全文获取类型
收费全文 | 1803篇 |
免费 | 178篇 |
国内免费 | 616篇 |
专业分类
化学 | 2022篇 |
晶体学 | 9篇 |
力学 | 102篇 |
综合类 | 15篇 |
数学 | 40篇 |
物理学 | 409篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 94篇 |
2021年 | 75篇 |
2020年 | 109篇 |
2019年 | 99篇 |
2018年 | 86篇 |
2017年 | 92篇 |
2016年 | 100篇 |
2015年 | 96篇 |
2014年 | 132篇 |
2013年 | 166篇 |
2012年 | 134篇 |
2011年 | 191篇 |
2010年 | 114篇 |
2009年 | 160篇 |
2008年 | 145篇 |
2007年 | 154篇 |
2006年 | 122篇 |
2005年 | 112篇 |
2004年 | 91篇 |
2003年 | 78篇 |
2002年 | 41篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2597条查询结果,搜索用时 15 毫秒
921.
Huayang Zhu Robert J. Kee Longhua Chen Jingjing Cao Min Xu Yuyin Zhang 《Combustion Theory and Modelling》2013,17(4):715-735
A computational model is developed and applied to study the vaporisation behaviour of three liquid fuels. This fundamental study is motivated by a need to understand how the performance of direct-injection-spark-ignition (DISI) engines may be affected by changes in fuel composition, especially alcohols. Currently, most DISI engines are designed for homogeneous-charge combustion, where the in-cylinder fuel injection, vaporisation and mixing is accomplished during the intake and early in the compression process. Thus the temperature and pressure are low, compared to post-compression conditions. The two-phase axisymmetric model is based upon an ideal opposed stagnation flow field. Liquid droplets are carried in one air stream that is met by an opposed air flow. Because of stagnation-flow similarity, the mathematical model can be represented as a one-dimensional boundary-value problem. Results show significant differences between methanol, ethanol and heptane fuels, which have potentially important impacts on the design and modification of fuel-injection systems for direct-injection engines with alternative fuels. 相似文献
922.
Sema ASLAN 《Turkish Journal of Chemistry》2021,45(3):661
Electrocatalytic effect of the untreated and TiO2+polyacrylonitrile (PAN) modified discarded battery coal (DBC) and pencil graphite electrodes (PGE) were evaluated in fuel cell (FC) applications. TiO2+PAN solution is coated on PGE and DBC electrodes by electrospinning. According to the FESEM and EDS characterizations, TiO2 and PAN nanofibers are found to be approximately 40 and 240 nm in size. TiO2+PAN/PGE showed the best FC performances with 2.00 A cm–2 current density and 5.05 W cm–2 power density values, whereas TiO2+PAN/DBC showed 0.68 A cm–2 current density and 0.62 W cm–2 power density values. Electrochemical characterizations of PGE and TiO2+PAN/PGE electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Finally, long-term FC measurement results of developed electrodes exhibited very reasonable recovery values. Along with the comparison of the electrode performances, the recovery of DBCs as electrodes for renewable energy production has been achieved. 相似文献
923.
RuxCoySez纳米簇合物对阴极氧还原反应的催化性能 总被引:1,自引:0,他引:1
以Ru3(CO)12、Co4(CO)12和Se为原料,采用低温回流技术在1,6-己二醇中合成了RuxCoySez纳米簇合物.利用SEM和XRD测试表征了催化剂的微观形貌和相结构,催化剂粉末以六方结构的Rux簇为主相,同时形成无定形相,呈现高度均匀聚集的纳米颗粒.利用旋转圆盘电极研究了催化剂对氧还原反应电催化活性.在0.5molL-1H2SO4溶液中,RuxCoySez催化剂对氧还原的催化活性和电化学稳定性明显高于RuxSey,开路电位达到0.91V(vs.NHE). 相似文献
924.
ZHAO Hui LI Qiang & SUN LiPing Key Laboratory of Functional Inorganic Material Chemistry Ministry of Education School of Chemistry Materials Science Heilongjiang University Harbin China 《中国科学B辑(英文版)》2011,(6)
One of the major challenges to develop intermediate temperature solid oxide fuel cells is finding a novel cathode material, which can meet the following requirements: (1) high electronic conductivity; (2) chemical compatibility with the electrolyte; (3) a matched thermal expansion coefficient (TEC); (4) stability in a wide range of oxygen partial pressure; and (5) high catalytic activity for the oxygen reduction reaction (ORR). In this short review, a survey of these requirements for K2NiF4-type material wi... 相似文献
925.
Polypropylene was cracked thermally and catalytically in the presence of kaoline and silica alumina in a semi batch reactor in the temperature range 400℃~550℃ in order to obtain suitable liquid fuels.The dependencies between process temperatures,types of catalyst,feed compositions and product yields of the obtained fuel fractions were found.It was observed that up to 450℃ thermal cracking temperature,the major product of pyrolysis was liquid oil and the major product at other higher temperatures(475℃~550℃) ... 相似文献
926.
927.
928.
929.
用电化学还原法在炭布上电沉积铂-氢钨青铜复合催化剂作为质子交换膜燃料电池(PEMFC)阳极。 利用X射线衍射、扫描电子显微镜、单电池极化性能测试以及电化学阻抗谱(EIS)法研究了催化剂的组成、分散性及其对氢氧化的电催化性能。 实验结果表明,阴极还原顺序对催化剂的形貌及分散有较大的影响。 采用分步还原法制备的HxWO3/Pt电极(先沉积铂,后沉积氢钨青铜)对氢氧化具有较高的催化活性,氢钨青铜与铂形成协同催化效应,提高了铂对氢氧化的催化活性。 而共沉积制备的Pt-HxWO3催化剂的电催化活性较差,这是因为共沉积过程中,由于受到2种电解液共存的影响,电极催化层中没有或较少得到氢钨青铜,且铂催化剂出现明显的团聚现象。 相似文献
930.
同步脱氮除硫工艺以硝态氮作为电子受体,硫化物作为电子供体,通过以废治废,去除氮硫污染物。本文构建了双室型微生物燃料电池(microbial fuel cell,MFC),将同步脱氮除硫工艺与MFC相结合,在处理废水的同时生产电能。与化学对照组相比,该同步脱氮除硫MFC具有高基质去除性能和产电性能。当进水硝态氮和硫化物的浓度分别为95.54和540 mg·L-1,反应时间为20 h时,硝态氮和硫化物的去除率分别高达96.50%和99.64%;最大电流密度达457.20 mA·m-2,稳定电流密度为30.33 mA·m-2。通过循环伏安法、极化曲线法和电化学阻抗分析,探究了同步脱氮除硫MFC的电化学特性。结果表明,在同步脱氮除硫MFC电极上,同步发生了脱氮除硫反应,该MFC最大功率密度为75.70 mW·m-3,内阻约为2 474 Ω,其对同步脱氮除硫MFC电化学性能具有制约作用。 相似文献