全文获取类型
收费全文 | 2839篇 |
免费 | 231篇 |
国内免费 | 323篇 |
专业分类
化学 | 1121篇 |
晶体学 | 3篇 |
力学 | 125篇 |
综合类 | 44篇 |
数学 | 737篇 |
物理学 | 1363篇 |
出版年
2024年 | 8篇 |
2023年 | 29篇 |
2022年 | 124篇 |
2021年 | 131篇 |
2020年 | 120篇 |
2019年 | 67篇 |
2018年 | 89篇 |
2017年 | 78篇 |
2016年 | 86篇 |
2015年 | 89篇 |
2014年 | 124篇 |
2013年 | 215篇 |
2012年 | 106篇 |
2011年 | 157篇 |
2010年 | 124篇 |
2009年 | 178篇 |
2008年 | 184篇 |
2007年 | 210篇 |
2006年 | 141篇 |
2005年 | 114篇 |
2004年 | 83篇 |
2003年 | 97篇 |
2002年 | 84篇 |
2001年 | 79篇 |
2000年 | 117篇 |
1999年 | 63篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 59篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有3393条查询结果,搜索用时 15 毫秒
1.
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
2.
《Current Applied Physics》2015,15(11):1296-1302
One-dimensional ZnO materials have been promising for field-emission (FE) application, but how to facially control the alignment of ZnO emitters is still a great challenge especially for patterned display application. Here, we report the fabrication of novel ZnO nanowire (NW) line and bundle arrays for patterned field-electron emitters. The effects of PS template size and heating time on the resulted ZnO nanoarrays were systematically studied. The deformation degree of PS templates was controlled and hence utilized to adjust the alignment of electrochemically deposited ZnO arrays. It was found that the length of NW lines and the density of NW bundles can effectively tuned by the PS template heating time. The optimal FE performance with turn-on electric field as low as of 4.4 V μm−1 and the field-enhancement factor as high as of 1450 were achieved through decreasing the screening effect among the patterned field-electron emitters. 相似文献
3.
数据包络分析(DEA)是评价供应链系统(Supply chain system)间相对有效性的一种重要的工具,但是传统的DEA不考虑供应链的内部结构,对系统效率评价偏高;而本文所研究两阶段串联供应链系统,考虑把部分中间产品作为最终产品输出,增加额外中间投入的情形.基于所提出的供应链系统结构,本文建立相应的串联结构下的网络DEA模型,并针对所建立模型进行相关理论的研究,给出了串联结构下的生产可能集和规模收益情况判定方法.最后,进行数值实验,以验证我们提出的结论. 相似文献
4.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
5.
6.
7.
R. J. Saykally K. M. Evenson D. A. Jennings L. R. Zink A. Scalabrin 《International Journal of Infrared and Millimeter Waves》1987,8(6):653-662
Twenty new cw FIR laser lines in CD3OH, optically pumped by a CO2 laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO2 lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 107.Contribution of the U.S. Government, not subject to copyright. 相似文献
8.
A localH-theorem is derived for a recently proposed extension of Enskog kinetic theory to a dense model fluid composed of particles with interactions extending beyond a hard core.On leave from: Katedra Fizyki, Uniwersytetu Szczecinskiego, 70-451 Szczecin, Poland. 相似文献
9.
Semra Harmandar 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):395-407
A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing-emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing-emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach. 相似文献
10.
We develop a production policy that controls work-in-process (WIP) levels and satisfies demand in a multistage manufacturing system with significant uncertainty in yield, rework, and demand. The problem addressed in this paper is more general than those in the literature in three aspects: (i) multiple products are processed at multiple workstations, and the capacity of each workstation is limited and shared by multiple operations; (ii) the behavior of a production policy is investigated over an infinite-time horizon, and thus the system stability can be evaluated; (iii) the representation of yield and rework uncertainty is generalized. Generalizing both the system structure and the nature of uncertainty requires a new mathematical development in the theory of infinite-horizon stochastic dynamic programming. The theoretical contributions of this paper are the existence proofs of the optimal stationary control for a stochastic dynamic programming problem and the finite covariances of WIP and production levels under the general expression of uncertainty. We develop a simple and explicit sufficient condition that guarantees the existence of both the optimal stationary control and the system stability. We describe how a production policy can be constructed for the manufacturing system based on the propositions derived. 相似文献