全文获取类型
收费全文 | 5114篇 |
免费 | 375篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 39篇 |
综合类 | 2篇 |
化学工业 | 1064篇 |
金属工艺 | 97篇 |
机械仪表 | 116篇 |
建筑科学 | 249篇 |
矿业工程 | 10篇 |
能源动力 | 160篇 |
轻工业 | 409篇 |
水利工程 | 68篇 |
石油天然气 | 17篇 |
无线电 | 407篇 |
一般工业技术 | 1252篇 |
冶金工业 | 721篇 |
原子能技术 | 9篇 |
自动化技术 | 888篇 |
出版年
2024年 | 9篇 |
2023年 | 58篇 |
2022年 | 97篇 |
2021年 | 171篇 |
2020年 | 144篇 |
2019年 | 147篇 |
2018年 | 170篇 |
2017年 | 160篇 |
2016年 | 199篇 |
2015年 | 156篇 |
2014年 | 252篇 |
2013年 | 336篇 |
2012年 | 396篇 |
2011年 | 490篇 |
2010年 | 310篇 |
2009年 | 260篇 |
2008年 | 343篇 |
2007年 | 301篇 |
2006年 | 255篇 |
2005年 | 209篇 |
2004年 | 165篇 |
2003年 | 133篇 |
2002年 | 144篇 |
2001年 | 87篇 |
2000年 | 64篇 |
1999年 | 42篇 |
1998年 | 46篇 |
1997年 | 42篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 13篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有5508条查询结果,搜索用时 0 毫秒
51.
Kensey Daly Shahryar K. Ahmad Matthew Bonnema Claire Beveridge Faisal Hossain Bart Nijssen Gordon Holtgrieve 《Lakes & Reservoirs: Research and Management》2020,25(2):133-142
Tonle Sap Lake in Cambodia is arguably the world's most productive freshwater ecosystems, as well as the dominant source of animal protein for the country. The rapid rise of hydropower schemes, deforestation, land development and climate change impacts in the Mekong River Basin, however, now represent serious concerns in regard to Tonle Sap Lake's ecological health and its role in future food security. To this end, the present study identifies significant recent warming of lake temperature and discusses how each of these anthropogenic perturbations in Tonle Sap's floodplain and the Mekong River Basin may be influencing this trend. The lake's dry season monthly average temperature increased by 0.03°C/year between 1988 and 2018, being largely in synchrony with warming trends of the local air temperature and upstream rivers. The impacts of deforestation and agriculture development in the lake's floodplain also exhibited a high correlation with an increased number of warm days observed in the lake, particularly in its southeast region (agriculture R2 = .61; deforestation R2 = .39). A total of 79 dams, resulting in 72 km3 of volumetric water capacity, were constructed between 2003 and 2018 in the Mekong River Basin. This dam development coincided with a decreasing trend in the number of dry season warm days per year in the lower Mekong River, while Tonle Sap Lake's number of dry season warm days continued to increase during this same period. The present study revealed that Tonle Sap Lake's temperature trends are highly influenced by temperature trends in the local climate, agriculture development and deforestation of the lake's watershed. Although there were no noticeable impacts observed from upstream dam development in the Mekong River Basin, local‐to‐regional agricultural and land management of the lake's watershed appear to be effective strategies for maintaining a stable thermal regime in the lake in order to facilitate maximum ecosystem health. 相似文献
52.
Mollie B. Schear Arianna Neal Jadah S. Clarke Andrew P. Saab Carl B. Giller Riccardo Casalini Matthew Laskoski 《应用聚合物科学杂志》2021,138(12):50053
The preparation of highly aromatic elastomers from a bisphenol A-based divinyl-terminated resin and polymerization with various aromatic silane containing compounds utilizing a room temperature hydrosilylation reaction is demonstrated. The polymers exhibit high thermal and oxidative stability with 5% weight losses around 430 and 350°C and char yields ranging from 35% to 40%. The thermosets maintained their elastomeric properties with good hardness and mechanical properties as measured by elongation measurements. The toughness of the thermosets was not improved with the inclusion of aromatic moieties but the hardness did appear to increase with the addition of more aromatic groups. 相似文献
53.
Daniel S. Camarda Matthew J. Lampe Alan J. Lesser Philippe Desbois Klaus Stoll Claus Gabriel Rupert Konradi 《应用聚合物科学杂志》2021,138(41):51203
The creation of graft copolymers by selectively grafting a second polymer to the amorphous fraction of a semi-crystalline polymer in supercritical CO2 is demonstrated herein. The graft copolymer is synthesized by free radical polymerization of a vinyl monomer within the semi-crystalline polymer below its melt temperature. Such conditions afford selective grafting on the amorphous regions (block “B”) while leaving the crystalline domains (block “A”) unmodified. Accordingly, unique A-B, A-B-A, A-B-A-B-A, and so forth. block structures are formed. In this work, styrene is polymerized within polyamide 6, polyethylene terephthalate, and isotactic polypropylene. Purification of these material is performed to remove the un-grafted homopolymer, allowing for determination of the graft yield, the portion of polymer which covalently bonds to the semi-crystalline matrix. Grafting yields achieved in polyamide 6, polyethylene terephthalate, and isotactic polypropylene were 98%, 59%, and 15%, respectively. Property enhancements were observed upon further characterization of polystyrene-polyamide 6 copolymers, including high glass transition temperatures, the ability to be remelted, and tunable grafting molecular weight. Additionally, hydrophobicity is controlled by varying polystyrene composition. The remarkable range of accessed properties demonstrates this as a potential route to upcycling plastics. 相似文献
54.
Michael P. Balogh Camille Y. Jones J.F. Herbst Louis G. Hector Jr. Matthew Kundrat 《Journal of Alloys and Compounds》2006,420(1-2):326-336
Half-Heusler compounds of Sn-doped TiCoSb “TiCoSnxSb1−x (x = 0.0, 0.01, and 0.05)” were prepared and their thermoelectric properties were measured above room temperature. From the EDX analysis, all the samples have three phases: the TiCoSnxSb1−x, Co-rich, and Ti-rich phases. The values of the thermoelectric power increase with Sn doping, and a positive thermoelectric power is obtained in the sample of TiCoSn0.05Sb0.95. The thermal conductivity decreases both with increasing temperature and with Sn content. The maximum value of ZT for p-type material is 0.030 at 988 K in the sample of TiCoSn0.05Sb0.95. 相似文献
55.
Chloride rich reinforced concrete prisms were coupled to chloride-free prisms and exposed to diurnal and seasonal temperature cycles typical of those found in the UK. Acoustic emissions (AE) and galvanic currents were continuously monitored and correlated with ambient temperature. AE and galvanic currents were found to emulate the evolution of temperature in the diurnal cycles, although no specific relationship between AE and galvanic current could be obtained. The influence of seasonal variations in galvanic current had no obvious influence on AE Energy per second over the range of corrosion rates studied. The findings suggest that AE is more sensitive to short term (diurnal) changes in corrosion rates than the longer (seasonal) effects. It was hypothesised that this is due to transitory changes in the internal microclimate of the concrete. 相似文献
56.
The study of numerical abilities, and how they are acquired, is being used to explore the continuity between ontogenesis and environmental learning. One technique that proves useful in this exploration is the artificial simulation of numerical abilities with neural networks, using different learning paradigms to explore development. A neural network simulation of subitization, sometimes referred to as visual enumeration, and of counting, a recurrent operation, has been developed using the so-called multi-net architecture. Our numerical ability simulations use two or more neural networks combining supervised and unsupervised learning techniques to model subitization and counting. Subitization has been simulated using networks employing unsupervised self-organizing learning, the results of which agree with infant subitization experiments and are comparable with supervised neural network simulations of subitization reported in the literature. Counting has been simulated using a multi-net system of supervised static and recurrent backpropagation networks that learn their individual tasks within an unsupervised, competitive framework. The developmental profile of the counting simulation shows similarities to that of children learning to count and demonstrates how neural networks can learn how to be combined together in a process modelling development. 相似文献
57.
This paper reports the development of a novel ultrasonic inspection technique that detects radial fatigue cracks on the far side of thin airframe stiffener ‘weep’ holes. These cracks are located on the upper part of the weep hole (12 o'clock position), away from the lower skin of the wing. Cracks in this position are not readily detectable by conventional ultrasonic inspection techniques, particularly for short cracks. A special technique using circumferential creeping waves was adapted to inspect for these cracks. The conventional creeping wave technique experiences a strong specular reflection from the near surface of the hole that masks the creeping wave signal that arrives later in time. In order to overcome this difficulty, a split-aperture (two-element) transducer was used that resulted in the specular and creeping wave echoes being approximately equal in magnitude. The two separate transducers allowed us to alternate between pulse-echo and pitch-catch modes of operation with a resulting improvement in detection sensitivity. In the case of 0.25-inch-diameter weep holes, optimum sensitivity was calculated to be around 5 MHz. The detection threshold was found to be approximately 0.003 inches and the signal saturated at crack lengths in excess of 0.020 inches. The original paint and surface finish had no substantial adverse effects on the technique's sensitivity. Similarly, changing the weep hole diameter or chamfer conditions did not significantly affect the technique's performance. These results were obtained using specimens with both machined notches and real fatigue cracks. 相似文献
58.
59.
60.