全文获取类型
收费全文 | 3299篇 |
免费 | 28篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 3328篇 |
出版年
2023年 | 9篇 |
2022年 | 27篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 25篇 |
2012年 | 14篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 25篇 |
2008年 | 21篇 |
2007年 | 31篇 |
2006年 | 21篇 |
2005年 | 15篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 114篇 |
1998年 | 925篇 |
1997年 | 526篇 |
1996年 | 360篇 |
1995年 | 179篇 |
1994年 | 154篇 |
1993年 | 187篇 |
1992年 | 15篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 33篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1983年 | 3篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 34篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 57篇 |
1976年 | 104篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有3328条查询结果,搜索用时 0 毫秒
101.
Haseeb MD. Irfanullah 《The International journal of environmental studies》2013,70(4):654-667
Armed conflict affects the biological diversity and biological research regime of a country. This paper takes a low-intensity armed conflict in the biologically and ethnically diverse Chittagong Hill Tracts (CHT) of Bangladesh, as an example, and assesses the response of biologists to this conflict. The study spans the last 50 years dividing it into three periods: pre-conflict (1961?1974), conflict (1975–1997) and post-conflict (1998–2011). Interactions with selected researchers and a literature survey showed that sporadic, intermittent biological research was conducted in this region even during the conflict. The number of research initiatives substantially increased and became more diverse over the last decade. Research opportunity has increased mainly because of improved security and accessibility. Nevertheless, despite the research capacity and a positive attitude among the researchers, some fundamental issues still limit long-term research in this area. The continuing volatile situation due to slow implementation of the 1997 Peace Accord and the tension between rebel factions and indigenous and settler communities in some areas continue to be serious concerns for studying and conserving the biodiversity of this region. Innovative research approaches and the full implementation of the peace agreement are vital to improving the situation for biological research in the CHT. The paper underlines the importance of a biologist’s self-motivation to respond to low-intensity armed conflicts. 相似文献
102.
Md Sazzadur Rahman MD Nahin Islam Shiblee Kumkum Ahmed Ajit Khosla Jun Ogawa Masaru Kawakami Hidemitsu Furukawa 《大分子材料与工程》2020,305(9)
In this work, 3D printable gel polymer electrolytes (GPEs) based on N,N‐dimethylacrylamide (DMAAm) and polyvinylidene fluoride (PVDF) in lithium chloride containing ethylene glycol solution are synthesized and their physicochemical properties are investigated. 3D printing is carried out with a customized stereolithography type 3D gel printer named “Soft and Wet Intelligent Matter‐Easy Realizer” and free forming GPE samples having variable shapes and sizes are obtained. Printed PVDF/PDMAAm‐based GPEs exhibit tunable mechanical properties and favorable thermal stability. Electrochemical proprieties of the printed GPEs are carried out via impedance spectroscopy in the temperature range of 25–90 °C by varying PVDF content. Ionic conductivity as high as 6.5 × 10?4 S cm?1 is achieved at room temperature for GPE containing low PVDF content (5 wt%) and conductivity of the GPEs is increased as temperature rises. 相似文献
103.
Novella Grassi 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(5):825-831
Extensive PIXE investigations have been performed at the LABEC accelerator laboratory in Florence on the painting “Ritratto Trivulzio” by Antonello da Messina, one of the great Italian masters of XV Century and a pioneer in modern oil painting.It is well known that a complete and unambiguous characterisation of materials in paintings is often difficult, owing to their complex structure. For the “Ritratto Trivulzio”, the combination of advanced variants of PIXE, such as differential and scanning-mode analysis, provided a relevant contribution to the characterisation of paint layers, in terms of composition and structure, in a totally non-invasive and non-destructive way.Single-spot mode PIXE with external proton beams of about half millimetre diameter was first used for a general characterisation of different areas of the painting. Differential PIXE performed in many spots led to reconstruct the sequence of paints employed by the artist and to estimate in some cases the local paint layer thickness.A second run carried out with the external scanning microbeam facility, using a 3 MeV proton beam of about 80 μm size, was then crucial to clarify some issues raised by the first analysis. In particular, elemental maps from selected areas helped to understand the way some colour shades had been obtained on the red mantle of the portrayed gentleman, using different pigments irregularly distributed on the surface. 相似文献
104.
Crespo JF Retzek M Foetisch K Sierra-Maestro E Cid-Sanchez AB Pascual CY Conti A Feliu A Rodriguez J Vieths S Scheurer S 《Molecular nutrition & food research》2006,50(3):282-290
Oranges are clinically relevant allergenic foods. To date, orange allergens have not been characterized in detail. The study is aimed at analyzing the sensitization profile in orange-sensitized subjects with and without clinical allergy, and to identify orange allergens. Fifty-six sensitized subjects with self-reported reactions to orange were grouped into reactors (anaphylaxis or multiple episodes of immediate reactions and/or positive challenge tests) and non-reactors (negative open food challenge tests). Allergens were characterized by IgE immunoblotting, N-terminal sequencing, IgE-inhibition assays, and mediator release assays were performed to determine the allergenic potency of orange profilin. Of 56 subjects, 23 were classified as orange allergic showing mainly an oral allergy syndrome. Of 23 subjects classified as orange allergic, 22 were sensitized to profilin, Cit s 2. In patients with mono-sensitization to profilin in vitro histamine releases up to 75% from basophils were induced using orange extract and purified plant profilins. Of the allergic patients 78% were sensitized to germin-like protein, Cit s 1. Both allergens showed retained IgE reactivity in heat-processed orange juice. Interestingly, subjects with and without clinical allergy showed a comparable sensitization profile. Profilin and germin-like proteins are major orange allergens. The potential clinical relevance of orange profilin was indicated by its strong capacity to release histamine from basophils. However, a predominant sensitization to both allergens in subjects without symptoms also indicates a high frequency of clinically insignificant sensitization. 相似文献
105.
Vallati Carlo Mingozzi Enzo Tanganelli Giacomo Buonaccorsi Novella Valdambrini Nicola Zonidis Nikolaos Martínez Belén Mamelli Alessandro Sommacampagna Davide Anggorojati Bayu Kyriazakos Sofoklis Prasad Neeli Nieto Francisco Javier Rodriguez Oliver Barreto 《Wireless Personal Communications》2016,87(3):1071-1091
Wireless Personal Communications - The integration of everyday objects into the Internet represents the foundation of the forthcoming Internet of Things (IoT). Smart objects will be the building... 相似文献
106.
Mobile ad hoc networking: imperatives and challenges 总被引:14,自引:0,他引:14
Mobile ad hoc networks (MANETs) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self-organize into arbitrary and temporary, “ad-hoc” network topologies, allowing people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking concept is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad hoc paradigm. Recently, the introduction of new technologies such as the Bluetooth, IEEE 802.11 and Hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent evolutions have been generating a renewed and growing interest in the research and development of MANET. This paper attempts to provide a comprehensive overview of this dynamic field. It first explains the important role that mobile ad hoc networks play in the evolution of future wireless technologies. Then, it reviews the latest research activities in these areas, including a summary of MANET’s characteristics, capabilities, applications, and design constraints. The paper concludes by presenting a set of challenges and problems requiring further research in the future. 相似文献
107.
Syed Adeel Ali Shah Ejaz Ahmed Muhammad Ahsan Qureshi Sadeeq Jan Rafidah MD Noor 《International Journal of Communication Systems》2019,32(13)
In safety‐critical scenarios, reliable reception of beacons transmitted by a subject vehicle is critical to avoid vehicle collision. According to the employed contention window sizes in IEEE 802.11p, beacons are transmitted with a small contention window size. As a result, multiple vehicles contend for the shared channel access by selecting the same back‐off slot. This is a perfect recipe for synchronous collisions wherein reliable beacon delivery cannot be guaranteed for any vehicle. We consider the problem of selecting the back‐off slots from the current contention window to provide reliable delivery of beacons transmitted by a subject vehicle to its neighbors. Given a safety scenario, we propose a Pseudo‐Random Number Generator (PRNG)‐inspired back‐off selection (PBS) technique. The proposed technique works on the hypothesis that synchronous collisions of beacons transmitted by a subject vehicle can be reduced if all its neighbors select different back‐off slots (ie, not the back‐off slot selected by the subject vehicle). The discrete‐event simulations demonstrate that PBS can increase the overall message reception from a subject vehicle, in comparison with the uniform random probability back‐off selection in IEEE 802.11p. 相似文献
108.
Novella Bartolini Tiziana Calamoneri Annalisa Massini Simone Silvestri 《Mobile Networks and Applications》2011,16(1):134-145
The use of mobile sensors is of great relevance to monitor critical areas where sensors cannot be deployed manually. The presence
of data collector sinks causes increased energy depletion in their proximity, due to the higher relay load under multi-hop
communication schemes (sink-hole phenomenon). We propose a new approach towards the solution of this problem by means of an
autonomous deployment algorithm that guarantees the adaptation of the sensor density to the sink proximity and enables their
selective activation. The proposed algorithm also permits a fault tolerant and self-healing deployment, and allows the realization
of an integrated solution for deployment, dynamic relocation and selective sensor activation. We formally prove the termination
of our algorithm. Performance comparisons between our proposal and previous approaches show how the former can efficiently
reach a deployment at the desired variable density with moderate energy consumption under a wide range of operative settings. 相似文献
109.
Morrone Isabella; Declercq Christelle; Novella Jean-Luc; Besche Chrystel 《Canadian Metallurgical Quarterly》2010,25(3):697
The inhibitory deficit hypothesis has often been cited as a possible explanation for cognitive changes related to age. The aim of this study was to develop a new procedure for evaluating effortful inhibition on the basis of the comprehension of metaphors. Our experiment was carried out on younger and older adults, in whom we also measured inhibitory capacity, working memory, and processing speed. The results show that older participants required a longer time and made more frequent errors in rejecting metaphors versus literally false statements. The interference effect was predicted by the psychometric tests designed to evaluate inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
In this paper we present and evaluate ContentPlace, a data dissemination system for opportunistic networks, i.e., mobile networks in which stable simultaneous multi-hop paths between communication endpoints cannot be provided. We consider a scenario in which users both produce and consume data objects. ContentPlace takes care of moving and replicating data objects in the network such that interested users receive them despite possible long disconnections, partitions, etc. Thanks to ContentPlace, data producers and consumers are completely decoupled, and might be never connected to the network at the same point in time. The key feature of ContentPlace is learning and exploiting information about the social behaviour of the users to drive the data dissemination process. This allows ContentPlace to be more efficient both in terms of data delivery and in terms of resource usage with respect to reference alternative solutions. The performance of ContentPlace is thoroughly investigated both through simulation and analytical models. 相似文献