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排序方式: 共有3449条查询结果,搜索用时 15 毫秒
981.
This paper presents the design, analysis, and performance evaluation of a novel cascade observer for attitude estimation. A sensor-based observer, which resorts to rate gyro readings and a set of vector observations, estimates the rate gyro bias. Afterwards, a cascaded observer explicitly estimates the attitude in the form of a rotation matrix based on the rate gyro measurements, the vector observations, and the estimated gyro bias. The overall error dynamics are globally exponentially stable and the proposed system is computationally efficient. Finally, the resulting estimator is successfully evaluated, in simulation and experimentally, with ground truth data in both cases. 相似文献
982.
Rodolfo Carneiro Cavalcante Alan Pedro da Silva 《Expert systems with applications》2012,39(5):4835-4846
Multi-agent systems (MAS) are a relatively new software paradigm that is being widely accepted in several application domains to address large and complex tasks. However, with the use of MAS in open, distributed and heterogeneous applications, the security issues may endanger the success of the application. The goal of this research is to identify the security issues faced by MAS and to survey the current state of the art of this field of knowledge. In order to do it, this paper examines the basic concepts of security in computing, and some characteristics of agents and multi-agent systems that introduce new threats and ways to attack. After this, some models and architectures proposed in the literature are presented and analyzed. 相似文献
983.
Luis Pérez Luis Velasco Juan Rodríguez Pedro Capelastegui Guillem Hernández-Sola Lorena Calavia Antonio Marqués Borja Iribarne Amador Pozo Antoine De Poorter 《Computer Networks》2012,56(4):1183-1199
The emerging use of real-time 3D-based multimedia applications imposes strict quality of service (QoS) requirements on both access and core networks. These requirements and their impact to provide end-to-end 3D videoconferencing services have been studied within the Spanish-funded VISION project, where different scenarios were implemented showing an agile stereoscopic video call that might be offered to the general public in the near future. In view of the requirements, we designed an integrated access and core converged network architecture which provides the requested QoS to end-to-end IP sessions. Novel functional blocks are proposed to control core optical networks, the functionality of the standard ones is redefined, and the signaling improved to better meet the requirements of future multimedia services. An experimental test-bed to assess the feasibility of the solution was also deployed. In such test-bed, set-up and release of end-to-end sessions meeting specific QoS requirements are shown and the impact of QoS degradation in terms of the user perceived quality degradation is quantified. In addition, scalability results show that the proposed signaling architecture is able to cope with large number of requests introducing almost negligible delay. 相似文献
984.
Iago Augusto Reis Pedro Ivo Cunha Claro Andre Luis Marcomini Luiz Henrique Capparelli Mattoso Sandro Pereira da Silva Alfredo Rodrigues de Sena Neto 《Polymer Engineering and Science》2021,61(7):2097-2104
In this study, we investigated the influence of isothermal treatment of poly(lactic acid) (PLA) 3D printed samples at different crystallization temperatures. In this case, we analyzed the effect of each crystallization temperature on spherulites formation in printed PLA, affecting the final mechanical properties of pieces. For such, the thermomechanical properties, morphological structure, and crystallization kinetics were analyzed before and after thermal treatment. The 3D printed samples were heat treated at 80°C, 90°C, 100°C, 110°C, and 119°C. With annealing, we observed an improvement in the mechanical PLA properties; however, the exothermic crystallization peak was different for the samples. Pieces before annealing were found to have a low crystallinity index (Ic) of 2%–7%, and the pieces after annealing presented a considerable Ic (27%–34%). Annealing temperatures of 100°C, 110°C, and 119°C produced the fastest crystallization kinetics, while annealing temperatures of 80°C and 90°C resulted in the lowest crystallization kinetics for complete crystallization. After annealing, improvement in the flexural strength (34%–47%) and Young's modulus (26%–51%) for all annealed pieces occurred. The appropriate condition was observed at 100°C, which was the onset temperature of crystallization, owing to the combination of the shorter time of crystallization with the increased mechanical properties. 相似文献
985.
Daniela Malafaia Ana Oliveira Pedro A. Fernandes Maria J. Ramos Hlio M. T. Albuquerque Artur M. S. Silva 《International journal of molecular sciences》2021,22(8)
Alzheimer’s disease (AD) is a complex multifactorial disorder, mainly characterized by the progressive loss of memory and cognitive, motor, and functional capacity. The absence of effective therapies available for AD alongside the consecutive failures in the central nervous system (CNS) drug development has been motivating the search for new disease-modifying therapeutic strategies for this disease. To address this issue, the multitarget directed ligands (MTDLs) are emerging as a therapeutic alternative to target the multiple AD-related factors. Following this concept, herein we describe the design, synthesis, and biological evaluation of a family of chromeno[3,4-b]xanthones as well as their (E)-2-[2-(propargyloxy)styryl]chromone precursors, as first-in-class acetylcholinesterase (AChE) and β-amyloid (Aβ) aggregation dual-inhibitors. Compounds 4b and 10 emerged as well-balanced dual-target inhibitors, with IC50 values of 3.9 and 2.9 μM for AChE and inhibitory percentages of 70 and 66% for Aβ aggregation, respectively. The molecular docking showed that most of the compounds bound to AChE through hydrogen bonds with residues of the catalytic triad and π-stacking interactions between the main scaffold and the aromatic residues present in the binding pocket. The interesting well-balanced activities of these compounds makes them interesting templates for the development of new multitarget compounds for AD. 相似文献
986.
Angelo Pedro Jacomino Ilana Urbano Bron Claire Isabel Grígoli de Luca Sarantpoulos Jos Maria Monteiro Sigrist 《Packaging Technology and Science》2005,18(2):71-76
The objective of this study was to evaluate the influence of package materials on the preservation of cold‐stored ‘Kumagai’ guavas. The treatments were: PO2, co‐extruded polyolephinic film with gas injection (5% O2/5% CO2/N2); PO3, co‐extruded polyolephinic film with gas injection (5% O2/5% CO2/N2); LDPE, linear low density polyethylene film; LDPE‐gas, linear low density polyethylene film with gas injection (3% O2/8% CO2/N2); PVC, polyvinylchloride stretch film; PO1, co‐extruded polyolephinic film and control: non‐packaged guavas. Guavas were stored at 10 ± 1°C/80–90% RH for 21 days, and then transferred to room temperature. Gas composition within the package headspace was analysed during storage and the physical and chemical characteristics of the guavas were evaluated daily during ripening. The modified atmosphere provided by PO1 film was insufficient to promote the benefit of senescence control. Although PVC provided an atmosphere close to that recommended, it did not preserve the colour and pulp firmness. PO2, PO3, LDPE and LDPE‐gas retarded the senescence process of the guavas during 21 days at 10°C plus 2 days at room temperature, but harmed the normal ripening of guavas in some aspects. This can be explained by reduced O2 and elevated CO2 levels within these four packages. None of the packages influenced the titratable acidity and the soluble solids, but they did harm ascorbic acid synthesis. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
987.
Pedro M. A. Areias Jeong‐Hoon Song Ted Belytschko 《International journal for numerical methods in engineering》2005,64(9):1166-1206
This paper improves the 16 degrees‐of‐freedom quadrilateral shell element based on pointwise Kirchhoff–Love constraints and introduces a consistent large strain formulation for this element. The model is based on classical shell kinematics combined with continuum constitutive laws. The resulting element is valid for large rotations and displacements. The degrees‐of‐freedom are the displacements at the corner nodes and one rotation at each mid‐side node. The formulation is free of enhancements, it is almost fully integrated and is found to be immune to locking or unstable modes. The patch test is satisfied. In addition, the formulation is simple and amenable to efficient incorporation in large‐scale codes as no internal degrees‐of‐freedom are employed, and the overall calculations are very efficient. Results are presented for linear and non‐linear problems. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
988.
Yago Saez Pedro Isasi Javier Segovia Julio C. Hernandez 《New Generation Computing》2005,23(2):129-142
Evolutionary Computation encompasses computational models that follow a biological evolution metaphor. The success of these
techniques is based on the maintenance of the genetic diversity, for which it is necessary to work with large populations.
However, it is not always possible to deal with such large populations, for instance, when the adequacy values must be estimated
by a human being (Interactive Evolutionary Computation, IEC). This work introduces a new algorithm which is able to perform
very well with a very low number of individuals (micropopulations) which speeds up the convergence and it is solving problems
with complex evaluation functions. The new algorithm is compared with the canonical genetic algorithm in order to validate
its efficiency. Two experimental frameworks have been chosen: table and logotype designs. An objective evaluation measures
has been proposed to avoid user interaction in the experiments. In both cases the results show the efficiency of the new algorithm
in terms of quality of solutions and convergence speed, two key issues in decreasing user fatigue.
Yago Saez: He received the Computer Engineering degree from the Universidad Pontificia de Salamanca in 1999 Spain. He now is a Ph.D.
student and works as assistant professor at the EVANNAI Group at the Computer Science Department of CARLOS III, Madrid, Spain.
His main research areas encompasses the interactive evolutionary computation, the design applications and the optimization
problems.
Pedro Isasi, Ph.D.: He received Computer Science degree and Ph.D. degree from the Universidad Politécnica de Madrid (UPM), Spain in 1994. He
is now working as professor at the EVANNAI Group at the Computer Science Department of CARLOS III, Madrid, Spain. His main
research areas are Machine Learning, Evolutionary, Computation and Neural Networks and Applications to Optimization Problems.
Javier Segovia, Ph.D.: He is a receiving physicist, Ph.D. degree in Computer Science (with honours) from the Universidad Politécnica de Madrid
(UPM). Currently Dean of the UPM School of Computer Science, and is editor and/or author of more than 70 scientific publications
in the fields of genetic algorithms, data and web mining, artificial intelligence and intelligent interfaces.
Julio C. Hernandez, Ph.D.: He has received degree in Maths, Ph.D. degree in Computer Science. His main research area is the artificial intelligence
applied to criptography and net security. His unofficial hobbies are chess and go. Currently, he is working as invited researcher
at INRIA, France. 相似文献
989.
This paper presents an integral sliding mode technique robustifying the optimal controller for linear stochastic systems with input and observation delays, which is based on integral sliding mode compen‐sation of disturbances. The general principles of the integral sliding mode compensator design are modified to yield the basic control algorithm oriented to time‐delay systems, which is then applied to robustify the optimal controller. As a result, two integral sliding mode control compensators are designed to suppress disturbances in state and observation equations, respectively, from the initial time moment. Moreover, it is shown that if certain matching conditions hold, the designed compensator in the state equation can simultaneously suppress observation disturbances, as well as the designed compensator in the observation equation can simultaneously suppress state disturbances. The obtained robust control algorithm is verified by simulations in the illustrative example, where the compensator in the observation equation provides simultaneous suppression of state and observation disturbances. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
990.
Tree Induction for Probability-Based Ranking 总被引:13,自引:0,他引:13
Tree induction is one of the most effective and widely used methods for building classification models. However, many applications require cases to be ranked by the probability of class membership. Probability estimation trees (PETs) have the same attractive features as classification trees (e.g., comprehensibility, accuracy and efficiency in high dimensions and on large data sets). Unfortunately, decision trees have been found to provide poor probability estimates. Several techniques have been proposed to build more accurate PETs, but, to our knowledge, there has not been a systematic experimental analysis of which techniques actually improve the probability-based rankings, and by how much. In this paper we first discuss why the decision-tree representation is not intrinsically inadequate for probability estimation. Inaccurate probabilities are partially the result of decision-tree induction algorithms that focus on maximizing classification accuracy and minimizing tree size (for example via reduced-error pruning). Larger trees can be better for probability estimation, even if the extra size is superfluous for accuracy maximization. We then present the results of a comprehensive set of experiments, testing some straightforward methods for improving probability-based rankings. We show that using a simple, common smoothing method—the Laplace correction—uniformly improves probability-based rankings. In addition, bagging substantially improves the rankings, and is even more effective for this purpose than for improving accuracy. We conclude that PETs, with these simple modifications, should be considered when rankings based on class-membership probability are required. 相似文献