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   89187篇
  免费   7619篇
  国内免费   4074篇
电工技术   4972篇
技术理论   7篇
综合类   6306篇
化学工业   15160篇
金属工艺   5526篇
机械仪表   5583篇
建筑科学   6961篇
矿业工程   2972篇
能源动力   2717篇
轻工业   5366篇
水利工程   1639篇
石油天然气   5878篇
武器工业   726篇
无线电   9508篇
一般工业技术   10436篇
冶金工业   4578篇
原子能技术   952篇
自动化技术   11593篇
  2024年   356篇
  2023年   1369篇
  2022年   2317篇
  2021年   3369篇
  2020年   2522篇
  2019年   2307篇
  2018年   2529篇
  2017年   2789篇
  2016年   2478篇
  2015年   3365篇
  2014年   4179篇
  2013年   4897篇
  2012年   5307篇
  2011年   5788篇
  2010年   5316篇
  2009年   4997篇
  2008年   4845篇
  2007年   4776篇
  2006年   4918篇
  2005年   4174篇
  2004年   3115篇
  2003年   3310篇
  2002年   3875篇
  2001年   3257篇
  2000年   2388篇
  1999年   2489篇
  1998年   1809篇
  1997年   1508篇
  1996年   1543篇
  1995年   1229篇
  1994年   911篇
  1993年   707篇
  1992年   541篇
  1991年   384篇
  1990年   299篇
  1989年   243篇
  1988年   213篇
  1987年   125篇
  1986年   83篇
  1985年   57篇
  1984年   52篇
  1983年   38篇
  1982年   37篇
  1981年   20篇
  1980年   32篇
  1979年   7篇
  1978年   3篇
  1977年   2篇
  1974年   1篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
21.
22.
Peng  Jing  Yu  Lei  Zhong  Xiang  Dong  Tiansong 《Water Resources Management》2022,36(3):1043-1055
Water Resources Management - The low impact development (LID) concept aims to control storm runoff and pollution through decentralized, small-scale source control to bring the development area as...  相似文献   
23.
The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine.  相似文献   
24.
Sensitivity and multi-directional motivation are major two factors for developing optimized humidity-response materials, which are promising for sensing, energy production, etc. Organic functional groups are commonly used as the water sensitive units through hydrogen bond interactions with water molecules in actuators. The multi-coordination ability of inorganic ions implies that the inorganic ionic compounds are potentially superior water sensitive units. However, the particle forms of inorganic ionic compounds produced by classical nucleation limit the number of exposed ions to interact with water. Recent progress on the inorganic ionic oligomers has broken through the limitation of classical nucleation, and realized the molecular-scaled incorporation of inorganic ionic compounds into an organic matrix. Here, the incorporation of hydrophilic calcium carbonate ionic oligomers into hydrophobic poly(vinylidene fluoride) (PVDF) is demonstrated. The ultra-small calcium carbonate oligomers within a PVDF film endow it with an ultra-sensitive, reversible, and bidirectional response. The motivation ability is superior to other bidirectional humidity-actuators at present, which realizes self-motivation on an ice surface, converting the chemical potential energy of the humidity gradient from ice to kinetic energy.  相似文献   
25.
Liu  Yi  Zhou  Guihua  Chen  Guo 《Wireless Networks》2021,27(1):195-209
Wireless Networks - TCP latency is critical to the performance of Web services. However, packet loss greatly impairs the TCP performance due to its poor loss recovery mechanisms. Recent work FUSO...  相似文献   
26.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics.  相似文献   
27.
With the emergence of large-scale knowledge base, how to use triple information to generate natural questions is a key technology in question answering systems. The traditional way of generating questions require a lot of manual intervention and produce lots of noise. To solve these problems, we propose a joint model based on semi-automated model and End-to-End neural network to automatically generate questions. The semi-automated model can generate question templates and real questions combining the knowledge base and center graph. The End-to-End neural network directly sends the knowledge base and real questions to BiLSTM network. Meanwhile, the attention mechanism is utilized in the decoding layer, which makes the triples and generated questions more relevant. Finally, the experimental results on SimpleQuestions demonstrate the effectiveness of the proposed approach.  相似文献   
28.
29.
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   
30.
Networks and Spatial Economics - The relationship between shipping accessibility and maritime transport demand is studied based on the relationship between production and consumption and stochastic...  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