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   10940篇
  免费   1040篇
  国内免费   505篇
电工技术   588篇
综合类   754篇
化学工业   1877篇
金属工艺   624篇
机械仪表   676篇
建筑科学   843篇
矿业工程   288篇
能源动力   292篇
轻工业   759篇
水利工程   212篇
石油天然气   558篇
武器工业   87篇
无线电   1431篇
一般工业技术   1316篇
冶金工业   486篇
原子能技术   118篇
自动化技术   1576篇
  2024年   61篇
  2023年   202篇
  2022年   344篇
  2021年   472篇
  2020年   340篇
  2019年   294篇
  2018年   329篇
  2017年   415篇
  2016年   345篇
  2015年   374篇
  2014年   543篇
  2013年   658篇
  2012年   647篇
  2011年   694篇
  2010年   638篇
  2009年   576篇
  2008年   513篇
  2007年   556篇
  2006年   556篇
  2005年   399篇
  2004年   365篇
  2003年   491篇
  2002年   580篇
  2001年   487篇
  2000年   314篇
  1999年   263篇
  1998年   202篇
  1997年   156篇
  1996年   157篇
  1995年   112篇
  1994年   95篇
  1993年   65篇
  1992年   47篇
  1991年   51篇
  1990年   34篇
  1989年   24篇
  1988年   17篇
  1987年   12篇
  1986年   17篇
  1985年   10篇
  1984年   8篇
  1983年   6篇
  1982年   4篇
  1981年   4篇
  1980年   4篇
  1979年   3篇
  1973年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
针对目前大多数智能PID控制器存在的诸如设计复杂、计算量大、收敛速度慢以及控制精度相对较差等问题,提出一种基于混沌优化的小波神经网络免疫PID控制器的设计方法,该方法用小波神经网络逼近免疫PID的非线性函数,并且引入混沌机制优化免疫PID的参数,进而将该控制器用于工业加热炉的控制,仿真与实验结果表明,该控制器的控制性能优于其它类型的智能PID控制器以及常规PID控制器.  相似文献   
72.
Huang C  You M 《Applied ergonomics》1994,25(3):186-187
This note describes the results of research into the anthropometric measurements of women in Taiwan, for use in pantihose design.  相似文献   
73.
轨道角动量(orbital angular momentum, OAM)的引入丰富了光通信领域内的调制维度,为寻找更高效快捷的通信方式提供了新思路,相较于传统携带涡旋相位的涡旋光束,部分相干扭曲光束携带的OAM性质更为复杂。本文针对椭圆多高斯关联扭曲光束在梯度折射率(gradient-index, GRIN)光纤中的OAM传输,基于GRIN光纤的ABCD光学传输矩阵,着重分析了多高斯关联扭曲光束在GRIN光纤传输的OAM的传输演化特性。研究结果表明,光束的光强、OAM通量密度以及归一化OAM通量密度在光纤传输过程中均呈现周期性变化,通过对关联结构以及扭曲因子的调控不仅可以改变光束OAM通量密度的分布,还可以调控单光子携带OAM的大小。本文的研究有助于丰富扭曲部分相干光束在GRIN光纤中传输的理论结果,在光纤通信中具有潜在的应用前景。  相似文献   
74.
Electron–phonon interactions play an essential role in charge transport and transfer processes in semiconductors. For most structures, tailoring electron–phonon interactions for specific functionality remains elusive. Here, it is shown that, in hybrid perovskites, coherent phonon modes can be used to manipulate charge transfer. In the 2D double perovskite, (AE2T)2AgBiI8 (AE2T: 5,5“-diylbis(amino-ethyl)-(2,2”-(2)thiophene)), the valence band maximum derived from the [Ag0.5Bi0.5I4]2– framework lies in close proximity to the AE2T-derived HOMO level, thereby forming a type-II heterostructure. During transient absorption spectroscopy, pulsed excitation creates sustained coherent phonon modes, which periodically modulate the associated electronic levels. Thus, the energy offset at the organic–inorganic interface also oscillates periodically, providing a unique opportunity for modulation of interfacial charge transfer. Density-functional theory corroborates the mechanism and identifies specific phonon modes as likely drivers of the coherent charge transfer. These observations are a striking example of how electron–phonon interactions can be used to manipulate fundamentally important charge and energy transfer processes in hybrid perovskites.  相似文献   
75.
Surface chemistry and interlayer engineering determines the electrical properties of 2D MXene. However, it remains challenging to regulate the surface and interfacial chemistry of MXene simultaneously. Herein, simultaneous modulation of Ti3C2Tx MXene surface termination and layer spacing by alkali treatment are achieved. The electrical and electromagnetic properties of Ti3C2Tx are investigated in detail with respect to KOH and ammonia concentration dependence. A high concentration of KOH caused the Ti3C2Tx layer spacing to expand to 13.7 Å and the surface O/F ratio to increase to 33.84. Because of its weaker ionization effect, ammonia provides finer tuning compared to the drastic intercalation of KOH with a thorough sweeping of the F-containing groups. Ti3C2Tx is enriched with conductive -OH termination after ammonia treatment, which achieves an effective balance with the increased interlayer resistance. Therefore, NH3H2O-Ti3C2Tx achieves broad-band impedance matching and exhibits an efficient microwave loss of −49.1 dB at a low thickness of 1.7 mm, with an effective frequency bandwidth of 3.9 GHz. The results herein optimize the electrical properties of Ti3C2Tx using surface and interfacial chemistry to achieve broad microwave absorption, providing a framework for enhancing the electromagnetic wave loss of intrinsic MXene.  相似文献   
76.
The exceptional photophysical properties of 3D organic–inorganic lead halide hybrids (OILHs) endow their significant potential for usage in optoelectronics, which has sparked intense research on novel 3D OILHs and associated applications. However, constructing new 3D OILHs based on large organic cations suffers from tough challenges due to the limitation of the Goldschmidt tolerance factor rule, let alone further explorations of their practical applications. Herein, a brand-new 3D lead chloride hybrid, (1MPZ)Pb4Cl10·H2O ( 1 , 1MPZ = 1-methylpiperazine) is reported, featuring a dense 3D lead chloride framework made of the corner-, edge-, and face-shared lead chloride polyhedra. 1 presents a broadband white light emission with a large Stokes shift and a nanosecond photoluminescence lifetime, which originates from radiative recombination of self-trapped excitons (STEs) induced by the highly distorted structure. Such a reabsorption-free and fast-decayed STEs emission coupling with the dense 3D architecture further enables 1 with effective X-ray scintillation with good sensitivity. Impressively, 1 also shows superior environmental and radiation stability. This study provides a new 3D OILH with appealing luminescence, not only expanding the 3D OILH family but also inspiring the exploitation of their optoelectronic applications.  相似文献   
77.
Bismuth (Bi3+)-included lead-free metal halide (LFMH) materials attract much attention in lighting, display, photodetectors, X-ray detectors, and photovoltaic fields, due to the tunable luminescence and optoelectronic performance in response to crystal and electronic structure, morphology, and particle sizes. This review summarizes Bi3+-included LFMH materials about their preparation approach, crystal and electronic structure properties, luminescence performance, and emerging applications. Notably, Bi3+ ions not only can act as framework cation to construct stable LFMH structure, but can also incorporate into LFMH materials as activators or sensitizers to generate remarkable luminescence tuning and band engineering. The Bi3+ effect on the luminescence and optoelectronic properties of LFMH materials, including, promotion of exciton localization, enhancement of light absorption in near-ultraviolet region, action as sensitizer ions to transfer energy to rare earth or transition metal ions and emission of highly-efficient light is systematically summarized. The proposed structure-luminescence relationship offers guidance for the optimization of current Bi3+-included LFMH materials and the exploitation of new LFMH derivatives.  相似文献   
78.
目前,以资源优化可利用和绿色出行为理念的共享经济蓬勃发展,基于此,本发明针对用户遇到突发性降雨天气时对雨伞临时需求,本文设计并实现了一款共享雨伞。本设计发明设计一类伞上装有电子标签的雨伞及雨伞借还系统,使用射频识别技术读取电子标签,使用Java技术编写微信小程序,利用STM32单片机控制伞桩的内部运行,便捷用户突遇突发性天气时及时满足用户对伞的需求,还提高社会资源的利用率。  相似文献   
79.
Recently, interspecies quorum quenching (QQ) by bacteria has been reported as a novel approach in biofouling control in membrane bioreactor (MBR) for wastewater treatment. In this study, seven QQ bacteria, named RO1 to RO7, were isolated from fouling reverse osmosis (RO) membrane and were encapsulated in the microbial filters for biofouling control in MBR. Results showed that all isolates have extracellular QQ activity, and RO1 to RO6 were characterized as heat-stable enzymatic degradation of N-acyl homoserine lactones (AHLs), while RO7 was mainly pH-dependent. Analysis of the 16S rRNA gene indicated that RO7 was a species of Pseudomonas sp., others belonged to the species of Bacillus, Stenotrophomonas maltophilia and Delftia tsuruhatensis, respectively. Then, the microbial filters encapsulated each isolate were applied in a laboratory-scaled MBR and proved the substantial inhibition effect on membrane biofouling except for RO7, indicating that QQ bacteria employing enzymes to degrade AHLs have great potential in biofouling control in MBR.  相似文献   
80.
The self‐assembly of amyloidogenic peptides into β‐sheet‐rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimer's disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid‐associated neurotoxicity. This study reports that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimer's β‐amyloid (Aβ) self‐assembly and function as a β‐sheet breaker disintegrating preformed Aβ aggregates. This study synthesizes CDs using ammonium citrate through one‐pot hydrothermal treatment and passivates their surface with branched polyethylenimine (bPEI). The bPEI‐coated CDs (bPEI@CDs) exhibit hydrophilic and cationic surface characteristics, which interact with the negatively charged residues of Aβ peptides, suppressing the aggregation of Aβ peptides. Under light illumination, bPEI@CDs display a more pronounced effect on Aβ aggregation and on the dissociation of β‐sheet‐rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. The light‐triggered attenuation effect of Aβ aggregation using a series of experiments, including photochemical and microscopic analysis, is verified. Furthermore, the cell viability test confirms the ability of photoactivated bPEI@CDs for the suppression of Aβ‐mediated cytotoxicity, indicating bPEI@CDs' potency as an effective anti‐Aβ neurotoxin agent.  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