全文获取类型
收费全文 | 1860篇 |
免费 | 242篇 |
国内免费 | 192篇 |
专业分类
电工技术 | 53篇 |
综合类 | 112篇 |
化学工业 | 553篇 |
金属工艺 | 140篇 |
机械仪表 | 37篇 |
建筑科学 | 24篇 |
矿业工程 | 94篇 |
能源动力 | 44篇 |
轻工业 | 93篇 |
水利工程 | 3篇 |
石油天然气 | 160篇 |
武器工业 | 8篇 |
无线电 | 301篇 |
一般工业技术 | 241篇 |
冶金工业 | 321篇 |
原子能技术 | 79篇 |
自动化技术 | 31篇 |
出版年
2024年 | 11篇 |
2023年 | 42篇 |
2022年 | 55篇 |
2021年 | 79篇 |
2020年 | 63篇 |
2019年 | 53篇 |
2018年 | 61篇 |
2017年 | 79篇 |
2016年 | 66篇 |
2015年 | 64篇 |
2014年 | 121篇 |
2013年 | 130篇 |
2012年 | 115篇 |
2011年 | 129篇 |
2010年 | 89篇 |
2009年 | 98篇 |
2008年 | 89篇 |
2007年 | 102篇 |
2006年 | 119篇 |
2005年 | 88篇 |
2004年 | 84篇 |
2003年 | 72篇 |
2002年 | 71篇 |
2001年 | 57篇 |
2000年 | 64篇 |
1999年 | 51篇 |
1998年 | 39篇 |
1997年 | 33篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有2294条查询结果,搜索用时 15 毫秒
71.
72.
73.
针对原棉杂质检测准确率不高的问题,以新疆棉花为研究对象,提出基于残差与注意力机制的原棉杂质检测算法。该算法为2阶段算法,准确率较高。首先,采集原棉杂质图象后对图像进行标注,再进行数据增广,可以避免训练过程中的过拟合现象,接着在原框架引入视觉注意力机制,通过改进算法结构来提高原棉杂质检测的准确率。其次,通过分析对比几种不同网络对原棉杂质检测的准确度,选取ResNet50为特征提取网络,该网络提高了算法的复杂特征提取能力。最后,采用RoI Align来减少量化误差,从而提高检测原棉杂质的准确性。实验结果表明,改进的算法虽然略微增多检测时间,但其整体检测准确率明显优于原算法,整体识别的准确率可达到94.84%,较改进前Faster R-CNN(faster region-based convolutional neural network)的识别率提高了5.58%。同时通过对比不同网络模型,结果显示改进后的Faster R-CNN对原棉杂质检测的效果更好。 相似文献
74.
75.
76.
77.
78.
海南炼化聚丙烯装置采用非对称外给电子体技术生产高速BOPP膜料。利用连续自成核热分级技术对3个样品进行等规度序列分布表征,结果表明3个样品的片晶厚度分布系数为1.07~1.08,样品的Ipeak1/Ipeak2值为1.36~1.58,说明采用非对称外给电子体技术生产的高速BOPP膜料具有较宽的等规度分布,且高等规度组分含量大于低等规度组分含量。与传统的BOPP膜料相比,采用非对称电子体技术生产的高速BOPP膜料不仅具有良好的成膜性,而且还具有较高的挺度。 相似文献
79.
AbstractThe quasi-two-dimensional molecular conductor α-(BEDT-TTF)2I3 exhibits anomalous transport phenomena where the temperature dependence of resistivity is weak but the ratio of the Hall coefficient at 10 K to that at room temperature is of the order of 104. These puzzling phenomena were solved by predicting massless Dirac fermions, whose motions are described using the tilted Weyl equation with anisotropic velocity. α-(BEDT-TTF)2I3 is a unique material among several materials with Dirac fermions, i.e. graphene, bismuth, and quantum wells such as HgTe, from the view-points of both the structure and electronic states described as follows. α-(BEDT-TTF)2I3 has the layered structure with highly two-dimensional massless Dirac fermions. The anisotropic velocity and incommensurate momenta of the contact points, ±k0, originate from the inequivalency of the BEDT-TTF sites in the unit cell, where ±k0 moves in the first Brillouin zone with increasing pressure. The massless Dirac fermions exist in the presence of the charge disproportionation and are robust against the increase in pressure. The electron densities on those inequivalent BEDT-TTF sites exhibit anomalous momentum distributions, reflecting the angular dependences of the wave functions around the contact points. Those unique electronic properties affect the spatial oscillations of the electron densities in the vicinity of an impurity. A marked behavior of the Hall coefficient, where the sign of the Hall coefficient reverses sharply but continuously at low temperatures around 5 K, is investigated by treating the interband effects of the magnetic field exactly. It is shown that such behavior is possible by assuming the existence of the extremely small amount of electron doping. The enhancement of the orbital diamagnetism is also expected. The results of the present research shed light on a new aspect of Dirac fermion physics, i.e. the emergence of unique electronic properties owing to the structure of the material. 相似文献
80.
Solution-processed organic bulk-heterojunction (BHJ) photovoltaic cells using random copolymeric donor materials have been extensively reported due to their suitable film-forming characteristics and phase-separated nano-morphology. Here, ratio-controlled toluene-versus benzene-chemical group based diketopyrrolopyrrole (DPP) donor polymers mixed with a fullerene acceptor were investigated to fabricate an efficient photovoltaic active layer with improved electrical properties through a vacuum treatment. The vacuum process leads to an increase in the phase-separation with a low surface roughness and nanoscale-distributed crystallinity due to securing the dry time of the residual solvent and solvent additive within the active layer. Moreover, the optimized DPP-based donor with toluene (T) versus benzene (B) linkers and electron transporting layer leads to an improvement in the power conversion efficiencies of up to 6.31% under AM 1.5G illumination due to the contributions of an efficient charge transfer and reduced series resistance. Therefore, the organic semiconductor obtained with the ratio-controlled molecular structure and proper solvent drying process plays an important role in increasing the electrical and morphological properties to produce efficient organic solar cells. 相似文献