全文获取类型
收费全文 | 16673篇 |
免费 | 1916篇 |
国内免费 | 1016篇 |
专业分类
电工技术 | 3532篇 |
综合类 | 1310篇 |
化学工业 | 1625篇 |
金属工艺 | 989篇 |
机械仪表 | 877篇 |
建筑科学 | 1039篇 |
矿业工程 | 452篇 |
能源动力 | 971篇 |
轻工业 | 938篇 |
水利工程 | 671篇 |
石油天然气 | 901篇 |
武器工业 | 85篇 |
无线电 | 2098篇 |
一般工业技术 | 1431篇 |
冶金工业 | 753篇 |
原子能技术 | 442篇 |
自动化技术 | 1491篇 |
出版年
2024年 | 105篇 |
2023年 | 304篇 |
2022年 | 617篇 |
2021年 | 719篇 |
2020年 | 654篇 |
2019年 | 511篇 |
2018年 | 472篇 |
2017年 | 620篇 |
2016年 | 658篇 |
2015年 | 658篇 |
2014年 | 1057篇 |
2013年 | 1194篇 |
2012年 | 1116篇 |
2011年 | 1286篇 |
2010年 | 974篇 |
2009年 | 984篇 |
2008年 | 846篇 |
2007年 | 1052篇 |
2006年 | 927篇 |
2005年 | 810篇 |
2004年 | 662篇 |
2003年 | 529篇 |
2002年 | 546篇 |
2001年 | 425篇 |
2000年 | 352篇 |
1999年 | 281篇 |
1998年 | 198篇 |
1997年 | 188篇 |
1996年 | 169篇 |
1995年 | 134篇 |
1994年 | 131篇 |
1993年 | 84篇 |
1992年 | 63篇 |
1991年 | 56篇 |
1990年 | 35篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1964年 | 2篇 |
1960年 | 1篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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
42.
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
43.
44.
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
45.
农电企业降损节能工作的探讨 总被引:1,自引:0,他引:1
阐述了农网降损节能的意义和技术上,管理上的有效措施,指出在线损管理中,只有将理论计算,准确统计,科学分析,营业管理和严打窃电等一系列办法有机地结合起来,才会有良好的效果。 相似文献
46.
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
47.
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
48.
用屏蔽暂堵技术封堵水平井裂缝性漏层 总被引:1,自引:1,他引:0
克拉玛依油田HW702水平井的大斜度段和水平段,将穿越纵向裂缝发育的二叠系佳木河组储层。为安全钻进和保护油层,用超细碳酸钙和磺化沥青复配后加入复合离子钻井液中成屏蔽暂堵的堵漏钻井液。室内用岩心试验,屏蔽暂堵后渗透率可降为0,暂堵深度小于3cm,可用酸化和射孔解堵。现场使用效果也很好,使HW702水平井顺利完钻,并获得工业油气流。 相似文献
49.
50.
The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust. 相似文献