全文获取类型
收费全文 | 1865篇 |
免费 | 90篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 24篇 |
综合类 | 16篇 |
化学工业 | 569篇 |
金属工艺 | 30篇 |
机械仪表 | 31篇 |
建筑科学 | 142篇 |
矿业工程 | 3篇 |
能源动力 | 27篇 |
轻工业 | 175篇 |
水利工程 | 12篇 |
石油天然气 | 3篇 |
无线电 | 117篇 |
一般工业技术 | 373篇 |
冶金工业 | 68篇 |
原子能技术 | 16篇 |
自动化技术 | 354篇 |
出版年
2023年 | 27篇 |
2022年 | 49篇 |
2021年 | 66篇 |
2020年 | 36篇 |
2019年 | 47篇 |
2018年 | 43篇 |
2017年 | 41篇 |
2016年 | 51篇 |
2015年 | 47篇 |
2014年 | 73篇 |
2013年 | 97篇 |
2012年 | 89篇 |
2011年 | 159篇 |
2010年 | 99篇 |
2009年 | 111篇 |
2008年 | 102篇 |
2007年 | 84篇 |
2006年 | 85篇 |
2005年 | 75篇 |
2004年 | 68篇 |
2003年 | 54篇 |
2002年 | 51篇 |
2001年 | 44篇 |
2000年 | 42篇 |
1999年 | 41篇 |
1998年 | 29篇 |
1997年 | 28篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1967年 | 3篇 |
1939年 | 1篇 |
1931年 | 3篇 |
排序方式: 共有1960条查询结果,搜索用时 15 毫秒
1.
2.
3.
We define and study an optimization problem that is motivated by bandwidth allocation in radio networks. Because radio transmissions are subject to interference constraints in radio networks, physical space is a common resource that the nodes have to share in such a way, that concurrent transmissions do not interfere. The bandwidth allocation problem we study under these constraints is the following. Given bandwidth (traffic) demands between the nodes of the network, the objective is to schedule the radio transmissions in such a way that the traffic demands are satisfied. The problem is similar to a multicommodity flow problem, where the capacity constraints are replaced by the more complex notion of non-interfering transmissions. We provide a formal specification of the problem that we call round weighting . By modeling non-interfering radio transmissions as independent sets, we relate the complexity of round weighting to the complexity of various independent set problems (e.g. maximum weight independent set, vertex coloring, fractional coloring). From this relation, we deduce that in general, round weighting is hard to approximate within n1−ε (n being the size of the radio network). We also provide polynomial (exact or approximation) algorithms e.g. in the following two cases: (a) when the interference constraints are specific (for instance for a network whose vertices belong to the Euclidean space), or (b) when the traffic demands are directed towards a unique node in the network (also called gathering, analogous to single commodity flow). 相似文献
4.
Zeolite based trace humidity sensor for high temperature applications in hydrogen atmosphere 总被引:1,自引:0,他引:1
We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (10–110 ppmV) under harsh conditions, e.g. reducing atmosphere (H2) and high temperature (up to 600 °C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required. 相似文献
5.
Dipl.-Wirt.-Inform. Daniel Beverungen Dr. Ralf Knackstedt Dipl.-Wirt.-Inform. Oliver Müller 《WIRTSCHAFTSINFORMATIK》2008,50(3):220-234
Offering product-service bundles (consisting of products and services) is becoming more important for companies. Modifying the organizational structure of the cooperation as well as adapting to changing customer demands requires versatile information systems. Implementing Service Oriented Architectures (SOA) is one attempt to provide this flexibility. Currently, there is little methodical guidance for the identification, specification and implementation of services as building blocks of Service Oriented Architectures. Accounting for this need, a conceptual approach is designed, which adapts approaches of customer integration, and combines a business and IT analysis. The applicability of the method is demonstrated by designing a Service Oriented Architecture for the recycling of electronic equipment. Implementing services for other product-service bundles will support additional integration scenarios. By standardizing services, a sound integration of products and services can be backed by providing a reference architecture. 相似文献
6.
Integrating products and services to customized solutions can help firms to differentiate from their competitors. In practice, however, various companies fall short in extracting value from their customers. Therefore this paper focuses on pricing aspects as central means for value appropriation in the context of solutions. Following the resource-based view of the firm, we adopt a process-oriented perspective on pricing practices in order to identify crucial factors and activities. Based on 15 in-depth interviews with practitioners from various industries we derive six steps of a price management process for value appropriation in the context of solution selling and present critical activities and routines within each step. 相似文献
7.
8.
Anne Martens Heiko Koziolek Lutz Prechelt Ralf Reussner 《Empirical Software Engineering》2011,16(5):587-622
Model-based performance evaluation methods for software architectures can help architects to assess design alternatives and save costs for late life-cycle performance fixes. A recent trend is component-based performance modelling, which aims at creating reusable performance models; a number of such methods have been proposed during the last decade. Their accuracy and the needed effort for modelling are heavily influenced by human factors, which are so far hardly understood empirically. Do component-based methods allow to make performance predictions with a comparable accuracy while saving effort in a reuse scenario? We examined three monolithic methods (SPE, umlPSI, Capacity Planning (CP)) and one component-based performance evaluation method (PCM) with regard to their accuracy and effort from the viewpoint of method users. We conducted a series of three experiments (with different levels of control) involving 47 computer science students. In the first experiment, we compared the applicability of the monolithic methods in order to choose one of them for comparison. In the second experiment, we compared the accuracy and effort of this monolithic and the component-based method for the model creation case. In the third, we studied the effort reduction from reusing component-based models. Data were collected based on the resulting artefacts, questionnaires and screen recording. They were analysed using hypothesis testing, linear models, and analysis of variance. For the monolithic methods, we found that using SPE and CP resulted in accurate predictions, while umlPSI produced over-estimates. Comparing the component-based method PCM with SPE, we found that creating reusable models using PCM takes more (but not drastically more) time than using SPE and that participants can create accurate models with both techniques. Finally, we found that reusing PCM models can save time, because effort to reuse can be explained by a model that is independent of the inner complexity of a component. The tasks performed in our experiments reflect only a subset of the actual activities when applying model-based performance evaluation methods in a software development process. Our results indicate that sufficient prediction accuracy can be achieved with both monolithic and component-based methods, and that the higher effort for component-based performance modelling will indeed pay off when the component models incorporate and hide a sufficient amount of complexity. 相似文献
9.
Jörg Becker Daniel F. Beverungen Ralf Knackstedt 《Information Systems and E-Business Management》2010,8(1):33-66
Confronted with decreasing margins and a rising customer demand for integrated solutions, manufacturing companies integrate
complementary services into their portfolio. Offering value bundles (consisting of services and physical goods) takes place
in integrated product–service systems, spanning the coordinated design and delivery of services and physical goods for customers.
Conceptual Modeling is an established approach to support and guide such efforts. Using a framework for the design and delivery
of value bundles as an analytical lens, this study evaluates the current support of reference models and modeling languages
for setting up conceptual models for an integrated design and delivery of value bundles. Consecutively, designing modeling
languages and reference models to fit the requirements of conceptual models in product–service systems are presented as upcoming
challenges in Service Research. To guide further research, first steps are proposed by exemplarily integrating reference models
and modeling languages stemming from the service and manufacturing domains. 相似文献
10.
A two-layer architecture for dynamic real-time optimization (or nonlinear modelpredictive control (NMPC) with an economic objective) is presented, where the solution of the dynamic optimization problem is computed on two time-scales. On the upper layer, a rigorous optimization problem is solved with an economic objective function at a slow time-scale, which captures slow trends in process uncertainties. On the lower layer, a fast neighboring-extremal controller is tracking the trajectory in order to deal with fast disturbances acting on the process. Compared to a single-layer architecture, the two-layer architecture is able to address control systems with complex models leading to high computational load, since the rigorous optimization problem can be solved at a slower rate than the process sampling time. Furthermore, solving a new rigorous optimization problem is not necessary at each sampling time if the process has rather slow dynamics compared to the disturbance dynamics. The two-layer control strategy is illustrated with a simulated case study of an industrial polymerization process. 相似文献