全文获取类型
收费全文 | 37090篇 |
免费 | 5085篇 |
国内免费 | 3855篇 |
专业分类
电工技术 | 3730篇 |
综合类 | 5538篇 |
化学工业 | 2528篇 |
金属工艺 | 943篇 |
机械仪表 | 2222篇 |
建筑科学 | 1909篇 |
矿业工程 | 774篇 |
能源动力 | 819篇 |
轻工业 | 1779篇 |
水利工程 | 1066篇 |
石油天然气 | 1173篇 |
武器工业 | 554篇 |
无线电 | 5408篇 |
一般工业技术 | 3794篇 |
冶金工业 | 858篇 |
原子能技术 | 299篇 |
自动化技术 | 12636篇 |
出版年
2024年 | 157篇 |
2023年 | 549篇 |
2022年 | 1030篇 |
2021年 | 1187篇 |
2020年 | 1326篇 |
2019年 | 1302篇 |
2018年 | 1167篇 |
2017年 | 1491篇 |
2016年 | 1642篇 |
2015年 | 1739篇 |
2014年 | 2295篇 |
2013年 | 2963篇 |
2012年 | 2764篇 |
2011年 | 2973篇 |
2010年 | 2266篇 |
2009年 | 2315篇 |
2008年 | 2315篇 |
2007年 | 2610篇 |
2006年 | 2094篇 |
2005年 | 1853篇 |
2004年 | 1550篇 |
2003年 | 1305篇 |
2002年 | 1134篇 |
2001年 | 995篇 |
2000年 | 843篇 |
1999年 | 702篇 |
1998年 | 521篇 |
1997年 | 516篇 |
1996年 | 395篇 |
1995年 | 358篇 |
1994年 | 289篇 |
1993年 | 236篇 |
1992年 | 200篇 |
1991年 | 183篇 |
1990年 | 161篇 |
1989年 | 119篇 |
1988年 | 80篇 |
1987年 | 62篇 |
1986年 | 39篇 |
1985年 | 32篇 |
1984年 | 45篇 |
1983年 | 44篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1980年 | 26篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
Detection of multiple cracks using frequency measurements 总被引:2,自引:0,他引:2
D.P. Patil 《Engineering Fracture Mechanics》2003,70(12):1553-1572
A method for detection of multiple open cracks in a slender Euler-Bernoulli beams is presented based on frequency measurements. The method is based on the approach given by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841], transverse vibration modelling through transfer matrix method and representation of a crack by rotational spring. The beam is virtually divided into a number of segments, which can be decided by the analyst, and each of them is considered to be associated with a damage parameter. The procedure gives a linear relationship explicitly between the changes in natural frequencies of the beam and the damage parameters. These parameters are determined from the knowledge of changes in the natural frequencies. After obtaining them, each is treated in turn to exactly pinpoint the crack location in the segment and determine its size. The forward, or natural frequency determination, problems are examined in the passing. The method is approximate, but it can handle segmented beams, any boundary conditions, intermediate spring or rigid supports, etc. It eliminates the need for any symbolic computation which is envisaged by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841] to obtain mode shapes of the corresponding uncracked beams. The proposed method gives a clear insight into the whole analysis. Case studies (numerical) are presented to demonstrate the method effectiveness for two simultaneous cracks of size 10% and more of section depth. The differences between the actual and predicted crack locations and sizes are less than 10% and 15% respectively. The numbers of segments into which the beam is virtually divided limits the maximum number of cracks that can be handled. The difference in the forward problem is less than 5%. 相似文献
182.
Hakan Boyaci 《Sadhana》2006,31(1):1-8
A simply supported damped Euler-Bernoulli beam with immovable end conditions are considered. The concept of non-ideal boundary
conditions is applied to the beam problem. In accordance, the boundaries are assumed to allow small deflections and moments.
Approximate analytical solution of the problem is found using the method of multiple scales, a perturbation technique. 相似文献
183.
文中主要针对多爆炸成型弹丸空爆战斗部,在分析区域识别和占空比识别两种不同扫描准则的基础上,应用蒙特卡洛方法计算了战斗部对目标的毁伤概率.通过仿真计算结果对比分析,获得了不同扫描准则对毁伤概率的影响,结果可为多爆炸成型弹丸空爆战斗部设计和选择使用扫描准则提供参考依据. 相似文献
184.
介绍了桃林口水库大坝人工监测项目管理软件研制的意义。对软件结构、开发环境、基本计算原理、主要功能进行了详细阐述;并以大坝垂直位移分析为例,详细讲述了回归分析在资料分析中的具体应用。该软件的应用使工程管理水平上了一个新台阶。 相似文献
185.
A new curvature technique calculation for surface tension contribution in PLIC-VOF method 总被引:1,自引:0,他引:1
The volume of fluid (VOF) methods have been used for numerous numerical simulations. Among these techniques used to define
the moving interface, the piecewise linear interface reconstruction (PLIC-VOF) is one of the most accurate. A study of the
superficial tension impact on two-phase flow with free surface is presented. A new method based on direct staggered grid is
developped to include surface tension in PLIC-VOF. The new numerical curvature calculation method doesn't need smoothed colour
function and leads to less “spurious current”. This technique is applied to the calculus of surface tension force in the case
of the rise of air bubble in viscous liquid and the fall of liquid drop in the same liquid on free surface. Droplets, thin
layer and capillarity waves are observed after the free surface rupture for different Bond number. The influence of surface
tension calculus is then obvioused and when the drop hit the free surface, wavelets propagate toward the virtual boundaries
imposed. 相似文献
186.
William E Acree Jr Michael H Abraham 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(8):1441-1446
The contentions made in an earlier paper [J Chem Technol Biotechnol 80 : 133–137 (2005)] that the coefficients of the Abraham solvation equation do not provide meaningful information on the molecular properties of ionic liquid solvents is refuted. The objections noted in the earlier paper disappear when the solvation equation model is correctly applied to the experimental data. It is further shown that the coefficients of the Abraham solvation equations can be used to characterize ionic liquids and can be used to select solvents for the solubility of gaseous solutes. Copyright © 2006 Society of Chemical Industry 相似文献
187.
High accuracy path tracking for vehicles in presence of sliding: Application to farm vehicle automatic guidance for agricultural tasks 总被引:1,自引:0,他引:1
Roland Lenain Benoit Thuilot Christophe Cariou Philippe Martinet 《Autonomous Robots》2006,21(1):79-97
When designing an accurate automated guidance system for vehicles, a major problem is sliding and pseudo-sliding effects. This is especially the case in agricultural applications, where five-centimetre accuracy with respect to the desired trajectory is required, although the vehicles are moving on slippery ground. It has been established that RTK GPS was a very suitable sensor to achieve automated guidance with such high precision: several control laws have been designed for vehicles equipped with this sensor, and provide the expected guidance accuracy as long as the vehicles do not slide. In previous work, further control developments have been proposed to take sliding into account: guidance accuracy in slippery environments has been shown to be preserved, except transiently at the beginning/end of curves. In this paper, the design of this control law is first recalled and discussed. A Model Predictive Control method is then applied in order to preserve accuracy of guidance even during these curvature transitions. Finally, the overall control scheme is implemented, and improvements with respect to previous guidance laws are demonstrated through full-scale experiments. 相似文献
188.
189.
190.
This paper derives the admissible decompositions for a time series dynamic linear model, assuming only that the model is observable. The decompositions depend on factorizations of the characteristic polynomial of the state evolution matrix G into relatively prime factors. This generalizes the method of West (1997 ) which considers one decomposition in the particular case where G is diagonalizable. Conditions are derived for a decomposition to be independent. These results show that no autoregressive process of order d has an independent decomposition for any integer d . Two illustrations of this procedure are discussed in detail. 相似文献