首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22932篇
  免费   3076篇
  国内免费   1295篇
电工技术   4442篇
技术理论   1篇
综合类   2294篇
化学工业   1848篇
金属工艺   904篇
机械仪表   1724篇
建筑科学   1296篇
矿业工程   630篇
能源动力   683篇
轻工业   602篇
水利工程   373篇
石油天然气   854篇
武器工业   305篇
无线电   6171篇
一般工业技术   2052篇
冶金工业   516篇
原子能技术   214篇
自动化技术   2394篇
  2024年   47篇
  2023年   401篇
  2022年   572篇
  2021年   737篇
  2020年   816篇
  2019年   681篇
  2018年   613篇
  2017年   897篇
  2016年   955篇
  2015年   1122篇
  2014年   1505篇
  2013年   1363篇
  2012年   1723篇
  2011年   1962篇
  2010年   1411篇
  2009年   1402篇
  2008年   1434篇
  2007年   1673篇
  2006年   1454篇
  2005年   1173篇
  2004年   937篇
  2003年   783篇
  2002年   709篇
  2001年   582篇
  2000年   469篇
  1999年   343篇
  1998年   284篇
  1997年   228篇
  1996年   225篇
  1995年   175篇
  1994年   156篇
  1993年   104篇
  1992年   78篇
  1991年   66篇
  1990年   49篇
  1989年   48篇
  1988年   27篇
  1987年   26篇
  1986年   17篇
  1985年   11篇
  1984年   9篇
  1983年   4篇
  1982年   7篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1977年   2篇
  1974年   2篇
  1959年   2篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
林加富 《玻璃》2022,49(2):53-57
双玻光伏组件以其抗PID性强、防隐裂、防水汽透过、抗蜗牛纹、可靠性优异、轻量化等诸多优点,在晶硅太阳能组件市占比逐步提高。双玻光伏组件用背板玻璃一般需要预留出线孔,光伏背板玻璃的出线孔主要有两种打孔方式:金钢钻上下同步钻孔的模式和激光打孔。激光打孔以其易维护、可异形孔加工、效率高、生产成本低等优势得到各大玻璃厂的认可。通过分析在实际生产中激光打孔出现的打孔缺陷问题,提出了改善措施,有助于工厂的降本增效。  相似文献   
2.
针对现有基于视频监控的人流量统计方案成本高、算法复杂且不利于个人隐私保护的局限性,利用毫米波雷达体积小、成本低、分辨率高的特点,提出了一种基于双时间点检测的人流量监测方法。该方法先获取人体目标散射点位置和多普勒频移信息来构成点云数据,然后根据多普勒频移正负来判断人体的运动方向,并筛选具有高多普勒频移值的点云数据以降低干扰点对聚类结果的影响;在双时间点对特定区域内人员数量进行统计,并根据双时间点之间所获取的点云数据聚类结果对所统计人员数据进行修正。实验结果表明,该方法能够用匿名的方式以较高的正确率统计人员进出。  相似文献   
3.
摘 要:为了提高码索引调制(code index modulation,CIM)系统的传输效率,提出了一种具有更低复杂度的单输入单输出(single input single output,SISO)的广义正交码索引调制(generalized orthogonal code index modulation,GQCIM)系统。CIM 系统使用扩频码和星座符号传输信息,但只能激活两个扩频码索引和一个调制符号。而 GQCIM 系统以一种新颖的方式克服了只激活一个调制符号的限制,同时充分利用了调制符号的正交性,增加扩频码索引以传输更多的额外信息位,提高了系统的传输效率。此外,分析了GQCIM系统的理论性能,推导了误码率性能的上界。通过蒙特卡罗仿真验证了GQCIM系统的性能,对比发现GQCIM系统的理论和仿真性能一致。而且在相同的传输效率下,结果显示GQCIM系统的性能优于同样具有正交性的调制系统,如广义码索引调制(generalized code index modulation,GCIM)系统、CIM系统、码索引调制-正交空间调制(code index modulation aided quadrature spatial modulation,CIM-QSM)系统、码索引调制-正交空间调制(code index modulation aided spatial modulation,CIM-SM)系统、脉冲索引调制(pulse index modulation,PIM)系统。  相似文献   
4.
《Ceramics International》2022,48(7):9124-9133
The main obstacles in lithium-ion battery are limited by rate performance and the rapid capacity fading of LiNi0.8Co0.1Mn0.1O2 (NCM811). Herein, a novel three-dimensional (3D) hierarchical coating material has been fabricated by in situ growing carbon nanotubes (CNTs) on the surfaces of Ni–Al double oxide (Ni–Al-LDO) sheets (named as LDO&CNT) with Ni–Al double hydroxide (Ni–Al-LDH) as both the substrate and catalyst precursor. The resultant LDO&CNT nanocomposites are uniformly coated on the surfaces of NCM811 by the physical mixing method. The rate capability of the resultant cathode material retains to 78.80% at a current rate of 3C. Its capacity retention increases by 6.7–14.42% compared with pristine NCM811 after 100 cycles within a potential range of 2.75–4.3 V at 0.5C. The improved rate capability and cycle performance of NCM811 are assigned to the synergistic effects between Ni–Al-LDO and CNTs. The hierarchical LDO&CNT nanocomposites coating on the surface of NCM811 avoids the aggregation of conductive CNTs and the stacking of Ni–Al-LDO nanosheets. Furthermore, it accelerates Li+ and electrons shuttle and reduces the reaction of Li2O with H2O and CO2 in air, which results in Li2CO3 and LiOH alkali formation on the NCM811 surface.  相似文献   
5.
In this paper, Zn-doped VO2 nanoparticles have been successfully fabricated by a two-step hydrothermal-annealing process, and the thermally induced visible light transmittance enhancement of Zn-doped VO2 has been studied for the first time. It is found that Zn-doped VO2 not only exhibits excellent solar modulation ability (ΔTsol = 15.27%) but also can reduce the phase transition temperature and increase the visible light transmittance after the heat-induced phase transition (ΔTlum=+5.78%). Moreover, with the increase of Zn doping concentration, the phase transition temperature (Tc) and phase transition hysteresis (ΔT) both decrease. It is shown that the Zn-doped VO2-PU films not only have good solar light modulation ability and properties of improving visible light transmission after phase transition, but also have good durability. The research result is of great significance for improving the visible light transmittance after phase transition and realizing the practical application of VO2 in the field of smart windows.  相似文献   
6.
The long-underestimated role of extracellular vesicles in cancer is now reconsidered worldwide by basic and clinical scientists, who recently highlighted novel and crucial activities of these moieties. Extracellular vesicles are now considered as king transporters of specific cargoes, including molecular components of parent cells, thus mediating a wide variety of cellular activities both in normal and neoplastic tissues. Here, we discuss the multifunctional activities and underlying mechanisms of extracellular vesicles in neuroblastoma, the most frequent common extra-cranial tumor in childhood. The ability of extracellular vesicles to cross-talk with different cells in the tumor microenvironment and to modulate an anti-tumor immune response, tumorigenesis, tumor growth, metastasis and drug resistance will be pinpointed in detail. The results obtained on the role of extracellular vesicles may represent a panel of suggestions potentially useful in practice, due to their involvement in the response to chemotherapy, and, moreover, their ability to predict resistance to standard therapies—all issues of clinical relevance.  相似文献   
7.
采用光学显微镜(OM)、电子背散射衍射(EBSD)等研究了铌对取向硅钢冷轧过程中的组织与织构的影响。结果表明:含铌正火板和不含铌正火板经冷轧后都是条带状组织,但含铌冷轧板在宽度方向更窄。铌元素的存在对织构也具有优化作用,经过中间退火后,含铌冷轧板二次冷轧织构得到明显改善,相较于不含铌二次冷轧板拥有强度较低的旋转立方织构以及强度较高的{111}<112>织构,其取向密度最高可达12.460。  相似文献   
8.
Lead-free relaxor ferroelectrics (Ca0.28Ba0.72)2.1Na0.8Nb5-xSbxO15 (CBNNS) and (Ca0.28Ba0.72)2.1Na0.8Nb5-yTayO15 (CBNNT) with tungsten bronze structure were fabricated via solid-state reactions. The obtained CBNNS and CBNNT ceramics showed different dielectric behaviors. Only the CBNNS ceramics revealed an intensified diffusion and relaxor-like characteristics, which could be verified by the modified Curie–Weiss law. The relaxor behaviors in CBNNS were attributed to the radii difference between Sb5+ and Nb5+ ions co-occupying in B-sites. For the substitution of Nb5+ by Sb5+ in CBNNS ceramics, the change from macroscopic polarization to local polarization could also give rise to the obvious relaxor behavior. The Raman spectra verified a larger off-centering of the cation and a higher distortion degree for BO6 octahedron in the ab plane for CBNNS ceramics when compared with those of CBNNT. In addition, the ferroelectric properties of CBNNS ceramics further indicated the relaxor ferroelectric nature, and also confirmed that the relaxor behavior helped to improve the energy-storage performance.  相似文献   
9.
张扬  王聪  张雷 《微处理机》2020,(3):43-47
永磁无刷直流电机是近些年发展起来的一种新型电机,具有效率高、调速性能好、启动转矩大等诸多优点,在运动控制领域中的应用日趋广泛。基于电机专用控制芯片MC33035,采用单片机C8051F500为主控芯片,设计一款无刷直流电机智能控制器,实现对无刷直流电机启动停止、正反转、调速、转速显示等控制。通过简要介绍无刷直流电机工作原理,使用MATLAB/Simulink对控制系统进行建模仿真,对无刷直流电机控制系统进行软、硬件设计。实验结果表明,该控制系统运行稳定,抗干扰性强,具有良好的市场应用价值。  相似文献   
10.
The importance of data processing and storage to colleges and universities is increasing day by day. However, many colleg- es and universities are still at a low level in the process of data recovery and application reduction, and its RPO and RTO indicators need to be improved by adopting the dual active technology architecture. Taking the Guizhou Vocational Technology Institute as an example, this paper focuses on the analysis of the architecture of the double active data center, aiming at the actual situation of the college, and gradually realizes multiple disaster recovery level of data level, application level and business level.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号