全文获取类型
收费全文 | 31857篇 |
免费 | 4310篇 |
国内免费 | 1858篇 |
专业分类
电工技术 | 8223篇 |
综合类 | 3658篇 |
化学工业 | 1443篇 |
金属工艺 | 755篇 |
机械仪表 | 2365篇 |
建筑科学 | 6362篇 |
矿业工程 | 1033篇 |
能源动力 | 1626篇 |
轻工业 | 625篇 |
水利工程 | 1303篇 |
石油天然气 | 728篇 |
武器工业 | 283篇 |
无线电 | 1686篇 |
一般工业技术 | 3041篇 |
冶金工业 | 1051篇 |
原子能技术 | 147篇 |
自动化技术 | 3696篇 |
出版年
2024年 | 181篇 |
2023年 | 435篇 |
2022年 | 825篇 |
2021年 | 946篇 |
2020年 | 1103篇 |
2019年 | 946篇 |
2018年 | 928篇 |
2017年 | 1216篇 |
2016年 | 1288篇 |
2015年 | 1407篇 |
2014年 | 2186篇 |
2013年 | 1819篇 |
2012年 | 2332篇 |
2011年 | 2520篇 |
2010年 | 1888篇 |
2009年 | 1938篇 |
2008年 | 1892篇 |
2007年 | 2152篇 |
2006年 | 1935篇 |
2005年 | 1618篇 |
2004年 | 1328篇 |
2003年 | 1298篇 |
2002年 | 1166篇 |
2001年 | 1029篇 |
2000年 | 843篇 |
1999年 | 723篇 |
1998年 | 388篇 |
1997年 | 403篇 |
1996年 | 295篇 |
1995年 | 210篇 |
1994年 | 191篇 |
1993年 | 110篇 |
1992年 | 79篇 |
1991年 | 60篇 |
1990年 | 69篇 |
1989年 | 65篇 |
1988年 | 68篇 |
1987年 | 31篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1966年 | 2篇 |
1957年 | 2篇 |
1956年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Strain rate is not only an important measure to characterize the deformation property, but also an important parameter to analyze the dynamic mechanical properties of rock materials. In this paper, by using the SHPB test system improved with high temperature device, the dynamic compressive tests of sandstone at seven temperatures in the range of room temperature to 1000 °C and five impact velocities in the range of 11.0–15.0 m/s were conducted. Investigations were carried out on the influences of strain rate on dynamic compressive mechanical behaviors of sandstone. The results of the study indicate that the enhancement effects of strain rates on dynamic compressive strength, peak strain, energy absorption ratio of sandstone under high temperatures still exist. However, the increase ratios of dynamic compressive strength, peak strain, and energy absorption ratio of rock under high temperature compared to room temperature have no obvious strain rate effects. The temperatures at which the strain rates affect dynamic compressive strength and peak strain most, are 800, and 1000 °C, respectively. The temperatures at which the strain rates affect dynamic compressive strength and peak strain weakest, are 1000 °C, and room temperature, respectively. At 200 and 800 °C, the strain rate effect on energy absorption ratio are most significant, while at 1000 °C, it is weakest. There are no obvious strain rate effects on elastic modulus and increase ratio of elastic modulus under high temperatures. According to test results, the relationship formula of strain rate with high temperature and impact load was derived by internalizing fitting parameters. Compared with the strain rate effect at room temperature condition, essential differences have occurred in the strain rate effect of rock material under the influence of high temperature. 相似文献
2.
The load applied to a machine tool feed drive changes during the machining process as material is removed. This load change alters the Coulomb friction of the feed drive. Because Coulomb friction accounts for a large part of the total friction the friction compensation control accuracy of the feed drives is limited if this nonlinear change in the applied load is not considered. This paper presents a new friction compensation method that estimates the machine tool load in real time and considers its effect on friction characteristics. A friction observer based on a Kalman filter with load estimation is proposed for friction compensation control considering the applied load change. A specially designed feed drive testbed that enables the applied load to be modified easily was constructed for experimental verification. Control performance and friction estimation accuracy are demonstrated experimentally using the testbed. 相似文献
3.
对CFG桩质量缺陷的探讨 总被引:2,自引:2,他引:0
根据具体工程的概况及水文地质条件,分析了CFG桩在地下水位出现大面积缩颈现象和复合地基载荷试验达不到设计要求的原因,并介绍了地基补强措施,以满足工程质量的要求。 相似文献
4.
This article presents a method that can be applied to molten AA-6101 alloy to improve electrical properties of the aluminium part of the optical ground wire (OPGW) used in overhead transmission lines to protect phase conductors from lightning strike and to transmit signals and data. AA-6101 alloy in casting of the log as 6 m length and 178 mm diameter for extrusion has been inoculated by AlB2 to decrease detrimental effects of Cr, Ti, V, and Zr on the conductivity of the material. After inoculation, improved billets were extruded as 9.5 mm diameter feedstock. Required wires drawn from the feedstock according to the construction types of OPGW to be tested were exposed to aging at 175°C, 6 h (T-8). Upon completion of the back-twist and performing-type stranding process, resistance, and short-circuit current capacity and breaking load of the OPGW 88/44 constructions with other metal combinations have been examined and tested to show improvement. Results are summarized in tables and graphically. 相似文献
5.
通过对百色等水文站泥沙资料分析 ,并结合广西河流及泥沙特性和社会对泥沙资料的精度要求 ,得出了在广西实行悬移质泥沙简测的可行性。为满足广西国民经济可持续发展需要 ,提出了在广西改革悬移质泥沙测验方式的必要性和紧迫性 相似文献
6.
7.
8.
准噶尔盆地侏罗系储集层的基本特征及其主控因素分析 总被引:28,自引:8,他引:20
从描述储集层基本特征、分析储集层性质的主控因素、建立储集层成因模式和评价、预测储集层性质这 4个层次 ,研究准噶尔盆地重点勘探目标区的侏罗系储集层。系统总结侏罗系储集层岩石学特征 ,认为成岩压实作用强弱是控制储集层性质的关键因素 ;指出相对优质储集层均为剩余原生粒间孔隙型储集层 ,溶蚀作用对渗透率贡献小 ;非煤系储集层的孔隙保存条件明显比煤系储集层好 ,这是三工河组、头屯河组和吐谷鲁群的物性普遍优于八道湾组和西山窑组的原因。在确定储集层性质的控制因素和控制机理基础上 ,建立了煤系和非煤系两大类储集层的成因 演化模型。在上述研究的基础上 ,分地区、分层位评价了储集层 ,并预测了不同渗透率储集层的深度界线及相对优质储集层的平面分布。图 6参 10 相似文献
9.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献
10.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献