全文获取类型
收费全文 | 43140篇 |
免费 | 5388篇 |
国内免费 | 4116篇 |
专业分类
电工技术 | 1953篇 |
技术理论 | 1篇 |
综合类 | 4634篇 |
化学工业 | 6776篇 |
金属工艺 | 886篇 |
机械仪表 | 1843篇 |
建筑科学 | 11080篇 |
矿业工程 | 1629篇 |
能源动力 | 1054篇 |
轻工业 | 3456篇 |
水利工程 | 3553篇 |
石油天然气 | 1579篇 |
武器工业 | 245篇 |
无线电 | 4572篇 |
一般工业技术 | 3944篇 |
冶金工业 | 1020篇 |
原子能技术 | 417篇 |
自动化技术 | 4002篇 |
出版年
2024年 | 229篇 |
2023年 | 668篇 |
2022年 | 1276篇 |
2021年 | 1551篇 |
2020年 | 1656篇 |
2019年 | 1495篇 |
2018年 | 1385篇 |
2017年 | 1682篇 |
2016年 | 1818篇 |
2015年 | 1829篇 |
2014年 | 2960篇 |
2013年 | 2612篇 |
2012年 | 3268篇 |
2011年 | 3355篇 |
2010年 | 2702篇 |
2009年 | 2695篇 |
2008年 | 2448篇 |
2007年 | 2911篇 |
2006年 | 2568篇 |
2005年 | 2367篇 |
2004年 | 1993篇 |
2003年 | 1658篇 |
2002年 | 1251篇 |
2001年 | 1073篇 |
2000年 | 958篇 |
1999年 | 797篇 |
1998年 | 650篇 |
1997年 | 483篇 |
1996年 | 388篇 |
1995年 | 344篇 |
1994年 | 315篇 |
1993年 | 231篇 |
1992年 | 166篇 |
1991年 | 148篇 |
1990年 | 123篇 |
1989年 | 93篇 |
1988年 | 74篇 |
1987年 | 61篇 |
1986年 | 61篇 |
1985年 | 51篇 |
1984年 | 63篇 |
1983年 | 37篇 |
1982年 | 47篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 40篇 |
1976年 | 6篇 |
1964年 | 4篇 |
1959年 | 4篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
介绍了以菱锌矿为原料生产轻质氧化锌的方法,论述了反应酸浓度,煅烧温度,溶液PH值对实验的影响,并对生产工艺条件进行了研究。其工艺流程是将粉碎后的菱锌矿进行循环酸浸,净化后再直接和碳化母液反应,经沉降后再煅烧分解为轻质氧化锌,产品质量符合国家标准,视比容大,活性强,成本低,经济效益显著。 相似文献
62.
63.
64.
Modeling and assimilation of root zone soil moisture using remote sensing observations in Walnut Gulch Watershed during SMEX04 总被引:1,自引:0,他引:1
Soil moisture status in the root zone is an important component of the water cycle at all spatial scales (e.g., point, field, catchment, watershed, and region). In this study, the spatio-temporal evolution of root zone soil moisture of the Walnut Gulch Experimental Watershed (WGEW) in Arizona was investigated during the Soil Moisture Experiment 2004 (SMEX04). Root zone soil moisture was estimated via assimilation of aircraft-based remotely sensed surface soil moisture into a distributed Soil-Water-Atmosphere-Plant (SWAP) model. An ensemble square root filter (EnSRF) based on a Kalman filtering scheme was used for assimilating the aircraft-based soil moisture observations at a spatial resolution of 800 m × 800 m. The SWAP model inputs were derived from the SSURGO soil database, LAI (Leaf Area Index) data from SMEX04 database, and data from meteorological stations/rain gauges at the WGEW. Model predictions are presented in terms of temporal evolution of soil moisture probability density function at various depths across the WGEW. The assimilation of the remotely sensed surface soil moisture observations had limited influence on the profile soil moisture. More specifically, root zone soil moisture depended mostly on the soil type. Modeled soil moisture profile estimates were compared to field measurements made periodically during the experiment at the ground based soil moisture stations in the watershed. Comparisons showed that the ground-based soil moisture observations at various depths were within ± 1 standard deviation of the modeled profile soil moisture. Density plots of root zone soil moisture at various depths in the WGEW exhibited multi-modal variations due to the uneven distribution of precipitation and the heterogeneity of soil types and soil layers across the watershed. 相似文献
65.
In this paper we suggest a new statistical method of correcting the results of hot-line experiments for the effects of background sources and we use the new method to reassess the adequacy of three probability distributions proposed in the literature for image spread from line sources. The data are from sources labelled with 125I in semi-thin resin sections 0·4-0·8 μm in thickness. The new method reveals that two of the models describe the empirical distributions more closely than earlier analysis had suggested, and it confirms an increasing relationship between half distance of image spread and the thickness of the source. However, it also confirms that considerable ‘inter hot-line’ experimental variation remains, even after background correction. This suggests that multiple experiments are needed to produce reliable estimates of half distance. 相似文献
66.
首先介绍了光幕测量高度的原理 ,给出了高度测量光幕的一种实现方法 ,分析了由该方法设计的系统结构和主要性能。从而彻底解决了相邻通路间的干扰 ,提高了测量精度。 相似文献
67.
68.
Keita Ikeue Shingo Ando Tomohiro Mitsuyama Yusuke Ohta Keishi Arayama Akiko Tsutsumi Masato Machida 《Topics in Catalysis》2008,47(3-4):175-180
Lanthanide-based oxysulfides and sulfide, LnTaO3.5S0.5, Ln10OS14 (Ln = La, Pr, Nd, Sm) and La4In5S13, were successively synthesized by sulfurization in a flowing H2S. The sulfurization decreased the band-gap energies from >4 eV to <3eV, because of the formation of occupied S3p orbitals
on the top of valence band. In accordance with the small band gap, the H2 evolution from a 0.01 M Na2S and 0.01 M Na2SO3 solution system was observed under irradiation of light up to >500 nm. The rate of H2 evolution under light irradiation of >500 nm increased in the order of Ni/LaTaO3.5S0.5 < Ru/La10OS14 < Pt/La4In5S13. 相似文献
69.
IRIS/AP型电感耦合等离子体光谱仪激发光源常见故障分析 总被引:1,自引:0,他引:1
本文介绍IRIS/AP型ICP的激发光源(炬管),并较为全面地阐述和分析其不能正常激发点燃的常见故障及其原因。 相似文献
70.
简要介绍了国内地化录井技术的发展历程,分析了该技术的特点及在油气勘探开发应用中取得的成效。认为中国地化录井技术在引进、消化、吸收的基础上,扩展了该技术的应用领域和范围,目前该专业的整体技术水平处于国际领先地位。在以统计资料及应用实例报道该技术的应用成果及独特技术优势的同时,也分析了存在的问题,指出了解决问题的主要途径。 相似文献