essential characteristics of voice quality in classical singing. Professional singers seem to develop vibrato automatically, without actively striving to acquire it. In this longitudinal investigation, the vocal vibrato of 22 singing students was examined at the beginning of and after 3 years of professional singing education. Subjects sang an ascending-descending triad pattern in slow tempo on vowel [a:] at a comfortable pitch level twice at soft (piano) and twice at medium (mezzoforte) loudness. The top note of the triad pattern was sustained for approximately 5s. The mean and the standard deviation (SD) of the vibrato rate were measured for this note. Results revealed that after 3 years of training, voices with vibrato slower than 5.2 Hz were found to have a faster vibrato, and voices with vibrato faster than 5.8 Hz were found to have a slower vibrato. Standard deviation of vibrato rate was higher in soft than in medium loudness, particularly before the education. Also high values of SD of vibrato rate, exceeding 0.65 Hz, had decreased after the education. These findings confirm that vibrato characteristics can be affected by singing education. 相似文献
73.
74.
C. Kirchner V. Schwegler F. Eberhard M. Kamp K. J. Ebeling
P. Prystawko
M. Leszczynski I. Grzegory S. Porowski 《Progress in Crystal Growth and Characterization of Materials》2000,41(1-4):57-83Epitaxial growth on GaN bulk single crystal substrates sets new standards in GaN material quality. The outstanding properties provide insights into fundamental material parameters (e.g. lattice constants, exciton binding energies, etc.) with a precision not obtainable from heteroepitaxial growth on sapphire or SiC. With metalorganic vapor phase epitaxy (MOVPE) we realized unstrained GaN layers with dislocation densities about six orders of magnitude lower than in heteroepitaxy. By the use of dry etching techniques for surface preparation, an important improvement of crystal quality is achieved. Those layers reveal an exceptional optical quality as determined by a reduction of the low-temperature photoluminescence (PL) linewidth from 5 meV to 0.1 meV and a reduced X-ray diffraction (XRD) rocking curve width from 400 to 20 arcsec. As a consequence of the narrow PL linewidths, new features as, e. g. a fivefold fine structure of the donor-bound exciton line at 3.471 eV was detected. Additionally, all three free excitons as well as their excited states are visible in PL at 2 K.
Dry etching techniques for surface preparation allow morphologies of the layers suitable for device applications. We report on InGaN/GaN multi-quantum-well (MQW)_ structures as well as GaN pn- and InGaN/GaN double heterostructure light emitting diodes (LEDs) on GaN bulk single crystal substrates. Those LEDs are twice as bright as their counterparts grown on sapphire. In addition they reveal an improved high power characteristics, which is attributed to an enhanced crystal quality and an increased p-doping. 相似文献
75.
Ohne Zusammenfassung 相似文献
76.
77.
78.
79.
80.