全文获取类型
收费全文 | 108128篇 |
免费 | 12042篇 |
国内免费 | 7747篇 |
专业分类
电工技术 | 8665篇 |
技术理论 | 1篇 |
综合类 | 10830篇 |
化学工业 | 15765篇 |
金属工艺 | 6475篇 |
机械仪表 | 6771篇 |
建筑科学 | 8042篇 |
矿业工程 | 3338篇 |
能源动力 | 2509篇 |
轻工业 | 13244篇 |
水利工程 | 3155篇 |
石油天然气 | 4176篇 |
武器工业 | 1362篇 |
无线电 | 11737篇 |
一般工业技术 | 9876篇 |
冶金工业 | 4159篇 |
原子能技术 | 1814篇 |
自动化技术 | 15998篇 |
出版年
2024年 | 406篇 |
2023年 | 1759篇 |
2022年 | 3878篇 |
2021年 | 4990篇 |
2020年 | 3762篇 |
2019年 | 2791篇 |
2018年 | 2919篇 |
2017年 | 3188篇 |
2016年 | 2971篇 |
2015年 | 4600篇 |
2014年 | 6041篇 |
2013年 | 6951篇 |
2012年 | 8414篇 |
2011年 | 9126篇 |
2010年 | 8703篇 |
2009年 | 8463篇 |
2008年 | 8522篇 |
2007年 | 8088篇 |
2006年 | 7199篇 |
2005年 | 5871篇 |
2004年 | 4243篇 |
2003年 | 3062篇 |
2002年 | 3021篇 |
2001年 | 2738篇 |
2000年 | 2063篇 |
1999年 | 1142篇 |
1998年 | 594篇 |
1997年 | 464篇 |
1996年 | 434篇 |
1995年 | 355篇 |
1994年 | 229篇 |
1993年 | 182篇 |
1992年 | 136篇 |
1991年 | 113篇 |
1990年 | 84篇 |
1989年 | 86篇 |
1988年 | 68篇 |
1987年 | 41篇 |
1986年 | 40篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1976年 | 4篇 |
1965年 | 2篇 |
1959年 | 11篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 494 毫秒
12.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
13.
现代学徒制是一项深化产教融合、校企合作的育人机制,是创新技术技能人才的现代培养模式.山西铁道职业技术学院与山西安泰控股集团有限公司深度合作开展山西省现代学徒制试点项目,合作目的之一是培养企业煤化工专业人才.学校教师结合学生(员工)在企业车间岗位上的技能知识,系统地讲授煤化工专业课程"煤质分析及煤化工产品检验"理论知识,同时针对企业员工日常学习思想政治知识较少的实际,润物细无声地加入思政元素,实现专业知识与实践技能相结合,技能知识与思政教育相融合,真正培养知识型、技能型、创新型高素质技能人才,努力构建职业教育产业发展命运共同体. 相似文献
15.
图像中的天空区域对于基于视觉的地面机器人导航具有重要意义,为了识别图像中的天空部分,本文提出了一种基于像素偏转模型的BP神经网络天空识别方法.首先,制作天空图像集和非天空图像集,天空图像集由各种天气情况下的天空提取而成,非天空图像集由非天空的景物构成,主要包括建筑、汽车、树木、植物等;其次,使用提出的像素偏转模型提取天空图像集和非天空图像集的像素特征并进行处理,对天空像素点和非天空像素点进行标注,利用BP神经网络对像素特征进行训练,得到权重文件;最后,使用得到的权重文件进行天空的识别.为了更好的说明本文算法和模型的优越性,使用本文算法与Otsu算法、YeHu算法、Graph-cut算法和Mask-Rcnn算法模型进行了比较,并设计了两组组对比实验,第一组实验进行识别效果的主观评价,第二组实验利用CamVid数据集的天空类进行算法精度的定量分析. 相似文献
16.
根据微化工技术发展的主要趋势,针对4-溴-3-甲基苯甲醚间歇非均相合成技术存在的问题,以微筛孔反应器与玻璃微珠填充床为核心功能微设备单元构建了模块化微反应系统,并在此模块化微反应系统内对液-液非均相连续溴化合成4-溴-3-甲基苯甲醚开展研究。通过优化操作条件,在溴浓度( )为17.5%(质量分数)、溴与间甲基苯甲醚摩尔比( /nM)为1.01、反应起始温度(T)为 0℃、停留时间为0.78 min条件下,4-溴-3-甲基苯甲醚的收率大于98%,多溴代副产物的含量仅为1%。与传统间歇溴化反应相比,模块化微反应系统内连续溴化反应具有十分明显的优势:可将间歇过程连续化,在保证安全的基础上极大地提升了反应的效率(时空收率为6.5×104 kg/(m3·h));另外,该过程是由传质控制的,微反应器的传质性能优异,可极大地改善产品的选择性(多溴代副产物的量减少50%)。该研究为4-溴-3-甲基苯甲醚的连续高效安全合成提供了技术和设备依据。 相似文献
17.
18.
Rong Zhang Hailong Hu Hai Chen Siqi Li Cheng Ying Shuai Huang Qingting Liu Xudong Fu Shengfei Hu Ching-Ping Wong 《应用聚合物科学杂志》2020,137(39):49186
Recently, thermal interface materials (TIMs) are in great demands for modern electronics. For mechanically mixed polymer composite TIMs, the thermal conductivity and the mechanical properties are generally lower than expected values due to the sharply increased viscosity and poor filler dispersion. This work shows that addition of a small amount of polyester-based hyperbranched polymer (HBP) avoided the trade-off in mechanically mixed ABS/hexagonal boron nitride (h-BN) composites. After adding 0.5 wt% HBP, the maximum h-BN content in the composites increased from 50 to 60 wt%. The out-of-plane, in-plane thermal conductivity, and tensile strength of ABS/h-BN with 50 wt% h-BN were 0.408, 0.517 W/mK, and 18 MPa, respectively, and were increased to 0.729, 0.847 W/mK, and 32 MPa by adding 0.5 wt% HBP, while 0.972, 1.12 W/mK, and 29.5 MPa were achieved for ABS/h-BN/HBP with 60 wt% h-BN. The morphological and rheological results proved that these enhancements are due to the improved h-BN dispersion by decreasing viscosity of composites during mixing. Theoretical modeling based on the modified effective medium theory confirmed such results and showed that the interfacial thermal resistance also decreased slightly. Thus, this work demonstrates a facile and scalable method for simultaneously improving the thermal conductivity and mechanical properties of thermoplastic-based TIMs. 相似文献
19.
Chuntao Lan Haiyang Zou Longfei Wang Meng Zhang Shuang Pan Ying Ma Yiping Qiu Zhong Lin Wang Zhiqun Lin 《Advanced materials (Deerfield Beach, Fla.)》2020,32(47):2005481
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc. 相似文献
20.
Wireless Personal Communications - The existing long term evolution networks originally designed for human-to-human communications are hard to tackle numerous and bursty random access requests from... 相似文献