全文获取类型
收费全文 | 16511篇 |
免费 | 1588篇 |
国内免费 | 1252篇 |
专业分类
化学 | 5069篇 |
晶体学 | 150篇 |
力学 | 1143篇 |
综合类 | 204篇 |
数学 | 8028篇 |
物理学 | 4757篇 |
出版年
2023年 | 141篇 |
2022年 | 237篇 |
2021年 | 378篇 |
2020年 | 501篇 |
2019年 | 471篇 |
2018年 | 474篇 |
2017年 | 478篇 |
2016年 | 576篇 |
2015年 | 473篇 |
2014年 | 748篇 |
2013年 | 1473篇 |
2012年 | 732篇 |
2011年 | 869篇 |
2010年 | 739篇 |
2009年 | 922篇 |
2008年 | 998篇 |
2007年 | 1081篇 |
2006年 | 884篇 |
2005年 | 791篇 |
2004年 | 764篇 |
2003年 | 723篇 |
2002年 | 611篇 |
2001年 | 550篇 |
2000年 | 513篇 |
1999年 | 450篇 |
1998年 | 372篇 |
1997年 | 340篇 |
1996年 | 283篇 |
1995年 | 239篇 |
1994年 | 219篇 |
1993年 | 158篇 |
1992年 | 133篇 |
1991年 | 132篇 |
1990年 | 87篇 |
1989年 | 69篇 |
1988年 | 82篇 |
1987年 | 77篇 |
1986年 | 56篇 |
1985年 | 88篇 |
1984年 | 65篇 |
1983年 | 46篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 31篇 |
1979年 | 48篇 |
1978年 | 28篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1975年 | 11篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
41.
曾六川 《数学物理学报(A辑)》2002,22(3):336-341
设犈是一致凸Banach空间,满足Opial条件或具有Frechet可微范数,犆是犈的非空闭凸子集,且犜:犆→犆是非扩张映象.又设对任何初始数据狓1 ∈犆,序列{狓狀}由下列修改了的Ishikawa迭代程序生成:狓狀+1 =狋狀犜狀(狊狀犜狀狓狀+ (1-狊狀)狓狀)+ (1-狋狀)狓狀, 狀≥1, (I)其中,数列{狋狀}与{狊狀}满足下列条件(i)和(ii)之一:(i)狋狀∈ [犪,犫]且狊狀∈ [0,犫];(ii)狋狀∈ [犪,1]且狊狀∈ [犪,犫],这里,常数犪,犫满足0<犪≤犫<1.作者证明了,犜有不动点的充要条件是,{狓狀}
弱收敛且{‖狓狀-犜狓狀‖}收敛到0.而且,由此即知,若犜有不动点,则{狓狀}弱收敛到犜的一个不动点. 相似文献
42.
We derive an explicit autocorrelation function (ACF) formula of state of polarization for a fiber transmission system with polarization mode dispersion (PMD) and polarization dependent loss (PDL), which is found to agree well with Monte Carlo simulation. Then we use the new ACF to investigate the combined effect of PMD and PDL on the polarization multiplexed scheme. We find the performance of the polarization multiplexed scheme can be deteriorated more severely than the case without PDL. 相似文献
43.
During the course of our investigation of the electron transfer properties of some redox species through highly hydrophobic
long chain alkanethiol molecules on gold in aqueous and non-aqueous solvents, we obtained some intriguing results such as
unusually low interfacial capacitance, very high values of impedance and film resistance, all of which pointed to the possible
existence of a nanometer size interfacial gap between the hydrophobic monolayer and aqueous electrolyte. We explain this phenomenon
by a model for the alkanethiol monolayer—aqueous electrolyte interface, in which the extremely hydrophobic alkanethiol film
repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively
increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance.
This behaviour is very much akin to the ‘drying transition’ proposed by Lum, Chandler and Weeks in their theory of length
scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize
around them without sacrificing their hydrogen bonds. Since for an extended hydrophobic unit, the existence of hydrogen bonded
water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading
to the possible creation of a hydrophobic interfacial gap. 相似文献
44.
Jeannette H. C. Woerner 《商业与工业应用随机模型》2005,21(1):27-44
In the framework of stochastic volatility models we examine estimators for the integrated volatility based on the pth power variation (i.e. the sum of pth absolute powers of the log‐returns). We derive consistency and distributional results for the estimators given high‐frequency data, especially taking into account what kind of process we may add to our model without affecting the estimate of the integrated volatility. This may on the one hand be interpreted as a possible flexibility in modelling, for example adding jumps or even leaving the framework of semimartingales by adding a fractional Brownian motion, or on the other hand as robustness against model misspecification. We will discuss possible choices of p under different model assumptions and irregularly spaced data. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
45.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
46.
Jeong Ryeol Choi 《International Journal of Theoretical Physics》2004,43(4):947-958
We derived the WKB wave function for the general time-dependent quadratic Hamiltonian system using a unitary transformation method. We applied our research to sinusodially drived Caldirola–Kanai oscillator and confirmed that the time evolution of our approximated WKB wave function is similar to that of the exact one. This wave function can be used to analyze the interference between the probability amplitudes contributed by the area of overlap in phase space of quantum states. 相似文献
47.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
48.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
49.
Simonetta Orlandi 《Tetrahedron letters》2004,45(8):1747-1749
A mild, decarboxylative, aldol-type addition of malonic acid hemithioesters to aldehydes has been shown to occur with up to 39% enantioselectivity when the reaction was carried out in the presence of catalytic amounts of a Cu(II) salt, an enantiopure, tartaric acid-derived bis-benzimidazole and an achiral base. 相似文献
50.
The paper deals with the riskiness analysis for a large portfolio of life annuities. By means of the limiting distribution of the present value of the portfolio, in the first part of the paper a model for evaluating the investment and the projection risks is presented. In the second part, with regard to the investment risk's effects, the insolvency risk is measured considering the cumulative probability distribution function of the discounted average cost per policy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献