全文获取类型
收费全文 | 64591篇 |
免费 | 8370篇 |
国内免费 | 6109篇 |
专业分类
电工技术 | 5202篇 |
技术理论 | 4篇 |
综合类 | 7816篇 |
化学工业 | 7708篇 |
金属工艺 | 4093篇 |
机械仪表 | 5387篇 |
建筑科学 | 8657篇 |
矿业工程 | 2331篇 |
能源动力 | 1732篇 |
轻工业 | 1946篇 |
水利工程 | 1934篇 |
石油天然气 | 1851篇 |
武器工业 | 1110篇 |
无线电 | 4183篇 |
一般工业技术 | 7934篇 |
冶金工业 | 4256篇 |
原子能技术 | 379篇 |
自动化技术 | 12547篇 |
出版年
2024年 | 408篇 |
2023年 | 1178篇 |
2022年 | 2089篇 |
2021年 | 2336篇 |
2020年 | 2495篇 |
2019年 | 2118篇 |
2018年 | 2131篇 |
2017年 | 2527篇 |
2016年 | 2812篇 |
2015年 | 2891篇 |
2014年 | 3913篇 |
2013年 | 4001篇 |
2012年 | 4890篇 |
2011年 | 5077篇 |
2010年 | 3976篇 |
2009年 | 3961篇 |
2008年 | 3802篇 |
2007年 | 4491篇 |
2006年 | 3908篇 |
2005年 | 3353篇 |
2004年 | 2720篇 |
2003年 | 2342篇 |
2002年 | 1934篇 |
2001年 | 1670篇 |
2000年 | 1369篇 |
1999年 | 1117篇 |
1998年 | 906篇 |
1997年 | 772篇 |
1996年 | 619篇 |
1995年 | 509篇 |
1994年 | 452篇 |
1993年 | 341篇 |
1992年 | 266篇 |
1991年 | 219篇 |
1990年 | 205篇 |
1989年 | 178篇 |
1988年 | 117篇 |
1987年 | 77篇 |
1986年 | 59篇 |
1985年 | 44篇 |
1984年 | 61篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 50篇 |
1979年 | 43篇 |
1965年 | 32篇 |
1964年 | 49篇 |
1963年 | 39篇 |
1959年 | 33篇 |
1955年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
系统研究了Ti-Ni形状记忆合金丝(SMA)应力-应变曲线、特征点应力、耗能能力、等效阻尼比随材料直径、应变幅值、加载速率、加载循环次数的变化规律;针对SMA唯象Brinson本构模型无法描述SMA动态力学性能的缺点,结合前述试验结果,提出了一种可考虑加/卸载速率影响的SMA简化本构模型。应用该模型对试验用SMA丝进行模拟,所得应力-应变曲线各特征点平均误差仅为3%,结果表明:所建立的速率相关SMA简化本构模型可较为精确地描述SMA在应力诱发相变过程中的超弹性力学行为,同时可反映加/卸载速率和应变幅值等主要因素对其动力本构模型的影响;该模型结构形式简单,具有较好的工程应用前景。 相似文献
993.
Hossam F. H. Abdelfattah Khalid Al-Shamsi Khalifa Al-Jabri 《International Journal of Pavement Engineering》2018,19(7):630-640
Copper slag (CS) is a by-product of the copper extraction process, which can be used as coarse and/or fine aggregate in hot mix asphalt (HMA) pavements. This study used CS as a replacement of the fine aggregate with a percentage of up to 40% by total aggregate weight. The objective of this study was to evaluate the effect of CS on the rutting potential of the asphalt concrete mix using two methods. One method is based on the Dynamic modulus |E*| testing result. Actual pavement temperature data from a test section were used with the developed |E*| master curves. EverStressFE finite element program was used to perform a linear elastic load-deformation analysis for a pavement section and to determine the vertical resilient strain in a 40-mm HMA surface layer. The M-E PDG permanent deformation model was used with and Excel Visual Basic for Applications code to predict the accumulated rutting for different CS mixes for 10 million ESALs. The other method used the data from the flow number (FN) test. Based on the |E*| approach, the results indicated that adding 5% CS in the mix increased the predicted rutting from 0.59 to 0.98 mm at 10 million ESALs (increase by 68%). When 40% CS was used, rutting increased by more than 700% compared with the control mix. After analysing the FN results with the Francken model, the results indicated a decrease in FN as CS content is increased, indicating higher rutting potential. The decrease in FN ranged from 9% for 5% CS to 95% for 40% CS. The mixes containing up to 10% CS satisfied the minimum FN criteria for rutting. A calibration process for the M-E PDG distress prediction models that allows the use of waste and by-product materials such as CS should be considered in the future. 相似文献
994.
Gaoyong Lin Yuyong Wei Ke Zhou Hongyang Wang Weiyuan Song 《Materials and Manufacturing Processes》2018,33(2):232-238
AZ80 hollow profile was produced by porthole-die extrusion. The mechanical behavior and microstructure characteristic of extrusion welds in AZ80 hollow profile during different T5 heat treatments were investigated. Five kinds of morphologies of β-Mg17Al12 were observed in turn in weld regions under various temperatures. Extrusion weld is not weakest region in AZ80 hollow profile in terms of hardness, the peak hardness of weld regions is roughly equal to the weld-free regions at different aging temperatures, which is attributed to similar volume fraction, morphology, and size of β-Mg17Al12 precipitate in weld regions and weld-free regions. The precipitate-free zones (PFZs) usually form near the welds interface in aging process, and the hardness of PFZs is usually lower than those of weld regions and weld-free regions. Aging at 200°C for 24?h is suitable heat treatment system for AZ80 hollow profile, which can achieve excellent mechanical property and simultaneously reduce the width of PFZs. 相似文献
995.
Étude O'Neel‐Judy Dylan Nicholls John Castañeda John G. Gibbs 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(32)
Using a dynamic fabrication process, hybrid, photoactivated microswimmers made from two different semiconductors, titanium dioxide (TiO2) and cuprous oxide (Cu2O) are developed, where each material occupies a distinct portion of the multiconstituent particles. Structured light‐activated microswimmers made from only TiO2 or Cu2O are observed to be driven in hydrogen peroxide and water most vigorously under UV or blue light, respectively, whereas hybrid structures made from both of these materials exhibit wavelength‐dependent modes of motion due to the disparate responses of each photocatalyst. It is also found that the hybrid particles are activated in water alone, a behavior which is not observed in those made from a single semiconductor, and thus, the system may open up a new class of fuel‐free photoactive colloids that take advantage of semiconductor heterojunctions. The TiO2/Cu2O hybrid microswimmer presented here is but an example of a broader method for inducing different modes of motion in a single light‐activated particle, which is not limited to the specific geometries and materials presented in this study. 相似文献
996.
997.
《材料科学技术学报》2019,35(12):2950-2956
For the C/SiC T-section structures, fabrication defects such as pores and local delaminations can be easily formed in the intersection zone which significantly affect the load bearing capacity. In this work, the mechanical behavior of C/SiC T-section under pulling load was investigated, and especially the delamination behavior was studied by introducing the cohesive zone model into the finite element modeling. It was found that for C/SiC T-section under pulling load, the maximum critical delamination load was about 1075 N in the present work, and the interface delamination was the main failure mode. It was verified that the effective interfacial strength influenced the critical delamination load, and the strain energy release affected the delamination behavior of the T-section specimen. The failure mechanisms of C/SiC T-section under pulling load depend on the interface bonding states. When the interface is well bonded, the failure mechanisms mainly include matrix stripping, matrix fracture and fiber breakage. Otherwise, only the matrix stripping can be found at the interface of the C/SiC T-section specimen. 相似文献
998.
999.
首先,根据Reddy给出的考虑高阶剪切效应的层合理论,气动弹性活塞理论,利用Hamilton原理,对考虑采用基于活塞理论的一阶非线性气动力和面内参数激励的联合作用下的轴向可伸缩复合材料悬臂梁进行非线性动力学进行建模,得到其偏微分动力学控制方程.然后对控制方程无量纲化,利用Galerkin方法对控制方程进行了截断,得到三个可反映可伸缩悬臂梁横向振动的无量纲形式的常微分非线性动力学方程,只要选取适合的复合材料及其相关参数,使用数值方法就对模型在外伸和回收过程中的相关振动特性进行了分析. 相似文献
1000.
郭丹丹 《计算机测量与控制》2014,22(12)
云模型控制理论是智能控制学科的新兴领域,因此如何扩展云模型的应用范围并使其走向工程化和实用化成为其研究重点;针对船舶运动模型具有不确定性和外部扰动随机性等特点,尝试将云模型应用于船舶动力定位的控制过程中;由于云模型控制器存在参数难以整定的问题,提出了基于粒子群算法的优化设计方法;针对标准粒子群优化算法容易出现早熟收敛的问题,引入自适应粒子群优化算法;仿真研究表明云模型控制及粒子群优化的可行性和有效性。 相似文献