全文获取类型
收费全文 | 27285篇 |
免费 | 1952篇 |
国内免费 | 1157篇 |
专业分类
电工技术 | 1831篇 |
技术理论 | 1篇 |
综合类 | 1294篇 |
化学工业 | 5641篇 |
金属工艺 | 919篇 |
机械仪表 | 1282篇 |
建筑科学 | 1269篇 |
矿业工程 | 253篇 |
能源动力 | 8696篇 |
轻工业 | 400篇 |
水利工程 | 304篇 |
石油天然气 | 2112篇 |
武器工业 | 585篇 |
无线电 | 650篇 |
一般工业技术 | 1552篇 |
冶金工业 | 844篇 |
原子能技术 | 1524篇 |
自动化技术 | 1237篇 |
出版年
2024年 | 86篇 |
2023年 | 505篇 |
2022年 | 866篇 |
2021年 | 1024篇 |
2020年 | 1070篇 |
2019年 | 965篇 |
2018年 | 806篇 |
2017年 | 912篇 |
2016年 | 883篇 |
2015年 | 807篇 |
2014年 | 1734篇 |
2013年 | 1958篇 |
2012年 | 1827篇 |
2011年 | 2546篇 |
2010年 | 1889篇 |
2009年 | 1682篇 |
2008年 | 1524篇 |
2007年 | 1654篇 |
2006年 | 1390篇 |
2005年 | 1042篇 |
2004年 | 991篇 |
2003年 | 752篇 |
2002年 | 694篇 |
2001年 | 595篇 |
2000年 | 466篇 |
1999年 | 358篇 |
1998年 | 257篇 |
1997年 | 251篇 |
1996年 | 183篇 |
1995年 | 131篇 |
1994年 | 109篇 |
1993年 | 81篇 |
1992年 | 75篇 |
1991年 | 47篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1959年 | 12篇 |
1957年 | 2篇 |
1956年 | 3篇 |
1955年 | 3篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
161.
论述R-X图解法计算多级串联理想混合反应器的基本原理,并结合实例,对R-X法的计算步骤予以详细介绍,为多级串联反应器的设计与计算,提供一种新颖适用的图解计算方法。 相似文献
162.
Phase-change thermal energy storage using spherical capsules: performance of a test plant 总被引:1,自引:0,他引:1
J.P Bédécarrats F Strub B Falcon J.P Dumas 《International Journal of Refrigeration》1996,19(3):187-196
The aim of this paper is the study of an industrial process of energy storage usable for air conditioning or refrigeration, investigating a test plant which is a tank with a reduced size, filled with randomly dispersed commercial nodules, placed in a refrigeration loop. The nodules are spherical capsules in which phase change materials (PCM) are encapsulated. This test plant permits the study at length of the behaviour of the tank with, in particular, the charge mode taking into account the undercooling and the discharge mode. A simulation program that considers aspects of both the surrounding heat transfer fluid and the phase-change material packed inside the nodules is developed here in the cases of the charge and the discharge processes. The simulation results are then compared with experimental observations. 相似文献
163.
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
164.
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
165.
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
166.
高速公路水毁成因及防治措施 总被引:1,自引:0,他引:1
从高速公路水泥混凝土路面裂缝,挖方地段护面墙开裂、拦水带与路面衔接部位裂缝,急流槽水泥砂浆勾缝脱落等方面分析了高速公路水毁的成因,并提出了切实可行的防治措施,保证了高速公路的正常运营。 相似文献
167.
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
168.
169.
170.
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