全文获取类型
收费全文 | 46320篇 |
免费 | 5614篇 |
国内免费 | 2965篇 |
专业分类
电工技术 | 1905篇 |
技术理论 | 6篇 |
综合类 | 4281篇 |
化学工业 | 10255篇 |
金属工艺 | 4821篇 |
机械仪表 | 1869篇 |
建筑科学 | 8146篇 |
矿业工程 | 1504篇 |
能源动力 | 1061篇 |
轻工业 | 2144篇 |
水利工程 | 2607篇 |
石油天然气 | 980篇 |
武器工业 | 633篇 |
无线电 | 1770篇 |
一般工业技术 | 9471篇 |
冶金工业 | 1538篇 |
原子能技术 | 110篇 |
自动化技术 | 1798篇 |
出版年
2024年 | 287篇 |
2023年 | 762篇 |
2022年 | 1413篇 |
2021年 | 1690篇 |
2020年 | 1750篇 |
2019年 | 1435篇 |
2018年 | 1388篇 |
2017年 | 1779篇 |
2016年 | 1862篇 |
2015年 | 1840篇 |
2014年 | 2718篇 |
2013年 | 2539篇 |
2012年 | 3263篇 |
2011年 | 3483篇 |
2010年 | 2720篇 |
2009年 | 2968篇 |
2008年 | 2398篇 |
2007年 | 3242篇 |
2006年 | 3022篇 |
2005年 | 2417篇 |
2004年 | 1964篇 |
2003年 | 1783篇 |
2002年 | 1462篇 |
2001年 | 1322篇 |
2000年 | 1102篇 |
1999年 | 873篇 |
1998年 | 676篇 |
1997年 | 594篇 |
1996年 | 472篇 |
1995年 | 402篇 |
1994年 | 315篇 |
1993年 | 279篇 |
1992年 | 179篇 |
1991年 | 144篇 |
1990年 | 85篇 |
1989年 | 69篇 |
1988年 | 50篇 |
1987年 | 36篇 |
1986年 | 12篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1965年 | 3篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
水生生物环境诊断(AOD)技术应用研究 总被引:4,自引:0,他引:4
介绍一种新型的毒性试验方法——水生生物环境诊断(AOD)技术,该方法将冷冻浓缩和生物测试技术有机地相结合,较好地解决了低毒性水体的毒性测试问题。应用本项技术以红鳍鱼为受试生物,分别对湖北武汉马伧湖、墨水湖、广东深圳河、长江干流寸滩等几个断面、丹江口水库白河、丹江河口、老灌河等不同水体进行AOD测试,所得48hr-LC\-50结果与实际水质状况基本相符。 相似文献
102.
103.
研究了铸造WCP/Ni基合金梯度复合涂层组织与摩擦磨损特性。结果表明,梯度复合涂层与基材实现了良好的冶金结合,涂层内有γ-Ni枝晶组织,γ-Ni+M23C 6共晶组织以及凝固结晶析出的M6C、M23C6、M7C3等块状或条状组织;随着铸造WCP体积分数的增加,复合涂层摩擦系数减小,耐磨性增加。19-4试样的耐磨性最高值为4.61,是基材的3倍以上。梯度涂层的磨损机理为磨粒磨损与粘着磨损的复合作用。 相似文献
104.
105.
Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m?2 in 2003, 127 ± 17 g‐dry wt m?2 in 2004 and 149 ± 23 g‐dry wt m?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m?2 and 5.2 to 19.9 g‐C m?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
106.
Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya 总被引:1,自引:0,他引:1
William A. Shivoga Mucai Muchiri Samuel Kibichi Jethro Odanga Scott N. Miller Tracy J. Baldyga Eric M. Enanga Maina C. Gichaba 《Lakes & Reservoirs: Research and Management》2007,12(2):97-105
Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land‐cover types and subwatersheds contributing run‐off to the sampling sites in the River Njoro. Standard Digital Elevation Model‐based routines were used to establish the watershed area contributing run‐off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land‐use types and the size of the subwatersheds. The mid‐stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large‐scale farming with intense, well‐preserved riparian and in‐stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small‐scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid‐reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land‐use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near‐stream land uses. We suggest that conservation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem. 相似文献
107.
108.
关于建立纺织用染化料生态安全性评价体系的设想 总被引:2,自引:1,他引:1
从可持续发展战略和“绿色”、环保、生态等方面的需要提出关于建立纺织用染化料生态安全性评价体系的意义,并建议了列入安全性评价体系的项目及实施办法,同时也提出了需要解决的问题。 相似文献
109.
单壁纳米碳管/纳米铝基复合材料的增强效果 总被引:12,自引:0,他引:12
用半连续氢电弧法和活性氢等离子蒸发法分别制备出单壁纳米碳管(SWNTs)和纳米A1粉体,然后用提纯后的SWNTs和纳米A1粉体制备出SWNTs含量(质量分数)分别为0、2.5%、5.0%、7.5%和10.0%的单壁纳米碳管/纳米铝基块体复合材料.SWNTs对高强度纳米A1基体具有显著的增强作用,当SWNTs含量小于5.0%时,材料的硬度随着SWNTs含量的提高线性上升.其中5%SWNTs和纳米A1的复合增强效果最好,其硬度可达2.89GPa,大约是粗晶A1(0.15GPa)的20倍.当SWNTs含量超过5.0%时,增强效果开始缓慢的下降.讨论了单壁纳米碳管增强纳米铝基复合材料的强化机制. 相似文献
110.