全文获取类型
收费全文 | 39671篇 |
免费 | 3756篇 |
国内免费 | 2279篇 |
专业分类
电工技术 | 3181篇 |
技术理论 | 3篇 |
综合类 | 3220篇 |
化学工业 | 5450篇 |
金属工艺 | 1583篇 |
机械仪表 | 2184篇 |
建筑科学 | 3950篇 |
矿业工程 | 1577篇 |
能源动力 | 4189篇 |
轻工业 | 1649篇 |
水利工程 | 1156篇 |
石油天然气 | 2872篇 |
武器工业 | 343篇 |
无线电 | 4537篇 |
一般工业技术 | 3435篇 |
冶金工业 | 1991篇 |
原子能技术 | 569篇 |
自动化技术 | 3817篇 |
出版年
2024年 | 161篇 |
2023年 | 578篇 |
2022年 | 1021篇 |
2021年 | 1255篇 |
2020年 | 1369篇 |
2019年 | 1245篇 |
2018年 | 1118篇 |
2017年 | 1431篇 |
2016年 | 1608篇 |
2015年 | 1663篇 |
2014年 | 2614篇 |
2013年 | 2505篇 |
2012年 | 2852篇 |
2011年 | 3100篇 |
2010年 | 2289篇 |
2009年 | 2471篇 |
2008年 | 2211篇 |
2007年 | 2507篇 |
2006年 | 2336篇 |
2005年 | 1768篇 |
2004年 | 1517篇 |
2003年 | 1375篇 |
2002年 | 1156篇 |
2001年 | 988篇 |
2000年 | 855篇 |
1999年 | 710篇 |
1998年 | 519篇 |
1997年 | 444篇 |
1996年 | 403篇 |
1995年 | 325篇 |
1994年 | 263篇 |
1993年 | 169篇 |
1992年 | 136篇 |
1991年 | 128篇 |
1990年 | 99篇 |
1989年 | 85篇 |
1988年 | 50篇 |
1987年 | 45篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 9篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1964年 | 13篇 |
1957年 | 13篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
62.
63.
Suitability of sweet sorghum in Greece, where irrigation supply during crop development is limited as rainfall is scarce and
evapotranspiration loss is high, is examined in relation with radiation availability. A two-year field experiment was conducted,
in central Greece, imposing four soil water regimes via different irrigation treatments: (1) Highly irrigated, (2) Highly
irrigated till anthesis when irrigation stopped, (3) Medium irrigated, and (4) Low irrigated. It was found that above-ground
dry biomass production from non-water-stressed sweet sorghum plants suggests a high productivity potential among C4 crops. Under water shortage, radiation use efficiency may be significantly lower. Radiation use efficiency seems to be linearly
related to water consumption. Stressed plants (probably except severely stressed) seem to use available water more efficiently
than unstressed plants. The slope of the line relating dry matter produced and water evapotranspired increases the sooner
the stress is sensed. Yield reduction resulting from post-anthesis irrigation stopage is very little. High water use efficiency
values tend to be related with low radiation use efficiency values. 相似文献
64.
建立了热采注汽系统热效率的计算模型。根据XX油田数据计算了2个注汽系统的热效率。提出了提高注汽系统热效率的三项措施:(1)降低锅炉的过剩空气系数;(2)按最大允许热损失设计地面输汽管线的保温层厚度;(3)使用视导热系数小的隔热油管,按箍增加隔热结构,防止热封隔器的泄漏等。 相似文献
65.
A method was developed to assess the heat insulation performance of intumescent coatings. The method consists of temperature measurements using the bench‐scaled experimental set‐up of a cone calorimeter and finite difference simulation to calculate the effective thermal conductivity dependent on time/temperature. This simulation procedure was also adapted to the small scale test furnace, in which the standard time–temperature curve is applied to a larger sample and thus which provides results relevant for approval. Investigations on temperature and calculated effective thermal conduction were performed on intumescent coatings in both experimental set‐ups using various coating thicknesses. The results correspond to each other as well as showing the limits of transferability between both fire tests. It is shown that bench‐scaled cone calorimeter tests are a valuable tool for assessing and predicting the performance of intumescent coatings in larger tests relevant for approval. The correlation fails for processes at surface temperatures above 750°C, which are not reached in the cone calorimeter, but are attained in the small scale furnace set‐up. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
66.
本文给出了在P_(507)-HNO_3体系中去除氧化镧中放射性的工艺流程及用混合澄清槽作为萃取设备,在上海跃龙化工厂完成的扩大试验结果。试验表明:α放射性、铁和钙的去污系数都大于1000,镧的回收率大于96%,产品中α放射性小于1计数/h,Fe_2O_3<5ppm,CaO<50ppm,达到了荧光级氧化镧的要求。该流程操作简便、设备简单、稳定性好,可以应用于工业生产。 相似文献
67.
HHD型核子秤电离室已成功地使用于HCS型核子秤.对它的各种物理性能指标进行了检测,各项性能指标都达到了设计要求。 相似文献
68.
A silicide coating was prepared on Ti3SiC2-based ceramic by pack cementation to improve the oxidation resistance of Ti3SiC2, which is a technologically important material for high temperature applications. The microstructure, phase composition and
oxidation resistance of the coated sample were investigated. The results demonstrated that the silicide coating was mainly
composed of TiSi2 and SiC. A single layer of a mixture of SiO2 and TiO2 was formed on the surface of the coated sample during isothermal oxidation at 1100 °C and 1200 °C for 20h. Compared to Ti3SiC2, the parabolic rate constant of silicide coated Ti3SiC2 decreased by 2~3 orders of magnitude. Furthermore, the coated sample showed much better cyclic oxidation resistance than
Ti3SiC2 during the cyclic oxidation at 1100 °C for 400 times. However, during the preparation of the coating, a number of fine cracks
formed in the outer layer of the coating. When these cracks penetrated the whole coating during the cyclic oxidation, the
oxidation rate was accelerated, which degraded the oxidation resistance.
Electronic Publication 相似文献
69.
70.