全文获取类型
收费全文 | 42649篇 |
免费 | 4981篇 |
国内免费 | 2809篇 |
专业分类
电工技术 | 4474篇 |
技术理论 | 3篇 |
综合类 | 5256篇 |
化学工业 | 3871篇 |
金属工艺 | 1220篇 |
机械仪表 | 2934篇 |
建筑科学 | 4523篇 |
矿业工程 | 2064篇 |
能源动力 | 1706篇 |
轻工业 | 3639篇 |
水利工程 | 2311篇 |
石油天然气 | 2679篇 |
武器工业 | 653篇 |
无线电 | 3811篇 |
一般工业技术 | 3352篇 |
冶金工业 | 1471篇 |
原子能技术 | 357篇 |
自动化技术 | 6115篇 |
出版年
2024年 | 170篇 |
2023年 | 574篇 |
2022年 | 1237篇 |
2021年 | 1437篇 |
2020年 | 1442篇 |
2019年 | 1248篇 |
2018年 | 1190篇 |
2017年 | 1484篇 |
2016年 | 1650篇 |
2015年 | 1734篇 |
2014年 | 2583篇 |
2013年 | 2607篇 |
2012年 | 3165篇 |
2011年 | 3472篇 |
2010年 | 2550篇 |
2009年 | 2630篇 |
2008年 | 2517篇 |
2007年 | 3146篇 |
2006年 | 2739篇 |
2005年 | 2304篇 |
2004年 | 1833篇 |
2003年 | 1562篇 |
2002年 | 1224篇 |
2001年 | 1046篇 |
2000年 | 888篇 |
1999年 | 754篇 |
1998年 | 586篇 |
1997年 | 522篇 |
1996年 | 420篇 |
1995年 | 380篇 |
1994年 | 305篇 |
1993年 | 219篇 |
1992年 | 180篇 |
1991年 | 157篇 |
1990年 | 97篇 |
1989年 | 100篇 |
1988年 | 77篇 |
1987年 | 35篇 |
1986年 | 36篇 |
1985年 | 10篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1977年 | 3篇 |
1975年 | 5篇 |
1959年 | 7篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m?2 in 2003, 127 ± 17 g‐dry wt m?2 in 2004 and 149 ± 23 g‐dry wt m?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m?2 and 5.2 to 19.9 g‐C m?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
103.
104.
陈新瑜 《电网与水力发电进展》2003,19(3):39-41
在统计分析的基础上,归纳总结了陕西南部各类路基病害的分布特征,并从自然因素和人为因素两个方面分析了各类路基病害发生的主要控制因素。 相似文献
105.
大豆蛋白纤维的性能及产品开发 总被引:11,自引:4,他引:7
主要描述了大豆蛋白纤维的性能,介绍了大豆蛋白纤维的生产以及大豆蛋白纺织新产品的开发。 相似文献
106.
Yukio Sato Tomohito Tanaka Fumiyasu Oba Takahisa Yamamoto Yuichi Ikuhara Taketo Sakuma 《Science and Technology of Advanced Materials》2003,4(6):137
SrTiO3 and ZnO bicrystals with various types of boundaries were fabricated in order to examine their current–voltage characteristics across single grain boundaries. Their grain boundary structures were also investigated by high-resolution transmission electron microscopy. In Nb-doped SrTiO3, electron transport behaviors depend on the type of boundaries. Random type boundaries exhibit highly non-linear current–voltage characteristics, while low angle boundaries show a slight non-linearity. On the contrary, undoped ZnO does not exhibit non-linear current–voltage characteristics in any type of boundaries including random ones. It is suggested that the differences observed in current–voltage properties between the two systems are mainly due to the difference in the accumulation behavior of acceptor-like native defects at grain boundaries. A clear non-linearity is obtained by means of Co-doping even for the highly coherent Σ1 boundary in a ZnO bicrystal. This is considered to result from the production of acceptor-like native defects by Co-doping. 相似文献
107.
湿法生产线的技术更新改造有异地新建新型干法生产线和原地改成湿磨干法生产线二种。浙江虎山集团(?)3.0 m×88.68 m湿法线的改造,经方案比较和生产原料的状况,采用了湿磨干烧方案。其中,料浆脱水采用了真空吸滤法,浇成系统采用了南京院专有技术。改造投产后,获得了优质、高产、低耗和安全生产的技改效果。 相似文献
108.
109.
110.
Sivakumar Bakthavachalu Miguel A. Labrador 《International Journal of Communication Systems》2004,17(8):763-778
The TFRC protocol has been proposed as a TCP‐friendly protocol to transport streaming media over the Internet. However, its deployment is still questionable because it has not been compared to other important protocols, analysed in the presence of important mechanisms, such as the explicit congestion notification (ECN), and studied under more realistic network conditions. In this paper, we address these three aspects, including other congestion control protocols not considered before in the same investigation, such as TCP Tahoe, Reno, Newreno, Vegas, Sack, GAIMD, and the Binomial algorithms, the effect of using ECN in the friendliness of the protocols, and the fairness of the protocols under static and dynamic network conditions. We found that TFRC can be safely deployed in the Internet if competing with TCP Tahoe, New Reno and SACK since fairness is achieved under all scenarios considered. We also found that ECN actually helps in achieving better fairness. However, fairness problems arise when TFRC competes with TCP Reno, GAIMD, SQRT or IIAD in static or dynamic conditions, or both. We used normalized throughput, fairness index, and convergence time as the main performance metrics for comparison. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献