全文获取类型
收费全文 | 51909篇 |
免费 | 5541篇 |
国内免费 | 3449篇 |
专业分类
电工技术 | 4068篇 |
技术理论 | 2篇 |
综合类 | 4720篇 |
化学工业 | 7020篇 |
金属工艺 | 3347篇 |
机械仪表 | 3655篇 |
建筑科学 | 4321篇 |
矿业工程 | 1835篇 |
能源动力 | 1306篇 |
轻工业 | 5030篇 |
水利工程 | 1451篇 |
石油天然气 | 2333篇 |
武器工业 | 642篇 |
无线电 | 5295篇 |
一般工业技术 | 5148篇 |
冶金工业 | 2059篇 |
原子能技术 | 711篇 |
自动化技术 | 7956篇 |
出版年
2024年 | 261篇 |
2023年 | 921篇 |
2022年 | 1946篇 |
2021年 | 2509篇 |
2020年 | 1846篇 |
2019年 | 1394篇 |
2018年 | 1396篇 |
2017年 | 1608篇 |
2016年 | 1361篇 |
2015年 | 2165篇 |
2014年 | 2761篇 |
2013年 | 3288篇 |
2012年 | 3923篇 |
2011年 | 4095篇 |
2010年 | 3930篇 |
2009年 | 3622篇 |
2008年 | 3641篇 |
2007年 | 3674篇 |
2006年 | 3229篇 |
2005年 | 2812篇 |
2004年 | 1888篇 |
2003年 | 1417篇 |
2002年 | 1301篇 |
2001年 | 1239篇 |
2000年 | 1064篇 |
1999年 | 818篇 |
1998年 | 522篇 |
1997年 | 441篇 |
1996年 | 380篇 |
1995年 | 327篇 |
1994年 | 253篇 |
1993年 | 159篇 |
1992年 | 146篇 |
1991年 | 131篇 |
1990年 | 104篇 |
1989年 | 83篇 |
1988年 | 62篇 |
1987年 | 35篇 |
1986年 | 41篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1959年 | 5篇 |
1957年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
针对颗粒滚动摩擦作用对筒仓中玉米颗粒的力链空间分布进行研究,通过EDEM离散元软件建立筒仓模型与仿真玉米颗粒模型进行卸粮仿真模拟,并与筒仓卸料实验作流态对比,验证模型与仿真结果的准确性。通过对模拟仓进行切片观察和数据处理,对比分析了不同摩擦情况下力链的细观参数随时间演化规律。模拟结果表明:颗粒间摩擦系数越大,卸粮完成的最终时间越长;颗粒间滚动摩擦系数越小,颗粒由整体流转变为管状流的时间越早。对于有漏斗的筒仓来说,减小颗粒间摩擦会改变整体流和管状流之间的极限,从而增加产生管状流的面积。标准滚动摩擦系数下玉米颗粒在卸料过程中会出现起拱-塌陷效应;减小滚动摩擦,玉米颗粒卸料较稳定,未出现起拱的应力突增、以及拱塌陷的应力衰减;增大颗粒间滚动摩擦不但会增加拱效应,且出现成拱高度距离漏斗口更高。 相似文献
3.
4.
食品安全示范城市创建是食品安全治理体系的重要载体。本文系统性回顾食品安全治理体系相关研究,从“党政同责”、政府监管、市场主体、社会共治等四个治理主体,构建生产规范、产业转型升级等27个评价指标的治理标准,利用层次分析法实证分析了浙江省食品安全示范城市创建情况。结果表明:采用暗查暗访、现场检查、体系评估、示范引领答辩等形式,按照一定的评价流程、评价标准的食品安全示范城市创建,是实现食品安全现代化目标的重要载体。食品安全治理体系包括“治理载体—治理主体—治理标准—治理目标”。食品安全治理成效与跟踪评价、群众满意度以及体系评估高度关联。 相似文献
5.
Yujie Chen Yiping Song Zhen Zhang Yali Chen Qiliang Deng Shuo Wang 《Advanced functional materials》2021,31(41):2104885
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs. 相似文献
6.
Myelodysplastic syndromes (MDS) are highly heterogeneous myeloid neoplasms, and a large number of
patients are difficult to diagnose and classify by blood and bone marrow examination. As a surface marker of
granulocyte, studies have shown CD10 can be used to define the degree of granulocyte maturation in MDS patients.
However, whether it can be used for differential diagnosis of MDS and other hematological diseases remains
inconclusive. To explore the value of CD10 for differential diagnosis of MDS, 60 newly diagnosed MDS, 20 aplastic
anemia (AA) patients, and 35 iron-deficient anemia (IDA) patients were selected for this study. Bone marrow (BM)
specimens were processed for surface marker analysis and labeled with pre-conjugated monoclonal antibodies. Stained
cells were detected by flow cytometry. Our results indicated that CD10-positive granulocytes were significantly
decreased in BM of MDS patients than AA and IDA patients, and the level of CD10-positive mature granulocytes was
not associated with the clinical stages of malignancy. Receiver operating characteristic (ROC) areas under the curve
(AUC) of CD10-positive granulocytes was 0.86 and 0.85, respectively, in MDS patients than the IDA group and AA
group with good specificity and sensitivity. Further, CD10-positive granulocytes were increased after effective
treatment. In conclusion, we found the decrease in CD10-positive granulocytes has a differential diagnostic value of MDS. 相似文献
7.
8.
9.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
10.