全文获取类型
收费全文 | 73568篇 |
免费 | 5409篇 |
国内免费 | 2787篇 |
专业分类
电工技术 | 3893篇 |
技术理论 | 6篇 |
综合类 | 4441篇 |
化学工业 | 12696篇 |
金属工艺 | 3969篇 |
机械仪表 | 4811篇 |
建筑科学 | 5204篇 |
矿业工程 | 2405篇 |
能源动力 | 2232篇 |
轻工业 | 4769篇 |
水利工程 | 1002篇 |
石油天然气 | 5284篇 |
武器工业 | 461篇 |
无线电 | 7658篇 |
一般工业技术 | 9440篇 |
冶金工业 | 3951篇 |
原子能技术 | 750篇 |
自动化技术 | 8792篇 |
出版年
2024年 | 302篇 |
2023年 | 1263篇 |
2022年 | 2107篇 |
2021年 | 2916篇 |
2020年 | 2204篇 |
2019年 | 1963篇 |
2018年 | 2301篇 |
2017年 | 2507篇 |
2016年 | 2076篇 |
2015年 | 2698篇 |
2014年 | 3441篇 |
2013年 | 4220篇 |
2012年 | 4354篇 |
2011年 | 4859篇 |
2010年 | 4175篇 |
2009年 | 3954篇 |
2008年 | 3854篇 |
2007年 | 3716篇 |
2006年 | 3797篇 |
2005年 | 3435篇 |
2004年 | 2287篇 |
2003年 | 2087篇 |
2002年 | 1878篇 |
2001年 | 1640篇 |
2000年 | 1801篇 |
1999年 | 2051篇 |
1998年 | 1768篇 |
1997年 | 1427篇 |
1996年 | 1410篇 |
1995年 | 1186篇 |
1994年 | 957篇 |
1993年 | 718篇 |
1992年 | 546篇 |
1991年 | 429篇 |
1990年 | 327篇 |
1989年 | 254篇 |
1988年 | 226篇 |
1987年 | 142篇 |
1986年 | 120篇 |
1985年 | 96篇 |
1984年 | 66篇 |
1983年 | 41篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1945年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
972.
Ni Zhong Xian-Lin Dong Da-zhi Sun Ping-hua Xiang Hui Du 《Materials Research Bulletin》2004,39(2):175-184
Ferroelectrics 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) + x mol% WO3 (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO3-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3+2 mol% WO3. Dielectric peak temperature decreased with WO3 doping, indicating that W6+ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of Kmax. Both piezoelectric constant (d33) and electromechanical coupling factors (kp) were enhanced by doping 0.1 mol% WO3, which results from the introduction of “soft” characteristics into PMN-PT, while further WO3 addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO3. 相似文献
973.
高速连铸结晶器保护渣流变特性的研究 总被引:2,自引:0,他引:2
用改进的可变转速粘度仪测定了连铸保护渣(%:1.47MgO,12.98Al2O3,47.57SiO2,7.71Na2O,28.52CaO,1.75TiO2)的流变特性,以试验总误差为测量牛顿流体时所容许的最大偏差,由试验得到不同转速下剪切速率D和剪切应力τ,作出τ~D对数曲线,经回归得出熔渣本构方程,以判别熔体是否为非牛顿流体。结果表明,在1200℃较低温度下,该保护渣仍为牛顿流体,如再加入较多的CaO,则保护渣变为非牛顿流体。 相似文献
974.
马钢用60 t顶底复吹转炉冶炼,钢包炉吹氩、喂线和成分微调,异型坯(mm750×450×120)弧形连铸和H型钢万能轧机轧制工艺研制了碳当量Ceq≤0.42%的V-Nb微合金高强度热轧H型钢(%)0.14~0.17C,0.43~0.55Si,1.28~1.45Mn,0.010~0.028S,0.010~0.027P,0.03~0.05Nb,0.08~0.12V.检验统计数据表明,BS 55C热轧H型钢组织为铁素体+珠光体,实际晶粒度9级,屈服强度均在420 MPa以上. 相似文献
975.
A method for testing interlaminar dynamic fracture toughness of polymeric composites 总被引:2,自引:0,他引:2
Static and dynamic Mode I delamination fracture in two polymeric fiber composites was studied using a WIF test method. The dynamic test was conducted on a Split Hopkinson Pressure Bar apparatus. Crack speeds up to 1000 m/s were achieved. Dynamic fracture and crack propagation were modeled by the finite element method. Dynamic initiation fracture toughness of S2/8552 and IM7/977-3 composites were obtained. The dynamic fracture toughness of IM7/977-3 associated with the high speed propagating crack was extracted from the finite element simulation based on the measured data. It was found that the dynamic fracture toughness of the delamination crack propagating at a speed up to 1000 m/s approximately equals the static fracture toughness. 相似文献
976.
Zhiping Sun Rulin Zuo Cong Li Baoluo Shen Jing Yan Sijiu Huang 《Materials Characterization》2004,53(5):403-409
High chromium white irons solidify with a substantially austenitic matrix supersaturated with chromium and carbon. The subcritical heat treatment can destabilize the austenite by precipitating chromium-rich secondary carbides and other special carbides. In the as-cast condition the eutectic carbides are (Fe,Cr)7C3 and (Fe4.3Cr2.5Mo0.1)C3. The initial secondary carbide precipitated is (Fe,Cr)23C6 after heat-treating at 853 K for 10 h. There are MoC, Fe2MoC and -carbide precipitating, and (Fe,Cr)23C6 transforms to M3C after 16 h at 853 K. The -carbide and (Fe,Cr)23C6 accomplish transformation to M3C and the matrix changes from martensitic to pearlitic after 22 h at 853 K. Thereby, in the subcritical heat treatment process, the initial secondary carbide precipitated is (Fe,Cr)23C6, followed by -carbide, MoC and Fe2MoC. In addition, there are two in situ transformations from (Fe,Cr)23C6 and -carbide to M3C carbides. 相似文献
977.
This paper presents a unified global and local interconnect testing scheme for field programmable gate arrays. Adjacency graphs are used to model interconnect resources and their test requirements, and an efficient computer algorithm for automatic derivation of test configurations is given. A device configuration generation tool was developed to reduce the test development cost. 相似文献
978.
RS-485接口具有良好的抗噪声干扰性,长的传输距离和多站能力等优点使其成为分布式测量控制系统首选的串行接口.本文介绍了一种基于RS-485总线的多路温度测试系统,应用于装甲车辆实车测试中.数据采集模块挂接在RS-485总线上构成RS-485总线网络,PC机与其进行数据通信.利用工业组态软件、VISUAL BASIC 与数据库合作快速处理各类数据,来保证测试精度和速度,实现了对装甲车辆实车多路温度信号的实时采集、管理、显示、打印与分析等功能.同时本系统可以扩展为其它类型参数或混合类型参数的测量控制系统. 相似文献
979.