全文获取类型
收费全文 | 9164篇 |
免费 | 746篇 |
国内免费 | 505篇 |
专业分类
电工技术 | 477篇 |
综合类 | 562篇 |
化学工业 | 1459篇 |
金属工艺 | 599篇 |
机械仪表 | 470篇 |
建筑科学 | 686篇 |
矿业工程 | 476篇 |
能源动力 | 203篇 |
轻工业 | 492篇 |
水利工程 | 181篇 |
石油天然气 | 810篇 |
武器工业 | 77篇 |
无线电 | 1120篇 |
一般工业技术 | 1100篇 |
冶金工业 | 450篇 |
原子能技术 | 99篇 |
自动化技术 | 1154篇 |
出版年
2024年 | 58篇 |
2023年 | 171篇 |
2022年 | 337篇 |
2021年 | 430篇 |
2020年 | 368篇 |
2019年 | 311篇 |
2018年 | 297篇 |
2017年 | 334篇 |
2016年 | 293篇 |
2015年 | 411篇 |
2014年 | 439篇 |
2013年 | 607篇 |
2012年 | 585篇 |
2011年 | 632篇 |
2010年 | 547篇 |
2009年 | 520篇 |
2008年 | 446篇 |
2007年 | 483篇 |
2006年 | 469篇 |
2005年 | 416篇 |
2004年 | 273篇 |
2003年 | 232篇 |
2002年 | 184篇 |
2001年 | 172篇 |
2000年 | 182篇 |
1999年 | 230篇 |
1998年 | 192篇 |
1997年 | 145篇 |
1996年 | 130篇 |
1995年 | 117篇 |
1994年 | 106篇 |
1993年 | 66篇 |
1992年 | 62篇 |
1991年 | 48篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
为了深入地研究表面等离子(Surface Plasmon,SP)在传播方向上的太赫兹(THz)电动势,采用了在纳米线结构上对表面等离子激元(Surface Plasmon Polariton,SPP)的脉冲中电子进行整流的方法,分析了SP感应引力的整流作用,讨论了SPP横向模式在长脉冲和短脉冲情况下的电动势模型。研究结果表明,脉冲整流会产生一个幅值较大的电动势,该电动势可达10 V。由于受纳米等离子的限制,在放大过程几乎是非共振的,考虑强纳米等离子限制和纵向SPP波局域条件下,整流作用在金属表面会产生更高的局域THz电场ER,其最大强度EmR=105~106V/cm。整流后SPP脉冲表现为快速,THz场频率,带宽5~20 THz的特性。SPP脉冲中THz电动势的分析对纳米级飞秒光学场的探测,半导体设备的纳米等离子激元耦合,以及非线性THz光谱研究都具有重要意义。 相似文献
72.
Gao-Peng Dang Wen Qin Qian-Qian Wan Jun-Ting Gu Kai-Yan Wang Zhao Mu Bo Gao Kai Jiao Franklin R. Tay Li-Na Niu 《Advanced functional materials》2023,33(2):2210275
Tendon–bone interface is prevalent in the human body. It is divided into four zones: tendon (soft tissue), unmineralized fibrocartilage, mineralized fibrocartilage, and bone (hard tissue). Tendon–bone interface is characterized by a cell phenotype gradient that appears in the different zones. The cell phenotype gradients at the tendon–bone interface are orchestrated by specific intracellular molecular mechanisms, extracellular factors, immune signals, and neurovascular factors. These features have inspired scientists to design systems that mimic natural cell phenotype gradients. These biomimetic systems include the construction of cell sheets, regulation of cellular microenvironments, and the design of gradient functional scaffolds. Exploration of methods to mimic cell phenotype gradients is instructional for future clinical applications in reconstituting the tendon–bone interface. The present review elucidates the gradient composition of the tendon–bone interface. The associated regulatory mechanisms and applications are discussed, with the anticipation of creating a mise en scène for future research in interface tissue engineering. 相似文献
73.
Qian Zhang Qing Chen Fan Yang Xuemin Shen Zhisheng Niu 《IEEE network》2007,21(1):14-20
Moving toward 4G, wireless ad hoc networks receive growing interest due to users' provisioning of mobility, usability of services, and seamless communications. In ad hoc networks fading environments provide the opportunity to exploit variations in channel conditions, and transmit to the user with the currently "best" channel. In this article two types of opportunistic transmission, which leverage time diversity and multi-user diversity, respectively, are studied. Considering the co-channel interference and lack of a central controller in ad hoc networks, the "cooperative and opportunistic transmission" concept is promoted. For opportunistic transmission that exploits time diversity, it is observed that the inequality in channel contention due to the hidden terminal phenomenon tends to result in energy inefficiency. Under this design philosophy, we propose a distributed cooperative rate adaptation (CRA) scheme to reduce overall system power consumption. Taking advantage of the time-varying channel among different users/receivers and being aware of the potential contention among neighboring transmissions, we propose a QoS-aware cooperative and opportunistic scheduling (COS) scheme to improve system performance while satisfying QoS requirements of individual flows. Simulation results show that by leveraging node cooperation, our proposed schemes, CRA and COS, achieve higher network throughput and provide better QoS support than existing work 相似文献
74.
All‐in‐One Theranostic Nanoplatform Based on Hollow TaOx for Chelator‐Free Labeling Imaging,Drug Delivery,and Synergistically Enhanced Radiotherapy 下载免费PDF全文
Guosheng Song Yu Chao Yuyan Chen Chao Liang Xuan Yi Guangbao Yang Kai Yang Liang Cheng Qiao Zhang Zhuang Liu 《Advanced functional materials》2016,26(45):8243-8254
Despite extensive use of radiotherapy in cancer treatment, there has been huge demand to improve its efficacy and accuracy in tumor destruction. To this end, nanoparticle‐based radiosensitizers, particularly those with high‐Z elements, have been explored to enhance radiotherapy. Meanwhile, imaging is an essential tool prior to the individual planning of precise radiotherapy. Here, hollow tantalum oxide (H‐TaOx) nanoshells are prepared using a one‐pot template‐free method and then modified with polyethylene glycol (PEG), yielding H‐TaOx‐PEG nanoshells for imaging‐guided synergistically enhanced radiotherapy. H‐TaOx‐PEG nanoshells show strong intrinsic binding with metal ions such as Fe3+ and 99mTc4+ upon simple mixing, enabling magnetic resonance imaging and single photon emission computed tomography imaging, respectively, which are able to track in vivo distribution of those nanoshells and locate the tumor. With mesoporous shells and large cavities, those H‐TaOx‐PEG nanoshells show efficient loading of 7‐ethyl‐10‐hydroxycamptothecin (SN‐38), a hydrophobic chemotherapeutic drug. By means of the radiosensitization effect of Ta to deposit X‐ray energy inside tumors, as well as SN‐38‐induced cell cycle arrest into radiation‐sensitive phases, H‐TaOx‐PEG@SN‐38 can offer remarkable synergistic therapeutic outcome in the combined chemoradiotherapy. Without appreciable systemic toxicity, such hollow‐TaOx nanostructure may therefore find promising applications in multimodal imaging and enhanced cancer radiotherapy. 相似文献
75.
支持向量机算法及应用 总被引:13,自引:4,他引:13
系统介绍了统计学习理论和支持向量机的基本思想,总结、比较了二分类和多分类2种情况下支持向量机的主要训练算法。与人工神经网络相比,分析了支持向量机的优点。归纳了支持向量机在模式识别、函数逼近、时间序列预测、故障预测和识别、信息安全、电力系统以及电力电子中的应用。 相似文献
76.
In this paper, we study scheduling schemes for two‐user two‐way wireless relaying systems. Two transmission modes are considered: point‐to‐point direct transmission and two‐way amplify‐and‐forward relaying. An optimal scheduling scheme that opportunistically selects the best transmission mode for each user is proposed to minimize the sum bit error rate (BER). The performance lower bound of the optimal scheduling scheme is analyzed, and closed‐form expression of the lower‐bound BER is derived. However, for optimal scheduling, the scheduler requires the knowledge of channel state information (CSI) of all links. To reduce the feedback information of CSI, we also propose a suboptimal scheduling scheme that selects the transmission mode using only the CSI of two direct links. Simulation results show that there are 4 dB to 8 dB gains for the proposed optimal and suboptimal schemes over the fixed direct transmission and fixed two‐way relayed transmission scheme. The performance gap between the optimal and suboptimal scheduling schemes is small, which implies a good trade‐off between implementation complexity and system performance. 相似文献
77.
Self‐Powered Trajectory,Velocity, and Acceleration Tracking of a Moving Object/Body using a Triboelectric Sensor 下载免费PDF全文
Fang Yi Long Lin Simiao Niu Jin Yang Wenzhuo Wu Sihong Wang Qingliang Liao Yue Zhang Zhong Lin Wang 《Advanced functional materials》2014,24(47):7488-7494
Motion tracking is of great importance in a wide range of fields such as automation, robotics, security, sports and entertainment. Here, a self‐powered, single‐electrode‐based triboelectric sensor (TES) is reported to accurately detect the movement of a moving object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the movement of an object on the top surface of a polytetrafluoroethylene (PTFE) layer induces changes in the electrical potential of the patterned aluminum electrodes underneath. From the measurements of the output performance (open‐circuit voltage and short‐circuit current), the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values. Moreover, the TES can detect motions of more than one objects moving at the same time. In addition, applications of the TES are demonstrated by using LED illuminations as real‐time indicators to visualize the movement of a sliding object and the walking steps of a person. 相似文献
78.
通过应用多次Al离子注入和CVD中的高温退火技术,在SiC片表面形成了p型层。p型层中各深度下Al的浓度均为11019cm-3,层厚为550nm。本文应用三种不同的退火工艺对注入后的SiC进行退火。通过测量和比较表面粗糙度,发现通过石墨层覆盖来保护表面的退火工艺可以很好的阻止SiC表面在高温退火下的粗化,粗糙度保持在3.8nm。通过其他两种(在氩气保护下、在SiC保护片的覆盖下)退火工艺退火所得到的表面有明显的台阶,粗糙度分别为12.2nm和6.6nm。 相似文献
79.
80.
介绍了中国移动多媒体广播CMMB基本情况,对CMMB地面覆盖进行了初步探讨,对CMMB单频网的组建方式、建网要求等作了简要论述。 相似文献