全文获取类型
收费全文 | 27814篇 |
免费 | 3201篇 |
国内免费 | 1643篇 |
专业分类
电工技术 | 3720篇 |
综合类 | 2210篇 |
化学工业 | 2565篇 |
金属工艺 | 3561篇 |
机械仪表 | 3998篇 |
建筑科学 | 1943篇 |
矿业工程 | 962篇 |
能源动力 | 1129篇 |
轻工业 | 1226篇 |
水利工程 | 859篇 |
石油天然气 | 1364篇 |
武器工业 | 225篇 |
无线电 | 2183篇 |
一般工业技术 | 3233篇 |
冶金工业 | 1262篇 |
原子能技术 | 500篇 |
自动化技术 | 1718篇 |
出版年
2024年 | 198篇 |
2023年 | 535篇 |
2022年 | 927篇 |
2021年 | 1110篇 |
2020年 | 1064篇 |
2019年 | 934篇 |
2018年 | 924篇 |
2017年 | 1141篇 |
2016年 | 1154篇 |
2015年 | 1127篇 |
2014年 | 1594篇 |
2013年 | 1866篇 |
2012年 | 1807篇 |
2011年 | 1994篇 |
2010年 | 1496篇 |
2009年 | 1583篇 |
2008年 | 1328篇 |
2007年 | 1782篇 |
2006年 | 1633篇 |
2005年 | 1381篇 |
2004年 | 1240篇 |
2003年 | 936篇 |
2002年 | 812篇 |
2001年 | 719篇 |
2000年 | 645篇 |
1999年 | 497篇 |
1998年 | 379篇 |
1997年 | 346篇 |
1996年 | 303篇 |
1995年 | 264篇 |
1994年 | 190篇 |
1993年 | 143篇 |
1992年 | 124篇 |
1991年 | 101篇 |
1990年 | 69篇 |
1989年 | 68篇 |
1988年 | 72篇 |
1987年 | 35篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 21篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1964年 | 2篇 |
1959年 | 9篇 |
1958年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Rates of ammonia (NH3) loss from a ryegrass sward measured using a system of small wind tunnels were compared with concurrent measurements made using a micrometeorological mass balance method. Measurements were made during two experiments within a circular plot (radius 10m) treated with urea at a rate of 200kgNha?1. In the first experiment, air speed through the tunnels was adjusted as necessary to maintain a value of approximately 1ms?1. This value differed on most occasions from the mean ambient wind speed which was measured at a height of 250mm and which ranged from 0.61 to 2.95ms?1. Rates of loss measured using the wind tunnels differed by a factor of between two and five from those measured using the mass balance method; there was no consistent pattern in the differences between the rates of loss. The total losses of NH3 measured during 15 days were equivalent to 49.1 and 30.2kg Nha?1 for the mass balance and wind tunnel methods, respectively. In the second experiment, air speed through the tunnels was adjusted as necessary to maintain a value as close as possible to the mean ambient wind speed measured at a height of 250mm. Rates of NH3 loss measured using the two methods did not differ significantly; total losses of NH3 during 17 days were equivalent to 96.9 and 101kg Nha?1 for the mass balance and wind tunnel methods, respectively. The difference between the findings of the two experiments could be attributed to the direct effect of air speed through the tunnels rather than to differences between ambient temperatures and those inside the tunnels. During and following periods of rain the rates of loss measured using the tunnels were up to six times greater than those observed with the mass balance method. Rates of loss measured by the two methods became similar again when the tunnels were moved following rain. The study demonstrates that enclosures can be designed and operated to provide reliable measurements of the rate of NH3 loss from grassland. Potential applications of the two methods are discussed. 相似文献
32.
We analyze the wear resistance of plasma coatings for a constant work of friction. The dependences of the wear resistance
of the coatings are obtained for a broad range of loading conditions. It is shown that the minimum sensitivity to loading
conditions is exhibited by the molybdenum coatings. It is also established that the wear resistance of the coatings decreases
as the amplitude of displacements increases and the cyclic frequency of the tests decreases due to the intensification of
fatigue processes on the surfaces. The comparative characteristics of coatings are presented.
__________
Translated from Problemy Prochnosti, No. 5, pp. 94–100, September–October, 2007. 相似文献
33.
热带城市垃圾典型组分的热解特性研究 总被引:7,自引:0,他引:7
对热带城市垃圾的几种典型组分进行了热解实验,得到了它们的失重曲线,通过对失重曲线进行分析,得到了这几种典型组分的热解规律,并通过建立热解动力学模型,求出了其中两种组分的活化能E和频率因子A。 相似文献
34.
35.
The dynamic properties of high-cis (98%) and cis-trans (42% cis) polybutadienes, crosslinked with 0.1 to 1.0% of crosslinking agent, have been studied using a torsion pendulum method over the temperature range ?170 to +20°C. For the high-cis rubber plots of damping factor (tan δ) against temperature showed the expected peak in the glass-transition region with an additional peak in the neighbourhood of 0°C attributable to crystallization. The cis-trans rubber showed two damping maxima in the transition region, separated by 30 to 40°C (depending on the degree of crosslinking), suggesting incipient phase separation of the component structures. The rebound resilience of the high-cis rubber at room temperature exceeded that of the cis-trans, reaching 92% at the highest crosslink density. Plots of resilience versus temperature for both rubbers showed a single minimum in the glass transition region. 相似文献
36.
37.
用于频率合成器的低损耗声表面波滤波器 总被引:2,自引:2,他引:0
简述了产生声表面波滤波器插入损耗的主要机理和获得低损耗的原则;介绍了根据此原则对100~500MHz5种滤波器的研制过程和结果。实验表明,采用镜像阻抗连接换能器结构可达到3~4dB的低损耗,并成功地应用于频率合成器中。 相似文献
38.
AN EXTENDED MODELING OF TIDE-WAVE MOTION 总被引:1,自引:1,他引:0
Zhang Qing hua Xu Hao Qu Yuan yuan First Institute of Oceanography State Oceanic Administration Qingdao China Key Laboratory of Marine Science Numerical Modeling State Oceanic Administration Qingdao China 《水动力学研究与进展(B辑)》2001,(3)
1 . INTRODUCTIONTostudythemotionofthetide waves,theshallowwaterequations ,i.e .theverticalintergra tionofthecontinuityequationandmomentumequa tion ,isconsideredasthegoverningequations.Byaboveequationstwoequationsrelatedtothehorizon talfluxofthetide currentsa… 相似文献
39.
40.
In keeping with the advance of more compact and more power-saving electronic equipment, the demand is increasing for smaller and more efficient switching power supply. Therefore, it is necessary to provide the adequate magnetic power ferrite materials to satisfy the demand. Such ferrite materials have to meet the following main requirement: 1) high initial permeability (μ i ); 2) high saturation magnetic induction (Bs); 3) high Curie temperature (Tc); 4) high electrical resistivity (ρ ); 5)… 相似文献