收费全文 | 22729篇 |
免费 | 1536篇 |
国内免费 | 198篇 |
电工技术 | 387篇 |
综合类 | 100篇 |
化学工业 | 5962篇 |
金属工艺 | 563篇 |
机械仪表 | 891篇 |
建筑科学 | 865篇 |
矿业工程 | 39篇 |
能源动力 | 1540篇 |
轻工业 | 2142篇 |
水利工程 | 366篇 |
石油天然气 | 345篇 |
武器工业 | 9篇 |
无线电 | 2338篇 |
一般工业技术 | 4060篇 |
冶金工业 | 703篇 |
原子能技术 | 165篇 |
自动化技术 | 3988篇 |
2024年 | 104篇 |
2023年 | 454篇 |
2022年 | 916篇 |
2021年 | 1484篇 |
2020年 | 1259篇 |
2019年 | 1461篇 |
2018年 | 1675篇 |
2017年 | 1530篇 |
2016年 | 1507篇 |
2015年 | 880篇 |
2014年 | 1430篇 |
2013年 | 2332篇 |
2012年 | 1511篇 |
2011年 | 1644篇 |
2010年 | 1117篇 |
2009年 | 977篇 |
2008年 | 653篇 |
2007年 | 528篇 |
2006年 | 451篇 |
2005年 | 295篇 |
2004年 | 274篇 |
2003年 | 212篇 |
2002年 | 176篇 |
2001年 | 117篇 |
2000年 | 113篇 |
1999年 | 101篇 |
1998年 | 158篇 |
1997年 | 132篇 |
1996年 | 121篇 |
1995年 | 89篇 |
1994年 | 61篇 |
1993年 | 73篇 |
1992年 | 57篇 |
1991年 | 55篇 |
1990年 | 55篇 |
1989年 | 46篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1975年 | 13篇 |
The limitation of freshwater resources and the growing demand for water, make the issue of water resource development planning and water allocation among stakeholders even more important. Ideally, water allocation should be economically efficient and socially equitable. In this study, a water allocation model is presented in an integrated framework that considers the interaction of water supply and demand according to economic and social factors. To achieve this, a reliability-based multi-objective optimization - simulation approach has been employed. The objective functions of the problem are: 1) maximizing GDP from agricultural sectors and 2) maximizing social equality in different provinces of the basin (measured using the Williamson coefficient). The fair development and allocation among the shared provinces in the basin can reduce conflicts in the region. Karkheh basin has been considered as a case study and decision variables of the problem are area under cultivation of agricultural development sectors in different provinces. The results show that, without harming the income of the agricultural sector, the spatial distribution of development projects can be done in such a way that equality (according to income level and the number of people working in each province) is achieved. One of the solutions of Pareto front compared to previous studies shows that, in addition to an increase of about 12% of the objective function 1 (GDP), the value of the objective function 2 (Williamson coefficient) decreased from 1.19 to 0.98. This indicates a decrease in income inequality among the provinces of the basin.
相似文献The paper proposes a novel metaheuristic based on integrating chaotic maps into a Henry gas solubility optimization algorithm (HGSO). The new algorithm is named chaotic Henry gas solubility optimization (CHGSO). The hybridization is aimed at enhancement of the convergence rate of the original Henry gas solubility optimizer for solving real-life engineering optimization problems. This hybridization provides a problem-independent optimization algorithm. The CHGSO performance is evaluated using various conventional constrained optimization problems, e.g., a welded beam problem and a cantilever beam problem. The performance of the CHGSO is investigated using both the manufacturing and diaphragm spring design problems taken from the automotive industry. The results obtained from using CHGSO for solving the various constrained test problems are compared with a number of established and newly invented metaheuristics, including an artificial bee colony algorithm, an ant colony algorithm, a cuckoo search algorithm, a salp swarm optimization algorithm, a grasshopper optimization algorithm, a mine blast algorithm, an ant lion optimizer, a gravitational search algorithm, a multi-verse optimizer, a Harris hawks optimization algorithm, and the original Henry gas solubility optimization algorithm. The results indicate that with selecting an appropriate chaotic map, the CHGSO is a robust optimization approach for obtaining the optimal variables in mechanical design and manufacturing optimization problems.
相似文献Shear connectors play a prominent role in the design of steel-concrete composite systems. The behavior of shear connectors is generally determined through conducting push-out tests. However, these tests are costly and require plenty of time. As an alternative approach, soft computing (SC) can be used to eliminate the need for conducting push-out tests. This study aims to investigate the application of artificial intelligence (AI) techniques, as sub-branches of SC methods, in the behavior prediction of an innovative type of C-shaped shear connectors, called Tilted Angle Connectors. For this purpose, several push-out tests are conducted on these connectors and the required data for the AI models are collected. Then, an adaptive neuro-fuzzy inference system (ANFIS) is developed to identify the most influencing parameters on the shear strength of the tilted angle connectors. Totally, six different models are created based on the ANFIS results. Finally, AI techniques such as an artificial neural network (ANN), an extreme learning machine (ELM), and another ANFIS are employed to predict the shear strength of the connectors in each of the six models. The results of the paper show that slip is the most influential factor in the shear strength of tilted connectors and after that, the inclination angle is the most effective one. Moreover, it is deducted that considering only four parameters in the predictive models is enough to have a very accurate prediction. It is also demonstrated that ELM needs less time and it can reach slightly better performance indices than those of ANN and ANFIS.
相似文献Todays, XML as a de facto standard is used to broadcast data over mobile wireless networks. In these networks, mobile clients send their XML queries over a wireless broadcast channel and recieve their desired XML data from the channel. However, downloading the whole XML data by a mobile device is a challenge since the mobile devices used by clients are small battery powered devices with limited resources. To meet this challenge, the XML data should be indexed in such a way that the desired XML data can be found easily and only such data can be downloaded instead of the whole XML data by the mobile clients. Several indexing methods are proposed to selectively access the XML data over an XML stream. However, the existing indexing methods cause an increase in the size of XML stream by including some extra information over the XML stream. In this paper, a new XML stream structure is proposed to disseminate the XML data over a broadcast channel by grouping and summarizing the structural information of XML nodes. By summarizing such information, the size of XML stream can be reduced and therefore, the latency of retrieving the desired XML data over a wirless broadcast channel can be reduced. The proposed XML stream structure also contains indexes in order to skip from the irrelevant parts over the XML stream. It therefore can reduce the energy consumption of mobile devices in downloading the results of XML queries. In addition, our proposed XML stream structure can process different types of XML queries and experimental results showed that it improves the performace of XML query processing over the XML data stream compared to the existing research works in terms of access and tuning times.
相似文献