全文获取类型
收费全文 | 24362篇 |
免费 | 1692篇 |
国内免费 | 1023篇 |
专业分类
电工技术 | 2139篇 |
技术理论 | 1篇 |
综合类 | 1376篇 |
化学工业 | 4371篇 |
金属工艺 | 607篇 |
机械仪表 | 795篇 |
建筑科学 | 1198篇 |
矿业工程 | 529篇 |
能源动力 | 8511篇 |
轻工业 | 440篇 |
水利工程 | 487篇 |
石油天然气 | 1462篇 |
武器工业 | 238篇 |
无线电 | 563篇 |
一般工业技术 | 1250篇 |
冶金工业 | 825篇 |
原子能技术 | 1484篇 |
自动化技术 | 801篇 |
出版年
2024年 | 84篇 |
2023年 | 494篇 |
2022年 | 756篇 |
2021年 | 918篇 |
2020年 | 993篇 |
2019年 | 903篇 |
2018年 | 737篇 |
2017年 | 808篇 |
2016年 | 727篇 |
2015年 | 596篇 |
2014年 | 1368篇 |
2013年 | 1735篇 |
2012年 | 1503篇 |
2011年 | 2230篇 |
2010年 | 1689篇 |
2009年 | 1576篇 |
2008年 | 1505篇 |
2007年 | 1635篇 |
2006年 | 1333篇 |
2005年 | 994篇 |
2004年 | 872篇 |
2003年 | 727篇 |
2002年 | 613篇 |
2001年 | 525篇 |
2000年 | 400篇 |
1999年 | 278篇 |
1998年 | 219篇 |
1997年 | 176篇 |
1996年 | 142篇 |
1995年 | 114篇 |
1994年 | 93篇 |
1993年 | 59篇 |
1992年 | 60篇 |
1991年 | 38篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1960年 | 1篇 |
1959年 | 11篇 |
1957年 | 1篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
赵建民 《微电子学与计算机》1996,13(1):20-21,29
本文从锅炉运行技术指标台帐微机管理的实际出发,提出了热量计算中主蒸汽流量修正系数C和给水焓值Z两项参数回归的计算公式,提高了热量计算数值精度。 相似文献
52.
An overview of current nuclear power generation and fuel cycle strategies in Europe is presented, with an emphasis on options for the management of separated plutonium in the medium to long term. Countries which have opted for reprocessing of spent fuel have had to contend with increasing inventories of separated plutonium. Of the various potential options for utilisation or disposition of these stockpiles, only light water reactor (LWR) mixed-oxide (MOX) fuel programmes are sufficiently technologically mature to be fully operational in several European countries at present. Such reprocessing-recycling programmes allow for a stabilisation of the overall separated plutonium stocks, but not for a significant reduction in the stockpile. Moreover, the quality of recycled plutonium decreases at each potential step of re-irradiation. Therefore, optimised or new ways of managing the plutonium stocks in the medium to long term are required. In the present overview we consider the most promising options for reactor utilisation of plutonium in both near-term future reactor and Generation IV systems. 相似文献
53.
This paper evaluated the capacity of SPOT VEGETATION time-series to monitor herbaceous fuel moisture content (FMC) in order to improve fire risk assessment in the savanna ecosystem of Kruger National Park in South Africa. In situ herbaceous FMC data were used to assess the Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Vegetation Dryness Index (VDI), Improved VDI (IVDI), and Accumulated Relative NDVI Decrement (ARND) during the dry season. The effect of increasing amounts of dead vegetation on the monitoring capacity of derived indices was studied by sampling mixed live and dead FMC. The IVDI was proposed as an improvement of the VDI to monitor herbaceous FMC during the dry season. The IVDI is derived by replacing NDVI with the integrated Relative Vegetation Index (iRVI), as an approximation of yearly herbaceous biomass, when analyzing the 2-dimensional space with NDWI. It was shown that the iRVI offered more information than the NDVI in combination with NDWI to monitor FMC. The VDI and IVDI exhibited a significant relation to FMC with R2 of 0.25 and 0.73, respectively. The NDWI, however, correlated best with FMC (R2 = 0.75), while the correlation of ARND and FMC was weaker (R2 = 0.60) than that found for NDVI, NDWI, and IVDI. The use of in situ herbaceous FMC consequently indicated that NDWI is appropriate as spatio-temporal information source of herbaceous FMC variation which can be used to optimize fire risk and behavior assessment for fire management in savanna ecosystems. 相似文献
54.
本文从科学技术的角度,分析我国国民经济增长对核能发展的需求,探讨我国核能的近中期发展战略构想,指出为实现其发展战略目标而应重点研究的关键科学技术与问题,并提出一些相关的政策建议,为国家制定核能中长期发展规划提供参考。 相似文献
55.
GTL 工艺技术评述 总被引:7,自引:0,他引:7
介绍了1990年以来GTL工艺技术开发的进展情况,其中以Sasol-SSPD和Syntruleum两种工艺最受关注,从现有数据分析。Syntruleum虽采用含氮合成气生产工艺,但并未使装置的单位投资明显改善,因此,近10年来GTL工艺技术开发虽取得了长足的进步,但其装置投资仍偏高,从而又严重影响了产品成本,按南非Sasol公司的经验。开展资源综合利用是降低液体燃料生产成本的有效途径,目前国外GTL工艺技术的开发仍很活跃,我国也已形成大量实验室成果。建议尽快组织力量完成工业性试验。 相似文献
56.
57.
Barry D. Solomon 《Energy Policy》1985,13(1):97-101
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing. 相似文献
58.
A three-dimensional (3D), two-phase, isothermal model of direct methanol fuel cells (DMFCs) was employed to investigate effects of electron transport through the backing layer and the land in bipolar plates. It was found that the electronic resistance of the backing layer, affected by backing layer electronic conductivity, backing layer thickness and flow channel width, played a relatively important role in determining the current density distribution and cell performance. In order to ignore the electron transport effect on the average current density, the minimum electronic conductivity of the backing layer has to be 1000 S m−1, with the relative error in the average current density less than 5%, under the given conditions. 相似文献
59.
The feasibility of a new alloy design concept utilizing the principle of ‘tungsten bronze effect’ is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H3PO4 and H2SO4 solutions at 80 °C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W6+ to W5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the ‘tungsten bronze effect’ is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC. 相似文献
60.
为实现区域水网水量的高效调控,从水量、水生态、水质和闸坝管理等4个方面构建包含10个指标的闸坝优选评价指标体系,以廊坊市凤河-永定河区域水网为研究对象,计算区域内32座闸坝的综合关键指数并给出影响程度排序,采用水动力数学模型验证关键闸坝选取的合理性。结果表明:优选出的永丰闸和东张务闸是区域水网的关键闸坝,通过调节这两座闸坝的开度即可满足区域水网的生态需水和防洪排涝调度目标,保持区域水网较优的水力连通能力,提高区域水网水量调控效率。 相似文献