全文获取类型
收费全文 | 120507篇 |
免费 | 11594篇 |
国内免费 | 6610篇 |
专业分类
电工技术 | 8376篇 |
综合类 | 9597篇 |
化学工业 | 15768篇 |
金属工艺 | 6536篇 |
机械仪表 | 6333篇 |
建筑科学 | 6983篇 |
矿业工程 | 3919篇 |
能源动力 | 3401篇 |
轻工业 | 14573篇 |
水利工程 | 3249篇 |
石油天然气 | 3173篇 |
武器工业 | 1571篇 |
无线电 | 10212篇 |
一般工业技术 | 10969篇 |
冶金工业 | 17020篇 |
原子能技术 | 1664篇 |
自动化技术 | 15367篇 |
出版年
2024年 | 673篇 |
2023年 | 1718篇 |
2022年 | 4107篇 |
2021年 | 5341篇 |
2020年 | 3818篇 |
2019年 | 2817篇 |
2018年 | 3100篇 |
2017年 | 3508篇 |
2016年 | 3230篇 |
2015年 | 4541篇 |
2014年 | 5739篇 |
2013年 | 7204篇 |
2012年 | 8511篇 |
2011年 | 9078篇 |
2010年 | 8341篇 |
2009年 | 7766篇 |
2008年 | 7776篇 |
2007年 | 7461篇 |
2006年 | 6326篇 |
2005年 | 5133篇 |
2004年 | 4084篇 |
2003年 | 2972篇 |
2002年 | 2697篇 |
2001年 | 2456篇 |
2000年 | 1970篇 |
1999年 | 1259篇 |
1998年 | 4668篇 |
1997年 | 2804篇 |
1996年 | 1892篇 |
1995年 | 1161篇 |
1994年 | 944篇 |
1993年 | 1053篇 |
1992年 | 324篇 |
1991年 | 396篇 |
1990年 | 342篇 |
1989年 | 303篇 |
1988年 | 294篇 |
1987年 | 238篇 |
1986年 | 236篇 |
1985年 | 232篇 |
1984年 | 139篇 |
1983年 | 107篇 |
1982年 | 156篇 |
1981年 | 161篇 |
1980年 | 185篇 |
1979年 | 107篇 |
1978年 | 85篇 |
1977年 | 296篇 |
1976年 | 507篇 |
1975年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Yunlei Li Dick de Ridder Robert P.W. Duin Marcel J.T. Reinders 《Pattern recognition》2008,41(1):320-330
Samples can be measured with different precisions and reliabilities in different experiments, or even within the same experiment. These varying levels of measurement noise may deteriorate the performance of a pattern recognition system, if not treated with care. Here we seek to investigate the benefit of incorporating prior knowledge about measurement noise into system construction. We propose a kernel density classifier which integrates such prior knowledge. Instead of using an identical kernel for each sample, we transform the prior knowledge into a distinct kernel for each sample. The integration procedure is straightforward and easy to interpret. In addition, we show how to estimate the diverse measurement noise levels in a real world dataset. Compared to the basic methods, the new kernel density classifier can give a significantly better classification performance. As expected, this improvement is more obvious for small sample size datasets and large number of features. 相似文献
72.
20世纪以来,人类采用技术工程治理、法律制裁和经济惩罚等措施,一定意义上改善了局部的生态环境,但是未能遏制住全球环境问题的恶化态势。生态危机的根本解决,关键在于人类自身必须进行深刻的利益观念和价值观念的变革。重新审视人与自然界的关系,对自然进行伦理关怀,寻求和建立以保护地球环境和人类生存与可持续发展的生态平衡理念。 相似文献
73.
74.
Marta Fernndez-García Pedro Francisco Caamero Jos Luis de la Fuente 《Reactive and Functional Polymers》2008,68(9):1384-1391
Epoxy-functional spontaneous gradient copolymers of glycidyl methacrylate (G) and n-butyl acrylate (B) were synthesized via atom transfer radical polymerization (ATRP). The copolymerization reactions were carried out in toluene solution at 70 °C, using methyl 2-bromopropionate (MBrP) as initiator and copper chloride with N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The kinetic behaviour of the statistical copolymerizations was studied in a wide composition interval with molar fractions of G ranging from 0.10 to 0.75. The synthesized copolymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. 1H NMR was employed to determine the copolymer composition, demonstrating the gradient character of the copolymers along the main chain in the whole monomer conversion interval. Apart from this, the sequence distribution and stereoregularity were analyzed. These microstructural experimental data agreed well with those calculated from Mayo-Lewis terminal model (MLTM) and a Bernoullian statistic with an isotacticity parameter of σG = 0.28 and a coisotacticity parameter of σ = 0.30. 相似文献
75.
如何对接入网络的用户进行身份认证、授予相应权限并进行计费,是卫星移动通信系统网络管理需解决的重要问题。简要介绍认证、授权、计费(AAA)的基本概念,分析Diameter协议框架、协议原理以及协议应用于网络接入的特点。阐述协议中包含的各种应用,给出Diameter NASREQ应用的一种系统模型。重点研究Diameter NASREQ协议在卫星移动通信系统中的应用,详述应用中客户机和服务器中各模块的功能和工作原理。通过分析,说明该应用的可行性及有效性。 相似文献
76.
77.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
78.
The catalysts of CeO2 and the mixture of CeO2 and CuO were prepared, and the activities of these catalysts for completely oxidizing benzene were studied.The results show that the optimal proportion of CeO2/CuO is 6: 4.The highest temperature at which benzene was completely oxidized on these catalysts at different airspeed was measured.Compared these catalysts with the noble metal used, our catalysts had superiority in the resources and the industrial cost besides good activities. 相似文献
79.
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
80.
马勇 《金属材料与冶金工程》2003,31(1):21-24
通过煤种,入窑球冷态强度和还原过程强度,以及钛精矿与煤灰混合物的软化温度等分析探讨了钛精矿预热球团回转窑直接还原产生结圈的可能性,获得了可以避免结圈的结论。 相似文献