全文获取类型
收费全文 | 22377篇 |
免费 | 650篇 |
国内免费 | 137篇 |
专业分类
电工技术 | 109篇 |
综合类 | 215篇 |
化学工业 | 2886篇 |
金属工艺 | 389篇 |
机械仪表 | 405篇 |
建筑科学 | 5698篇 |
矿业工程 | 382篇 |
能源动力 | 2033篇 |
轻工业 | 1001篇 |
水利工程 | 1158篇 |
石油天然气 | 104篇 |
无线电 | 242篇 |
一般工业技术 | 5012篇 |
冶金工业 | 243篇 |
原子能技术 | 119篇 |
自动化技术 | 3168篇 |
出版年
2024年 | 24篇 |
2023年 | 375篇 |
2022年 | 350篇 |
2021年 | 479篇 |
2020年 | 620篇 |
2019年 | 683篇 |
2018年 | 728篇 |
2017年 | 969篇 |
2016年 | 1379篇 |
2015年 | 1210篇 |
2014年 | 1520篇 |
2013年 | 1739篇 |
2012年 | 1074篇 |
2011年 | 1332篇 |
2010年 | 1266篇 |
2009年 | 1197篇 |
2008年 | 661篇 |
2007年 | 975篇 |
2006年 | 936篇 |
2005年 | 803篇 |
2004年 | 576篇 |
2003年 | 571篇 |
2002年 | 577篇 |
2001年 | 476篇 |
2000年 | 283篇 |
1999年 | 317篇 |
1998年 | 183篇 |
1997年 | 124篇 |
1996年 | 189篇 |
1995年 | 142篇 |
1994年 | 93篇 |
1993年 | 86篇 |
1992年 | 59篇 |
1991年 | 67篇 |
1990年 | 57篇 |
1989年 | 66篇 |
1988年 | 144篇 |
1987年 | 356篇 |
1986年 | 316篇 |
1985年 | 93篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
1.
Diffusers are widely-used to quickly dilute effluents in receiving water bodies. This study proposed a novel diffuser that pre-mixes effluent with ambient water before discharging and that uses the swirling jet to further enhance near-field dilution. The nozzle of the diffuser was examined in two ambient flow conditions: co-flow and counter-flow that are commonly-met in the environment such as oceans due to tidal effect. Physical experiments were first conducted in co-flow on its dilution performance and hydrodynamics, using heated water as the effluent. A 3-D CFD model was developed and calibrated the co-flow scenarios, and then used to investigate the diffuser in counter-flow. The results showed that the nozzle can effectively reduce the maximum temperature rise of the effluent by about 50 % before discharging. The swirling jet from the outlet has a larger shear area, half-width and entrainment rate, enabling the effluent to be rapidly diluted to a minimum of around 10 times at x/D = 6 in co-flow, whereas the dilution for conventional nozzles is about 1 because of the potential core. The flow amplification ratio (α) decreases gradually with increasing velocity ratio in co-flow but increases with increasing velocity ratio in counter-flow. The counter-flow reduces the water drawn into the device; however, the pre-dilution effect at the outlet remains stable. The near-field dilution in counter-flow was significantly enhanced than that in co-flow. Environmental regulations at outfalls and mixing zones can be more easily met using this novel diffuser. 相似文献
2.
In recent years, artificial intelligence (AI) is being increasingly utilised in disaster management activities. The public is engaged with AI in various ways in these activities. For instance, crowdsourcing applications developed for disaster management to handle the tasks of collecting data through social media platforms, and increasing disaster awareness through serious gaming applications. Nonetheless, there are limited empirical investigations and understanding on public perceptions concerning AI for disaster management. Bridging this knowledge gap is the justification for this paper. The methodological approach adopted involved: Initially, collecting data through an online survey from residents (n = 605) of three major Australian cities; Then, analysis of the data using statistical modelling. The analysis results revealed that: (a) Younger generations have a greater appreciation of opportunities created by AI-driven applications for disaster management; (b) People with tertiary education have a greater understanding of the benefits of AI in managing the pre- and post-disaster phases, and; (c) Public sector administrative and safety workers, who play a vital role in managing disasters, place a greater value on the contributions by AI in disaster management. The study advocates relevant authorities to consider public perceptions in their efforts in integrating AI in disaster management. 相似文献
3.
Sucrose and zinc oxide (ZnO) are effective cement hydration retarders. The goal of this study was to provide a new look into the ZnO cement hydration mechanism and to investigate impacts of various supplementary cementitious materials (SCMs) on retardation behavior of ZnO and sucrose. Changes in the pore solution composition and reaction kinetics were measured for cementitious systems with ZnO or sucrose that contained rice straw ash (RSA), wheat straw ash, silica fume, metakaolin, and fly ash. Among the SCMs used, RSA dramatically suppressed ZnO and sucrose retardation. Experimental results indicated that the mechanism by which ZnO retards hydration reaction could be nucleation and/or growth poisoning of C-S-H. Reduced retardation of paste samples containing RSA was attributed to the ability of RSA to provide nucleation sites for C-S-H precipitation. This study provides a better understanding of the interaction between SCMs and cement hydration retarders essential in predicting retarder–dose effects. 相似文献
4.
《Cities》2018
There is a general perception that Dubai is built for the well-off. The construction of mega developments feeds a longstanding narrative that Dubai is solely a luxurious place. This study assesses this portrayal of Dubai and explores Dubai's residential landscape in terms of morphology and affordability. In particular, we ask: What are the different housing patterns prevailing in Dubai's built landscape? What are the major driving factors that influenced Dubai's housing transformation? How affordable is Dubai to its residents? Does Dubai's built landscape accommodate a large spectrum of income classes?The study argues that to fully assess the affordability of a city's housing, it's necessary to understand its spatial forms, morphogenesis, and the forces that shaped these patterns. Taking Dubai as a case, the study uses geospatial mapping to reveal nine distinct residential patterns in the city's history. The identified patterns are presented under six thematic periods stretching from 1900 to 2016 to highlight the contributing forces that shaped Dubai's housing landscape. Results expand the terms of discussions of affordable housing issues to address concerns related to authoritarian land use control and its impact on housing forms. Findings reveal that Dubai's land use policy creates spatial and housing affordability challenges. The state housing policy of providing large plots and exclusive suburbs for natives and the government's partnership with the private sector to brand Dubai through projects for the well-off have created a formidable housing challenge for the middle class. One major challenge is the lack of sufficient affordable housing units for the middle-class population; rental figures for this group are at crisis point. Only 23% of total housing units, which corresponds to a mere 7% of the total housing floor area in Dubai, are affordable for this group. To eradicate these ills of housing affordability, the planning profession in Dubai must derive practices from a number of internationally recognized planning and rental control policies. 相似文献
5.
《International Journal of Hydrogen Energy》2019,44(11):5189-5202
Independent hydrogen production from petrochemical wastewater containing mono-ethylene glycol (MEG) via anaerobic sequencing batch reactor (ASBR) was extensively assessed under psychrophilic conditions (15–25 °C). A lab-scale ASBR was operated at pH of 5.50, and different organic loading rates (OLR) of 1.00, 1.67, 2.67, and 4.00 gCOD/L/d. The hydrogen yield (HY) progressed from 134.32 ± 10.79 to 189.09 ± 22.35 mL/gMEGinitial at increasing OLR from 1.00 to 4.00 gCOD/L/d. The maximum hydrogen content of 47.44 ± 3.60% was achieved at OLR of 4.0 gCOD/L/d, while methane content remained low (17.76 ± 1.27% at OLR of 1.0 gCOD/L/d). Kinetic studies using four different mathematical models were conducted to describe the ASBR performance. Furthermore, two batch-mode experiments were performed to optimize the nitrogen supplementation as a nutrient (C/N ratio), and assess the impact of salinity (as gNaCl/L) on hydrogen production. HY substantially dropped from 62.77 ± 4.09 to 6.02 ± 0.39 mL/gMEGinitial when C/N ratio was increased from 28.5 to 114.0. Besides, the results revealed that salinity up to 10.0 gNaCl/L has a relatively low inhibitory impact on hydrogen production. Eventually, the cost/benefit analysis showed that environmental and energy recovery revenues from ASBR were optimized at OLR of 4.0 gCOD/L/d (payback period of 7.13 yrs). 相似文献
6.
Transmission system restoration with co-optimization of repairs,load pickups,and generation dispatch
This paper studies the restoration of a transmission system after a significant disruption such as a natural disaster. It considers the co-optimization of repairs, load pickups, and generation dispatch to produce a sequencing of the repairs that minimizes the size of the blackout over time. The core of this process is a Restoration Ordering Problem (ROP), a non-convex mixed-integer nonlinear program that is outside the capabilities of existing solver technologies. To address this computational barrier, the paper examines two approximations of the power flow equations: The DC model and the recently proposed LPAC model. Systematic, large-scale testing indicates that the DC model is not sufficiently accurate for solving the ROP. In contrast, the LPAC power flow model, which captures line losses, reactive power, and voltage magnitudes, is sufficiently accurate to obtain restoration plans that can be converted into AC-feasible power flows. An experimental study also suggests that the LPAC model provides a robust and appealing tradeoff between accuracy and computational performance for solving the ROP. 相似文献
7.
8.
This paper presents the Kriging model approach for stochastic free vibration analysis of composite shallow doubly curved shells. The finite element formulation is carried out considering rotary inertia and transverse shear deformation based on Mindlin’s theory. The stochastic natural frequencies are expressed in terms of Kriging surrogate models. The influence of random variation of different input parameters on the output natural frequencies is addressed. The sampling size and computational cost is reduced by employing the present method compared to direct Monte Carlo simulation. The convergence studies and error analysis are carried out to ensure the accuracy of present approach. The stochastic mode shapes and frequency response function are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results using Kriging model and its performance. 相似文献
9.
Effective management of the risks associated with acid rock drainage (ARD) requires the ability to identify material with a potential to generate ARD reliably. With the increasing prevalence of quantitative mineralogy (Quantitative XRD, auto-SEM), opportunity exists to use mineralogy at all stages in ARD characterisation and prediction. This study uses a mineralogical approach across the head grade samples and the residues obtained under leach conditions of several common ARD characterisation tests (Acid Neutralising Capacity, Net Acid Generation), as well as the University of Cape Town (UCT) biokinetic test to evaluate the extent to which acid-neutralising minerals react. The results show the contribution of the carbonates to the acid neutralising capacity, as well as the partial dissolution of intermediate weathering silicate minerals such as chlorite and mica. 相似文献
10.