全文获取类型
收费全文 | 57606篇 |
免费 | 5813篇 |
国内免费 | 4239篇 |
专业分类
电工技术 | 5588篇 |
技术理论 | 2篇 |
综合类 | 6540篇 |
化学工业 | 2698篇 |
金属工艺 | 1205篇 |
机械仪表 | 3149篇 |
建筑科学 | 6203篇 |
矿业工程 | 1413篇 |
能源动力 | 1562篇 |
轻工业 | 901篇 |
水利工程 | 1165篇 |
石油天然气 | 1520篇 |
武器工业 | 825篇 |
无线电 | 9392篇 |
一般工业技术 | 3103篇 |
冶金工业 | 1781篇 |
原子能技术 | 325篇 |
自动化技术 | 20286篇 |
出版年
2024年 | 244篇 |
2023年 | 639篇 |
2022年 | 1088篇 |
2021年 | 1320篇 |
2020年 | 1520篇 |
2019年 | 1319篇 |
2018年 | 1236篇 |
2017年 | 1689篇 |
2016年 | 1913篇 |
2015年 | 2137篇 |
2014年 | 4044篇 |
2013年 | 3720篇 |
2012年 | 4043篇 |
2011年 | 4550篇 |
2010年 | 3511篇 |
2009年 | 3756篇 |
2008年 | 3848篇 |
2007年 | 4653篇 |
2006年 | 3671篇 |
2005年 | 3197篇 |
2004年 | 2585篇 |
2003年 | 2533篇 |
2002年 | 1986篇 |
2001年 | 1604篇 |
2000年 | 1290篇 |
1999年 | 1020篇 |
1998年 | 771篇 |
1997年 | 691篇 |
1996年 | 576篇 |
1995年 | 499篇 |
1994年 | 393篇 |
1993年 | 292篇 |
1992年 | 248篇 |
1991年 | 179篇 |
1990年 | 153篇 |
1989年 | 125篇 |
1988年 | 87篇 |
1987年 | 69篇 |
1986年 | 41篇 |
1985年 | 53篇 |
1984年 | 74篇 |
1983年 | 59篇 |
1982年 | 53篇 |
1981年 | 46篇 |
1980年 | 31篇 |
1979年 | 25篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 6篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ContextEnterprise software systems (e.g., enterprise resource planning software) are often deployed in different contexts (e.g., different organizations or different business units or branches of one organization). However, even though organizations, business units or branches have the same or similar business goals, they may differ in how they achieve these goals. Thus, many enterprise software systems are subject to variability and adapted depending on the context in which they are used.ObjectiveOur goal is to provide a snapshot of variability in large scale enterprise software systems. We aim at understanding the types of variability that occur in large industrial enterprise software systems. Furthermore, we aim at identifying how variability is handled in such systems.MethodWe performed an exploratory case study in two large software organizations, involving two large enterprise software systems. Data were collected through interviews and document analysis. Data were analyzed following a grounded theory approach.ResultsWe identified seven types of variability (e.g., functionality, infrastructure) and eight mechanisms to handle variability (e.g., add-ons, code switches).ConclusionsWe provide generic types for classifying variability in enterprise software systems, and reusable mechanisms for handling such variability. Some variability types and handling mechanisms for enterprise software systems found in the real world extend existing concepts and theories. Others confirm findings from previous research literature on variability in software in general and are therefore not specific to enterprise software systems. Our findings also offer a theoretical foundation for describing variability handling in practice. Future work needs to provide more evaluations of the theoretical foundations, and refine variability handling mechanisms into more detailed practices. 相似文献
2.
3.
A new matching cost computation method based on nonsubsampled contourlet transform (NSCT) for stereo image matching is proposed in this paper. Firstly, stereo image is decomposed into high frequency sub-band images at different scales and along different directions by NSCT. Secondly, by utilizing coefficients in high frequency domain and grayscales in RGB color space, the computation model of weighted matching cost between two pixels is designed based on the gestalt laws. Lastly, two types of experiments are carried out with standard stereopairs in the Middlebury benchmark. One of the experiments is to confirm optimum values of NSCT scale and direction parameters, and the other is to compare proposed matching cost with nine known matching costs. Experimental results show that the optimum values of scale and direction parameters are respectively 2 and 3, and the matching accuracy of the proposed matching cost is twice higher than that of traditional NCC cost. 相似文献
4.
《Energy Policy》2015
In this paper we construct an indirect measure of the supply marginal cost function for the main generators from the observed bid data in the Italian electricity market in the period 2004–2007. We compute the residual demand function for each generator, taking explicitly into account the issue of transmission line congestion. This procedure allows recovering correct zonal Lerner index and the implied measure of the marginal cost function. We find evidence of a stable U-shaped marginal cost function for three main Italian generators, but a flat function for ENEL, the former national monopolist. The policy relevance of our approach lies in the possibility to offer some empirical knowledge of the marginal cost function of each generator to the regulator to design appropriate policy measures geared to the promotion of competitive market conditions. We propose a new market surveillance mechanism, which is based on the principle of sanctioning excessive deviations from the estimated measure of the marginal cost function presented in this work. 相似文献
5.
This study is to evaluate the potential for development of a cellulosic ethanol facility in Vietnam. Rice straw is abundant in Vietnam and highly concentrated in the Mekong Delta, where about 26 Mt year−1 of rice straw has been yearly produced. To minimize the overall production cost (PC) of ethanol from rice straw, it is crucial to choose the optimal facility size. The delivered cost of rice straw varied from 20.5 to 65.4 $ dry t−1 depending on transportation distance. The Mekong Delta has much lower rice straw prices compared with other regions in Vietnam because of high density and quantity of rice straw supply. Thus, this region has been considered as the most suitable location for deploying ethanol production in Vietnam. The optimal plant size of ethanol production in the region was estimated up to 200 ML year−1. The improvement in solid concentration of material in the hydrothermal pre-treatment step and using residues for power generation could substantially reduce the PC in Vietnam, where energy costs account for the second largest contribution to the PC, following only enzyme costs. The potential for building larger ethanol plants with low rice straw costs can reduce ethanol production costs in Vietnam. The current estimated production cost for an optimal plant size of 200 ML year−1 was 1.19 $ L−1. For the future scenario, considering improvements in pre-treatment, enzyme hydrolysis steps, specific enzyme activity, and applying residues for energy generation, the ethanol production cost could reduce to 0.45 $ L−1 for a plant size of 200 ML year−1 in Vietnam. These data indicated that the cost-competitiveness of ethanol production could be realized in Vietnam with future improvements in production technologies. 相似文献
6.
随着BIM技术的进步,建筑行业越来越重视BIM技术的应用,并在应用过程中取得一定的成效。本文从工程造价决策、设计、招投标、施工、竣工五个阶段阐述BIM技术在建筑工程造价中的应用对策。 相似文献
7.
8.
降低成品油二次物流运输成本的思考 总被引:4,自引:0,他引:4
介绍了传统成品油进货和管理模式存在的诸如成品油物流以行政区划、中问环节多、信息化程度不高、运输路线未优化造成物流成本提高等问题。提出要降低成品油二次物流运输成本,当务之急是加强成品油物流的信息化建设;调整管理模式,打破行政区域界限,开展经济辐射半径内的库站物流配送;引进竞争机制,打破运输垄断,一、二次物流结合,大、小车型搭配,提高运营效率;做好运杂费全面预算、核算及运行费用的过程控制。 相似文献
9.
为实现电源设备乃至通信机房的少人或无人值守和集中维护,必须建立一套完善的电信局动力环境集中监控系统。文中结合番禺区电信局的实际,讨论了提高系统运行可靠性的几点措施,包括硬件方面与软件方面的手段,关键在于加强系统的运行管理。 相似文献
10.
基于多相滤波器的信道化接收机及其应用研究 总被引:16,自引:0,他引:16
本文主要研究了应用多相滤波技术的信道化接收机建模问题。在给定信道频谱划分方案下,推导了基于多相 滤波器的信道化接收机数学模型。并由此模型设计了一个四信道模拟系统。最后用仿真实验结果验证了模型的正确性。 相似文献