全文获取类型
收费全文 | 5808篇 |
免费 | 554篇 |
国内免费 | 330篇 |
专业分类
电工技术 | 299篇 |
综合类 | 884篇 |
化学工业 | 464篇 |
金属工艺 | 169篇 |
机械仪表 | 574篇 |
建筑科学 | 1005篇 |
矿业工程 | 136篇 |
能源动力 | 175篇 |
轻工业 | 174篇 |
水利工程 | 113篇 |
石油天然气 | 184篇 |
武器工业 | 117篇 |
无线电 | 582篇 |
一般工业技术 | 562篇 |
冶金工业 | 109篇 |
原子能技术 | 87篇 |
自动化技术 | 1058篇 |
出版年
2024年 | 13篇 |
2023年 | 52篇 |
2022年 | 84篇 |
2021年 | 124篇 |
2020年 | 119篇 |
2019年 | 127篇 |
2018年 | 110篇 |
2017年 | 143篇 |
2016年 | 175篇 |
2015年 | 176篇 |
2014年 | 298篇 |
2013年 | 348篇 |
2012年 | 387篇 |
2011年 | 458篇 |
2010年 | 339篇 |
2009年 | 375篇 |
2008年 | 351篇 |
2007年 | 433篇 |
2006年 | 393篇 |
2005年 | 353篇 |
2004年 | 277篇 |
2003年 | 232篇 |
2002年 | 205篇 |
2001年 | 162篇 |
2000年 | 150篇 |
1999年 | 118篇 |
1998年 | 110篇 |
1997年 | 95篇 |
1996年 | 83篇 |
1995年 | 68篇 |
1994年 | 61篇 |
1993年 | 47篇 |
1992年 | 50篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 19篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1973年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有6692条查询结果,搜索用时 15 毫秒
1.
2.
《Ceramics International》2021,47(19):27177-27187
BaZrO3-based materials doped with a trivalent cation have excellent chemical stability and relatively high proton conductivity which makes them potential proton conducting oxide materials for various electrochemical device applications such as hydrogen processing, high-temperature electrolysis, and solid electrolyte in fuel cells. However, BaZrO3 showed poor sinterability, requiring high sintering temperatures (1700–2100 °C) with longtime sintering (20–100 h) to achieve the desired microstructure and grain growth. This sintering problem can be solved by slightly doping BaZrO3 with a sintering aid element. Therefore, in this study, two different zirconate proton conductors: BaZr0·9Y0·1O3-α (BZY) and BaZr0·955Y0·03Co0·015O3-α (BZYC) were sintered in an air atmosphere and an oxygen atmosphere for 20 h in the temperature range of 1500–1640 °C. The sinterability was evaluated by analyzing the XRD diffraction patterns, lattice constant, lattice strain, crystallite size, relative density, open porosity, closed porosity, surface morphology, grain size, and grain boundary distribution, using the XRD, SEM, EDX, and Archimedes density measurement methods. It is concluded that in an oxygen atmosphere, sintering aid Co not only improves the relative density but also produces highly dense fine particles with clear grain boundaries which are promising for electrochemical hydrogen device applications. 相似文献
3.
黄浦江为感潮河流,低潮位重现期的确定对黄浦江航道的设计具有重要意义。为了准确估计黄浦江低潮位的重现期,以黄浦江下游吴淞口站年最低潮位序列为例,在对样本进行三性审查的基础上,分别采用传统的数理统计方法和时变矩方法进行水文频率分析。结果表明:吴淞口站年最低潮位序列在1996年发生了变异;还现修正后的序列服从位置参数线性时变的GEV模型,低潮位存在缓慢的上升趋势;一致性条件下百年一遇低潮位约为0.261 m,在非一致性条件下其重现期增大为150 a。非一致性条件下的重现期增大说明黄浦江现有的航道设计标准偏安全,航道通航保证率提高。 相似文献
4.
《岩石力学与岩土工程学报(英文版)》2020,12(6):1214-1225
With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D50), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed. 相似文献
5.
Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards. 相似文献
6.
7.
U. KEICH 《时间序列分析杂志》2003,24(2):173-192
Abstract. In Keich (2000 ),we define a stationary tangent process, or a locally optimal stationary approximation, to a real non-stationary smooth Gaussian process. This paper extends the idea by constructing a discrete tangent – a `locally' optimal stationary approximation – for a discrete time, real Gaussian process. Analogously to the smooth case, our construction relies on a generalization of the recursion formula for the orthogonal polynomials of the spectral distribution function. More precisely, we use a generalization of the Schur parameters to identify the stationary tangent. By way of discretizing, we later demonstrate how this tangent can be used to obtain `good' local stationary approximations to non-smooth continuous time, real Gaussian processes. Further, we demonstrate how, analogously to the curvatures in the smooth case, the Schur parameters can be used to determine the order of stationarity of a non-smooth process. 相似文献
8.
微带型Wilkinson功分器设计与实现 总被引:2,自引:0,他引:2
小型低功耗器件是射频电路设计的研究热点,而微带技术具有小型化低功耗的优点,为此在介绍微带型Wilkin-son功分器工作原理的基础上,使用基于矩量法的ADS软件设计、仿真和优化计算相关数据参数,并制作了一个微带功分器实例,最后对加工的样品进行实测,获得与仿真值吻合较好的预期结果。 相似文献
9.
10.
首次提出了水流泥沙运动水深平均及其力矩方程的概念 ,并从理论上推导出这套方程组。提出水流泥沙运动力矩方程的目的有两个 ,一是在不增加空间维数的情况下可以有效地恢复水流泥沙因子沿水深分布信息 ,克服目前普遍使用的水深平均方程过多地忽略沿水深分布信息的缺点 ;二是增强模型的模拟能力。针对这两个目的是否能真正得到体现 ,分别从理论和实验室资料两个方面对新推导的力矩方程进行了全面的检验。理论验证结果表明 ,一维的力矩方程除了能模拟水深平均的流速和含沙量 ,还能够较好地模拟水流泥沙因子沿水深分布信息 ,这充分说明了一维力矩方程的二维特性。为了检验力矩方程的模拟能力 ,特别选取了一些极端的水流泥沙运动实验 ,如清水冲刷、点源加沙和深槽回淤等。模拟结果表明 ,力矩方程对于这些极端的水沙运动具有较好的模拟能力 相似文献