全文获取类型
收费全文 | 10147篇 |
免费 | 993篇 |
国内免费 | 457篇 |
专业分类
电工技术 | 570篇 |
技术理论 | 3篇 |
综合类 | 662篇 |
化学工业 | 1789篇 |
金属工艺 | 496篇 |
机械仪表 | 736篇 |
建筑科学 | 913篇 |
矿业工程 | 365篇 |
能源动力 | 282篇 |
轻工业 | 577篇 |
水利工程 | 208篇 |
石油天然气 | 727篇 |
武器工业 | 98篇 |
无线电 | 988篇 |
一般工业技术 | 1179篇 |
冶金工业 | 461篇 |
原子能技术 | 130篇 |
自动化技术 | 1413篇 |
出版年
2024年 | 38篇 |
2023年 | 170篇 |
2022年 | 349篇 |
2021年 | 495篇 |
2020年 | 375篇 |
2019年 | 310篇 |
2018年 | 343篇 |
2017年 | 342篇 |
2016年 | 327篇 |
2015年 | 456篇 |
2014年 | 552篇 |
2013年 | 567篇 |
2012年 | 662篇 |
2011年 | 710篇 |
2010年 | 599篇 |
2009年 | 617篇 |
2008年 | 541篇 |
2007年 | 516篇 |
2006年 | 517篇 |
2005年 | 462篇 |
2004年 | 308篇 |
2003年 | 329篇 |
2002年 | 302篇 |
2001年 | 253篇 |
2000年 | 259篇 |
1999年 | 237篇 |
1998年 | 166篇 |
1997年 | 130篇 |
1996年 | 136篇 |
1995年 | 117篇 |
1994年 | 88篇 |
1993年 | 61篇 |
1992年 | 60篇 |
1991年 | 63篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1975年 | 1篇 |
1959年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
Lu Zhang Junjie Shang Tim Pelton Leslee Francis Pelton 《Journal of Computer Assisted Learning》2020,36(4):540-548
With the advent of mobile technologies, well-designed fraction apps can be used to help children gain fraction knowledge, a challenging topic for both teachers and students. The present pilot study adopted a quasi-experimental design to investigate whether children can learn fraction concepts equally well if half of the lesson time (20 min) is replaced with game-based learning. Keeping the total lesson time (40 min) identical, the control group (N = 33) received traditional instruction, and the experimental group (N = 32) was presented with a blended learning approach spending half of the class time (20 min) playing tablet-based fraction games, where each of the learners had their own tablet. The results suggested that in the posttest, the experimental group achieved similar learning gains to the control group and appear to have achieved better performance in the transfer test than the control group. This paper also discusses the efficiency of game-based learning, the mechanism of how fraction games might enhance learning, and the potential of integrating game-based learning in educational settings. 相似文献
3.
4.
5.
6.
研究了具有新型结构的双膦胺镍配合物N,N-双(二苯膦基)-对甲氧基苯胺二氯化镍-甲基铝氧烷(PNP-N i-MAO)催化体系对苯乙烯聚合的催化性能,考察了聚合温度、n(A l)∶n(PNP-N i)、PNP-N i的浓度和苯乙烯的浓度对催化活性、苯乙烯转化率、聚苯乙烯相对分子质量及其分布的影响,并用核磁共振和凝胶色谱对聚苯乙烯的结构进行了表征。实验结果表明,在聚合温度25℃、聚合时间1h、n(A l)∶n(PNP-N i)=300、c(苯乙烯)=2.3m ol/L、c(PNP-N i)=0.4mm ol/L、甲苯为溶剂的适宜条件下,苯乙烯的转化率可达95%以上,催化活性达到5×105g/(m ol.h)左右。核磁共振和凝胶色谱表征结果显示,所得聚苯乙烯为无规结构,重均相对分子质量约为1×104,相对分子质量分布Mw/Mn约为2。 相似文献
7.
8.
Weijia Shang O'Keefe M.T. Fortes J.A.B. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(2):193-204
This paper describes several loop transformation techniques for extracting parallelism from nested loop structures. Nested loops can then be scheduled to run in parallel so that execution time is minimized. One technique is called selective cycle shrinking, and the other is called true dependence cycle shrinking. It is shown how selective shrinking is related to linear scheduling of nested loops and how true dependence shrinking is related to conflict-free mappings of higher dimensional algorithms into lower dimensional processor arrays. Methods are proposed in this paper to find the selective and true dependence shrinkings with minimum total execution time by applying the techniques of finding optimal linear schedules and optimal and conflict-free mappings proposed by W. Shang and A.B. Fortes 相似文献
9.
根据延迟焦化流程的特点,分析了延迟焦化装置扩大生产能力的瓶颈,探讨了基于能量综合优化的装置扩能解除瓶颈的策略方法,基于过程能量综合优化,运用流程模拟技术,通过配套的加热炉优化,分馏塔操作优化,换热网络柔性设计等手段,实现了装置扩大生产能力的目的,并运用所提出的策略对某延迟焦化装置进行了基于能量系统优化的扩能改造,在原流程与设备的基础上,装置处理量增大18.2%,装置物耗,能耗大幅度降低,改造设备投资少,说明能量综合优化对工艺装置扩能改造具有重要意义。 相似文献
10.
Multiuser detection for DS-CDMA UWB in the home environment 总被引:20,自引:0,他引:20
We demonstrate the effectiveness of multiuser detection for an ultra-wideband (UWB) pulse based direct sequence spread spectrum system using code division multiple access. Extensive simulations were run using channel soundings of the 2-8 GHz band collected in a residential setting and characterized by a high level of multipath fragmentation. We show that the adaptive minimum mean square error (MMSE) multiuser detection (MUD) receivers are able to gather multipath energy and reject intersymbol and interchip interference for these channels to a much greater extent than RAKE receivers with 4 and 8 arms. We also demonstrate the adaptive MMSE is able to reject a narrowband IEEE 802.11a OFDM interferer, even for signal-to-interference ratio as severe as -30 dB. We show the adaptive MMSE exhibits only a 6 dB penalty relative to the single user case for the heavy multi-access interference (number of asynchronous users equal to spreading code length). The practical RAKE receivers were incapable of effectively rejecting either the strong narrowband interference or the heavily loaded wideband interference. Even more moderate levels of interference caused significant degradation in the performance of the practical RAKE receivers. 相似文献