全文获取类型
收费全文 | 6074篇 |
免费 | 591篇 |
国内免费 | 471篇 |
专业分类
电工技术 | 147篇 |
综合类 | 834篇 |
化学工业 | 606篇 |
金属工艺 | 356篇 |
机械仪表 | 300篇 |
建筑科学 | 823篇 |
矿业工程 | 150篇 |
能源动力 | 111篇 |
轻工业 | 375篇 |
水利工程 | 308篇 |
石油天然气 | 220篇 |
武器工业 | 40篇 |
无线电 | 235篇 |
一般工业技术 | 715篇 |
冶金工业 | 790篇 |
原子能技术 | 36篇 |
自动化技术 | 1090篇 |
出版年
2024年 | 16篇 |
2023年 | 105篇 |
2022年 | 190篇 |
2021年 | 242篇 |
2020年 | 211篇 |
2019年 | 203篇 |
2018年 | 174篇 |
2017年 | 196篇 |
2016年 | 203篇 |
2015年 | 203篇 |
2014年 | 380篇 |
2013年 | 375篇 |
2012年 | 359篇 |
2011年 | 491篇 |
2010年 | 357篇 |
2009年 | 388篇 |
2008年 | 389篇 |
2007年 | 442篇 |
2006年 | 369篇 |
2005年 | 335篇 |
2004年 | 305篇 |
2003年 | 234篇 |
2002年 | 204篇 |
2001年 | 162篇 |
2000年 | 107篇 |
1999年 | 93篇 |
1998年 | 58篇 |
1997年 | 46篇 |
1996年 | 48篇 |
1995年 | 40篇 |
1994年 | 47篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 20篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1966年 | 3篇 |
1964年 | 3篇 |
1961年 | 4篇 |
1959年 | 3篇 |
1957年 | 3篇 |
1956年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有7136条查询结果,搜索用时 140 毫秒
91.
基于粒子群遗传算法的航天产品装配顺序优化方法 总被引:1,自引:0,他引:1
航天产品的装配顺序优化(ASPFAP)具有多目标和非线性的特点,针对传统算法在该问题求解上的不足,将粒子群算法和遗传算法结合起来(PSO-GA),提出一种新的面向航天产品的装配顺序优化方法。使用优先约束关联模型(APCRM)来描述零件间的优先约束关系和关联关系;研究了粒子群遗传算法的基因组、染色体以及粒子的编码表达方法;综合考虑装配连续性、装配资源和仪器设备的影响,提出了有工程意义的适应度函数的表达式;根据APCRM生成随机的可行初始装配序列,并利用粒子群算法重构遗传算法的交叉算子对装配顺序进行优化。实例表明该方法有较好的收敛性和稳定性,优化结果具有实际工程意义。 相似文献
92.
93.
94.
浙江省风土建筑类型多样,成因复杂。文章借助建筑人类学、语言学研究成果,从主匠关系出发,引入分级风土特征图谱的概念,探讨浙江省范围内风土建筑区域的划分方法。 相似文献
95.
Project success is a widely studied and discussed phenomenon of project management. Whilst certain success criteria and success factors are common across different project types, there are unique criteria and factors that apply only to specific projects. This paper presents the development and investigation of the attributes of the success criteria and factors of organisational event projects, as well as an analysis of the relationship between the criteria and factor areas. The study is based on a questionnaire survey of world and European championships. The findings of the study are of interest because they distinguish the success factors that represent relationship orientation and task focus. An analysis of the correlations suggests that relationship-oriented success factors, such as communication, co-operation and project leadership, play a crucial role in carrying out successful organisational event projects. 相似文献
96.
本文主要以我国东部、东北部、中部和西部为研究对象,从能源资源潜力、能源勘探开发现状、能源资源开发利用布局等方面,探究能源资源开发利用和国土资源节约集约之间的耦合关系,并提出相关建议,这将对我国走结构优化、节约集约、效率提升的绿色发展新路具有一定的参考价值。 相似文献
97.
软岩巷道变形破坏是煤矿深部开采软岩巷道支护的重大灾害之一。基于刘庄矿区深部泥岩现场三轴流变试验和数值模拟,对软岩巷道变形破坏机理及支护技术进行了分析,采用最小二乘法中的阻尼最小二乘法(Marquardt法)逐次线性化的间接方法,利用非线性流变力学模型,拟合得到泥岩蠕变本构方程,分析得出刘庄矿区深部软岩巷道的合理支护方式:(1)采用反底拱和全封闭的施工方式,减小巷道的维修工作量;(2)顺层掘进的重要峒室,其锚杆的方位应尽可能和层面垂直,将弱面串联成一体;(3)底板锚注控制底板大变形。 相似文献
98.
In this paper,the formation mechanism of mesoporous CeO_2 synthesized by thermal decomposition of Ce-MOF and its performance of benzene catalytic combustion,as well as the structure-activity relationship between them were studied in depth.The self-assembly process and physicochemical properties of CeO_2 were characterized by thermogravimetry analysis,powder X-ray diffraction,N_2 adsorption/desorption,high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy techniques.Characterization results show that Ce-MOF is completely decomposed into pure mesoporous CeO_2 when the decomposition temperature is higher than 400℃.At this threshold temperature,CeO_2(400) has the largest specific surface area and pore volume of 114 m~2/g and 0.152 cm3/g,respectively.CeO_2(400) exhibits very high catalytic activity for benzene combustion,which can completely catalyze the degradation of benzene at 260℃.Meanwhile,the mesoporous CeO_2(400) supported Pt nanocrystalline catalysts were prepared by high temperature solution-phase reduction method.Pt/CeO_2(400)can completely degrade benzene at about 200℃ and represents high durability and good waterresistance for benzene combustion during 100 h of continuous reaction. 相似文献
99.
Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaOx(OH)y),and deposited platinum(Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaOx(OH)y catalysts.However,we find that these catalysts perform a poor stability for the CO oxidation reaction.The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),transmission electron microscopy(TEM),temperature-programmed reduction by carbon monoxide(CO-TPR) and thermogravimetric analysis(TGA),to demonstrate that the oxidized platinum atoms or clusters,without any component of Pt-Pt metallic bond,are highly dispersed on the surface of LaOx(OH)y.Furthermore,the as-formed lanthanum carbonate(La2O2CO3) during the exposure to ambient circumstances or in the reaction atmosphere of CO+O2,severely impair the reactivity of Pt/LaOx(OH)y.On the basis of the obtained experimental results,we have drawn a conclusion that the oxidized PtOx atoms or PtxOy clusters are the active species for CO oxidation,while the formation of lanthanum carbonate is the origin of deactivation on reactivity. 相似文献
100.
The original unified hardening (UH) model, in which a straight Hvorslev envelope was employed to determine the potential peak stress ratio of overconsolidated soils, is revised using a smoothed Hvorslev envelope (Hermite-Hvorslev envelope). The strength at the intersection between the straight Hvorslev envelope and the critical state surface (i.e. Mohr-Coulomb envelope) can be undefined due to the discontinuous change in the slope of the two linear strength envelopes mentioned above. A smoothed Hvorslev envelope is derived through Hermite interpolation to ensure a smooth change between the proposed Hvorslev envelope and the zero-tension surface as well as a smoothed transition between the proposed Hvorslev envelope and the critical state surface. The Hermite-Hvorslev envelope is then integrated into the original UH model, and then the UH models with four different functions of the Hvorslev envelope are compared with each other. The UH model revised by the Hermite-Hvorslev envelope can well predict the mechanical behaviors of normally consolidated and overconsolidated soils in drained and undrained conditions with the same parameters in the modified Cam-Clay model. 相似文献