全文获取类型
收费全文 | 203610篇 |
免费 | 1297篇 |
国内免费 | 428篇 |
专业分类
化学 | 105200篇 |
晶体学 | 3397篇 |
力学 | 10276篇 |
综合类 | 10篇 |
数学 | 21863篇 |
物理学 | 64589篇 |
出版年
2021年 | 1993篇 |
2020年 | 2028篇 |
2019年 | 2592篇 |
2018年 | 3679篇 |
2017年 | 3694篇 |
2016年 | 4823篇 |
2015年 | 2357篇 |
2014年 | 4316篇 |
2013年 | 8628篇 |
2012年 | 6846篇 |
2011年 | 8075篇 |
2010年 | 6480篇 |
2009年 | 6666篇 |
2008年 | 7664篇 |
2007年 | 7636篇 |
2006年 | 6725篇 |
2005年 | 5946篇 |
2004年 | 5662篇 |
2003年 | 5184篇 |
2002年 | 5175篇 |
2001年 | 5618篇 |
2000年 | 4140篇 |
1999年 | 3142篇 |
1998年 | 2703篇 |
1997年 | 2761篇 |
1996年 | 2549篇 |
1995年 | 2215篇 |
1994年 | 2328篇 |
1993年 | 2229篇 |
1992年 | 2527篇 |
1991年 | 2646篇 |
1990年 | 2553篇 |
1989年 | 2623篇 |
1988年 | 2536篇 |
1987年 | 2551篇 |
1986年 | 2411篇 |
1985年 | 3035篇 |
1984年 | 3105篇 |
1983年 | 2598篇 |
1982年 | 2562篇 |
1981年 | 2528篇 |
1980年 | 2338篇 |
1979年 | 2708篇 |
1978年 | 2672篇 |
1977年 | 2871篇 |
1976年 | 2873篇 |
1975年 | 2664篇 |
1974年 | 2602篇 |
1973年 | 2713篇 |
1972年 | 2086篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Rehan A. Kazi Vyas M.N. Prasad Jeeve Kanagalingam Christopher M. Nutting Peter Clarke Peter Rhys-Evans Kevin J. Harrington 《Journal of voice》2007,21(6):661-668
The objective of this study was to assess the difference in voice quality as defined by acoustical analysis using sustained vowel in laryngectomized patients in comparison with normal volunteers. This was designed as a retrospective single center cohort study. An adult tertiary referral unit formed the setting of this study. Fifty patients (40 males) who underwent total laryngectomy and 31 normal volunteers (18 male) participated. Group comparisons with the first three formant frequencies (F1, F2, and F3) using linear predictive coding (LPC) (Laryngograph Ltd, London, UK) was performed. The existence of any significant difference of F1, F2, and F3 between the two groups using the sustained vowel /i/ and the effects of other factors namely, tumor stage (T), chemoradiotherapy, pharyngectomy, cricothyroid myotomy, closure of pharyngoesophageal segment, and postoperative complication were analyzed. Formant frequencies F1, F2, and F3 were significantly different in male laryngectomees compared to controls: F1 (P<0.001, Mann-Whitney U test), F2 (P<0.001, Student's t test), and F3 (P=0.008, Student's t test). There was no significant difference between females in both groups for all three formant frequencies. Chemoradiotherapy and postoperative complications (pharyngocutaneous fistula) caused a significantly lower formant F1 in men, but showed little effect in F2 and F3. Laryngectomized males produced significantly higher formant frequencies, F1, F2, and F3, compared to normal volunteers, and this is consistent with literature. Chemoradiotherapy and postoperative complications significantly influenced the formant scores in the laryngectomee population. This study shows that robust and reliable data could be obtained using electroglottography and LPC in normal volunteers and laryngectomees using a sustained vowel. 相似文献
992.
993.
Mechanisms for the formation of toxisterol A are suggested. The connection between the conformation of the initial previtamin and the stereochemistry of the reaction products is discussed.Lensoviet Leningrad Technological Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 225–229, March–April, 1989. 相似文献
994.
995.
996.
The renormalization of the dispersion law for two-dimensional excitons in a magnetic field is studied by the Green's-function method taking into account multiphonon processes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–7, April, 1987. 相似文献
997.
998.
999.
G. Carelli A. Di Siena N. Ioli A. Moretti G. Moruzzi F. Strumia 《International Journal of Infrared and Millimeter Waves》1994,15(4):619-633
We have measured the frequencies of four CH3OH far-infrared laser lines that were previously known only by wavelength measurement. Two of these lines turned out to be doublets, bringing the total number of measured lines to six. We can now confirm the assignments of five of them and definitely disprove the assignments proposed for the sixth.In particular we confirm the assignments for the four strong laser lines at 205 and 208 µm pumped by the 9-P(34) CO2 laser line. These lines share a common upper level in the first excited CO-stretch state, and terminate in the upper and lower levels of a hybrid state with J=5. Heterodyne frequency measurements and conventional microwave spectroscopy show that both lines are split into two components approximately 3.5 MHz apart. The origin of this further splitting is interpreted as a perturbed K-splitting.Work supported by Consiglio Nazionale delle Ricerche -Italia 相似文献
1000.
Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 27, No. 7, pp. 103–109, July, 1991. 相似文献