全文获取类型
收费全文 | 104654篇 |
免费 | 8532篇 |
国内免费 | 4322篇 |
专业分类
电工技术 | 5995篇 |
技术理论 | 8篇 |
综合类 | 6947篇 |
化学工业 | 17785篇 |
金属工艺 | 6291篇 |
机械仪表 | 6600篇 |
建筑科学 | 9243篇 |
矿业工程 | 2983篇 |
能源动力 | 2826篇 |
轻工业 | 6452篇 |
水利工程 | 1843篇 |
石油天然气 | 5969篇 |
武器工业 | 849篇 |
无线电 | 11267篇 |
一般工业技术 | 12416篇 |
冶金工业 | 5205篇 |
原子能技术 | 1228篇 |
自动化技术 | 13601篇 |
出版年
2024年 | 306篇 |
2023年 | 1698篇 |
2022年 | 2559篇 |
2021年 | 4026篇 |
2020年 | 3162篇 |
2019年 | 2591篇 |
2018年 | 2948篇 |
2017年 | 3321篇 |
2016年 | 2907篇 |
2015年 | 3943篇 |
2014年 | 4941篇 |
2013年 | 5957篇 |
2012年 | 6570篇 |
2011年 | 6974篇 |
2010年 | 6005篇 |
2009年 | 5838篇 |
2008年 | 5721篇 |
2007年 | 5461篇 |
2006年 | 5732篇 |
2005年 | 5124篇 |
2004年 | 3545篇 |
2003年 | 2988篇 |
2002年 | 2805篇 |
2001年 | 2458篇 |
2000年 | 2717篇 |
1999年 | 3078篇 |
1998年 | 2514篇 |
1997年 | 2074篇 |
1996年 | 2092篇 |
1995年 | 1696篇 |
1994年 | 1395篇 |
1993年 | 1021篇 |
1992年 | 803篇 |
1991年 | 626篇 |
1990年 | 473篇 |
1989年 | 396篇 |
1988年 | 307篇 |
1987年 | 208篇 |
1986年 | 136篇 |
1985年 | 91篇 |
1984年 | 66篇 |
1983年 | 42篇 |
1982年 | 56篇 |
1981年 | 35篇 |
1980年 | 42篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1973年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
不同含量低污染水对人工湿地中细菌的影响研究 总被引:1,自引:0,他引:1
探究水平流人工湿地(HFCW)系统处理低污染水过程中,相同COD/ρ(TN)下不同碳氮含量对细菌群落结构的影响。结果表明,进水为较高碳氮含量的HFCW(HF1)和进水为较低碳氮含量的HFCW(HF2)对COD和TN的去除效率具有一定的差异,HF1和HF2对COD的去除效率分别为48.26%和28.89%,对TN的去除率分别为79.06%和81.87%。HF1中细菌的丰富度和多样性均高于HF2,HF1中富集的优势细菌为Chloroflexaceae、Comamonadaceae和Rhodocyclaceae,均具有异养反硝化功能,HF2中富集的优势细菌为Xanthomonadaceae和Rhodocyclaceae,其中Xanthomonadaceae具有自养反硝化功能。COD、NH4^+-N和NO3^--N对HF1中细菌群落的影响大于对HF2中细菌群落的影响,HF1中COD对细菌群落的影响大于NH4^+-N和NO3^--N。 相似文献
52.
研究制备了海绵负载纳米Al2O3微球的复合吸附剂(NAS),并用于对Se(Ⅳ)和Se(Ⅵ)的吸附。结果表明,合成的纳米Al2O3微球(NAO)的平均尺寸为200~400 nm,在海绵上负载NAO会使其分散性更好。当NAO负载量分别为80 mg/g和60 mg/g时,NAS对Se(Ⅳ)和Se(Ⅵ)的吸附性能为佳,分别需要60、120 min达到平衡,适应pH为2~5;两者均符合准2级动力学模型;NAS对Se(Ⅳ)、Se(Ⅵ)的最大吸附容量分别为137.2、143.9 mg/g,能很好地与Freundlich模型拟合,说明NAS表面不均匀,且属于多层吸附。经过2次的循环,对Se(Ⅳ)和Se(Ⅵ)的去除率有所降低,但均仍保持在一定的水平,说明NAS可再生循环利用。NAS作为一种新型吸附剂去除水中Se具有较好的应用前景。 相似文献
53.
54.
55.
Bing Yang Yu Zhou Wenjie Yu Song Zhang Hongxiang Chen Ju Ye 《Polymer International》2019,68(4):675-683
In order to improve the dispersity and stability of the nano‐SiO2 aqueous system with high solid content, a kind of polyacrylic acid dispersant with methoxysilicon end groups (KH590‐PAA) was synthesized by photopolymerization of acrylic acid (AA) initiated with (3‐mercaptopropyl)trimethoxysilane (KH590). After adding KH590‐PAA into the nano‐SiO2 aqueous dispersion system (20 wt% solid content), the viscosity and the curing time of the system were measured with a rotational viscometer and the inverted bottle method. Moreover, the dispersion mechanism of KH590‐PAA for the nano‐SiO2 aqueous system was researched by measuring the adsorption capacity, the particle size and the zeta potential of the nanoparticles with a conductivity meter, dynamic light scattering, SEM and TEM, respectively. The results showed that the methoxysilicon groups in KH590‐PAA could react with hydroxyl groups on the surface of nano‐SiO2 in the process of stirring, which enhanced the adsorption capacity of the dispersant and then increased the surface charge of the particles. Therefore, electrostatic repulsion and steric hindrance effects between the SiO2 nanoparticles could be further enhanced by adding the KH590‐PAA dispersant, and then the nano‐SiO2 aqueous system exhibited better dispersity and stability. Besides, the dispersion properties of SiO2 nanoparticles in water were closely related to the addition amount and the molecular weight of the KH590‐PAA dispersant. © 2018 Society of Chemical Industry 相似文献
56.
Kang Zhang Rong‐rong Wang Kai‐rui Zhang Fei Cheng Yu Tian Yi Lin Mi Zhou Pu‐xin Zhu 《Polymer International》2020,69(3):274-279
A series of hyperbranched poly(citric polyethylene glycol) (PCPEG) materials with varied polyethylene glycol (PEG) chain lengths as plasticizers were mixed with maize starch (MS) via cooking and film‐forming. The structure, pasting property, plasticization, aging property, moisture absorption and compatibility of plasticized starches were studied by means of Fourier transform infrared spectroscopy, X‐ray diffraction, rapid viscosity analysis, tension testing, moisture absorption measurements and scanning electron microscopy. Compared with PEG and citric acid, PCPEG was more effective in promoting starch chain movement and inhibiting the retrogradation of starch film. Also, PCPEG/MS had smaller moisture content. The longer the plasticizer chain, the better were the aging resistance and moisture resistance of starch. But with an increase of PEG chain length, mechanical properties of PCPEG/MS deteriorated and the compatibility between PCPEG and MS decreased. The hyperbranched derivative of PEG with longer chain exhibited improved plasticization and compatibility with starch. © 2019 Society of Chemical Industry 相似文献
57.
58.
The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless person- 相似文献
59.
Chaoxin Li Yi Zhou Yuming Tian Yuanyuan Zhao Kaiyue Wang Guomin Li Yuesheng Chai 《Ceramics International》2019,45(5):5613-5616
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources. 相似文献
60.