全文获取类型
收费全文 | 391090篇 |
免费 | 4290篇 |
国内免费 | 1325篇 |
专业分类
化学 | 204654篇 |
晶体学 | 6220篇 |
力学 | 16965篇 |
综合类 | 5篇 |
数学 | 47190篇 |
物理学 | 121671篇 |
出版年
2020年 | 2945篇 |
2019年 | 3332篇 |
2018年 | 4944篇 |
2017年 | 5010篇 |
2016年 | 6846篇 |
2015年 | 4391篇 |
2014年 | 6611篇 |
2013年 | 17689篇 |
2012年 | 13391篇 |
2011年 | 15951篇 |
2010年 | 10898篇 |
2009年 | 10919篇 |
2008年 | 14289篇 |
2007年 | 14231篇 |
2006年 | 13341篇 |
2005年 | 14614篇 |
2004年 | 13428篇 |
2003年 | 11160篇 |
2002年 | 9768篇 |
2001年 | 11220篇 |
2000年 | 8426篇 |
1999年 | 6611篇 |
1998年 | 5540篇 |
1997年 | 5456篇 |
1996年 | 5140篇 |
1995年 | 4819篇 |
1994年 | 4626篇 |
1993年 | 4664篇 |
1992年 | 5165篇 |
1991年 | 5121篇 |
1990年 | 4878篇 |
1989年 | 4807篇 |
1988年 | 4861篇 |
1987年 | 4716篇 |
1986年 | 4519篇 |
1985年 | 6110篇 |
1984年 | 6292篇 |
1983年 | 5314篇 |
1982年 | 5725篇 |
1981年 | 5463篇 |
1980年 | 5345篇 |
1979年 | 5502篇 |
1978年 | 5767篇 |
1977年 | 5580篇 |
1976年 | 5785篇 |
1975年 | 5291篇 |
1974年 | 5422篇 |
1973年 | 5859篇 |
1972年 | 3705篇 |
1971年 | 2953篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
181.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献
182.
183.
184.
185.
186.
187.
188.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated
ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base
results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated
ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy.
For Part 3, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997. 相似文献
189.
R.C. Viscovini E.M. Telles A. Scalabrin D. Pereira 《Applied physics. B, Lasers and optics》1997,65(1):33-35
2 laser of wide tunability to pump 13CD3OD we could observe 10 new far infrared laser lines ranging from 109 μm to 472 μm. The lines were generated by pumping infrared
absorbing transitions of large offset appertaining to the C-O stretching Q-branch. All lines were characterised in wavelength,
polarisation, optimum pressure of operation and precise offset measurements.
Received: 17 September 1996/Revised version: 18 November 1996 相似文献
190.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献