全文获取类型
收费全文 | 10410篇 |
免费 | 1127篇 |
国内免费 | 382篇 |
专业分类
电工技术 | 164篇 |
综合类 | 606篇 |
化学工业 | 4800篇 |
金属工艺 | 547篇 |
机械仪表 | 117篇 |
建筑科学 | 206篇 |
矿业工程 | 412篇 |
能源动力 | 142篇 |
轻工业 | 2120篇 |
水利工程 | 35篇 |
石油天然气 | 443篇 |
武器工业 | 11篇 |
无线电 | 290篇 |
一般工业技术 | 1061篇 |
冶金工业 | 629篇 |
原子能技术 | 293篇 |
自动化技术 | 43篇 |
出版年
2024年 | 24篇 |
2023年 | 173篇 |
2022年 | 266篇 |
2021年 | 370篇 |
2020年 | 403篇 |
2019年 | 371篇 |
2018年 | 338篇 |
2017年 | 394篇 |
2016年 | 412篇 |
2015年 | 377篇 |
2014年 | 569篇 |
2013年 | 728篇 |
2012年 | 805篇 |
2011年 | 761篇 |
2010年 | 514篇 |
2009年 | 517篇 |
2008年 | 446篇 |
2007年 | 577篇 |
2006年 | 601篇 |
2005年 | 507篇 |
2004年 | 441篇 |
2003年 | 358篇 |
2002年 | 342篇 |
2001年 | 283篇 |
2000年 | 259篇 |
1999年 | 221篇 |
1998年 | 164篇 |
1997年 | 124篇 |
1996年 | 97篇 |
1995年 | 82篇 |
1994年 | 69篇 |
1993年 | 69篇 |
1992年 | 52篇 |
1991年 | 43篇 |
1990年 | 31篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1961年 | 1篇 |
1959年 | 4篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
61.
The use of activated carbon beds for the removal of natural humic and fulvic substances found in water supplies, has recently received considerable attention in water treatment operation (Lee et al., 1980; Le Cloirec et al., 1983). Moreover, the use of carbon adsorption for the reduction of haloform precursors (Anderson et al., 1981) and trihalomethanes produced by chlorination process, has contributed to a comprehensive investigation of adsorption characteristics of natural organic compounds (McCreary and Snoeyink, 1981). Many recent works showed the influence of adsorption system characteristics, such as pH, salt type, salt concentration and ionic heterogeneity in multicomponent adsorption systems, on the removal efficiency of humic and fulvic substances by activated carbon (McCreary and Snoeyink, 1980; Randtke and Jepsen, 1982; Weber et al., 1983). The purpose of this study is to examine the effect of a main component of domestic detergents, sodium triphosphate (STP), on the adsorptive capacities of powdered activated carbon (PAC) for commercially supplied humic acids, at different pH values in distilled water. Also, the effect of STP concentration and pH on the adsorption affinity of the PAC for humic acids, is discussed in relation with electrokinetic properties of carbon particles (zeta potential measurements).A first batch equilibrium study (Figs 1 and 2), showed an effective enhancement of adsorption capacity for humic acids as a function of STP concentration, in a non buffered media (pH of distilled water, close to 5.0). For example, visible absorption analysis of humic acids indicates an increase of 93% (500 mg l?1 PAC) and 133% (1000 mg l?1 PAC) in the carbon adsorption efficiency for a STP concentration from 0.2 to 1.0mM. A second batch equilibrium study (Figs 3 and 4) led to adsorption isotherms for humic acids in distilled water, as a function of STP concentration and initial pH value of the non buffered multicomponent system. Freundlich isotherms showed an increase in the adsorption capacity of the PAC for humic acids, with a decrease in pH and an increase in STP concentration. However, the adsorption capacity for humic acids is quite reduced at high pH values in presence of STP, in comparison with results obtained with distilled water.Electrokinetic measurements on PAC suspensions (Fig. 5) indicates that both humic acids and STP induce a negative variation of the zeta potential of carbon particles. In such a binary system, the zeta potential is a linear function of the pH; the negative surface charge of the carbon increasing with an elevation of pH (Fig. 6). Therefore, it appears that some adsorption of triphosphate polyanion from solution could occur, contributing then to the apparent negative surface charge of PAC particles.It has been previously showed that the type of anion in sodium salts, had little effect on the enhancement of adsorptive capacities of activated carbon for humic substances (Lafrance and Mazet, 1985), due to Na+ ions. However, adsorption of TP anions on the carbon surface may produce a source of repulsive charges, unfavourable to the co-adsorption of humic acids as the pH of the binary system reach more basic conditions. The influence of possible electrostatic interactions between adsorbates at the carbon surface, on the adsorption efficiency for humic acids, could then be studied by zeta potential measurements of PAC particles during the adsorption process. 相似文献
62.
63.
研制了海藻酸钠包埋壳聚糖凝胶小球和海藻酸钠/聚乙二醇4000复合包埋纳米过氧化钙缓释凝胶小球复配处理剂,考察其对水体中磷和有机物的去除效果及机理,采用X射线衍射、扫描电镜、元素能谱仪技术表征材料物化及形貌特征。该处理剂能够高效去除水中单一的磷和有机污染物,且对磷和甲基橙复合污染也具有较高的去除率;在实际河道水体中,该处理剂对高浓度的磷也具有较强的吸附能力,其缓慢释氧作用可保持水体溶解氧质量浓度在4.5 mg/L以上,为泥水界面处的好氧微生物提供了良好的好氧条件,可提高水体自净能力。 相似文献
64.
The effects of SO2 and SO3 in the environment on the hot corrosion behavior of Ni in the temperature range 750–950°C has been studied. Below the melting point of Na2SO4 (884°C), rapid corrosion takes place by formation of a Na2SO4-NiSO4 melt, which can penetrate the porous oxide scale and give rise to sulfide information by coming in contact with the metal. The distribution of the sulfides depends on the SO2 level in the ambient gas. Continued corrosion occurs by a sulfidation-oxidation mechanism. At temperatures above the melting point of Na2SO4, accelerated degradation occurs via dissolution of the surface scale, followed by reprecipitation of the oxide in a nonprotective form.Deceased 相似文献
65.
突发钠层(Sporadic Sodium Layer, NaS)是中高层大气金属层最为显著的一种现象,其发生机制目前尚无定论。突发E层(Sporadic E layer, ES)是等离子体密度异常增大的薄层,被认为与NaS密切相关。为进一步研究NaS及ES事件之间相关性及影响因素,利用中国科学院“子午工程”2010~2018年合肥科大站宽带钠荧光共振激光雷达观测结果,并结合武汉左岭镇站数字测高仪及九峰站大气电场仪数据,分析大气电场倒转(即北向电场)对NaS以及ES事件的影响。在统计的91例NaS事件中,发生于大气电场倒转时的比例为20/91; 同时,在发生NaS事件的事例中,ES消失或中断的比例较大(14/20),表明ES可能以提供钠源的形式转化为NaS。此外,在分析武汉左岭镇站数字测高仪数据的同时进行概率统计,结果表明:当大气电场倒转时,ES临界频率减小甚至消失的概率较大(187/242),少数情况下可能造成临界频率增大甚至激发ES生成(55/242); ES虚高消失比例为179/242,ES不变比例为27/242,ES上升比例为23/242。综上所述,大气北向电场在一定程度上对ES事件的发生有抑制作用,并对ES事件的发生高度有明显影响。最后,对一种与电场倒转相关的突发钠层机制也进行了讨论。 相似文献
66.
液相化学还原法制备不同形貌的多晶纳米镍 总被引:1,自引:0,他引:1
采用液相化学还原法,在1,2-丙二醇体系中,分别使用吐温-80(Tween-80)、聚乙二醇-6000(PEG-6000)和十二烷基硫酸钠(SDS)与聚乙二醇-6000(PEG-6000)的混合物作为修饰剂,利用1,2-丙二醇还原相同母体醋酸镍,制备形貌分别为海绵体、纤维状、雪花状的多晶纳米镍;在水体系中,使用SDS为修饰剂,利用水合肼还原相同母体醋酸镍,制备球形多晶纳米镍。通过X射线衍射(XRD)、透射电子显微镜(TEM)、选区电子衍射(SAED)对纳米镍进行表征。利用傅立叶红外(FTIR)分析初步解释不同形貌纳米镍的形成机理。 相似文献
67.
68.
研究了N,N?二甲基?二硫代甲酰胺丙磺酸钠(DPS)作为添加剂对以四羟丙基乙二胺(THPED)为单一配位剂的化学镀铜体系的沉积速率、镀层形貌和晶体结构的影响。结果发现,当DPS的质量浓度从0 mg/L增大到1.0 mg/L时,沉积速率从2.91μm/h提高到6.73μm/h,所得镀层结晶均匀、细致。线性扫描伏安测量结果表明,DPS是通过促进甲醛的阳极氧化来加速化学镀过程。本体系的Cu镀层主要呈面心立方多晶取向,DPS的添加会令晶面取向从(220)转变为(111)。 相似文献
69.
70.