全文获取类型
收费全文 | 21357篇 |
免费 | 2643篇 |
国内免费 | 2186篇 |
专业分类
电工技术 | 1527篇 |
综合类 | 3083篇 |
化学工业 | 1609篇 |
金属工艺 | 1426篇 |
机械仪表 | 1344篇 |
建筑科学 | 1614篇 |
矿业工程 | 543篇 |
能源动力 | 1002篇 |
轻工业 | 831篇 |
水利工程 | 1112篇 |
石油天然气 | 892篇 |
武器工业 | 242篇 |
无线电 | 1748篇 |
一般工业技术 | 3458篇 |
冶金工业 | 700篇 |
原子能技术 | 211篇 |
自动化技术 | 4844篇 |
出版年
2024年 | 149篇 |
2023年 | 565篇 |
2022年 | 666篇 |
2021年 | 889篇 |
2020年 | 906篇 |
2019年 | 773篇 |
2018年 | 629篇 |
2017年 | 689篇 |
2016年 | 696篇 |
2015年 | 726篇 |
2014年 | 974篇 |
2013年 | 1319篇 |
2012年 | 1308篇 |
2011年 | 1340篇 |
2010年 | 1035篇 |
2009年 | 1168篇 |
2008年 | 1154篇 |
2007年 | 1379篇 |
2006年 | 1372篇 |
2005年 | 1175篇 |
2004年 | 1039篇 |
2003年 | 902篇 |
2002年 | 708篇 |
2001年 | 703篇 |
2000年 | 612篇 |
1999年 | 558篇 |
1998年 | 440篇 |
1997年 | 382篇 |
1996年 | 367篇 |
1995年 | 290篇 |
1994年 | 248篇 |
1993年 | 195篇 |
1992年 | 179篇 |
1991年 | 146篇 |
1990年 | 133篇 |
1989年 | 113篇 |
1988年 | 92篇 |
1987年 | 45篇 |
1986年 | 26篇 |
1985年 | 14篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1964年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
介绍了一种基于人工神经网络(ANN)的声目标识别系统,概述了用MATLAB专用工具箱对神经网络权值进行训练及仿真的过程,叙述了ANN目标识别系统的数字信号处理器(DSP)实时实现过程,并着重分析定点实现过程中程序变量的定标、非线性运算的实现、溢出的处理等关键步骤.对不同字长的识别结果进行比较表明,基于定点实时实现的系统数据保持很高的精度,可以得到与浮点处理相同的识别率. 相似文献
52.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
53.
YOSHIHARU KARIYA TADATOMO SUGA 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(5):413-419
This paper details the deformation mechanism and low‐cycle fatigue life of eutectic solder alloys at high temperature (around 0.8Tm). Grain boundary sliding generally nucleates a wedge‐type cavity that reduces the low‐cycle fatigue life of metals. In this study, grain boundary sliding has promoted intergranular failure contributing to the reduction in fatigue life of Sn–Ag–Cu alloy. However, grain boundary sliding has exerted no deleterious effects on fatigue resistance of eutectic Pb–Sn and Bi–Sn alloys. The phase boundary sliding with very fine microstructure induces exceptional ductility in these alloys leading to superior low‐cycle fatigue endurance for theses eutectic Pb–Sn and Bi–Sn alloys. 相似文献
54.
Boundary objects are a critical, but understudied, theoretical construct in CSCW. Through a field study of aircraft technical
support, we examined the role of boundary objects in the practical achievement of safety by service engineers. Their resolution
of repair requests was preserved in the organization’s memory via three compound boundary objects. These crystallizations
did not manifest a static interpretation, but instead were continually reinterpreted in light of meta-negotiations. This suggests
design implications for organizational memory systems which can more fluidly represent the meta-negotiations surrounding boundary
objects. 相似文献
55.
杨加峰 《武汉理工大学学报(材料科学英文版)》2005,20(Z1)
1Introduction HA(hydroxyapatite)wasakindofbioactiveceram ics,whichhadexcellentbiocompatibilityandtissueaffin ityinthatitscomponentsweresimilartothoseofhuman bone[1].Soitwasthebestknownhumanbonesubstitute,andunprecedentedeffecthadbeenharvestedinrecenttwo d… 相似文献
56.
Li Jian-zhong Niu Zheng-meng Chen Gang Tan Li-xing Shaanxi Institute of Mechanical Engineering Xi''''an P.R.China 《水动力学研究与进展(B辑)》1993,(4)
This paper will introduce experimental studies and numerical calculation onturbulent boundary layer of water flow along curved surface in our country in recent years.Onthe basis of the experimental studies,the effects of curvature and roughness on velocitydistribution and pressure distribution and the change of turbulent flow boundary layer onoverflow bucket concave surface is discussed.We proposed the empirical formula of velocity,pressure and the change of turbulent flow boundary layer on outlet bucket concave.According tothe momentum principle,we have deduced the momentum integral equation full water depthboundary layer and using the element as control unit inside the boundary layer on concavesurface of bucket.Combining with continuity equation,we have computed the boundary layerdevelopment on the bucket of a spillway.Compared with the field experimental data,thecalculation results are available.Under polar coordinates,a mathematical model for simulatingtime-averaged flow characteristics in concave surface of bucket is established.The turbulent flowfield on concave surface of bucket is calculated by SIMPLE method and this mathematicalmodel.The flow velocity field,pressure field,distribution of turbulent kinetic energy,distribution of turbulent energy dissipating rate and distribution of shear stress are available.Thecalculation value is consistent with measured test data. 相似文献
57.
58.
饱和—非饱和土体非稳定渗流数值分析 总被引:56,自引:0,他引:56
本文对一般的非饱和渗流有限元计算方法加以改进,有效地消除了非饱和渗流数值计算中存在的数值弥散现象。同时还提出了一种简便有效的逸出面处理新方法,并给出了非饱和非稳定渗流计算的实例。 相似文献
59.
Forecasts by rational agents contain embedded initial and terminal boundary conditions. Standard time series models generate two types of long-run boundary values or steady-state 'endpoints' – fixed endpoints and moving average endpoints. Neither can explain the shifting endpoints implied by postwar movements in the cross-section of forward rate forecasts in the term structure or by post-1979 changes in survey estimates of expected long-run inflation. Multiperiod forecasts by a broader class of 'moving endpoint' time series models provide substantially improved tracking of the historical term structure and generally support the internal consistency of the ex ante long-run expectations of bond traders and survey respondents. 相似文献
60.