全文获取类型
收费全文 | 470543篇 |
免费 | 37170篇 |
国内免费 | 19104篇 |
专业分类
电工技术 | 27394篇 |
技术理论 | 43篇 |
综合类 | 30062篇 |
化学工业 | 77944篇 |
金属工艺 | 25803篇 |
机械仪表 | 29857篇 |
建筑科学 | 37038篇 |
矿业工程 | 14653篇 |
能源动力 | 13474篇 |
轻工业 | 29391篇 |
水利工程 | 8064篇 |
石油天然气 | 29908篇 |
武器工业 | 3507篇 |
无线电 | 54090篇 |
一般工业技术 | 54927篇 |
冶金工业 | 24804篇 |
原子能技术 | 4869篇 |
自动化技术 | 60989篇 |
出版年
2024年 | 1609篇 |
2023年 | 7016篇 |
2022年 | 13240篇 |
2021年 | 18456篇 |
2020年 | 13921篇 |
2019年 | 11395篇 |
2018年 | 13112篇 |
2017年 | 14836篇 |
2016年 | 13294篇 |
2015年 | 17936篇 |
2014年 | 22924篇 |
2013年 | 27738篇 |
2012年 | 29880篇 |
2011年 | 32371篇 |
2010年 | 28182篇 |
2009年 | 26926篇 |
2008年 | 26212篇 |
2007年 | 24850篇 |
2006年 | 25739篇 |
2005年 | 22552篇 |
2004年 | 15175篇 |
2003年 | 12933篇 |
2002年 | 11562篇 |
2001年 | 10580篇 |
2000年 | 11108篇 |
1999年 | 12992篇 |
1998年 | 11067篇 |
1997年 | 9268篇 |
1996年 | 8594篇 |
1995年 | 7150篇 |
1994年 | 5749篇 |
1993年 | 4178篇 |
1992年 | 3324篇 |
1991年 | 2555篇 |
1990年 | 1948篇 |
1989年 | 1590篇 |
1988年 | 1224篇 |
1987年 | 808篇 |
1986年 | 620篇 |
1985年 | 462篇 |
1984年 | 317篇 |
1983年 | 241篇 |
1982年 | 269篇 |
1981年 | 207篇 |
1980年 | 166篇 |
1979年 | 93篇 |
1978年 | 72篇 |
1977年 | 68篇 |
1976年 | 101篇 |
1975年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Vibration cavitation erosion tests were carried out on Ni-Mn-Ga alloys of three different crystal structures: (1) the cubic austenite, (2) the non-modulated tetragonal martensite (T) and (3) the five-layered martensite (5M). All Ni-Mn-Ga alloys exhibited cavitation behaviour characterized by a step-wise curve of mass loss versus test time. This behaviour is correlated to the microstructural nature of the alloys as well as the surface conditions of the pre-test samples. The type and concentration of the defects at the surfaces were critical to the cavitation resistance of the alloys. The best cavitation resistant alloy was of a cubic austenitic structure, followed with the alloy of a tetragonal T-martensite. The largest material loss was found in the alloy with a 5M martensite. All the studied Ni-Mn-Ga alloys had an excellent cavitation resistance compared to that of the reference stainless steel, and they even excelled some NiTi alloys found in literature. This may be due to the superelasticity of the cubic austenite and the twinning of the martensitic phases. 相似文献
993.
对在五坐标数控加工中心上铣制三元流叶轮时出现的叶轮附面尺寸误差问题,进行了详细分析,并提出了问题的解决方法,有效地避免了加工中产生的超差。 相似文献
994.
充分关注水质科学保障饮水安全 总被引:12,自引:6,他引:6
从我国饮水安全的现状入手,分析城乡饮水安全存在的问题,强调保障饮水安全是构建和谐社会的必然要求和水利工作的切实要务。从加强监测、科学规划,加强关键技术研究及推广应用,保护水源地、修复水环境,建立合理的体制与机制四个方面提出了做好保障饮水安全工作的建议。 相似文献
995.
The effects of NOx on the performance of proton exchange membrane (PEM) fuel cell were investigated through the introduction of a mixture containing NO and NO2, in a ratio of 9:1, into the cathode stream of a single PEM fuel cell. The NOx concentrations used in the experiments were 1480 ppm, 140 ppm and 10 ppm, which cover a range of three orders. The experimental results obtained from the tests of durability, polarization, reversibility and electrochemical impedance spectroscopy (EIS) showed a detrimental effect of NOx on the cell performance. The electrochemical measurements results suggested that the impacts of NOx are mainly resulted from the superposition of the oxygen reduction reaction (ORR), NO and HNO2 oxidation reactions, and the increased cathodic impedance. Complete recovery of the cell performance was reached after operating the cell with clean air and then purging with N2 for hours. 相似文献
996.
Yawei Li Shaobai Sang Shengli Jin Chunyan Yang Nan Li 《Journal of Materials Science》2006,41(18):5815-5819
Synthesis of Mg-α-Sialon has been investigated by the mixture of silicon, aluminum and magnesia powders in a flowing nitrogen atmosphere in the range of 1300–1600 °C, when Mg-α-Sialon is designed with a chemical formulation of Mg
x
Si12−3x
Al3x
O
x
N16−x
in present work. The results showed that Mg-α-sialon initially occurred at 1400 °C and basically increased with elevated temperatures. For the samples of x = 0.6, 0.8 and 1.0 the products mainly consisted of Mg-α-Sialon with small amounts of Si, AlN and 21R AlN-polytypoid phases at 1600° C. However, in final products of x = 1.2, 1.4 and 1.6 only a little of Mg-α-Sialon formed and a great amount of Si remained in these samples at all the fired temperatures. Fortunately, the content of Mg-α-Sialon in these samples were obviously increased by adding a small amount of α-Si3N4 as seeds before nitridation. 相似文献
997.
998.
999.
1000.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection. 相似文献