全文获取类型
收费全文 | 7868篇 |
免费 | 703篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 90篇 |
综合类 | 2篇 |
化学工业 | 2021篇 |
金属工艺 | 187篇 |
机械仪表 | 222篇 |
建筑科学 | 301篇 |
矿业工程 | 21篇 |
能源动力 | 269篇 |
轻工业 | 1235篇 |
水利工程 | 59篇 |
石油天然气 | 51篇 |
无线电 | 665篇 |
一般工业技术 | 1707篇 |
冶金工业 | 448篇 |
原子能技术 | 45篇 |
自动化技术 | 1255篇 |
出版年
2024年 | 37篇 |
2023年 | 83篇 |
2022年 | 140篇 |
2021年 | 274篇 |
2020年 | 240篇 |
2019年 | 231篇 |
2018年 | 377篇 |
2017年 | 403篇 |
2016年 | 458篇 |
2015年 | 300篇 |
2014年 | 367篇 |
2013年 | 792篇 |
2012年 | 451篇 |
2011年 | 530篇 |
2010年 | 429篇 |
2009年 | 434篇 |
2008年 | 398篇 |
2007年 | 360篇 |
2006年 | 263篇 |
2005年 | 205篇 |
2004年 | 192篇 |
2003年 | 150篇 |
2002年 | 173篇 |
2001年 | 100篇 |
2000年 | 86篇 |
1999年 | 80篇 |
1998年 | 141篇 |
1997年 | 136篇 |
1996年 | 111篇 |
1995年 | 76篇 |
1994年 | 59篇 |
1993年 | 54篇 |
1992年 | 35篇 |
1991年 | 35篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 29篇 |
1987年 | 15篇 |
1985年 | 30篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1974年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有8578条查询结果,搜索用时 15 毫秒
61.
SIR-C data quality and calibration results 总被引:5,自引:0,他引:5
Freeman A. Alves M. Chapman B. Cruz J. Kim Y. Shaffer S. Sun J. Turner E. Sarabandi K. 《Geoscience and Remote Sensing, IEEE Transactions on》1995,33(4):848-857
The SIR-C/X-SAR imaging radar took its first flight on the Space Shuttle Endeavour in April 1994 and flew for a second time in October 1994. This multifrequency radar has fully polarimetric capability at L- and C-band, and a single polarization at X-band (X-SAR). The Endeavour missions were designated the Space Radar Laboratory-1 (SRL-1) and -2 (SRL-2). Calibration of polarimetric L- and C-band data for all the different modes SIR-C offers is an especially complicated problem. The solution involves extensive analysis of pre-flight test data to come up with a model of the system, analysis of in-flight test data to determine the antenna pattern and gains of the system during operation, and analysis of data from over fourteen calibration sites distributed around the SIR-C/X-SAR orbit track. The SRL missions were the first time a multifrequency polarimetric imaging radar employing a phased array antenna has been flown in space. Calibration of SIR-C data products involved some unique technical problems given the complexity of the radar system. In this paper, the approach adopted for calibration of SIR-C data is described and the calibration performance of the data products is presented 相似文献
62.
The effects of an elevated temperature and a 5 wt% silicon addition on the resultant microstructure and inherent phases of Stellite 6 were investigated by using room and high temperature optical microscopy, X-ray diffraction, scanning electron microscopy (SEM) and also bulk hardness and microhardness measurements. It has been observed that exposing Stellite 6 to heat treatments at 1000°C results in a characteristic textured structure and coarsening of interdendritic regions due to bulk diffusion. In addition, both dendritic and interdendritic hardness values increase due to texture formation and increased amounts of carbide and intermetallic phases, respectively. On the other hand, silicon addition to Stellite 6 causes the transformation of the original spongy dendritic microstructure in as-cast Stellite 6 to a eutectic dendritic and skeleton interdendritic structure. Also, when silicon added Stellite 6 was heat treated at 1000°C, particulates emanating from the interdendritic skeleton become irregularly dispersed in the dendritic region. In addition, similarly to Stellite 6; a high temperature heat treatment results in an increase in hardness values of silicon added Stellite 6 due to the presence of an Co2 Si intermetallic phase. 相似文献
63.
CM Lucas ED Franke MI Cachay A Tejada ME Cruz RD Kreutzer DC Barker SH McCann DM Watts 《Canadian Metallurgical Quarterly》1998,59(2):312-317
Asymmetric acetylcholinesterase (AChE) is anchored to the basal lamina (BL) of cholinergic synapses via its collagenic tail, yet the complement of matrix receptors involved in its attachment remains unknown. The development of a novel overlay technique has allowed us to identify two Torpedo BL components that bind asymmetric AChE: a polypeptide of approximately 140 kDa and a doublet of 195-215 kDa. These were found to stain metachromatically with Coomassie blue R-250, were solubilized by acetic acid, and were sensitive to collagenase treatment. Upon sequence analysis, the 140 kDa polypeptide yielded a characteristic collagenous motif. Another AChE-binding BL constituent, identified by overlay, corresponded to a heparan sulfate proteoglycan. Lastly, we established that this proteoglycan, but not the collagenous proteins, interacted with at least one heparin binding domain of the collagenic tail of AChE. Our results indicate that at least two BL receptors are likely to exist for asymmetric AChE in Torpedo electric organ. 相似文献
64.
65.
Alex H. Barbat Miguel Cervera Alex Hanganu Cruz Cirauqui Eugenio Oñate 《Nuclear Engineering and Design》1998,180(3):251-270
The evaluation of the failure pressure of the containment building of a large dry PWR-W three loops nuclear power plant, based on computer numerical simulation, is described in this paper. The proposed method considers fully three-dimensional finite element models in order to take into account the effect of the most significant structural characteristics (presence of three buttresses, penetrations, additional reinforcement around the penetrations, etc.), the lack of symmetry of the forces generated by the prestressing system, as well as the nonlinear behaviour of the materials and the sensitivity of the results to uncertainties associated with several parameters. The computational model is completely described, including the constitutive equations for the concrete, the reinforcing steel and prestressing tendons, the spatial discretization—isoparametric elements including the reinforcement are used. The structural models and the analyses performed for their calibration are also described. The influence on the failure pressure of incorporating the foundation slab in the structural model, and the influence of the thermal effects, are discussed. One of the conclusions of the numerical study is that the failure process can be appropriately simulated by means of a structural model which does not include either the foundation slab or the thermal effects. Finally, results of a probabilistic simulation of the failure pressure are given. 相似文献
66.
67.
Mark Olokotum Marc Troussellier Arthur Escalas Sahima Hamlaoui William Okello Ronald Semyalo Jean-François Humbert Cécile Bernard 《Journal of Great Lakes research》2021,47(4):985-996
Eutrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytoplankton biomass, richness, diversity and dissimilarity, and related the dynamics of the dominant species to the limnological and climatic conditions. The results confirmed that Napoleon Gulf and Murchison Bay showed large differences in eutrophication status, with lower nutrient concentrations in Napoleon Gulf than in Murchison Bay, where a strong gradient was observed from inshore to offshore areas. These nutrient dynamics resulted in a 4 to 10 fold higher chlorophyll-a in Murchison Bay than in Napoleon Gulf. From the embayments, 135 phytoplankton taxa were recorded with no significant differences in alpha diversity. However, high dissimilarity in community structure was observed in beta diversity, mostly due to a turnover among the dominant toxigenic species. Thus, from a similar species pool, there was a shift in the dominant toxigenic cyanobacteria from Microcystis flos-aquae and M. aeruginosa in Murchison Bay, Dolichospermum circinale and Planktolyngbya circumcreta in Napoleon Gulf to D. circinale in the offshore stations. These cyanobacteria are toxigenic taxa with known health hazards. Using partial least square models, we showed that both climatic variables (e.g. wind, solar radiation) and levels of inorganic dissolved nutrients (e.g. SRP, NO3–, and NH4+) are the main drivers of differences and dominance in cyanobacteria communities in northern Lake Victoria. 相似文献
68.
Messing Karen Lefrançois Mélanie Saint-Charles Johanne 《Computer Supported Cooperative Work (CSCW)》2021,30(2):215-249
Computer Supported Cooperative Work (CSCW) - Work activity ergonomics (sometimes called francophone ergonomics) draws heavily on observation in order to support transformation of work to arrive at... 相似文献
69.
L. M. da Cruz Simões 《Structural and Multidisciplinary Optimization》1992,5(1-2):76-83
Virtually all structural optimization based on system reliability was conducted considering continuous design variables. The solution of the reliability-based design problem is obtained by solving alternatively a reliability assessment problem and an optimal sizing program until the best reliability-based design occurs. The reliability assessment problem is formulated as a linearly constrained concave quadratic program. By introducing the concept of segmental members, the discrete optimum design is achieved based upon linear programming. Examples are solved by employing the proposed computational technique.Presented at NATO ASI Optimization of Large Structural Systems, Berchtesgaden, Germany, Sept. 23 – Oct. 4, 1991 相似文献
70.
Luis O. Soto-Rojas Mar Pacheco-Herrero Paola A. Martínez-Gmez B. Berenice Campa-Crdoba Ricardo Aptiga-Prez Marcos M. Villegas-Rojas Charles R. Harrington Fidel de la Cruz Linda Garcs-Ramírez Jos Luna-Muoz 《International journal of molecular sciences》2021,22(4)
Alzheimer’s disease (AD) is the most common neurodegenerative disease worldwide. Histopathologically, AD presents with two hallmarks: neurofibrillary tangles (NFTs), and aggregates of amyloid β peptide (Aβ) both in the brain parenchyma as neuritic plaques, and around blood vessels as cerebral amyloid angiopathy (CAA). According to the vascular hypothesis of AD, vascular risk factors can result in dysregulation of the neurovascular unit (NVU) and hypoxia. Hypoxia may reduce Aβ clearance from the brain and increase its production, leading to both parenchymal and vascular accumulation of Aβ. An increase in Aβ amplifies neuronal dysfunction, NFT formation, and accelerates neurodegeneration, resulting in dementia. In recent decades, therapeutic approaches have attempted to decrease the levels of abnormal Aβ or tau levels in the AD brain. However, several of these approaches have either been associated with an inappropriate immune response triggering inflammation, or have failed to improve cognition. Here, we review the pathogenesis and potential therapeutic targets associated with dysfunction of the NVU in AD. 相似文献