首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5624篇
  免费   84篇
  国内免费   49篇
电工技术   6篇
综合类   155篇
化学工业   2990篇
金属工艺   103篇
机械仪表   43篇
建筑科学   302篇
矿业工程   205篇
能源动力   351篇
轻工业   164篇
水利工程   29篇
石油天然气   183篇
武器工业   3篇
无线电   44篇
一般工业技术   884篇
冶金工业   163篇
原子能技术   62篇
自动化技术   70篇
  2023年   40篇
  2022年   97篇
  2021年   143篇
  2020年   152篇
  2019年   145篇
  2018年   120篇
  2017年   144篇
  2016年   152篇
  2015年   111篇
  2014年   244篇
  2013年   335篇
  2012年   252篇
  2011年   347篇
  2010年   234篇
  2009年   417篇
  2008年   369篇
  2007年   319篇
  2006年   382篇
  2005年   314篇
  2004年   304篇
  2003年   269篇
  2002年   206篇
  2001年   96篇
  2000年   67篇
  1999年   68篇
  1998年   45篇
  1997年   36篇
  1996年   43篇
  1995年   40篇
  1994年   33篇
  1993年   35篇
  1992年   33篇
  1991年   22篇
  1990年   16篇
  1989年   11篇
  1988年   27篇
  1987年   23篇
  1986年   13篇
  1985年   7篇
  1984年   13篇
  1983年   12篇
  1982年   6篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   2篇
  1975年   2篇
  1974年   6篇
排序方式: 共有5757条查询结果,搜索用时 16 毫秒
1.
Adsorbents and membranes consisting of carbon nanotube (CNT) pores with diameters of molecular dimensions are highly desirable for hydrogen storage and selective, high-flux membrane separation. However, fabrication of such materials with precise pore sizes and monodispersity as well as evaluation of the mechanisms associated to adsorption and molecular transport are challenging. Herein, we grew aluminophsphate zeolites (CoAPO-5, AFI crystal structure) consisting of one-dimensional, monodisperse parallel pores with diameter of ~7 Å, and utilized them as templates to grow singe-walled CNTs (SWNTs) inside the pores. The resulting materials were examined as adsorbents and membranes for hydrogen storage and separation, respectively, using single-gas and real mixture feeds. Detailed mechanistic analysis and fundamental investigation of permeance and adsorption behavior of the resulting CNT-in-zeolite systems via combined adsorption, equilibrium, and kinetic studies were carried out. A superior gravimetric hydrogen uptake of 1.2 wt% at 35 °C and 1 bar was achieved in the case of the SWNTs grown in the cobalt-richer AFI host. Permeability measurements were performed on the respective Co(x)APO@SWNT membranes with the Co-richAPO@SWNT membrane exhibiting the highest permeance for all studied gases as a consequence of larger and more densely packed AFI crystals along with higher number of SWNT-filled pores, assets attributed to the higher Co catalyst content. Notably, the produced composite membranes exhibited gas permeability values that were two orders of magnitude higher than what predicted by the Knudsen mechanism.  相似文献   
2.
《Ceramics International》2022,48(21):31695-31704
In this study, ceramic membranes made of montmorillonite, perlite and iron were used to remove As(III) from water. Membranes prepared with 0.0, 0.5, 1.0, and 1.5 wt% of iron content were used to filtrate As(III) synthetic water and surface water solutions. As(III) adsorption capacity and removal efficiency, and other parameters such as cations and anions content, turbidity, pH, electrical conductivity were used to evaluate the membranes' performance. Results show that the As(III) adsorption/removal capacity of membranes was improved by the addition of iron. Adsorption capacity of 7.5 μg As(III)/g and removal efficiency of 97% can be achieved in membranes with 1.0 wt% of iron filings content for surface water; however, a greater amount of iron in the membrane structure limits the adsorption capacity of As(III). Besides the capacity of ceramic membranes to adsorb/remove As(III), membranes were also effective to remove other ions, turbidity, and electrical conductivity from the surface water. The addition of iron to the ceramic membranes enhanced their capacity to remove such surface water constituents. These results are important from the practical viewpoint showing the potential of ceramic membranes for the removal of metalloids and other water constituents. Langmuir isotherm model best described the adsorption process in ceramic membranes, suggesting that adsorption of As(III) happened on a monolayered surface of the ceramic membrane.  相似文献   
3.
In the present study, hexagonal boron nitride (h-BN) was synthesized from boric acid and melamine by thermal annealing method in a nitrogen atmosphere. The pure h-BN was used as an efficient sorbent for the uptake of Cd2+ ions from the solution phase. The kinetics and sorption studies of metal ions onto the h-BN were carried out in batch adsorption experiments at different temperature, time, pH, sorbent dosage, and concentration of metal ions. The optimum pH for the removal of the Cd2+ ions was found to be pH 7. The effect of temperature showed that the process of Cd2+ sorption remained endothermic in the range of 298 K–328 K. The Lagergren's first and Ho's second kinetic models were tested to interpret the adsorption kinetic data, however the present data was explained well by Ho's model for kinetics. The thermodynamic perameters ΔG, ΔS and ΔH were determined using the available adsorption data at different temperatures. The physicochemical properties of the synthesized product were also characterized before and after adsorption by different analytical techniques like FT-IR, TGA, XRD and Point of Zero Charge (PZC). The morphology of the surface was analyzed with the help of Scanning Electron Microscopy. The h-BN proved to be an efficient adsorbent for the uptake of the Cd2+ ions from aqueous media.  相似文献   
4.
Silica gel or zeolites AlPO-5 and SAPO-34 are recommended as adsorbents in water-driven heat pumps because of their selective water uptake. Secondary energy, like solar energy, can be used for regeneration of loaded adsorbers. In case of the availability of only low energy levels, the use of dealuminated Y zeolite (DAY) is the better choice because of the infinitely variation of its hydrophilic properties by tailoring of the framework Si/Al ratio. Actual data on the hydrothermal stability of DAY are lacking. Thus, we report on the long-term behavior of DAY zeolites with different Si/Al ratios.  相似文献   
5.
In the present study we made an effort to deploy eco-friendly synthesized reduced graphene oxide/Lanthanum Alluminate nanocomposites (RGO-LaAlO3) and Lanthanum Alluminate (LaAlO3) as adsorbents to remove dye from the synthetic media. XRD, SEM, BET surface area and EDX have been used to characterize the above-mentioned adsorbents. The impacts of different factors like adsorbent dosage, the concentration of adsorbate and PH on adsorption were studied. The best fit linear and nonlinear equations for the adsorption isotherms and kinetic models had been examined. The sum of the normalized errors and the coefficient of determination were used to determine the best fit model. The experimental data were more aptly fitted for nonlinear forms of isotherms and kinetic equations. Pseudo-second-order and Freundlich isotherm model fits the equilibrium data satisfactorily. Methyl orange (MO) has been used as model dye pollutant and maximum adsorption capacity was found to be 469.7 and 702.2 mg g?1 for LaAlO3 and RGO-LaAlO3, respectively.  相似文献   
6.
Adsorption process is considered to be the most promising alternative for the CO2 capture to the traditional energy-intensive amine absorption process, and the development of feasible and efficient CO2 adsorbents is still a challenge. In this work, the NiO@USY (ultrastable Y) composites with different NiO loadings were prepared for the CO2 adsorption using Ni(NO3)2 as the precursor. The composites were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, nitrogen adsorption–desorption test, scanning electron microscopy analysis, and thermogravimetric analysis, and were evaluated for the CO2 adsorption capacity, CO2/N2 adsorption selectivity and CO2 cycle adsorption capacity. The characterization results show that after the activation at 423 K, the Ni(NO3)2 species were well dispersed into the surface of zeolite USY, and after the further activation at 823 K, Ni(NO3)2 could be converted into highly dispersed NiO. The adsorption results show that the presence of the active component NiO plays an important role in improving the CO2 adsorption performance, and the NiO@USY composite with a NiO loading of 1.5 mmol·g-1 USY support displays a high adsorption capacity and adsorption selectivity for CO2, and shows a good cycle stability. In addition, the Clausius–Clapeyron equation was used to evaluate the isosteric heat of adsorption of CO2 on the NiO(1.5)@USY composite, and the heat of adsorption was 17.39–38.34 kJ·mol-1.  相似文献   
7.
采用pH恒定共沉淀法合成了双金属氢氧化物Mg?Al?LDH,采用X射线衍射(XRD)、扫描电镜(SEM)、能谱(EDS)及BET等手段对其微观形貌、结构和组成进行表征。结果表明,成功制备出具有层状结构且有序程度较高的LDHs,其孔径属于介孔范畴。采用甲苯?正庚烷法将塔河沥青质(TA)分离成重组分(A1)和轻组分(A2),并对其进行元素分析,得知A1的极性最大,其次依次为TA和A2。进一步考察了Mg?Al?LDH对塔河沥青质及其亚组分A1、A2的吸附性能,研究发现Mg?Al?LDH对TA及其亚组分A1、A2的吸附可在2~3 h达到平衡,实验数据与准二级动力学拟合较好,所得吸附等温线符合Langmuir模型,Mg?Al?LDH对TA及其亚组分A1、A2的吸附量分别为71.38、140.65、39.31 mg/g。  相似文献   
8.
We briefly describe the adsorbent performance of the chitosan complex with aminophosphonic groups and cobalt in the removal process of Sr2+ ions from aqueous solutions. The strontium adsorption was studied as a function of pH, contact time, and initial strontium concentration. Adsorption isotherms such as Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin were used to analyze the equilibrium data at different concentrations. The kinetics of the Sr2+ sorption was analyzed using the pseudo-first-order and pseudo-second-order kinetic models. The results clearly indicate that the chitosan complex with aminophosphonic groups and cobalt is an efficient adsorbent with respect to its capacity to absorb Sr2+ ions from aqueous solutions.  相似文献   
9.
In this study, hydrogen (H2) adsorption on sepiolite and bentonite and those of acid treated forms were studied at 77 K using volumetric apparatus up to 100 kPa. Both clay minerals were treated with 100 ml of 0.5, 1.0, 2.0 and 4.0 M H2SO4 solutions at 80 °C for 5 h. Differences in the structures of the sepiolite and bentonite samples before and after the acid treatments were determined by XRD, XRF, TG, DTA and N2 adsorption methods. The level of H2 adsorption of original and acid treated sepiolite samples (1.332–2.252 mmol/g) was higher than those of the bentonite samples (0.341–1.003 mmol/g). The variation in the H2 adsorption capacities during the acid treatment was also discussed.  相似文献   
10.
Zr, Mo and W doped Vanadium oxide nanotube were considered as remarkable materials for hydrogen storage applications. Monte Carlo molecular simulation was performed to study the adsorption behavior of hydrogen molecules on Vanadium oxide nanotubes (VONTs). The effects of temperature, pressure and mole percent of hydrogen on adsorption capacity of VONTs were investigated to provide deep insight of adsorption behavior. The results represented that hydrogen adsorption is an increasing function of pressure and at about 50 MPa all three metal doped VONT has maximum hydrogen capacity. At 5 MPa and room temperature, the hydrogen capacities of Mo, W and Zr doped VONTs were 1.39, 0.88 and 1.43 w% respectively. With temperature increment up to room temperature, more reduction in initial hydrogen capacity were observed in Mo and Zr doped VONTs.Evaluating hydrogen adsorption of Zr doped VONT from pure and hydrogen /nitrogen mixtures at 300 K indicated that under 2 Mpa, modifications in adsorption capacities were insignificant after N2 addition to the environment. Therefore, Zr doped VONT in hydrogen /nitrogen mixture environment can act as a capable adsorbent for Hydrogen storage system in comparison with Mo and W doped VONTs.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号