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61.
Wujie Zhang Xiangjun Li Muhammad A. Nawaz Jiahao Pan Jiancheng Cao Dianhua Liu 《加拿大化工杂志》2020,98(5):1148-1156
Polyoxymethylene dimethyl ethers (PODEn) are extremely effective diesel additives to reduce soot formation during combustion. We introduce a series of Fe-Zn composite solid acid catalysts (SO42−/xFe2O3-yZnO), for the condensation reaction of methanol and paraformaldehyde (PF) with a cheap and feasible route to efficiently synthesize PODEn. These catalysts were characterized by different characterization techniques, namely BET, XRD, SEM, EDS, FTIR, and NH3-TPD and the results showed that Fe/Zn molar ratios strongly influenced the physicochemical characteristics of catalysts, thus affecting the methanol conversion and PODE1-6 and PODE3-6 selectivity. Accordingly, the methanol conversion was decreased and the selectivity of PODE3-6 was increased after increasing the Zn molar content. Comparatively, SO42−/Fe2O3-2ZnO exhibited superior catalytic activity among the various investigated catalysts due to the high acid density of strong acid sites. The optimal reaction conditions were observed to be at a 3.0 wt% catalyst loading (catalyst/reactant mass ratio), 2.5 hours ours of reaction time, a reaction temperature of 403 K, and a molar ratio of 3:1 of CH2O to methanol, achieving a high selectivity of 99.09% PODE1-6 and 28.23% PODE3-6 with 55.16% methanol conversion during the reaction. 相似文献
62.
《International Journal of Hydrogen Energy》2020,45(43):23056-23068
A series of monometallic and bimetallic palladium gold catalyst were prepared and studied for the formic acid dehydrogenation reaction. Different Pd/Au compositions were employed (PdxAu100-x, where x = 25; 50 and 75) and their impact on alloy structure, particle size and dispersion was evaluated. Active phase composition and reaction parameters such as temperature, formic acid concentration or formate/formic acid ratio were adjusted to obtain active and selective catalyst for hydrogen production. An important particle size effect was observed and related to Pd/Au composition for all bimetallic catalysts. 相似文献
63.
《International Journal of Hydrogen Energy》2020,45(16):9624-9634
Decomposition of formic acid biomass to generate hydrogen is vital for coping with fossil energy depletion, environmental pollution, and developing clean, efficient, safe, and sustainable modern energy system. In this study, a PdAu/C−C bimetallic catalyst was prepared by the co-impregnation method followed by an atmospheric pressure (AP) cold plasma treatment to synthesize PdAu/C−P catalysts. The resulting PdAu/C−P showed excellent catalytic activity for the formic acid dehydrogenation (FAD) reaction. The total volume of H2 and CO2 released from the FAD reaction was about 375 mL after 4 h at 50 °C, and the initial turnover frequency (TOFinitial) was 808.6 h−1. We used X−ray diffractometry (XRD), temperature programmed reduction (TPR) and high-resolution transmission electron microscopy (HRTEM) to show that plasma can effectively promote the redispersion of Pd−Au particles on the surface of the support. The average particle size of PdAu/C−P (3.5 ± 1.5 nm) was less than PdAu/C−C (4.4 ± 1.9 nm) and uniformly distributed. X-ray photoelectron spectroscopy (XPS), TPR, and HRTEM showed that PdAu/C−P has a higher degree of alloying. In addition, the strong electric field in the plasma facilitated more metal sites located on the outer surface of the support in PdAu/C−P, and the atomic ratio of M/C (M = Pd and Au) (0.0134) was much larger than that of PdAu/C−C (0.0060). The apparent activation energy (Ea) of PdAu/C−P for the FAD reaction was only 27.25 kJ mol−1, and it had much higher activity and stability than the commercial Pd/C (Sigma−Aldrich). The total volume of H2 and CO2 produced over the PdAu/C−P for three cycles was 1.33, 5.87, and 8.56 times that of commercial Pd/C. Overall, the cold plasma enhanced the degree of alloying, promoted the redispersion of agglomerated particles, and regulated the surface enrichment of the active metal components. This is of great significance for guiding the preparation of high−performance multi-metal catalysts by cold plasma. 相似文献
64.
65.
Studies on the extraction and separation of vanadium(V) from mixed hydrochloric acid/ammonium thiocyanate solution with CYANEX 921 and CYANEX 925 in kerosene were carried out. The effects of various factors affecting the extraction process as well as temperature were investigated. Addition of thiocyanate to the chloride solution was found to enhance markedly the extraction of vanadium. HCl solution efficiently stripped V(V). The number of stages required for extraction and stripping of vanadium ions was determined from the McCabe–Thiele diagram. Based on the obtained results, the separation of V(V) from spent catalyst leach indicates the efficiency of the proposed process. 相似文献
66.
A systematic research about the liquefaction of alkali lignin in supercritical ethanol using ZSM‐5 zeolite catalysts is reported, which includes the synergistic effect of temperature, catalytic content, and reaction time on product yield and distribution. Fourier transform infrared and gas chromatography‐mass spectrometry analysis were carried out to evaluate the compositions of bio‐oil and solid residue. Under moderate condition, maximum conversion and yield of bio‐oil were satisfactorily high. With the help of ZSM‐5 catalyst, lignin could be successfully converted into aromatic compounds. 相似文献
67.
Effect of Different Cosolvents on Transesterification of Waste Cooking Oil in a Microreactor 下载免费PDF全文
Biodiesel was prepared from waste cooking oil combined with methanol. The process was performed via transesterification in a microreactor using kettle limescale as a heterogeneous catalyst and various cosolvents under different conditions. n‐Hexane and tetrahydrofuran were selected as cosolvents to investigate fatty acid methyl esters (FAMEs). To optimize the reaction conditions, the main parameters affecting FAME% including reaction temperature, catalyst concentration, oil‐to‐methanol volumetric ratio, and cosolvent‐to‐methanol volumetric ratio were studied via response surface methodology. Under optimal reaction conditions and in the presence of the cosolvents n‐hexane and tetrahydrofuran, high FAME purities were achieved. Considering the experimental results, the limescale catalyst is a unique material, and the cosolvent method can reduce significantly the reaction time and biodiesel production cost. 相似文献
68.
二氧化碳(CO2)加氢制甲醇对于解决CO2排放和能源紧缺问题具有重要意义,催化剂的研究是这项技术的关键。铜基催化剂因高效廉价而被广泛研究,但目前的生产效率离实现工业化仍有距离。本文针对铜基催化剂,首先探讨了活性中心的存在形式,然后从活性组分负载量、载体、助剂、制备方法及条件、预处理条件这5个方面,分别分析其对催化剂的活性、选择性以及稳定性等的影响,以期为CO2高值转化为甲醇的铜基催化剂的制备和筛选提供参考。按照广泛接受的双位点机理可知,CO2转化率与铜表面积密切相关,甲醇选择性与强碱位点含量密切相关。因此,各方面因素通过影响催化剂比表面积、铜表面积、铜分散度、碱性位点、铜与载体的协同作用等物理化学参数,进而影响CO2转化率与甲醇选择性。 相似文献
69.
利用小型固定床实验台实验研究了铁氧化物在典型流化床温度和CO还原性气氛下的形态迁移及其生成物对NO的催化还原作用,采用分级还原结合X射线衍射(XRD)表征分析,确定铁氧化物与CO和NO反应后生成物的价态及各种铁氧化物对NO的还原机制。结果表明,Fe2O3在实验条件下可依次被CO还原为Fe3O4、FeO和单质铁,反应过程中随着还原度的增加,还原速率逐级下降,从Fe2O3还原到Fe3O4的速率最高,FeO还原到Fe速率最低,在实验温度范围内,床温升高有利于提高Fe2O3到Fe3O4的还原速率和还原度。不同形态的铁氧化物对NO的催化还原特性不同,Fe2O3及其部分还原后生成的Fe3O4都不能直接与NO反应,Fe2O3对CO催化还原NO的效果很弱,而Fe3O4对CO还原NO的反应却有很强的催化作用,而进一步还原生成FeO与单质铁还可直接与NO反应。 相似文献
70.
以硫酸改性后的硅藻土为载体,Keggin结构磷钨酸为活性组分,通过浸渍法制备出负载型催化剂H3PW12O40/改性硅藻土,并对催化剂进行傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电镜(SEM)、X射线能谱(EDS)和N2-程序升温脱附(N2-TPD)表征。结果表明:酸改性后硅藻土的微孔增大增多,比表面积增大。H3PW12O40均匀分布在改性硅藻土载体上,负载后磷钨酸仍保持Keggin结构。以H3PW12O40/改性硅藻土为催化剂催化乙酸和正丁醇液相合成乙酸正丁酯,通过正交试验探索优化工艺条件。在较优工艺条件下,即w(40%H3PW12O40/改性硅藻土)=1.1%(基于反应物质量),n(酸)∶n(醇)=1∶3,125℃反应2.0h,酯化率高达98.1%。催化剂重复催化使用5次,酯化率仍可达86.1%。H3PW12O40/改性硅藻土可作为催化合成乙酸正丁酯的高效催化剂,具有活性高、用量少、价格低廉、制备简单、后处理简便、无废液排放等优点。 相似文献