全文获取类型
收费全文 | 174557篇 |
免费 | 1926篇 |
国内免费 | 525篇 |
专业分类
化学 | 90743篇 |
晶体学 | 2597篇 |
力学 | 7284篇 |
综合类 | 3篇 |
数学 | 20152篇 |
物理学 | 56229篇 |
出版年
2020年 | 1462篇 |
2019年 | 1638篇 |
2018年 | 2035篇 |
2017年 | 2135篇 |
2016年 | 3361篇 |
2015年 | 1992篇 |
2014年 | 3259篇 |
2013年 | 7906篇 |
2012年 | 6030篇 |
2011年 | 7199篇 |
2010年 | 5218篇 |
2009年 | 5196篇 |
2008年 | 6815篇 |
2007年 | 6717篇 |
2006年 | 6308篇 |
2005年 | 5748篇 |
2004年 | 5297篇 |
2003年 | 4773篇 |
2002年 | 4601篇 |
2001年 | 5270篇 |
2000年 | 3918篇 |
1999年 | 3015篇 |
1998年 | 2521篇 |
1997年 | 2427篇 |
1996年 | 2300篇 |
1995年 | 2165篇 |
1994年 | 2141篇 |
1993年 | 2033篇 |
1992年 | 2325篇 |
1991年 | 2269篇 |
1990年 | 2223篇 |
1989年 | 2156篇 |
1988年 | 2083篇 |
1987年 | 2081篇 |
1986年 | 1979篇 |
1985年 | 2608篇 |
1984年 | 2667篇 |
1983年 | 2332篇 |
1982年 | 2466篇 |
1981年 | 2281篇 |
1980年 | 2258篇 |
1979年 | 2412篇 |
1978年 | 2450篇 |
1977年 | 2385篇 |
1976年 | 2427篇 |
1975年 | 2358篇 |
1974年 | 2318篇 |
1973年 | 2487篇 |
1972年 | 1603篇 |
1971年 | 1324篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
We have recently demonstrated that polarization transfer using an adiabatic passage through the Hartmann-Hahn condition (APHH-CP) by a variation of the radio-frequency amplitude can substantially improve the transfer efficiency over Hartmann-Hahn cross polarization. Here we show that APHH-CP can be combined with fast magic angle sample spinning (MAS). The heteronuclear dipolar order, established in the course of the transfer, can indeed be created and preserved. 相似文献
102.
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
103.
104.
Paolo Bertozzini Roberto Conti Roberto Longo 《Communications in Mathematical Physics》1998,193(2):471-492
Let ? be a local conformal net of von Neumann algebras on S
1 and ρ a M?bius covariant representation of ?, possibly with infinite dimension. If ρ has finite index, ρ has automatically
positive energy. If ρ has infinite index, we show the spectrum of the energy always to contain the positive real line, but,
as seen by an example, it may contain negative values. We then consider nets with Haag duality on ℝ, or equivalently sectors
with non-solitonic extension to the dual net; we give a criterion for irreducible sectors to have positive energy, namely
this is the case iff there exists an unbounded M?bius covariant left inverse. As a consequence the class of sectors with positive
energy is stable under composition, conjugation and direct integral decomposition.
Received: 21 April 1997 / Accepted: 23 September 1997 相似文献
105.
106.
107.
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
108.
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
109.
A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons
coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a
high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either
absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally
quantized levels can be up to 66%.
Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997) 相似文献
110.
V. M. Shopa B. N. Polevoi I. I. Popadyuk V. I. Tusevich 《Journal of Mathematical Sciences》1993,63(3):398-401
We propose a method of determining the contact pressures between the shells in a packet under the influence of nonlinear internal and constant external pressure. Using the equations of the general moment theory of shells we determine the stress-deformed state of a packet of finite cylindrical shells taking account of frictional forces on the contacting surfaces. One table. Bibliography: 10 titles.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 30, 1989, pp. 94–98. 相似文献