全文获取类型
收费全文 | 50781篇 |
免费 | 4913篇 |
国内免费 | 2972篇 |
专业分类
电工技术 | 3033篇 |
技术理论 | 1篇 |
综合类 | 6605篇 |
化学工业 | 2826篇 |
金属工艺 | 4416篇 |
机械仪表 | 7446篇 |
建筑科学 | 7968篇 |
矿业工程 | 1763篇 |
能源动力 | 1478篇 |
轻工业 | 1157篇 |
水利工程 | 1945篇 |
石油天然气 | 1689篇 |
武器工业 | 731篇 |
无线电 | 2177篇 |
一般工业技术 | 9460篇 |
冶金工业 | 2064篇 |
原子能技术 | 544篇 |
自动化技术 | 3363篇 |
出版年
2024年 | 89篇 |
2023年 | 531篇 |
2022年 | 1026篇 |
2021年 | 1297篇 |
2020年 | 1375篇 |
2019年 | 1191篇 |
2018年 | 1196篇 |
2017年 | 1538篇 |
2016年 | 1731篇 |
2015年 | 2014篇 |
2014年 | 3002篇 |
2013年 | 3034篇 |
2012年 | 3890篇 |
2011年 | 4232篇 |
2010年 | 3143篇 |
2009年 | 3371篇 |
2008年 | 3111篇 |
2007年 | 3800篇 |
2006年 | 3295篇 |
2005年 | 2713篇 |
2004年 | 2243篇 |
2003年 | 1873篇 |
2002年 | 1537篇 |
2001年 | 1208篇 |
2000年 | 1138篇 |
1999年 | 955篇 |
1998年 | 732篇 |
1997年 | 681篇 |
1996年 | 533篇 |
1995年 | 503篇 |
1994年 | 401篇 |
1993年 | 292篇 |
1992年 | 255篇 |
1991年 | 170篇 |
1990年 | 159篇 |
1989年 | 126篇 |
1988年 | 95篇 |
1987年 | 58篇 |
1986年 | 32篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1973年 | 1篇 |
1959年 | 3篇 |
1954年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
71.
A three-dimensional FE analysis of large deformations for impact loadings using tetrahedral elements
A three-dimensional dynamic program for the anaysis of large deformations in contact-penetration problems is developed using
the finite element Lagrangian method with explicit time integration. By incorporating a tetrahedral element, which allows
a single-point integration without a special hourglass control scheme, this program can be more effective to the present problem.
The position code algorithm is used to search contact surface. Eroding surfaces are also considered. The defense node algorithm
was slightly modified for the calculation of contact forces. A study of obliquity effects on metallic plate perforation and
ricochet processes in thin plates impacted by a sphere was conducted. It is well simulated that on separation of two parts
of the sphere, the portion still within the crater tends to perforate, while the portion in contact with the plate surface
ricochets. This deformation pattern is observed in experiments, especially at high obliquities. A long rod that impacts an
oblique steel plate at high impact velocity was also simulated in order to study the dynamics of the rod caused by the three
dimensional asymmetric contact. The agreement between simulated and experimental results is quite good. Fracture phenomena
occuring at high obliquity deserves further investigations.
Received: 20 February 2002 / Accepted: 20 September 2002 相似文献
72.
Maenghyo Cho Hee Yuel Roh 《International journal for numerical methods in engineering》2003,56(1):81-115
In the present study first‐order shear deformable shell finite elements based on general curvilinear co‐ordinates are proposed. For the development of the present shell elements, a partial mixed variational functional with independently assumed strains is provided in order to avoid the severe locking troubles known as transverse shear and membrane lockings. Bubble functions are included in the shape function of displacement to improve the performance of the developed element. The proposed assumed strain four‐ and nine‐node elements based on the general tensor shell theory provide an efficient linkage framework for shell surface modelling and finite element analysis. In the several benchmark problems, the present shell elements with exact geometric representations demonstrate their performance compared to previously reported results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
73.
In the present study, attempts are made to extend the application of the mechanical model for the fatigue crack initiation (FCI) and the FCI life formula of metallic notched elements in laboratory air to those in the corrosive environment. The test results and analysis of the corrosion FCI (CFCI) life of aluminum alloys and Ti---6A1---4V show that the expression of the CFCI life obtained by modifying the FCI life formula in laboratory air can give a good fit to the test results of the CFCI life. The salt water (3.5% NaCl) environment has no effects on the CFCI resistant coefficient compared with the FCI resistant coefficient in laboratory air. However, 3.5% NaCl environment greatly decreases the CFCI threshold of aluminum alloy, but has little effect on the CFCI threshold of Ti---6A1---4V. The loading frequency ranging from 1 Hz to 10 Hz has no appreciable effect on the CFCI life, and thus, the CFCI threshold of aluminum alloys investigated. Hence, the expression for the CFCI life of metallic notched elements proposed in this study is a better one, which reveals a correlation between the CFCI life and the governing parameters, such as, the geometry of the notched elements, the nominal stress range, the stress ratio, the tensile properties and the CFCI threshold. However, this new expression of the CFCI life needs to be verified by more test results. 相似文献
74.
本文介绍一种不同于磁性翻牌显示屏和LED显示屏的新型电子显示屏,采用非发光体,针对显示屏彩色和动画图象对象素的要求,讨论了显示屏象素的多面色体变换的电路设计及软件实现。 相似文献
75.
仿生型步进式直线驱动器的研究 总被引:19,自引:0,他引:19
本文提出一种新型直线驱动器的仿生动作原理,并设计出两种机械结构及其控制器。实验表明,这类驱动器具有精度高,步距可变,输出力大,行程长,结构简单,体积小,内藏传感器,具有极好输出特性等特点。这类驱动器适用于一切超高精度的直接驱动。 相似文献
76.
77.
考虑变质量湍流影响的水平井流入动态分析 总被引:1,自引:0,他引:1
在水平井生产过程中,井筒内管流与地层渗流互相制约、互相影响、互为边界条件,从而构成了一个完整的水动力学体系。根据水平井生产时井筒内管流与油藏的相互作用关系,建立了水平井筒存在压力梯度的变质量湍流与地层渗流的耦合计算新方法。关于井筒内流的计算;应用了经典的kεM湍流模型,关于地层的渗流计算,采用了有限元法。通过耦合模拟获得了井筒内湍流场流速分布及总压能损耗的规律,根据耦合模拟计算结果绘出了较为准确的水平井流入动态曲线。该计算方法为描述水平井流入动态、评价水平井产能、确定合理生产制度提供了可靠的手段. 相似文献
78.
前向反冲分析和非卢瑟福背散射 总被引:1,自引:0,他引:1
赵国庆 《理化检验(物理分册)》2002,38(2):88-91
介绍了弹性散射分析中的另外两种分析方法——前向反冲分析和非卢瑟福背散射分析。前向反冲分析适用于材料中H和He同位素分析。高能质子和He离子背散射分析可提高对重基体中C,N和O等轻元素分析的灵敏度。给出了这两种分析方法的应用实例。 相似文献
79.
80.
G. M. Kulikov S. V. Plotnikova 《International journal for numerical methods in engineering》2002,55(10):1167-1183
The precise representation of rigid body motions in the displacement patterns of curved Timoshenko–Mindlin (TM) shell elements is considered. This consideration requires the development of the strain–displacement relationships of the TM shell theory with regard to their consistency with the rigid body motions. For this purpose a refined TM theory of multilayered anisotropic shells is elaborated. The effects of transverse shear deformation and bending‐extension coupling are included. The fundamental unknowns consist of five displacements and eight strains of the face surfaces of the shell, and eight stress resultants. On the basis of this theory the simple and efficient mixed models are developed. The elemental arrays are derived using the Hu–Washizu mixed variational principle. Numerical results are presented to demonstrate the high accuracy and effectiveness of the developed 4‐node shell elements and to compare their performance with other finite elements reported in the literature. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献