全文获取类型
收费全文 | 122343篇 |
免费 | 11351篇 |
国内免费 | 4573篇 |
专业分类
电工技术 | 6085篇 |
技术理论 | 10篇 |
综合类 | 10173篇 |
化学工业 | 24085篇 |
金属工艺 | 2011篇 |
机械仪表 | 2526篇 |
建筑科学 | 14963篇 |
矿业工程 | 20361篇 |
能源动力 | 7663篇 |
轻工业 | 5495篇 |
水利工程 | 19015篇 |
石油天然气 | 9500篇 |
武器工业 | 219篇 |
无线电 | 1553篇 |
一般工业技术 | 4665篇 |
冶金工业 | 5323篇 |
原子能技术 | 1161篇 |
自动化技术 | 3459篇 |
出版年
2024年 | 325篇 |
2023年 | 1152篇 |
2022年 | 2659篇 |
2021年 | 3484篇 |
2020年 | 3927篇 |
2019年 | 2877篇 |
2018年 | 2867篇 |
2017年 | 3306篇 |
2016年 | 3910篇 |
2015年 | 4040篇 |
2014年 | 7824篇 |
2013年 | 7550篇 |
2012年 | 10216篇 |
2011年 | 9574篇 |
2010年 | 7022篇 |
2009年 | 7242篇 |
2008年 | 6396篇 |
2007年 | 8130篇 |
2006年 | 7447篇 |
2005年 | 6751篇 |
2004年 | 5226篇 |
2003年 | 4810篇 |
2002年 | 4075篇 |
2001年 | 3452篇 |
2000年 | 2863篇 |
1999年 | 2237篇 |
1998年 | 1611篇 |
1997年 | 1379篇 |
1996年 | 1082篇 |
1995年 | 959篇 |
1994年 | 695篇 |
1993年 | 500篇 |
1992年 | 417篇 |
1991年 | 298篇 |
1990年 | 223篇 |
1989年 | 219篇 |
1988年 | 158篇 |
1987年 | 165篇 |
1986年 | 119篇 |
1985年 | 282篇 |
1984年 | 309篇 |
1983年 | 225篇 |
1982年 | 172篇 |
1981年 | 11篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
This research investigates the utility of passive microwave remote sensing instruments to accurately determine snow water equivalent (SWE) over large spatial extents. Three existing Special Sensor Microwave Imager (SSM/I) snow water equivalent algorithms produced by Chang, Tait and Goodison were evaluated for their ability to determine snow water equivalent in a snowpack containing substantial depth hoar, large faceted snow crystals. The Kuparuk River Watershed (8140 km2) test site on the North Slope of Alaska was chosen for its snowpack containing a think depth hoar layer and long history of ground truth data. A new regional snow water equivalent algorithm was developed to determine if it could produce better results than the existing algorithms in an area known to contain significant depth hoar. The four algorithms were tested to see how well they could determine snow water equivalent: (1) on a per pixel basis, (2) across swath-averaged spatial bands of approximately 850 km2, and (3) on a watershed scale. The algorithms were evaluated to see if they captured the annual spatial distribution in snow water equivalent over the watershed. Results show that the algorithms developed by Chang and from this research are generally within 3 cm of the spatially averaged snow water equivalents over the entire watershed. The algorithms produced by Chang, Tait, and in this research were able to predict the basin-wide ground measured snow water equivalent value within a percent error range from −32.4% to 24.4% in the years with a typical snowpack. None of the algorithms produce accurate results on a pixel-by-pixel scale, with errors ranging from −26% to 308%. 相似文献
54.
金沙江防洪(库容)规划的探讨 总被引:1,自引:0,他引:1
在分析长江灾害洪水特征的基础上,全面深入地研究了全沙江水库的防洪库客、防洪目标、防洪特点和调度原则,并对防洪库容的作用进行了估算和分析。从多方面比较了虎跳峡高坝方案与低坝方案,结果表明:高坝方案的效益明显高于低坝方案,而两者所需付出的代价相差不大。 相似文献
55.
Yun‐Hwei Shen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(5):581-586
A novel strategy of sweep coagulation to treat low turbidity water is presented herein. Study findings demonstrated that an Na+‐saturated bentonite with medium cation exchange capacity (CEC) resulted in significant turbidity removal at a bentonite dosage of 30 mg dm?3. Bentonite dispersion with fully delaminated platelets tended to undergo a more porous type of coagulation with intense face‐to‐face interactions of platelets and effectively entrapped TiO2 particles in band‐type structures. This type of coagulation usually results in a large volume of settled flocs with a fluffy structure and excellent turbidity removal efficiency for sweep coagulation. The sign and magnitude of electrical charge on TiO2 particles has a minor effect on the efficiency of sweep coagulation. Copyright © 2005 Society of Chemical Industry 相似文献
56.
Inertinite concentrates from three Australian bituminous coals were hydrogenated at various temperatures ranging from 350 to 475 °C in the presence of tetralin without any added catalyst. Both conversion yields and microscopic observations of the benzene-extracted hydrogenation residues have revealed that the hydrogenation of the inertinite macerals becomes significant only > 400 °C, whereas the dissolution-hydrogenation of the accompanying vitrinite macerals occurs mainly between 350 and 400 °C. The major reaction pathway for the inertinite particles in the hydrogenation process appears to be one of initial mild carbonization followed by hydrogenation. A simplified reaction scheme is proposed which describes the reaction pathway involved in the hydrogenation of inertinite. 相似文献
57.
The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state. 相似文献
58.
In this paper we present some preliminary results about the coupling of shallow water equations for free surface flows and Darcy equation for groundwater flows. A suitable set of interface conditions is discussed: the Beavers and Joseph formula for the bottom stress is used. An iterative algorithm to solve the coupled problem is proposed and some numerical results are presented. 相似文献
59.
介绍了天铁炼钢厂中间包水模实验原理和过程,分析了斜、直、圆三种型式挡渣墙模拟结果,提出了合理的挡渣控流方案,在生产实践中使用效果良好。 相似文献
60.