全文获取类型
收费全文 | 41799篇 |
免费 | 4014篇 |
国内免费 | 2050篇 |
专业分类
电工技术 | 2604篇 |
技术理论 | 3篇 |
综合类 | 2786篇 |
化学工业 | 6817篇 |
金属工艺 | 2483篇 |
机械仪表 | 2491篇 |
建筑科学 | 3110篇 |
矿业工程 | 1207篇 |
能源动力 | 1166篇 |
轻工业 | 2749篇 |
水利工程 | 818篇 |
石油天然气 | 2640篇 |
武器工业 | 394篇 |
无线电 | 5023篇 |
一般工业技术 | 4969篇 |
冶金工业 | 1874篇 |
原子能技术 | 426篇 |
自动化技术 | 6303篇 |
出版年
2024年 | 258篇 |
2023年 | 872篇 |
2022年 | 1590篇 |
2021年 | 2191篇 |
2020年 | 1595篇 |
2019年 | 1204篇 |
2018年 | 1436篇 |
2017年 | 1509篇 |
2016年 | 1238篇 |
2015年 | 1751篇 |
2014年 | 2268篇 |
2013年 | 2507篇 |
2012年 | 2853篇 |
2011年 | 3063篇 |
2010年 | 2721篇 |
2009年 | 2271篇 |
2008年 | 2419篇 |
2007年 | 2157篇 |
2006年 | 2100篇 |
2005年 | 1798篇 |
2004年 | 1172篇 |
2003年 | 1004篇 |
2002年 | 981篇 |
2001年 | 837篇 |
2000年 | 839篇 |
1999年 | 1010篇 |
1998年 | 777篇 |
1997年 | 613篇 |
1996年 | 582篇 |
1995年 | 481篇 |
1994年 | 402篇 |
1993年 | 263篇 |
1992年 | 244篇 |
1991年 | 175篇 |
1990年 | 131篇 |
1989年 | 102篇 |
1988年 | 88篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 39篇 |
1984年 | 31篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
采用正交试验法进行冷冻除湿机变风量运行试验,通过交互作用显著性分析,发现对应最大单位能耗除湿量的最优风量受冷冻除湿机进口空气的相对湿度的影响远大于受温度的影响. 相似文献
992.
Molecular‐Level Design of Hierarchically Porous Carbons Codoped with Nitrogen and Phosphorus Capable of In Situ Self‐Activation for Sustainable Energy Systems 下载免费PDF全文
Wei Ai Xuewan Wang Chenji Zou Zhuzhu Du Zhanxi Fan Hua Zhang Peng Chen Ting Yu Wei Huang 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(8)
Hierarchically porous carbons are attracting tremendous attention in sustainable energy systems, such as lithium ion battery (LIB) and fuel cell, due to their excellent transport properties that arise from the high surface area and rich porosity. The state‐of‐the‐art approaches for synthesizing hierarchically porous carbons normally require chemical‐ and/or template‐assisted activation techniques, which is complicate, time consuming, and not feasible for large scale production. Here, a molecular‐level design principle toward large‐scale synthesis of nitrogen and phosphorus codoped hierarchically porous carbon (NPHPC) through an in situ self‐activation process is proposed. The material is fabricated based on the direct pyrolysis of a well‐designed polymer, melamine polyphosphate, which is capable of in situ self‐activation to generate large specific surface area (1479 m2 g?1) and hierarchical pores in the final NPHPC. As an anode material for LIB, NPHPC delivers a high reversible capacity of 1073 mAh g?1 and an excellent cyclic stability for 300 cycles with negligible capacity decay. The peculiar structural properties and synergistic effect of N and P codopants also enable NPHPC a promising electrocatalyst for oxygen reduction reaction, a key cathodic reaction process of many energy conversion devices (for example, fuel cells and metal air batteries). Electrochemical measurements show NPHPC a comparable electrocatalytic performance to commercial Pt/C catalyst (onset potential of 0.88 V vs reversible hydrogen electrode in alkaline medium) with excellent stability (89.8% retention after 20 000 s continuous operation) and superior methanol tolerance. 相似文献
993.
通过简单超声法制备了球状NiO纳米颗粒、NiO/石墨薄片(NiO/GNS)和NiO/GNS/Ag纳米复合材料。在NiO/GNS和NiO/GNS/Ag复合材料中,GNS作为NiO和Ag纳米颗粒分散的模板,不仅有效避免了NiO和Ag纳米颗粒的团聚,还改善了复合材料的电化学性能。采用场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射对样品的成分、形貌和结构进行了表征。NiO/GNS/Ag复合材料(GNS质量分数为0.5%,Ag质量分数为3%)电极表现出优异的电化学性能。在1A/g时,其初始比电容为501.66F/g,2000次循环后其比电容衰减为440.45F/g。这表明所制备的复合材料是一种有应用价值的超级电容器电极材料。 相似文献
994.
目的优化电炖锅包装,比较EPS与瓦楞纸内衬的包装效果,以及替代可能性。方法参考电炖锅产品流通过程中的环境参数,对产品进行有限元建模和约束处理,基于Ansys Workbench中的有限元思想,通过模态分析、随机振动、跌落等情况,分析得到不同力学载荷作用下产品的变形、应力、应变,以及破损情况,通过改变包装内衬实现电炖锅的包装优化设计。对优化后的包装件进行仿真分析,并与原包装件进行比较。结果最大应力出现在产品的螺栓连接处。裸机、EPS泡沫包装件和瓦楞纸(B楞)包装件的最大应力分别为353.25,115.69,171.84 MPa。结论瓦楞衬垫的抗压强度、抗冲击性能、抗振性虽都差于EPS泡沫包装,但还是可以很好地保护电炖锅,因此具有良好包装结构设计的瓦楞纸包装可以取代传统EPS泡沫包装。 相似文献
995.
Yateng Wang Jianru Fan Hao Zhao Xiaoming Song Zhe Ji Congxia Xie Fushan Chen Yao Meng 《International journal of molecular sciences》2022,23(10)
The starch composite films (SCFs) will be one of the best alternative packaging materials to petroleum based plastic films, which mitigates white pollution and energy consumption. However, weak mechanical stability, water resistance, and dyeability has hindered the application of SCFs. Herein, a bioinspired robust SCFs with super-hydrophobicity and excellent structural colors were prepared by fiber-reinforcement and assembling SiO2/Polydimethylsiloxane (PDMS) amorphous arrays on the surface of SCFs. The properties of the designed SCFs were investigated by various methods including scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), a tensile test, contact angle (CA) test, and an optical test. The results showed that the obtained SCFs possessed a higher tensile strength (55.17 MPa) attributed to the formed abundant hydrogen bonds between the molecular chains of the starch, cellulose fiber, and polyvinyl alcohol. Benefiting from the nanostructure with rough surface which were modified by materials with low surface free energy, the contact angle and sliding angle of the film reached up to 154° and 2°, respectively. The colors which were produced by the constructive interference of the coherent scattered light could cover all of the visible regions by tuning the diameters of the SiO2 nanoparticles. The strategy in the present study not only reinforces the mechanical strength and water resistance of SCFs but also provides an environmentally friendly way to color the them, which shows unprecedented application potential in packaging materials of the starch composite films. 相似文献
996.
Yingying Zhang Shuang Wang Lu Wang Xiaoyan Chang Yongxiao Fan Meiqing He Dawei Yan 《International journal of molecular sciences》2022,23(10)
Plasmodesmata (PD) are plant-specific channels connecting adjacent cells to mediate intercellular communication of molecules essential for plant development and defense. The typical PD are organized by the close apposition of the plasma membrane (PM), the desmotubule derived from the endoplasmic reticulum (ER), and spoke-like elements linking the two membranes. The plasmodesmal PM (PD-PM) is characterized by the formation of unique microdomains enriched with sphingolipids, sterols, and specific proteins, identified by lipidomics and proteomics. These components modulate PD to adapt to the dynamic changes of developmental processes and environmental stimuli. In this review, we focus on highlighting the functions of sphingolipid species in plasmodesmata, including membrane microdomain organization, architecture transformation, callose deposition and permeability control, and signaling regulation. We also briefly discuss the difference between sphingolipids and sterols, and we propose potential unresolved questions that are of help for further understanding the correspondence between plasmodesmal structure and function. 相似文献
997.
998.
Yao Yu Lu Ma Xinying Wang Zhi Zhao Wei Wang Yunxin Fan Kunquan Liu Tingting Jiang Ziwei Xiong Qisheng Song Changqing Li Panting Wang Wenjing Ma Huanan Xu Xinyu Wang Zijing Zhao Jianfei Wang Hongsheng Zhang Yongmei Bao 《International journal of molecular sciences》2022,23(10)
Rice blast is one of the main diseases in rice and can occur in different rice growth stages. Due to the complicated procedure of panicle blast identification and instability of panicle blast infection influenced by the environment, most cloned rice resistance genes are associated with leaf blast. In this study, a rice panicle blast resistance gene, Pb2, was identified by genome-wide association mapping based on the panicle blast resistance phenotypes of 230 Rice Diversity Panel 1 (RDP1) accessions with 700,000 single-nucleotide polymorphism (SNP) markers. A genome-wide association study identified 18 panicle blast resistance loci (PBRL) within two years, including 9 reported loci and 2 repeated loci (PBRL2 and PBRL13, PBRL10 and PBRL18). Among them, the repeated locus (PBRL10 and PBRL18) was located in chromosome 11. By haplotype and expression analysis, one of the Nucleotide-binding domain and Leucine-rich Repeat (NLR) Pb2 genes was highly conserved in multiple resistant rice cultivars, and its expression was significantly upregulated after rice blast infection. Pb2 encodes a typical NBS-LRR protein with NB-ARC domain and LRR domain. Compared with wild type plants, the transgenic rice of Pb2 showed enhanced resistance to panicle and leaf blast with reduced lesion number. Subcellular localization of Pb2 showed that it is located on plasma membrane, and GUS tissue-staining observation found that Pb2 is highly expressed in grains, leaf tips and stem nodes. The Pb2 transgenic plants showed no difference in agronomic traits with wild type plants. It indicated that Pb2 could be useful for breeding of rice blast resistance. 相似文献
999.
为了在超分辨率中对非欧数据的3D点云进行局部信息高效提取,提出采用动态残差图卷积的3D点云超分辨率网络(PSR-DRGCN),该网络包括特征提取模块、DRGCN模块及上采样模块.对于输入的3D点云,特征提取模块采用k-近邻(k-NN)算法在3D空间中找到每个点对应的k个邻居,通过逐点卷积把局部几何信息转换到高维特征空间中;DRGCN模块利用多层图卷积操作将3D空间中每个点的局部几何特征抽象为语义特征,在每一层对点的近邻空间进行动态调整以增加感受野范围,并通过残差连接融合多层次语义信息,从而对局部几何信息高效提取;上采样模块将特征空间中的点进行上采样并转换到3D空间中.实验结果表明,PSR-DRGCN生成的高分辨率点云在放大尺度为2倍时,相似性指标CD、 EMD、 F-score相比第2网络分别优化了10.00%, 4.76%,16.84%;当放大尺度为6倍时,相似性指标相比第2网络分别优化了2.35%,40.00%,0.58%;在所有情况下的均值与标准差指标上达到最优效果,生成的高分辨率点云质量高. 相似文献
1000.