全文获取类型
收费全文 | 35934篇 |
免费 | 4747篇 |
国内免费 | 2819篇 |
专业分类
电工技术 | 9568篇 |
技术理论 | 1篇 |
综合类 | 2884篇 |
化学工业 | 2186篇 |
金属工艺 | 899篇 |
机械仪表 | 3500篇 |
建筑科学 | 1249篇 |
矿业工程 | 823篇 |
能源动力 | 880篇 |
轻工业 | 1755篇 |
水利工程 | 473篇 |
石油天然气 | 909篇 |
武器工业 | 614篇 |
无线电 | 9813篇 |
一般工业技术 | 2711篇 |
冶金工业 | 641篇 |
原子能技术 | 238篇 |
自动化技术 | 4356篇 |
出版年
2024年 | 85篇 |
2023年 | 468篇 |
2022年 | 828篇 |
2021年 | 1139篇 |
2020年 | 1282篇 |
2019年 | 999篇 |
2018年 | 1039篇 |
2017年 | 1310篇 |
2016年 | 1430篇 |
2015年 | 1744篇 |
2014年 | 2659篇 |
2013年 | 2356篇 |
2012年 | 3297篇 |
2011年 | 3306篇 |
2010年 | 2298篇 |
2009年 | 2291篇 |
2008年 | 2201篇 |
2007年 | 2548篇 |
2006年 | 2245篇 |
2005年 | 1768篇 |
2004年 | 1469篇 |
2003年 | 1216篇 |
2002年 | 907篇 |
2001年 | 869篇 |
2000年 | 677篇 |
1999年 | 557篇 |
1998年 | 432篇 |
1997年 | 360篇 |
1996年 | 327篇 |
1995年 | 259篇 |
1994年 | 252篇 |
1993年 | 189篇 |
1992年 | 149篇 |
1991年 | 124篇 |
1990年 | 105篇 |
1989年 | 82篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 18篇 |
1984年 | 32篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
采用中红外光谱结合化学计量学的方法对车用保险杠碎片进行鉴别,分别对52个车用保险杠碎片样本的全波段光谱数据、指纹区光谱数据和主成分分析降维后的光谱数据建立Fisher判别分析和K近邻算法2种分类模型,并对分类结果进行比较。结果表明,主成分分析提取特征变量后构建的分类模型,分类的准确率更高,对聚丙烯(PP)、PP/滑石粉、PP/滑石粉/碳酸钙(CaCO3)3种类型的样本分类准确率达到92.3 %,对PP/滑石粉类型中的10种品牌样本分类准确率达到88.9 %,分类结果理想;在构建的2种分类模型中,Fisher判别分析模型的分类率远高于K近邻算法模型,分析认为K近邻算法模型受到样本不均衡的影响;中红外光谱结合化学计量学可以实现对车用保险杠碎片的准确区分,且满足快速、无损的检验要求。 相似文献
62.
针对煤快速热解研究中样品添加量少(mg级)、焦油收集难等问题,本研究利用压片法制备微薄厚度(mm级)的煤层,并采用红外加热装置考察大添加量(g级)、微薄煤层的快速热解特性。对比堆积煤样和不同煤压片厚度(1.5~3 mm)与个数(1~2)的压片煤样热解特性发现,压片煤层热解过程的二次反应受到明显抑制,焦油产率急剧增加,在1000℃时达9.96%,为格金分析的1.5倍,实现油气产量的同步增长。模拟蒸馏分析发现,堆积状态下焦油以沥青质为主,而微薄煤层制焦油含大量轻油、酚油、萘油、洗油和蒽油。GC-MS和FTIR分析表明,随煤层厚度和个数的减少,焦油组分和含量提高,芳香烃类和含氧官能团吸收增加,进一步验证煤快速热解过程中煤层厚度对焦油产率和品质的影响,揭示在二次反应充分抑制下煤高温热解的初级反应特性。 相似文献
63.
Raja Jelassi Hajer Khemaissia Chedliya Ghemari Maryline Raimond Catherine Souty‐Grosset Karima Nasri‐Ammar 《Microscopy research and technique》2020,83(2):148-155
The hepatopancreas of crustaceans species has been recognized as an essential target organ to assess trace elements' effects. Due to its dynamic and capability of detoxifying trace metal, this organ often indicates distinct pathological disturbances. In the present work, we intend to evaluate the bioaccumulation of trace metal in three Orchestia species (Orchestia montagui, Orchestia gammarellus, and Orchestia mediterranea) living in symmetry in the banks of Bizerte lagoon (37°13′8″N 09°55′1″E) after their exposure during 14 days to a mixture of copper and zinc, and to highlight the effect of these metals on their hepatopancreas ultrastructure using transmission electron microscopy. At the end of the experiment, results showed that the mortality and the body mass varied according to the used nominal concentrations. Significant alterations were noted in all the treatment groups. The degree of these alterations depends on the used concentration, and they are represented especially by the cells remoteness and the border lyses, the reduction of the nuclear volume, the increase in the cytoplasm density with the presence of trace metal in the nucleus as well as in the vacuole, the disorganization and the destruction of microvilli, the condensation of the majority of cellular organelles and mitochondria swelling. Through this study, Orchestia genus could be an attractive candidate for the biochemical study of trace metal toxicity in Tunisian wetlands. 相似文献
64.
65.
《Intermetallics》2015
The stability of a Co-based alloy designed to possess a microstructure comprising of L12, γ′ Co3Ti-type precipitates embedded in an A1, γ Co solid solution matrix has been investigated. The alloy showed acute microstructural instabilities upon ageing at 700 °C, resulting in the degeneration of the γ-γ′ aggregate into i) a faulted Co-based martensite and Co3Ti and ii) a lamellar aggregate of A3-Co and Co3Ti. The faulted Co-based phase was formed by isothermal diffusionless transformation of the metastable A1-phase, whilst the lamellar aggregate was a discontinuous reaction product. 相似文献
66.
During the last few decades, photothermal radiometry (PTR) has been greatly developed and widely applied in the field of nondestructive testing. However, the traditional PTR system employs an expensive lock-in amplifier to detect the weak photothermal signal, which leads to high cost and long test time. In this paper, a fast transmission PTR system based on sampling by using an internal computer sound card was developed to lower the system cost and shorter the test time. A piece of amorphous silicon (a:Si) thin film solar cells with artificial defects was prepared and tested by the system. The results show that the sharpened defects can be identified easily and quickly according to the significant peaks of the original infrared signal sampled by the internal computer sound card. Furthermore, more detailed defects can be investigated by processing the infrared signal. These validate the effectiveness of the proposed transmission PTR system as a low cost and efficient non-destructive test technique. 相似文献
67.
基于全景温度场的电力设备在线自动识别与诊断 总被引:1,自引:0,他引:1
68.
本文采用傅立叶变换光谱法对13种不同品牌的白色牙刷柄塑料进行了红外光谱分析,实验结果表明,依据红外光谱数据的异同,能够对不同品牌的牙刷柄样品进行鉴别。 相似文献
69.
《Intermetallics》2015
An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process. 相似文献
70.