全文获取类型
收费全文 | 2722篇 |
免费 | 73篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 169篇 |
综合类 | 3篇 |
化学工业 | 591篇 |
金属工艺 | 84篇 |
机械仪表 | 31篇 |
建筑科学 | 37篇 |
能源动力 | 81篇 |
轻工业 | 180篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 270篇 |
一般工业技术 | 378篇 |
冶金工业 | 777篇 |
原子能技术 | 56篇 |
自动化技术 | 141篇 |
出版年
2023年 | 11篇 |
2022年 | 22篇 |
2021年 | 41篇 |
2020年 | 27篇 |
2019年 | 14篇 |
2018年 | 30篇 |
2017年 | 32篇 |
2016年 | 56篇 |
2015年 | 21篇 |
2014年 | 55篇 |
2013年 | 109篇 |
2012年 | 67篇 |
2011年 | 98篇 |
2010年 | 70篇 |
2009年 | 109篇 |
2008年 | 98篇 |
2007年 | 76篇 |
2006年 | 80篇 |
2005年 | 79篇 |
2004年 | 61篇 |
2003年 | 62篇 |
2002年 | 67篇 |
2001年 | 46篇 |
2000年 | 44篇 |
1999年 | 74篇 |
1998年 | 306篇 |
1997年 | 206篇 |
1996年 | 131篇 |
1995年 | 71篇 |
1994年 | 75篇 |
1993年 | 86篇 |
1992年 | 42篇 |
1991年 | 39篇 |
1990年 | 33篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 38篇 |
1974年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有2800条查询结果,搜索用时 15 毫秒
161.
This article reviews our approach to render 12CaO · 7Al2O3 (C12A7) electronically active using a new concept of ‘active anion manipulation’, where nanostructures embedded within the
C12A7 crystal lattice are intentionally utilized to generate chemically unstable (‘water-free active’) anions. Anionic active
oxygen radicals, O− and O2−, are formed efficiently in C12A7 cages under high oxygen activity conditions. The configuration and dynamics of O2− in cages are revealed by a combination of continuous-wave and pulsed electron paramagnetic resonance (EPR). It is demonstrated
that metal-loaded C12A7 is a promising oxidation catalyst for syngas (CO + H2) formation from methane. Furthermore, the O− ion, the strongest oxidant among active oxygen species, can be extracted from the cage into an external vacuum by applying
an electric field with thermal assistance, generating a high-density O− beam in the order of μA cm−2. In contrast, heat treatment of C12A7 in a hydrogen atmosphere forms H− ions in the cages. The resultant C12A7:H− exhibits a persistent insulator-conductor conversion upon ultraviolet-light or electron-beam irradiation. The irradiation-induced
conversion mechanism is examined by first-principle theoretical calculations. Furthermore, the presence of a severely reducing
environment causes the complete substitution of electrons for anions in the cages. The resulting C12A7:e−, which exhibits excellent stability and an electrical conductivity greater than 100 S cm−1, is regarded as an ‘electride’, an ionic compound in which electrons serve as anions. The C12A7 electride exhibits a high
potential for applications involving cold cathode and thermal field electron emissions due to its small work function. Electride
fabrication methods suitable for large-scale production via melt processing are described. It is also demonstrated that proton
or inert gas ion implantations into C12A7 thin films at elevated temperatures are effective for both H− and electron doping. 相似文献
162.
Miyuki Hayashi Hirokage Yamada Naozumi Nabeshima Kazuhiro Nagata 《International Journal of Thermophysics》2007,28(1):83-96
The temperature dependences of the velocity of sound in liquid Pb, Sn, Ge, and Si have been measured by means of the pulse
transmission technique over temperature ranges of 610–1078 K, 608–1463 K, 1215–1443 K, and 1723–1888 K, respectively. In both
liquid Pb and Sn, the velocities of sound decrease linearly with increasing temperature, which is the same temperature dependence
as shown in many other liquid metals. On the other hand, the velocities of sound in liquid Ge and Si exhibit anomalous temperature
dependences. In Ge, the velocity of sound has a distinct maximum around 1280 K and decreases linearly at higher temperatures.
In Si, the velocity of sound increases monotonically with increasing temperature in the temperature range investigated. It
is considered that these results predict that the coordination numbers of liquid Ge and Si increase with increasing temperature. 相似文献
163.
Morishita F. Hayashi I. Gyohten T. Noda H. Ipposhi T. Shimano H. Dosaka K. Arimoto K. 《Solid-State Circuits, IEEE Journal of》2007,42(4):853-861
A twin-transistor random access memory (TTRAM) can provide high speed, low power and high density with CMOS compatible SOI process. However it is difficult to handle as the unified memory required for advanced SoC because it needs the simple control sensing operation for memory compiler, higher cell efficiency, and lower voltage operation for dynamic frequency and voltage control. Enhanced TTRAM (ET2RAM) applies the actively body-bias control technique to realize the low voltage array operation, and never require the negative voltage source. The ET2RAM can realize both 263 MHz at 0.8 V and 10.2 mW at 0.5 V random-cycle operation, higher cell efficiency, and process scalability. It also provides the simple control method suitable for the unified macro for system-level power management SoC with keeping the merits of TTRAM as CMOS compatibility 相似文献
164.
Kanami Ikegami Tomoya Kawashima Shinji Hayashi Norihisa Moriya 《Journal of the Society for Information Display》2007,15(3):193-197
Abstract— A polymerizable liquid crystal (PLC), the orientation of which can be frozen, is useful for making retardation layers. In this paper, a new color filter (CF) with retardation‐controlling layers made of PLC is reported. It has a positive A‐plate and a negative C‐plate, both directly stacked on a color‐filter layer. These two retardation layers exhibit good orientation ability, and function well as retarders, even when they are only 1/10 or less as thick as ordinary retardation films. The new CF also has excellent thermal stability. The change in retardation after heat treatment at 200°C for 30 min is around 5%, and there is no observable peeling. A prototype VA‐LCD made with our new CF provides good optical compensation, with the light leakage being extremely low in all azimuthal directions. This technology is very useful for making thin, highly reliable color filters for LCDs, even with other modes. 相似文献
165.
F. Tao M. Yokozawa Z. Zhang Y. Hayashi Y. Ishigooka 《International journal of remote sensing》2013,34(19):5461-5478
Land surface phenology dynamics reflect the response of the Earth's biosphere to inter‐ and intra‐annual dynamics of the Earth's climate and hydrologic regimes. Investigations of land surface phenology dynamics and its relation to long‐term climate variation could help us to detect the response of regional vegetation to climate variation. The present study developed a new algorithm for detecting regional land surface phenology dynamics (ARLSPD) and demonstrated it in detecting the vegetation response to inter‐annual climate variability in the North East China Transect (NECT), a mid‐latitude semi‐arid terrestrial transect with strong gradients in environmental conditions and vegetation formations. The spatial–temporal patterns of greenup‐onset date, maturity date, and senescence date during the period of 1982–2000 are presented. The resultant spatial–temporal patterns of land surface phenology were quite consistent with the land‐cover characteristics, moisture, and temperature gradients. The relations between inter‐annual variations in phenology and seasonal climate were investigated. It was found that besides human disturbance, land surface phenology depended primarily on the combined effects of preseason temperature and precipitation. The relative influence of preseason temperature and precipitation on land surface phenology was changing, which led to the different responses of land surface dynamics to climate variation along the moisture gradient in the NECT. In the arid and semi‐arid region of NECT, the dates of onset for phonological events in temperate typical grassland were most significantly related to the precipitation during the preceding 2–4 months. Temperature‐induced drought stress during the preceding months could delay greenup onset in cropland/grassland mosaic, and advance senescence in temporal typical grassland, and in cropland/grassland mosaic. The regional phenology algorithm, theoretically also applicable for complex ecosystems characterized by annual multiple growth cycles, is expected to couple with large‐scale biogeochemical models to regulate dynamically land surface phenology. 相似文献
166.
Manabu Shimada Heru Setyawan Yutaka Hayashi Nobuki Kashihara Kikuo Okuyama Sugeng Winardi 《Aerosol science and technology》2013,47(5):408-414
The effects of gas flow rate on particle formation and film deposition during the preparation of silica thin film using a TEOS/O2 plasma were investigated. Particle formation and growth are suppressed with increasing gas flow rates. The film deposition rate increases with increasing gas flow rate, reaches a maximum value, and eventually decreases again. However, the uniformity of the film tends to degrade at high gas flow rates. At a high gas flow rate, some particles trapped in the sheath near the grounded electrode pass through the sheath to reach the substrate and are then embedded in the growing film. A self-consistent sheath model combined with particle force balance based on charge fluctuation was developed to explain these experimental findings qualitatively. The model reveals that charge fluctuation is a key factor for the particle to overcome the potential barrier of the negatively charged particles to pass through the sheath, eventually reaching the substrate. The model further shows that the probability of a particle being deposited on the substrate is higher for increased gas flow rates, which correctly predicts the experimentally observed trend. 相似文献
167.
Naka R. Watanabe K. Kawarabayashi J. Uritani A. Iguchi T. Hayashi N. Kojima N. Yoshida T. Kaneko J. Takeuchi H. Kakuta T. 《IEEE transactions on nuclear science》2001,48(6):2348-2351
The purpose of this study is to develop a radiation distribution monitor using a normal plastic optical fiber. The monitor has a long operating length and can obtain continuous radiation distributions. A principle of the position sensing is based on a time-of-flight technique. The monitor is sensitive to beta rays or charged particles, gamma rays, and fast neutrons. The spatial resolutions for beta-rays ( 90Sr-90Y), gamma-rays (137Cs), and D-T neutrons are 30, 37, and 13 cm, respectively. The detection efficiencies for the beta-rays, gamma-rays, and D-T neutrons are 0.11%, 1.6×10 -5% and 1.2×10-4%, respectively. The effective attenuation length of the detection efficiency is 18 m. In this paper, we describe the basic characteristics of this monitor 相似文献
168.
Fast Labelling of Natural Scenes Using Enhanced Knowledge 总被引:1,自引:0,他引:1
Hiroki Hayashi Mineichi Kudo Jun Toyama Masaru Shimbo 《Pattern Analysis & Applications》2001,4(1):20-27
A new technique for labelling natural scenes is proposed. This technique labels disjoint regions on an image of a natural
scene on the basis of knowledge about the relationship among objects. The proposed technique consists of three stages: (1)
segmentation, (2) initial labelling, and (3) label improvement. One of the most promising previous techniques uses simulated
annealing to find the solution, while our technique uses local hill-climbing with enhanced knowledge for speeding up the processing.
Local hill-climbing is known to be easy to be captured by a local minimum. We solved this problem by enhancing the knowledge
being used as constraints for the search. Our knowledge represents 1-to-n relationships among regions, pair-wise relationships of regions, and relative locations of the regions to the image. In addition,
we introduced two region features: an entropy in intensity; and a linearity of contours of each region. The linearity evaluation
aims to distinguish artificial objects from natural objects. The validity of the technique is supported by some experiments.
These experiments showed that the proposed technique is much faster with the almost same accurate. 相似文献
169.
Summary
Dynamic light scattering measurements have been made on 14 samples of a polymacromonomer consisting of polystyrene with 15
styrene side-chain units in cyclohexane at 34.5°C (the theta point) to determine the translational diffusion coefficient D as a function of molecular weight. The dependence of D on the main-chain length is analyzed on the basis of the wormlike chain by taking into account the end effect arising from
side chains near the main-chain ends. The model parameters describing this dependence, i.e., the Kuhn segment length (11.5
± 1.5 nm), the linear mass density (5600 ± 700 nm−1), the diameter (5.2 ± 0.5 nm), and the end-effect parameter δ (2.5 ± 0.3 nm), are close to those determined previously from
<S
2>z (the z-average mean-square radius of gyration) and [η] (the intrinsic viscosity), leading to the conclusion that the wormlike chain
model is capable of consistently explaining <S
2>z, [η], and D of the polymacromonomer in the Θ solvent.
Received: 8 February 2000/Accepted: 18 February 2000 相似文献
170.
Kensuke Miyahara Saburo Matsuoka Tohru Hayashi 《Metallurgical and Materials Transactions A》2001,32(3):761-768
A nanoindentation hardness testing system, including an atomic-force microscope (AFM)-based nanoindentation tester and a calibration
method using electrolytically polished single-crystal metals as references, was proposed. This was applied to a study of the
mechanical properties of fine-grained ferritic steel (grain size of 1.2 μm) and coarse-grained ferritic steel (30 μm). An
empirical function giving the macroscopic hardness for all four reference metals from the nanoindentation force curves was
established. The converted Vickers hardness (HV*) of the coarse-grained steel is almost independent of the indent size. The
fine-grained steel shows only HV* 130 with an indent of only 100 nm, compared with a macroscopic hardness of HV 210. The difference,
HV 80, is considered to reflect the amount of grain-boundary strengthening. The critical indent size for the hardness transition
seems to be around 1 μm, comparable to the grain size of the specimen. This result supports the explanation of grainboundary
strengthening. It is also consistent with Pickering’s work on low-carbon steel, as the estimated locking parameter (k of 2.6×105 N/m3/2) in the Hall-Petch relationship is in good agreement with his value of 2.4×105 N/m3/2. 相似文献