全文获取类型
收费全文 | 1859篇 |
免费 | 167篇 |
国内免费 | 101篇 |
专业分类
电工技术 | 79篇 |
综合类 | 169篇 |
化学工业 | 283篇 |
金属工艺 | 20篇 |
机械仪表 | 63篇 |
建筑科学 | 52篇 |
矿业工程 | 18篇 |
能源动力 | 85篇 |
轻工业 | 23篇 |
水利工程 | 112篇 |
石油天然气 | 30篇 |
武器工业 | 8篇 |
无线电 | 624篇 |
一般工业技术 | 151篇 |
冶金工业 | 105篇 |
原子能技术 | 42篇 |
自动化技术 | 263篇 |
出版年
2024年 | 4篇 |
2023年 | 39篇 |
2022年 | 79篇 |
2021年 | 104篇 |
2020年 | 61篇 |
2019年 | 49篇 |
2018年 | 45篇 |
2017年 | 51篇 |
2016年 | 68篇 |
2015年 | 79篇 |
2014年 | 104篇 |
2013年 | 97篇 |
2012年 | 121篇 |
2011年 | 121篇 |
2010年 | 96篇 |
2009年 | 126篇 |
2008年 | 123篇 |
2007年 | 136篇 |
2006年 | 123篇 |
2005年 | 92篇 |
2004年 | 74篇 |
2003年 | 60篇 |
2002年 | 61篇 |
2001年 | 39篇 |
2000年 | 24篇 |
1999年 | 18篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 25篇 |
1994年 | 15篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1964年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有2127条查询结果,搜索用时 15 毫秒
1.
2.
G. J. Scott 《Food Reviews International》2003,19(1):203-219
Identifying markets for new or improved products for minor crops threatened with extinction is one critical component of any strategy intended to enhance prospects for sustainable production and use. Typically, however, activities linked to the sustainability of these commodities avoid addressing questions associated with assessing their commercial potential. After a brief review of this avoidance syndrome, this article presents a sample of practical, low-cost procedures to help evaluate the market prospects and procedures for crops like quinoa, while citing references to other methodological materials covering similar topics. 相似文献
3.
Bedload Transport in Alluvial Channels 总被引:1,自引:0,他引:1
Miguel Bravo-Espinosa W. R. Osterkamp Vicente L. Lopes 《Canadian Metallurgical Quarterly》2003,129(10):783-795
Hydraulic, sediment, land-use, and rock-erosivity data of 22 alluvial streams were used to evaluate conditions of bedload transport and the performance of selected bedload-transport equations. Transport categories of transport-limited (TL), partially transport-limited (PTL), and supply-limited (SL) were identified by a semiquantitative approach that considers hydraulic constraints on sediment movement and the processes that control sediment availability at the basin scale. Equations by Parker et al. in 1982, Schoklitsch in 1962, and Meyer-Peter and Muller in 1948 adequately predicted sediment transport in channels with TL condition, whereas the equations of Bagnold in 1980, and Schoklitsch, in 1962, performed well for PTL and SL conditions. Overall, the equation of Schoklitsch predicted well the measured bedload data for eight of 22 streams, and the Bagnold equation predicted the measured data in seven streams. 相似文献
4.
5.
Graziosi Fabio Ruggieri Marina Santucci Fortunato 《Wireless Personal Communications》2002,21(2):141-162
In this paper the performance of a packet mobile radio network is studied inthe presence of shadow fading outage intervals.Under quite general assumptions for the medium access protocol,the probability mass function of the sequence of packets that may be lostdue to an outage interval is derived. It is seen that long sequences of lostpackets are likely to occur for typical values of the mobile speed andshadowing correlation parameters.For delay constrained sources, e.g., voice, the analysis is mainly focused atderiving the probability function of the sequence of dropped packetsand the probability of dropping. For data sources, the delay statistic isalso derived. In the latter case, the effect of finite buffer length isaddressed. Simulation is used to verify the accuracy of approximations introduced in the analysis. 相似文献
6.
Jan A. Derecki 《Journal of Great Lakes research》1985,11(3):201-207
Periodic man-made changes in the outlet of Lake Huron through the St. Clair River date back to the middle of the last century. These artificial channel changes have been well documented during the present century. They consist of dredging for commercial gravel removal in the upper river during 1908–25 and uncompensated navigation improvements for the 7.6-m (25-ft) and 8.2-m (27-ft) projects completed in 1933 and 1962, respectively. The total effect of these changes on the levels of Lakes Michigan and Huron (hydraulically one lake) and on the upper St. Clair River profile was determined with dynamic flow models. The ultimate effect of the above dredging was a permanent lowering of the Lake Michigan-Huron levels 0.27 m (0.89 ft), which represents a tremendous loss of freshwater resource [32 km3 (7.7 mi3)]. 相似文献
7.
The estimation of the Direction-Of-Arrival (DOA) and the variance of the angular spread, using an array of sensors in the
case of a Ricean channel is considered, using the Maximum-Likelihood, Least-Squares and Weighted Least Squares criteria. The
Cramér-Rao bound is also obtained for the problem of interest. Simplification of the cost functions to reduce the dimension
of the problem has been carried out and the performance of the methods has been studied based on numerical experiments.
A major part of the work was carried out when K V S Hari was visiting the Department of Signals, Sensors and Systems during
Jul–Sep 1995, on leave from the Indian Institute of Science 相似文献
8.
9.
准确估算集群系统所需无线信道数是工程设计中的一个重要的关键环节。本文从讨论系统业务、系统话务量出发,提出了一种正确使用爱尔兰—B公式(或巴姆表)确定集群系统中无线信道数的新方法。继而,较为详细地定量分析了集群方式对系统话务量的影响。最后,针对实际工程设计,推荐了一个集群系统容量计算的经验公式。 相似文献
10.
为了能够实现定位精度的自适应,本文分析了认知无线电定位系统(cognitive positioning systems,CPS)的原理。该系统利用频谱及环境感知等模块中的传感器单元来获取所需的定位参数,并将其与到达时间(time of arrival,TOA)定位估计算法相结合,以克拉美罗下界(Cramer-Rao lower bound,CRLB)为准则分析最大似然(maximum likelihood,ML)定位精度自适应算法。本文还对单径和多径环境条件下定位精度自适应性能进行了比较。仿真结果表明,该算法能够实现定位精度的自适应,并能通过改善系统可用的频带带宽、分散频谱的数目、信号的调制方式等因素来提高定位精度。 相似文献