全文获取类型
收费全文 | 239533篇 |
免费 | 22304篇 |
国内免费 | 11913篇 |
专业分类
电工技术 | 16123篇 |
技术理论 | 13篇 |
综合类 | 22795篇 |
化学工业 | 31747篇 |
金属工艺 | 13758篇 |
机械仪表 | 20371篇 |
建筑科学 | 24589篇 |
矿业工程 | 9242篇 |
能源动力 | 9304篇 |
轻工业 | 19010篇 |
水利工程 | 8595篇 |
石油天然气 | 11307篇 |
武器工业 | 2545篇 |
无线电 | 12986篇 |
一般工业技术 | 22434篇 |
冶金工业 | 12474篇 |
原子能技术 | 2929篇 |
自动化技术 | 33528篇 |
出版年
2024年 | 435篇 |
2023年 | 2685篇 |
2022年 | 5346篇 |
2021年 | 6782篇 |
2020年 | 7142篇 |
2019年 | 5842篇 |
2018年 | 5531篇 |
2017年 | 6948篇 |
2016年 | 8439篇 |
2015年 | 8989篇 |
2014年 | 15210篇 |
2013年 | 15415篇 |
2012年 | 18005篇 |
2011年 | 19616篇 |
2010年 | 14103篇 |
2009年 | 14400篇 |
2008年 | 13218篇 |
2007年 | 16213篇 |
2006年 | 14478篇 |
2005年 | 12319篇 |
2004年 | 10471篇 |
2003年 | 9026篇 |
2002年 | 7430篇 |
2001年 | 6174篇 |
2000年 | 5110篇 |
1999年 | 4176篇 |
1998年 | 3486篇 |
1997年 | 2827篇 |
1996年 | 2462篇 |
1995年 | 2061篇 |
1994年 | 1821篇 |
1993年 | 1299篇 |
1992年 | 1194篇 |
1991年 | 883篇 |
1990年 | 702篇 |
1989年 | 600篇 |
1988年 | 490篇 |
1987年 | 326篇 |
1986年 | 281篇 |
1985年 | 248篇 |
1984年 | 289篇 |
1983年 | 270篇 |
1982年 | 211篇 |
1981年 | 111篇 |
1980年 | 117篇 |
1979年 | 77篇 |
1978年 | 57篇 |
1977年 | 59篇 |
1976年 | 49篇 |
1959年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
根据叶用甜菜品种的观赏特性,运用层次分析法初步建立叶用甜菜品种观赏价值的评价模型,包含叶梗、叶片和整体感3个方面共11个评价因子。结果表明:叶梗是评价叶用甜菜观赏价值的核心要素;叶梗色、叶梗厚、叶丛型是重要因子,分别以红、粉红、粉白叶梗,叶梗厚度厚和直立型叶丛为优良性状。利用该评价模型对8个甜菜品种进行观赏价值综合评价,筛选出‘Clnx-blush2018'、'Clnx-fen2018’和‘荷兰必久'3个观赏价值高、适于市场推广叶品种。 相似文献
22.
23.
24.
25.
Reliable prediction of flooding conditions is needed for sizing and operating packed extraction columns. Due to the complex interplay of physicochemical properties, operational parameters and the packing-specific properties, it is challenging to develop accurate semi-empirical or rigorous models with a high validity range. State of the art models may therefore fail to predict flooding accurately. To overcome this problem, a data-driven model based on Gaussian processes is developed to predict flooding for packed liquid-liquid and high-pressure extraction columns. The optimized Gaussian process for the liquid-liquid extraction column results in an average absolute relative error (AARE) of 15.23 %, whereas the algorithm for the high-pressure extraction column results in an AARE of 13.68 %. Both algorithms can predict flooding curves for different packing geometries and chemical systems precisely. 相似文献
26.
Kirti M. Yenkie Jean Pimentel Ákos Orosz Heriberto Cabezas Ferenc Friedler 《American Institute of Chemical Engineers》2021,67(7):e17253
Wastewater treatment consists of three or four sequential stages: preliminary, primary, secondary, and tertiary. Each stage can comprise multiple alternative technologies that can perform the same tasks with different efficiencies, operating times, and costs. Thus, we propose a systematic approach for designing wastewater treatment networks by utilizing principles of mathematical modeling and generating an exhaustive enumeration of all the possible technologies and their connections during the early stages of designing a treatment facility. Some of these structures are nonintuitive and include recycling, reprocessing, bypasses, and multiple technologies in parallel or series to remove the same contaminant. The nonintuitive structures with multiple technologies may provide a measure of resilience compared to typical heuristic designs. Thus, the combination of P-graph methodology and the sequence of treatment technologies predicted via the optimization algorithm from the maximal structure is based on holistic considerations and does not lead to suboptimal solutions. 相似文献
27.
为解决沧州市涉地税源管理手段单一等问题,文中提出以测绘地理信息技术为支撑,通过对多源数据组织管理,建立风险分析指标,采用多种GIS空间分析方法构建了涉地风险税源识别模式并在沧州进行应用。结果表明:该模式能有效识别多种涉地风险,为涉地税源管理提供了支撑。 相似文献
28.
According to the circle-packing theorem, the packing efficiency of a hexagonal lattice is higher than an equivalent square tessellation. Consequently, in several contexts, hexagonally sampled images compared to their Cartesian counterparts are better at preserving information content. In this paper, novel mapping techniques alongside the wavelet compression scheme are presented for hexagonal images. Specifically, we introduce two tree-based coding schemes, referred to as SBHex (spirally-mapped branch-coding for hexagonal images) and BBHex (breadth-first block-coding for hexagonal images). Both of these coding schemes respect the geometry of the hexagonal lattice and yield better compression results. Our empirical results show that the proposed algorithms for hexagonal images produce better reconstruction quality at low bits per pixel representations compared to the tree-based coding counterparts for the Cartesian grid. 相似文献
29.
《中国有色金属学会会刊》2021,31(10):2939-2948
The uniaxial tensile test of the 5A06-O aluminium–magnesium (Al–Mg) alloy sheet was performed in the temperature range of 20–300 °C to obtain the true stress–true strain curves at different temperatures and strain rates. The constitutive model of 5A06-O Al–Mg alloy sheet with the temperature range from 150 to 300°C was established. Based on the test results, a unique finite element simulation platform for warm hydroforming of 5A06-O Al–Mg alloy was set up using the general finite element software MSC.Marc to simulate warm hydroforming of classic specimen, and a coupled thermo-mechanical finite element model for warm hydroforming of cylindrical cup was built up. Combined with the experiment, the influence of the temperature field distribution and loading conditions on the sheet formability was studied. The results show that the non-isothermal temperature distribution conditions can significantly improve the forming performance of the material. As the temperature increases, the impact of the punching speed on the forming becomes particularly obvious; the optimal values of the fluid pressure and blank holder force required for forming are reduced. 相似文献
30.
Shi-yuan XU Chu-ming LIU Ying-chun WAN Guang ZENG Yong-hao GAO Shu-nong JIANG 《中国有色金属学会会刊》2021,31(5):1291-1302
The corrosion behaviour of Mg-6Gd-3Y-1Zn-0.3Ag (wt.%) alloy components with different sizes after cooling was investigated. The alloys in the small components (SC) cooled fast, which were composed of α-Mg matrix and coarse long-period stacking ordered (LPSO) phases. The alloys in the large components (LC) cooled slowly, and there were thin lamellar LPSO phases precipitating inside the grains, except for α-Mg matrix and coarse LPSO phases. The hydrogen evolution test revealed that the corrosion rate of LC sample was higher than that of SC sample. Electrochemical impedance spectroscopy (EIS) test showed that the surface film on LC alloys provided worse protection. The corrosion morphologies indicated that the precipitation of the thin lamellar LPSO phases in LC sample caused severe micro-galvanic corrosion, which accelerated the rupture of the surface film. 相似文献