全文获取类型
收费全文 | 114196篇 |
免费 | 4748篇 |
国内免费 | 2976篇 |
专业分类
电工技术 | 3664篇 |
综合类 | 5683篇 |
化学工业 | 14785篇 |
金属工艺 | 6972篇 |
机械仪表 | 5310篇 |
建筑科学 | 4551篇 |
矿业工程 | 1656篇 |
能源动力 | 1828篇 |
轻工业 | 7403篇 |
水利工程 | 2376篇 |
石油天然气 | 1201篇 |
武器工业 | 522篇 |
无线电 | 12329篇 |
一般工业技术 | 18835篇 |
冶金工业 | 3638篇 |
原子能技术 | 736篇 |
自动化技术 | 30431篇 |
出版年
2024年 | 163篇 |
2023年 | 526篇 |
2022年 | 1338篇 |
2021年 | 1640篇 |
2020年 | 1134篇 |
2019年 | 799篇 |
2018年 | 15193篇 |
2017年 | 14259篇 |
2016年 | 10699篇 |
2015年 | 1961篇 |
2014年 | 1879篇 |
2013年 | 2266篇 |
2012年 | 5666篇 |
2011年 | 12058篇 |
2010年 | 10907篇 |
2009年 | 7998篇 |
2008年 | 9263篇 |
2007年 | 10338篇 |
2006年 | 2171篇 |
2005年 | 2914篇 |
2004年 | 2356篇 |
2003年 | 2018篇 |
2002年 | 1325篇 |
2001年 | 854篇 |
2000年 | 793篇 |
1999年 | 286篇 |
1998年 | 112篇 |
1997年 | 75篇 |
1996年 | 66篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 40篇 |
1988年 | 18篇 |
1969年 | 24篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1963年 | 29篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 40篇 |
1958年 | 37篇 |
1957年 | 37篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
3.
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
4.
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
5.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
6.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献
7.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
8.
9.
10.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献