全文获取类型
收费全文 | 1086篇 |
免费 | 129篇 |
国内免费 | 157篇 |
专业分类
化学 | 879篇 |
晶体学 | 13篇 |
力学 | 66篇 |
综合类 | 5篇 |
数学 | 28篇 |
物理学 | 381篇 |
出版年
2023年 | 12篇 |
2022年 | 33篇 |
2021年 | 36篇 |
2020年 | 40篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 56篇 |
2016年 | 37篇 |
2015年 | 47篇 |
2014年 | 52篇 |
2013年 | 79篇 |
2012年 | 64篇 |
2011年 | 56篇 |
2010年 | 42篇 |
2009年 | 59篇 |
2008年 | 79篇 |
2007年 | 68篇 |
2006年 | 70篇 |
2005年 | 51篇 |
2004年 | 41篇 |
2003年 | 45篇 |
2002年 | 34篇 |
2001年 | 37篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 24篇 |
1997年 | 27篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1977年 | 1篇 |
排序方式: 共有1372条查询结果,搜索用时 15 毫秒
871.
为了探讨移动床生物膜反应器中不同填料对废水脱氮除磷效果的影响,采用碳纤维球和聚乙烯塑料两种不同悬浮填料进行对比试验。在不同运行条件下,分别测定氨氮、总氮、总磷、COD等指标,对比挂膜和脱氮除磷效果。结果表明,碳纤维球填料挂膜速度快,在不同运行条件下均比聚乙烯塑料填料对COD、NH4+-N、TN、TP等的去除效果好,去除率分别可达91.2%、98.0%、77.5%、68.1%。这说明比表面积大、孔隙率高的填料挂膜更快,挂膜量更多,更有利于实现同时生物脱氮除磷。 相似文献
872.
873.
本文采用等体积浸渍制备了掺杂不同金属助剂改性的Ni基催化剂,考察了其催化浆态床CO甲烷化的性能。通过XRD、H2-TPR、HR-TEM等表征对催化剂进行了分析,结果表明,掺杂Zr、Co、Ce、Zn、La助剂促进了Ni物种在载体表面的分散,减小了Ni的晶粒尺寸,降低了催化剂的还原温度;掺杂Mg助剂则导致催化剂的还原温度升高。浆态床活性评价结果表明,掺杂Zr、Co、Ce、Zn、La助剂提高了催化剂的甲烷化性能,其中以La助剂的效果最明显,通过对La负载量进一步优化后发现,当La负载量为8%时,催化剂的甲烷化催化性能最优,CO转化率、CH4选择性和时空收率分别达到96.3%、87.1%和179.6 g·kg-1·h-1;掺杂Mg助剂则降低了催化剂的甲烷化活性。 相似文献
874.
3D Printed High‐Throughput Hydrothermal Reactionware for Discovery,Optimization, and Scale‐Up
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Philip J. Kitson Ross J. Marshall Dr. Deliang Long Dr. Ross S. Forgan Prof. Leroy Cronin 《Angewandte Chemie (International ed. in English)》2014,53(47):12723-12728
3D printing techniques allow the laboratory‐scale design and production of reactionware tailored to specific experimental requirements. To increase the range and versatility of reactionware devices, sealed, monolithic reactors suitable for use in hydrothermal synthesis have been digitally designed and realized. The fabrication process allows the introduction of reaction mixtures directly into the reactors during the production, and also enables the manufacture of devices of varying scales and geometries unavailable in traditional equipment. The utility of these devices is shown by the use of 3D printed, high‐throughput array reactors to discover two new coordination polymers, optimize the synthesis of one of these, and scale‐up its synthesis using larger reactors produced on the same 3D printer. Reactors were also used to produce phase‐pure samples of coordination polymers MIL‐96 and HKUST‐1, in yields comparable to synthesis in traditional apparatus. 相似文献
875.
《Comptes Rendus Chimie》2014,17(7-8):656-671
Kinetics has been proven to be a powerful method to probe catalytic surfaces under reaction conditions in order to elucidate, at molecular level, complex chemical processes. Numerous techniques and methodologies have been already implemented (surface science approaches, TAP, SSITKA…) running in very different pressure ranges (pressure gap) which led to controversial statements regarding suggested mechanism schemes, especially for DeNOx reactions. Two typical reactions taking place over NGV catalysts have been selected to illustrate which information can be tackled from kinetic measurements. Both reactions occur in different temperature ranges and are sensitive to the structure of the catalyst, to the surface composition of bimetallic particles, with possible surface enrichments, and to the participation of the support. Hence, it will be tentatively demonstrated that kinetic combined with spectroscopic or theoretical methods can be appropriate to establish relevant correlations between kinetic parameters and the topology of the catalyst surface. 相似文献
876.
《Comptes Rendus Chimie》2014,17(7-8):701-706
Storing renewable electricity in a natural gas grid is a new approach for seasonal storage. Using the existing natural gas infrastructure, a chemical energy source (methane) is stored efficiently, distributed and made available for use as required. Thus, the main step in the storage process is CO methanation. Modelling of an isothermal methanation catalytic reactor based on a kinetic scheme was carried out with Aspen plus™ software in a temperature range between 520 and 600 K and a H2/CO molar ratio of 3, in the presence of CO2 and steam. The model was validated by comparing simulation results with experimental ones. The maximum relative error is 10.87%. The effects of temperature, pressure and CO2 addition in feed gas (syngas) on CO conversion and the outlet gas composition were carefully investigated. 相似文献
877.
工业酸性气体是造成环境污染的最主要因素之一.本文围绕国家环保超低排放新要求,提出了超重力反应强化理论原理和新途径,利用超重力反应器数量级强化传质和超短停留时间优势,高选择性地从混合酸性气体中反应脱除SO2、H2S或CO2,实现了硫化物超低排放;提出了"科学实验+微观机理模型+宏观CFD模拟"三位一体的超重力反应器放大方法,实现了超重力反应器的工程放大,研制出国际规模最大的超重力反应器(转子直径3.5 m、外壳5 m,气体处理量20×104 m3/h)并投入产业化应用;该强化新技术现已在工业尾气脱SO2、石油炼厂气和海洋天然气脱H2S、电厂烟气脱CO2等环保工程中实现了工业应用和推广. 相似文献
878.
Application of microtube reactor for the continuous synthesis of biodiesel has been widely studied due to excellent performance in liquid-liquid phase reaction. In order to commercialize biodiesel production, integration of microtube reactor is highly recommended. Therefore, in this study, synthesis of biodiesel was carried out in capillary millichannel reactor with inner diameter of 1.59 mm using methanol and potassium hydroxide (KOH) as base catalyst with palm oil as a feedstock. The influences of reaction temperature, methanol to oil molar ratio, and KOH concentration on the production of fatty acid methyl ester (FAME) were examined. The highest FAME yield was achieved at 60 ˚C with 23:1 methanol to oil molar ratio and 5 wt% of KOH concentration. 相似文献
879.
Gasification uses steam increases H2 content in the syngas. Kinetics of gasification process can be improved by using K2CO3 catalyst. Controlled heating rate in pyrolysis step determines the pore size of charcoal that affects yield gas and H2 and CO content in the syngas. In previous research, pyrolisis step was performed without considering heating rate in pyrolysis step. This experiment was performed by catalytic steam gasification using lignite char from pyrolysis with controlled heating rate intended to produce maximum yield of syngas with mole ratio of H2/CO ≈ 2. Slow heating rate (3 °C/min) until 850 °C in the pyrolysis step has resulted in largest surface area of char. This study was performed by feeding Indonesian lignite char particles and K2CO3 catalyst into a fixed bed reactor with variation of steam/char mole ratio (2.2; 2.9; 4.0) and gasification temperature (750 °C, 825 °C, and 900 °C). Highest ratio of H2/CO (1.682) was obtained at 750 °C and steam/char ratio 2.2. Largest gas yield obtained from this study was 0.504 mol/g of char at 900 °C and steam/char ratio 2.9. Optimum condition for syngas production was at 750 °C and steam/char mole ratio 2.2 with gas yield 0.353 mol/g of char and H2/CO ratio 1.682. 相似文献
880.