全文获取类型
收费全文 | 10081篇 |
免费 | 986篇 |
国内免费 | 324篇 |
专业分类
电工技术 | 649篇 |
技术理论 | 1篇 |
综合类 | 900篇 |
化学工业 | 3590篇 |
金属工艺 | 362篇 |
机械仪表 | 140篇 |
建筑科学 | 1670篇 |
矿业工程 | 855篇 |
能源动力 | 550篇 |
轻工业 | 374篇 |
水利工程 | 243篇 |
石油天然气 | 153篇 |
武器工业 | 36篇 |
无线电 | 107篇 |
一般工业技术 | 1015篇 |
冶金工业 | 555篇 |
原子能技术 | 39篇 |
自动化技术 | 152篇 |
出版年
2024年 | 15篇 |
2023年 | 100篇 |
2022年 | 235篇 |
2021年 | 308篇 |
2020年 | 285篇 |
2019年 | 235篇 |
2018年 | 242篇 |
2017年 | 298篇 |
2016年 | 332篇 |
2015年 | 352篇 |
2014年 | 575篇 |
2013年 | 461篇 |
2012年 | 678篇 |
2011年 | 718篇 |
2010年 | 536篇 |
2009年 | 657篇 |
2008年 | 481篇 |
2007年 | 734篇 |
2006年 | 637篇 |
2005年 | 542篇 |
2004年 | 492篇 |
2003年 | 445篇 |
2002年 | 385篇 |
2001年 | 290篇 |
2000年 | 277篇 |
1999年 | 216篇 |
1998年 | 154篇 |
1997年 | 146篇 |
1996年 | 107篇 |
1995年 | 84篇 |
1994年 | 76篇 |
1993年 | 66篇 |
1992年 | 53篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
以福州红庙岭生活垃圾焚烧炉渣为试验对象,测试不同吸水时间和干湿循环次数下炉渣试件无侧限抗压强度和CBR的变化规律,揭示炉渣填料在水作用下的强度变化特征。结果表明:炉渣试件无侧限抗压强度和CBR随吸水时间和干湿循环次数的增加而增大,具有良好的水稳定性。炉渣的强度主要依靠水泥熟料和活性物质化学反应产生水化产物形成的,这使得炉渣在潮湿路基的回填、管槽周边的回填具有显著优势。 相似文献
42.
《Ceramics International》2022,48(15):21638-21647
Municipal solid waste incineration (MSWI) fly ash (FA) is a typical hazardous waste due to its high contents of toxic heavy metals, and hence its disposal has attracted global concern. In this work, it was recycled into environmental-friendly CaO–Al2O3–SiO2 system glass-ceramics via adding coal fly ash (CFA) and waste glass (WG). The effects of CaO/SiO2 ratios and sintering temperatures on the crystalline phases, morphologies, mechanical and chemical properties, heavy metals leaching and potential ecological risks of glass-ceramics were investigated. The results showed that wollastonite (CaSiO3), anorthite (CaAl2Si2O8) and gehlenite (Ca2Al2SiO7) were the dominant crystals in the glass-ceramics, which were not affected by CaO/SiO2 ratio and sintering temperature. The compressive strength increased, while the Vickers hardness and microhardness decreased as increasing the sintering temperatures from 850 to 1050 °C, which reached their maximum values of 660.69 MPa, 6.14 GPa, and 7.43 GPa, respectively. However, the increase of CaO/SiO2 ratio resulted into the reduction of the three mechanical parameters. As varying CaO/SiO2 ratio from 0.48 to 0.86, the maximum compressive strength, Vickers hardness and microhardness were 611.80 MPa, 5.43 GPa, and 6.56 GPa, respectively. Besides, all the glass-ceramics exhibited high alkali resistance of >97%. The extremely low heavy metals leaching concentrations and low potential ecological risk of glass-ceramics further revealed its environmentally friendly property and potential application feasibility. 相似文献
43.
Phase change materials (PCMs) contributed to building energy‐saving and thermal comfort through increasing the thermal capacity of building envelopes. In this study, a phase change material composite was developed by using the PCMs mixture of capric acid (CA) and lauric acid (LA) as the primary phase change energy storage agent and using the solid waste fly ash as a carrier material. The results showed that for Guangdong, the ideal PCMs mixture should have a transition temperature of 25.5oC, which could be obtained by using a mass ratio of CA/LA of 4:6. Then, experiment results also indicate that the optimum adsorption ratio of 2:1 (FA/PCMs) was detected for the synthesis of this FA/PCMs composite, which has the latent heat of 45.38 J/g and exists excellent thermal reliability. Moreover, simulation results by using EnergyPlus show that the proposed composite has a good building energy‐saving effect. 相似文献
44.
M.A. Azmah Hanim C.K. Wei T.T. Dele-Afolabi O.S. Azlina 《Materialwissenschaft und Werkstofftechnik》2021,52(9):943-951
In this study, the mechanical performance of the rice husk ash-reinforced tin-0.7 copper composite solder was investigated. 0.01 wt.%, 0.05 wt.% and 0.1 wt.% of rice husk ash (RHA) were added to the solder matrix to prepare the composite solders. In order, to replace the costly electroless nickel immersion gold surface finish on the copper substrate, the effect of electroless nickel immersion silver (ENIAg) as the surface finish was studied. The differential scanning calorimetry (DSC) analysis showed that the composite solder exhibited lower melting temperature relative to the plain solder owing to the inclusion of rice husk ash. Shear strength analysis was carried out to investigate the influence of rice husk ash and electroless nickel immersion silver surface finish on the shear strength of the developed composite solders. The results proved that the rice husk ash failed to enhance the shear strength of tin-0.7 copper lead-free solder with the plain solder exhibiting the highest shear strength. 相似文献
45.
《International Journal of Hydrogen Energy》2021,46(70):34679-34688
The endless and dramatic increase of global energy demand makes it imperative to develop sustainable, affordable, and efficient materials to act as electrocatalysts in the clean energy technologies. Electrocatalysts based on coal chars are promising materials as they can be considered as value-added by-products from coal combustion contributing to industrial ecology and circular economy. Therefore, herein we report the application of three sets of coal char (char concentrates before and after carbonization and demineralized and graphitized char concentrates) obtained from four different countries (Portugal, Romania, Poland, and South Africa) as oxygen reduction reaction (ORR) electrocatalysts. All electrocatalysts presented moderate ORR activity with some showing selectivity for the indirect two-electron process while others for a mixed regime between the two- and four-electron process. Still, the positive results obtained are better or in some cases comparable to commercial graphene. Moreover, all electrocatalysts presented good tolerance to methanol poisoning. More importantly, the results of this study demonstrate that pristine coal chars are promising materials to prepare efficient ORR electrocatalysts which will be of great importance in the near future. 相似文献
46.
Yishu XU Xiaowei LIU Jiuxin QI Tianpeng ZHANG Minghou XU Fangfang FEI Dingqing LI 《Frontiers in Energy》2021,15(2):449
Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers. Therefore, the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied, including the platen (PS), the high-temperature (HTS), the upper and the lower low-temperature superheaters (LTS). The results showed that the deposits in the PSs and HTSs were thin (several millimeters) and compact, consisting of a yellow outer layer and snow-white inner layer near the tube surface. The deposits in the upper LTS appeared to be toughly sintered ceramic, while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface. Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K (approximately 70%) in the form of KCl. Interestingly, the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S. The contents of Ca and Si increased from approximately 10% to approximately 60% in the deposits from the high temperature surfaces to the low temperature ones. It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS. In addition, although the condensation of KCl in the LTSs also happened, the deposition of ash particles played a more important role. 相似文献
47.
48.
Luana Machado Barros Ana Lúcia Nunes Gutjahr Ruth Leila Ferreira‐ Keppler Renato Tavares Martins 《Microscopy research and technique》2019,82(3):178-189
In the dipteran genus Hermetia, only 6 of the 78 valid species have documented immature stages: H. albitarsis Fabricius, 1805, H. aurata Bellardi, 1859, H. concinna Williston, 1900, H. illucens (Linnaeus, 1758), H. panamensis Greene, 1940 and H. pulchra Weidemann, 1830. In particular, H. illucens stands out due to its reported applicability for forensic, medical and economic purposes. Here, we described the morphology of eggs and immature stages of this species, with a view to detecting differences between instars and in the pupal stage, which should eventually help properly identifying larval age. We utilized both optical and scanning electron microscopy tools. The eggs are elliptical and elongated, and color varies from cream white to yellowish. The larvae are apodal, hemichephalic and holopneustic, flattened dorso‐ventrally and may be recognized by the head elongated, dorsal and ventral chaetotaxy of the cephalic capsule, thoracic and abdominal segments, and the morphology of the anterior and posterior spiracles. The pupae are adecticous and coarctate, tegument dark brown and pruinescence varying from brown to golden. The overall morphology across instars is similar, but marked variations were observed in the shape of the antennal articuli and the shape of the setae (first instar compared to the others). Our results supplement the biological information on Hermetia illucens and should aid the proper identification and aging of juveniles in the field, as a way to minimize errors in the calculation of the post‐mortem interval. 相似文献
49.
Omdeo Kishorrao Gohatre Manoranjan Biswal Smita Mohanty Sanjay K. Nayak 《应用聚合物科学杂志》2021,138(19):50387
The silane treatment on properties of fly ash (FA) and development of its composite using recycled poly(vinyl chloride) (r-PVC) material retrieve from waste wires and cable insulation are investigated in this work. The use of (3-aminopropyl)triethoxysilane was employed as a coupling agent with some other essential additives. The composites sheet was prepared by means of the melt mixing process and go along with the compression molding process. The superior properties on compatibility between silane-modified FA (FA(Si)) and r-PVC were successfully studied using rheological, thermomechanical, morphological, and water absorption analysis. Primary analysis of r-PVC and FA was employed using Fourier transform infrared spectroscopy analysis. The thermal stability of composites was stable up to 187°C. In addition, significant enhancement on tensile strength as well as young's modulus of composite as compared to untreated r-PVC/FA composites. Morphological properties of silane treated FA based composites presented the good distribution and excellent uniformity with higher wettability of FA particles within r-PVC matrix. The water absorption test showed decrease in water absorption with increase silane treatment concentration FA in the r-PVC matrix. It was remarkable to note that silane treated FA can be prepared as a composite using r-PVC matrix with further modified properties. 相似文献
50.
The present study proposes the mix design method of Fly Ash (FA) based geopolymer concrete using Response Surface Methodology (RSM). In this method, different factors, including binder content, alkali/binder ratio, NS/NH ratio (sodium silicate/sodium hydroxide), NH molarity, and water/solids ratio were considered for the mix design of geopolymer concrete. The 2D contour plots were used to setup the mix design method to achieve the target compressive strength. The proposed mix design method of geopolymer concrete is divided into three categories based on curing regime, specifically one ambient curing (25 °C) and two heat curing (60 and 90 °C). The proposed mix design method of geopolymer concrete was validated through experimentation of M30, M50, and M70 concrete mixes at all curing regimes. The observed experimental compressive strength results validate the mix design method by more than 90% of their target strength. Furthermore, the current study concluded that the required compressive strength can be achieved by varying any factor in the mix design. In addition, the factor analysis revealed that the NS/NH ratio significantly affects the compressive strength of geopolymer concrete. 相似文献