全文获取类型
收费全文 | 11889篇 |
免费 | 819篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 70篇 |
综合类 | 5篇 |
化学工业 | 2401篇 |
金属工艺 | 101篇 |
机械仪表 | 284篇 |
建筑科学 | 432篇 |
矿业工程 | 20篇 |
能源动力 | 215篇 |
轻工业 | 1984篇 |
水利工程 | 68篇 |
石油天然气 | 20篇 |
无线电 | 683篇 |
一般工业技术 | 1739篇 |
冶金工业 | 3112篇 |
原子能技术 | 23篇 |
自动化技术 | 1561篇 |
出版年
2024年 | 35篇 |
2023年 | 140篇 |
2022年 | 114篇 |
2021年 | 325篇 |
2020年 | 270篇 |
2019年 | 270篇 |
2018年 | 347篇 |
2017年 | 354篇 |
2016年 | 464篇 |
2015年 | 419篇 |
2014年 | 545篇 |
2013年 | 989篇 |
2012年 | 859篇 |
2011年 | 646篇 |
2010年 | 468篇 |
2009年 | 465篇 |
2008年 | 490篇 |
2007年 | 423篇 |
2006年 | 392篇 |
2005年 | 244篇 |
2004年 | 226篇 |
2003年 | 197篇 |
2002年 | 191篇 |
2001年 | 121篇 |
2000年 | 120篇 |
1999年 | 165篇 |
1998年 | 866篇 |
1997年 | 502篇 |
1996年 | 367篇 |
1995年 | 224篇 |
1994年 | 209篇 |
1993年 | 217篇 |
1992年 | 50篇 |
1991年 | 63篇 |
1990年 | 52篇 |
1989年 | 56篇 |
1988年 | 64篇 |
1987年 | 49篇 |
1986年 | 43篇 |
1985年 | 54篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 47篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 103篇 |
1976年 | 218篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
The liver microsomal Δ9 and Δ6 desaturase activities have been studied in rats with carbon tetrachloride-induced hepatitis. Immediately after poisoning,
significant decreases were observed for both types of desaturase activity. However, recovery kinetics were slower for the
Δ6 desaturase than for the Δ9 desaturase. The activities of NADH-ferricyanide and NADH-cytochrome C reductases, proteins involved in the electron transfers
associated with microsomal desaturation, were also measured. There was a fall in both activities after poisoning, but this
decrease was less than that of the desaturase activities. 相似文献
82.
The alignment of information systems with the business goals of an organisation, although a topic of great importance, is not always properly valued or taken into consideration. In general, managers have different opinions to chief information officers (CIOs) in relation to IS, especially with regard to their importance and value to the business and also in terms of investment needs. Here, we discuss and study new approaches to methods and tools for assessing the relative importance of each information system to business, focusing on the financial sector including banks and insurance companies. We suggest the introduction of new key indicators for better decision support and to identify investment priorities, and present results regarding the relative importance of each process to support the business strategy. The primary goal for the inherent research project is to analyse the main problems and difficulties encountered by IS and IT managers, featuring different players and how they relate. The main contributions of this work are the CRUDi framework as a tool to improve alignment between business and IS strategies and the CRUDi survey and its results qualifying the financial sector's opinion regarding the relative importance of processes and investments. 相似文献
83.
Jose Saldana Julián Fernández-Navajas José Ruiz-Mas Eduardo Viruete-Navarro Luis Casadesus 《Multimedia Tools and Applications》2014,71(3):1823-1856
First Person Shooters are a genre of online games in which users demand a high interactivity, because the actions and the movements are very fast. They usually generate high rates of small packets which have to be delivered to the server within a deadline. When the traffic of a number of players shares the same link, these flows can be aggregated in order to save bandwidth. Certain multiplexing techniques are able to merge a number of packets, in a similar way to voice trunking, creating a bundle which is transmitted using a tunnel. In addition, the headers of the original packets can be compressed by means of standard algorithms. The characteristics of the buffers of the routers which deliver these bundled packets may have a strong influence on the network impairments (mainly delay, jitter and packet loss) which determine the quality of the game. A subjective quality estimator has been used in order to study the mutual influence of the buffer and multiplexing techniques. Taking into account that there exist buffers which size is measured in terms of bytes, and others measured in packets, both kinds of buffers have been tested, using different sizes. Traces from real game parties have been merged in order to obtain the traffic of 20 simultaneous players sharing the same Internet access. The delay and jitter produced by the buffer of the access router have been obtained using simulations. In general, the quality is expected to be reduced as the background traffic grows, but the results show an anomalous region in which the quality rises with the background traffic amount. Small buffers present better subjective quality results than bigger ones. When the total traffic amount gets above the available bandwidth, the buffers measured in bytes add to the packets a fixed delay, which grows with buffer size. They present a jitter peak when the offered traffic is roughly the link capacity. On the other hand, buffers which size is measured in packets add a smaller delay, but they increase packet loss for gaming traffic. The obtained results illustrate the need of knowing the characteristics of the buffer in order to make the correct decision about traffic multiplexing. As a conclusion, it would be interesting for game developers to identify the behaviour of the router buffer so as to adapt the traffic to it. 相似文献
84.
André Lourenço Hugo Plácido da Silva Carlos Carreiras Ana Priscila Alves Ana L. N. Fred 《Multimedia Tools and Applications》2014,70(1):433-460
With the advent of wearable sensing and mobile technologies, biosignals have seen an increasingly growing number of application areas, leading to the collection of large volumes of data. One of the difficulties in dealing with these data sets, and in the development of automated machine learning systems which use them as input, is the lack of reliable ground truth information. In this paper we present a new web-based platform for visualization, retrieval and annotation of biosignals by non-technical users, aimed at improving the process of ground truth collection for biomedical applications. Moreover, a novel extendable and scalable data representation model and persistency framework is presented. The results of the experimental evaluation with possible users has further confirmed the potential of the presented framework. 相似文献
85.
The problem of state-parameter estimation is considered in terms of decoupling the estimation procedure. First, the theoretical preliminaries necessary for the mathematical statement of the problem are defined. Then using the extended Kalman filter (EKF) approach, the state and parameter are estimated by applying the solution techniques to a distributed parameter system. Next, the state estimation problem is decoupled from the parameter estimation problem and by using a numerical example, the advantage of this decoupling procedure is demonstrated. The numerical results show that convergence can be improved when this decoupling procedure is employed. The effect of the location of the measurements on the estimation problem is also analysed in this work. The results show that the convergence of the problem depends on the location as well as the number of measurements. 相似文献
86.
José Sánchez-Sánchez Félix Escrig Pallarés Maria Teresa Rodríguez-León 《Nexus Network Journal》2014,16(1):135-150
Sometimes the complex structures of nature inspire human constructions. Gothic construction has shown that forces can cross space along intricate paths that may even be arbitrary if correctly dimensioned. In some way, ribbed structures are like trees where the branches conduct forces instead of sap; they operate as branches and trunks descending by fractal ways. Here we discuss reciprocal tree-like fractal structures and the difficulty in their design and erection and solutions for constructive details, as well as the possible analytical questions and automatic generation by means of proper software. The results are shown in the design of the Natural Interpretation Centre in Melilla where we have proposed two connected trees like shown at figures included below. 相似文献
87.
Søren N. Sørensen René Sørensen Erik Lund 《Structural and Multidisciplinary Optimization》2014,50(1):25-47
This paper presents a gradient based topology optimization method for Discrete Material and Thickness Optimization of laminated composite structures, labelled the DMTO method. The capabilities of the proposed method are demonstrated on mass minimization, subject to constraints on the structural criteria; buckling load factors, eigenfrequencies, and limited displacements. Furthermore, common design guidelines or rules, referred to as manufacturing constraints, are included explicitly in the optimization problem as series of linear inequalities. The material selection and thickness variation are optimized simultaneously through interpolation functions with penalization. Numerical results for several parameterizations of a finite element model of a generic main spar from a wind turbine blade are presented. The different parameterizations represent different levels of complexity with respect to manufacturability. The results will thus give insight into the relation between potential weight saving and design complexity. The results show that the DMTO method is capable of solving the problems robustly with only few intermediate valued design variables. 相似文献
88.
Summary The Stefan-Winkelmann diffusion technique has been used to determine vapor pressures of high boiling point compound-solvents mixtures. Data are reported at a temperature of 67°C for the mixtures polyphenyl ether (6 rings) — benzene and carbowax 1500 — benzene and at a temperature of 100°C for the mixtures polyphenyl ether (6 rings) — toluene and tricresylphosphate-toluene. The range of concentration is only limited by the appearance of a solid phase, and results are in good agreement with those determined by vapor pressure osmometry.Nomenclature A
Vapour source
- B
Flowing gas phase
- c
Concentration, g-mol/cm3
- DAB
Molecular diffusion coefficient, cm2/s
- hi
Total interface depth, cm
- K
Parameter defined by equation (6), dimensionless
- I
Polymer or high boiling point compound
- MA
Molecular weight
- NAZ
Molar flux, g-mol/(cm2) (s)
- PA
Partial pressure at the interface, atm
- P
Total pressure, atm
- R
Gas constant, (atm) (cm3) / (°K) (g-mol)
- T
Temperature, °K
- t
Time, s
- YA
Molar fraction at the interface, dimensionless
- zo
Initial interface depth, cm
- zi
Drop of the interface depth, cm
- z
Interface position
Greek Letters A
Density of the liquid phase, g/cm3 相似文献
89.
In this paper, we present an invariant‐set‐based method for actuator and sensor fault detection and isolation in Lure systems. The Lure plant is controlled by an observer‐based feedback tracking controller, designed for the nominal (fault‐free) system. Suitable residual signals are constructed from measurable system outputs and estimates associated with the nominal observer. Faults are diagnosed by online contrasting the residual signal trajectories against sets of values that the residuals are shown to attain under healthy or faulty operation. These values are obtained via set‐invariance analysis of the system closed‐loop trajectories. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
90.
Cláudio Teixeira Joaquim Sousa Pinto Ricardo Azevedo Tiago Batista André Monteiro 《Journal of Network and Systems Management》2014,22(1):75-99
Traditional cloud computing providers enable developers to program and deploy applications in the cloud by using platform as a service (PaaS) providers. Despite the benefits of such an approach, this service model usually comes with a high level of the lock in effect into the service provider. The lock in effect occurs when a software developer needs to change its cloud provider. When this happens, it usually means a major application rewrite, specific for the new PaaS. This paper details the initial results of a project whose goal is to build a PaaS where vendor lock in does not occur. With this PaaS, developers wishing to deploy their applications into the cloud may continue to program using their usual development environments. There are no necessary changes required to make the application PaaS compatible. As a proof of concept, we developed an open source PaaS management application as a regular web application and then deployed it on the cloud. 相似文献