全文获取类型
收费全文 | 355967篇 |
免费 | 2418篇 |
国内免费 | 823篇 |
专业分类
化学 | 178634篇 |
晶体学 | 5468篇 |
力学 | 17832篇 |
综合类 | 11篇 |
数学 | 41916篇 |
物理学 | 115347篇 |
出版年
2020年 | 3247篇 |
2019年 | 3805篇 |
2018年 | 5373篇 |
2017年 | 5427篇 |
2016年 | 7129篇 |
2015年 | 3819篇 |
2014年 | 6555篇 |
2013年 | 15017篇 |
2012年 | 11774篇 |
2011年 | 14095篇 |
2010年 | 10605篇 |
2009年 | 10594篇 |
2008年 | 13120篇 |
2007年 | 13254篇 |
2006年 | 12301篇 |
2005年 | 10997篇 |
2004年 | 10363篇 |
2003年 | 9297篇 |
2002年 | 9293篇 |
2001年 | 10597篇 |
2000年 | 8019篇 |
1999年 | 6153篇 |
1998年 | 5258篇 |
1997年 | 5105篇 |
1996年 | 4699篇 |
1995年 | 4374篇 |
1994年 | 4219篇 |
1993年 | 4113篇 |
1992年 | 4486篇 |
1991年 | 4744篇 |
1990年 | 4600篇 |
1989年 | 4488篇 |
1988年 | 4457篇 |
1987年 | 4440篇 |
1986年 | 4130篇 |
1985年 | 5282篇 |
1984年 | 5556篇 |
1983年 | 4664篇 |
1982年 | 4913篇 |
1981年 | 4796篇 |
1980年 | 4465篇 |
1979年 | 4817篇 |
1978年 | 5054篇 |
1977年 | 5147篇 |
1976年 | 5285篇 |
1975年 | 4878篇 |
1974年 | 4830篇 |
1973年 | 5091篇 |
1972年 | 3667篇 |
1971年 | 3131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The present paper establishes sufficient conditions for the uniformly bounded of any solution of (1.1) and which tend to zero as t → ∞. 相似文献
992.
M.I.Gil' 《Annals of Differential Equations》2004,20(2):145-154
The nonlocal initial problem for nonlinear nonautonomous evolution equati-ons in a Banach space is considered. It is assumed that the nonlinearities havethe local Lipschitz properties. The existence and uniqueness of mild solutionsare proved. Applications to integro-differential equations are discussed.The main tool in the paper is the normalizing mapping (the generalizednorm). 相似文献
993.
Frank T. D. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,37(2):139-142
The European Physical Journal B - We compute autocorrelation functions from nonlinear Fokker-Planck equations that describe nonlinear families of Markov diffusion processes and illustrate this... 相似文献
994.
The coalescence of branches in the Y junctions of single-wall carbon nanotubes (10 nm long) is predicted to occur when the branches approach each other under the action of a load (~10 nN) applied to their ends. A transition to the new state with parallel branches bound by molecular interactions was simulated and the energy characteristics were calculated by the molecular dynamics method. The Y junctions with parallel branches are stable at temperatures up to 2000 K. It is established that there is a threshold distance between the branch ends, below which the branches exhibit spontaneous sticking under the action of molecular attraction forces. If the branches are unloaded before this threshold distance is reached, they oscillate (acting as a nanodimensional “tuning fork”) at a frequency of ~100 GHz. 相似文献
995.
The pseudopotential augmented-plane-wave method was used to study the surface structure of thin copper films with monolayers of Co, Ni, and Cs. Local densities of electron states, distributions of charge densities in the layers, and electron energy spectra are analyzed. The effect of adsorbates on the electronic properties of the Cu(001) surface and work function are discussed. Satisfactory agreement with available experimental data has been obtained. 相似文献
996.
Mathematical Notes - We consider functions f(z), z ∈ D ? ?, determining the mappings w = f(z) that, at the points ζ of the domain D, have the same dilatation ratio along the... 相似文献
997.
I T Vieira P R Harper A K Shahani V De Senna 《The Journal of the Operational Research Society》2003,54(7):713-722
Mother-to-child transmission (MTCT) of HIV is the most significant source of HIV infection in children below the age of 15 years. In 2000 alone, about 600 000 new infections occurred, the vast majority from mothers living in developing countries who were not aware of their HIV-positive status. To date, at least 4.3 million children have died from AIDS. In this paper, we discuss the development of an operational model that can be used to evaluate intervention options for the prevention of MTCT of HIV. The problem was approached by defining suitable pregnancy risk groups, prevention options and the required model outputs to evaluate different intervention strategies. The method chosen to approach the problem was a discrete-event, three-phase simulation, built in Visual Basic, with a stochastic semi-Markov structure. The developed model takes individual pregnant women through each stage of their pregnancy, labour and birth. Different intervention strategies may be modelled at any time, including short-course antiretroviral drugs and cessation of breastfeeding. The model is demonstrated with data from Botswana, which has one of the highest HIV-infection rates in the world. 相似文献
998.
999.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献
1000.
Nonlinear processes caused by the propagation of low-frequency and high-frequency acoustic pulses in an unbounded medium and the propagation of continuous waves in a ring resonator are theoretically studied on the basis of two hysteretic equations of state for media with imperfect elasticity. The profiles and parameters of pulses, the resonance curve and the Q factor of the resonator, and the ratio of the nonlinear resonance frequency shift to the nonlinear damping decrement are determined. For nonlinear wave processes in such media, the distinctive features that allow one to choose an appropriate hysteretic equation of state for analytically describing the experimental data are revealed. 相似文献