全文获取类型
收费全文 | 5092篇 |
免费 | 560篇 |
国内免费 | 125篇 |
专业分类
电工技术 | 218篇 |
技术理论 | 1篇 |
综合类 | 343篇 |
化学工业 | 381篇 |
金属工艺 | 61篇 |
机械仪表 | 133篇 |
建筑科学 | 992篇 |
矿业工程 | 36篇 |
能源动力 | 300篇 |
轻工业 | 271篇 |
水利工程 | 634篇 |
石油天然气 | 63篇 |
武器工业 | 8篇 |
无线电 | 418篇 |
一般工业技术 | 401篇 |
冶金工业 | 204篇 |
原子能技术 | 83篇 |
自动化技术 | 1230篇 |
出版年
2024年 | 8篇 |
2023年 | 58篇 |
2022年 | 104篇 |
2021年 | 129篇 |
2020年 | 165篇 |
2019年 | 165篇 |
2018年 | 178篇 |
2017年 | 167篇 |
2016年 | 216篇 |
2015年 | 224篇 |
2014年 | 272篇 |
2013年 | 360篇 |
2012年 | 286篇 |
2011年 | 432篇 |
2010年 | 324篇 |
2009年 | 323篇 |
2008年 | 320篇 |
2007年 | 291篇 |
2006年 | 225篇 |
2005年 | 215篇 |
2004年 | 195篇 |
2003年 | 255篇 |
2002年 | 155篇 |
2001年 | 158篇 |
2000年 | 93篇 |
1999年 | 56篇 |
1998年 | 31篇 |
1997年 | 36篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 52篇 |
1993年 | 23篇 |
1992年 | 20篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1964年 | 1篇 |
排序方式: 共有5777条查询结果,搜索用时 31 毫秒
41.
自然保护地不仅对保护生物多样性具有重要意义,也在减缓气候变化、实现碳中和目标方面起到关键作用。中国自然保护地的碳中和贡献尚未得到充分的认识和关注,相关研究尚处于起步阶段。首先对中国陆域自然保护地的碳储量、碳吸收能力、人为碳排放水平展开初步评估,发现陆域自然保护地在保护高碳中和贡献生态系统方面存在不足。随后提出了中国自然保护地碳中和贡献研究的3个关键课题,分别是自然保护地碳循环作用机理研究、自然保护地碳中和贡献评估与管理、生物多样性保护和碳中和的协同治理。最后围绕关键课题提出14个具体研究问题,为中国自然保护地减缓气候变化的科学研究与管理实践构建系统框架。 相似文献
42.
Impacts of climate and land‐cover changes on water resources in a humid subtropical watershed: a case study from East Texas,USA 下载免费PDF全文
Joonghyeok Heo Jaehyung Yu John R. Giardino Huidae Cho 《Water and Environment Journal》2015,29(1):51-60
This study investigates the response of water resources regarding the climate and land‐cover changes in a humid subtropical watershed during the period 1970–2009. A 0.7°C increase in temperature and a 16.3% increase in precipitation were observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land‐cover change was conversion of vegetation and barren lands to developed and crop lands affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and land‐cover changes resulted in increases of surface run‐off (15.0%), soil water content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge (9.2%). We found that surface run‐off is relatively stable with precipitation, whereas groundwater discharge and soil water content are sensitive to changes in land cover, especially land cover brought about by human intervention. 相似文献
43.
Atmospheric circulation patterns influencing variations in organic carbon fluxes in the River Oulujoki,Finland 下载免费PDF全文
Hannu Marttila Masoud Irannezhad Jaakko Saukkoriipi Bjørn Kløve 《Water and Environment Journal》2015,29(4):474-481
Atmospheric circulation generally influences regional climate variability and thereby controls catchment hydrology and consequently transport of elements in natural riverine systems. This study examined dependencies between total organic carbon (TOC) variability in the River Oulujoki (Finland) during 1963–2011 and prominent atmospheric circulation patterns (ACPs), which manifest natural climatic conditions over Finland and control hydrological processes in the river catchment. North Atlantic Oscillation, Scandinavia, East Atlantic and East Atlantic/West Russia patterns were statistically significant ACPs affecting variations in TOC export at River Oulujoki lower basin area. In the River Oulujoki, TOC export was largely controlled by changes in TOC fluxes generated from tributaries of river and near areas to its main channel. Besides, runoff from Lake Oulujärvi slightly influenced TOC export variability in the River Oulujoki. Understanding such responses of TOC fluxes to ACPs is a useful tool for sustainable water resources planning and management on regional and local scales. 相似文献
44.
Philip Sandwell Geoffrey Duggan Jenny Nelson Ned Ekins‐Daukes 《Progress in Photovoltaics: Research and Applications》2016,24(11):1458-1472
We present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3 MJ and 27.9 kgCO2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the lifetimes of the systems are found to be 6.5–9.8 g CO2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
45.
Char particles from pyrolyzed biomass vary in particle size and shape. On average, the particles are more elongated the larger their size. The average size‐specific elongation is almost alike for all investigated samples, i.e. independent from their source material and process. The particle collectives cannot be characterized accurately with classical particle size distributions, which assume spherical particle shape. Accounting for their shape, they can be described more accurately with particle size distributions that are based on an ellipsoid model. The high bulk porosity is mainly attributed to the spaces between particles. 相似文献
46.
In spite of its great importance for the dry classification of fine powders, the processes in deflector wheel classifiers are to a large extent unknown. Therefore, in the present work a commercial available classifier was modified to gain an optical access to the deflector wheel. For the first time, the obtained photographs enable an observation of the gas flow and the particle motion between the blades of the deflector wheel. Especially the importance of particle‐particle‐ and particle‐blade‐collisions could be shown. 相似文献
47.
This paper quantifies the influence of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a Turbo-BII-HP boiling surface. Nanolubricants with 10 nm diameter Al2O3 nanoparticles of various volume fractions (1.6%, 2.3%, and 5.1%) in the base polyolester lubricant were mixed with R134a at two different mass fractions (0.5% and 1%). The study showed that nanolubricants can improve R134a boiling on a reentrant cavity surface as long as the nanoparticles remain well dispersed in the lubricant and are at sufficiently large concentration. For example, three of the refrigerant/nanolubricant mixtures with the smallest nanoparticle mass fraction exhibited average enhancements over the entire heat flux range of approximately 10%. However, when the nanoparticle mass fraction was increased to a point that likely encouraged agglomeration, an average heat transfer degradation of approximately 14% resulted. An existing model was used to predict the boiling heat transfer. 相似文献
48.
49.
50.