全文获取类型
收费全文 | 63047篇 |
免费 | 6897篇 |
国内免费 | 4295篇 |
专业分类
电工技术 | 4327篇 |
技术理论 | 1篇 |
综合类 | 5657篇 |
化学工业 | 9508篇 |
金属工艺 | 3869篇 |
机械仪表 | 4146篇 |
建筑科学 | 4453篇 |
矿业工程 | 1884篇 |
能源动力 | 1492篇 |
轻工业 | 6758篇 |
水利工程 | 1593篇 |
石油天然气 | 2589篇 |
武器工业 | 683篇 |
无线电 | 7254篇 |
一般工业技术 | 6795篇 |
冶金工业 | 2350篇 |
原子能技术 | 776篇 |
自动化技术 | 10104篇 |
出版年
2024年 | 300篇 |
2023年 | 939篇 |
2022年 | 2073篇 |
2021年 | 2682篇 |
2020年 | 2031篇 |
2019年 | 1638篇 |
2018年 | 1857篇 |
2017年 | 1985篇 |
2016年 | 1847篇 |
2015年 | 2703篇 |
2014年 | 3460篇 |
2013年 | 4269篇 |
2012年 | 4952篇 |
2011年 | 5372篇 |
2010年 | 4933篇 |
2009年 | 4859篇 |
2008年 | 4688篇 |
2007年 | 4532篇 |
2006年 | 4120篇 |
2005年 | 3381篇 |
2004年 | 2517篇 |
2003年 | 1847篇 |
2002年 | 1752篇 |
2001年 | 1506篇 |
2000年 | 1110篇 |
1999年 | 732篇 |
1998年 | 401篇 |
1997年 | 342篇 |
1996年 | 278篇 |
1995年 | 218篇 |
1994年 | 183篇 |
1993年 | 158篇 |
1992年 | 113篇 |
1991年 | 94篇 |
1990年 | 67篇 |
1989年 | 55篇 |
1988年 | 41篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
本文将完全互补码(Complete Complementary Code, CCC)应用于多输入多输出(Multiple Input Multiple Output, MIMO)雷达目标探测中,针对具有非零多普勒的多目标检测问题,提出一种基于广义普洛黑-修-莫尔斯(Generalized Prouhet-Thue-Morse, GPTM)序列和二项式系数加权的信号处理方法。该方法分别在发射端和接收端进行处理,在发射端采用GPTM序列设计方法调整脉冲的发射顺序,以降低由多普勒引起的距离旁瓣;在接收端通过二项式设计(Binomial Design, BD)方法为各接收脉冲加上不同权重,扩大目标多普勒附近的清洁区。为综合上述两次处理的优势,将两次处理得到的距离多普勒谱进行逐点最小化处理,得到最终的距离多普勒谱,然后进行有序恒虚警检测。仿真结果表明,本文所提的信号处理方法具有良好的旁瓣抑制效果和多普勒分辨率,能够有效检测出非零多普勒目标。 相似文献
2.
Xiao Zhu Chen Yanxun Jiang Hongbo Hu Zhenzhen Lui John C. S. Min Geyong Dustdar Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of... 相似文献
4.
针对现有的混凝土裂缝检测算法在各种复杂环境中检测精度不够、鲁棒性不强的问题,根据深度学习理论和U-net模型,提出一种全U型网络的裂缝检测算法。首先,依照原U-net模型路线构建网络;然后,在每个池化层后都进行一次上采样,恢复其在池化层之前的特征图规格,并将其与池化之前的卷积层进行融合,将融合之后的特征图作为新的融合层与原U-net网络上采样之后的网络层进行融合;最后,为了验证算法的有效性,在测试集中进行实验。结果表明,所提算法的平均精确率可达到83.48%,召回率为85.08%,F1为84.11%,相较于原U-net分别提升了1.48%,4.68%和3.29%,在复杂环境中也能提取完整裂缝,保证了裂缝检测的鲁棒性。 相似文献
5.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献
6.
Journal of Porous Materials - Co3O4 has been widely investigated as a promising candidate anode material for lithium-ion batteries. We report on the porous Co3O4 column synthesized via a simple... 相似文献
7.
8.
Zhenkun Ke Xin Cao Chuanli Shan Lifen Shi Pingping Wang Yong Yang Fengyang Zhao Jiedong Cui Jinwei Li Gang Zhou Min Guan Tao Yu 《Ceramics International》2021,47(14):19605-19613
The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R2O–CaO–B2O3–SiO2) systematically. Because the glass would emulsify when Li2O was added to the glass batch, this article did not discuss Li2O. The results showed that when the amount of Na2O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na2O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased. 相似文献
9.
Tumor cell aggregation is critical for cell survival following the loss of extracellular matrix attachment and dissemination. However, the underlying mechanotransduction of clustering solitary tumor cells is poorly understood, especially in non-small cell lung cancers (NSCLC). Here, we examined whether cell surface protrusions played an important role in facilitating the physical contact between floating cells detached from a substrate. We employed poly-2-hydroxyethyl methacrylate-based 3D culture methods to mimic in vivo tumor cell cluster formation. The suprastructural analysis of human NSCLC A549 cell spheroids showed that finger-like protrusions clung together via the actin cytoskeleton. Time-lapse holotomography demonstrated that the finger-like protrusions of free-floating cells in 3D culture displayed exploratory coalescence. Global gene expression analysis demonstrated that the genes in the organic hydroxyl transport were particularly enriched in the A549 cell spheroids. Particularly, the knockdown of the water channel aquaporin 3 gene (AQP3) impaired multicellular aggregate formation in 3D culture through the rearrangement of the actomyosin cytoskeleton. Moreover, the cells with reduced levels of AQP3 decreased their transmigration. Overall, these data indicate that cell detachment-upregulated AQP3 contributes to cell surface protrusions through actomyosin cytoskeleton remodeling, causing the aggressive aggregation of free-floating cells dependent on the property of the substratum and collective metastasis. 相似文献
10.