全文获取类型
收费全文 | 188篇 |
免费 | 36篇 |
国内免费 | 21篇 |
专业分类
化学 | 36篇 |
晶体学 | 3篇 |
力学 | 66篇 |
综合类 | 3篇 |
数学 | 25篇 |
物理学 | 53篇 |
无线电 | 59篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1986年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有245条查询结果,搜索用时 48 毫秒
51.
WU Ren-Ping YU Yan GU Ying Yun GUO Jin-Yu 《结构化学》2007,26(5):562-566
Deep color glass-ceramics is prepared by using gold tailings as the main raw material, and Cr2O3 is added as nucleation agent. Influence of different Cr2O3 additions on crystallization structure and properties of CaO-MgO-Al2O3-SiO2 glass-ceramics has been discussed so as to select optimum additions. DTA is employed to determine optimum crystallization and nucleation temperatures; XRD and SEM are used to characterize microstructure of each sample; and performance indexes, such as water absorption, bulk density, flexural strength and so on, are also determined. Experimental results show that when 3wt% Cr2O3 is introduced, fine glass-ceramics with diopside as the main crystal and Ca-Fe diopside as the second-crystal is obtained, and its corresponding performance indexes are as follows: water absorption 0.12%, bulk density 2.56 g/cm3, and flexural strength 70.01 Mpa. 相似文献
52.
One of the greatest challenges in structural engineering nowadays is the strengthening, upgrading, and retrofitting of existing
structures. The use of fibre-reinforced polymers (FRPs) bonded to the tension face of a structural member is an attractive
technique in this field of application. The strengthening of reinforced concrete structures by means of an externally bonded
reinforcement (EBR) is achieved by gluing a FRP laminate to the concrete substrate. For an efficient utilization of the FRP
EBR systems, an effective stress transfer is required between the FRP and concrete. The paper discusses the bond behaviour
between a FRP and concrete in the case of flexural strengthening of continuous beams. With respect to this type of beams,
only a few studies have been reported, though continuous members often occur in concrete constructions. The structural behaviour
of statically indeterminate elements is typically characterized by redistributions of the internal forces. These distributions
are related to the nonlinear deformations of the beams and has also a distinct influence on the bond behaviour between the
FRP and concrete.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 389–402, May–June, 2008. 相似文献
53.
In 1925 a paper on kinetic analysis of data obtained with thermobalances for isothermal mass loss of some natural products for electrical insulation was published. This is the first theoretical and experimental approach to accelerated test of electrical insulating materials and also to kinetic analysis of thermal analysis data at isoconversional points. In succeeeding papers, change in chemical composition and kinetics under temperature change were dealt with. A historical review of these two topics is described in this review article, especially on the basic concept commonly induced for these two fields. 相似文献
54.
《Mechatronics》2022
This paper presents a systematic study of the design optimization, development, vibration analysis and flight testing of a single power plant variable pitch quadrotor Unmanned Aerial System (UAS) for industrial applications. The use of variable pitch rotors enables the use of a two-stroke internal combustion engine for powering the four rotors through a mechanical transmission. The proposed methodology is described by carrying out the design of a quadrotor UAS with 2–3 kg payload capacity and have endurance in excess of one hour. The study is conducted in a systematic manner. First, the design of rotors is optimized for minimum power consumption during hover as well as forward flight condition using physics based simulation developed and validated for this purpose. From the rotor optimization, an untwisted rotor blade with taper ratio of 0.6 and aspect ratio of 10 appeared to be an optimal choice for the current design. Next, the powerplant selection is carried out based on the optimized rotor designed earlier. Next, two different approaches for mechanical power transmission design is considered: torque tube-bevel gear and belt–pulley system based designs. The transmission system designed using belt and pulley was nearly 14% lighter and showed greater tolerance to manufacturing imperfections. Next, two prototypes are designed and its static and dynamic analysis is carried out to ensure its airworthiness. A Proportional Integral Derivative (PID) based attitude controller is developed using quarternions for attitude stabilization and trajectory tracking to test the flight in simulation and then subsequently on the actual vehicle by implementing it on PixHawk autopilot board. Finally, system integration is carried out to build two prototypes of engine powered quadrotor UAS. Then, vibration data is recorded using the sensors onboard to conduct the vibration analysis and design an efficient vibration isolator. Performance analysis is also, carried out to estimate the speed for best endurance (11 m/s) and best range (27 m/s) for the variable pitch quadrotor designed. The estimated best endurance achieved is 2.2 h and estimated best range is more than 150 km. This design revisits and solves the challenge of developing an agile helicopter without cyclic pitch control which was first explored nearly a century ago. 相似文献
55.
Use of Thermoanalytical Methods in Prediction of Thermal Endurance of Insulating Impregnating Varnishes 总被引:1,自引:0,他引:1
Z. Kowalewski J. Zawadzka B. Górnicka 《Journal of Thermal Analysis and Calorimetry》2000,60(1):279-286
The results of testing the thermal properties of insulating impregnated varnishes obtained by thermoanalytical methods and
based on the IEC 216 standard are presented. It was found that the temperature index determined by means of thermoanalytical
testing is quite close to that derived by a conventional standardized procedure. It was also established that thermoanalytical
methods could be used in the recipe selection for the development of a new varnish.
The results obtained confirmed the possibility of using thermoanalytical methods for a quick, prognostic estimation of the
thermal endurance of insulating impregnating varnishes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
56.
57.
《Surface and interface analysis : SIA》2018,50(6):603-607
Bamboo fiber (BF) as organic filler is characterized by mechanical properties analysis and morphology examination for polypropylene (PP) and polystyrene (PS) matrix blends. Effects of different filler content on tensile strength, flexural properties, and impact strength are proposed. It is observed from scanning electron microscopy (SEM) studies that addition of BF is beneficial in increasing mechanical strength via increasing the interface dispersed phase. The optimum tensile properties and impact properties of BF content were at 40 wt% for PP/PS/BF composite on melt mixing conditions. The results showed a significant improvement in mechanical properties of PP/PS/BF ternary blend composite. Comparing with untreated BF, content of carbon and nitrogen of treated BF decreased to 66.57 and 2.31%, oxygen content increased to 21.07%, and silicon content increased from 0 to 10.04%. The element ratio of O/C, N/C, and Si/C changed to 31.65, 3.47, and 15.08, respectively. 相似文献
58.
本文以径向分层的孔、裂隙地层多极子井孔声场理论为基础,利用孔、裂隙介质弹性波动统一理论,数值模拟了井壁上有侵入时,单极和偶极声源激发的井孔声场随原状地层含气饱和度变化的特征和规律。结果表明:当原状地层裂隙发育时,相较于饱含水,饱含气时纵波幅度衰减严重,横波波至提前,波幅增大,斯通利波幅度变化不明显,低频时弯曲波到时提前,幅度增大;当原状地层裂隙不发育时,单极子、偶极子波形都对流体性质没有明显响应。可见,原状地层中裂隙的存在加剧了含气对纵波、横波的幅度以及到时的影响,而侵入带的存在使得斯通利波和高频弯曲波对原状地层流体性质变化不敏感。数值计算结果为利用声波响应特征识别致密气层提供了参考。 相似文献
59.
60.
Write/erase degradation after endurance cycling due to electron trapping events in triple-gate flash mem-ory have been detected and analyzed using a tYV erasure method. Different from the commonly degradation phe-nomenon, write-induced electron trapping in the floating gate oxide, electron trapping in tunneling oxide is observed in triple-gate flash memory. Further, the degradation due to single-electron locally trapping/de-trapping in horn-shaped SuperFlash(R) does not occur in the triple-gate flash cell. This is because of planar poly-to-poly erasing in the triple-gate flash cell instead of tip erasing in the horn-shaped SuperFlash(R) cell. Moreover, by TCAD simulation, the trap location is identified and the magnitude of its density is quantified roughly. 相似文献