全文获取类型
| 收费全文 | 3530篇 |
| 免费 | 216篇 |
| 国内免费 | 82篇 |
专业分类
| 电工技术 | 67篇 |
| 综合类 | 53篇 |
| 化学工业 | 615篇 |
| 金属工艺 | 178篇 |
| 机械仪表 | 75篇 |
| 建筑科学 | 107篇 |
| 矿业工程 | 37篇 |
| 能源动力 | 256篇 |
| 轻工业 | 116篇 |
| 水利工程 | 70篇 |
| 石油天然气 | 41篇 |
| 武器工业 | 1篇 |
| 无线电 | 469篇 |
| 一般工业技术 | 594篇 |
| 冶金工业 | 110篇 |
| 原子能技术 | 54篇 |
| 自动化技术 | 985篇 |
出版年
| 2025年 | 18篇 |
| 2024年 | 87篇 |
| 2023年 | 103篇 |
| 2022年 | 96篇 |
| 2021年 | 126篇 |
| 2020年 | 97篇 |
| 2019年 | 81篇 |
| 2018年 | 63篇 |
| 2017年 | 156篇 |
| 2016年 | 112篇 |
| 2015年 | 122篇 |
| 2014年 | 233篇 |
| 2013年 | 260篇 |
| 2012年 | 241篇 |
| 2011年 | 288篇 |
| 2010年 | 241篇 |
| 2009年 | 205篇 |
| 2008年 | 196篇 |
| 2007年 | 209篇 |
| 2006年 | 164篇 |
| 2005年 | 83篇 |
| 2004年 | 72篇 |
| 2003年 | 66篇 |
| 2002年 | 55篇 |
| 2001年 | 41篇 |
| 2000年 | 33篇 |
| 1999年 | 36篇 |
| 1998年 | 36篇 |
| 1997年 | 22篇 |
| 1996年 | 31篇 |
| 1995年 | 22篇 |
| 1994年 | 19篇 |
| 1993年 | 24篇 |
| 1992年 | 11篇 |
| 1991年 | 14篇 |
| 1990年 | 11篇 |
| 1989年 | 11篇 |
| 1988年 | 12篇 |
| 1987年 | 21篇 |
| 1986年 | 39篇 |
| 1985年 | 10篇 |
| 1984年 | 4篇 |
| 1982年 | 5篇 |
| 1981年 | 5篇 |
| 1980年 | 3篇 |
| 1972年 | 5篇 |
| 1971年 | 5篇 |
| 1967年 | 4篇 |
| 1966年 | 7篇 |
| 1962年 | 4篇 |
排序方式： 共有3828条查询结果，搜索用时 15 毫秒
101.
In this letter, a new method for sidelobe suppression in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) systems is proposed. Unlike the conventional approach, sidelobes are suppressed by iteratively adjusting the constellation points for the subcarriers that are close to the edges of the used bandwidth. The constellation points corresponding to the maximum sidelobe suppression are chosen for transmission. Simulation results show that the proposed algorithm yields good performance improvement in terms of sidelobe suppression, and does not have a significant impact on the peak-to-average power ratio (PAPR). 相似文献
102.
The MnSb(Zn) and MnSb(Cu) solid solutions with NiAs-type of crystal structure have been obtained. The existence regions of mono-phase solutions have been determined. Zn and Cu can substitute 10% atomic for Mn. On the basis of magnetic measurements it was supposed that the Cu or Zn atoms preferable occupy the MeII sites of NiAs-structure if the amount of nonmagnetic substitution not exceed 10% atomic. The preferable occupation of MeII sites by nonmagnetic atom manifests in rising of the Curie temperature of solid solutions relatively unsubstituted alloy. 相似文献
103.
104.
近四十年西江磨刀门水道河床演变分析 总被引：4，自引：0，他引：4
将西江磨刀门水道1962、1977、1999年的河道地形图数字化,建立磨刀门水道三个年份的水下数字高程模型(DEM),在此基础上将河道分为上、中、下三段进行了河床演变及其成因分析。结果表明:磨刀门水道1977年前后河道发生过明显的河道冲淤转化;1962年至1977年磨刀门水道处于淤积状态,淤积量达9.92×106 m3,河道上游向窄深发展,下游则向宽浅演变;而从1977至1999年磨刀门水道则处于冲刷状态,冲刷量为25.53×106 m3,河道平均水深增加,逐渐向窄深演变。磨刀门水道河床演变是自然环境变化和人类活动共同作用的结果,其中人类活动的影响最为强烈。 相似文献
105.
Cu Cui Qinghui Zhang 《International journal for numerical methods in engineering》2020,121(14):3066-3082
Generalized or eXtended finite element methods (GFEM/XFEM) for crack problems have been studied extensively. The GFEM/XFEM are called extrinsic if additional functions are enriched at every node in certain domains, while they are called degree of freedom (DOF)-gathering if the singular enriched functions are gathered using cutoff functions. The DOF-gathering GFEM/XFEM save the additional DOFs compared with the extrinsic approach. Both extrinsic and DOF-gathering GFEM/XFEM suffer from difficulties of stabilities in a sense that their scaled condition numbers (SCN) of stiffness matrices could be much larger than those of the standard FEM. A GFEM/XFEM is referred to as stable GFEM (SGFEM) if it reaches optimal convergence orders, and its SCN is of same order as that of FEM. An extrinsic SGFEM was established in Zhang et al for the Poisson crack problems. Objective of this article is to propose the SGFEM for elasticity crack problems; both extrinsic and DOF-gathering schemes are addressed. The main idea is to modify the enriched functions by subtracting their FE interpolants, which was developed by Babuška and Banerjee. To remove local almost linear dependence introduced by multifold enrichments at one node, we propose a local principal component analysis technique to identify and analyze “contributions” of multifold enrichments at one node. Numerical studies demonstrate that the proposed SGFEM and DOF-gathering SGFEM are of optimal convergence and have the SCNs of same order as in the FEM. 相似文献
106.
Accurate forecasting of future urban land expansion can provide useful information for policy makers and urban planners to better plan for the impacts of future land use and land cover change (LULCC) on the ecosystem. However, most current studies do not emphasize spatial variations in the influence intensities of the various driving forces, resulting in unreliable predictions of future urban development. This study aimed to enhance the capability of the SLEUTH model, a cellular automaton model that is commonly used to measure and forecast urban growth and LULCC, by embedding an urban suitability surface from geographically weighted logistic regression (GWLR). Moreover, to examine the performance of the loosely-coupled GWLR-SLEUTH model, a layer with only water bodies excluded and a layer combining the former with an urban suitability surface from logistic regression (LR) were also used in SLEUTH in separate model calibrations. This study was applied to the largest metropolitan area in central China, the Wuhan metropolitan area (WMA). Results show that the integrated GWLR-SLEUTH model performed better than either the traditional SLEUTH model or the LR-SLEUTH model. Findings demonstrate that spatial nonstationarity existed in the drivers' impacts on the urban expansion in the study area and that terrain, transportation and socioeconomic factors were the major drivers of urban expansion in the study area. Finally, with the optimal calibrated parameter sets from the GWLR-SLEUTH model, an urban land forecast from 2017 to 2035 was conducted under three scenarios: 1) business as usual; 2) under future planning policy; and 3) ecologically sustainable growth. Findings show that future planning policy may promise a more sustainable urban development if the plan is strictly obeyed. This study recommended that spatial heterogeneity should be taken into account in the process of land change modeling and the integrated model can be applied to other areas for further validation and forecasts. 相似文献
107.
《International Journal of Hydrogen Energy》2020,45(15):8649-8658
ZnO nanotube arrays were synthesized by the electrodeposition method and Cu2O microcrystals with two kinds of morphologies were deposited on ZnO nanotube arrays successfully. At the deposition potential of −0.5 or −0.7 V, the cubic or spherical Cu2O microcrystals were selectively deposited on ZnO nanotube arrays. By adjusting the deposition time, Cu2O microcrystals with different sizes were obtained. The optical properties and photo-electrochemical performance of ZnO/Cu2O were measured. The results showed that the as-prepared ZnO/Cu2O heterojunction exhibited improved visible light absorption and enhanced photocurrent due to the excellent ability of Cu2O microcrystals for harvesting visible light, and the effective separation and transfer of photo-generated electrons and holes owing to p-n junction between ZnO and Cu2O. The experimental results demonstrate that the photo-electrochemical performance of ZnO/Cu2O heterojunction nanotube arrays can be manipulated by controlling the morphology and the size of Cu2O microcrystals. 相似文献
108.
109.
研究河口近底边界层水动力结构对进一步研究河口地区水流能量耗散和物质输运具有重要意义,2006年7月26～28日在珠江虎门口采用ADV、ADP及OBS和CDT组合置底支架观测系统对近底边界层水流、泥沙和温盐度进行了水下定点观测,本文通过分析流速观测数据,对该潮汐河口近底边界层的水流结构、阻力特性和紊动尺度进行研究,结果表明除憩流附近外,近底边界层内时均流速分布均可采用对数剖面,摩阻流速值与时均流速基本成正比,平均摩阻流速为0.014m/s,粗糙长度为0.09mm,切应力梯度为0.426N/m~2·m;脉动流速统计分析结果符合典型潮汐河口底边界层的紊动特点,距床面0.15m处,落急时刻宏尺度紊动的时间尺度和长度尺度分别为3s和0.06m;垂向脉动分速以及瞬时雷诺应力自相关分析表明转流附近时段的湍流主要以低频大尺度紊动为主.测量分析结果可为下一步研究近底边界层泥沙运动提供依据,并为数值模拟计算提供水动力分析条件和特征参数. 相似文献
110.