全文获取类型
收费全文 | 11197篇 |
免费 | 955篇 |
国内免费 | 95篇 |
学科分类
工业技术 | 12247篇 |
出版年
2024年 | 40篇 |
2023年 | 223篇 |
2022年 | 392篇 |
2021年 | 747篇 |
2020年 | 638篇 |
2019年 | 771篇 |
2018年 | 903篇 |
2017年 | 837篇 |
2016年 | 849篇 |
2015年 | 520篇 |
2014年 | 836篇 |
2013年 | 1245篇 |
2012年 | 826篇 |
2011年 | 880篇 |
2010年 | 562篇 |
2009年 | 474篇 |
2008年 | 288篇 |
2007年 | 215篇 |
2006年 | 182篇 |
2005年 | 130篇 |
2004年 | 121篇 |
2003年 | 78篇 |
2002年 | 70篇 |
2001年 | 47篇 |
2000年 | 36篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 20篇 |
1996年 | 31篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 22篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A new, efficient and recoverable heterogeneous catalyst was successfully synthesized by functionalization of mesoporous silica FSM-16. The FSM-16/CPTMS-Rh- 相似文献
22.
Sahar Hashemi Daryan Jafar Javadpour Alireza Khavandi Mohammad Erfan 《Ceramics International》2018,44(16):19743-19750
Well-ordered and surface engineered hierarchical hydroxyapatite microspheres (HAM) were prepared via a template free hydrothermal process. Ethylene diamine tetra (methylene phosphonic acid) (EDTMP) was used as chelating or regulating agent for the first time in this study. The results indicated the formation of sheet-like particles in the absence of EDTMP. On the other hand, microspheres with radially grown nanorods (HAMNR) or nanosheets (HAMNS) on the surface were obtained (with average diameter of 5?µm) in the presence of EDTMP. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the crystalline phases in the synthesized samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that EDTMP concentration played an important part in regulating the morphology to form well organized microspheres with nanosheets or nanorods on the surface. Brunauer-Emmett-Teller (BET) revealed an increase in the specific surface area with the change in morphology from the HAMNS to HAMNR. Possible mechanisms are proposed to account for the formation of different morphologies based upon thermodynamic and kinetic theories. 相似文献
23.
24.
25.
26.
27.
Alinda Samsuri Mohd Nor Latif Mohd Razali Shamsuddin Fairous Salleh Maratun Najiha Abu Tahari Tengku Shafazila Tengku Saharuddin Norliza Dzakaria Mohd Ambar Yarmo 《International Journal of Hydrogen Energy》2021,46(48):24831-24844
Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO3) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO3 catalyst was attained with different reductant types and concentration (10% H2/N2, 10% and 20% CO/N2 (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700 °C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700 °C. Hydrogen temperature programmed reduction (H2-TPR) results showed the reduction progression of three-stage reduction of MoO3 (Mo6+ → Mo5+ → Mo4+ → Mo0) with Mo5+ and Mo4+. XRD analysis confirmed the formation of Mo4O11 phase as an intermediate phase followed by MoO2 phase. After 60 min of isothermal reduction, peaks of metallic molybdenum (Mo) appeared. Whereas, FESEM analysis showed porous crater-like structure on the surface cracks of MoO2 layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO3 catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo9O26 at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO2 phase, resulted in the formation of Mo2C rather than the formation of metallic Mo, as confirmed by XPS analysis. Therefore, the presented study shows that hydrogen gave better reducibility due to smaller molecular size, which contributed to high diffusion rate and achieved deeper penetration into the MoO3 catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO3 in carbon monoxide atmosphere promoted the formation of Mo2C which was in agreement with the thermodynamic assessment. 相似文献
28.
AbstractBuilding thermal inertia and operation control strategies have impacted on the thermal performance of a radiant floor heating system. This study conducts a two-dimensional numerical analysis of an intermittently operated radiant floor heating system using the Re-Normalization Group model with Discrete Ordinates Radiation model. A detailed numerical simulation setups and various analyses are provided, including grid independency analysis, initial condition, time step sizes and external boundary conditions. Three different weekend day intermittent operation strategies are investigated. The results showed that Case 3 designed with pre-heating of 20?h has better performance compared to Case 1 designed with pre-heating of 8?h and Case 2 designed with pre-heating of 14?h. The average indoor air temperature differences of approximate 2.1, 1.6 and 1.2 K are observed for Case 1, Case 2 and Case 3, respectively, when comparing two-time slot at 8:00am on Friday morning and Monday morning. This significantly highlights the effect of thermal inertia and the potential of energy saving due to the utilization of intermittent operation. Therefore, the current study presents numerical simulation potential in evaluating the radiant floor heating effects on indoor thermal environment, taking into account building thermal inertia and transient external climatic conditions. 相似文献
29.
30.
In this paper, the presence of source stack and heterogeneous gate dielectric material in the structure of an n-channel tunnel FET (TFET) is investigated. 相似文献