全文获取类型
收费全文 | 305498篇 |
免费 | 31388篇 |
国内免费 | 7579篇 |
专业分类
电工技术 | 31255篇 |
技术理论 | 7篇 |
综合类 | 10261篇 |
化学工业 | 56791篇 |
金属工艺 | 22517篇 |
机械仪表 | 18667篇 |
建筑科学 | 31542篇 |
矿业工程 | 20328篇 |
能源动力 | 13453篇 |
轻工业 | 27746篇 |
水利工程 | 7119篇 |
石油天然气 | 13535篇 |
武器工业 | 712篇 |
无线电 | 21469篇 |
一般工业技术 | 19833篇 |
冶金工业 | 32259篇 |
原子能技术 | 2288篇 |
自动化技术 | 14683篇 |
出版年
2024年 | 1000篇 |
2023年 | 6603篇 |
2022年 | 14114篇 |
2021年 | 16752篇 |
2020年 | 17487篇 |
2019年 | 9101篇 |
2018年 | 7523篇 |
2017年 | 6855篇 |
2016年 | 9429篇 |
2015年 | 15168篇 |
2014年 | 30975篇 |
2013年 | 31177篇 |
2012年 | 40577篇 |
2011年 | 33872篇 |
2010年 | 22822篇 |
2009年 | 20846篇 |
2008年 | 8965篇 |
2007年 | 12457篇 |
2006年 | 10428篇 |
2005年 | 4562篇 |
2004年 | 2093篇 |
2003年 | 1934篇 |
2002年 | 1918篇 |
2001年 | 1758篇 |
2000年 | 1647篇 |
1999年 | 1663篇 |
1998年 | 1448篇 |
1997年 | 1205篇 |
1996年 | 1014篇 |
1995年 | 696篇 |
1994年 | 635篇 |
1993年 | 591篇 |
1992年 | 503篇 |
1991年 | 487篇 |
1990年 | 412篇 |
1989年 | 377篇 |
1988年 | 357篇 |
1987年 | 260篇 |
1986年 | 275篇 |
1985年 | 322篇 |
1984年 | 364篇 |
1983年 | 324篇 |
1982年 | 317篇 |
1981年 | 342篇 |
1980年 | 341篇 |
1979年 | 330篇 |
1978年 | 249篇 |
1977年 | 236篇 |
1976年 | 221篇 |
1975年 | 188篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
《Ceramics International》2022,48(20):29959-29966
High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m?1 K?1 to 167 W m?1 K?1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry. 相似文献
22.
《Ceramics International》2022,48(20):29892-29899
It is very challenging for 3D printing based on the selective laser melting (SLM) technology to obtain cermet bulk materials with high density and homogeneous microstructures. In this work, the SLM process of the cermet powders was studied by both simulations and experiments using the WC-Co cemented carbides as an example. The results indicated that the evolution of the ceramic and metallic phases in the cermet particle during the heating, melting and solidification processes were all significantly inhomogeneous from atomic scale to mesoscale microstructures. As a consequence, the microstructural defects were caused intrinsically in the printed bulk material. The formation and growth of the bonding necks between the particles were mainly completed at the later stage of laser heating and the early stage of solidification. Both simulations and experiments demonstrated that thin amorphous layers formed at the ceramics/metal interfaces. This work disclosed the mechanisms for the evolution from the atomic scale to microstructure during the SLM printing of cermet powders, and discovered the origin of the defects in the printed cermet bulk materials. 相似文献
23.
Xiao-juan Li Yi-xiang Xu Xiang Li Zhi-jiang Jin Jin-yuan Qian 《International Journal of Hydrogen Energy》2021,46(7):5537-5547
Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers. 相似文献
24.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
25.
26.
根据水泥烧成热耗的组成,降低高温设备表面散热是降低水泥烧成热耗的重要途径之一,而减少高温窑炉墙壁的热传导可有效降低设备的表面散热。本文在介绍无机内保温涂层隔热原理的基础上,对保温涂层的应用效果进行了对比研究,通过在传统耐火隔热材料的基础上增加新型无机内保温涂层,可有效降低高温设备外表面温度,减少水泥生产中的散热损失,达到节能降耗的目的。 相似文献
27.
《International Journal of Hydrogen Energy》2021,46(73):36291-36300
A new reverse build-up method is developed to fabricate an economical H2-permeable composite membrane. Sputtering and electroplating are used for the formation of a membrane comprised of a 3.7-μm-thick Pd60Cu40 (wt.%) alloy layer and a 13-μm-thick porous Ni support layer, respectively. The H2-permeation measurements are performed under the flow of a gaseous mixture of H2 and He at 300–320 °C and 50–100 kPa of H2 partial pressure. The H2/He selectivity values exceed 300. The activation energy at 300–320 °C is 10.9 kJ mol−1. The H2 permeability of the membrane is 1.25 × 10−8 mol m−1 s−1 Pa−0.5 at 320 °C after 448 h. The estimated Pd cost of the proposed membrane is approximately 1/8 of the cost for a pure Pd60Cu40 membrane. This study demonstrates that the proposed method allows the facile production of low-cost, Pd-based membranes for H2 separation. 相似文献
28.
29.
30.
Tongling Xia Yue Qi Xilei Dai Jinyu Liu Can Xiao Ruoyu You Dayi Lai Junjie Liu Chun Chen 《Indoor air》2021,31(6):2020-2032
To evaluate the separate impacts on human health and establish effective control strategies, it is crucial to estimate the contribution of outdoor infiltration and indoor emission to indoor PM2.5 in buildings. This study used an algorithm to automatically estimate the long-term time-resolved indoor PM2.5 of outdoor and indoor origin in real apartments with natural ventilation. The inputs for the algorithm were only the time-resolved indoor/outdoor PM2.5 concentrations and occupants’ window actions, which were easily obtained from the low-cost sensors. This study first applied the algorithm in an apartment in Tianjin, China. The indoor/outdoor contribution to the gross indoor exposure and time-resolved infiltration factor were automatically estimated using the algorithm. The influence of outdoor PM2.5 data source and algorithm parameters on the estimated results was analyzed. The algorithm was then applied in four other apartments located in Chongqing, Shenyang, Xi'an, and Urumqi to further demonstrate its feasibility. The results provided indirect evidence, such as the plausible explanations for seasonal and spatial variation, to partially support the success of the algorithm used in real apartments. Through the analysis, this study also identified several further development directions to facilitate the practical applications of the algorithm, such as robust long-term outdoor PM2.5 monitoring using low-cost light-scattering sensors. 相似文献