全文获取类型
收费全文 | 23526篇 |
免费 | 1776篇 |
国内免费 | 744篇 |
专业分类
电工技术 | 1811篇 |
综合类 | 1492篇 |
化学工业 | 5893篇 |
金属工艺 | 872篇 |
机械仪表 | 1397篇 |
建筑科学 | 2232篇 |
矿业工程 | 1166篇 |
能源动力 | 386篇 |
轻工业 | 1892篇 |
水利工程 | 468篇 |
石油天然气 | 841篇 |
武器工业 | 372篇 |
无线电 | 1106篇 |
一般工业技术 | 2543篇 |
冶金工业 | 1425篇 |
原子能技术 | 160篇 |
自动化技术 | 1990篇 |
出版年
2024年 | 72篇 |
2023年 | 186篇 |
2022年 | 505篇 |
2021年 | 627篇 |
2020年 | 581篇 |
2019年 | 447篇 |
2018年 | 394篇 |
2017年 | 532篇 |
2016年 | 712篇 |
2015年 | 689篇 |
2014年 | 1574篇 |
2013年 | 1362篇 |
2012年 | 1914篇 |
2011年 | 1979篇 |
2010年 | 1406篇 |
2009年 | 1514篇 |
2008年 | 1163篇 |
2007年 | 1652篇 |
2006年 | 1498篇 |
2005年 | 1288篇 |
2004年 | 1077篇 |
2003年 | 1054篇 |
2002年 | 889篇 |
2001年 | 672篇 |
2000年 | 492篇 |
1999年 | 401篇 |
1998年 | 279篇 |
1997年 | 237篇 |
1996年 | 188篇 |
1995年 | 147篇 |
1994年 | 104篇 |
1993年 | 89篇 |
1992年 | 78篇 |
1991年 | 45篇 |
1990年 | 25篇 |
1989年 | 34篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1975年 | 3篇 |
1965年 | 3篇 |
1962年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Bernette Maria Oosterlaken Heiner Friedrich Gijsbertus de With 《Microscopy research and technique》2022,85(1):412-417
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed. 相似文献
2.
燕麦为西藏自治区典型牧草之一,由于种植区地域辽阔,灌溉试验结果受限,西藏燕麦主要种植区的灌溉定额尚不明确。本文在西藏燕麦主要种植区内选取28个典型站点进行资料收集,遵循农业气候相似原则进行区域划分,基于水量平衡法揭示了西藏燕麦主要种植区灌溉定额的空间分布特征,并根据统计学原理分析了其影响因素。研究表明:燕麦主要种植区的灌溉定额呈由西藏中部至东部呈现先递增后递减的趋势,50%水文年下的燕麦灌溉定额在56~265 mm之间变化。降雨量是影响研究区内燕麦灌溉定额的主要因素(R2为0.515),ET0次之(R2为0.152);其它气象因素中,日照时数对研究区燕麦灌溉定额影响较大(R2为0.462),且呈正相关关系;相对湿度对燕麦灌溉定额影响较小。西藏燕麦主要种植区的灌溉定额及其空间分布可为西藏自治区灌溉用水管理提供支撑。 相似文献
3.
4.
5.
伏彩萍 《有色金属(冶炼部分)》2020,(6):66-69
针对现有柠檬酸铋制备工艺合成时间长、能耗高、产品纯度不高等不足,介绍了一种常温下制备柠檬酸铋的新工艺。新工艺制备时间短,制备的柠檬酸铋产品质量好,合成过程产生的废水可循环利用,废气经碱液循环吸收可生产硝酸钠副产品。 相似文献
6.
As suggested by the uncanny valley hypothesis, robots that resemble humans likely elicit feelings of eeriness. Based on the psychological model of meaning maintenance, we expected that the uncanny valley experience could be mitigated through a fictional story, due to the meaning-generating function of narratives. A field experiment was conducted, in which 75 participants interacted with the humanlike robot Telenoid. Prior to the interaction, they either read a short story, a non-narrative leaflet about the robot, or they received no preliminary information. Eeriness ratings were significantly lower in the science fiction condition than in both other conditions. This effect was mediated by higher perceived human-likeness of the robot. Our findings suggest that science fiction may provide meaning for otherwise unsettling future technologies. 相似文献
7.
8.
Aircraft maintenance organisation is a complex socio-technical setup, where human factors influence the quality of aircraft maintenance service. Maintenance service quality is assessed based on the commitment of management and its ability to provide suitable facility, tools, spares and manpower supported with comfortable environment and maintenance procedures. Assessment of the service quality of the aircraft maintenance organisation is a complex process. Airlines, regulators, insurance companies and other agencies need decision support system, to assess the performance of a maintenance organisation. This paper provides criteria and scientific approach for assessing the maintenance organisation; it presents a methodology of applying Analytical Hierarchy Process to prioritise the key functions and to rank the maintenance organisations under study. The study has established that maintenance service quality in airline is directly correlated to its fleet size. 相似文献
9.
The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30?kV, 30?nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30?kV and 30?nA is 700?K for ZrO2. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083?°C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5?kV, 4.8?nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia. 相似文献
10.
以亚欧海底光缆S2段为例,介绍亚欧海底光缆远供电源(PFE)的供电方式,以及其在正常运行时和故障维修时的维护管理方法。探讨在实际维护中如何贯彻落实及灵活运用系统联合维护文档,总结适合中国国情的远供电源维护经验,确保亚欧海底光缆远供电源安全稳定运行。 相似文献