全文获取类型
收费全文 | 16386篇 |
免费 | 1318篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 215篇 |
综合类 | 13篇 |
化学工业 | 3716篇 |
金属工艺 | 610篇 |
机械仪表 | 891篇 |
建筑科学 | 401篇 |
矿业工程 | 11篇 |
能源动力 | 627篇 |
轻工业 | 1566篇 |
水利工程 | 56篇 |
石油天然气 | 22篇 |
无线电 | 2553篇 |
一般工业技术 | 3539篇 |
冶金工业 | 1719篇 |
原子能技术 | 178篇 |
自动化技术 | 1618篇 |
出版年
2023年 | 143篇 |
2022年 | 96篇 |
2021年 | 405篇 |
2020年 | 320篇 |
2019年 | 395篇 |
2018年 | 473篇 |
2017年 | 530篇 |
2016年 | 589篇 |
2015年 | 517篇 |
2014年 | 736篇 |
2013年 | 1141篇 |
2012年 | 999篇 |
2011年 | 1283篇 |
2010年 | 927篇 |
2009年 | 899篇 |
2008年 | 863篇 |
2007年 | 673篇 |
2006年 | 588篇 |
2005年 | 513篇 |
2004年 | 498篇 |
2003年 | 462篇 |
2002年 | 399篇 |
2001年 | 322篇 |
2000年 | 295篇 |
1999年 | 286篇 |
1998年 | 614篇 |
1997年 | 426篇 |
1996年 | 281篇 |
1995年 | 207篇 |
1994年 | 203篇 |
1993年 | 201篇 |
1992年 | 131篇 |
1991年 | 113篇 |
1990年 | 106篇 |
1989年 | 106篇 |
1988年 | 74篇 |
1987年 | 60篇 |
1986年 | 67篇 |
1985年 | 91篇 |
1984年 | 78篇 |
1983年 | 48篇 |
1982年 | 45篇 |
1981年 | 51篇 |
1980年 | 47篇 |
1979年 | 44篇 |
1978年 | 35篇 |
1977年 | 56篇 |
1976年 | 88篇 |
1975年 | 42篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
92.
93.
Cross-phase-modulation-induced nonlinear phase noise in WDM direct-detection DPSK systems 总被引:3,自引:0,他引:3
Hoon Kim 《Lightwave Technology, Journal of》2003,21(8):1770-1774
In direct-detection differential-phase-shift-keying (DPSK) systems, the signal-spontaneous emission beat noise introduces phase noise due to Kerr nonlinearity. In wavelength-division-multiplexed (WDM) systems, this nonlinear phase noise comes not only from the channel itself through self-phase modulation (SPM) but also from the other channels through cross-phase modulation (XPM). In this paper, we theoretically and experimentally investigate XPM-induced nonlinear phase noise. We calculate the performance degradation of DPSK systems caused by XPM-induced nonlinear phase noise in addition to SPM-induced phase noise and experimentally verify it using a 600-km nonzero-dispersion-shifted-fiber link. 相似文献
94.
A microprocessor clock generator based on an analog phase-locked loop (PLL) is described for deskewing the internal logic control lock to an external system lock. This PLL is fully generated onto a 1.2-million-transistor microprocessor in 0.8-μm CMOS technology without the need for external components. It operates with a lock range from 5 to 110 MHz. The clock skew is less than 0.1 ns, with a peak-to-peak jitter of less than 0.3 ns for a 50-MHz system clock frequency 相似文献
95.
Hoon C. Park Chahngmin Cho Sung W. Lee 《International journal for numerical methods in engineering》1995,38(24):4101-4122
The present paper describes an assumed strain finite element model with six degrees of freedom per node designed for geometrically non-linear shell analysis. An important feature of the present paper is the discussion on the spurious kinematic modes and the assumed strain field in the geometrically non-linear setting. The kinematics of deformation is described by using vector components in contrast to the conventional formulation which requires the use of trigonometric functions of rotational angles. Accordingly, converged solutions can be obtained for load or displacement increments that are much larger than possible with the conventional formulation with rotational angles. In addition, a detailed study of the spurious kinematic modes and the choice of assumed strain field reveals that the same assumed strain field can be used for both geometrically linear and non-linear cases to alleviate element locking while maintaining kinematic stability. It is strongly recommended that the element models, described in the present paper, be used instead of the conventional shell element models that employ rotational angles. 相似文献
96.
Young Nam Chun Jen-Shih Chang Alexander A. Berezin J. Mizeraczyk 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(1):119-124
Numerical modelling of the flow velocity fields for the near corona wire electrohydrodynamic (EHD) flow was conducted. Solutions of the steady, two-dimensional momentum equations have been computed for a wire-plate type electrostatic precipitator (ESP). The equations were solved in the conservative finite-difference form on a fine uniform rectilinear grid of sufficient resolution to accurately capture the momentum boundary layers. The numerical procedure for the differential equations was used by SIMPLEST algorithm. The CFD code coupled with Poisson's electric field, ion transport equations and the momentum equation with electric body force, was used for the numerical simulation with the Chen-Kim k-epsiv turbulent model. The numerical results show that EHD secondary flow was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re cw=12.4). Secondary flow vortices caused by the EHD increases with increasing discharge current or EHD number, hence pressure drop of ESP increases 相似文献
97.
The effects of sample size, liquid loading, particle size, column length, and column temperature on retention volumes were
studied and separation factor, column efficiency, partition coefficient, and heat of solution were also obtained by gas-liquid
chromatography. The feed materials were chosen by similar boiling points as diethylether, dimethoxymethane and dichloromethane.
The relations between retention volume and above mentioned various variables were obtained. Separation factor was more affected
by column temperature than other variables, and decreased with the temperature. HETP increased almost linearly with sample
size. From the exponential relationship between partition coefficient and column temperature heat of solution of each material
was calculated. 相似文献
98.
99.
Phase Transformations in Dicalcium Silicate: II, TEM Studies of Crystallography, Microstructure, and Mechanisms 总被引:2,自引:0,他引:2
Young Joong Kim Ian Nettleship Waltraud M. Kriven 《Journal of the American Ceramic Society》1992,75(9):2407-2419
The crystallography, microstructures, and phase transformation mechanisms in dicalcium silicate (Ca2 SiO4 ) were studied by TEM. Three types of superlattice structures were observed in the α'L and β phases. Almost all β grains were twinned and strained. Symmetry-related domain structures inherited from previous high-temperature transformations were observed in β grains. Both the α→α'H and α'L →β transformations were considered to be ferroelastic, and spontaneous strains were calculated. In terms of the crystal structures, the major driving force for the β→γ transformation is proposed to be strains and cation charge repulsions in the β structure. This mechanism can be displacive, but it needs to overcome a comparatively high energy barrier. 相似文献
100.