全文获取类型
收费全文 | 16520篇 |
免费 | 109篇 |
国内免费 | 484篇 |
专业分类
电工技术 | 240篇 |
综合类 | 83篇 |
化学工业 | 1766篇 |
金属工艺 | 591篇 |
机械仪表 | 903篇 |
建筑科学 | 974篇 |
矿业工程 | 329篇 |
能源动力 | 100篇 |
轻工业 | 3332篇 |
水利工程 | 329篇 |
石油天然气 | 303篇 |
武器工业 | 69篇 |
无线电 | 860篇 |
一般工业技术 | 5948篇 |
冶金工业 | 323篇 |
原子能技术 | 164篇 |
自动化技术 | 799篇 |
出版年
2021年 | 38篇 |
2018年 | 19篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 45篇 |
2014年 | 57篇 |
2013年 | 78篇 |
2012年 | 1785篇 |
2011年 | 2326篇 |
2010年 | 488篇 |
2009年 | 235篇 |
2008年 | 1482篇 |
2007年 | 1397篇 |
2006年 | 1144篇 |
2005年 | 1021篇 |
2004年 | 880篇 |
2003年 | 693篇 |
2002年 | 676篇 |
2001年 | 533篇 |
2000年 | 563篇 |
1999年 | 372篇 |
1998年 | 211篇 |
1997年 | 187篇 |
1996年 | 166篇 |
1995年 | 139篇 |
1994年 | 159篇 |
1993年 | 127篇 |
1992年 | 121篇 |
1991年 | 151篇 |
1990年 | 153篇 |
1989年 | 155篇 |
1988年 | 124篇 |
1987年 | 142篇 |
1986年 | 116篇 |
1985年 | 156篇 |
1984年 | 150篇 |
1983年 | 154篇 |
1982年 | 137篇 |
1981年 | 105篇 |
1980年 | 97篇 |
1979年 | 98篇 |
1978年 | 52篇 |
1977年 | 24篇 |
1976年 | 33篇 |
1975年 | 33篇 |
1974年 | 25篇 |
1973年 | 18篇 |
1965年 | 25篇 |
1964年 | 25篇 |
1958年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are
reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates
by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier
transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of
the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron
microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously
exhibited PL from Si-np and Nd3+ demonstrating the efficient energy transfer between Si-np and Nd3+ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive
quenching of the Nd3+ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments.
Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested
that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd3+. 相似文献
992.
Helfrich M Gröger R Förste A Litvinov D Gerthsen D Schimmel T Schaadt DM 《Nanoscale research letters》2011,6(1):211
In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum
dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning
of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed
at the end of sample preparation in order to get rid of remaining organic contamination. 相似文献
993.
994.
Dominiczak M Otubo L Alamarguy D Houzé F Volz S Noël S Bai J 《Nanoscale research letters》2011,6(1):335
Using an atomic force microscope (AFM) at a controlled contact force, we report the electrical signal response of multi-walled carbon nanotubes (MWCNTs) disposed on a golden thin film. In this investigation, we highlight first the theoretical calculation of the contact resistance between two types of conductive tips (metal-coated and doped diamond-coated), individual MWCNTs and golden substrate. We also propose a circuit analysis model to schematize the «tip-CNT-substrate» junction by means of a series-parallel resistance network. We estimate the contact resistance R of each contribution of the junction such as Rtip-CNT, RCNT-substrate and Rtip-substrate by using the Sharvin resistance model. Our final objective is thus to deduce the CNT intrinsic radial resistance taking into account the calculated electrical resistance values with the global resistance measured experimentally. An unwished electrochemical phenomenon at the tip apex has also been evidenced by performing measurements at different bias voltages with diamond tips. For negative tip-substrate bias, a systematic degradation in color and contrast of the electrical cartography occurs, consisting of an important and non-reversible increase of the measured resistance. This effect is attributed to the oxidation of some amorphous carbon areas scattered over the diamond layer covering the tip. For a direct polarization, the CNT and substrate surface can in turn be modified by an oxidation mechanism. 相似文献
995.
Hernandez-Ramirez F Prades JD Hackner A Fischer T Mueller G Mathur S Morante JR 《Nanoscale》2011,3(2):630-634
Gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. These devices were found to work at much lower temperatures (T≈280 °C) and bias voltages (V≈2 V) than their micro-counterparts, thereby demonstrating the inherent potential of individual nanostructures in building functional nanodevices. High selectivity of our miniaturized sensors emerges from the dissimilar sensing mechanisms of those typical of standard resistive-type sensors (RES). Therefore, by employing this detection principle (SI) together with RES measurements, better selectivity than that observed in standard metal oxide sensors could be demonstrated. Simplicity and specificity of the gas detection as well as low-power consumption make these single nanowire devices promising technological alternatives to overcome the major drawbacks of solid-state sensor technologies. 相似文献
996.
Evidence that nanoscale surface properties stimulate and guide various molecular and biological processes at the implant/tissue interface is fostering a new trend in designing implantable metals. Cutting-edge expertise and techniques drawn from widely separated fields, such as nanotechnology, materials engineering and biology, have been advantageously exploited to nanoengineer surfaces in ways that control and direct these processes in predictable manners. In this review, we present and discuss the state-of-the-art of nanotechnology-based approaches currently adopted to modify the surface of metals used for orthopedic and dental applications, and also briefly consider their use in the cardiovascular field. The effects of nanoengineered surfaces on various in vitro molecular and cellular events are firstly discussed. This review also provides an overview of in vivo and clinical studies with nanostructured metallic implants, and addresses the potential influence of nanotopography on biomechanical events at interfaces. Ultimately, the objective of this work is to give the readership a comprehensive picture of the current advances, future developments and challenges in the application of the infinitesimally small to biomedical surface science. We believe that an integrated understanding of the in vitro and particularly of the in vivo behavior is mandatory for the proper exploitation of nanostructured implantable metals and, indeed, of all biomaterials. 相似文献
997.
Song J Chen M Olesen MB Wang C Havelund R Li Q Xie E Yang R Bøggild P Wang C Besenbacher F Dong M 《Nanoscale》2011,3(12):4966-4971
Core-sheath silver nanowire/polyvinylpyrrolidone (AgNW/PVP) nanocables have been fabricated via an efficient single-spinneret electrospinning method. The core-sheath structure is revealed by combining several characterization methods. A possible formation mechanism of the AgNW/PVP nanocable involving a strong stretching during the electrospinning process is proposed. Further, electrical measurements were performed on AgNW/PVP nanocables as well as bare AgNWs, which indicated the nanocables became insulating due to the isolation of highly conductive AgNWs by insulating PVP sheath. Therefore, the described fabrication method holds potential for the fabrication of low-cost metal/polymer composite materials for nanoelectronic applications in general. 相似文献
998.
In this article, a scanning probe method based on nanoscale capacitance measurements was used to investigate the lateral homogeneity
of the electron mean free path both in pristine and ion-irradiated graphene. The local variations in the electronic transport
properties were explained taking into account the scattering of electrons by charged impurities and point defects (vacancies).
Electron mean free path is mainly limited by charged impurities in unirradiated graphene, whereas an important role is played
by lattice vacancies after irradiation. The local density of the charged impurities and vacancies were determined for different
irradiated ion fluences. 相似文献
999.
New Si-based multilayers for solar cell applications 总被引:1,自引:0,他引:1
In this article, we have fabricated and studied a new multilayer structure Si-SiO2/SiN
x
by reactive magnetron sputtering. The comparison between SiO2 and SiN
x
host matrices in the optical properties of the multilayers is detailed. Structural analysis was made on the multilayer structures
using Fourier transform infrared spectroscopy. The effect of specific annealing treatments on the optical properties is studied
and we report a higher visible luminescence with a control over the thermal budget when SiO2 is replaced by the SiN
x
matrix. The latter seems to be a potential candidate to replace the most sought SiO2 host matrix. 相似文献
1000.
Iron oxide/SnO(2) magnetic semiconductor core-shell heterostructures with high purity were synthesized by a low-cost, surfactant-free and environmentally friendly hydrothermal strategy via a seed-mediated method. The morphology and structure of the hybrid nanostructures were characterized by means of high-resolution transmission electron microscopy and X-ray diffraction. The morphology evolution investigations reveal that the Kirkendall effect directs the diffusion and causes the formation of iron oxide/SnO(2) quasi-hollow particles. Significantly, the as-obtained iron oxides/SnO(2) core-shell heterostructures exhibited enhanced visible light or UV photocatalytic abilities, remarkably superior to as-used α-Fe(2)O(3) seeds and commercial SnO(2) products, mainly owing to the effective electron hole separation at the iron oxides/SnO(2) interfaces. 相似文献