全文获取类型
收费全文 | 20762篇 |
免费 | 1879篇 |
国内免费 | 1394篇 |
学科分类
工业技术 | 24035篇 |
出版年
2024年 | 54篇 |
2023年 | 327篇 |
2022年 | 550篇 |
2021年 | 760篇 |
2020年 | 604篇 |
2019年 | 492篇 |
2018年 | 505篇 |
2017年 | 649篇 |
2016年 | 529篇 |
2015年 | 836篇 |
2014年 | 1157篇 |
2013年 | 1294篇 |
2012年 | 1501篇 |
2011年 | 1554篇 |
2010年 | 1529篇 |
2009年 | 1442篇 |
2008年 | 1468篇 |
2007年 | 1408篇 |
2006年 | 1260篇 |
2005年 | 1055篇 |
2004年 | 826篇 |
2003年 | 746篇 |
2002年 | 796篇 |
2001年 | 697篇 |
2000年 | 497篇 |
1999年 | 353篇 |
1998年 | 249篇 |
1997年 | 181篇 |
1996年 | 160篇 |
1995年 | 134篇 |
1994年 | 118篇 |
1993年 | 65篇 |
1992年 | 70篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 33篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
换流阀是实现高压直流输电的核心设备,在闭锁检修过程中换流阀残留能量泄放时间直接影响着故障后恢复供电时间长短,对电网运行可靠性具有重要意义。根据换流站的实际结构,搭建单极直流输电系统EMTDC/PSCAD仿真模型,对换流阀中各关键元件的电场和磁场能量泄放过程进行了研究,并对换流站残余能量主要的影响因素进行分析。研究结果表明:晶闸管吸收电容储存的电场能是换流阀闭锁后阀厅残余能量主要来源,该部分能量衰减时间大于7 s,主要泄放通道为直流出线接地开关和换流变阀侧接地开关;仅采用4把接地开关同样能够在3 s内将换流阀电压降低至36 V以下,这为下一步换流站接地开关配置方式的研究提供了技术支撑。 相似文献
992.
极间短路条件下柔性直流输电系统电磁暂态特性分析 总被引:1,自引:0,他引:1
以南澳±160kV中压柔性直流系统为例,配合直流断路器的应用,利用PSCAD/EMTDC仿真软件分析了极间短路故障时系统的暂态特性。首先介绍了南澳直流工程的系统拓扑和主回路参数,然后结合不同保护策略分析了系统对直流断路器的参数要求,提出了系统与断路器配合时直流限流电抗的调整思路。最后研究了线路长度、故障位置和断路器动作对暂态特性的影响。仿真结果表明,直流断路器可以快速开断故障电流,限制电流峰值,通过调整直流限流电抗可以实现系统与断路器的配合。研究结果对柔性直流输电系统参数设置和器件及设备选型有一定参考价值。 相似文献
993.
采用原位生成的纳米SiO2/环氧聚酯改性有机硅树脂制备了TH1178-2耐电晕无溶剂绝缘漆,并与采用直接掺杂法制备的纳米SiO2改性有机硅耐电晕漆TH1178-1的耐电晕性能进行了比较分析。结果表明:原位生成纳米SiO2改性比纳米SiO2直接掺杂改性的粒子分散更加均匀,无明显颗粒团聚现象;TH1178-2耐电晕漆比TH1178-1的耐电晕时间增长幅度更明显,耐电晕性能更好,同时具有优良的电气性能和力学性能,适用于H级以上电机或电器的耐电晕绝缘结构浸渍处理。 相似文献
994.
995.
为获得雷电流冲击下110 k V变压器不接地中性点上的过电压,采用线饼模型对110 k V变压器绕组进行建模,并用PSCAD仿真软件对该模型进行仿真计算。利用该模型对广州地区110 k V变压器中性点击穿事故进行仿真分析,结果表明对变压器中性点仅加装放电间隙不足以防止雷电侵害,并且雷电波入侵变压器时中性点故障率高达到0.686次/年,说明需要结合其他防护措施对这一地区变压器中性点进行保护。根据仿真结果提出采用130 mm的间隙并联Y1.5W-72/186避雷器实施改造措施。 相似文献
996.
997.
998.
Matthew L. Breeze Elisa Leyva‐Guerrero Grant R. Yeaman Yelena Dudin Ryan Akel Phil Brune Fred Claussen Cecil Dharmasri Jenny Golbach Rong Guo Carl Maxwell Laura Privalle Hilary Rogers Kai Liu Guomin Shan Michele Yarnall Denise Thiede Nancy Gillikin 《Journal of the American Oil Chemists' Society》2015,92(8):1085-1092
Soybean agglutinin (SBA) protein, also known as soybean lectin, is regarded as an anti‐nutrient due to its negative effect on the ability of monogastric animals to gain weight following consumption of raw soybean seed. Historically, SBA has been measured using a time‐consuming and cumbersome hemagglutination procedure. The objective of our research was to obtain a validated methodology that is precise and accurate in the measurement of SBA while allowing minimally equipped laboratories to effectively conduct the analysis, thus our focus was on evaluating an existing commercially available ELISA, an enzyme‐linked‐lectin‐assay (ELLA), and a hybrid ELISA/ELLA. A new ELLA technique that can detect and quantify lectins was chosen and modified specifically for the quantitation of SBA in soybean seed. The proposed ELLA methodology is similar to a standard sandwich ELISA, and uses polyacrylamide‐linked N‐acetylgalactosamine (Gal–NAc–PAA) for a capture phase and the biotinylated version (Gal–NAc–PAA–Biotin) for detection. Based upon the validation data, the ELLA method can precisely and accurately determine soybean lectin levels in soybean seed. The validated ELLA method was used to quantify SBA in nine commercial soybean varieties introduced between 1972 and 2008 and demonstrated that the natural variability of SBA is subject to the effects of genotype and environment. 相似文献
999.
The Effects of Annealing Atmosphere on the Electrical Properties of MgNb2O6/ITO Heterostructures 下载免费PDF全文
Yi‐Da Ho Kung‐Rong Chen Pei‐Ching Yu Cheng‐Liang Huang 《Journal of the American Ceramic Society》2015,98(2):580-586
The effects of annealing atmosphere (N2, air and O2) on the electrical properties of sol–gel‐derived MgNb2O6/ITO heterostructures are discussed in this work. All samples exhibited the amorphous phase and were highly transparent. The percentage of Nb4+ content increased when the films were annealed in the oxygen‐deficient conditions, which could lead to semiconducting films. In addition, the results show that the electrical properties of sol–gel‐derived MgNb2O6 thin films could be tuned based on the annealing atmosphere. Moreover, the conduction mechanisms of MgNb2O6/ITO heterostructures are also discussed in this study. The results show that MgNb2O6 thin films have potential for use in multifunctional optoelectronic applications, due to their flexible electrical properties and good transparency. 相似文献
1000.
Guo‐Zhong Zang Huan‐Huan Liu Jian‐Fei Lei Xiao‐Fei Wang Li‐Ben Li Jing‐Xiao Cao Guo‐Rong Li 《Journal of the American Ceramic Society》2015,98(7):2112-2116
SnO2–Zn2SnO4 composite ceramics with a colossal dielectric permittivity and varistor behavior are prepared by traditional ceramic processing. By increasing bias voltage from 0 to 10 V at a low frequency (~103 Hz) and at room temperature, the relative permittivity decreased rapidly from about 20 000 to several thousand, whereas the radius of the semicircle in the complex impedance decreased and the tail gradually disappeared. However, the peak height and the position of the imaginary part of the complex modulus in the spectra were independent of the applied DC voltage. The slope deduced from the bias voltage‐dependent straight lines of the double‐logarithmic imaginary permittivity spectra were constant with a value of ?0.63 at high frequencies and they decreased to ?1 at low frequencies. The results strongly indicate that a number of weekly trapped charges existed in the ceramic bulk. From the temperature‐dependent dielectric and electric modulus spectra, the trapped charge activation energy was about 0.32 eV, which may be associated with the oxygen vacancies. Based on the results, a modified equivalent circuit related to the colossal dielectric permittivity and varistor properties was proposed, in which a Warburg impedance was added in parallel with the resistance and capacitance. 相似文献