全文获取类型
收费全文 | 2670篇 |
免费 | 180篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 756篇 |
金属工艺 | 59篇 |
机械仪表 | 92篇 |
建筑科学 | 86篇 |
矿业工程 | 7篇 |
能源动力 | 102篇 |
轻工业 | 726篇 |
水利工程 | 20篇 |
石油天然气 | 17篇 |
无线电 | 114篇 |
一般工业技术 | 353篇 |
冶金工业 | 233篇 |
原子能技术 | 16篇 |
自动化技术 | 246篇 |
出版年
2024年 | 9篇 |
2023年 | 21篇 |
2022年 | 138篇 |
2021年 | 134篇 |
2020年 | 74篇 |
2019年 | 77篇 |
2018年 | 84篇 |
2017年 | 117篇 |
2016年 | 88篇 |
2015年 | 76篇 |
2014年 | 105篇 |
2013年 | 213篇 |
2012年 | 200篇 |
2011年 | 191篇 |
2010年 | 153篇 |
2009年 | 131篇 |
2008年 | 130篇 |
2007年 | 123篇 |
2006年 | 91篇 |
2005年 | 68篇 |
2004年 | 62篇 |
2003年 | 61篇 |
2002年 | 43篇 |
2001年 | 40篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 84篇 |
1997年 | 43篇 |
1996年 | 39篇 |
1995年 | 34篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 14篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1975年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有2850条查询结果,搜索用时 31 毫秒
41.
Daniel Dominguez Gouvêa Cyro de A. Assis D. Muniz Gilson A. Pinto Alberto Avritzer Rosa Maria Meri Leão Edmundo de Souza e Silva Morganna Carmem Diniz Vittorio Cortellessa Luca Berardinelli Julius C. B. Leite Daniel Mossé Yuanfang Cai Michael Dalton Lucia Happe Anne Koziolek 《Software and Systems Modeling》2013,12(4):765-787
In this paper, we report on our experience with the application of validated models to assess performance, reliability, and adaptability of a complex mission critical system that is being developed to dynamically monitor and control the position of an oil-drilling platform. We present real-time modeling results that show that all tasks are schedulable. We performed stochastic analysis of the distribution of task execution time as a function of the number of system interfaces. We report on the variability of task execution times for the expected system configurations. In addition, we have executed a system library for an important task inside the performance model simulator. We report on the measured algorithm convergence as a function of the number of vessel thrusters. We have also studied the system architecture adaptability by comparing the documented system architecture and the implemented source code. We report on the adaptability findings and the recommendations we were able to provide to the system’s architect. Finally, we have developed models of hardware and software reliability. We report on hardware and software reliability results based on the evaluation of the system architecture. 相似文献
42.
Mathematical simulation has been widely used in biomedical and biological sciences. In the case of the surface electromyographic (SEMG) activity, some models have been proposed aiming to study muscle contraction strategies that are used during different tasks and conditions. Most of SEMG simulators are based on energy modulation of a Gaussian noise. This work proposes a novel simulator in which the user-defined parameters are associated with the motor units (MUs) recruitment and their firing rate. Comparison between the mean spectrum of real SEMG signals collected in isometric contraction of the muscle biceps brachii and the mean spectrum obtained from simulated SEMG signals showed a good agreement, pointing the proposed simulator seems to be capable to generate consistent electromyographic signals in time and frequency domains and that can be used in many studies, in particular in the evaluation of automatic methods aimed to detect muscular contraction. 相似文献
43.
The popularity of distance education has grown rapidly over the last decade in Taiwan’s higher education, yet many fundamental teaching–learning issues are still in debate. While teacher–student interaction is a key success factor in distance education, little work has been done on the teachers. The intent of this research was to clarify teacher’s perceptions on key distance education issues and to develop a discernible typology of different groups of teachers based on their perceptions. Because there may be a gulf between teachers and the technology used in distance education, the target of this study was teachers in information related departments in Taiwan’s colleges, who were more familiar with current technology. Factor analysis and cluster analysis were used to derive the typology. Five higher-level issue constructs emerged from the factor analysis: learning effect, customization, administrative challenges, geographic and resource integration, and instructional design challenges. Four groups of teachers, namely the skeptics, the optimists, the mild-promising group, and the outlier, were identified using cluster analysis of teachers’ perceptions on these five higher-level issue constructs. The profiles of the four groups of teachers were summarized and implications were discussed, which should provide useful insights to the policy makers of higher education on distance education decisions. 相似文献
44.
Marcello La Rosa Wil M. P. van der Aalst Marlon Dumas Arthur H. M. ter Hofstede 《Software and Systems Modeling》2009,8(2):251-274
Variability management is a recurrent issue in systems engineering. It arises for example in enterprise systems, where modules
are configured and composed to meet the requirements of individual customers based on modifications to a reference model.
It also manifests itself in the context of software product families, where variants of a system are built from a common code
base. This paper proposes an approach to capture system variability based on questionnaire models that include order dependencies
and domain constraints. The paper presents analysis techniques to detect circular dependencies and contradictory constraints
in questionnaire models, as well as techniques to incrementally prevent invalid configurations by restricting the space of
allowed answers to a question based on previous answers. The approach has been implemented as a toolset and has been used
in practice to capture configurable process models for film post-production.
相似文献
Arthur H. M. ter HofstedeEmail: |
45.
Rosa RG Tarsitano CA Hyslop S Yamada AT Toledo OM Joazeiro PP 《Microscopy research and technique》2008,71(3):169-178
In some animals, such as mice and guinea pigs, a hormonally controlled mechanism increases the flexibility of the pubic symphysis and enhances the cervical remodeling necessary for safe delivery. Cervical ripening during pregnancy is associated with a paradoxical influx of leukocytes. However, the changes in cell metabolism during relaxation of the mouse pubic symphysis for delivery have not been extensively studied. In this work, we used light microscopy and transmission and scanning electron microcopy, as well as immunohistochemistry and Western blotting for MMP-8, to investigate the involvement of granulocytes or resident stromal cells in the relaxation of the virgin pubic symphysis during late pregnancy (days 18 and 19, before delivery) in vivo and in explanted joints. MMP-8 was studied because this collagenase is a hallmark for cervical ripening associated with the influx of granulocytes during late pregnancy. Extensive dissolution and disorganization of the extracellular matrix was seen around fibroblastic-like cells in late pregnancy. In contrast to the cervix (positive control), morphological and immunohistochemical analyses revealed that there was no characteristic cellular inflammatory response in the interpubic tissue. Staining for MMP-8 was observed in chondroid and fibroblastic-like cells of virgin and relaxed interpubic ligament, respectively. However, no granulocytes were seen during the extensive remodeling of the pubic joint in late pregnancy. These results indicate that constitutive stromal cells may have an important role in tissue relaxation during remodeling of the pubic symphysis in pregnancy. 相似文献
46.
The goal of this paper is twofold : at first, to present the stochastic timed Pétri nets model by emphasizing its ability to express the main characteristics of real time distributed systems (parallelism, synchronization by message exchange, time attributes and in particular time constraints) and to allow both qualitative and quantitative analysis (concept of randomized states graph); second, to show a modeling methodology based on this model that allows a rigorous modeling of theDqdb protocol (Qa access, bwb mechanism role,Pa access influence). A new contribution to theQa mechanism has been done (1). 相似文献
47.
We discuss the application of digital systems to the automatic control of dual-wave optical interferometers. We show that, if the mechanical-modulation technique is used for error-signal extraction, digital techniques can be used both for error-signal extraction and for control-signal generation. Therefore, apart from two front/end amplifiers that are necessary to match the dynamics of the detectors and actuators to the dynamics of the analog-to-digital converters and digital-to-analog converters, no other analog devices are required. In particular, the mechanical-modulation technique requires the synchronous demodulation of the photodiode output signal. Hence we need to implement a digital lock-in amplifier whose algorithm is described here. Finally, we describe one of the possible applications of this digital control procedure, such as the control of a classic Mach-Zehnder interferometer in air. 相似文献
48.
Depalo Nicoletta Iacobazzi Rosa Maria Valente Gianpiero Arduino Ilaria Villa Silvia Canepa Fabio Laquintana Valentino Fanizza Elisabetta Striccoli Marinella Cutrignelli Annalisa Lopedota Angela Porcelli Letizia Azzariti Amalia Franco Massimo Curri Maria Lucia Denora Nunzio 《Nano Research》2017,10(7):2431-2448
Currently,sorafenib is the only systemic therapy capable of increasing overall survival of hepatocellular carcinoma patients.Unfortunately,its side effects,particularly its overall toxicity,limit the therapeutic response that can be achieved.Superparamagnetic iron oxide nanoparticles (SPIONs) are very attractive for drug delivery because they can be targeted to specific sites in the body through application of a magnetic field,thus improving intratumoral accumulation and reducing adverse effects.Here,nanoformulations based on polyethylene glycol modified phospholipid micelles,loaded with both SPIONs and sorafenib,were successfully prepared and thoroughly investigated by complementary techniques.This nanovector system provided effective drug delivery,had an average hydrodynamic diameter of about 125 nm,had good stability in aqueous medium,and allowed controlled drug loading.Magnetic analysis allowed accurate determination of the amount of SPIONs embedded in each micelle.An in vitro system was designed to test whether the SPION micelles can be efficiently held using a magnetic field under typical flow conditions found in the human liver.Human hepatocellular carcinoma (HepG2) cells were selected as an in vitro system to evaluate tumor cell targeting efficacy of the superparamagnetic micelles loaded with sorafenib.These experiments demonstrated that this delivery platform is able to enhance sorafenib's antitumor effectiveness by magnetic targeting.The magnetic nanovectors described here represent promising candidates for targeting specific hepatic tumor sites,where selective release of sorafenib can improve its efficacy and safety profile. 相似文献
49.
50.