全文获取类型
收费全文 | 189074篇 |
免费 | 17826篇 |
国内免费 | 9926篇 |
专业分类
电工技术 | 15315篇 |
技术理论 | 9篇 |
综合类 | 19443篇 |
化学工业 | 18154篇 |
金属工艺 | 7440篇 |
机械仪表 | 16251篇 |
建筑科学 | 24777篇 |
矿业工程 | 7239篇 |
能源动力 | 8576篇 |
轻工业 | 13812篇 |
水利工程 | 7944篇 |
石油天然气 | 8707篇 |
武器工业 | 2092篇 |
无线电 | 10682篇 |
一般工业技术 | 17825篇 |
冶金工业 | 8015篇 |
原子能技术 | 2554篇 |
自动化技术 | 27991篇 |
出版年
2024年 | 748篇 |
2023年 | 2267篇 |
2022年 | 4590篇 |
2021年 | 5378篇 |
2020年 | 5734篇 |
2019年 | 4727篇 |
2018年 | 4690篇 |
2017年 | 5698篇 |
2016年 | 6930篇 |
2015年 | 7273篇 |
2014年 | 12575篇 |
2013年 | 12263篇 |
2012年 | 14031篇 |
2011年 | 15349篇 |
2010年 | 11112篇 |
2009年 | 11561篇 |
2008年 | 10800篇 |
2007年 | 13094篇 |
2006年 | 11170篇 |
2005年 | 9298篇 |
2004年 | 7876篇 |
2003年 | 6859篇 |
2002年 | 5501篇 |
2001年 | 4468篇 |
2000年 | 3828篇 |
1999年 | 3175篇 |
1998年 | 2680篇 |
1997年 | 2243篇 |
1996年 | 1862篇 |
1995年 | 1523篇 |
1994年 | 1354篇 |
1993年 | 1003篇 |
1992年 | 921篇 |
1991年 | 676篇 |
1990年 | 578篇 |
1989年 | 489篇 |
1988年 | 407篇 |
1987年 | 276篇 |
1986年 | 236篇 |
1985年 | 221篇 |
1984年 | 258篇 |
1983年 | 247篇 |
1982年 | 198篇 |
1981年 | 97篇 |
1980年 | 96篇 |
1979年 | 68篇 |
1978年 | 56篇 |
1977年 | 46篇 |
1976年 | 44篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
31.
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
32.
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
33.
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
34.
With the emergence of distributed ledger technology (DLT), numerous practitioners and researchers have proclaimed its beneficial impact on supply chain transactions in the future. However, the vast majority of DLT initiatives are discontinued after a short period. With the full potential of DLT laying far down the road, especially managers in supply chain management (SCM) seek for short-term cost-saving effects of DLT in order to achieve long-term benefits of DLT in the future. However, the extant research has bypassed grounding long-term as well as short-term effects of DLT on supply chain transaction with empirical data. We address this shortcoming, following an abductive research approach and combining empirical data from a multiple case study design with the corresponding literature. Our study reveals that the effects of DLT on supply chain transactions are two-sided. We found six effects of DLT solutions that have a cost-reducing or cost avoidance impact on supply chain transactions. In addition, we found two effects that change the power distribution between buyers and suppliers in transactions and a single effect that reduces the dependency of supply chain transactions on third parties. While cost-reducing and avoidance as well as dependency-reducing effects are positive effects, the change in power distribution might come with disadvantages. With these findings, the paper provides the first empirical evidence of the impact of DLT on supply chain transactions, which will enable managers to improve their assessment of DLT usage in supply chains. 相似文献
35.
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
36.
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
37.
In the first critical assessment of knowledge economy dynamic paths in Africa and the Middle East, but for a few exceptions, we find overwhelming support for diminishing cross-country disparities in knowledge-based economy dimensions. The paper employs all the four components of the World Bank's Knowledge Economy Index (KEI): economic incentives, innovation, education, and information infrastructure. The main finding suggests that sub-Saharan African (SSA) and the Middle East and North African (MENA) countries with low levels of KE dynamics and catching-up their counterparts of higher KE levels. We provide the speeds of integration and time necessary to achieve full (100%) integration. Policy implications are also discussed. 相似文献
38.
39.
植物肉的出现为动物肉类食品供应短缺和养殖业环境污染问题带来希望。食品加工技术的快速发展弥补了植物基肉制品外观和口感的不足, 但其营养价值和安全性也应引起重视。本文综述了以植物蛋白为主要原料所制肉类替代品的营养价值, 包括植物肉中碳水化合物、蛋白质、脂肪、水分、维生素和矿物质的相对含量和营养性质。分析了植物肉在生产及食用过程中可能出现的物理、化学、生物因素在内的安全问题, 并探讨目前植物肉发展所存在的局限性与挑战, 以期为我国植物蛋白肉制品的研发与推广提供理论参考。 相似文献
40.
The study presents the preparation of the new magnetic nanocomposite based on PLGA and magnetite. The PLGA used to obtain the magnetic nanocomposites was synthesized by the copolymerization of lactic acid with glycolic acid, in the presence of tin octanoate [Sn(Oct)2] as catalyst, by polycondensation procedure. Magnetite was obtained by co-precipitation from aqueous salt solutions FeCl2/FeCl3. The particles size of magnetite was 420 nm, and the saturation magnetization 62.78 emu/g, while the PLGA/magnetite nanocomposite size was 864 nm and the saturation magnetization 39.44 emu/g. The magnetic nanocomposites were characterized by FT-IR, DLS technique, SEM, VSM and simultaneous thermal analyses (TG–FTIR–MS). The polymer matrix PLGA acts as a shell and carrier for the active component, while magnetite is the component which makes targeting possible by external magnetic field manipulation. Based on the gases resulted by thermal degradation of PLGA copolymer, using the simultaneous analysis TG–FTIR–MS, a possible degradation mechanism was proposed. 相似文献