全文获取类型
收费全文 | 73411篇 |
免费 | 8971篇 |
国内免费 | 3728篇 |
专业分类
电工技术 | 5842篇 |
综合类 | 6518篇 |
化学工业 | 11092篇 |
金属工艺 | 6146篇 |
机械仪表 | 3712篇 |
建筑科学 | 6341篇 |
矿业工程 | 1144篇 |
能源动力 | 8900篇 |
轻工业 | 2834篇 |
水利工程 | 842篇 |
石油天然气 | 2622篇 |
武器工业 | 807篇 |
无线电 | 7145篇 |
一般工业技术 | 7490篇 |
冶金工业 | 4031篇 |
原子能技术 | 1481篇 |
自动化技术 | 9163篇 |
出版年
2024年 | 376篇 |
2023年 | 1062篇 |
2022年 | 2007篇 |
2021年 | 2275篇 |
2020年 | 2471篇 |
2019年 | 2094篇 |
2018年 | 1905篇 |
2017年 | 2426篇 |
2016年 | 2748篇 |
2015年 | 2790篇 |
2014年 | 4473篇 |
2013年 | 4858篇 |
2012年 | 5141篇 |
2011年 | 5643篇 |
2010年 | 4145篇 |
2009年 | 4322篇 |
2008年 | 3766篇 |
2007年 | 4887篇 |
2006年 | 4227篇 |
2005年 | 3720篇 |
2004年 | 3128篇 |
2003年 | 2802篇 |
2002年 | 2525篇 |
2001年 | 2037篇 |
2000年 | 1696篇 |
1999年 | 1440篇 |
1998年 | 1161篇 |
1997年 | 1073篇 |
1996年 | 844篇 |
1995年 | 770篇 |
1994年 | 623篇 |
1993年 | 492篇 |
1992年 | 452篇 |
1991年 | 294篇 |
1990年 | 253篇 |
1989年 | 237篇 |
1988年 | 153篇 |
1987年 | 117篇 |
1986年 | 89篇 |
1985年 | 83篇 |
1984年 | 119篇 |
1983年 | 78篇 |
1982年 | 92篇 |
1981年 | 49篇 |
1980年 | 37篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1959年 | 30篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
利用保温裸露因数的概念来反映保温层保温性能的变化,提出采用统一原则来建立适用于单元系统和复合系统保温层热经济寿命的数学模型,并通过实例证明在热经济寿命终了时更新保温层,可使系统的运行具有最大的经济性。 相似文献
92.
93.
94.
Abstract. The estimation of the spectral density function of a stationary Gaussian process at the input of an instantaneous nonlinearity is considered when the nonlinearity is known and a finite set of observations of the output process is given. A class of spectral estimates is considered and their quadratic-mean consistency is established; precise asymptotic expressions for their bias and covariance are derived and their asymptotic normality is obtained. 相似文献
95.
40000m~3/h空分设备主换热器的设计及制造 总被引:1,自引:0,他引:1
通过对进口 4 0 0 0 0m3 /h空分设备主换热器进行结构分析及对比模拟计算 ,用国产传热翅片进行设计、采用真空钎焊工艺制造的主换热器 ,经并网运行 ,设计指标优于原空分设备 ,为今后成套大型空分设备板翅式换热器国产化设计、制造创造了条件。 相似文献
96.
97.
J. Balakrishnan W. A. Sethares C. R. Johnson 《International Journal of Adaptive Control and Signal Processing》2002,16(4):309-323
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
98.
99.
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
100.
In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献