全文获取类型
收费全文 | 5092篇 |
免费 | 319篇 |
国内免费 | 153篇 |
专业分类
电工技术 | 363篇 |
技术理论 | 1篇 |
综合类 | 397篇 |
化学工业 | 758篇 |
金属工艺 | 355篇 |
机械仪表 | 606篇 |
建筑科学 | 491篇 |
矿业工程 | 123篇 |
能源动力 | 858篇 |
轻工业 | 91篇 |
水利工程 | 41篇 |
石油天然气 | 226篇 |
武器工业 | 54篇 |
无线电 | 158篇 |
一般工业技术 | 472篇 |
冶金工业 | 256篇 |
原子能技术 | 72篇 |
自动化技术 | 242篇 |
出版年
2024年 | 11篇 |
2023年 | 35篇 |
2022年 | 92篇 |
2021年 | 139篇 |
2020年 | 158篇 |
2019年 | 91篇 |
2018年 | 98篇 |
2017年 | 91篇 |
2016年 | 129篇 |
2015年 | 129篇 |
2014年 | 319篇 |
2013年 | 317篇 |
2012年 | 354篇 |
2011年 | 389篇 |
2010年 | 292篇 |
2009年 | 291篇 |
2008年 | 228篇 |
2007年 | 348篇 |
2006年 | 303篇 |
2005年 | 282篇 |
2004年 | 230篇 |
2003年 | 214篇 |
2002年 | 180篇 |
2001年 | 160篇 |
2000年 | 135篇 |
1999年 | 94篇 |
1998年 | 85篇 |
1997年 | 87篇 |
1996年 | 65篇 |
1995年 | 46篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 21篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有5564条查询结果,搜索用时 0 毫秒
1.
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
2.
Tatsuya Hanaoka Hisashi Ishitani Ryuji Matsuhashi Yoshikuni Yoshida 《Applied Energy》2002,72(3-4):705-721
The objective of this study is to evaluate the potential for recovering fluorocarbons as measures for the abatement of global warming. In this study, we focused on the three different kinds of fluorocarbons: CFCs, HCFCs and HFCs, and targeted refrigerant use because of the availability of relevant data. We first estimated future fluorocarbon emissions from the targeted appliances; we next compared those emissions in the units of CO2 equivalent to the level of CO2 emissions in 1990 from a quantitative point of view. As the result of this study, it was found that fluorocarbon emissions in 1999 and 2010 would be equal to approximately 7 and 3% of the level of CO2 emissions in 1990 respectively. Moreover, if we implement a 100% recovery rate in every recovery route, we can reduce a large amount of emissions which correspond to approximately 2–5% of the level of CO2 emissions in 1990, even if we take into account the energy-related CO2 emissions by the transportation and decomposition of fluorocarbons. 相似文献
3.
A nuclear microprobe with high spatial resolution and high analytical sensitivity was applied to analyze trace elements,especially lead,in vehicle exhaust of Shanghai city.The result shows that the chemical composition and its corresponding x-ray relative intensity are different among different vehicle exhausts.There are many kinds of metal elements in particles of vehicle exhaust.most are harmful to people,such as Ti,Cr,Mn,Pb,etc.We found that the lead concentration was 6820μg/g and the bromine concentration was 5300μg/g in the exhaust from Santana using leaded gasoline(SULG).which is higher than any other kinds of vehicle exhausts.We have also detected the minimum lead in the particles of unleaded gasoline and its content varies from one to another.Its mean concentration was 450μg/g and the highest reached 6210μg/g.The unleaded gasoline‘s Pb existed in the whole particle while the leaded gasoline‘s enriched in the surface of the particle and was more harmful to the human beings. 相似文献
4.
5.
6.
The behavior of an ultrasonic shot peening process is observed and analyzed by using a model of inelastic hard spheres in a gravitational field that are fluidized by a vibrating bottom wall (sonotrode) in a cylindrical chamber. A marked heterogeneous distribution of impacts appears when the collision between the shot and the side wall becomes inelastic with constant dissipation. This effect is one order of magnitude larger than the simple heterogeneity arising from boundary collision on the cylinder. Variable restitution coefficients bring the simulation closer to the general observation and allow the investigation of peening regimes with changing shot density. We compute within this model other physical quantities (impact velocities, impact angle, temperature and density profile) that are influenced by the number N of spheres. 相似文献
7.
8.
住宅厨房共用排烟系统性能比较 总被引:3,自引:1,他引:2
介绍了当地住宅厨房通风设计的发展简况,比较了两种房共用排烟系统的构造,尺寸,性能,造价及能耗,对厨房通风设计和施工提出了建议。 相似文献
9.
Modeling mercury speciation is an important requirement for estimating harmful emissions from coal-fired power plants and developing strategies to reduce them. First-principle models based on chemical, kinetic, and thermodynamic aspects exist, but these are complex and difficult to develop. The use of modern data-based machine learning techniques has been recently introduced, including neural networks. Here we propose an alternative approach using abductive networks based on the group method of data handling (GMDH) algorithm, with the advantages of simplified and more automated model synthesis, automatic selection of significant inputs, and more transparent input–output model relationships. Models were developed for predicting three types of mercury speciation (elemental, oxidized, and particulate) using a small dataset containing six inputs parameters on the composition of the coal used and boiler operating conditions. Prediction performance compares favourably with neural network models developed using the same dataset, with correlation coefficients as high as 0.97 for training data. Network committees (ensembles) are proposed as a means of improving prediction accuracy, and suggestions are made for future work to further improve performance. 相似文献
10.
作为汽车重要组成部分的发动机 ,一直是人们研究的重点。汽车发动机性能的提高 ,在很大程度上依赖于材料的选用和加工工艺等因素。本文介绍了现代汽车发动机主要零部件新材料选用、结构设计及工艺现状 ,指出了未来汽车发动机新材料的发展趋势和应用前景 相似文献