全文获取类型
收费全文 | 1291篇 |
免费 | 76篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 26篇 |
综合类 | 1篇 |
化学工业 | 333篇 |
金属工艺 | 13篇 |
机械仪表 | 17篇 |
建筑科学 | 38篇 |
矿业工程 | 1篇 |
能源动力 | 50篇 |
轻工业 | 214篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 88篇 |
一般工业技术 | 246篇 |
冶金工业 | 72篇 |
原子能技术 | 14篇 |
自动化技术 | 247篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 77篇 |
2021年 | 91篇 |
2020年 | 45篇 |
2019年 | 43篇 |
2018年 | 40篇 |
2017年 | 41篇 |
2016年 | 53篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 81篇 |
2012年 | 87篇 |
2011年 | 102篇 |
2010年 | 79篇 |
2009年 | 75篇 |
2008年 | 69篇 |
2007年 | 59篇 |
2006年 | 59篇 |
2005年 | 38篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 27篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1369条查询结果,搜索用时 15 毫秒
101.
G. Campi C. Dell'omo D. Di Castro S. Agrestini M. Filippi G. Bianconi L. Barba A. Cassetta M. Colapietro N. L. Saini A. Bianconi 《Journal of Superconductivity and Novel Magnetism》2004,17(1):137-142
Structural properties of La2CuO4.1 single crystal are studied by high-resolution synchrotron X-ray diffraction as a function of temperature and of X-ray fluence. Superstructures with a periodicity 2, along the c axis, due to a 3D long-range oxygen ordering, have been observed. The temperature-dependent study has allowed us to distinguish two order–disorder phase transitions, at 350 and 375 K for two different ordered phases, respectively. After rapid quenching from 380 to 100 K we were able to induce disorder-to-order-like transition because of a 2D rearrangement of the excess oxygen atoms in the temperature range of 130–180 K. The oxygen ordering could also be produced by X-ray beam illumination; a clear signature of X-ray-photo-induced phase transition has been found by placing the sample under high X-ray flux at 300 and 220 K. 相似文献
102.
Scintillation and beam-wander analysis in an optical ground station-satellite uplink 总被引:4,自引:0,他引:4
In an optical communication link between an optical ground station and a geostationary satellite the main problems appear in the uplink and are due to beam wander and to scintillation. Reliable methods for modeling both effects simultaneously are needed to provide an accurate tool with which the robustness of the communication channel can be tested. Numerical tools, especially the split-step method (also referred to as the fast-Fourier-transform beam propagation method), have demonstrated their ability to deal with problems of optical propagation during atmospheric turbulence. However, obtaining statistically significant results with this technique is computationally intensive. We present an analytical-numerical hybrid technique that provides good information on the variance in optical irradiance with an important saving of time and computational resources. 相似文献
103.
We evaluate the use of a smoothed space-frequency distribution (SSFD) to retrieve optical phase maps in digital speckle pattern interferometry (DSPI). The performance of this method is tested by use of computer-simulated DSPI fringes. Phase gradients are found along a pixel path from a single DSPI image, and the phase map is finally determined by integration. This technique does not need the application of a phase unwrapping algorithm or the introduction of carrier fringes in the interferometer. It is shown that a Wigner-Ville distribution with a smoothing Gaussian kernel gives more-accurate results than methods based on the continuous wavelet transform. We also discuss the influence of filtering on smoothing of the DSPI fringes and some additional limitations that emerge when this technique is applied. The performance of the SSFD method for processing experimental data is then illustrated. 相似文献
104.
A simplified dynamic model for fuel cells is developed, based on the concept of instantaneous characteristic, which is the set of values of current and voltage that a fuel cell can reach instantaneously. This is used to derive a theorem that indicates the conditions under which the power output of fuel cells can, in theory, be perfectly controlled. A fuel cell connected to a DC/DC converter is simulated numerically, with a control system based on switching rules in order to control the converter’s output voltage. The resulting transients settle in about 5–10 ms. The converter is then used as an actuator in a cascade control loop to control the torque output of a DC electric motor with a PI controller in the external loop. In this loop, the resulting in transients settle in less than 0.2 s. 相似文献
105.
Federico González María-Elena Villafuerte-Castrejón Alfonso Huanosta 《Journal of Electroceramics》2007,18(3-4):323-327
A Pb0.98Eu0.02(ZryTi1−y
)0.995O3 compound series, with y = 0.60, 0.53 and 0.45 was prepared. PZT samples were synthesized by sol–gel technique. The crystallization and quality of
the compounds were analyzed by powder X-ray diffraction and electron microscopy. The shape of the ε′(ω) vs T curves can be considered typical of a ferro-paraelectric transition. The ferro-paraelectric transition temperature
for each composition was 348, 328 and 307°C, for the y = 0.45, 0.53 and 0.60, respectively. σ′(ω) is strongly influenced by short range processes. For the logσ′(ω) curves as function of temperature, there is evidence of a non dispersive dc-conductivity component for the high temperature
region. The associated dc-activation energies are larger than those calculated for the ac region (at lower temperatures). 相似文献
106.
G. Campi T. Proffen X. Qiu E. S. Bozin S. J. L. Billinge S. Agrestini N. L. Saini A. Bianconi 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):505-510
We have studied temperature evolution of the local as well as the average crystal structure of MgB2 and Mg0.5Al0.5B2 using real-space atomic pair distribution function (PDF) measured by high resolution neutron powder diffraction in a wide
temperature range of T=10–600 K. The mean square relative displacements (MSRD) of atomic B–B, B–Mg (B–Al) pairs are compared with mean-square displacements
(MSD) to calculate atomic correlations. In spite of the enhanced atomic disorder in Mg0.5Al0.5B2, where the boron–boron, and boron–magnesium pair motions are found to be small, we find that the same atomic correlations
in MgB2 assume even slightly lower values and remain nearly constant in a wide temperature range of 0–600 K. This anomalous behavior
and its physical interpretation provoke new questions on our understanding to the local lattice dynamics in this material. 相似文献
107.
Chenglin Yan Haiguang Zhao Dmitrii F. Perepichka Federico Rosei 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(29):3888-3907
Lanthanide doped upconverting nanoparticles (UCNPs) have emerged as a new class of luminescent materials, with major discoveries and overall significant progress during the last decade. Unlike multiphoton absorption in organic dyes or semiconductor quantum dots, lanthanide doped UCNPs involve real intermediate quantum states and convert infrared (IR) into visible light via sequential electronic excitation. The relatively high efficiency of this process even at low radiation flux makes UCNPs particularly attractive for many current and emerging areas of technology. The aim of this article is to highlight several recent advances in this rapidly growing field, emphasizing the relationships between structure and properties of UCNPs. Additionally, various strategies developed for the synthesis of UCNPs with a focus on the various synthetic approaches that yield high‐quality monodisperse samples with controlled size, shape and crystalline phase are reviewed. Emerging synthetic approaches towards designed structure to improve the optical and electronic properties of UCNPs are discussed. Finally, recent examples of applications of UCNPs in biomedical and optoelectronics research, giving our own perspectives on future directions and emerging possibilities of the field are described. 相似文献
108.
Isabel F. Cruz Matteo Palmonari Federico Caimi Cosmin Stroe 《Artificial Intelligence Review》2013,40(2):127-145
The creation of links between schemas of published datasets is a key part of the Linked Open Data (LOD) paradigm. The ability to discover these links “on the go” requires that ontology matching techniques achieve good precision and recall within acceptable execution times. In this paper, we add similarity-based and mediator-based ontology matching methods to the Agreementmaker ontology matching system, which aim to efficiently discover high precision subclass mappings between LOD ontologies. Similarity-based matching methods discover subclass mappings by extrapolating them from a set of high quality equivalence mappings and from the interpretation of compound concept names. Mediator-based matching methods discover subclass mappings by comparing polysemic lexical annotations of ontology concepts and by considering external web ontologies. Experiments show that when compared with a leading LOD approach, Agreementmaker achieves considerably higher precision and F-measure, at the cost of a slight decrease in recall. 相似文献
109.
Marco Alberti Marco Gavanelli Evelina Lamma Federico Chesani Paola Mello Paolo Torroni 《Applied Artificial Intelligence》2013,27(2-4):133-157
In open societies of agents, where agents are autonomous and heterogeneous, it is not realistic to assume that agents will always act so as to comply with interaction protocols. Thus, the need arises for a formalism to specify constraints on agent interaction, and for a tool able to observe and check for agent compliance with interaction protocols. In this paper we present a JAVA-PROLOG software component built on logic programming technology, which can be used to verify compliance of agent interaction to protocols, and that has been integrated with the PROSOCS platform. 相似文献
110.
Evaluation of Reliability Indicators for WDNs with Demand-Driven and Pressure-Driven Models 总被引:1,自引:1,他引:0
Tonino Liserra Marco Maglionico Valentina Ciriello Vittorio Di Federico 《Water Resources Management》2014,28(5):1201-1217
Reliability of water distribution networks (WDNs) has received much attention in recent years due to progressive aging of infrastructures and climate change. Several reliability indicators, focusing on hydraulic aspects rather than water quality, have been proposed in literature. Reliability is generally assessed resorting to well established methods coupling hydraulic simulations and stochastic techniques that describe the WDNs hydraulic performance and component availability respectively. Two main algorithms are employed to simulate WDNs: the demand driven approach (DDA) that disregards the physical relationship between actual water demand and nodal pressure, and the pressure driven approach (PDA) that explicitly incorporates it. In this paper, we show how the choice of hydraulic solver may affect reliability indicators. We modify existing quantitative indicators at nodal and network level, and define novel indicators to consider water quality aspects. These indicators are evaluated for three example WDNs; discrepancies between results obtained with the two approaches depend on network size, feeding scheme and skeletonization. Results suggest to use with caution the DDA for reliability assessment at both local and global level. 相似文献