全文获取类型
收费全文 | 1770篇 |
免费 | 185篇 |
国内免费 | 223篇 |
专业分类
化学 | 1000篇 |
晶体学 | 6篇 |
力学 | 61篇 |
综合类 | 25篇 |
数学 | 651篇 |
物理学 | 249篇 |
无线电 | 186篇 |
出版年
2024年 | 5篇 |
2023年 | 27篇 |
2022年 | 50篇 |
2021年 | 62篇 |
2020年 | 86篇 |
2019年 | 83篇 |
2018年 | 55篇 |
2017年 | 62篇 |
2016年 | 81篇 |
2015年 | 50篇 |
2014年 | 76篇 |
2013年 | 122篇 |
2012年 | 117篇 |
2011年 | 93篇 |
2010年 | 67篇 |
2009年 | 112篇 |
2008年 | 98篇 |
2007年 | 122篇 |
2006年 | 86篇 |
2005年 | 78篇 |
2004年 | 71篇 |
2003年 | 65篇 |
2002年 | 85篇 |
2001年 | 56篇 |
2000年 | 66篇 |
1999年 | 49篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2178条查询结果,搜索用时 15 毫秒
11.
By using the averaging technique, we obtain new oscillation criteria for second order delay differential equation with nonlinear neutral term. These results generalize and improve some known results about neutral delay differential equation of second order. 相似文献
12.
考虑二阶半线性中立型差分方程给出了方程(1)的解的振动性的充分条件.所有结果推广和改进了关于中立和时滞差分方程已有结果. 相似文献
13.
We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We
have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than
we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs
only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence
intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 554–556, July–August, 2006. 相似文献
14.
一类脉冲中立型时滞抛物方程组的振动性 总被引:7,自引:0,他引:7
研究一类脉冲中立型时滞抛物方程组解的振动性,得到了该类方程组在两类不同边界条件下所有解振动的若干充分条件. 相似文献
15.
Differential algebraic equations with after-effect 总被引:4,自引:0,他引:4
C. T. H. Baker C. A. H. Paul H. Tian 《Journal of Computational and Applied Mathematics》2002,140(1-2):63-80
In this paper, we are concerned with the solution of delay differential algebraic equations. These are differential algebraic equations with after-effect, or constrained delay differential equations. The general semi-explicit form of the problem consists of a set of delay differential equations combined with a set of constraints that may involve retarded arguments. Even simply stated problems of this type can give rise to difficult analytical and numerical problems. The more tractable examples can be shown to be equivalent to systems of delay or neutral delay differential equations. Our purpose is to highlight some of the complexities and obstacles that can arise when solving these problems, and to indicate problems that require further research. 相似文献
16.
18.
Liang Ruixi Peng Jun Shen Jianhua 《Annals of Differential Equations》2006,22(4):502-510
The boundedness of the every solution and the asymptotic behavior of all solutions of the nonlinear neutral delay differential equation [x(t) - P(t)x(t - t)]' Q1 (t)f(x{t-σ1))-Q2(t)f(x(t -σ2))=0,t≥t0 are investigated, whereτ,σ1,σ2∈(0,∞), P∈C([t0,∞),R), and Q1,Q2∈C([t0,∞),R), f∈C(R,R). The sufficient conditions obtained improve the existing results in the literatures. 相似文献
19.
In this paper the sufficient conditions for the existence of positive solutions of the neutral difference equations with positive and negative coefficients are established. The results improve some known conclusions in the literature 相似文献
20.
Kh.A. Abdullin Yu.V. Gorelkinskii S.M. Kikkarin B.N. Mukashev A.S. Serikkanov S.Zh. Tokmoldin 《Materials Science in Semiconductor Processing》2004,7(4-6):447
Electrical and optical properties of bistable shallow donors in monocrystalline silicon, which are introduced by proton implantation followed by annealing at 450 °C, have been studied. The temperature dependences of equilibrium and non-equilibrium carrier concentration and relaxation kinetics were investigated. IR absorption lines of bistable shallow donor electronic excitations were detected. The obtained experimental data demonstrate that the bistable shallow donors can be identified as quantum wire defect nanoclusters. 相似文献