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   203224篇
  免费   25895篇
  国内免费   7373篇
电工技术   10333篇
技术理论   15篇
综合类   10740篇
化学工业   43318篇
金属工艺   9189篇
机械仪表   10653篇
建筑科学   14640篇
矿业工程   4602篇
能源动力   5409篇
轻工业   17391篇
水利工程   3193篇
石油天然气   9435篇
武器工业   1288篇
无线电   27074篇
一般工业技术   31178篇
冶金工业   8699篇
原子能技术   1844篇
自动化技术   27491篇
  2024年   816篇
  2023年   2928篇
  2022年   5055篇
  2021年   6979篇
  2020年   6425篇
  2019年   7032篇
  2018年   7674篇
  2017年   8478篇
  2016年   8236篇
  2015年   9909篇
  2014年   11490篇
  2013年   14264篇
  2012年   12890篇
  2011年   13431篇
  2010年   12404篇
  2009年   11677篇
  2008年   11285篇
  2007年   10498篇
  2006年   10420篇
  2005年   9061篇
  2004年   6569篇
  2003年   5911篇
  2002年   5649篇
  2001年   5194篇
  2000年   5032篇
  1999年   5064篇
  1998年   3852篇
  1997年   3315篇
  1996年   2993篇
  1995年   2510篇
  1994年   2033篇
  1993年   1577篇
  1992年   1294篇
  1991年   960篇
  1990年   771篇
  1989年   628篇
  1988年   491篇
  1987年   364篇
  1986年   269篇
  1985年   223篇
  1984年   149篇
  1983年   121篇
  1982年   115篇
  1981年   79篇
  1980年   72篇
  1979年   45篇
  1978年   38篇
  1977年   37篇
  1976年   48篇
  1973年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Volumetric muscle loss (VML) caused by injury or trauma affects the quality of life directly, due to its high incidence, lingering healing, and prolonged duration. Tissue engineered scaffolds have been widely used in muscle regeneration for patients with massive muscle injury. Melatonin (MLT) is a bioactive substance secreted by the pineal gland, which can promote muscle recovery by inhibiting oxidative stress and inflammation. Herein, a biocompatible scaffold is developed using thiolated hyaluronic acid (HA‐SH), collagen I (COL I), and polycaprolactone/melatonin (PCL/MLT) electrospun membranes. This scaffold mimics extracellular matrix (ECM) and architectural features of native muscle, possesses appropriate mechanical property, stiffness and promotes vascularization. It can provide adhesion sites for C2C12 cells and induce their proliferation and differentiation. Moreover, VML rat model is established to evaluate its effect on muscle regeneration. Results demonstrate that this scaffold possesses a practical application for VML.  相似文献   
992.
Metallic mesh materials are promising candidates to replace traditional transparent conductive oxides such as indium tin oxide (ITO) that is restricted by the limited indium resource and its brittle nature. The challenge of metal based transparent conductive networks is to achieve high transmittance, low sheet resistance, and small perforation size simultaneously, all of which significantly relate to device performances in optoelectronics. In this work, trilayer dielectric/metal/dielectric (D/M/D) nanomesh electrodes are reported with precisely controlled perforation size, wire width, and uniform hole distribution employing the nanosphere lithography technique. TiO2/Au/TiO2 nanomesh films with small hole diameter (≤700 nm) and low thickness (≤50 nm) are shown to yield high transmittance (>90%), low sheet resistance (≤70 Ω sq?1), as well as outstanding flexural endurance and feasibility for large area patterning. Further, by tuning the surface wettability, these films are applied as easily recyclable flexible electrodes for electrochromic devices. The simple and cost‐effective fabrication of diverse D/M/D nanomesh transparent conductive films with tunable optoelectronic properties paves a way for the design and realization of specialized transparent electrodes in optoelectronics.  相似文献   
993.
Soft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated.  相似文献   
994.
Unbalanced charge injection is deleterious for the performance of colloidal quantum dot (CQD) light‐emitting diodes (LEDs) as it deteriorates the quantum efficiency, brightness, and operational lifetime. CQD LEDs emitting in the infrared have previously achieved high quantum efficiencies but only when driven to emit in the low‐radiance regime. At higher radiance levels, required for practical applications, the efficiency decreased dramatically in view of the notorious efficiency droop. Here, a novel methodology is reported to regulate charge supply in multinary bandgap CQD composites that facilitates improved charge balance. The current approach is based on engineering the energetic potential landscape at the supra‐nanocrystalline level that has allowed to report short‐wave infrared PbS CQD LEDs with record‐high external quantum efficiency in excess of 8%, most importantly, at a radiance level of ≈5 W sr?1 m2, an order of magnitude higher than prior reports. Furthermore, the balanced charge injection and Auger recombination reduction has led to unprecedentedly high operational stability with radiance half‐life of 26 068 h at a radiance of 1 W sr?1 m?2.  相似文献   
995.
996.
With the advent of the fifth generation of mobile radio communication by 2020, there will be many challenges such as increasing service demand with low delay in providing billions of end users called the satellite mobile users. It is expected that terrestrial communication systems will be faced with a dense network having many small cells anywhere and anytime. Therefore, there are some remote regions in the world where terrestrial systems cannot provide any services to end users. Furthermore, because of lack of spectral resources, it is very important that the spectrum is shared between satellite systems and terrestrial equipment by a suitable solution to interference management. In this paper, a heterogeneous satellite network that includes low earth orbit (LEO) satellite constellation and terrestrial equipment is proposed to provide low delay services. In this type of structure, interference management based on transmission power control between LEO satellite systems and mobile users is very important for obtaining high throughput. Moreover, in order to mitigate interference, transmission power control is shown based on noncooperative Stackelberg game under many subgames through pricing‐based algorithm and convex optimization method. Finally, the simulation results show that the performance of this study's system model will be improved through the proposed algorithm.  相似文献   
997.
对硅基二氧化硅阵列波导光栅解复用器(AWG DEMUX)的偏振相关损耗(PDL)进行了优化。理论分析了引起AWG偏振相关性的物理因素以及消除偏振相关性的工艺方法和条件。利用化学气相沉积、光刻和刻蚀等半导体工艺制备了AWG DEMUX芯片,并结合理论分析对包层材料中的硼(B)、磷(P)含量进行了优化调整,成功地将芯片的PDL降低至0.12 dB,使PDL参数满足芯片的商用化需求。  相似文献   
998.
在很多应用场合,需要在System View与MATLAB之向进行数据通信。本文提出了一种以M-LINK为桥梁的通信方式,并给出了具体操作步骤。为了验证通信方式的可行性,以PCM为例,探讨如何通过M-LINK模块进行两种软件的数据通信,实现通信系统联合仿真。仿真结果表明,本文提出的通信方式是可行的。  相似文献   
999.
本文对通信机房的电磁干扰问题及相关规范做了详细的综述,并以某省通信生产楼拟建局址电磁环境的实测数据为例,对高压输变电系统对通信机房的电磁干扰影响进行分析和论证.对今后通信机房的建设及相关规范的更新与制定具有较好的参考价值.  相似文献   
1000.
基于IMS的多媒体彩铃业务的设计和实现   总被引:2,自引:0,他引:2  
多媒体彩铃(MRBT)业务是一种采用多种媒体作为回铃音的增值业务.结合IMS网络体系结构和MRBT业务属性,提出一种利用多媒体彩铃业务平台来实现MRBT业务的方案,包括系统设计和基于SIP(会话发起协议)的信令流程.同时,给出相关的特点分析并进行总结.  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