全文获取类型
收费全文 | 29344篇 |
免费 | 2778篇 |
国内免费 | 1702篇 |
专业分类
电工技术 | 1889篇 |
技术理论 | 2篇 |
综合类 | 2608篇 |
化学工业 | 4635篇 |
金属工艺 | 1307篇 |
机械仪表 | 1682篇 |
建筑科学 | 2208篇 |
矿业工程 | 689篇 |
能源动力 | 641篇 |
轻工业 | 3265篇 |
水利工程 | 652篇 |
石油天然气 | 1339篇 |
武器工业 | 247篇 |
无线电 | 3327篇 |
一般工业技术 | 3008篇 |
冶金工业 | 1176篇 |
原子能技术 | 352篇 |
自动化技术 | 4797篇 |
出版年
2024年 | 119篇 |
2023年 | 402篇 |
2022年 | 807篇 |
2021年 | 1073篇 |
2020年 | 846篇 |
2019年 | 645篇 |
2018年 | 783篇 |
2017年 | 852篇 |
2016年 | 783篇 |
2015年 | 1129篇 |
2014年 | 1551篇 |
2013年 | 1817篇 |
2012年 | 2157篇 |
2011年 | 2299篇 |
2010年 | 2216篇 |
2009年 | 2036篇 |
2008年 | 2136篇 |
2007年 | 2080篇 |
2006年 | 1803篇 |
2005年 | 1546篇 |
2004年 | 1124篇 |
2003年 | 889篇 |
2002年 | 917篇 |
2001年 | 742篇 |
2000年 | 649篇 |
1999年 | 491篇 |
1998年 | 397篇 |
1997年 | 284篇 |
1996年 | 236篇 |
1995年 | 218篇 |
1994年 | 173篇 |
1993年 | 141篇 |
1992年 | 102篇 |
1991年 | 90篇 |
1990年 | 74篇 |
1989年 | 61篇 |
1988年 | 35篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1969年 | 4篇 |
1959年 | 3篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 407 毫秒
181.
In this paper, a dynamic modeling method and an active vibration control scheme for a smart flexible four-bar linkage mechanism featuring piezoelectric actuators and strain gauge sensors are presented. The dynamics of this smart mechanism is described by the Discrete Time Transfer Matrix Method of Multibody System (MS-DTTMM). Then a nonlinear fuzzy neural network control is employed to suppress the vibration of this smart mechanism. For improving the dynamic performance of the fuzzy neural network, a genetic algorithm based on the MS-DTTMM is designed offline to tune the initial parameters of the fuzzy neural network. The MS-DTTMM avoids the global dynamics equations of the system, which results in the matrices involved are always very small, so the computational efficiency of the dynamic analysis and control system optimization can be greatly improved. Formulations of the method as well as a numerical simulation are given to demonstrate the proposed dynamic method and control scheme. 相似文献
182.
支持向量机是一类新型机器学习方法,成功应用于各个领域,算法在分类性能上优于其它学习算法。该文在字符特征提取基础上,将支持向量机理论应用于车牌识别系统,提高识别率和识别速度,具有很好的推广价值。 相似文献
183.
应用可视化技术构造卫星运行的虚拟场景,实时显示卫星运行状态及星下点轨迹,可为卫星轨道设计、卫星运行状态监控及卫星应用提供直观的分析和指导。通过对卫星轨道计算方法、几何建模、虚拟场景装配及虚拟场景驱动方法研究,本文开发了卫星运行三维场景及星下点轨迹可视化软件。本文详细给出了地球模型、卫星模型的建模及由此模型组装卫星运行场景的方法,卫星轨道计算及星下点轨迹可视化方法。该软件可实时模拟卫星在太空中的运行场景,给出卫星的即时经纬度坐标及星下点位置坐标。该软件已在实践中得到应用。 相似文献
184.
185.
186.
Ling Yin Eric Y. J. Vancoille Kuppuswamy Ramesh Han Huang 《International Journal of Machine Tools and Manufacture》2004,44(6):607-615
Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining was carried out to investigate microfracture, residual damage, and surface roughness associated with material removal and surface generation. Brittle versus plastic deformation was studied using Vickers indention and nano-indentation. To characterize the abrasive machining response, the 6H-SiC (0001) substrates were ground using diamond wheels with grit sizes of 25, 15 and 7 μm, and then polished with diamond suspensions of 3 and 0.05 μm. It is found that in indentation, there was a scale effect for brittle versus plastic deformation in 6H-SiC substrates. Also, in grinding, the scales of fracture and surface roughness of the substrates decreased with a decrease in diamond grit size. However, in polishing, a reduction in grit size of diamond suspensions gave no significant improvement in surface roughness. Furthermore, the results showed that fracture-free 6H-SiC (0001) surfaces were generated in polishing with the existence of the residual crystal defects, which were associated with the origin of defects in single crystal growth. 相似文献
187.
Nano SiO2 was filled into gypsum particleboard. Effect of the amount of nano SiO2 particles filled, ultrasonic dissipating duration and treating the nano particles with different coupling agents on the mechanical properties of the board were studied respectively. The results show that nano SiO2 is helpful for the improvement of the properties. Adding 3%(mass fraction) nano SiO2 is the best for the improvement of both modulus of rupture(MOR) and modulus of elasticity(MOE) of the boards formed at 30 ℃ or 40 ℃. For the boards formed at 30 ℃, their MOR and MOE can be improved by 8.77% and 12.24%, and MOR and MOE of the boards formed at 40 ℃ can be improved by 44.44% and 108.38%.3% is also the best addition proportion to improve internal bond(IB) of the boards formed at 30 ℃, while 5% is the best for that of the boards formed at 40 ℃. At room temperature, dissipating nano Si02 into flake by ultrasonic has better effect on the properties of the final products. Through ultrasonic treating for 1 h and the best treating duration, the MOR and MOE can be increased by 41.99% and 47.80%. In addition, different coupling agents have different effects on the final properties too, and silane coupling agent KH570 is better for the improvement of properties of the boards formed at room temperature. 相似文献
188.
189.
利用多功能改进型索氏提取器为提取工具,以人参须根粉为原料,盐酸为催化剂,分子筛辅助下高效制备了稀有人参皂苷Rg5,并通过单因素实验优化了工艺条件。实验结果表明:当以30 mL的甲醇为溶剂、加入0.3 g 4 A分子筛、于65 ℃提取4 h时,人参总皂苷的提取率达到10.2%,稀有人参皂苷Rg5的得率达到3.20%,与传统索氏提取器相比可以显著提高人参皂苷Rg5的制备效率。分子筛辅助下利用多功能改进型索氏提取器从人参须根粉提取制备稀有人参皂苷Rg5,不仅得率较高,而且操作简单快捷,是一种快速制备人参皂苷Rg5的工艺方法。 相似文献
190.
现有的大多数特征点提取算法适用于处理纹理丰富的图像,而对于弱纹理图像则无法提取有效的特征点. 对此,提出了多邻域结构张量特征(MNSTF)算法. 基于一系列固定的邻域和图像结构张量,通过表达局部图像的结构和纹理信息,解决了弱纹理和无纹理场景下特征点提取和匹配等相关问题;同时,通过计算邻域之间的相对方向,实现了MNSTF算法特征描述子的旋转不变性. 实验结果表明,MNSTF算法在经过旋转的弱纹理图像测试集上的特征点匹配准确率达到了99.9%以上,验证了其良好的适用性、旋转不变性和鲁棒性. 相似文献