全文获取类型
收费全文 | 89321篇 |
免费 | 6840篇 |
国内免费 | 3473篇 |
专业分类
电工技术 | 4932篇 |
技术理论 | 5篇 |
综合类 | 5697篇 |
化学工业 | 15705篇 |
金属工艺 | 5404篇 |
机械仪表 | 5482篇 |
建筑科学 | 7858篇 |
矿业工程 | 2580篇 |
能源动力 | 2375篇 |
轻工业 | 5363篇 |
水利工程 | 1564篇 |
石油天然气 | 5254篇 |
武器工业 | 683篇 |
无线电 | 9337篇 |
一般工业技术 | 10637篇 |
冶金工业 | 4503篇 |
原子能技术 | 1066篇 |
自动化技术 | 11189篇 |
出版年
2024年 | 359篇 |
2023年 | 1492篇 |
2022年 | 2419篇 |
2021年 | 3362篇 |
2020年 | 2620篇 |
2019年 | 2182篇 |
2018年 | 2536篇 |
2017年 | 2872篇 |
2016年 | 2454篇 |
2015年 | 3262篇 |
2014年 | 4124篇 |
2013年 | 5060篇 |
2012年 | 5544篇 |
2011年 | 5926篇 |
2010年 | 5032篇 |
2009年 | 4963篇 |
2008年 | 4760篇 |
2007年 | 4578篇 |
2006年 | 4880篇 |
2005年 | 4336篇 |
2004年 | 2894篇 |
2003年 | 2497篇 |
2002年 | 2294篇 |
2001年 | 2023篇 |
2000年 | 2300篇 |
1999年 | 2679篇 |
1998年 | 2183篇 |
1997年 | 1775篇 |
1996年 | 1824篇 |
1995年 | 1483篇 |
1994年 | 1210篇 |
1993年 | 858篇 |
1992年 | 700篇 |
1991年 | 554篇 |
1990年 | 402篇 |
1989年 | 332篇 |
1988年 | 270篇 |
1987年 | 184篇 |
1986年 | 123篇 |
1985年 | 88篇 |
1984年 | 57篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1981年 | 34篇 |
1980年 | 23篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry 相似文献
82.
Fabrizo Granelli Honggang Zhang Xiaofei Zhou Stefano Maranò 《Mobile Networks and Applications》2006,11(4):487-499
The paper illustrates the novel concept of Cognitive UWB Radio, a wireless system based on UWB transmission able to self-adapt to the characteristics of the surrounding environment. First, salient features of UWB transmission are reviewed, and then, application of UWB characteristics to the problem of cognitive radio systems is discussed. Current ongoing studies and achieved results on a possible physical layer based on Prolate Spheroidal Wave Functions and consistent with the Cognitive UWB Radio paradigm are presented and analyzed, and their application to the sensor network scenario is discussed. 相似文献
83.
Parity space approach and H2 approach are two important fault detection approaches. This paper studies the relationship between these two approaches, which reveals frequency domain characteristics of the optimal solution of the parity space approach on the one side and provides a numerical solution of the H2-optimal design of residual generators on the other side. 相似文献
84.
Alleviation Effect of Lanthanum on Cadmium Stress in Seedling Hydroponic Culture of Kidney Bean and Corn 总被引:4,自引:0,他引:4
Since1970s,rare earths(RE)have been exten-sively used as micro-fertilizers for crops in China.Ithas already been proved that REcani mprove the pro-duction and quality of crops.However,there havebeen a fewinvestigations about using RE as regulatorin pollution ecology.For example,An et al[1]studiedthe effects of O3on wheat growth and the protectiveeffect of RE.Yan and Zhou et al[2,3]discussed theprotective effect of RE on plants under acid rainstress.Jia et al[4]and Hu et al[5]reported th… 相似文献
85.
本文研究了梯恩梯-吉纳(TNT-DINA)和地恩梯-太安(DNT-PETN)体系的自旋爆轰现象,爆轰波是以低频脉冲方式传播.这些体系具有的爆速、爆热分别为DJ=7.3~7.4km/s和Qv=(5.40±0.01)MJ/kg.不同组成的爆速和爆压PJ通过SW程序计算.用扩散区的爆压P3和爆温T3来评估爆轰波的衰减和重新点火.敏化剂含量相同,梯恩梯-黑索金(TNT-RDX)体系的爆压PJ大于TNT-DINA的爆压,TNT-RDX体系的温度T3比TNT-DINA高60~100K.计算值与实验结果吻合较好. 相似文献
86.
Z Chen A Spies R Hein X Zhou BC Thomas ML Richter P Gegenheimer 《Canadian Metallurgical Quarterly》1995,270(29):17124-17132
F1F0-ATP synthases utilize protein conformational changes induced by a transmembrane proton gradient to synthesize ATP. The allosteric cooperativity of these multisubunit enzymes presumably requires numerous protein-protein interactions within the enzyme complex. To correlate known in vitro changes in subunit structure with in vivo allosteric interactions, we introduced the beta subunit of spinach chloroplast coupling factor 1 ATP into a bacterial F1 ATP synthase. A cloned atpB gene, encoding the complete chloroplast beta subunit, complemented a chromosomal deletion of the cognate uncD gene in Escherichia coli and was incorporated into a functional hybrid F1 ATP synthase. The cysteine residue at position 63 in chloroplast beta is known to be located at the interface between alpha and beta subunits and to be conformationally coupled, in vitro, to the nucleotide binding site > 40 A away. Enlarging the side chain of chloroplast coupling factor 1 beta residue 63 from Cys to Trp blocked ATP synthesis in vivo without significantly impairing ATPase activity or ADP binding in vitro. The in vivo coupling of nucleotide binding at catalytic sites to transmembrane proton movement may thus involve an interaction, via conformational changes, between the amino-terminal domains of the alpha and beta subunits. 相似文献
87.
研究了杂多酸催化无水乙醇和环氧乙烷(EO)制备乙醇乙醚的醚化反应,考察了不同种类的杂多酸以及醚化反应工艺条件对反应活性和选择性的影响.结果表明,PW_(12)催化剂的反应活性高、反应温度低、选择性好,当用PW_(12)作催化剂,乙醇与环氧化乙烷之比为3.0(mol),反应温度45℃,反应时间1h时,转化率和选择性均超过97%. 相似文献
88.
89.
一种可切削玻璃陶瓷的压痕断裂特性 总被引:4,自引:2,他引:2
将断裂韧性测试的压痕方法与压痕弯曲方法相结合,独立地分离出了压痕残余应力因子x,使其成为可测参量,并建立了压痕一压痕弯曲的断裂韧性测试方法.将这种方法应用于一种可切削玻璃陶瓷的测试,获得的K1c值为K1c=2.03MPa·m1/2,与单边切口法(SENB)获得的K1c值有较好的一致性.测得的残余应力因子X=0.093,符合Anstis经验公式的预测. 相似文献
90.
宽波段高灵敏快响应热释电型光卡计的研究 总被引:1,自引:1,他引:0
采用热释电材料,设计并研制了适用于红外-可见-X光波段的高灵敏、快响应光能量计。针算了卡计的参数,对1.06μm、0.53/μm激光和0.1~10keV的软X射线进行了能量测量,灵敏度达300mV/μJ,时间响应小于2ns。 相似文献