全文获取类型
收费全文 | 415789篇 |
免费 | 35087篇 |
国内免费 | 21509篇 |
专业分类
电工技术 | 29359篇 |
技术理论 | 58篇 |
综合类 | 51788篇 |
化学工业 | 44075篇 |
金属工艺 | 16273篇 |
机械仪表 | 28731篇 |
建筑科学 | 55168篇 |
矿业工程 | 20495篇 |
能源动力 | 14969篇 |
轻工业 | 25937篇 |
水利工程 | 20075篇 |
石油天然气 | 18453篇 |
武器工业 | 4339篇 |
无线电 | 25688篇 |
一般工业技术 | 33317篇 |
冶金工业 | 21115篇 |
原子能技术 | 4931篇 |
自动化技术 | 57614篇 |
出版年
2024年 | 1191篇 |
2023年 | 4055篇 |
2022年 | 8330篇 |
2021年 | 10240篇 |
2020年 | 10543篇 |
2019年 | 8884篇 |
2018年 | 8402篇 |
2017年 | 10340篇 |
2016年 | 12628篇 |
2015年 | 13878篇 |
2014年 | 24396篇 |
2013年 | 23227篇 |
2012年 | 29017篇 |
2011年 | 31400篇 |
2010年 | 23944篇 |
2009年 | 24759篇 |
2008年 | 23142篇 |
2007年 | 29354篇 |
2006年 | 27005篇 |
2005年 | 23324篇 |
2004年 | 19809篇 |
2003年 | 17519篇 |
2002年 | 14360篇 |
2001年 | 12037篇 |
2000年 | 10210篇 |
1999年 | 8386篇 |
1998年 | 6630篇 |
1997年 | 5735篇 |
1996年 | 5101篇 |
1995年 | 4310篇 |
1994年 | 3811篇 |
1993年 | 2853篇 |
1992年 | 2553篇 |
1991年 | 1885篇 |
1990年 | 1650篇 |
1989年 | 1412篇 |
1988年 | 1153篇 |
1987年 | 782篇 |
1986年 | 616篇 |
1985年 | 530篇 |
1984年 | 526篇 |
1983年 | 417篇 |
1982年 | 349篇 |
1981年 | 248篇 |
1980年 | 217篇 |
1979年 | 168篇 |
1978年 | 104篇 |
1977年 | 109篇 |
1976年 | 90篇 |
1975年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Jie-Long He An-Te Chen Jyong-Huei Lee Shih-Kang Fan 《International journal of molecular sciences》2015,16(9):22319-22332
The basic structural and functional unit of a living organism is a single cell. To understand the variability and to improve the biomedical requirement of a single cell, its analysis has become a key technique in biological and biomedical research. With a physical boundary of microchannels and microstructures, single cells are efficiently captured and analyzed, whereas electric forces sort and position single cells. Various microfluidic techniques have been exploited to manipulate single cells through hydrodynamic and electric forces. Digital microfluidics (DMF), the manipulation of individual droplets holding minute reagents and cells of interest by electric forces, has received more attention recently. Because of ease of fabrication, compactness and prospective automation, DMF has become a powerful approach for biological application. We review recent developments of various microfluidic chips for analysis of a single cell and for efficient genetic screening. In addition, perspectives to develop analysis of single cells based on DMF and emerging functionality with high throughput are discussed. 相似文献
72.
This paper presents a fast distance relay for series compensated transmission lines based on the R–L differential-equation algorithm using the theory of equal transfer process of transmission lines. The measuring distances based on the proposed algorithm can fast approach the actual value of fault distance when a fault occurs in front of the series capacitor. When a fault occurs behind of the series capacitor, the fault loop, including the series capacitor, does not match the R–L transmission line model, so the measuring distances fluctuate severely. Based on this, the relative position of the fault with respect to the series capacitor can be judged effectively according to the fluctuation range of the measuring distances, and the accurate fault location can be obtained fast. A variety of PSCAD/EMTDC simulation tests show that the new relay has fast operating speed and high accuracy when applied to the long series compensated transmission lines. 相似文献
73.
This paper provides a unified approach for the optimization of measurements placements employed for power system online monitoring through state estimation. The proposed methodology, which can be suitable for the mixed measure system, preserves state estimation observability and bad-data processing capability by employing numerical algorithms for observability checking, critical measurements and critical couple identification. First, node injection radix measurements and measurement categories are defined. According to the above definitions, the coefficient matrix can be solved. The analysis on the column vectors of the coefficient matrix can determine each measurement classification. Furthermore, the numbers of each measurement class contains can determine bad-data processing capability. The observability can be checked by the type number of measurements. The proposed method is illustrated with the IEEE39-bus system and the IEEE118-bus system. Results from the case studies are presented to demonstrate that the approach adequately fulfills the desired properties related to observability, bad-data processing, cost, and robustness. 相似文献
74.
The complexity and spatial heterogeneity of ecosystem processes driving ecosystem service delivery require spatially explicit models that take into account the different parameters affecting those processes. Current attempts to model ecosystem service delivery on a broad, regional scale often depend on indicator-based approaches that are generally not able to fully capture the complexity of ecosystem processes. Moreover, they do not allow quantification of uncertainty on their predictions. In this paper, we discuss a QGIS plug-in which promotes the use of Bayesian belief networks for regional modelling and mapping of ecosystem service delivery and associated uncertainties. Different types of specific Bayesian belief network output maps, delivered by the plug-in, are discussed and their decision support capacities are evaluated. This plug-in, used in combination with firmly developed Bayesian belief networks, has the potential to add value to current spatial ecosystem service accounting methods. The plug-in can also be used in other research domains dealing with spatial data and uncertainty. 相似文献
75.
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。 相似文献
76.
Susan Sabra Khalid Mahmood Malik Muhammad Afzal Vian Sabeeh Ahmad Charaf Eddine 《Expert Systems》2020,37(1):e12388
Clinical narratives such as progress summaries, lab reports, surgical reports, and other narrative texts contain key biomarkers about a patient's health. Evidence-based preventive medicine needs accurate semantic and sentiment analysis to extract and classify medical features as the input to appropriate machine learning classifiers. However, the traditional approach of using single classifiers is limited by the need for dimensionality reduction techniques, statistical feature correlation, a faster learning rate, and the lack of consideration of the semantic relations among features. Hence, extracting semantic and sentiment-based features from clinical text and combining multiple classifiers to create an ensemble intelligent system overcomes many limitations and provides a more robust prediction outcome. The selection of an appropriate approach and its interparameter dependency becomes key for the success of the ensemble method. This paper proposes a hybrid knowledge and ensemble learning framework for prediction of venous thromboembolism (VTE) diagnosis consisting of the following components: a VTE ontology, semantic extraction and sentiment assessment of risk factor framework, and an ensemble classifier. Therefore, a component-based analysis approach was adopted for evaluation using a data set of 250 clinical narratives where knowledge and ensemble achieved the following results with and without semantic extraction and sentiment assessment of risk factor, respectively: a precision of 81.8% and 62.9%, a recall of 81.8% and 57.6%, an F measure of 81.8% and 53.8%, and a receiving operating characteristic of 80.1% and 58.5% in identifying cases of VTE. 相似文献
77.
78.
This calibration device of radio comprehensive tester is studied and established in this paper. It solves the verification and
calibration of a large number of general-purpose radio comprehensive testers. The calibration device consists of four calibration sub-
systems and calibration software system, including RF generator, audio generator, audio analyzer and RF analyzer. It also researches
on the configuration of standard equipment and analyzes the uncertainty of the calibration devices, ensuring accurate and reliable val-
ue transfer. 相似文献
79.
本文针对典型高温气冷堆乏燃料厂房在双发商用飞机撞击载荷下的响应及结构完整性开展研究,并探讨结构特性对撞击损伤的影响。对乏燃料厂房及飞机分别建立有限元模型,通过弹体-目标相互作用分析模拟了飞机撞击过程,综合IAEA与NRC的评价准则对乏燃料厂房在飞机撞击下的损伤程度进行评估。数值结果表明:厂房上对应于机身及发动机的撞击位置发生可接受的局部损伤;乏燃料贮存井墙体对于提高构筑物抗飞机撞击能力有重要作用。此外,构筑物外形对损伤有很大影响,圆柱形壳体的抗飞机撞击能力显著强于方形厂房,是核电厂厂房设计的优化方向之一。 相似文献
80.
冯鹏一 《信息通信技术与政策》2020,(1):12-15
以电信用户入网协议为切入点,电信用户的携号转网行为应受到《合同法》《消费者权益保护法》等私法规范的保护与限制。该行为引起的格式条款解释、合同终止、违约责任、损失赔偿等问题,不能仅靠《电信条例》等公法规范来调整。应当积极引导广大消费者用户以私法领域相关规定为依据,转变争议解决思维,拓宽纠纷处理途径,合理选择维权手段,以保护自身合法民事权益,与行业监管部门共同推动电信行业有序发展。 相似文献