全文获取类型
收费全文 | 475321篇 |
免费 | 52069篇 |
国内免费 | 37173篇 |
专业分类
电工技术 | 38553篇 |
技术理论 | 39篇 |
综合类 | 43710篇 |
化学工业 | 72190篇 |
金属工艺 | 24284篇 |
机械仪表 | 32050篇 |
建筑科学 | 43822篇 |
矿业工程 | 19329篇 |
能源动力 | 18950篇 |
轻工业 | 29989篇 |
水利工程 | 16178篇 |
石油天然气 | 20303篇 |
武器工业 | 7841篇 |
无线电 | 47572篇 |
一般工业技术 | 42735篇 |
冶金工业 | 17445篇 |
原子能技术 | 5761篇 |
自动化技术 | 83812篇 |
出版年
2024年 | 1174篇 |
2023年 | 6613篇 |
2022年 | 11974篇 |
2021年 | 16245篇 |
2020年 | 15613篇 |
2019年 | 12618篇 |
2018年 | 11920篇 |
2017年 | 15699篇 |
2016年 | 18491篇 |
2015年 | 20790篇 |
2014年 | 29239篇 |
2013年 | 30399篇 |
2012年 | 36140篇 |
2011年 | 40266篇 |
2010年 | 29396篇 |
2009年 | 29334篇 |
2008年 | 29020篇 |
2007年 | 34245篇 |
2006年 | 31455篇 |
2005年 | 26877篇 |
2004年 | 22606篇 |
2003年 | 18573篇 |
2002年 | 14698篇 |
2001年 | 11753篇 |
2000年 | 9771篇 |
1999年 | 7899篇 |
1998年 | 6027篇 |
1997年 | 4944篇 |
1996年 | 3938篇 |
1995年 | 3362篇 |
1994年 | 2838篇 |
1993年 | 2098篇 |
1992年 | 1702篇 |
1991年 | 1303篇 |
1990年 | 1097篇 |
1989年 | 904篇 |
1988年 | 582篇 |
1987年 | 395篇 |
1986年 | 365篇 |
1985年 | 439篇 |
1984年 | 354篇 |
1983年 | 277篇 |
1982年 | 262篇 |
1981年 | 176篇 |
1980年 | 181篇 |
1979年 | 77篇 |
1978年 | 42篇 |
1977年 | 50篇 |
1959年 | 63篇 |
1951年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
101.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
102.
103.
隐患采空区是目前影响露天开采矿山安全生产的主要危害源之一。随着台阶开采的不断剥离,露天开采境界内各台阶与地下空区群的隔离层厚度越来越薄,随时有可能发生采空区顶板坍塌事故。考虑到露天矿采空区地质赋存条件和围岩稳固性等特征,以弓长岭露天铁矿浅层采空区为工程背景,运用现场监测和数值模拟相结合的手段综合分析了浅层采空区的稳定性。将液体静力水准地表沉降监测系统的监测数据与FLAC数值模拟结果对比,调整蠕变参数使得数值模拟的蠕变速率与现场监测结果一致,而后据此进行未来结果的预测。最终根据地表沉降数据确定的蠕变参数取值为A=1.0×10^-12、m=1.75、n=0.35。研究表明:静力水准测点地表最大沉降位移为-9.8 mm,蠕变计算结果顶板最大垂直位移约20.4 mm,应力最大值约25 MPa,综合分析显示该采空区较稳定。上述研究提供了一种基于采空区现场监测数据的数值模拟蠕变分析方法,可为类似矿山采空区稳定性分析提供借鉴。 相似文献
104.
105.
《Ceramics International》2020,46(4):4857-4863
Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at the outer edge of glass-ceramic layers, which are less for the hollow-full specimen. The simulation results show that for a specimen with either 9 mm thick square- or 6 mm thick triangular-flanges, locally enhanced tensile stresses almost disappear, resulting in a symmetric shear stress distribution. The difference between the analytically derived nominal shear strength and the real critical shear stress derived via simulation reduces with decreasing the fracture torque. 相似文献
106.
针对大型风力发电机机组中常见的脉动湍流、风机尾流与涡流等湍流信号,研究了利用自然梯度下降的独立分量分析方法的湍流频谱分离效果,以区分中心风速与湍流信号,提高风机机组的综合工作效率。首先分析了风机组中常见湍流信号的后向散射与频谱分布特点,然后依据这些特点设计了对应的独立分量分析模型。在仿真结果符合要求的基础上,进行了双目激光雷达天线的风速采集与实际分离效果检测。实验结果表明,在大气折射率结构常数C2n≤10-14同时广义大气常数α≥4的通常情况下,利用双目信号能够分离出一个湍流中心和一个中心风速。对1 s内两个谱峰的波动范围进行统计,获得(2.59±0.05)MHz的中心风速以及(1.22±0.19)MHz的湍流中心估计,且二者的平均信噪比分别为25.93 dB和31.01 dB,能够在获得稳定的中心风速估计的同时得到一个较为稳定的湍流中心估计。 相似文献
107.
《Journal of the European Ceramic Society》2020,40(8):2791-2800
Acoustic emission (AE) during tensile testing of three-dimensional woven SiC/SiC composites was analyzed by a statistical modeling method based on a Bayesian approach to quantitatively evaluate the fracture process. Gaussian mixture models and Weibull mixture models were utilized as candidate models describing the AE time-series data. After fitting AE time-series data to these models with Markov Chain Monte Carlo (MCMC) methods, the model selection was conducted by stochastic complexity. Among the candidate models, the two-component Weibull mixture model was automatically selected. It was confirmed that the component distributions in the two-component Weibull mixture model were corresponding to the evolution of matrix cracking and fiber breakage, respectively. Since the proposed AE analysis method can determine the number of component distributions without the decision of researchers and inspectors, it is expected to be useful for an understanding of the fracture process in newly developed materials and the reliability assessment in service. 相似文献
108.
以重庆市甄子岩29号危岩体为研究对象,基于现场调查和分析解剖,建立UDEC离散元数值计算模型,对其演化变形过程进行模拟分析。研究表明,在巨大的自重作用下,由于基座岩体岩质软,岩体较破碎,且基座外侧为直立的陡崖,具有完整的临空面,从而使基座岩体易发生压缩流变及剪切流变,进而使危岩体存在滑移垮塌的危险。 相似文献
109.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
110.
目的研究蛋类礼盒包装结构的缓冲性能。方法以蛋类尺寸为基础,建立可发性聚乙烯(expandable polyethylene. EPE)缓冲单元结构和组合结构,进行静态仿真分析和实验验证,比较结构在形状、叠合层数、组合形式等参数变化时的载荷与位移。结果结构层数变化相同时,单元结构的极限载荷从143N增加到236 N,组合结构的极限载荷从224 N增加到476 N,均呈近线性增长。结论蛋类礼盒包装中,组合结构的承载能力优于单元结构,通过单元结构的组合,可满足不同蛋类的包装要求。 相似文献