全文获取类型
收费全文 | 155087篇 |
免费 | 16326篇 |
国内免费 | 10268篇 |
专业分类
电工技术 | 12821篇 |
技术理论 | 3篇 |
综合类 | 19878篇 |
化学工业 | 16736篇 |
金属工艺 | 6548篇 |
机械仪表 | 11201篇 |
建筑科学 | 18968篇 |
矿业工程 | 6992篇 |
能源动力 | 5229篇 |
轻工业 | 8462篇 |
水利工程 | 7071篇 |
石油天然气 | 7237篇 |
武器工业 | 2277篇 |
无线电 | 11636篇 |
一般工业技术 | 19159篇 |
冶金工业 | 5610篇 |
原子能技术 | 2437篇 |
自动化技术 | 19416篇 |
出版年
2024年 | 583篇 |
2023年 | 1861篇 |
2022年 | 3739篇 |
2021年 | 4331篇 |
2020年 | 4831篇 |
2019年 | 4189篇 |
2018年 | 3949篇 |
2017年 | 4959篇 |
2016年 | 5586篇 |
2015年 | 5883篇 |
2014年 | 9389篇 |
2013年 | 9012篇 |
2012年 | 11997篇 |
2011年 | 12198篇 |
2010年 | 9391篇 |
2009年 | 9786篇 |
2008年 | 9042篇 |
2007年 | 11182篇 |
2006年 | 9741篇 |
2005年 | 8178篇 |
2004年 | 6673篇 |
2003年 | 5699篇 |
2002年 | 4768篇 |
2001年 | 3990篇 |
2000年 | 3506篇 |
1999年 | 3090篇 |
1998年 | 2413篇 |
1997年 | 2106篇 |
1996年 | 1795篇 |
1995年 | 1619篇 |
1994年 | 1370篇 |
1993年 | 977篇 |
1992年 | 864篇 |
1991年 | 625篇 |
1990年 | 527篇 |
1989年 | 502篇 |
1988年 | 363篇 |
1987年 | 207篇 |
1986年 | 168篇 |
1985年 | 79篇 |
1984年 | 76篇 |
1983年 | 50篇 |
1982年 | 52篇 |
1981年 | 63篇 |
1980年 | 42篇 |
1979年 | 40篇 |
1978年 | 23篇 |
1976年 | 15篇 |
1975年 | 17篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
271.
A method for constructing an approximation of the critical excitation that drives an elastoplastic system from rest to a target threshold at a specified time instant, referred to as the “suboptimal excitation,” is presented in this paper. It is based on the observations gained from study of the critical excitations in the companion paper. Essentially, for the usual case of interest where the failure time is not small compared to the natural period, the duration of the positive and negative pulses of the critical excitation are roughly equal to half of the natural period. This consideration allows for a simple intuitive approximation of the critical excitation. The amplitudes of the positive and negative pulses are obtained in closed forms using energy balance. Numerical investigations show that the critical excitations are well approximated by the suboptimal excitations. 相似文献
272.
In this paper, flexural behavior of horizontally curved prestressed (posttensioned) box bridges is studied by using three-dimensional and refined finite-element modeling and analysis. Bridge length, section geometry, and material properties are the same in all the models, while angle of curvature varies from 0 to 90°. The results of analysis show that in curved bridges, stress distribution is significantly different in comparison to straight bridges. Also, the level of stresses at some locations of section width is considerably high. It is proposed to vary the distribution of the prestressing tendons across section width in order to optimize the bridge capacity. Results show that by proper redistribution of prestressing in section width, significant reduction in resultant stress is possible. 相似文献
273.
Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known
method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless
nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method
of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller
particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically
contains the three substeps contact detection, force computation and integration. However, there exists a large variety of
different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe
the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different
types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations
are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally
demonstrated by means of application examples.
Commemorative Contribution. 相似文献
274.
275.
Here, we describe the development of a reacting flow multi-species/combustion methodology, implemented as an extension to the differential reduced ejector analysis (DREA) computer program [Mathematical and computer modeling, vol. 31, 2000, p. 21; Appl. Math. Model. 25 (2001) 427; Comput. Math. Appl. 43(10–11); NASA Contractor Report, 1998]. Use of the single fluid IVP solver framework that was developed for the original DREA model has been directly coupled into the combustion formulation. With these modifications, the analysis has an elementary single step reaction Fuel+Oxidizer→Product combustion capability. Though approximate in nature, the simplicity and efficiency of the DREA formulation make it suitable for its original niche, namely design and preliminary design environments where more complex and expensive models may be inappropriate. 相似文献
276.
FANGLiang XIAOFeng TAOZainan KusuhiroMukai 《武汉理工大学学报(材料科学英文版)》2005,20(2):67-70
The density of liquid Ni- Ta alloys was measured by using a modified sessile drop method. It is found that the density of the liquid Ni- Ta alloys decreases with the increasing temperature, but increases with the increase of tantalum concentration in the alloys. The molar volume of liquid Ni- Ta binary alloys increases with the increase of temperature ancl tantalum concentration. 相似文献
277.
278.
由于在机器人导航等领域新的图像装置不符合透视规则,无法运用传统的透视位置估计方法,采用吴氏零点分解方法,给出非透视3点问题的解析解.利用新图像装置的几何条件,建立了非透视3点方程系统. 相似文献
279.
We succeeded in the fabrication of bonded laser crystals composed of a neodymium-doped YVO4 laser crystal (Nd:YVO4) and its host crystals YVO4 by a newly developed dry etching technique using an argon ion beam. The optical distortion caused by the bonded interface of size 5 mm × 6 mm was estimated to be 0.05λ at 633 nm. From the comparison of laser performance pumped by a laser diode, the bonded crystals could increase the laser output power by nearly twice that of the non-bonded crystals with the same degree of polarization of 99.2%. To analyze the mechanism of the enhanced reduction of the thermal load in the bonded crystals, numerical simulations with a finite-element method were also performed. 相似文献
280.