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51.
Ti-substituted MCM-41 and Ti-grafted MCM-41 materials possessing both well-ordered long-range and pore structures have been used as catalysts for the hydroxylation of benzene in the liquid phase. The stability of the catalytic performance and the changes in the structural characteristics of Ti-modified MCM-41 resulting from the hydroxylation reaction have been investigated. It has been found that Ti-grafted MCM-41 exhibits better stability of catalytic performance than Ti-substituted MCM-41. For the Ti-substituted MCM-41, the migration of framework Ti into non-framework sites results in a decrease in the catalytic performance and the partial collapse of the pore structure. For the Ti-grafted MCM-41, the hydroxylation of benzene induces a smaller decrease in the pore volume and specific surface area than that observed for Ti-substituted MCM-41. 相似文献
52.
53.
采用电弧熔炼法熔炼Ni48Mn31Ga21和Ni50Mn255Ga25两种合金,并对这两种合金进行了热处理,借助交流磁化率测定、金相显微镜观察、X射线衍射等手段研究了热处理工艺条件对非化学计量比的Ni48Mn31Ga21合金马氏体相变和结构有序度的影响.结果表明(1)Ni48Mn31Ga21合金相变特征温度为Ms=305K,Mf=297K,As=313K,Af=318K,居里温度Tc=366K;(2)与空冷态相比,淬火态的马氏体转变量降低,经过400℃退火后,随着保温时间t的延长,马氏体转变量上升,当t=50h时达到最大值;(3)Ni48Mn31Ga21合金经过900℃×4d+400℃×50h热处理后,有序度明显提高. 相似文献
54.
Effect of inductively coupled plasma surface treatment on silica gel and mesoporous MCM-41 particles
J A JUAREZ-MORENO U CHACON-ARGAEZ J BARRON-ZAMBRANO C CARRERA-FIGUEIRAS P QUINTANA-OWEN W TALAVERA-PECH Y PEREZ-PADILLA A AVILA-ORTEGA 《等离子体科学和技术》2018,20(6):65506-113
Silica gel and MCM-41 synthesized mesoporous materials were treated with either oxygen (O2),hexamethyldisiloxane (HMDSO) and organic vapors like ethanol (EtOH),and acrylonitrile (AN) inductive plasma.The radiofrequency power for the modification was fixed to 120 W and 30 min,assuring a high degree of organic ionization energy in the plasma.The surface properties were studied by infrared spectroscopy (FTIR),scanning electron microscopy,x-ray photoelectron spectroscopy and dynamic light scattering technique was used for characterizing size distributions.When the silica and MCM-41 particles were modified by AN and HMDSO plasma gases,the surface morphology of the particles was changed,presenting another color,size or shape.In contrast,the treatments of oxygen and EtOH did not affect the surface morphology of both particles,but increased the oxygen content at the surface bigger than the AN and HMDSO plasma treatments.In this study,we investigated the influence of different plasma treatments on changes in morphology and the chemical composition of the modified particles which render them a possible new adsorbent for utilization in sorptive extraction techniques for polar compounds. 相似文献
55.
实验以MgO/MCM-22为催化剂,在气相连续流动固定床反应器上催化苯与草酸二乙酯(DEO)烷基化,合成乙苯(EB)。考察了MgO负载量变化和工艺条件的影响。以硝酸镁为前驱体通过等体积浸渍法制备了MgO/MCM-22催化剂,并以低温N_2吸附脱附、X射线衍射、NH_3-TPD、吡啶吸附IR等,对催化剂进行了表征。实验结果表明:随MgO负载量的增加,苯的转化率逐渐下降,而乙苯的选择性明显提高,这主要是由于负载MgO后催化剂的酸性位数量下降引起的。以MCM-22为催化剂,在最佳反应条件下:温度653 K,空速为2 h~(-1),原料配比n(苯):n(DEO)=4:1,苯的转化率为37.5%,乙苯选择性为80.3%。 相似文献
56.
Saori Umehara Masao Nomura Shin Okumura Toyohiko Yano Tadafumi Kishimoto 《Journal of Nuclear Science and Technology》2013,50(12):1473-1480
To develop the 48Ca enrichment process, a feasibility study on a band chromatography was made using 9 M HCl solution and crown ether resin synthesized in porous silica beads. Prior to the chromatographic experiments, distribution coefficients, Kd, of Ca2+ and Sr2+ were measured at different concentrations of these ionic species. The frontal boundary of the chromatography was made by a usual manner of the breakthrough mode of calcium feeding, and the rear boundary was made by introducing strontium as a following ion on the basis of the observed Kd values. It was confirmed that the heavy isotope 48Ca was depleted in the rear boundary region, while 48Ca was enriched in the front boundary region. The values of separation coefficient ε (= α – 1) in three chromatographic operations at different temperatures were observed as 2 × 10?3 ~ 3 × 10?3. The separation coefficients observed in the front boundary regions, where 48Ca was enriched, agreed with those observed in the rear boundary regions, where 40Ca was enriched. 相似文献
57.
采用二分掩膜技术向溅射沉积的(Co6Ag94)薄膜中组合注入Fe离子,制备成具有不同Fe含量的16单元Fe-(Co6Ag94)颗粒膜磁光芯片。对制备态和退火态的Fe-(Co6Ag94)颗粒膜的物相进行了XRD研究。不同退火温度下,物相的演变反映出了退火过程中Co、Fe相和FeCo相纳米微晶的析出长大过程。采用原子力显微镜(AFM)对薄膜表面的研究结果表明,在退火过程中形成了嵌于基底中的纳米颗粒相。对制备态和不同温度退火后芯片各单元的磁光性能进行了测量,结果表明极向Kerr旋转角晚随着注入Fe含量的增加而增大,这可归因于颗粒膜中铁磁相的增多。在500℃以下,随着退火温度的增加,Fe-(Co6Ag94)颗粒膜的克尔磁光效应增加。对不同温度退火的样品进行穆斯堡尔谱测量,结果证明一定尺寸纳米Fe微晶颗粒的出现是磁光效应提高的主要原因之一。 相似文献
58.
Cinchonidine and cinchonine have been grafted onto pure silica MCM-41. It has been shown that both supported alkaloids are active catalysts for the Michael addition of ethyl 2-oxocyclopentanecarboxylate and methyl vinyl ketone, anchored cinchonidine being more active and enantioselective than anchored cinchonine. The study of the influence of the polarity of the solvent and reaction temperature on the optical induction shows that there is not a direct correlation between solvent polarity and enantioselectivity, and the maximum optical yield was obtained between 278 and 273 K. 相似文献
59.
Both thermal and catalytic cracking of low-density polyethylene (LDPE) have been investigated using a screw kiln reactor. Thermal degradation gives rise to a broad product distribution, whereas catalytic cracking over Al-MCM-41 leads mainly to hydrocarbons within the gasoline range (C5–C12) with selectivities up to 80%. The increase of the screw speed between 3 and 15 rpm in the catalytic experiments allows the plastic feed rate to be varied in the range 20–41 g h−1. The changes observed in the TOF values when varying the screw speed point out a decrease of the activity per site with increasing residence times, which may be due to the catalyst deactivation or to a contribution of the degradative extrusion at higher screw speeds. Likewise, a certain increase in the selectivity towards the gasoline fraction is observed at short residence times. On the other hand, PIONA analyses indicate that, regardless of the screw speed, the main components of the gasoline are olefins (50%) and isoparaffins (20%), whereas the aromatic content is always below 6%, with a proportion of benzene lower than 0.1%. 相似文献
60.
Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41 总被引:1,自引:0,他引:1
Robert Mokaya William Jones Zhaohua Luan Maria D. Alba Jacek Klinowski 《Catalysis Letters》1996,37(1-2):113-120
The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity. 相似文献