全文获取类型
收费全文 | 23749篇 |
免费 | 2881篇 |
国内免费 | 2096篇 |
专业分类
电工技术 | 1731篇 |
技术理论 | 1篇 |
综合类 | 2095篇 |
化学工业 | 4295篇 |
金属工艺 | 1121篇 |
机械仪表 | 915篇 |
建筑科学 | 1726篇 |
矿业工程 | 685篇 |
能源动力 | 975篇 |
轻工业 | 1025篇 |
水利工程 | 582篇 |
石油天然气 | 1385篇 |
武器工业 | 335篇 |
无线电 | 2872篇 |
一般工业技术 | 3309篇 |
冶金工业 | 711篇 |
原子能技术 | 593篇 |
自动化技术 | 4370篇 |
出版年
2024年 | 50篇 |
2023年 | 534篇 |
2022年 | 659篇 |
2021年 | 832篇 |
2020年 | 951篇 |
2019年 | 808篇 |
2018年 | 809篇 |
2017年 | 945篇 |
2016年 | 1041篇 |
2015年 | 1090篇 |
2014年 | 1504篇 |
2013年 | 1678篇 |
2012年 | 1767篇 |
2011年 | 1948篇 |
2010年 | 1485篇 |
2009年 | 1420篇 |
2008年 | 1416篇 |
2007年 | 1612篇 |
2006年 | 1336篇 |
2005年 | 1146篇 |
2004年 | 942篇 |
2003年 | 800篇 |
2002年 | 602篇 |
2001年 | 565篇 |
2000年 | 402篇 |
1999年 | 358篇 |
1998年 | 285篇 |
1997年 | 275篇 |
1996年 | 251篇 |
1995年 | 205篇 |
1994年 | 183篇 |
1993年 | 133篇 |
1992年 | 113篇 |
1991年 | 110篇 |
1990年 | 99篇 |
1989年 | 88篇 |
1988年 | 66篇 |
1987年 | 38篇 |
1986年 | 36篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
61.
This note reconsiders the marginal density of a threshold moving average process and proposes a simple yet effective numerical algorithm to implement that by solving an associated integral equation. This algorithm can also be applied to calculate stationary probability density or distribution functions of a few other types of nonlinear stationary stochastic processes numerically. 相似文献
62.
当今的多相催化研究需要新的技术和方法从原子尺度上表征活性中心结构和反应中间体。本文作者课题组近期开发了理论模拟新技术来探索催化剂活性位点结构,即基于神经网络势函数的大规模原子模拟(LASP)软件中实现的全局神经网络势函数计算方法。本文介绍了该方法可以显著降低催化体系的计算代价,而维持与密度泛函理论同一级别的计算精度,从而解决多相催化中的许多复杂问题。本文对神经网络势函数方法的实现细节和目前已实现的应用场景进行了详细介绍。神经网络势函数可以用来预测材料晶体结构,理解高压氢化条件下TiO2表面的结构演化和确定三元氧化物ZnCrO晶相中合成气制甲醇活性位点。最后文章分析了神经网络势函数的局限性和今后可能的三个研究方向,即材料性质预测、多元素体系神经网络势函数构造和化学反应拟合。 相似文献
63.
采用普通涤纶、含1%云母颗粒的涤纶(1%云母/涤纶)以及含5%云母颗粒的涤纶(5%云母/涤纶)三种材质,上机纬密采用200根/10 cm、300根/10 cm、400根/10 cm,组织采用平纹、斜纹、缎纹试织试样。通过Hot Disk热常数分析仪,采用正交试验及极差、方差分析,研究了纤维材质、上机纬密、组织对凉感纤维织物导热系数的影响。结果表明:在试验设置变量范围内,纤维材质对导热系数的影响显著,上机纬密、组织对导热系数的影响高度显著,影响因素从大到小顺序为上机纬密>组织>纤维材质。 相似文献
64.
《Ceramics International》2020,46(1):592-597
The effects of activated carbon (AC) as an additive in multi-oxide nano composite LiNiCuZn–O for application as anode in solid oxide fuel cell (SOFC) is reported. The composite was synthesized using solid state reactions method with varying content of AC in range 0.1%–0.9% for use as anode in the cell. The cell was composed of the synthesized composite as anode, LiNiCuZn–O as cathode and Samaria doped ceria (SDC) as electrolyte. The prepared composites were characterized for morphology and crystal structure by scanning electron microscope (SEM) and x-ray diffraction (XRD) respectively. Furthermore, the crystallite sizes of LiNiCuZn–O and LiNiCuZn–O with AC as an additive have been found in the range from 50 nm to 70 nm. The prepared composite materials were observed porous and the porosity of the sample having 0.5% additive was found highest. The conductivity and power density of the SOFC were studied at temperature of 600 °C. The maximum value of conductivity was found as 4.79 S/cm for the composite containing 0.5% AC as measured by using 4-probe method. The maximum value of power density of the fuel cell with anode comprising of 0.5% AC along with the mentioned cathode and the electrolyte was 455 mW/cm2. Therefore, out of the compositions studied, the composite comprising of LiNiCuZn–O with 0.5% AC offered best performance for anode in the cell. This oxide composite is reported as a potential candidate for use as anode in low temperature SOFCs. 相似文献
65.
大坝运行监测易受自然环境和监测条件影响,存在时间和空间上的变异性,监测数据具有不确定性。以云理论的随机性和不确定性分析方法为基础,并与空间数据辐射思想相结合,建立了云滴概率密度分布估计模型,然后导出云概率密度分布函数,依据样本监测数据推求母体空间数据的分布特征,并设计了基于逆向云算法云变换的计算程序。分析陆浑水库1979~1999年测压管监测数据和位移变形数据的云概率密度分布特征和云数字特征,得出了20 a来大坝的数据分布特征和运行状态。监测数据分析结果表明,云概率密度分布估计不仅能有效合理地分析大坝的运行状态,而且能够依据云数字特征来判断监测状态和监测环境的异常变化。
相似文献
66.
Power generation characteristics of a sandwich‐type self‐heating thermoelectric generator with spatially varying embedded heat source 下载免费PDF全文
Soojin Shin Semi Bang Jiyeon Choi Hyo‐Ju Son Hyejin Yoon Hanla Yun Jung‐Hyun Choi Daehyun Wee 《国际能源研究杂志》2015,39(6):851-859
Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
67.
Xuan Xu Jiaminag Chen Yuemin Zhao Bo Lv 《Mineral Processing and Extractive Metallurgy Review》2019,40(5):299-306
ABSTRACTThe distribution plate structure plays an important role in the stability of air dense medium fluidized beds (ADMFB). Optimization of the distribution plate structure can reduce the generation of large bubbles. In the present work, the influence of the distribution plate structure on the fluidization characteristics of fluidized bed with agitator was investigated. Two different feedstock samples with the size fraction of 25–13 and 13–6 mm were tested individually. The experimental results showed that the fluidized bed density fluctuation was relatively small and the dead zone of gas-solids fluidized bed was significantly reduced by adding the stirring device into the fluidized bed under the optimal working conditions. Through a study of the sorting test, it was revealed that the separation performance can be effectively improved. This indicates that there is an obvious interrelationship between the structure of distribution plate and other process parameters, which affects the fluidization characteristics of ADMFB. 相似文献
68.
69.
Debin Wang Jingsong Liu Mengshi Zeng Chunmei Zhang Huiqin Li Hongtao Yu Ying Yuan Shuren Zhang 《Journal of the American Ceramic Society》2019,102(7):4029-4037
(1-x)Sr0.7Pb0.15Bi0.1TiO3-xBi4Ti3O12 ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range. 相似文献
70.
Seiya Suzuki Takuya Iwasaki K. Kanishka H. De Silva Shigeru Suehara Kenji Watanabe Takashi Taniguchi Satoshi Moriyama Masamichi Yoshimura Takashi Aizawa Tomonobu Nakayama 《Advanced functional materials》2021,31(5):2007038
Germanene, a 2D honeycomb germanium crystal, is grown at graphene/Ag(111) and hexagonal boron nitride (h-BN)/Ag(111) interfaces by segregating germanium atoms. A simple annealing process in N2 or H2/Ar at ambient pressure leads to the formation of germanene, indicating that an ultrahigh-vacuum condition is not necessary. The grown germanene is stable in air and uniform over the entire area covered with a van der Waals (vdW) material. As an important finding, it is necessary to use a vdW material as a cap layer for the present germanene growth method since the use of an Al2O3 cap layer results in no germanene formation. The present study also proves that Raman spectroscopy in air is a powerful tool for characterizing germanene at the interfaces, which is concluded by multiple analyses including first-principles density functional theory calculations. The direct growth of h-BN-capped germanene on Ag(111), which is demonstrated in the present study, is considered to be a promising technique for the fabrication of future germanene-based electronic devices. 相似文献