全文获取类型
收费全文 | 1453篇 |
免费 | 33篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 198篇 |
金属工艺 | 17篇 |
机械仪表 | 16篇 |
建筑科学 | 46篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 102篇 |
水利工程 | 9篇 |
石油天然气 | 5篇 |
无线电 | 135篇 |
一般工业技术 | 222篇 |
冶金工业 | 594篇 |
原子能技术 | 18篇 |
自动化技术 | 97篇 |
出版年
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 21篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 29篇 |
2013年 | 49篇 |
2012年 | 33篇 |
2011年 | 40篇 |
2010年 | 26篇 |
2009年 | 33篇 |
2008年 | 34篇 |
2007年 | 43篇 |
2006年 | 24篇 |
2005年 | 34篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 34篇 |
2001年 | 32篇 |
2000年 | 25篇 |
1999年 | 34篇 |
1998年 | 136篇 |
1997年 | 114篇 |
1996年 | 83篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 43篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 25篇 |
1989年 | 25篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 44篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 10篇 |
1968年 | 7篇 |
排序方式: 共有1486条查询结果,搜索用时 15 毫秒
41.
Water Resource Models in the Mekong Basin: A Review 总被引:6,自引:1,他引:5
Development of the water resources of the Mekong Basin is the subject of intense debate both within the Mekong region and
internationally. Water resources modelling is playing an increasingly important role in the debate, with significant effort
in building integrated modelling platforms to describe the hydrological, ecological, social and economic impacts of water
resource development. In the hydrological domain, a comprehensive set of models has been effective in building understanding
of the system, and in identifying and describing the issues and trade-offs involved in basin-scale water planning. In the
ecological and social domains, quantitative modelling has not progressed very far; geo-spatial analysis and qualitative frameworks
remain the most commonly used tools. Economic models have been used to assess the costs and benefits of water resources development
and to describe the trade-offs between different sectors and users. These analyses are likely to play an important role in
the policy and planning debate, but are hampered by uncertainties in valuation of ecosystem services. Future efforts should
focus on optimising the use of existing model platforms for the Mekong, including structured comparison of multiple hydrological
models to quantify errors and identify an optimum set of modelling tools for different applications. A comprehensive research
effort is needed to incorporate groundwater into hydrological models for regional planning. Options for social impact assessment
should be reassessed before major investments are made in complex modelling platforms, and participatory social survey methods
evaluated as part of an integrated assessment framework. 相似文献
42.
D. C. Johnston 《Journal of Low Temperature Physics》1976,25(1-2):145-175
LiTi
2
O
4
is one end member of the homogeneity range of the spinel phase Li
1+x
Ti
2–x
O
4
(0x1/3) and is superconducting at temperatures up to 13.7 K. Various measurements were carried out in order to characterize the superconducting and normal state properties of LiTi
2
O
4
and of other compositions within the homogeneity range of the spinel phase. These measurements establish LiTi
2
O
4
as ad-band superconductor and show thatT
c
decreases to <1.5 K forx0.1. This disappearance of superconductivity with increasingx was found to be correlated with anomalous changes in the lattice parameter with composition, and, from electrical resistivity measurements, is tentatively attributed to the occurrence of a composition-induced metal-semiconductor transition atx0.1. The metallic character of LiTi
2
O
4
and the composition dependence of the observed electrical properties are shown to follow from crystallographic considerations.Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under AFOSR Contract Number AFOSR/F-44620-C-0017. 相似文献
43.
C. Hassel K. Blaum T. Day Goodacre H. Dorrer Ch. E. Düllmann K. Eberhardt S. Eliseev C. Enss P. Filianin A. Fäßler A. Fleischmann L. Gastaldo M. Goncharov D. Hengstler J. Jochum K. Johnston M. Keller S. Kempf T. Kieck U. Köster M. Krantz B. Marsh C. Mokry Yu. N. Novikov P. C. O. Ranitzsch S. Rothe A. Rischka J. Runke A. Saenz F. Schneider S. Scholl R. X. Schüssler F. Simkovic T. Stora P. Thörle-Pospiech A. Türler M. Veinhard M. Wegner K. Wendt K. Zuber 《Journal of Low Temperature Physics》2016,184(3-4):910-921
44.
James D. Johnston Ashlin E. Cowger Robert J. Graul Ryan Nash Josie A. Tueller Nathan R. Hendrickson Daniel R. Robinson John D. Beard K. Scott Weber 《Indoor air》2019,29(6):1005-1017
Recent work suggests that evaporative coolers increase the level and diversity of bioaerosols, but this association remains understudied in low‐income homes. We conducted a cross‐sectional study of metropolitan, low‐income homes in Utah with evaporative coolers (n = 20) and central air conditioners (n = 28). Dust samples (N = 147) were collected from four locations in each home and analyzed for dust‐mite allergens Der p1 and Der f1, endotoxins, and β‐(1 → 3)‐d ‐glucans. In all sample locations combined, Der p1 or Der f1 was significantly higher in evaporative cooler versus central air conditioning homes (OR = 2.29, 95% CI = 1.05‐4.98). Endotoxin concentration was significantly higher in evaporative cooler versus central air conditioning homes in furniture (geometric mean (GM) = 8.05 vs 2.85 EU/mg, P < .01) and all samples combined (GM = 3.60 vs 1.29 EU/mg, P = .03). β‐(1 → 3)‐d ‐glucan concentration and surface loads were significantly higher in evaporative cooler versus central air conditioning homes in all four sample locations and all samples combined (P < .01). Our study suggests that low‐income, evaporative cooled homes have higher levels of immunologically important bioaerosols than central air‐conditioned homes in dry climates, warranting studies on health implications and other exposed populations. 相似文献
45.
Catrin O. Plumpton Ludmila I. Kuncheva Nikolaas N. Oosterhof Stephen J. Johnston 《Pattern recognition》2012,45(6):2101-2108
Functional magnetic resonance imaging (fMRI) provides a spatially accurate measure of brain activity. Real-time classification allows the use of fMRI in neurofeedback experiments. With limited labelled data available, a fixed pre-trained classifier may be inaccurate. We propose that streaming fMRI data may be classified using a classifier ensemble which is updated through naive labelling. Naive labelling is a protocol where in the absence of ground truth, updates are carried out using the label assigned by the classifier. We perform experiments on three fMRI datasets to demonstrate that naive labelling is able to improve upon a pre-trained initial classifier. 相似文献
46.
Background
Omnivorous diets are high in arachidonic acid (AA) compared to vegetarian diets. Research shows that high intakes of AA promote changes in brain that can disturb mood. Omnivores who eat fish regularly increase their intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), fats that oppose the negative effects of AA in vivo. In a recent cross-sectional study, omnivores reported significantly worse mood than vegetarians despite higher intakes of EPA and DHA. This study investigated the impact of restricting meat, fish, and poultry on mood. 相似文献47.
G. Santhosh G. P. Nayaka Johnston Aranha Siddaramaiah 《Transactions of the Indian Institute of Metals》2017,70(3):549-555
Polycarbonate (PC) nanocomposites were fabricated by solution intercalation method with halloysite nanotubes (HNTs) as reinforcement. The effects of HNT content on the structural and dielectric properties were investigated. The properties of the fabricated films were probed with the intention to establish the consequence of nano-fillers on electrical characteristics/behaviours with PC. The incorporation of HNT generates notable performance enhancements through reinforcement effect. The electrical conductivity of polycarbonate got better when more than 4 wt% HNT is added. Interestingly, the integration of HNT significantly increases the dielectric permittivity of composite films with low dielectric loss which makes the nanocomposites attractive in practical applications such as electrical devices, electrical packaging and capacitors. Furthermore, the structural aspects were elucidated by X-Ray diffraction studies, Fourier transform infrared spectroscopy and dispersion of nanofillers in PC matrix were evaluated by scanning electron microscopy. 相似文献
48.
One‐Pot Synthesis of Dealloyed AuNi Nanodendrite as a Bifunctional Electrocatalyst for Oxygen Reduction and Borohydride Oxidation Reaction
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jiali Wang Fuyi Chen Yachao Jin Yimin Lei Roy L. Johnston 《Advanced functional materials》2017,27(23)
A novel one‐pot approach for synthesizing the dealloyed nanomaterials at room temperature is introduced for the first time. In such a synthetic strategy, applying modulated potentials effectively simplifies the traditional dealloying route, which usually requires additional corrosion process to dissolve nonprecious metals. The dealloyed AuNi nanodendrites (AuNi NDs) with tunable composition and uniformly elemental distribution are well developed by the one‐pot strategy. Impressively, the as‐synthesized AuNi NDs exhibit a higher electrochemically active area and definite improvements in electrocatalytic activity for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) compared to the commercial Pt/C. In particular, the AuNi NDs are 81 mV more positive in half‐wave potential and about 3.1 times higher in specific activity (at 0.85 V) for the ORR than Pt/C, together with excellent stability and methanol tolerance. The superior BOR activity is highly promising compared to the previously reported catalysts. The unique nanodendritic structure with Au‐rich surface and bimetallic electronic effect is the main factor to greatly enhance the bifunctional catalytic performance for the AuNi NDs. Furthermore, such a newly developed facile method is of great significance because it is one of the first examples to effectively engineer dealloyed bimetallic nanostructures via the practical and low‐cost route for electrocatalytic applications. 相似文献
49.
E-tailers normally have more accurate information regarding their products and services than consumers due to the nature of online transactions. To reduce consumers’ concerns of hidden information, e-tailers can use lenient return policies to attempt to signal high product and service quality. This research proposes a model to investigate the signaling effect of two components of return policy, return window—short return window vs. long return window and return depth—full refund vs. partial refund, on product quality and service quality. Data was collected using an online survey and analyzed using structural equation modeling. The results show that both a long return window and a full refund signal high service quality, which then positively affects purchase intention. When it comes to product quality, return window does not have a signaling effect, while the signaling effect of return depth is moderated by service quality. 相似文献