全文获取类型
收费全文 | 715篇 |
免费 | 3篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 51篇 |
金属工艺 | 2篇 |
机械仪表 | 40篇 |
建筑科学 | 51篇 |
矿业工程 | 4篇 |
能源动力 | 4篇 |
轻工业 | 175篇 |
水利工程 | 68篇 |
石油天然气 | 12篇 |
武器工业 | 3篇 |
无线电 | 28篇 |
一般工业技术 | 224篇 |
冶金工业 | 5篇 |
原子能技术 | 4篇 |
自动化技术 | 48篇 |
出版年
2018年 | 2篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2013年 | 1篇 |
2012年 | 50篇 |
2011年 | 75篇 |
2010年 | 23篇 |
2009年 | 5篇 |
2008年 | 44篇 |
2007年 | 47篇 |
2006年 | 49篇 |
2005年 | 47篇 |
2004年 | 37篇 |
2003年 | 33篇 |
2002年 | 37篇 |
2001年 | 27篇 |
2000年 | 32篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 19篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 24篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1967年 | 1篇 |
1948年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有722条查询结果,搜索用时 15 毫秒
51.
Site 5 air sparging pilot test, Naval Air Station Cecil Field, Jacksonville, Florida 总被引:8,自引:0,他引:8
A 72-h air sparging pilot test was conducted at Site 5 (Operable Unit 2), Naval Air Station Cecil Field, Jacksonville, FL, to determine performance parameters necessary for full-scale design. The sparge well was completed to a depth of 29 ft, several feet below the groundwater plume contaminated with volatile organic compounds (VOCs), primarily benzene, toluene, ethylbenzene, and xylenes (BTEX). Air flow rates supplied to the sparge well were 3 cubic feet/min (cfm) during the first day, 2 cfm during the second day, and 1 cfm during the third day. Water levels in monitoring wells initially rose approximately 2 ft during the first 4-5 h of the test, then receded back to pre-test equilibrium levels over the next 15 h, for a total duration of water mounding of about 20 h. A small (approximately 0.5 ft) water table drop, with subsequent recovery to equilibrium level, occurred each time the air sparging rate was decreased. Although there is considerable variation depending on direction from the sparge well, the average radius of influence varied from approximately 30 ft at 1 cfm to 50 ft at 3 cfm. The air sparge system was capable of increasing the dissolved oxygen from 0 to 6 or 7 mg/l within 12-15 h of air channels reaching a given location. A lag time of approximately 13 h was observed before air channels reached a radius of 30 ft and dissolved oxygen levels began to increase at that radius. CO(2) (stripped out of the groundwater by the sparging) decreased from a pre-test concentration of 150 to 20 mg/l at r=5 ft, and from 150 to 50 mg/l at r=30 ft, within a period of about 24 h. The rate of VOC mass removal during the pilot test was 0.06 lb/day at a sparge rate of 3 cfm, and it appears that air sparging will effect a rapid cleanup of the VOCs in the Site 5 groundwater plume. 相似文献
52.
53.
54.
55.
Boehm PD Page DS Burns WA Bence AE Mankiewicz PJ Brown JS 《Environmental science & technology》2001,35(3):471-479
The dominant sources of the petrogenic hydrocarbon background in benthic sediments of Prince William Sound, AK (PWS), site of the 1989 Exxon-Valdez oil spill, are eroding Tertiary shales and residues of natural oil seepage. Mass balance considerations and statistical analyses of hydrocarbon fingerprints independently indicate that coal contributes generally less than 1% of the polycyclic aromatic hydrocarbons (PAH) and chemical biomarkers in this background. This is environmentally significant because of presumed differences in the bioavailability of PAH in coal, seep oil residues, and shales. Coal particles are present in PWS sediments, but their PAH and chemical biomarker contributions are overwhelmed by those of seep oil residues and organic particles from shales of low-to-high thermally maturity. In the late Tertiary or early Quaternary, the currently exposed and eroding shale formations were heated into the oil-generation window and, consequently, are now relatively rich in extractable PAH and chemical biomarkers. The exposed and eroding coals in the area, in contrast, experienced long hot burial and are now thermally overmature with respect to oil generation. The concentrations of thermally sensitive PAH and biomarker compounds in PWS sediments are not consistent with a mature coal origin but are consistent with the low-to-high maturity shales and seep oils in the area. 相似文献
56.
Jayaram V Agrawal H Welch WA Miller JW Cocker DR 《Environmental science & technology》2011,45(6):2286-2292
Emissions from harbor-craft significantly affect air quality in populated regions near ports and inland waterways. This research measured regulated and unregulated emissions from an in-use EPA Tier 2 marine propulsion engine on a ferry operating in a bay following standard methods. A special effort was made to monitor continuously both the total Particulate Mass (PM) mass emissions and the real-time Particle Size Distribution (PSD). The engine was operated following the loads in ISO 8178-4 E3 cycle for comparison with the certification standards and across biodiesel blends. Real-time measurements were also made during a typical cruise in the bay. Results showed the in-use nitrogen oxide (NOx) and PM(2.5) emission factors were within the not to exceed standard for Tier 2 marine engines. Comparing across fuels we observed the following: a) no statistically significant change in NO(x) emissions with biodiesel blends (B20, B50); b) ~ 16% and ~ 25% reduction of PM(2.5) mass emissions with B20 and B50 respectively; c) a larger organic carbon (OC) to elemental carbon (EC) ratio and organic mass (OM) to OC ratio with B50 compared to B20 and B0; d) a significant number of ultrafine nuclei and a smaller mass mean diameter with increasing blend-levels of biodiesel. The real-time monitoring of gaseous and particulate emissions during a typical cruise in the San Francisco Bay (in-use cycle) revealed important effects of ocean/bay currents on emissions: NO(x) and CO(2) increased 3-fold; PM(2.5) mass increased 6-fold; and ultrafine particles disappeared due to the effect of bay currents. This finding has implications on the use of certification values instead of actual in-use emission values when developing inventories. Emission factors for some volatile organic compounds (VOCs), carbonyls, and poly aromatic hydrocarbons (PAHs) are reported as supplemental data. 相似文献
57.
58.
博帕伦坝的改善与改造J.M.马希厄斯·马奎兹F主题词砼重力坝,工程维修,坝加高,坝加固,改建工程,施工方法,试验研究博伯伦坝为混凝土重力坝,坝轴线为直线。基础以上最大坝高35m,侧道处坝顶高程为321.3m该坝位于流经卡瑟里斯省的塔乔河右岸支流阿拉哥... 相似文献
59.
60.
Surdo EM Khan IA Choudhury AA Saleh NB Arnold WA 《Journal of hazardous materials》2011,188(1-3):334-340
Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations. 相似文献