全文获取类型
收费全文 | 329858篇 |
免费 | 40630篇 |
国内免费 | 23319篇 |
专业分类
电工技术 | 6944篇 |
技术理论 | 13篇 |
综合类 | 24621篇 |
化学工业 | 54367篇 |
金属工艺 | 27109篇 |
机械仪表 | 12528篇 |
建筑科学 | 10098篇 |
矿业工程 | 7981篇 |
能源动力 | 19763篇 |
轻工业 | 23930篇 |
水利工程 | 2674篇 |
石油天然气 | 3156篇 |
武器工业 | 2809篇 |
无线电 | 35161篇 |
一般工业技术 | 53911篇 |
冶金工业 | 14331篇 |
原子能技术 | 3706篇 |
自动化技术 | 90705篇 |
出版年
2024年 | 1710篇 |
2023年 | 10991篇 |
2022年 | 14690篇 |
2021年 | 16821篇 |
2020年 | 17178篇 |
2019年 | 14148篇 |
2018年 | 14617篇 |
2017年 | 17668篇 |
2016年 | 18483篇 |
2015年 | 19097篇 |
2014年 | 25344篇 |
2013年 | 26996篇 |
2012年 | 30060篇 |
2011年 | 28831篇 |
2010年 | 21995篇 |
2009年 | 22503篇 |
2008年 | 14229篇 |
2007年 | 18185篇 |
2006年 | 14110篇 |
2005年 | 7307篇 |
2004年 | 3901篇 |
2003年 | 4061篇 |
2002年 | 4045篇 |
2001年 | 3700篇 |
2000年 | 2584篇 |
1999年 | 2776篇 |
1998年 | 1815篇 |
1997年 | 1114篇 |
1996年 | 1236篇 |
1995年 | 995篇 |
1994年 | 923篇 |
1993年 | 766篇 |
1992年 | 739篇 |
1991年 | 711篇 |
1990年 | 694篇 |
1989年 | 611篇 |
1988年 | 1269篇 |
1987年 | 2468篇 |
1986年 | 2317篇 |
1985年 | 653篇 |
1984年 | 147篇 |
1983年 | 114篇 |
1982年 | 140篇 |
1981年 | 96篇 |
1980年 | 123篇 |
1979年 | 124篇 |
1978年 | 94篇 |
1977年 | 70篇 |
1976年 | 97篇 |
1975年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 219 毫秒
111.
112.
为缓解我国水、能源和粮食资源紧张问题,促进资源可持续利用,构建水-能源-粮食系统,利用耦合协调度模型对我国的30个省(自治区、直辖市)进行测算,并利用空间杜宾模型分析主要影响因素。结果表明:2003—2017年,我国能源、粮食评价[JP]指数高于水资源评价指数,系统综合评价指数逐年递增;大部分省份耦合协调度处于初级协调水平且呈现逐年上升的态势,个别省份耦合协调度濒临失调;耦合协调度空间自相关性较强,虽有明显波动,但是呈现逐年加强的态势;影响耦合协调度的主要因素有从业人口数、固定资产投资额、人均生产总值、人口总数、[JP]文盲人口占比、工业污染排放、城镇化。 相似文献
113.
《International Journal of Hydrogen Energy》2022,47(63):27279-27292
This study assesses a sustainable solution to greenhouse gases (GHGs) mitigation using constructed wetland-microbial fuel cells (CW-MFC). Roots of wetland plant Acorus Calamus L. are placed in biological anode to better enable anode microorganisms to obtain rhizosphere secretion for power improvement. Three selected cathode materials have a large difference in GHG emissions, and among them, carbon fiber felt (CFF) shows the lowest emissions of methane and nitrous oxide, which are 0.77 ± 0.04 mg/(m2·h) and 130.78 ± 13.08 μg/(m2·h), respectively. The CFF CW-MFC achieves the maximum power density of 2.99 W/m3. As the influent pH value is adjusted from acidic to alkaline, the GHGs emissions are reduced. The addition of Ni inhibits GHGs emission but decreases the electricity, the power density is reduced to 1.09 W/m3, and the methane and nitrous oxide emission fluxes decline to 0.20 ± 0.04 mg/(m2·h) and 15.49 ± 1.86 μg/(m2·h), respectively. Low C/N ratio reduces methane emission, while high C/N ratio effectively inhibits nitrous oxide emission. At the influent pH 8 and C/N = 5:1, the methane emission flux is approximately 10.60 ± 0.27 mg/(m2·h), and the nitrous oxide emission flux is only 10.90 ± 1.10 μg/(m2·h). Based on the above experimental results by controlling variable factors, it is proposed that CW-MFC offers an environment-friendly solution to regulate GHG emissions. 相似文献
114.
In this study, a kind of Ni-based superalloy specially designed for additive manufacturing (AM) was investigated. Thermo-Calc simulation and differential scanning calorimetry (DSC) analysis were used to determine phases and their transformation temperature. Experimental specimens were prepared by laser metal deposition (LMD) and traditional casting method. Microstructure, phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy (SEM), transmission scanning electron microscopy (TEM), X-ray diffraction (XRD) and tensile tests. The results show that this alloy contains two basic phases, γ/γ', in addition to these phases, at least two secondary phases may be present, such as MC carbides and Laves phases. Furthermore, the as-deposited alloy has finer dendrite, its mean primary dendrite arm space (PDAS) is about 30-45 μm, and the average size of γ' particles is 100-150 nm. However, the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500 μm with secondary and even third dendrite arms. Correspondingly, the alloy displays different tensile behavior with different processing methods, and the as-deposited specimen shows better ultimate tensile stress (1,085.7±51.7 MPa), yield stress (697±19.5 MPa) and elongation (25.8%±2.2%) than that of the as-cast specimen. The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites, γ', and Laves phase, and the segregation of elements, etc. Such important information would be helpful for alloy application as well as new alloy development. 相似文献
115.
Uzun İlhan Orak İkram Yağmur Hatice Karaer Karakaplan Mehmet Yalman Murat 《SILICON》2021,13(12):4703-4713
Silicon - 5-(2,4-dichlorophenyl)-2-furoic acid and anthraquinone-2-carboxylic acid were reacted separately with chitin. The synthesized products were characterized by various spectroscopic methods... 相似文献
116.
117.
To reduce the energy consumption of the shrimp blanching process and improve the economic value of the blanched product, a transcritical CO2 heat pump blanching system (THPB system) was designed in this paper. The trends of astaxanthin were investigated at atmospheric pressure near boiling temperature, combined with the color and structural properties of shrimp samples, and the optimal blanching times of 270 s and 240 s were obtained at 90°C and 95°C, respectively. In contrast to the fuel blanching system (FB system) at 100°C, the annual standard coal consumption of the THPB system with 90°C blanching is decreased by 79%, and the annual operating cost can be saved by CNY 63,800, with a payback period of about 3.13 years.Industrial relevanceBlanching is one of the effective ways to prolong the shelf life of shrimp. However, the research on the blanching time and temperature of shrimp is not comprehensive. In addition, the traditional fuel blanching process has high energy consumption and pollution, and can no longer meet the quality requirements of the modern food processing industry. Heat pump has been shown to have better performance in food drying, but it is less used in blanching. The information presented in this study may provide other insights into food processing. 相似文献
118.
Aniruddha Nag Mohammed Asif Ali Jiabei Zhou Makoto Ogawa Tatsuo Kaneko 《大分子材料与工程》2021,306(11):2100459
Aromatic and functional polymers with processibility derived from biobased starting materials are prerequisite considering sustainable society. Poly(2,5-benzimidazole)s are rigid-rod polymers to show ultrahigh thermal stability such as flame retardance, while usually suffer from poor solubility. Here, poly(benzimidazole-co-amide)s are synthesized from two biobased monomers, 3,4-diaminobenzoic acid and a semirigid comonomer, 4-aminohydrocinnamic acid. The copolymers with an amide composition of 80 mol% and higher are soluble in widely used polar solvents to fabricate the films keeping high flame retardance, which is comparable with popular high-performance polymers such as aromatic polyimides, polyetheretherketone, polyphenylene sulfide, etc. 相似文献
119.
《Ceramics International》2021,47(23):32521-32533
In the current report, pure V2O5, a series of Gd doped V2O5 (1 wt%, 3 wt%, 5 wt% and 10 wt%) and graphene integrated Gd–V2O5 photocatalysts have been prepared using a facile wet chemical approach. The effect of Gd+3 ions substitution and RGO support on V2O5 was studied by the different analytical techniques. X-ray diffraction (XRD) results showed the orthorhombic crystal structure of synthesized samples with crystallize size in range of 22–35 nm. Morphological analysis showed nanorods and nanorod arrays like appearance of V2O5, Gd–V2O5 and GdV-2O5/RGO, respectively. Gd–V2O5 and Gd–V2O5/RGO exhibited enhanced optical response in the visible region along with decrease in the band gap values for Gd doped V2O5 samples. BET surface area of Gd–V2O5 and Gd- V2O5/RGO was calculated as 12.39 g/m2 and 15.35 g/m2 that was found to be higher than pristine V2O5. To study the photocatalytic activity of synthesized photocatalysts, methylene blue (MB) was chosen as model pollutant. Among the Gd doped V2O5 samples, highest photocatalytic activity (45.62%) was achieved by optimal concentration of 5 wt% Gd–V2O5 that is accredited to effective separation of electron-hole pairs. While Gd–V2O5/RGO showed 2.1 times higher dye removal (97.12%) than unsupported Gd–V2O5, under the visible light irradiation. The significantly high photocatalytic activity of Gd–V2O5/RGO is due to the synergistic effect aroused by combined action of Gd+3 ions doping and advantageous properties of highly conductive and large surfaced graphene. Recycling experiments for V2O5 derivatives showed good stability and recyclability of photocatalysts. Additionally, Gd–V2O5/RGO was found to be more potential anti-bacterial agent than V2O5 and Gd–V2O5. 相似文献
120.
《International Journal of Hydrogen Energy》2022,47(4):2399-2411
15 wt.%Ni-12.5 wt.%Co–Al2O3 catalysts promoted with Fe, Mn, Cu, Zr, La, Ce, and Ba were prepared by a novel solid-state synthesis method and employed in CO2 methanation reaction. BET, XRD, EDS, SEM, TPR, TGA, and FTIR analyses were conducted to identify the chemicophysical characteristics of the prepared samples. The addition of Fe, Mn, La, Ce, and Ba was effective to improve the catalytic performance of the 15 wt%Ni-12.5 wt%Co–Al2O3 due to the higher CO2 adsorption capacity of the promoted catalysts. Among the studied promoters, the Fe-promoted catalyst possessed the highest catalytic activity (XCO2 = 61.2% and SCH4 = 98.87% at 300 °C). Also, the effect of calcination temperature, feed composition, and GHSV on the performance of the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst in CO2 methanation reaction was assessed. The outcomes confirmed that the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst with the BET area of 122.4 m2/g and the highest pore volume and largest pore diameter had the highest catalytic activity. Also, the catalytic performance in the methanation of carbon monoxide was studied, and 100% conversion of carbon monoxide was observed at 250 °C. 相似文献