全文获取类型
收费全文 | 42930篇 |
免费 | 5364篇 |
国内免费 | 2696篇 |
专业分类
电工技术 | 5275篇 |
技术理论 | 5篇 |
综合类 | 5257篇 |
化学工业 | 2446篇 |
金属工艺 | 1430篇 |
机械仪表 | 3299篇 |
建筑科学 | 7560篇 |
矿业工程 | 1400篇 |
能源动力 | 1084篇 |
轻工业 | 1271篇 |
水利工程 | 1411篇 |
石油天然气 | 2197篇 |
武器工业 | 572篇 |
无线电 | 5109篇 |
一般工业技术 | 4538篇 |
冶金工业 | 1162篇 |
原子能技术 | 360篇 |
自动化技术 | 6614篇 |
出版年
2024年 | 114篇 |
2023年 | 769篇 |
2022年 | 1350篇 |
2021年 | 1548篇 |
2020年 | 1800篇 |
2019年 | 1413篇 |
2018年 | 1133篇 |
2017年 | 1457篇 |
2016年 | 1546篇 |
2015年 | 1731篇 |
2014年 | 3012篇 |
2013年 | 2633篇 |
2012年 | 3425篇 |
2011年 | 3606篇 |
2010年 | 2720篇 |
2009年 | 2735篇 |
2008年 | 2517篇 |
2007年 | 3055篇 |
2006年 | 2487篇 |
2005年 | 2159篇 |
2004年 | 1814篇 |
2003年 | 1465篇 |
2002年 | 1152篇 |
2001年 | 1086篇 |
2000年 | 841篇 |
1999年 | 645篇 |
1998年 | 493篇 |
1997年 | 452篇 |
1996年 | 361篇 |
1995年 | 315篇 |
1994年 | 209篇 |
1993年 | 182篇 |
1992年 | 164篇 |
1991年 | 109篇 |
1990年 | 104篇 |
1989年 | 112篇 |
1988年 | 66篇 |
1987年 | 39篇 |
1986年 | 18篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 23篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1964年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
2.
3.
Donghai Xu Peng Feng Yang Wang Wanpeng Yang Yu Wang Shaoyan Sun 《American Institute of Chemical Engineers》2022,68(2):e17472
Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(52):22203-22214
The gas purging states affect electricity output and energy storage capacity of unitized regenerative fuel cells. In this study, a model of unitized regenerative fuel cell is established. Cell voltages and operating temperatures influences on the dynamic distribution of thermal fluid during purging process and the discharge of residual liquid water in electrolytic cell mode are investigated. The motivation of the present study is better understanding the gas purging characteristics and its effect on reaction behaviors of unitized regenerative fuel cells. Simulation results reveal a significant influence of purging gas temperature on the water flooding and a great effect of operating voltage on the water diffusion. The operating temperature of electrolytic cell model almost has little effect on purging results at different cell temperature and the same purging gas temperature. When the purging gas temperature is changed, higher temperatures of cell and purging gas facilitate liquid water discharging out from the cell regions. In cell water flooding situation, when having large liquid content, the purging gas has little effects on the water expelling process. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(78):33272-33281
According to the International Energy Agency, only a small part of the full potential of biomass energy is currently used in the world. The annual amount of agricultural waste in the Russian Federation is estimated at about 152 million tons, and the energy potential of animal waste is 201 PJ/year. Anaerobic digestion is an efficient method of converting organic waste into renewable energy sources. Previously, the positive effect of pretreatment of various organic feedstocks in vortex layer apparatus (VLA) on the characteristics of anaerobic digestion and energy efficiency was shown. Currently, there is a significant interest in the world in obtaining biohydrogen from organic waste using the dark fermentation (DF) process. During pretreatment in the VLA, the iron working bodies are abraded and iron particles are introduced into the feedstock of the DF reactor. This may have a positive effect on the production rate and yield of hydrogen, which has not been previously studied. This work is aimed at evaluating the possibility of using the VLA as a method for pretreatment of a dark fermentation feedstock for the intensification of biohydrogen production. To achieve this goal, an experimental setup was constructed. It consisted of a 45 L DF reactor, a VLA and a process control system to collect data on the DF process parameters every 5 min. At a hydraulic retention time in the DF reactor of 24 h and in the VLA of 30 s, the hydrogen content in the biogas increased from 51.1% to 52.2%. At the same time, the pH increased from 3.85 to 4.8–4.9, and the hydrogen production rate increased by 16% to 1.941 L/(L day). The hydrogen yield was 80.9 ml/g VS. Thus, pretreatment of the feedstock in VLA can be an effective way to intensify the DF process; however, further study of the VLA operating modes is required in order to optimize the concentrations of iron particles introduced into the feedstock for the most efficient continuous production of dark fermentative biohydrogen. 相似文献
6.
7.
《Mechatronics》2022
This paper considers the shared path following control of an unmanned ground vehicle by a single person. A passive measure of human intent is used to blend the human and machine inputs in a mixed initiative approach. The blending law is combined with saturated super-twisting sliding mode speed and heading controllers, so that exogenous disturbances can be counteracted via equivalent control. It is proven that when the proposed blending law is used, the combined control signals from both the human and automatic controller respect the actuator magnitude constraints of the machine. To demonstrate the approach, shared control experiments are performed using an unmanned ground vehicle, which follows a lawn mower pattern shaped path. 相似文献
8.
Ewa Bczyska Katarzyna Karolina Pels Subhadip Basu Jakub Wodarczyk Baej Ruszczycki 《International journal of molecular sciences》2021,22(8)
Numerous brain diseases are associated with abnormalities in morphology and density of dendritic spines, small membranous protrusions whose structural geometry correlates with the strength of synaptic connections. Thus, the quantitative analysis of dendritic spines remodeling in microscopic images is one of the key elements towards understanding mechanisms of structural neuronal plasticity and bases of brain pathology. In the following article, we review experimental approaches designed to assess quantitative features of dendritic spines under physiological stimuli and in pathological conditions. We compare various methodological pipelines of biological models, sample preparation, data analysis, image acquisition, sample size, and statistical analysis. The methodology and results of relevant experiments are systematically summarized in a tabular form. In particular, we focus on quantitative data regarding the number of animals, cells, dendritic spines, types of studied parameters, size of observed changes, and their statistical significance. 相似文献
9.
《中国有色金属学会会刊》2021,31(8):2468-2478
An acoustic emission (AE) experiment was carried out to explore the AE location accuracy influenced by temperature. A hollow hemispherical specimen was used to simulate common underground structures. In the process of heating with the flame, the pulse signal of constant frequency was stimulated as an AE source. Then AE signals received by each sensor were collected and used for comparing localization accuracy at different temperatures. Results show that location errors of AE keep the same phenomenon in the early and middle heating stages. In the later stage of heating, location errors of AE increase sharply due to the appearance of cracks. This provides some beneficial suggestions on decreasing location errors of structural cracks caused by temperature and improves the ability of underground structure disaster prevention and control. 相似文献
10.