全文获取类型
收费全文 | 6088篇 |
免费 | 285篇 |
国内免费 | 223篇 |
专业分类
电工技术 | 274篇 |
技术理论 | 1篇 |
综合类 | 1261篇 |
化学工业 | 394篇 |
金属工艺 | 217篇 |
机械仪表 | 281篇 |
建筑科学 | 898篇 |
矿业工程 | 420篇 |
能源动力 | 270篇 |
轻工业 | 267篇 |
水利工程 | 114篇 |
石油天然气 | 128篇 |
武器工业 | 19篇 |
无线电 | 220篇 |
一般工业技术 | 881篇 |
冶金工业 | 408篇 |
原子能技术 | 12篇 |
自动化技术 | 531篇 |
出版年
2023年 | 44篇 |
2022年 | 80篇 |
2021年 | 102篇 |
2020年 | 148篇 |
2019年 | 101篇 |
2018年 | 101篇 |
2017年 | 136篇 |
2016年 | 137篇 |
2015年 | 168篇 |
2014年 | 381篇 |
2013年 | 433篇 |
2012年 | 391篇 |
2011年 | 509篇 |
2010年 | 401篇 |
2009年 | 397篇 |
2008年 | 364篇 |
2007年 | 444篇 |
2006年 | 427篇 |
2005年 | 363篇 |
2004年 | 301篇 |
2003年 | 296篇 |
2002年 | 205篇 |
2001年 | 176篇 |
2000年 | 130篇 |
1999年 | 108篇 |
1998年 | 70篇 |
1997年 | 55篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1961年 | 3篇 |
1960年 | 3篇 |
1959年 | 3篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有6596条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2021,47(24):34361-34379
This paper aimed to design and optimize the structure of a thick thermal barrier coating by adding graded layers to achieve a balance between high thermal insulation capacity and durability. To this end, conventional TBC, conventional TTBC, and functionally graded TTBCs were deposited on the superalloy substrate by air plasma spraying. To determine the quality of the bond strength of the coatings, the bonding strength was measured. The durability of coatings was evaluated by isothermal oxidation and thermal shock tests. Then, at a temperature of 1000 °C, the thermal insulation capacity of the coatings was carried out. The microstructure of the coatings was characterized by a scanning electron microscope. The results showed that the thickness of the TGO layer formed on the bond coat in the conventional TBC and TTBC under the oxidation test at 1000 °C after 150 h was 2.79 and 2.11 μm, respectively, whereas, in the functionally graded TTBC samples, no continuous TGO layer was observed as a result of internal oxidation. The functionally graded TTBC presented higher durability than conventional TTBC due to improved bonding strength, thermal shock resistance, and the lack of a TGO layer at the bond/top coat interface. Also, the thermal insulation capacity of the functionally graded TTBC (with 1000 μm thickness of YSZ coating) was better than TTBC. 相似文献
2.
Mehmet Dorduncu Junuthula Narasimha Reddy 《Journal of Adhesion Science and Technology》2019,33(2):156-186
This study presents an improved mathematical model to analyse the stress wave propagation in adhesively bonded functionally graded (FG) circular cylinders (butt joint) under an axial impulsive load. The volume fractions of the material constituents in the upper and lower cylinders were functionally tailored through the thickness of each cylinder using a power-law. The effective material properties of both cylinders, which are made of aluminum (Al) and silicon carbide (SiC), at any point were predicted by using the Mori–Tanaka homogenization scheme. In this improved model, the governing equations of the wave propagation include the spatial derivatives of local mechanical properties and were discretized by means of the finite difference method. The influence of these spatial derivatives and the compositional gradient exponent on the displacement and stress distributions of the joint was investigated. The material composition variations of both cylinders affected the displacement and stress fields whereas the compositional gradient exponent had a minor effect. The stress concentrations were alleviated in time, the displacement and stress distributions/variations around/along the upper and lower cylinder-adhesive interfaces were significantly affected by the adhesive layer. The spatial derivatives also affected the temporal histories of the displacement and stress components evaluated at the selected critical points of the upper cylinder, adhesive layer and lower cylinder. The consideration of the spatial local material derivatives provided a more accurate mathematical model of wave propagations through the graded layered structures. 相似文献
3.
《Journal of the European Ceramic Society》2022,42(6):2957-2973
Functionally graded ceramics (FGC), which combine properties of different ceramics in one part, usually have better comprehensive function and structural efficiency. In this study, four different gradient transition Al2O3-ZrO2 FGC samples were prepared by laser directed energy deposition (LDED) method. The results show that there is an obvious interface in direct transition sample. The transition section bears tensile stress caused by difference of thermophysical properties of materials, resulting in significant longitudinal cracks. Element transition in interface region shows a step sharp transition. The direct transition sample shows intergranular fracture and the bonding strength is very low. Gradient transition mode can effectively suppress cracks, and avoid the step transition of microstructure and elements. Elements, microhardness of 25, 20 wt% FGC samples realized a nearly linear smooth transition. The interface fracture of FGC samples changed to transgranular fracture, bonding strength was significantly improved, and the maximum flexural strength reached 160.19 MPa. 相似文献
4.
A size-dependent governing equation is derived to investigate the torsional static behaviors of two-dimensionally functionally graded microtubes based on the modified couple stress theory. The shear modulus is assumed to vary along the tube’s length direction according to an exponential distribute function, and varies along the tube’s radius direction according to a power-law function. A generalized differential quadrature method is developed to determine the rotational angle and shear stresses. Some illustrative examples are given to investigate the effects of applied torques, the length scale parameter and various material compositions on the torsional angle and shear stresses. 相似文献
5.
分级加载电压技术能够有效延长电渗处理的时间,改善地基的处理效果并能有效降低能耗。在利用分级加载电压技术开展电渗试验时,随着土体的排水固结,土体各点的电势会发生明显的变化,这与现有的电渗固结理论假设土体各点电势保持不变有所差异。利用自主设计的电渗试验仪器开展了分级加载电压下的电渗室内试验,分析了电渗过程中土体有效电势变化的规律。基于该规律并结合Esrig固结理论建立了在阳极处不排水、阴极处排水条件下考虑土体有效电势变化的电渗固结理论,得到了分级加载电压条件下考虑土体有效电势变化的超静孔隙水压力和平均固结度的解析表达式。研究表明,在电压分级加载过程中,土体有效电势变化规律表现为随时间先基本保持不变,后呈抛物线状先增后减。通过试验案例验证了考虑土体有效电势变化所求得解析解的合理性,且该数值计算结果相较于Esrig数值计算结果,前者更加接近实测值,该固结方程的建立为后续分级加载电压技术的推广应用提供了理论依据,也为实际工程提供了参考。 相似文献
6.
Sarbjeet Kaushal Dheeraj Gupta Hiralal Bhowmick 《Materials and Manufacturing Processes》2018,33(8):822-828
Present study focuses on the development of four layered functionally graded clads (FGC) of Ni-WC based composite material on AISI 304 substrate through microwave heating route. Experimental trials were conducted inside a microwave applicator of domestic type at frequency range of 2.45?GHz. The optimal exposure time of 900?W microwave power was varied with compositional gradient and it was from 300 to 360?s. The mechanism of FGC formation through microwave heating was explained and developed FGC was subjected to mechanical and microstructure characterizations. The results of micro-structural analysis revealed that the FGC of ~1.8?mm thickness was produced and was free from any type of interfacial cracks and visible porosity. It was observed that WC particles were randomly dispersed in the nickel matrix. XRD study revealed the formation of inter-metallics, such as NiW4, NiSi, and Cr23C6. Maximum value of microhardness was observed in the top FGC layer and was 880?±?30?HV. 相似文献
7.
本文以竹荪为原料提取多糖成分并以乙醇分级制备竹荪多糖(DPs)不同组分,通过青春双歧杆菌体外增殖试验初步评价竹荪多糖及其分级醇沉组分的益生元功效。结果显示在α-淀粉酶溶液中水解4 h后,20%、40%、50%、60%竹荪多糖醇沉组分水解度分别为9.10%、8.02%、8.88%、11.67%,与对照组菊粉(水解度13.15%)相比差异显著(P<0.05);80%竹荪多糖醇沉组分、未分级醇沉组分与菊粉对照组相比差异不显著(P>0.05)。在模拟胃液中水解6 h后,20%、40%、50%竹荪多糖醇沉组分水解度分别为17.30%、14.52%、9.61%,与对照组菊粉(水解度5.72%)相比差异显著(P<0.05);60%竹荪多糖醇沉组分、80%竹荪多糖醇沉组分、未分级醇沉组分水解度与对照组相比无显著差异(P>0.05)。随着竹荪多糖添加量的增加,青春双歧杆菌的菌体浓度呈现先增大而后不断减小的趋势。分级醇沉浓度达到80%的竹荪多糖组分和未分级的多糖组分,青春双歧杆菌体外增殖作用与pH下降显著且效果优于菊粉(P<0.05),并在20 h的发酵时间内两者表现出相似的效果。不同竹荪多糖醇沉组分对青春双歧杆菌均有增殖效果,且不同竹荪多糖醇沉组分的增殖效果和抗水解能力随乙醇浓度的增加而增强,未分级的多糖组分同样可以加强青春双歧杆菌增殖能力,具有益生元潜力。 相似文献
8.
AbstractIn this paper, the effects of hygrothermal conditions on various behaviors, such as bending, free vibration, mechanical and thermal buckling, of exponentially graded microplates lying on two-parameter elastic foundations are investigated. The trigonometric four-variable plate theory incorporated to the modified couple stress theory (MCST) is employed to derive the equations of motion. The present MCST contains an internal material length scale parameter, thus it can capture the size effect. The microplate is assumed to be subjected to a temperature rise and moisture concentration which are varied linearly through the thickness of the plate. Based on an exponential law, the material properties of the microplate are graded only in z direction. The equations of motion are solved analytically to obtain the displacements, stresses, eigenfrequencies and critical buckling load and temperature of the microplates. The present results are validated by comparing them with those previously published. The numerical examples reveal that considering the size effect and/or the elastic foundations leads to an increment in plate stiffness and thereby leads to a decrement in the deflection and an increment in eigenfrequency and buckling loads. It is also shown that the size effect is negligible for the thicker plate. 相似文献
9.
王锦霞 《湖南工业职业技术学院学报》2015,(1)
近几十年来,全球范围内的巨灾风险发生的频率和损失的程度都呈上升趋势,对巨灾风险管理与监管工作提出了严峻的挑战。本文通过分析各国巨灾保险制度与监管的特点,结合我国巨灾风险管理的实际情况,提出建设市场与政府相结合的巨灾保险制度,加强巨灾保险市场行为与偿付能力及资本市场监管的几点建议。 相似文献