全文获取类型
收费全文 | 191010篇 |
免费 | 21650篇 |
国内免费 | 13834篇 |
专业分类
电工技术 | 16354篇 |
技术理论 | 3篇 |
综合类 | 19873篇 |
化学工业 | 24900篇 |
金属工艺 | 12977篇 |
机械仪表 | 13596篇 |
建筑科学 | 14592篇 |
矿业工程 | 7959篇 |
能源动力 | 4917篇 |
轻工业 | 20658篇 |
水利工程 | 5785篇 |
石油天然气 | 7908篇 |
武器工业 | 2871篇 |
无线电 | 20101篇 |
一般工业技术 | 16455篇 |
冶金工业 | 7609篇 |
原子能技术 | 2976篇 |
自动化技术 | 26960篇 |
出版年
2024年 | 1080篇 |
2023年 | 3181篇 |
2022年 | 7645篇 |
2021年 | 9919篇 |
2020年 | 7199篇 |
2019年 | 4841篇 |
2018年 | 5382篇 |
2017年 | 6165篇 |
2016年 | 5168篇 |
2015年 | 8570篇 |
2014年 | 10862篇 |
2013年 | 12494篇 |
2012年 | 15423篇 |
2011年 | 16221篇 |
2010年 | 15356篇 |
2009年 | 14583篇 |
2008年 | 14984篇 |
2007年 | 14049篇 |
2006年 | 12303篇 |
2005年 | 9910篇 |
2004年 | 7160篇 |
2003年 | 4882篇 |
2002年 | 4545篇 |
2001年 | 4055篇 |
2000年 | 3416篇 |
1999年 | 1776篇 |
1998年 | 957篇 |
1997年 | 734篇 |
1996年 | 666篇 |
1995年 | 561篇 |
1994年 | 461篇 |
1993年 | 341篇 |
1992年 | 294篇 |
1991年 | 222篇 |
1990年 | 195篇 |
1989年 | 157篇 |
1988年 | 115篇 |
1987年 | 87篇 |
1986年 | 74篇 |
1985年 | 52篇 |
1984年 | 47篇 |
1983年 | 48篇 |
1982年 | 35篇 |
1981年 | 43篇 |
1980年 | 60篇 |
1979年 | 42篇 |
1978年 | 12篇 |
1973年 | 12篇 |
1959年 | 29篇 |
1951年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
As accessing computing resources from the remote cloud inherently incurs high end-to-end (E2E) delay for mobile users, cloudlets, which are deployed at the edge of a network, can potentially mitigate this problem. Although some research works focus on allocating workloads among cloudlets, the cloudlet placement aiming to minimize the deployment cost (i.e., consisting of both the cloudlet cost and average E2E delay cost) has not been addressed effectively so far. The locations and number of cloudlets have a crucial impact on both the cloudlet cost in the network and average E2E delay of users. Therefore, in this paper, we propose the Cost Aware cloudlet PlAcement in moBiLe Edge computing (CAPABLE) strategy, where both the cloudlet cost and average E2E delay are considered in the cloudlet placement. To solve this problem, a Lagrangian heuristic algorithm is developed to achieve the suboptimal solution. After cloudlets are placed in the network, we also design a workload allocation scheme to minimize the E2E delay between users and their cloudlets by considering the user mobility. The performance of CAPABLE has been validated by extensive simulations. 相似文献
83.
Yejun Wu Bowen Yan Juan Zhou Huizhang Lian Xiaojun Yu Jianxin Zhao Hao Zhang Wei Chen Daming Fan 《Journal of food science》2020,85(10):3282-3292
84.
针对电站锅炉回转式空气预热器运行时上下表面不可见的问题,本文提出了一种视频监控与故障分析系统,可直接监测转子表面情况。该系统通过视频监控获取图像,结合改进的Retinex算法对其进行处理,实现了以下2个功能:1)能分析积灰程度以判断转子堵塞 情况;2)与温度场融合实时显示转子表面热点分布以预防二次燃烧。该系统已应用于某600 MW机组,实现了在热态环境下对空气预热器转子积灰程度、热点分布、堵塞程度的估算与可视化,大大提高了空气预热器运行的可靠性。 相似文献
85.
Hechun Cao Hui Zheng Lining Fan Zifeng Cheng Jianwei Zhou Qiong Wu Peng Zheng Liang Zheng Yang Zhang 《International Journal of Applied Ceramic Technology》2020,17(2):813-822
In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). 相似文献
86.
87.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献
88.
不确定性因素存在于火电机组负荷分配中,影响机组负荷分配、节能环保目标。本文综合考虑负荷预测不确定性、机组煤耗率不确定性与其CO2排放系数不确定性,分别构建火电机组一次能源消耗成本与CO2排放量最小目标下的火电机组负荷优化分配模型;以此为基础,引入析因分析方差分解方法,量化多源不确定性因素单独与交互作用下对节能、环保目标的影响程度。结果表明:负荷预测不确定性对火电机组节能、环保目标影响最为显著,相对影响程度分别为51.13%、62.70%;机组煤耗特性及其CO2排放系数影响次之,相对影响程度分别为47.58%、34.95%。此研究结果对不确定性条件下电力系统负荷分配具有借鉴价值。 相似文献
89.
水文过程相依性是水文变异的主要表现形式之一,应用自回归模型对其进行拟合时合理确定模型阶数是一个难点问题。本文在分析AIC和BIC准则的基础上,提出了一种以原序列与其相依成分的相关系数作为拟合度指标,同时借用信息熵形式的函数式,作为模型不确定性度量指标的自回归模型定阶准则(简称RIC准则)。以AR(1)、AR(2)、AR(3)和AR(4)模型为例进行统计试验,将不同序列长度下该准则的定阶准确率与其他定阶准则进行比较,试验结果表明,RIC准则对于上述模型均具有较好的适应性,且定阶准确率远高于AIC准则,其中对于前三阶模型RIC准则优于BIC准则,但四阶模型略低于BIC准则。RIC准则的优势是可以同时满足模型定阶、相依程度分级与模型检验的需求,将其应用于实测水文序列分析,结果显示,该准则能较准确地识别自回归模型的阶数,且符合提出的"相依有变异而残差无变异的最小阶数"的检验标准。 相似文献
90.
Natural Computing - The fiber stretching process plays the key role in the process of fiber production and its effects is measured by the stretching ratio. The stretching ratio is determined by the... 相似文献