全文获取类型
收费全文 | 101912篇 |
免费 | 10914篇 |
国内免费 | 5970篇 |
学科分类
工业技术 | 118796篇 |
出版年
2024年 | 243篇 |
2023年 | 1832篇 |
2022年 | 3360篇 |
2021年 | 5065篇 |
2020年 | 3815篇 |
2019年 | 2986篇 |
2018年 | 3342篇 |
2017年 | 3652篇 |
2016年 | 3175篇 |
2015年 | 4811篇 |
2014年 | 6142篇 |
2013年 | 7071篇 |
2012年 | 8270篇 |
2011年 | 8540篇 |
2010年 | 7591篇 |
2009年 | 7106篇 |
2008年 | 6675篇 |
2007年 | 6130篇 |
2006年 | 5584篇 |
2005年 | 4651篇 |
2004年 | 3006篇 |
2003年 | 2240篇 |
2002年 | 2063篇 |
2001年 | 1664篇 |
2000年 | 1622篇 |
1999年 | 1594篇 |
1998年 | 1177篇 |
1997年 | 1029篇 |
1996年 | 976篇 |
1995年 | 792篇 |
1994年 | 642篇 |
1993年 | 462篇 |
1992年 | 353篇 |
1991年 | 293篇 |
1990年 | 208篇 |
1989年 | 163篇 |
1988年 | 137篇 |
1987年 | 74篇 |
1986年 | 56篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 33篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 18篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 16篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Kechang Xie 《中国化学工程学报》2021,35(7):62-69
It is important to develop the advanced coal to chemicals industry (ACCI) against a backdrop of coal-based energy structures,excessive imported oil and natural gas,and strict environmental con-straints in China.In this study,the technology and industry of China's ACCI are reviewed to explain the effect of using coal to replace oil and natural gas,and the corresponding resource and environmental burdens that this will create.Development trends in technology and industry are also proposed to explore future scenarios.The review shows that although excellent progress has been made on an indus-trial scale,demonstrative level,and in terms of technology and equipment,the lack of strategic under-standing,severe external constraints,partly underdeveloped technologies,and weak foundations must be immediately addressed.Therefore,it is necessary to clarify the importance that the ACCI has on the energy revolution and energy system.Based on technological innovation,a variety of external factors should be considered as a whole with emphasis on filling the knowledge gap of theoretical foundations and industry standards to support high-quality development for ACCI. 相似文献
83.
董磊 《建设科技(建设部)》2021,(2):56-59,64
为发挥装配式IRF体系自身优势,施工现场需研发与体系相适应的施工技术.这对施工总承包单位在施工场地平面布置、预制构件安装、施工组织等方面提出了需求.装配式IRF体系依托天津葛沽镇定向安置房2018-03项目,研发出与施工技术相适应的工装系统,总结完善了高层建筑装配式IRF体系施工流程,进一步验证了体系的可行性. 相似文献
84.
85.
Zhang Huiyan Tang Xuyang Qian Yuehua Shi Lei Deng Kangyao 《Journal of Mechanical Science and Technology》2021,35(12):5699-5712
Journal of Mechanical Science and Technology - Controlling the turbo bypass valve is valid to enhance transient characteristic of turbocharging system. Appropriate fuel delivery is beneficial to... 相似文献
86.
Hao Yuan Haifeng Dai Wei Wu Jiaping Xie Jun Shen Xuezhe Wei 《International Journal of Hydrogen Energy》2021,46(7):5714-5728
In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance. 相似文献
87.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献
88.
Tian Xie Haixia Zhao Zunhang Lv Guangwen Xie Yan He 《International Journal of Hydrogen Energy》2021,46(1):581-588
This work demonstrates a facile Nb2O5-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb2O5/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb2O5/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm?2). 相似文献
90.
A series of ZnxNiyCrOm±δ catalysts were synthesized via a typical co-precipitation method, in which Zn-Cr layered double hydroxides (LDHs) were found and Ni-Zn intermetallic compound (IMC) was formed after reduction in hydrogen. During auto-thermal reforming (ATR) of acetic acid (HAc), the Ni-Zn IMC was transformed into Ni/(amorphous-ZnO)-ZnCr2O4 species with uniformed distribution and appropriate interaction within these Ni-Zn-Cr-O species; besides, the adsorbed oxygen promoted the activation and transfer of oxygen species; therefore, deactivation by oxidation, sintering and coking was inhibited. And the optimized Zn2.37Ni0.63CrO4.5±δ catalyst presented high activity and stability in a 45-h ATR test with HAc conversion near 100% and hydrogen yield at 2.7 mol-H2/mol-HAc, showing potential for hydrogen production via ATR of HAc. 相似文献