全文获取类型
收费全文 | 15167篇 |
免费 | 1305篇 |
国内免费 | 568篇 |
专业分类
电工技术 | 756篇 |
技术理论 | 1篇 |
综合类 | 990篇 |
化学工业 | 2502篇 |
金属工艺 | 765篇 |
机械仪表 | 931篇 |
建筑科学 | 1474篇 |
矿业工程 | 473篇 |
能源动力 | 448篇 |
轻工业 | 901篇 |
水利工程 | 248篇 |
石油天然气 | 954篇 |
武器工业 | 76篇 |
无线电 | 1820篇 |
一般工业技术 | 1925篇 |
冶金工业 | 717篇 |
原子能技术 | 170篇 |
自动化技术 | 1889篇 |
出版年
2024年 | 63篇 |
2023年 | 246篇 |
2022年 | 426篇 |
2021年 | 657篇 |
2020年 | 471篇 |
2019年 | 375篇 |
2018年 | 419篇 |
2017年 | 494篇 |
2016年 | 415篇 |
2015年 | 580篇 |
2014年 | 703篇 |
2013年 | 946篇 |
2012年 | 910篇 |
2011年 | 964篇 |
2010年 | 898篇 |
2009年 | 819篇 |
2008年 | 853篇 |
2007年 | 758篇 |
2006年 | 810篇 |
2005年 | 736篇 |
2004年 | 473篇 |
2003年 | 435篇 |
2002年 | 469篇 |
2001年 | 386篇 |
2000年 | 414篇 |
1999年 | 430篇 |
1998年 | 356篇 |
1997年 | 284篇 |
1996年 | 273篇 |
1995年 | 234篇 |
1994年 | 188篇 |
1993年 | 119篇 |
1992年 | 101篇 |
1991年 | 104篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction(XRD),BET areas,H2 temperature-programmed reduction(H2-TPR),and X-ray photoelectron spectroscopy(XPS).Through the test of catalytic partial oxidation of methane(CPOM),Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts. 相似文献
993.
Wang Jianli Cao Hongyan Zhong Junbo Gong Maochu Yan Shenghui Liu Zhimin Shen Mei Chen Yaoqiang 《中国稀土学报(英文版)》2007,25(1)
This article showed that the catalytic activity of MnOx/γ-Al2O3/Ce0.5Zr0.5O2 monolithic catalyst toward the catalytic combustion of ethanol in a fixed bed reactor could be greatly improved by doping three metal oxides into Ce0.5Zr0.5O2. The catalytic activity of MnOx/γ-Al2O3/Ce0.45Zr0.45M0.1Ox (M=Y, La, Mn) is better than that of MnOx/γ-Al2O3/Ce0.5Zr0.5O2. The order of activity of the catalysts is as follows: MnOx/γ-Al2O3/Ce0.45Zr0.45Y0.1Ox>MnOx/γ-Al2O3/Ce0.45Zr0.45La0.1Ox>MnOx/γ-Al2O3/Ce0.45Zr0.45Mn0.1Ox>MnOx/γ-Al2O3/Ce0.5Zr0.5O2. The influence of the loading amount of manganese oxide in enhancing the catalytic activity of MnOx/γ-Al2O3/Ce0.45Zr0.45Y0.1Ox was investigated. The results showed that when MnO2 loading amount was 10%(mass fraction), the MnOx/Al2O3/Ce0.45Zr0.45Y0.1Ox catalyst recorded the highest activity. 相似文献
994.
The response of a beam-column frame to impulsive ground shock, such as those induced by an underground explosion, has characteristics of both impact and natural earthquake responses. The critical effects may be governed by the dynamic response of individual elements as continuous mass systems, while to a certain extent the global vibration (as of lumped-mass systems) may also be involved. To incorporate both dynamic features, the present study proposes a combined continua and lumped parameter (CCLP) model, which consists of the basic beam-column element with distributed stiffness and mass, along with concentrated mass-springs at element ends to form the reduced dynamic system. To take into account of the shear deformation and rotary inertia which become important in the impulsive response, the governing equations are formulated based on the Timoshenko beam theory. The nonlinearities are described through three mechanisms, namely the distributed nonlinear flexural and diagonal shear behavior, and the direct sliding shear at the member ends. A generic restoring force model is adopted to describe the hysteretic behavior. Comparison with a scaled model test demonstrates that the CCLP model is capable of representing the primary dynamic features in a frame structure under impulsive ground shock. Extended parametric studies indicate that, with increase of the ground shock frequency, the failure tends to become shear dominant. For ground shocks of frequency at 20–30?Hz and above, the failure in a reinforced concrete column will require a peak ground velocity (PGV) on the order of 3?m/s, whereas failure in a beam would occur at PGV of about 1.5?m/s. 相似文献
995.
996.
以六甲基亚胺为模板剂,静态水热晶化法合成了MCM-56分子筛,通过X-射线衍射、N2等温吸附等方法对样品进行表征.当硅铝比低于20时易生成MCM-49和丝光沸石,加入少量碱能提高分子筛的相对结晶度,最佳合成温度为135~150 ℃,时间分别为3天.考察了MCM-56对苯和长链烯烃烷基化反应的催化活性,并与MCM-22进行了对比.实验表明,在最佳反应温度120 ℃时,烯烃的转化率为29.35%,烷基苯(LAB)的选择性为98.22%,MCM-56的催化活性明显低于MCM-22. 相似文献
997.
Orthogonal analysis of water model study on the optimization of flow control devices in a six-strand tundish 总被引:1,自引:0,他引:1
Zhengyan Wei Yanping Bao Jianhua Liu Wenxu Gong Baoming Wang 《北京科技大学学报(英文版)》2007,14(2):118-124
Improper flow control devices in a multi-strand tundish can cause some problems, for example, liquid steel cannot reach every nozzle at the same time and the liquid steel in nozzles far away from the entry zone has a lower temperature. The water model experiment of a six-strand tundish of Tianjin Iron & Steel Co. Ltd. was performed, a new "U" type baffle was obtained, and its parameters were defined by perpendicular analysis. The "U" baffle can not only improve those imperfections, but also prolong the residence time of nonmetallic inclusions, which is good for their flotation and separation. 相似文献
998.
A high optical quality Er3+-doped NaGd(WO4)2 single crystal with dimensions of ∅18 × 50 mm3 has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er3+ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm. 相似文献
999.
品质是一个产品乃至一个企业的生命,变频器是一种科技含量较高的产品,对质量的要求也就较高。评价试验是保证变频器质量的必要手段,贯穿于整个研发过程。三垦变频器作为进入中国最早的变频器品牌,已经建立了一套完整的试验评价体系。本文旨在介绍研发过程中的特性检测与试验方法,以供参考。 相似文献
1000.