全文获取类型
收费全文 | 20019篇 |
免费 | 1809篇 |
国内免费 | 1234篇 |
专业分类
电工技术 | 668篇 |
技术理论 | 1篇 |
综合类 | 1995篇 |
化学工业 | 1098篇 |
金属工艺 | 2610篇 |
机械仪表 | 1371篇 |
建筑科学 | 5141篇 |
矿业工程 | 796篇 |
能源动力 | 459篇 |
轻工业 | 202篇 |
水利工程 | 938篇 |
石油天然气 | 578篇 |
武器工业 | 177篇 |
无线电 | 396篇 |
一般工业技术 | 4465篇 |
冶金工业 | 1334篇 |
原子能技术 | 95篇 |
自动化技术 | 738篇 |
出版年
2024年 | 65篇 |
2023年 | 150篇 |
2022年 | 368篇 |
2021年 | 423篇 |
2020年 | 543篇 |
2019年 | 464篇 |
2018年 | 408篇 |
2017年 | 593篇 |
2016年 | 603篇 |
2015年 | 688篇 |
2014年 | 1077篇 |
2013年 | 970篇 |
2012年 | 1228篇 |
2011年 | 1353篇 |
2010年 | 1115篇 |
2009年 | 1287篇 |
2008年 | 1239篇 |
2007年 | 1626篇 |
2006年 | 1332篇 |
2005年 | 1229篇 |
2004年 | 911篇 |
2003年 | 874篇 |
2002年 | 799篇 |
2001年 | 674篇 |
2000年 | 559篇 |
1999年 | 421篇 |
1998年 | 351篇 |
1997年 | 349篇 |
1996年 | 240篇 |
1995年 | 217篇 |
1994年 | 170篇 |
1993年 | 120篇 |
1992年 | 125篇 |
1991年 | 102篇 |
1990年 | 93篇 |
1989年 | 88篇 |
1988年 | 48篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1965年 | 1篇 |
1961年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
基于高抗热震性能的陶瓷刀具材料的微观结构设计 总被引:1,自引:0,他引:1
本文以现有的抗热震断裂和抗热震损伤的评价理论为基础,通过对材料中微裂纹的长度进行预测,从而实现了对陶瓷刀具材料的抗热震性能的微观结构设计。根据此理论对现有材料的抗热震性能的进行预测,预测结果与实际的测量结果相符,验证了该理论的正确性。 相似文献
63.
Sol-gel methods offer many advantages over conventional slip-casting, including the ability to produce ceramic membranes. They are purer, more homogeneous, more reactive and contain a wider variety of compositions. We produced ormosil sol using sol-gel process under different molecular weight of polymer species [polyethylene glycol (PEG) ] in total system [Tetraethyl ortho silicate(TEOS)-polyethylene glycol (PEG)]. The properties of as-prepared ormosil sol such as,viscosity, gelation time were characterized. Also, the ceramic membrane was prepared by dip-coating with synthetic sol and its micro-structure was observed by scanning electron microscopy. The permeability and rejection efficiency of membrane for oil/water emulsion were evaluated as cross-flow apparatus. The ormosil sol coated Membrane is easily formed by steric effect of polymer and it improves flux efficiency because infiltration into porous support decreased. Its flux efficiency is elevated about 200(1/m2·h) compared with colloidal sol coated membrane at point of five minutes from starting test. 相似文献
64.
The correlation between the crack resistance measured from dynamic and quasi-static J-R tests has been investigated based on test data from instrumented Charpy impact tests and quasi-static single edge notched bend (SENB) J-R tests.The method originally proposed by Aurich et al. [Analyse und Weiterentwicklung Bruchmechanischer versagenskonzepte--Lokales Risswachstum, Ermittlung des Risswiderstandsverhaltens aus der Kerbslagarbeit. BAM Forschungsbericht 192, Berlin 1993, ISBN 3-89429-329-2], to develop a correlation coefficient between the net fracture resistance of Charpy V-notch (ISO) and quasi-static compact tension tests, was extended to establish correlations between so-called ductile-brittle transition fracture resistance curves obtained from instrumented Charpy V-notched (ISO) and fatigue precracked impact tests and quasi-static SENB J-R fracture resistance tests.The correlation between the dynamic and quasi-static crack resistance with regard to practical application to fracture assessments appears to be reasonably consistent, bearing in mind the inherent scatter in crack resistance data in general. The findings of the present research project from testing of ship grade NVE 36 and pressure vessel steel to ASTM A516 Gr. 70 as well as two weldments in the NVE 36 steel, are in excellent agreement with the results of the research conducted by Aurich et al. [Analyse und Weiterentwicklung Bruchmechanischer versagenskonzepte--Lokales Risswachstum, Ermittlung des Risswiderstandsverhaltens aus der Kerbslagarbeit. BAM Forschungsbericht 192, Berlin 1993, ISBN 3-89429-329-2] for structural and pressure vessel steels to the German DIN standard steels including St 52-3, StE 355 and StE 460. 相似文献
65.
This study focuses on numerical simulation of ductile failure in the Co binder phase of WC–Co hardmetal. The growth of edge cracks under mode I loading is considered. A computational micromechanics approach is taken where the Co binder ligaments are explicitly represented in finite element models. An embedding technique is employed. Crystal plasticity theory is used to represent plastic deformation in the Co ligaments. Crack propagation in the binder is simulated using an element removal technique based on a modified Rice and Tracey model for ductile void growth, and fracture resistance curves are generated. Parameter studies are performed for variations in microstructrual parameters such as numbers of Co ligaments ahead of the crack tip and local Co volume fraction. The importance of thermal residual stresses and finite element mesh density are also investigated. 相似文献
66.
Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications 总被引:1,自引:0,他引:1
The slow (subcritical) crack growth (SCG) resistance of Si3 N4 and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si3 N4 sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si3 N4 without additives. 相似文献
67.
Sixiong Han Yasuaki Ichikawa 《International journal for numerical methods in engineering》1995,38(24):4081-4100
In this paper, a mathematical model is proposed for the problem of the scattering of plane waves in a three-dimensional cracked materials. Instead of obtaining closed-form solutions as in conventional theoretical analysis methods, this approach, called the Equivalent Nodal Force (ENF) method formulates the mechanical effects of cracks as an equivalent nodal force in a numerical procedure, and physically translates cracked material into an equivalent continuous one. Several mechanical relations between waves and cracks are evident from this method. Also the results of several numerical calculations are presented and these are compared with those obtained by the conventional methods. 相似文献
68.
69.
70.
用正交设计法优化导叶分段关闭规律的参数 总被引:4,自引:1,他引:3
本文介绍了正交设计法优化水轮机导叶分段关闭规律参数的方法,实例表明,此方法具有简单,准确和直观的优点。 相似文献