全文获取类型
收费全文 | 388107篇 |
免费 | 32108篇 |
国内免费 | 20137篇 |
专业分类
电工技术 | 21518篇 |
技术理论 | 57篇 |
综合类 | 47222篇 |
化学工业 | 51715篇 |
金属工艺 | 16608篇 |
机械仪表 | 21189篇 |
建筑科学 | 54495篇 |
矿业工程 | 21315篇 |
能源动力 | 13790篇 |
轻工业 | 24870篇 |
水利工程 | 31122篇 |
石油天然气 | 19554篇 |
武器工业 | 3150篇 |
无线电 | 22049篇 |
一般工业技术 | 28919篇 |
冶金工业 | 19699篇 |
原子能技术 | 4060篇 |
自动化技术 | 39020篇 |
出版年
2024年 | 1187篇 |
2023年 | 4136篇 |
2022年 | 7684篇 |
2021年 | 9545篇 |
2020年 | 9987篇 |
2019年 | 8556篇 |
2018年 | 8105篇 |
2017年 | 9880篇 |
2016年 | 11407篇 |
2015年 | 12376篇 |
2014年 | 22059篇 |
2013年 | 21423篇 |
2012年 | 26975篇 |
2011年 | 28277篇 |
2010年 | 21889篇 |
2009年 | 22634篇 |
2008年 | 20867篇 |
2007年 | 27252篇 |
2006年 | 25553篇 |
2005年 | 22434篇 |
2004年 | 18721篇 |
2003年 | 16821篇 |
2002年 | 14154篇 |
2001年 | 11789篇 |
2000年 | 10066篇 |
1999年 | 8114篇 |
1998年 | 6150篇 |
1997年 | 5367篇 |
1996年 | 4794篇 |
1995年 | 4062篇 |
1994年 | 3487篇 |
1993年 | 2664篇 |
1992年 | 2298篇 |
1991年 | 1695篇 |
1990年 | 1483篇 |
1989年 | 1296篇 |
1988年 | 1025篇 |
1987年 | 719篇 |
1986年 | 566篇 |
1985年 | 500篇 |
1984年 | 461篇 |
1983年 | 331篇 |
1982年 | 282篇 |
1981年 | 189篇 |
1980年 | 161篇 |
1979年 | 141篇 |
1978年 | 68篇 |
1977年 | 80篇 |
1976年 | 60篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Against the background of smart manufacturing and Industry 4.0, how to achieve real-time scheduling has become a problem to be solved. In this regard, automatic design for shop scheduling based on hyper-heuristics has been widely studied, and a number of reviews and scheduling algorithms have been presented. Few studies, however, have specifically discussed the technical points involved in algorithm development. This study, therefore, constructs a general framework for automatic design for shop scheduling strategies based on hyper-heuristics, and various state-of-the-art technical points in the development process are summarized. First, we summarize the existing types of shop scheduling strategies and classify them using a new classification method. Second, we summarize an automatic design algorithm for shop scheduling. Then, we investigate surrogate-assisted methods that are popular in the current algorithm field. Finally, current problems and challenges are discussed, and potential directions for future research are proposed. 相似文献
44.
《International Journal of Hydrogen Energy》2022,47(62):25880-25898
Hydrogen as an energy carrier can play a significant role in reducing environmental emissions if it is produced from renewable energy resources. This research aims to assess hydrogen production from wind energy considering environmental, economic, and technical aspect for the East Azerbaijan province of Iran. The economic assessment is performed by calculation of payback period, levelized cost of hydrogen, and levelized cost of electricity. Since uncertainty in the power output of wind turbines may affect the payback period, all calculations are performed for four different turbine degradation rates. While it is common in the literature to choose the wind turbine based on a single criterion, this study implements Multi-Criteria Decision-Making (MCDM) techniques for this purpose. The results of Step-wise Weight Assessment Ratio Analysis illustrates that economic issue is the most important criterion for this research. The results of Weighted Aggregated Sum Product Assessment shows that Vestas V52 is the most suitable wind turbine for Ahar and Sarab cities, while Eovent EVA120 H-Darrieus is a better choice for other stations. The most suitable location for wind power generation is found to be Ahar, where it is estimated to annually generate 2914.8 kWh of electricity at the price of 0.045 $/kWh, and 47.2 tons of hydrogen at the price of 1.38 $/kg, which result in 583 tons of CO2 emission reduction. 相似文献
45.
Ahmad Reza Abbasian Alireza Mahvary Shahram Alirezaei 《Ceramics International》2021,47(17):23794-23802
The effects of three types of salt including NaF, KCl, and NaCl on the properties of NiFe2O4 nanoparticles using salt-assisted solution combustion synthesis (SSCS) have been investigated. The synthesized powders were evaluated by SEM, TEM, FTIR, XRD, and VSM analysis. Also, the specific surface area (SSA), as well as size distribution and volume of the porosities of NiFe2O4 powders were determined by the BET apparatus. The visual observations showed that the intensity and time of combustion synthesis of nanoparticles have been severely influenced by the type of salt. The highest crystallinity was observed in the synthesized powder using NaCl. The SSA has also been correlated completely to the type of salt. The quantities of SSA was achieved about 91.62, 64.88, and 47.22 m2g-1 for the powders synthesized by KCl, NaCl, and NaF respectively. Although the magnetic hysteresis loops showed the soft ferromagnetic behavior of the NiFe2O4 nanoparticles in all conditions, KCl salt could produce the particles with the least coercivity and remanent magnetization. Based on the present study, the salt type is a key parameter in the SSCS process for the preparation of spinel ferrites. Thermodynamic evaluation also showed that the melting point and heat capacity are important parameters for the proper selection of the salt. 相似文献
46.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation. 相似文献
47.
Yan He Kangren Kong Zhengxi Guo Weifeng Fang Zaiqiang Ma Haihua Pan Ruikang Tang Zhaoming Liu 《Advanced functional materials》2021,31(26):2101291
Sensitivity and multi-directional motivation are major two factors for developing optimized humidity-response materials, which are promising for sensing, energy production, etc. Organic functional groups are commonly used as the water sensitive units through hydrogen bond interactions with water molecules in actuators. The multi-coordination ability of inorganic ions implies that the inorganic ionic compounds are potentially superior water sensitive units. However, the particle forms of inorganic ionic compounds produced by classical nucleation limit the number of exposed ions to interact with water. Recent progress on the inorganic ionic oligomers has broken through the limitation of classical nucleation, and realized the molecular-scaled incorporation of inorganic ionic compounds into an organic matrix. Here, the incorporation of hydrophilic calcium carbonate ionic oligomers into hydrophobic poly(vinylidene fluoride) (PVDF) is demonstrated. The ultra-small calcium carbonate oligomers within a PVDF film endow it with an ultra-sensitive, reversible, and bidirectional response. The motivation ability is superior to other bidirectional humidity-actuators at present, which realizes self-motivation on an ice surface, converting the chemical potential energy of the humidity gradient from ice to kinetic energy. 相似文献
48.
49.
《International Journal of Hydrogen Energy》2022,47(66):28475-28485
Constructing efficient and stable bifunctional electrocatalysts for overall water splitting remains a challenge because of the sluggish reaction kinetics. Herein, the core-shell hybrids composed of Co(PO3)2 nanorod core and NiFe alloy shell in situ grown on nickel foam (NiFe/Co(PO3)2@NF) are synthesized. Owing to the hierarchical palm-leaf-like structures and strong adhesion between NiFe alloys, Co(PO3)2 and substrates, the catalyst provides a large surface area and rapid charge transfer, which facilitates active sites exposure and conductivity enhancement. The interfacial effect in the NiFe/Co(PO3)2 core-shell structure modulates the electronic structure of the active sites around the boundary, thereby boosting the intrinsic activity. Benefiting from the stable structure, the durability of the catalyst is not impaired by the inevitable surface reconfiguration. The NiFe/Co(PO3)2@NF electrode presents a low cell voltage of 1.63 V to achieve 10 mA cm?2 and manifests durability for up to 36 h at different current densities. 相似文献
50.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献