全文获取类型
收费全文 | 1317篇 |
免费 | 111篇 |
国内免费 | 84篇 |
专业分类
电工技术 | 15篇 |
综合类 | 47篇 |
化学工业 | 799篇 |
金属工艺 | 86篇 |
机械仪表 | 32篇 |
建筑科学 | 17篇 |
矿业工程 | 27篇 |
能源动力 | 16篇 |
轻工业 | 159篇 |
水利工程 | 2篇 |
石油天然气 | 43篇 |
武器工业 | 13篇 |
无线电 | 23篇 |
一般工业技术 | 83篇 |
冶金工业 | 72篇 |
原子能技术 | 69篇 |
自动化技术 | 9篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 91篇 |
2021年 | 94篇 |
2020年 | 37篇 |
2019年 | 48篇 |
2018年 | 37篇 |
2017年 | 41篇 |
2016年 | 45篇 |
2015年 | 43篇 |
2014年 | 87篇 |
2013年 | 127篇 |
2012年 | 78篇 |
2011年 | 75篇 |
2010年 | 47篇 |
2009年 | 51篇 |
2008年 | 48篇 |
2007年 | 71篇 |
2006年 | 63篇 |
2005年 | 58篇 |
2004年 | 55篇 |
2003年 | 49篇 |
2002年 | 44篇 |
2001年 | 38篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 22篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有1512条查询结果,搜索用时 0 毫秒
1.
2.
Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts 总被引:1,自引:0,他引:1
S. Stegenga R. van Soest F. Kapteijn J. A. Moulijn 《Applied catalysis. B, Environmental》1993,2(4):257-275
Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed. 相似文献
3.
Zakaria Chajar Michel Primet Hélène Praliaud Michèle Chevrier Catherine Gauthier Frédéric Mathis 《Catalysis Letters》1994,28(1):33-40
The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO2 and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C3H8 does not differ significantly from that of NO2. In the absence of oxygen, the reduction of NO2 by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO2 formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process. 相似文献
4.
Francisco J. Corpas Salvador Gonzlez-Gordo Jos M. Palma 《International journal of molecular sciences》2021,22(5)
The peroxisome is a single-membrane subcellular compartment present in almost all eukaryotic cells from simple protists and fungi to complex organisms such as higher plants and animals. Historically, the name of the peroxisome came from a subcellular structure that contained high levels of hydrogen peroxide (H2O2) and the antioxidant enzyme catalase, which indicated that this organelle had basically an oxidative metabolism. During the last 20 years, it has been shown that plant peroxisomes also contain nitric oxide (NO), a radical molecule than leads to a family of derived molecules designated as reactive nitrogen species (RNS). These reactive species can mediate post-translational modifications (PTMs) of proteins, such as S-nitrosation and tyrosine nitration, thus affecting their function. This review aims to provide a comprehensive overview of how NO could affect peroxisomal metabolism and its internal protein-protein interactions (PPIs). Remarkably, many of the identified NO-target proteins in plant peroxisomes are involved in the metabolism of reactive oxygen species (ROS), either in its generation or its scavenging. Therefore, it is proposed that NO is a molecule with signaling properties with the capacity to modulate the peroxisomal protein-protein network and consequently the peroxisomal functions, especially under adverse environmental conditions. 相似文献
5.
María Jos García Carlos Lucena Francisco Javier Romera 《International journal of molecular sciences》2021,22(9)
Iron (Fe) and phosphorus (P) are two essential elements for plant growth. Both elements are abundant in soils but with poor availability for plants, which favor their acquisition by developing morphological and physiological responses in their roots. Although the regulation of the genes related to these responses is not totally known, ethylene (ET) and nitric oxide (NO) have been involved in the activation of both Fe-related and P-related genes. The common involvement of ET and NO suggests that they must act in conjunction with other specific signals, more closely related to each deficiency. Among the specific signals involved in the regulation of Fe- or P-related genes have been proposed Fe-peptides (or Fe ion itself) and microRNAs, like miR399 (P), moving through the phloem. These Fe- or P-related phloem signals could interact with ET/NO and confer specificity to the responses to each deficiency, avoiding the induction of the specific responses when ET/NO increase due to other nutrient deficiencies or stresses. Besides the specificity conferred by these signals, ET itself could confer specificity to the responses to Fe- or P-deficiency by acting through different signaling pathways in each case. Given the above considerations, there are preliminary results suggesting that ET could regulate different nutrient responses by acting both in conjunction with other signals and through different signaling pathways. Because of the close relationship among these two elements, a better knowledge of the physiological and molecular basis of their interaction is necessary to improve their nutrition and to avoid the problems associated with their misuse. As examples of this interaction, it is known that Fe chlorosis can be induced, under certain circumstances, by a P over- fertilization. On the other hand, Fe oxides can have a role in the immobilization of P in soils. Qualitative and quantitative assessment of the dynamic of known Fe- and P-related genes expression, selected ad hoc and involved in each of these deficiencies, would allow us to get a profound knowledge of the processes that regulate the responses to both deficiencies. The better knowledge of the regulation by ET of the responses to these deficiencies is necessary to properly understand the interactions between Fe and P. This will allow the obtention of more efficient varieties in the absorption of P and Fe, and the use of more rational management techniques for P and Fe fertilization. This will contribute to minimize the environmental impacts caused by the use of P and Fe fertilizers (Fe chelates) in agriculture and to adjust the costs for farmers, due to the high prices and/or scarcity of Fe and P fertilizers. This review aims to summarize the latest advances in the knowledge about Fe and P deficiency responses, analyzing the similarities and differences among them and considering the interactions among their main regulators, including some hormones (ethylene) and signaling substances (NO and GSNO) as well as other P- and Fe-related signals. 相似文献
6.
简要介绍淮化集团浓硝酸生产工艺,通过对热发烟硝酸生产的关键设备高压釜的进料管,筛板的改造,增加氧气压力,提高N2O4纯度等工艺调整,使高压釜的生产能力由原设计的12.8t热酸/h增加到38.6t热酸/h。 相似文献
7.
8.
考察了Pd/Al2O3、In/Al2O3和Co/Al2O3对甲烷选择性还原NO的催化活性。结果表明,采用浸渍法制备的Pd/Al2O3、In/Al2O3和Co/Al2O3三种催化剂,在有氧气氛下,用CH4作还原剂催化还原NO时,Pd/Al2O3催化剂的活性最佳,热稳定性好,在550 ℃,用CH4选择还原NO,Pd/Al2O3催化剂表现出较强的催化能力,NO的转化率达到100%。在高空速实验中,该催化剂亦表现出较高的活性,其活性顺序为Pd/Al2O3>In/Al2O3>Co/Al2O3。实验研究了助催化剂、氧含量以及空速对Pd/Al2O3催化剂活性的影响。 相似文献
9.
Hydrochloric and nitric acid treated apatite is not directly used as a fertilizer because of the hygroscopic character of the products. Another problem arises from the volatility of these acids and that acidulated product undergo reversions during drying with loss of the acid. We have found that apatite beneficiated with hydrochloric and nitric acids dried at an optimum temperature ~120°C has high available phosphorous. The products can be stored in the solid form in sealed polythene bags.Sumanasekara Chair in Natural Science 相似文献
10.