全文获取类型
收费全文 | 152016篇 |
免费 | 13673篇 |
国内免费 | 8904篇 |
专业分类
电工技术 | 5227篇 |
技术理论 | 7篇 |
综合类 | 10555篇 |
化学工业 | 35628篇 |
金属工艺 | 14463篇 |
机械仪表 | 9457篇 |
建筑科学 | 7544篇 |
矿业工程 | 5074篇 |
能源动力 | 3705篇 |
轻工业 | 12756篇 |
水利工程 | 2469篇 |
石油天然气 | 6071篇 |
武器工业 | 1262篇 |
无线电 | 12691篇 |
一般工业技术 | 17780篇 |
冶金工业 | 9422篇 |
原子能技术 | 1453篇 |
自动化技术 | 19029篇 |
出版年
2024年 | 519篇 |
2023年 | 2262篇 |
2022年 | 3901篇 |
2021年 | 5120篇 |
2020年 | 4776篇 |
2019年 | 4003篇 |
2018年 | 3517篇 |
2017年 | 4415篇 |
2016年 | 5108篇 |
2015年 | 5305篇 |
2014年 | 8634篇 |
2013年 | 9113篇 |
2012年 | 10579篇 |
2011年 | 12206篇 |
2010年 | 8952篇 |
2009年 | 9641篇 |
2008年 | 8362篇 |
2007年 | 10256篇 |
2006年 | 9501篇 |
2005年 | 8088篇 |
2004年 | 6659篇 |
2003年 | 5876篇 |
2002年 | 4914篇 |
2001年 | 4001篇 |
2000年 | 3557篇 |
1999年 | 2905篇 |
1998年 | 2259篇 |
1997年 | 1787篇 |
1996年 | 1708篇 |
1995年 | 1324篇 |
1994年 | 1216篇 |
1993年 | 847篇 |
1992年 | 704篇 |
1991年 | 579篇 |
1990年 | 412篇 |
1989年 | 342篇 |
1988年 | 242篇 |
1987年 | 169篇 |
1986年 | 167篇 |
1985年 | 99篇 |
1984年 | 83篇 |
1983年 | 73篇 |
1982年 | 66篇 |
1981年 | 40篇 |
1980年 | 67篇 |
1979年 | 42篇 |
1978年 | 14篇 |
1977年 | 31篇 |
1976年 | 21篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
以重庆市甄子岩29号危岩体为研究对象,基于现场调查和分析解剖,建立UDEC离散元数值计算模型,对其演化变形过程进行模拟分析。研究表明,在巨大的自重作用下,由于基座岩体岩质软,岩体较破碎,且基座外侧为直立的陡崖,具有完整的临空面,从而使基座岩体易发生压缩流变及剪切流变,进而使危岩体存在滑移垮塌的危险。 相似文献
32.
33.
34.
35.
Olatunde Adebayo Adeoti Sunday Olawale Koleoso 《Quality and Reliability Engineering International》2020,36(6):2170-2186
Several modifications and enhancements to control charts in increasing the performance of small and moderate process shifts have been introduced in the quality control charting techniques. In this paper, a new hybrid control chart for monitoring process location is proposed by combining two homogeneously weighted moving average (HWMA) control charts. The hybrid homogeneously weighted moving average (HHWMA) statistic is derived using two smoothing constants λ1 and λ2 . The average run length (ARL) and the standard deviation of the run length (SDRL) values of the HHWMA control chart are obtained and compared with some existing control charts for monitoring small and moderate shifts in the process location. The results of study show that the HHWMA control chart outperforms the existing control charts in many situations. The application of the HHWMA chart is demonstrated using a simulated data. 相似文献
36.
37.
《International Journal of Hydrogen Energy》2019,44(5):2905-2917
In this study, a multi-tubular thermally coupled packed bed reactor in which simultaneous production of ammonia and methyl ethyl ketone (MEK) takes place is simulated. The simulation results are presented in two co-current and counter-current flow modes. Based on this new configuration, the released heat from the ammonia synthesis reaction as an extremely exothermic reaction in the inner tube is employed to supply the required heat for the endothermic 2-butanol dehydrogenation reaction in the outer tube. On the other hand, MEK and hydrogen are produced by the dehydrogenation reaction of 2-butanol in the endothermic side, and the produced hydrogen is used to supply a part of the ammonia synthesis feed in the exothermic side. Thus, 30.72% and 31.88% of the required hydrogen for the ammonia synthesis are provided by the dehydrogenation reaction in the co-current and counter-current configurations, respectively. Also, according to the thermal coupling, the required cooler and furnace for the ammonia synthesis and 2-butanol dehydrogenation conventional plants are eliminated, respectively. As a result, operational costs, energy consumption and furnace emissions are considerably decreased. Finally, a sensitivity analysis and optimization are applied to study the effect of the main process parameters variation on the system performance and obtain the minimum hydrogen make-up flow rate, respectively. 相似文献
38.
This paper presents a fast distance relay for series compensated transmission lines based on the R–L differential-equation algorithm using the theory of equal transfer process of transmission lines. The measuring distances based on the proposed algorithm can fast approach the actual value of fault distance when a fault occurs in front of the series capacitor. When a fault occurs behind of the series capacitor, the fault loop, including the series capacitor, does not match the R–L transmission line model, so the measuring distances fluctuate severely. Based on this, the relative position of the fault with respect to the series capacitor can be judged effectively according to the fluctuation range of the measuring distances, and the accurate fault location can be obtained fast. A variety of PSCAD/EMTDC simulation tests show that the new relay has fast operating speed and high accuracy when applied to the long series compensated transmission lines. 相似文献
39.
40.
C. Doga Demirhan William W. Tso Joseph B. Powell Efstratios N. Pistikopoulos 《American Institute of Chemical Engineers》2019,65(7):e16498
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019 相似文献