全文获取类型
收费全文 | 31319篇 |
免费 | 3719篇 |
国内免费 | 2576篇 |
专业分类
电工技术 | 2493篇 |
综合类 | 3806篇 |
化学工业 | 4208篇 |
金属工艺 | 2463篇 |
机械仪表 | 2109篇 |
建筑科学 | 2278篇 |
矿业工程 | 1436篇 |
能源动力 | 832篇 |
轻工业 | 3718篇 |
水利工程 | 1125篇 |
石油天然气 | 978篇 |
武器工业 | 576篇 |
无线电 | 3091篇 |
一般工业技术 | 2737篇 |
冶金工业 | 1286篇 |
原子能技术 | 475篇 |
自动化技术 | 4003篇 |
出版年
2024年 | 223篇 |
2023年 | 607篇 |
2022年 | 1349篇 |
2021年 | 1658篇 |
2020年 | 1232篇 |
2019年 | 841篇 |
2018年 | 948篇 |
2017年 | 994篇 |
2016年 | 952篇 |
2015年 | 1458篇 |
2014年 | 1785篇 |
2013年 | 2186篇 |
2012年 | 2536篇 |
2011年 | 2789篇 |
2010年 | 2575篇 |
2009年 | 2526篇 |
2008年 | 2545篇 |
2007年 | 2399篇 |
2006年 | 2109篇 |
2005年 | 1660篇 |
2004年 | 1200篇 |
2003年 | 717篇 |
2002年 | 696篇 |
2001年 | 668篇 |
2000年 | 486篇 |
1999年 | 177篇 |
1998年 | 42篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1959年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
将A-P值法应用于乡镇工业比较发达的新密市区域内大气中可吸入颗粒PM10和总悬浮颗粒TSP的总量控制研究中.结果表明,该方法对大气中颗粒物总量的模拟计算能得到较好的结果,与城区连续两年的环境监测数据有较好的一致性;城区附近区域的现状排放量已超过总量控制限值,而城区以外的多数区域现状大气中的PM10尚有较大的环境容量. 相似文献
992.
针对自限温伴热带在手工操表测试其性能时存在着效率低,误差较大等问题,利用AD590、功率传感器WBP412和模拟乘法器分别来测试伴热带的温度、功率和电压信号,开发了可实现自动测量的性能测试系统.实验结果表明,本测试系统操作简单,效率高,测试准确,其相对误差均低于2%. 相似文献
993.
994.
采用醇盐的乙醇溶液,制备了纳米锐钛矿相二氧化钛粉体.通过TEM和XRD分析测试手段,对所得粉体进行了表征.TiO2粒子外观呈球形,粒径为5~10nm.用此制备工艺新技术,操作简单,无污染,易于实现工业化. 相似文献
995.
996.
997.
Electropulse modification (EPM) process, a new physical field method for improving the solidification structure of metals was introduced.Different from other research, EPM is only acting pulse current on melt under liquid state.The solidification structure of Al-Si alloys, A1-Cu alloys,cast iron and steel can be modified obviously with this method: the solidification structure of ZL101 alloy presented the Na and Sr modification and the mechanical properties were enhanced; a large number of primary silicon appeared in the microstructure of ZL109 alloy; the equiaxed grain zone was expanded and the grains were fined in Al-5.0wt% Cu alloy; the graphitization took place in solidification process of molten cast iron; the grain sizes of solidification structure of T8 steel were reduced significantly and the shape of steel pearlites also changed; the equiaxed grain zone increased to 88% from original untreated 19%, the equiaxed grains were fined and the intercrystalline crack was avoided in concasting billet by continuously treating liquid electrical sheet steel in tundish.Effects of rare earths on casting Al-Si alloys were also summarized.The method of modifying the solidification structure of rare earth Al-Si alloys with EPM in producing the alloys was proposed. 相似文献
998.
Morphologies and Properties of Micro-Arc Oxidation on Plate and Cylinder 2024 Al Alloy 总被引:1,自引:0,他引:1
Samples with two different shapes of 2024 aluminum alloy were treated with micro-arc oxidation (MAO), and the formation process and mechanism of oxidation film was analyzed. The results show that different geometrical curvature of the material has an influence upon the uniformity of films and the corrosion-resistance. 相似文献
999.
The scanning electron microscopy (SEM) analysis results of Si distribution in the interface between SiC reinforcements and aluminum matrix of a stir casting SiCp/Al-Mg-Si composite were presented. Results show that there is Si precipitation deposit on the interface of the composite and Si connects with SiC reinforcements in one side and connects with aluminum matrix in the other side. Si phase plays as a connecting bridge, which contributes to the interfacial combination of SiCp/Al composite. 相似文献
1000.
GU Yuantao TANG Kun & CUI Huijuan State Key Laboratory on Microwave Digital Communications Department of Electronics Engineering Tsinghua University Beijing China Correspondence should be addressed to Gu Yuantao 《中国科学F辑(英文版)》2004,(2)
In several branches of adaptive filtering algorithms, the least mean square (LMS) algorithm is widely applied in many areas because of its low computational cost, good numerical stability and other features[1]. However, the contradiction between faster convergence and smaller steady-state mean squared error (MSE) affects its performance considerably. Step-size, as the key to the problem, can but offer only one choice of the two demands. Therefore, many variable step-size algorithms were prop… 相似文献