全文获取类型
收费全文 | 7002篇 |
免费 | 324篇 |
国内免费 | 266篇 |
专业分类
化学 | 899篇 |
晶体学 | 50篇 |
力学 | 205篇 |
综合类 | 51篇 |
数学 | 4528篇 |
物理学 | 1859篇 |
出版年
2023年 | 42篇 |
2022年 | 57篇 |
2021年 | 132篇 |
2020年 | 158篇 |
2019年 | 164篇 |
2018年 | 147篇 |
2017年 | 119篇 |
2016年 | 159篇 |
2015年 | 139篇 |
2014年 | 225篇 |
2013年 | 692篇 |
2012年 | 242篇 |
2011年 | 296篇 |
2010年 | 246篇 |
2009年 | 382篇 |
2008年 | 424篇 |
2007年 | 477篇 |
2006年 | 343篇 |
2005年 | 255篇 |
2004年 | 200篇 |
2003年 | 252篇 |
2002年 | 273篇 |
2001年 | 235篇 |
2000年 | 243篇 |
1999年 | 214篇 |
1998年 | 190篇 |
1997年 | 106篇 |
1996年 | 100篇 |
1995年 | 104篇 |
1994年 | 110篇 |
1993年 | 63篇 |
1992年 | 70篇 |
1991年 | 76篇 |
1990年 | 54篇 |
1989年 | 62篇 |
1988年 | 48篇 |
1987年 | 64篇 |
1986年 | 36篇 |
1985年 | 78篇 |
1984年 | 45篇 |
1983年 | 38篇 |
1982年 | 44篇 |
1981年 | 14篇 |
1980年 | 23篇 |
1979年 | 34篇 |
1978年 | 20篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1975年 | 15篇 |
1973年 | 12篇 |
排序方式: 共有7592条查询结果,搜索用时 15 毫秒
1.
This work focuses on optimal controls of a class of stochastic SIS epidemic models under regime switching. By assuming that a decision maker can influence the infectivity period, our aim is to minimize the expected discounted cost due to illness, medical treatment, and the adverse effect on the society. In addition, a model with the incorporation of vaccination is proposed. Numerical schemes are developed by approximating the continuous-time dynamics using Markov chain approximation methods. It is demonstrated that the approximation schemes converge to the optimal strategy as the mesh size goes to zero. Numerical examples are provided to illustrate our results. 相似文献
2.
Hydrodynamic cavitation experiments in microfluidic systems have been performed with an aqueous solution of luminol as the working fluid. In order to identify where and how much reactive radical species are formed by the violent bubble collapse, the resulting chemiluminescent oxidation reaction of luminol was scrutinized downstream of a constriction in the microchannel. An original method was developed in order to map the intensity of chemiluminescence emitted from the micro-flow, allowing us to localize the region where radicals are produced. Time averaged void fraction measurements performed by laser induced fluorescence experiments were also used to determine the cavitation cloud position. The combination void fraction and chemiluminescence two-dimensional mapping demonstrated that the maximum chemiluminescent intensity area was found just downstream of the cavitation clouds. Furthermore, the radical yield can be obtained with our single photon counting technique. The maximum radical production rates of 1.2*107 OH/s and radical production per processed liquid volume of 2.15*1010 HO/l were observed. The proposed technique allows for two-dimensional characterisation of radical production in the microfluidic flow and could be a quick, non-intrusive way to optimise hydrodynamic cavitation reactor design and operating parameters, leading to enhancements in wastewater treatments and other process intensifications. 相似文献
3.
4.
5.
6.
We consider the random‐cluster model (RCM) on with parameters p∈(0,1) and q ≥ 1. This is a generalization of the standard bond percolation (with edges open independently with probability p) which is biased by a factor q raised to the number of connected components. We study the well‐known Fortuin‐Kasteleyn (FK)‐dynamics on this model where the update at an edge depends on the global geometry of the system unlike the Glauber heat‐bath dynamics for spin systems, and prove that for all small enough p (depending on the dimension) and any q>1, the FK‐dynamics exhibits the cutoff phenomenon at with a window size , where λ∞ is the large n limit of the spectral gap of the process. Our proof extends the information percolation framework of Lubetzky and Sly to the RCM and also relies on the arguments of Blanca and Sinclair who proved a sharp mixing time bound for the planar version. A key aspect of our proof is the analysis of the effect of a sequence of dependent (across time) Bernoulli percolations extracted from the graphical construction of the dynamics, on how information propagates. 相似文献
7.
8.
《Stochastic Processes and their Applications》2020,130(5):2596-2638
In this paper we introduce a new generalisation of the relative Fisher Information for Markov jump processes on a finite or countable state space, and prove an inequality which connects this object with the relative entropy and a large deviation rate functional. In addition to possessing various favourable properties, we show that this generalised Fisher Information converges to the classical Fisher Information in an appropriate limit. We then use this generalised Fisher Information and the aforementioned inequality to qualitatively study coarse-graining problems for jump processes on discrete spaces. 相似文献
9.
We consider a continuous-time random walk which is the generalization, by means of the introduction of waiting periods on sites, of the one-dimensional non-homogeneous random walk with a position-dependent drift known in the mathematical literature as Gillis random walk. This modified stochastic process allows to significantly change local, non-local and transport properties in the presence of heavy-tailed waiting-time distributions lacking the first moment: we provide here exact results concerning hitting times, first-time events, survival probabilities, occupation times, the moments spectrum and the statistics of records. Specifically, normal diffusion gives way to subdiffusion and we are witnessing the breaking of ergodicity. Furthermore we also test our theoretical predictions with numerical simulations. 相似文献
10.
《Current Applied Physics》2020,20(1):82-88
A detailed investigation about the effect of Sc2O3: 1 mol%Ho3+/5 mol%Yb3+ co-doped with Ce4+ ions prepared by sol-gel methods was performed systematically. Under the excitation of 980 nm laser diode, both green emission (553 nm, 5F4/5S2→5I8) and red emission (672 nm, 5F5→5I8) were both observed in the emission spectra of the samples, which were found to be two-photon process and sensitized by Yb3+ ions. With the increasing of Ce4+ ions, the up-conversion green emission intensity are increased by 6.52, 8.69, 10.85, 13.92 and 16.66 fold, corresponding to the Ce4+ ions concentrations from 5 mol% to 13 mol%, respectively. The number of photons are necessary to populate the upper emitting state decreases to 2 and the infrared absorption coefficient is reduced, when the Ce4+ ions concentration increase to 13 mol%. Ce4+ ions play an important role in tailoring the local crystal field around Ho3+ ions, lowering the highest phonon cut-off energy of matrix and reducing the infrared absorption coefficient, thus hindering the non-radiative processes, which contribute to the increased emission intensity. The excellent enhancement makes it a promising multifunctional optical luminescence material. 相似文献