全文获取类型
收费全文 | 94035篇 |
免费 | 12158篇 |
国内免费 | 7460篇 |
专业分类
电工技术 | 8595篇 |
技术理论 | 3篇 |
综合类 | 9122篇 |
化学工业 | 12093篇 |
金属工艺 | 5956篇 |
机械仪表 | 6814篇 |
建筑科学 | 7426篇 |
矿业工程 | 3966篇 |
能源动力 | 2631篇 |
轻工业 | 10011篇 |
水利工程 | 3054篇 |
石油天然气 | 3544篇 |
武器工业 | 1407篇 |
无线电 | 10744篇 |
一般工业技术 | 8583篇 |
冶金工业 | 3714篇 |
原子能技术 | 1482篇 |
自动化技术 | 14508篇 |
出版年
2024年 | 634篇 |
2023年 | 1807篇 |
2022年 | 4241篇 |
2021年 | 5308篇 |
2020年 | 3901篇 |
2019年 | 2771篇 |
2018年 | 3043篇 |
2017年 | 3607篇 |
2016年 | 3091篇 |
2015年 | 4747篇 |
2014年 | 5759篇 |
2013年 | 6597篇 |
2012年 | 8183篇 |
2011年 | 8135篇 |
2010年 | 7461篇 |
2009年 | 6915篇 |
2008年 | 7080篇 |
2007年 | 6433篇 |
2006年 | 5498篇 |
2005年 | 4604篇 |
2004年 | 3274篇 |
2003年 | 2220篇 |
2002年 | 2153篇 |
2001年 | 1971篇 |
2000年 | 1578篇 |
1999年 | 656篇 |
1998年 | 326篇 |
1997年 | 275篇 |
1996年 | 213篇 |
1995年 | 180篇 |
1994年 | 153篇 |
1993年 | 129篇 |
1992年 | 111篇 |
1991年 | 89篇 |
1990年 | 77篇 |
1989年 | 80篇 |
1988年 | 50篇 |
1987年 | 34篇 |
1986年 | 44篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 35篇 |
1979年 | 24篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1959年 | 12篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
采用ETAG 004:2013《外墙外保温薄抹灰系统欧洲技术认证指南》中规定的静态泡沫块法,测试在单位面积上使用不同数量锚栓的岩棉板外保温系统的抗风压性能。通过试验可以得出:在混凝土墙体上单纯采用敲击式锚栓锚固岩棉板外保温系统时,拉伸强度可达12.9 k Pa;单位面积增加锚栓的使用量可以提高系统的抗拉承载力,但在不同条件下增加相同数量锚栓对系统抗风载能力提高的程度不同;在普通混凝土墙中,单纯锚固岩棉板保温系统破坏时,单个锚栓承载力平均值的最大值约为其拉拔承载力的50.3%。 相似文献
23.
Bo Wang Edison Huixiang Ang Yang Yang Yufei Zhang Hongbo Geng Minghui Ye Cheng Chao Li 《Advanced functional materials》2020,30(28)
Orthorhombic molybdenum trioxide (MoO3) is one of the most promising anode materials for sodium‐ion batteries because of its rich chemistry associated with multiple valence states and intriguing layered structure. However, MoO3 still suffers from the low rate capability and poor cycle induced by pulverization during de/sodiation. An ingenious two‐step synthesis strategy to fine tune the layer structure of MoO3 targeting stable and fast sodium ionic diffusion channels is reported here. By integrating partially reduction and organic molecule intercalation methodologies, the interlayer spacing of MoO3 is remarkably enlarged to 10.40 Å and the layer structural integration are reinforced by dimercapto groups of bismuththiol molecules. Comprehensive characterizations and density functional theory calculations prove that the intercalated bismuththiol (DMcT) molecules substantially enhanced electronic conductivity and effectively shield the electrostatic interaction between Na+ and the MoO3 host by conjugated double bond, resulting in improved Na+ insertion/extraction kinetics. Benefiting from these features, the newly devised layered MoO3 electrode achieves excellent long‐term cycling stability and outstanding rate performance. These achievements are of vital significance for the preparation of sodium‐ion battery anode materials with high‐rate capability and long cycling life using intercalation chemistry. 相似文献
24.
25.
Xi Chen Zhengkun Yu Chen Yang Yao Chen Chao Jin Yuejiao Ding Wenbin Li Zhongmin Wan 《International Journal of Hydrogen Energy》2021,46(19):11127-11139
Flow field structure can largely determine the output performance of Polymer electrolyte membrane fuel cell. Excellent channel configuration accelerates electrochemical reactions in the catalytic layer, effectively avoiding flooding on the cathode side. In present study, a three-dimensional, multi-phase model of PEMFC with a 3D wave flow channel is established. CFD method is applied to optimize the geometry constructions of three-dimensional wave flow channels. The results reveal that 3D wave flow channel is overall better than straight channel in promoting reactant gases transport, removing liquid water accumulated in microporous layer and avoiding thermal stress concentration in the membrane. Moreover, results show the optimal flow channel minimum depth and wave length of the 3D wave flow channel are 0.45 mm and 2 mm, respectively. Due to the periodic geometric characteristics of the wave channel, the convective mass transfer is introduced, improving gas flow rate in through-plane direction. Furthermore, when the cell output voltage is 0.4 V, the current density in the novel channel is 23.8% higher than that of conventional channel. 相似文献
26.
摘 要:目的 了解六六六(hexachlorocyclohexanes,HCHs)与滴滴涕(dichloro diphenyl trichloroethanes,DDTs)在杭州湾南岸滩涂沉积物中的污染现状。方法 于2018年4月,采集杭州湾南岸地区4个采样点不同深度(0~80 cm)滩涂沉积物,利用气相色谱-串联质谱法(gas chromatography tandem mass spectrometry, GC-MS/MS)测定了该区域中HCHs与DDTs的含量,对其分布规律进行分析,使用共识沉积物质量基准法对其生态学风险进行了评估。结果 所有样品中均检出,HCHs与DDTs含量分别为4.20~6.24 μg/kg与3.37~4.73 μg/kg,主要以β-HCH、δ-HCH以及DDE为主,其污染主要来源于历史性工业品,整体污染处于较低水平;20.3%的沉积物样品中DDEs含量以及28.1%的样品DDTs总量介于阈值效应浓度(threshold concentration, TECs) 和可能效应浓度(probable effect concentration, PECs)之间。结论 杭州湾南岸沉积物中HCHs与DDTs的污染处于较低水平,具有较小的生态学风险。 相似文献
27.
豫西熊耳山雷门沟钼矿床位于东秦岭多金属成矿带东段,是已探明的超大型斑岩型钼矿,前人研究程度高、地质成果丰硕,但对矿床开采技术条件方面研究较少。本次通过地质调查工程、水文地质试验等方法,从水文地质角度,对雷门沟钼矿床水文地质条件进行研究,填补了该方面的空白,丰富了研究成果;采用水文地质比拟法预测未来矿坑最大排水量2613 m3/d,经实践检验结果较为可靠;总结的采坑排水量预测方法、含水层特点、矿床充水因素以及防治水措施,以期对该区域水文地质工作具有参考价值。 相似文献
28.
29.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed. 相似文献
30.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes. 相似文献