全文获取类型
收费全文 | 111913篇 |
免费 | 9498篇 |
国内免费 | 5963篇 |
专业分类
电工技术 | 6520篇 |
技术理论 | 6篇 |
综合类 | 8949篇 |
化学工业 | 6874篇 |
金属工艺 | 19632篇 |
机械仪表 | 7583篇 |
建筑科学 | 19893篇 |
矿业工程 | 6645篇 |
能源动力 | 2405篇 |
轻工业 | 2275篇 |
水利工程 | 1944篇 |
石油天然气 | 3436篇 |
武器工业 | 1349篇 |
无线电 | 5954篇 |
一般工业技术 | 9308篇 |
冶金工业 | 15169篇 |
原子能技术 | 819篇 |
自动化技术 | 8613篇 |
出版年
2024年 | 207篇 |
2023年 | 1103篇 |
2022年 | 2678篇 |
2021年 | 3243篇 |
2020年 | 3485篇 |
2019年 | 2523篇 |
2018年 | 2168篇 |
2017年 | 3216篇 |
2016年 | 3674篇 |
2015年 | 4151篇 |
2014年 | 7606篇 |
2013年 | 6406篇 |
2012年 | 8807篇 |
2011年 | 9593篇 |
2010年 | 7297篇 |
2009年 | 7319篇 |
2008年 | 6165篇 |
2007年 | 7741篇 |
2006年 | 6796篇 |
2005年 | 5709篇 |
2004年 | 4669篇 |
2003年 | 4136篇 |
2002年 | 3396篇 |
2001年 | 2861篇 |
2000年 | 2402篇 |
1999年 | 1956篇 |
1998年 | 1486篇 |
1997年 | 1377篇 |
1996年 | 1177篇 |
1995年 | 885篇 |
1994年 | 784篇 |
1993年 | 549篇 |
1992年 | 443篇 |
1991年 | 322篇 |
1990年 | 262篇 |
1989年 | 229篇 |
1988年 | 163篇 |
1987年 | 70篇 |
1986年 | 51篇 |
1985年 | 45篇 |
1984年 | 33篇 |
1983年 | 34篇 |
1982年 | 30篇 |
1981年 | 17篇 |
1980年 | 42篇 |
1979年 | 9篇 |
1975年 | 4篇 |
1959年 | 18篇 |
1957年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
《Oil and Energy Trends》2020,45(1):56-58
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
22.
Yuanming Xie Tianda Yu Chaojun Deng Xuefei Hu 《Journal of Nuclear Science and Technology》2020,57(9):1074-1090
ABSTRACT In the lower chamber of pressurized water reactor (PWR), the flow distribution device is the core module to distribute coolant into the core. It has complex structure and numerous design parameters. Therefore, it has important theoretical and practical significance to optimize the device. The mesh independence verification, turbulence model selection, and data processing all can influence the numerical simulation results of the lower chamber, in order to research the influence, a numerical simulation method based on the original model of CNP1000 reactor lower chamber is proposed in this paper. In the method, an optimization design method of flow distribution device is established based on surrogate model. The main design variables and optimization objectives are determined based on the device’s structure and function characteristics. And then it respectively adopts Kriging algorithm and multi-objective genetic algorithm to establish a surrogate model of flow distribution device and optimize it globally. Finally, the optimal design variables are obtained. Compared with the device’s performance before optimization, the after optimization has smaller total pressure loss and more uniform flow. The effectiveness and practicability of proposed optimization design method can be verified. 相似文献
23.
24.
25.
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
26.
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
27.
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
28.
《Oil and Energy Trends》2020,45(5):56-58
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
29.
Optimal power flow with generation reallocation is a suitable method for better utilization of the existing system. In recent years, Flexible AC Transmission System (FACTS) devices, have led to the development of controllers that provide controllability and flexibility for power transmission. Out of the FACTS devices unified power flow controller (UPFC) is a versatile device, capable of controlling the power system parameters like voltage magnitude, phase angle and line impedance individually or simultaneously. The main aim of this paper is to minimize real power losses in a power system using BAT search algorithm without and with the presence of UPFC. Minimization of real power losses is done by considering the power generated by generator buses, voltage magnitudes at generator buses and reactive power injection from reactive power compensators. The proposed BAT algorithm based Optimal Power Flow (OPF) has been tested on a 5 bus test system and modified IEEE 30 bus system without and with UPFC. The results of the system with and without UPFC are compared in terms of active power losses in the transmission line using BAT algorithm. The obtained results are also compared with Genetic algorithm (GA). 相似文献
30.