全文获取类型
收费全文 | 834篇 |
免费 | 49篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 147篇 |
金属工艺 | 19篇 |
机械仪表 | 24篇 |
建筑科学 | 30篇 |
矿业工程 | 1篇 |
能源动力 | 23篇 |
轻工业 | 156篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 44篇 |
一般工业技术 | 156篇 |
冶金工业 | 52篇 |
原子能技术 | 12篇 |
自动化技术 | 208篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 23篇 |
2021年 | 28篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 26篇 |
2016年 | 28篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 63篇 |
2012年 | 69篇 |
2011年 | 57篇 |
2010年 | 56篇 |
2009年 | 61篇 |
2008年 | 39篇 |
2007年 | 33篇 |
2006年 | 31篇 |
2005年 | 23篇 |
2004年 | 26篇 |
2003年 | 22篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 3篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有884条查询结果,搜索用时 15 毫秒
31.
Luciano Cardellicchio 《Building Research & Information》2013,41(2):160-179
ABSTRACTThe Jubilee Church in the south-eastern outskirts of Rome is one of the first buildings constructed with super white reinforced concrete with self-cleaning photocatalytic cement. However, 16 years after the opening of the building, the self-cleaning and colour-preserving properties arising from the titania particles (TiO2) within the concrete mix are not meeting the design requirements and the concrete is showing premature evidence of decay. While the form of the decay is affecting the appearance of the building and not its structural soundness, the ageing pattern of the building's components is resulting in a high maintenance cost, one not easily affordable within the ordinary budget supported by a small parish. This study comprises the first comprehensive step in understanding the causes of the accelerated ageing pattern of the concrete, highlighting methods to improve the long-term durability of the concrete and therefore reduce the cost of its maintenance. Moreover, this research offered the opportunity to test the durability and the effectiveness of the TiO2 in the real conditions on an actual building featuring non-standard geometries. The findings highlight how the ageing pattern directly connects with the geometry of the building and inadequate consideration of the local weathering at the design stage. 相似文献
32.
The mode-matching analysis of rectangular waveguide networks requires a complex segmentation of the structure into simple elements. The way these elements are connected has a strong influence on the computing performance of the code. Moreover, for complex structures the size of the coefficient matrix of the main system can easily reach unaffordable dimensions, so that the use of an efficient solving strategy becomes indispensable. A new approach to the optimum automatic choice of the interconnections is presented, leading to a highly stable and outperforming method of analysis. A Butler 4 × 4 matrix, with six branch guide couplers and four phase shifters, containing 336 uniform waveguide sections and bifurcations, has been studied, and the presented strategy has allowed a performance increase up to two orders of magnitude. © 1996 John Wiley & Sons, Inc. 相似文献
33.
Luciano C. Ramires Gabriel Silva Santos Rafaela Pereira Ramires Lucas Furtado da Fonseca Madhan Jeyaraman Sathish Muthu Anna Vitria Lana Gabriel Azzini Curtis Scott Smith Jos Fbio Lana 《International journal of molecular sciences》2022,23(3)
Some say that all diseases begin in the gut. Interestingly, this concept is actually quite old, since it is attributed to the Ancient Greek physician Hippocrates, who proposed the hypothesis nearly 2500 years ago. The continuous breakthroughs in modern medicine have transformed our classic understanding of the gastrointestinal tract (GIT) and human health. Although the gut microbiota (GMB) has proven to be a core component of human health under standard metabolic conditions, there is now also a strong link connecting the composition and function of the GMB to the development of numerous diseases, especially the ones of musculoskeletal nature. The symbiotic microbes that reside in the gastrointestinal tract are very sensitive to biochemical stimuli and may respond in many different ways depending on the nature of these biological signals. Certain variables such as nutrition and physical modulation can either enhance or disrupt the equilibrium between the various species of gut microbes. In fact, fat-rich diets can cause dysbiosis, which decreases the number of protective bacteria and compromises the integrity of the epithelial barrier in the GIT. Overgrowth of pathogenic microbes then release higher quantities of toxic metabolites into the circulatory system, especially the pro-inflammatory cytokines detected in osteoarthritis (OA), thereby promoting inflammation and the initiation of many disease processes throughout the body. Although many studies link OA with GMB perturbations, further research is still needed. 相似文献
34.
Andrea Brenna Silvia Beretta Riccardo Uglietti Luciano Lazzari MariaPia Pedeferri Marco Ormellese 《腐蚀工程科学与技术》2017,52(4):253-260
The criterion used to verify the cathodic protection condition of a structure is based on structure-to-electrolyte potential measurement, which can include an ohmic drop contribution. Among the available techniques, the use of potential probes with internal reference electrode and of corrosion coupons with a so-called soil-access tube represents the most appropriate way to measure the IR-free potential, eliminating the ohmic drop contribution. An alternative is represented by on-off technique if equalising, galvanic or stray currents are not present. Laboratory tests have been carried out in soil-simulating solution on cathodically protected carbon steel in order to evaluate the effectiveness of off-potential for the assessment of cathodic protection. Instant-off potential is not reliable in overprotection condition; moreover, the accuracy of the measurement is strongly influenced by the presence of external current as galvanic or equalising currents. The effect of low-pass filter in the data acquisition system on the potential reading is discussed. 相似文献
35.
Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir 总被引:8,自引:0,他引:8
Vanessa Becker Luciano Caputo Rafael Marcé Joan Armengol Vera L.M. Huszar 《Water research》2010,44(11):3345-5109
The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a one-year cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L−1) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group Lo). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir. 相似文献
36.
Wireless mesh networks are an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building self-organized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a wireless mesh network towards a specific node (which acts as a gateway), within a given deadline. Scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio. Firstly, we present a theoretical model which allows us to formulate the task of deriving joint routing and scheduling as an integer linear programming problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms. To the best of our knowledge, these algorithms have never been used before for working out these kinds of optimization problems in a wireless mesh environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that genetic algorithms would seem to be quite promising for solving more complex models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels. 相似文献
37.
Guillermo Araya Luciano Castillo 《International Journal of Heat and Mass Transfer》2012,55(15-16):4003-4019
A technique, based on the Lund et al. (1998) [1] approach, is introduced in order to numerically prescribe time-dependent turbulent inflow conditions in spatially-developing thermal boundary layers. A major difference with Lund’s approach is that the new multi-scale approach considers different scaling laws for the inner and outer parts of the boundary layer. Direct numerical simulations (DNS) are performed for incompressible zero (ZPG) and adverse (APG) pressure gradient flows. To the best of our knowledge, the present DNS in ZPG flows at a momentum thickness Reynolds numbers (Reθ) of 2300 represents the evolving thermal boundary layer simulations at the highest Reθ in the turbulence community. The temperature is treated as a passive scalar with isothermal walls as a boundary condition and a molecular Prandtl number of 0.71. The predicted Stanton number shows fairly good agreement with empirical correlations, and experimental and numerical data from the literature. Moreover, the influences of the Reynolds number and the APG strength on thermal parameters are also examined. Furthermore, the budget of the temperature variance shows a significant increase of production, turbulent diffusion, and dissipation in the buffer layer at higher Reynolds numbers. The main effects of adverse pressure gradients on the temperature field are manifested by a decreasing trend of thermal fluctuations but an increasing trend of the wall-normal turbulent heat fluxes when normalized by wall units as the APG strength is augmented. 相似文献
38.
Luciano Senff Pedro A. Barbetta Wellington L. Repette Dachamir Hotza Helena Paiva Victor M. Ferreira João A. Labrincha 《Construction and Building Materials》2009,23(10):3107-3111
This paper reports the effects of distinct contents of silica fume (SF), superplasticizer (SP) and water/binder ratio (W/B) in mortars. Samples with SF (0–10 wt%), SP (1.0–1.2 wt%) and W/B ratio (0.30–0.35) were produced. Flow table test and rheometry were used as parameters to formulate mortars by means of a factorial design experiment. Setting time, water absorption, apparent porosity and compressive strength of mortars at 28 days were also determined. Mortar formulations with lower fluidity are restricting when a rheometer was used. For higher torques, adjustments with the regressive equation of the Bingham model are less accurate, since the flow behavior is less constant. On the other hand, mortars with higher fluidity it is limited by spread test. The spread value on flow table test is more related to yield stress than to plastic viscosity. The design experiments identified the main factors (SF, SP and W/B) and their interactions for all properties on the fresh and hardened state, showing that experimental design with multiple regression equations is an appropriate tool to be applied in this case. Water content was the controlling parameter for practically all properties studied. 相似文献
39.
Most automotive companies outsource the design, manufacturing and assembly of some complete cars to independent suppliers or full service vehicle companies (FSVs). FSVs represent a relatively unexplored form of outsourcing which combines joint efforts in developing a modular product with the externalisation of specific niche manufacturing processes. On the basis of comparative cases and of qualitative information collected within three FSVs and three OEMs, this study aims to investigate the associated advantages and risks for FSVs, commonalities/differences from the practices of outsourcing to component/module specialists that can be found in other industries and why and for what kind of products FSVs can be appropriate in automotive supply networks. The study contributes to the debate on outsourcing in the automotive industry by providing an original interpretation on why FSVs have recently seen a shakeout with some growing whilst others have faltered. 相似文献
40.