全文获取类型
收费全文 | 34123篇 |
免费 | 4212篇 |
国内免费 | 2631篇 |
学科分类
工业技术 | 40966篇 |
出版年
2024年 | 112篇 |
2023年 | 371篇 |
2022年 | 594篇 |
2021年 | 848篇 |
2020年 | 1109篇 |
2019年 | 850篇 |
2018年 | 876篇 |
2017年 | 1220篇 |
2016年 | 1395篇 |
2015年 | 1497篇 |
2014年 | 2204篇 |
2013年 | 2291篇 |
2012年 | 2761篇 |
2011年 | 2919篇 |
2010年 | 2375篇 |
2009年 | 2386篇 |
2008年 | 2331篇 |
2007年 | 2693篇 |
2006年 | 2389篇 |
2005年 | 1892篇 |
2004年 | 1456篇 |
2003年 | 1322篇 |
2002年 | 948篇 |
2001年 | 826篇 |
2000年 | 635篇 |
1999年 | 534篇 |
1998年 | 411篇 |
1997年 | 313篇 |
1996年 | 310篇 |
1995年 | 255篇 |
1994年 | 195篇 |
1993年 | 143篇 |
1992年 | 112篇 |
1991年 | 81篇 |
1990年 | 55篇 |
1989年 | 60篇 |
1988年 | 48篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
The paper deals with state estimation of the nonlinear stochastic systems by means of the unscented Kalman filter with a focus on specification of the σ-points. Their position is influenced by two design parameters—the scaling parameter determining the spread of the σ-points and a covariance matrix decomposition determining rotation of the σ-points. In this paper, a choice of the scaling parameter is analyzed. It is shown that considering other values than the standard choice may lead to increased quality of the estimate, especially if the scaling parameter is adapted. Several different criteria for the adaptation are proposed and techniques to reduce computational costs of the adaptation are developed. The proposed algorithm of the unscented Kalman filter with advanced adaptation of the scaling parameter is illustrated in a numerical example. 相似文献
114.
115.
Fluid flow in coupled free and porous domain, particularly when the porous medium is heterogeneous, is encountered in many hydro-environmental conditions, e.g., leakage from underground pipe, combined groundwater lake-subsurface interactions. One of the most difficult problems in the study of coupled flow behaviour has been the development of a universally applicable modelling scheme for combining the flow regimes. This is because the free/porous interfacial properties (e.g., shear-stress; velocity slip) that govern the coupled flow behaviour are difficult to determine experimentally under hydro-environmental conditions. On the other hand, the implications of various forms of heterogeneity in the porous media properties can be very different on the fluid-flow behaviour. Difficulties may also arise in direct coupling of the model equations that govern the fluid flow in the individual regions (e.g., Navier-Stokes for free-flow region and the Darcy's equation for the porous flow region). Consequently, models of coupled free and porous flow for hydro-environmental conditions are not very well developed at the moment. While there are some indications that fluids in coupled free and porous domains may circulate (i.e., development of flow cells), there is a lack of appropriate 3D analysis on how heterogeneities in porous media may affect such flow patterns. In this paper, we aim to analyse how porous media heterogeneity affects the dynamics of flow circulation in the porous side of a coupled free and porous domain. For this purpose, we analyse flow patterns in several model domains made up of two porous layers with differing permeabilities. The governing model equations are discretised and solved using the standard finite volume method on a staggered cell-centred mesh. The temporal discretisation is done using the explicit method. An in-house graphical user interface (GUI) has been created specifically to aid in the visualisation of otherwise complex flow patterns. The GUI contains many post-processing options and provides a comprehensive tool for the analysis of hydrodynamics and contaminant motion (not discussed in this paper) in coupled free and porous flow domains. This GUI is described in this paper briefly. The effects of altering the aspect ratio (i.e., multi-scale) of the domain on the coupled flow pattern have also been discussed. 相似文献
116.
Schaefer-Sindlinger A. Lappas I. Vogt C. D. Ito T. Kurachi H. Makino M. Takahashi A. 《Topics in Catalysis》2007,42(1-4):307-317
This paper will give an overview about the filter development for diesel particulate emission control in automotive applications.
The material development for passenger car diesel particulate filters led to new materials like silicon carbide while for
heavy duty applications still Cordierite plays a major role. But in the future other materials might also be used for passenger
cars. This paper will show the basic difference between both applications and describe the material design in terms of filter
properties (base material, back pressure aspects, filtration efficiency, coating impact). Current application on vehicles
with catalysed soot filters (CSF) with and without oxidation catalyst will be presented. Furthermore an outlook will be given
on materials for catalysed soot filters for the future. 相似文献
117.
118.
工业污水深度处理回用技术研究 总被引:2,自引:0,他引:2
通过对石化企业工业污水进行曝气生物滤池、连续微滤、反渗透等深度处理,使出水满足工业化用水的水质要求,从而得以回用。 相似文献
119.
E. Stamatakis C. Chatzichristos A.K. Stubos J. Muller 《Chemical engineering science》2006,61(21):7057-7067
The applicability of a newly developed radiotracer technique as a reliable laboratory procedure for the evaluation of scale inhibitors performance to prevent mineral precipitation is demonstrated. The performance of two new environmentally friendly inhibitors to prevent calcite and barite scale was evaluated experimentally in connection with a standard phosphonate-type scale inhibitor using the radioactive tracer technology. The radiotracers 47Ca and 131Ba were employed in order to monitor at real-time calcite and barite scale formation, respectively. The results show that the developed radiotracer technique can be established as a novel method for the determination of the minimum inhibitor concentration (MIC) under dynamic, reservoir conditions. In addition, the radioactive tritiated water (HTO) was used as a reference water tracer to identify the inhibitors’ properties, such as adsorption/desorption characteristics, in sandpack-flooding tests. Further issues regarding the implementation of the radiotracer technology for the laboratory evaluation of scale inhibitors performance are also discussed. 相似文献
120.
A new explicit numerical simulation (ENS) method based on lattice-gas automata (LGA) is introduced here for the flow of solid/fluid suspensions with deposition in porous media. The ENS method explicitly resolves the dynamics of the individual solid particles and the suspending fluid in the domain defined by the pore walls and solid particle surfaces. After describing the new method, it is applied to the study of solid/fluid suspension flow with deposition in a constriction and in a model random porous solid. This study clearly demonstrates that the deposits strongly influence the local flow fields, which in turn affect the deposition process indicating that this interplay should be modelled if accurate results are desired from trajectory methods. 相似文献