全文获取类型
收费全文 | 5072篇 |
免费 | 217篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 60篇 |
综合类 | 6篇 |
化学工业 | 993篇 |
金属工艺 | 84篇 |
机械仪表 | 84篇 |
建筑科学 | 241篇 |
矿业工程 | 26篇 |
能源动力 | 154篇 |
轻工业 | 416篇 |
水利工程 | 34篇 |
石油天然气 | 12篇 |
无线电 | 503篇 |
一般工业技术 | 915篇 |
冶金工业 | 920篇 |
原子能技术 | 50篇 |
自动化技术 | 800篇 |
出版年
2023年 | 29篇 |
2022年 | 24篇 |
2021年 | 105篇 |
2020年 | 72篇 |
2019年 | 76篇 |
2018年 | 85篇 |
2017年 | 81篇 |
2016年 | 104篇 |
2015年 | 95篇 |
2014年 | 139篇 |
2013年 | 309篇 |
2012年 | 187篇 |
2011年 | 290篇 |
2010年 | 235篇 |
2009年 | 224篇 |
2008年 | 224篇 |
2007年 | 199篇 |
2006年 | 186篇 |
2005年 | 181篇 |
2004年 | 162篇 |
2003年 | 145篇 |
2002年 | 132篇 |
2001年 | 74篇 |
2000年 | 80篇 |
1999年 | 96篇 |
1998年 | 149篇 |
1997年 | 96篇 |
1996年 | 98篇 |
1995年 | 73篇 |
1994年 | 86篇 |
1993年 | 92篇 |
1992年 | 71篇 |
1991年 | 63篇 |
1990年 | 48篇 |
1989年 | 64篇 |
1988年 | 58篇 |
1987年 | 47篇 |
1986年 | 56篇 |
1985年 | 59篇 |
1984年 | 59篇 |
1983年 | 39篇 |
1982年 | 44篇 |
1981年 | 51篇 |
1980年 | 38篇 |
1979年 | 41篇 |
1978年 | 41篇 |
1977年 | 48篇 |
1976年 | 61篇 |
1975年 | 27篇 |
1974年 | 29篇 |
排序方式: 共有5298条查询结果,搜索用时 234 毫秒
1.
2.
Patricia Seoane-Collazo Amparo Romero-Pic Eva Rial-Pensado Laura Liares-Pose nxela Estvez-Salguero Johan Fern Rubn Nogueiras Carlos Diguez Miguel Lpez 《International journal of molecular sciences》2021,22(4)
Several studies have reported that nicotine, the main bioactive component of tobacco, exerts a marked negative energy balance. Apart from its anorectic action, nicotine also modulates energy expenditure, by regulating brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. These effects are mainly controlled at the central level by modulation of hypothalamic neuropeptide systems and energy sensors, such as AMP-activated protein kinase (AMPK). In this study, we aimed to investigate the kappa opioid receptor (κOR)/dynorphin signaling in the modulation of nicotine’s effects on energy balance. We found that body weight loss after nicotine treatment is associated with a down-regulation of the κOR endogenous ligand dynorphin precursor and with a marked reduction in κOR signaling and the p70 S6 kinase/ribosomal protein S6 (S6K/rpS6) pathway in the lateral hypothalamic area (LHA). The inhibition of these pathways by nicotine was completely blunted in κOR deficient mice, after central pharmacological blockade of κOR, and in rodents where κOR was genetically knocked down specifically in the LHA. Moreover, κOR-mediated nicotine effects on body weight do not depend on orexin. These data unravel a new central regulatory pathway modulating nicotine’s effects on energy balance. 相似文献
3.
The discrete element method (DEM) has been extensively adopted to investigate many complex geotechnical related problems due to its capability to incorporate the discontinuous nature of granular materials. In particular, when simulating large deformations or distortion of soil (e.g. cavity expansion), DEM can be very effective as other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly to the problems concerning in situ testing, pile installation and so forth. In addition, the behaviour of geomaterials in a macro-level is utterly determined by microscopic properties, highlighting the importance of contact models. Despite the fact that there are numerous contact models proposed to mimic the realistic behaviour of granular materials, there are lack of studies on the effects of these contact models on the soil response. Hence, in this study, a series of three-dimensional numerical simulations with different contact constitutive models was conducted to simulate the response of sandy soils during cylindrical cavity expansion. In this numerical investigation, three contact models, i.e. linear contact model, rolling resistance contact model, and Hertz contact model, are considered. It should be noted that the former two models are linear based models, providing linearly elastic and frictional plasticity behaviours, whereas the latter one consists of nonlinear formulation based on an approximation of the theory of Mindlin and Deresiewicz. To examine the effects of these contact models, several cylindrical cavities were created and expanded gradually from an initial radius of 0.055 m to a final radius of 0.1 m. The numerical predictions confirm that the calibrated contact models produced similar results regarding the variations of cavity pressure, radial stress, deviatoric stress, volumetric strain, as well as the soil radial displacement. However, the linear contact model may result in inaccurate predictions when highly angular soil particles are involved. In addition, considering the excessive soil displacement induced by the pile installation (i.e. cavity expansion), a minimum distance of 11a (a is the cavity radius) is recommend for practicing engineers to avoid the potential damages to the existing piles and adjacent structures. 相似文献
4.
Nano Research - Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored... 相似文献
5.
Scientometrics - Journal rankings often show significant changes compared to previous rankings. This gives rise to the question of how well estimated the rank of a journal is. In this contribution,... 相似文献
6.
Volker Kahlenberg Johan P.R. de Villiers Dirk Odendaal Hannes Krüger Shengqiang Song Mithun Nath 《Journal of the American Ceramic Society》2019,102(11):6968-6979
Polycrystalline material of a novel phase in the system CaO–Al2O3–Cr2O3 has been obtained by solid-state reactions. Chemical analysis indicated the composition CaAl2Cr2O7. Single-crystal growth of the new compound using borax as a mineralizer was successful. Diffraction experiments at ambient conditions on a crystal with composition CaAl2.13Cr1.87O7 yielded the following basic crystallographic data: space group P 3, a = 7.7690(5) Å, c = 7.6463(5) Å, V = 399.68(6) Å3, Z = 3. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 2.3% for 1440 independent observed reflections and 113 parameters. To the best of our knowledge, the structure of CaAl2.13Cr1.87O7 or CaAl2Cr2O7 represents a new structure type. It belongs to the group of double layer structures where individual double layers contain octahedrally and tetrahedrally coordinated cation positions. Linkage between neighboring sheet packages is provided by additional calcium cations. Furthermore, thermal expansion has been studied in the interval between 29 and 790°C using in situ high-temperature single-crystal diffraction. No indications for a structural phase transition were observed. From the evolution of the lattice parameters the thermal expansion tensor has been obtained. A pronounced anisotropy is evident. The response of structural building units to variable temperature has been discussed. 相似文献
7.
8.
9.
Hiwot Abebe Haileslassie Carol J. Henry Robert T. Tyler 《International Journal of Food Science & Technology》2019,54(8):2540-2552
Pulses are processed in diverse ways prior to consumption. Soaking and germination are among the most common traditional, household-level food processing strategies. This study was carried out to determine the effects of soaking, germination, cooking and their combinations on the contents of selected nutrients and anti-nutrients of red dry bean and chickpea. In addition, the effects of pre-treatment on cooking time and the acceptability of dishes prepared from red dry bean and chickpea were determined. The nutrient compositions (zinc, iron and calcium) of most soaked-cooked and germinated-cooked red dry bean and chickpea samples were not significantly different than those of respective controls. However, soaking and germination pre-treatments significantly lowered the phytate and tannin contents of the red dry bean and chickpea samples, with a few exceptions, and overall, polyphenol contents were lower after soaking-cooking than after germination-cooking. Most scores for sensory attributes of bean-based and chickpea-based dishes prepared from soaked or germinated samples were not significantly different than those of the controls. For most red dry bean and chickpea samples, longer germination times yielded superior results in terms of reductions in cooking time, tannin content, and phytate:zinc and phytate:iron molar ratio. 相似文献
10.
When assessing the impact of extreme events, it is often not just a single component, but the combined behavior of several components which is important. Statistical modeling using multivariate generalized Pareto (GP) distributions constitutes the multivariate analogue of univariate peaks over thresholds modeling, which is widely used in finance and engineering. We develop general methods for construction of multivariate GP distributions and use them to create a variety of new statistical models. A censored likelihood procedure is proposed to make inference on these models, together with a threshold selection procedure, goodness-of-fit diagnostics, and a computationally tractable strategy for model selection. The models are fitted to returns of stock prices of four UK-based banks and to rainfall data in the context of landslide risk estimation. Supplementary materials and codes are available online. 相似文献