全文获取类型
收费全文 | 82849篇 |
免费 | 8138篇 |
国内免费 | 8426篇 |
专业分类
化学 | 35238篇 |
晶体学 | 538篇 |
力学 | 7949篇 |
综合类 | 1424篇 |
数学 | 26623篇 |
物理学 | 27641篇 |
出版年
2023年 | 707篇 |
2022年 | 1469篇 |
2021年 | 1622篇 |
2020年 | 1880篇 |
2019年 | 2035篇 |
2018年 | 1763篇 |
2017年 | 2107篇 |
2016年 | 2470篇 |
2015年 | 2210篇 |
2014年 | 3188篇 |
2013年 | 5789篇 |
2012年 | 3653篇 |
2011年 | 4027篇 |
2010年 | 3441篇 |
2009年 | 4735篇 |
2008年 | 5138篇 |
2007年 | 5373篇 |
2006年 | 4991篇 |
2005年 | 4218篇 |
2004年 | 3899篇 |
2003年 | 3888篇 |
2002年 | 3489篇 |
2001年 | 2966篇 |
2000年 | 2880篇 |
1999年 | 2529篇 |
1998年 | 2400篇 |
1997年 | 1938篇 |
1996年 | 1724篇 |
1995年 | 1574篇 |
1994年 | 1469篇 |
1993年 | 1241篇 |
1992年 | 1190篇 |
1991年 | 909篇 |
1990年 | 742篇 |
1989年 | 660篇 |
1988年 | 596篇 |
1987年 | 463篇 |
1986年 | 403篇 |
1985年 | 452篇 |
1984年 | 453篇 |
1983年 | 216篇 |
1982年 | 367篇 |
1981年 | 409篇 |
1980年 | 309篇 |
1979年 | 304篇 |
1978年 | 230篇 |
1977年 | 209篇 |
1976年 | 157篇 |
1974年 | 110篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
61.
62.
High index of refraction via quantum interference in a three-level system of Er^3+-doped yttrium aluminium garnet crystal 下载免费PDF全文
A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er^3+-doped yttrium aluminium garnet (YAG) crystal, which is achieved for a probe field between the excited state 4I13/2 and ground state 4I15/2 by adjusting a strong coherent driving field between the upper excited state 4I11/2 and 4I15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er^3+ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on. 相似文献
63.
Kenji Saijyou 《Applied Acoustics》2006,67(10):1031-1043
The relationship between the dominant mode of the submerged thin cylindrical shell and the flexural wave velocity is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, it is difficult to estimate the dominant mode, especially if two or more vibration modes are involved. To estimate the dominant mode of a thin shell in vacuo, the concept of “modified bending stiffness” has been introduced. In this paper, the concept of modified bending stiffness is extended to estimate the dominant mode of a submerged thin cylindrical shell. The dominant mode of a submerged thin cylindrical shell is theoretically discriminated from the other mode based on the smallness of the modified bending stiffness of the submerged shell. The validity of our theory is confirmed by a good agreement between theoretical and experimental results on flexural wave velocity. 相似文献
64.
《Electroanalysis》2006,18(6):595-604
The following two numerical models have been applied to zinc cations electroreduction in 1 M NaClO4 water solution: a classical EE model describing the concentration of involved species in solution (semi infinitive diffusion region), an extended EE model describing both: the concentration of involved species in solution and the concentration of metallic zinc inside mercury drop (in limited area of diffusion). In the latter model the inner part of mercury drop and surrounding solution were treated as dynamic interrelated system. Both models were applied to experimental cyclic voltammetric CV data in 1 M NaClO4, the results compared and discussed. The concentration profiles of all species including metallic zinc inside mercury drop were performed. The presented integrated model is essential for theoretical and analytical aspects of the electrochemistry of mercury soluble metal cations and amalgams. 相似文献
65.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献
66.
67.
Wei Gengping~ Shen Jianhua~ 《高校应用数学学报(英文版)》2006,21(3):320-326
This paper studies the nonautonomous nonlinear system of difference equationsΔx(n)=A(n)x(n)+f(n,x(n)),n∈Z,(*) where x(n)∈R~N,A(n)=(a_(ij)(n))N×N is an N×N matrix,with a-(ij)∈C(R,R) for i,j= 1,2,3,...,N,and f=(f_1,f_2,...,f_N)~T∈C(R×R~N,R~N),satisfying A(t+ω)=A(t),f(t+ω,z)=f(t,z) for any t∈R,(t,z)∈R×R~N andωis a positive integer.Sufficient conditions for the existence ofω-periodic solutions to equations (*) are obtained. 相似文献
68.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
69.
利用Riccati变换求解同谐谐振子的定态薛定谔方程,求得了能谱及态函数
关键词:
同调谐振子
本征值谱
Riccati变换法 相似文献
70.
根据GaN氢化物气相外延生长(HVPE)的原理,设计制作了双温区卧式HVPE系统.根据实际生长中出现的问题和CaN样品的测试情况,对系统进行了逐步的调试和改进. 相似文献