全文获取类型
收费全文 | 18941篇 |
免费 | 1044篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 195篇 |
综合类 | 24篇 |
化学工业 | 4331篇 |
金属工艺 | 364篇 |
机械仪表 | 365篇 |
建筑科学 | 746篇 |
矿业工程 | 39篇 |
能源动力 | 587篇 |
轻工业 | 2756篇 |
水利工程 | 150篇 |
石油天然气 | 46篇 |
无线电 | 1069篇 |
一般工业技术 | 3161篇 |
冶金工业 | 3010篇 |
原子能技术 | 119篇 |
自动化技术 | 3050篇 |
出版年
2023年 | 138篇 |
2022年 | 151篇 |
2021年 | 620篇 |
2020年 | 384篇 |
2019年 | 441篇 |
2018年 | 701篇 |
2017年 | 656篇 |
2016年 | 708篇 |
2015年 | 520篇 |
2014年 | 724篇 |
2013年 | 1213篇 |
2012年 | 1132篇 |
2011年 | 1316篇 |
2010年 | 941篇 |
2009年 | 891篇 |
2008年 | 905篇 |
2007年 | 785篇 |
2006年 | 666篇 |
2005年 | 584篇 |
2004年 | 450篇 |
2003年 | 435篇 |
2002年 | 376篇 |
2001年 | 279篇 |
2000年 | 277篇 |
1999年 | 269篇 |
1998年 | 1086篇 |
1997年 | 648篇 |
1996年 | 442篇 |
1995年 | 277篇 |
1994年 | 237篇 |
1993年 | 236篇 |
1992年 | 89篇 |
1991年 | 110篇 |
1990年 | 92篇 |
1989年 | 92篇 |
1988年 | 72篇 |
1987年 | 70篇 |
1986年 | 73篇 |
1985年 | 81篇 |
1984年 | 65篇 |
1983年 | 59篇 |
1982年 | 66篇 |
1981年 | 78篇 |
1980年 | 64篇 |
1979年 | 36篇 |
1978年 | 49篇 |
1977年 | 75篇 |
1976年 | 112篇 |
1975年 | 30篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 480 毫秒
61.
For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D3), and subsequently characterized by nuclear magnetic resonance (1H and 13C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies. 相似文献
62.
63.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
64.
Joaquín Cortés Eliana Valencia Gonzalo Aguila Esteban Orellana Paulo Araya 《Catalysis Letters》2008,126(1-2):63-71
An experimental study is made of the time decay of activity of the CO–NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models. 相似文献
65.
This paper reports the results of current fundamental research at the Department of Process Engineering, University of Miskolc on the processing of clean coal from Mecsek bituminous coal, Southern Hungary. The theoretical possibility of the separation of different petrographic components was proven experimentally and their liberation degree was determined based on the petrographic composition, flotation kinetic study of isolated components (groups of components), scanning electron microscopy and microprobe analyses. The mill with stirred ball media was chosen for the ultra-fine liberation of the coal components. It was revealed that along with the liberation of coal components, their surface oxidation and spontaneous agglomeration, entrapping the mineral impurities take place in ultra-fine grinding. This paper discusses the interfacial phenomena occurring in the ultra-fine grinding process and their influence on the flotation. The concept for the advanced preparation of clean coal was developed, tested and proved. The main steps of this concept are the ultra-fine liberation in the stirred-media mill, the de-agglomeration of flocs spontaneously formed during the ultra-fine grinding and the induced (hydrophobic) flocculation with the following two-step flotation in a flotation column. 相似文献
66.
Tams Insperger Gbor Stpn 《International journal for numerical methods in engineering》2004,61(1):117-141
An updated version of the semi‐discretization method is presented for periodic systems with a single discrete time delay. The delayed term is approximated as a weighted sum of two neighbouring discrete delayed state values and the transition matrix over a single period is determined. Stability charts are constructed for the damped and delayed Mathieu equation for different time‐period/time‐delay ratios. The convergence of the method is investigated by examples. Stability charts are constructed for 1 and 2 degree of freedom milling models. The codes of the algorithm are also attached in the appendix. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
67.
Stefan Turek Ludmila Rivkind Jaroslav Hron Roland Glowinski 《Journal of scientific computing》2006,28(2-3):533-547
In [Turek (1996). Int. J. Numer. Meth. Fluids
22, 987–1011], we had performed numerical comparisons for different time stepping schemes for the incompressible Navier–Stokes equations. In this paper, we present the numerical analysis in the context of the Navier–Stokes equations for a modified time-stepping θ-scheme which has been recently proposed by Glowinski [Glowinski (2003). In: Ciarlet, P. G., and Lions, J. L. (eds.), Handbook of Numerical Analysis, Vol. IX, North-Holland, Amsterdam, pp. 3–1176]. Like the well-known classical Fractional-Step-θ-scheme which had been introduced by Glowinski [Glowinski (1985). In Murman, E. M. and Abarbanel, S. S. (eds.), Progress and Supercomputing in Computational Fluid Dynamics, Birkh?user, Boston MA; Bristeau et al. (1987). Comput. Phys. Rep. 6, 73–187], too, and which is still one of the most popular time stepping schemes, with or without operator splitting techniques, this new scheme consists of 3 substeps with nonequidistant substepping to build one macro time step. However, in contrast to the Fractional-Step-θ-scheme, the second substep can be formulated as an extrapolation step for previously computed data only, and the two remaining substeps look like a Backward Euler step so that no expensive operator evaluations for the right hand side vector with older solutions, as for instance in the Crank–Nicolson scheme, have to be performed. This modified scheme is implicit, strongly A-stable and second order accurate, too, which promises some advantageous behavior, particularly in implicit CFD simulations for the nonstationary Navier–Stokes equations. Representative numerical results, based on the software package FEATFLOW [Turek (2000). FEATFLOW Finite element software for the incompressible Navier–Stokes equations: User Manual, Release 1.2, University of Dortmund] are obtained for typical flow problems with benchmark character which provide a fair rating of the solution schemes, particularly in long time simulations.Dedicated to David Gottlieb on the occasion of his 60th anniversary 相似文献
68.
69.
70.