全文获取类型
收费全文 | 1837篇 |
免费 | 55篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 60篇 |
综合类 | 4篇 |
化学工业 | 421篇 |
金属工艺 | 54篇 |
机械仪表 | 33篇 |
建筑科学 | 94篇 |
矿业工程 | 18篇 |
能源动力 | 40篇 |
轻工业 | 282篇 |
水利工程 | 12篇 |
石油天然气 | 3篇 |
无线电 | 85篇 |
一般工业技术 | 272篇 |
冶金工业 | 273篇 |
原子能技术 | 13篇 |
自动化技术 | 231篇 |
出版年
2022年 | 26篇 |
2021年 | 36篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 37篇 |
2017年 | 21篇 |
2016年 | 46篇 |
2015年 | 47篇 |
2014年 | 42篇 |
2013年 | 70篇 |
2012年 | 52篇 |
2011年 | 83篇 |
2010年 | 67篇 |
2009年 | 55篇 |
2008年 | 65篇 |
2007年 | 76篇 |
2006年 | 41篇 |
2005年 | 47篇 |
2004年 | 42篇 |
2003年 | 41篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 35篇 |
1998年 | 65篇 |
1997年 | 42篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1975年 | 25篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有1895条查询结果,搜索用时 15 毫秒
121.
The paper discusses how physically based material models can contribute to the development and optimization of new materials. In combination with using enhanced simulation techniques such as density functional theory a true multi scale material development can be established. 相似文献
122.
This paper explores the role of distant knowledge links and policy actions for the development of biotechnology clusters. It seeks to challenge the prevailing view that the birth and early development of high technology industries are always spontaneous phenomena which are mainly based on local knowledge. Departing from the theoretical concept of regional innovation systems (RIS), a distinction between “RIS with strong potentials for high technology industries” and “RIS with weak potentials for high technology industries” will be drawn. It will be argued that in the latter case the development of biotechnology clusters is more dependent on distant knowledge sources and proactive policy efforts to create a favourable environment for high technology activities. Furthermore, it will be shown that a far-reaching transformation of the regional innovation system is crucial for catching-up processes of regions which are latecomers in high technology sectors such as biotechnology. 相似文献
123.
The atomic structure of Al–5 wt.%Mn (Al–5Mn) alloy, prepared by rapid solidification, and pre-annealed at 623 and 773 K for
5 and 1 h, respectively, were characterized by X-ray powder diffraction (XRD) and extended X-ray absorption fine structure
(XAFS) techniques. The sample in as-quenched stage was found crystalline, consisting of metastable α-Al (Al–Mn solid solution)
and icosahedral quasicrystalline I-Al6Mn phases. Five hours annealing at 623 K proved thermal stability of both the phases. Pre-annealing at 773 K/1 h on the other
hand leads to α-Al phase decomposition and structural transformation of metastable I-Al6Mn to stable orthorhombic Al6Mn phase. The EXAFS results indicate that Mn atoms are located preferably on the outer shell of icosahedrons. During the I-Al6Mn→o-Al6Mn transformation the total Al atoms coordinating one Mn were found to be constant (∼10). Based on the results, only distance/symmetry
changes in atomic arrangement around Mn atoms were suggested. 相似文献
124.
Digital implementation of ultra-wideband receivers requires analog-to-digital conversion (ADC) at an extremely high speed, thereby limiting the available bit resolution. Herein, the effect of low bit resolution quantization on the performance of UWB transmitted reference receivers is investigated. It is verified that the gain of the automatic-gain-control (AGC) has a significant effect on the achievable performance. Because of the considerable performance loss of conventional transmitted reference receivers in the presence of a low resolution ADC a new family of receiver structures optimized and tailored to quantized observations is presented. In particular, the generalized- likelihood ratio test (GLRT) based on the quantized samples is derived and shown to provide modest performance gains relative to the infinite resolution GLRT rule employed on the quantized received signal suggesting that conventional receiver structures can also be employed in the presence of a low resolution ADC. Results reveal that four bits of resolution in combination with an optimal choice for the AGC gain are sufficient to closely approach the performance of an infinite resolution receiver. 相似文献
125.
Localized Synthesis of Iron Oxide Nanowires and Fabrication of High Performance Nanosensors Based on a Single Fe2O3 Nanowire 下载免费PDF全文
Oleg Lupan Vasile Postica Niklas Wolff Oleksandr Polonskyi Viola Duppel Victor Kaidas Eugen Lazari Nicolai Ababii Franz Faupel Lorenz Kienle Rainer Adelung 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(16)
A composed morphology of iron oxide microstructures covered with very thin nanowires (NWs) with diameter of 15–50 nm has been presented. By oxidizing metallic Fe microparticles at 255 °C for 12 and 24 h, dense iron oxide NW networks bridging prepatterned Au/Cr pads are obtained. X‐ray photoelectron spectroscopy studies reveal formation of α‐Fe2O3 and Fe3O4 on the surface and it is confirmed by detailed high‐resolution transmission electron microscopy and selected area electron diffraction (SAED) investigations that NWs are single phase α‐Fe2O3 and some domains of single phase Fe3O4. Localized synthesis of such nano‐ and microparticles directly on sensor platform/structure at 255 °C for 24 h and reoxidation at 650 °C for 0.2–2 h, yield in highly performance and reliable detection of acetone vapor with fast response and recovery times. First nanosensors on a single α‐Fe2O3 nanowire are fabricated and studied showing excellent performances and an increase in acetone response by decrease of their diameter was developed. The facile technological approach enables this nanomaterial as candidate for a range of applications in the field of nanoelectronics such as nanosensors and biomedicine devices, especially for breath analysis in the treatment of diabetes patients. 相似文献
126.
Pascal Friederich Velimir Meded Angela Poschlad Tobias Neumann Vadim Rodin Vera Stehr Franz Symalla Denis Danilov Reinhold F. Fink Ivan Kondov Florian von Wrochem Wolfgang Wenzel 《Advanced functional materials》2016,26(31):5757-5763
Small‐molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes to organic photovoltaics. However, the low carrier mobility severely limits their potential, e.g., for large area devices. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment, and polarizability. Presently, quantitative ab initio models to assess the influence of these molecule‐dependent properties are lacking. Here, a multiscale model is presented, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility, and allows for the decomposition of the carrier mobility into molecule‐specific quantities. Molecule‐specific quantitative measures are provided how two single molecule properties, the dependence of the orbital energy on conformation, and the dipole‐induced polarization determine mobility for hole‐transport materials. The availability of first‐principles based models to compute key performance characteristics of organic semiconductors may enable in silico screening of numerous chemical compounds for the development of highly efficient optoelectronic devices. 相似文献
127.
Mission scenarios beyond line of sight or with limited ground control station access require capabilities for autonomous safe
navigation and necessitate a continuous extension of existing and potentially outdated information about obstacles. The presented
approach is a novel synthesis of techniques for 3D environment perception and global path planning. A locally bounded sensor
fusion approach is used to extract sparse obstacles for global incremental path planning in an anytime fashion. During the
flight, a stereo camera checks the field of view along the flight path ahead by analyzing depth images. A 3D occupancy grid
is built incrementally. To reduce the high data rate and storage demands of grid-type maps, an approximated polygonal world
model is created. For a compacted representation, it uses prisms and ground planes. This enables the system to constantly
renew and update its knowledge about obstacles. An incremental heuristic path planner uses both a-priori information as well
as incremental obstacle updates to assure a collision-free path at any time. Mapping results from flight tests show the functionality
of onboard world modeling from real sensor data. Path planning feasibility is demonstrated within a simulation environment
considering world model changes inside the vehicle’s field of view. 相似文献
128.
Heat transport and void fraction in granulated debris 总被引:1,自引:0,他引:1
The paper discusses the boiling heat transfer from a porous bed with internal heat sources and refers to the configuration in a nuclear reactor after a partial core melt. The flow of coolant, the temperature and the local liquid/vapor distribution were investigated in a two-dimensional configuration. Experiments were conducted using monodisperse beds as well as a mixture of two different particle sizes with a total porosity below 20%. In some tests the bed was supported by a shell of porous material to create a gap along the bottom of the test container. Water was used for tests up to 9% of the critical pressure, while other tests were made with R134a up to 44% of the critical pressure. The maximum heating rate realized inductively was 730 kW/m2. The experiments have been compared to analytical results with a one-dimensional approach.It is shown that in contrary to the situation in small cylindrical configurations the heat transfer was increased by large buoyancy driven convective flows. If there was a gap along the container bottom an additional flow of liquid improved the coolability of the bottom region even if the upper part of the particle bed was already overheated. In case of high density ratios (water at low pressure), the measurements indicated a strong enhancement of the coolant flow above a certain minimum heating rate resulting in decreasing vapor fraction values which were nearly independent of the system pressure. This was assumed to be caused by the appearance of vertical channels through which the vapor could flow through the particle bed. 相似文献
129.
Mario Rothbauer Peter Ertl Barbara A. Theiler Magdalena Schlager Uwe B. Sleytr Seta Küpcü 《Advanced Materials Interfaces》2015,2(1)
The spatial arrangement of cells in their microenvironment is known to significantly influence cellular behavior, thus making the control of cellular organization an important parameter of in vitro co‐culture models. However, recent advances in micropatterning co‐culture methods within biochips do not address the simultaneous cultivation of anchorage‐dependent and non‐adherent cells. To address this methodological gap we combine S‐layer technology with microfluidics to pattern co‐cultures to study the cell‐to‐cell and cell‐to‐surface interactions under physiologically relevant conditions. We exploit the unique self‐assembly properties of SbpA and SbsB S‐layers to create an anisotropic protein nanobiointerface on‐chip with spatially‐defined cytophilic (adhesive) and cytophobic (repulsive) properties. While microfluidics control physical parameters such as shear force and flow velocities, our anisotropic protein nanobiointerface regulates the biological aspects of the co‐culture method including biocompatibility, biostability, and affinity to non‐adherent cells. The reliability and reproducibility of our microfluidic co‐culture strategy based on laminar flow patterned protein nanolayers is envisioned to advance in vitro models for biomedical research. 相似文献
130.
The k-nearest-neighbour (kNN) algorithm is widely applied for the estimation of forest attributes using remote sensing data. It requires a large amount of reference data to achieve satisfactory results. Usually, the number of available reference plots for the kNN-prediction is limited by the size of the area covered by a terrestrial reference inventory and remotely sensed imagery collected from one overflight. The applicability of kNN could be enhanced if adjacent images of different acquisition dates could be used in the same estimation procedure. Relative radiometric calibration is a prerequisite for this. This study focuses on two empirical calibration methods. They are tested on adjacent LANDSAT TM scenes in Austria. The first, quite conventional one is based on radiometric control points in the overlap area of two images and on the determination of transformation parameters by linear regression. The other, recently developed method exploits the kNN-cross-validation procedure. Performance and applicability of both methods as well as the impact of phenology are discussed. 相似文献