全文获取类型
收费全文 | 276575篇 |
免费 | 21404篇 |
国内免费 | 14424篇 |
专业分类
电工技术 | 17099篇 |
技术理论 | 52篇 |
综合类 | 37577篇 |
化学工业 | 31315篇 |
金属工艺 | 11533篇 |
机械仪表 | 14542篇 |
建筑科学 | 38474篇 |
矿业工程 | 15001篇 |
能源动力 | 8377篇 |
轻工业 | 16204篇 |
水利工程 | 14440篇 |
石油天然气 | 11572篇 |
武器工业 | 2609篇 |
无线电 | 18054篇 |
一般工业技术 | 22549篇 |
冶金工业 | 15808篇 |
原子能技术 | 2780篇 |
自动化技术 | 34417篇 |
出版年
2024年 | 556篇 |
2023年 | 2552篇 |
2022年 | 4681篇 |
2021年 | 6228篇 |
2020年 | 6387篇 |
2019年 | 5450篇 |
2018年 | 5040篇 |
2017年 | 6173篇 |
2016年 | 7386篇 |
2015年 | 8307篇 |
2014年 | 15306篇 |
2013年 | 14077篇 |
2012年 | 18172篇 |
2011年 | 19623篇 |
2010年 | 15582篇 |
2009年 | 16299篇 |
2008年 | 15248篇 |
2007年 | 19811篇 |
2006年 | 18696篇 |
2005年 | 16359篇 |
2004年 | 14075篇 |
2003年 | 12620篇 |
2002年 | 10439篇 |
2001年 | 8805篇 |
2000年 | 7482篇 |
1999年 | 6085篇 |
1998年 | 4693篇 |
1997年 | 4119篇 |
1996年 | 3792篇 |
1995年 | 3187篇 |
1994年 | 2842篇 |
1993年 | 2137篇 |
1992年 | 1925篇 |
1991年 | 1453篇 |
1990年 | 1276篇 |
1989年 | 1099篇 |
1988年 | 877篇 |
1987年 | 588篇 |
1986年 | 446篇 |
1985年 | 395篇 |
1984年 | 389篇 |
1983年 | 271篇 |
1982年 | 239篇 |
1981年 | 183篇 |
1980年 | 140篇 |
1979年 | 116篇 |
1978年 | 69篇 |
1977年 | 84篇 |
1976年 | 62篇 |
1975年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
《Advanced Powder Technology》2022,33(6):103628
The charge sources, as well as the charging mechanism of the contact electrification (CE) of polymers, are still debatable. Since CE is accompanied by destruction, it is considered that “hard contacting” via ball milling can induce covalent bond scission and produce naked-activated-charge sources. Regarding “soft contacting” via nano-scale sliding, which does not induce covalent bond scission, a frontier-electron, “f-electron,” of the naked-activated-charge source is crucial to electron transfer among the naked-activated-charge sources. Here, we configure naked-activated-charge-source models, naked-activated-mechano-anion, and naked-activated-mechano-cation, which are produced by mechanical energy induced heterogeneous covalent bond scission, as well as naked-activated-mechano-radicals that are produced by homogeneous covalent bond scission. Regarding “soft contacting” among naked-activated-charge sources in a vacuum, f-electron can be transferred from a donor to an acceptor if the energy level of the donor is higher than that of the acceptor. The net amount of the normalized transferred-f-electrons is obtained by adopting settings in which the average energy level of the naked-activated-charge sources (as the donors) is higher than that of the sources employed as acceptors. Thus, the surfaces comprising the donors and acceptors will exhibit positive and negative net surface charges, respectively. We conclude that net surface charges depend on the average energy level of naked-activated-charge sources. Further, we observe that the alignment of polyethylene (PE)-polyvinyl chloride (PVC)-polytetrafluoroethylene (PTFE) to the average energy level is identical to that of the triboelectric series. 相似文献
33.
34.
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
35.
36.
《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
37.
Carolyn A. Grimley Stephen Funni Christopher Green Elizabeth C. Dickey 《Journal of the European Ceramic Society》2021,41(4):2807-2817
In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary. 相似文献
38.
《International Journal of Hydrogen Energy》2022,47(95):40340-40348
The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS2 (N–CoS2) catalyst has been investigated through the facile hydrothermal process followed by N2 annealing treatment. An optimized N–CoS2 catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of ?0.137 and ?0.097 V at a current density of ?10 mA/cm2 (?0.309 and ?0.275 V at ?300 mA/cm2), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (?10 to ?100 mA/cm2) along with an excellent endurance up to 50 h even at ?100 mA/cm2. The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst. 相似文献
39.
《Journal of the European Ceramic Society》2022,42(15):7017-7026
Sr0.9La0.1TiO3 based textured ceramics (SLTT-S3T) with a texture fraction of 0.81 are successfully fabricated by the reactive template grain growth method, in which Sr0.9La0.1TiO3/20 wt%Ti was used as matrix and 10 wt% plate-like Sr3Ti2O7 template seeds were used as templates. The phase transition, microstructure evolution, and the anisotropic thermoelectric properties of SLTT-S3T ceramics were investigated. The results show that the ceramics are mainly composed of Sr0.9La0.1TiO3 and rutile TiO2 phases. Grains grow with a preferred orientation along (h00). A maximum ZT of 0.26 at 1073 K was achieved in the direction perpendicular to the tape casting direction. The low lattice thermal conductivity of 1.9 W/(m K) at 1073 K was obtained decreased by 34%, 40%, and 38% compared with non-textured, SrTiO3 and Sr0.9La0.1TiO3 ceramics prepared by the same process, can be attributed to the enhanced phonon scattering by the complex multi-scale boundaries and interfaces. This work provides a strategy of microstructural design for thermoelectric oxides to decrease intrinsic lattice thermal conductivity and further regulate thermoelectric properties via texture engineering. 相似文献
40.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献