全文获取类型
收费全文 | 197324篇 |
免费 | 2513篇 |
国内免费 | 718篇 |
专业分类
化学 | 105785篇 |
晶体学 | 3154篇 |
力学 | 7778篇 |
综合类 | 4篇 |
数学 | 24728篇 |
物理学 | 59106篇 |
出版年
2021年 | 1450篇 |
2020年 | 1713篇 |
2019年 | 1838篇 |
2018年 | 2243篇 |
2017年 | 2344篇 |
2016年 | 3743篇 |
2015年 | 2450篇 |
2014年 | 3717篇 |
2013年 | 8999篇 |
2012年 | 7054篇 |
2011年 | 8461篇 |
2010年 | 5922篇 |
2009年 | 5764篇 |
2008年 | 7872篇 |
2007年 | 7773篇 |
2006年 | 7480篇 |
2005年 | 6755篇 |
2004年 | 6289篇 |
2003年 | 5604篇 |
2002年 | 5427篇 |
2001年 | 5648篇 |
2000年 | 4253篇 |
1999年 | 3338篇 |
1998年 | 2844篇 |
1997年 | 2784篇 |
1996年 | 2618篇 |
1995年 | 2449篇 |
1994年 | 2451篇 |
1993年 | 2328篇 |
1992年 | 2609篇 |
1991年 | 2554篇 |
1990年 | 2456篇 |
1989年 | 2396篇 |
1988年 | 2368篇 |
1987年 | 2329篇 |
1986年 | 2258篇 |
1985年 | 2974篇 |
1984年 | 3039篇 |
1983年 | 2681篇 |
1982年 | 2821篇 |
1981年 | 2610篇 |
1980年 | 2609篇 |
1979年 | 2681篇 |
1978年 | 2753篇 |
1977年 | 2661篇 |
1976年 | 2654篇 |
1975年 | 2544篇 |
1974年 | 2520篇 |
1973年 | 2664篇 |
1972年 | 1732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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
112.
113.
114.
115.
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
116.
117.
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
118.
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
119.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
120.
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