全文获取类型
收费全文 | 25220篇 |
免费 | 2457篇 |
国内免费 | 2041篇 |
专业分类
电工技术 | 540篇 |
综合类 | 3600篇 |
化学工业 | 1410篇 |
金属工艺 | 3945篇 |
机械仪表 | 2014篇 |
建筑科学 | 5605篇 |
矿业工程 | 1744篇 |
能源动力 | 451篇 |
轻工业 | 327篇 |
水利工程 | 1938篇 |
石油天然气 | 655篇 |
武器工业 | 212篇 |
无线电 | 956篇 |
一般工业技术 | 2975篇 |
冶金工业 | 1501篇 |
原子能技术 | 77篇 |
自动化技术 | 1768篇 |
出版年
2024年 | 94篇 |
2023年 | 366篇 |
2022年 | 642篇 |
2021年 | 856篇 |
2020年 | 849篇 |
2019年 | 673篇 |
2018年 | 657篇 |
2017年 | 830篇 |
2016年 | 996篇 |
2015年 | 1034篇 |
2014年 | 1629篇 |
2013年 | 1461篇 |
2012年 | 1917篇 |
2011年 | 2160篇 |
2010年 | 1671篇 |
2009年 | 1587篇 |
2008年 | 1396篇 |
2007年 | 1738篇 |
2006年 | 1554篇 |
2005年 | 1222篇 |
2004年 | 1005篇 |
2003年 | 930篇 |
2002年 | 783篇 |
2001年 | 648篇 |
2000年 | 609篇 |
1999年 | 508篇 |
1998年 | 340篇 |
1997年 | 311篇 |
1996年 | 208篇 |
1995年 | 207篇 |
1994年 | 176篇 |
1993年 | 114篇 |
1992年 | 114篇 |
1991年 | 84篇 |
1990年 | 88篇 |
1989年 | 71篇 |
1988年 | 52篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1960年 | 4篇 |
1959年 | 8篇 |
1956年 | 5篇 |
1955年 | 6篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Z. PanF. Xu S.N. MathaudhuL.J. Kecskes W.H. YinX.Y. Zhang K.T. HartwigQ. Wei 《Acta Materialia》2012,60(5):2310-2323
We have systematically investigated the microstructural evolution of niobium (Nb) subjected to severe plastic deformation via equal channel angular extrusion (ECAE) up to 24 passes. The starting Nb billet material consists of a centimeter-scale grain size with a columnar structure. We have found that the grain size reduction of the Nb is almost saturated at ∼300 nm after eight passes of ECAE. However, the population of high-angle grain boundaries continues to increase with further ECAE, and no saturation appears to have been reached at 24 passes. We have evaluated the mechanical properties of the samples with different number of ECAE passes over a wide range of strain rates, from quasi-static to high strain rates. We have used strain-rate jump tests to examine the strain-rate sensitivity (SRS) of the processed samples and found that the SRS of the ECAE-processed Nb is ∼0.012, which is a factor of three smaller than that of the coarse-grained counterpart. The activation volume derived for plastic deformation indicates that the double-kink formation of screw dislocations is still the predominant deformation mechanism in the ECAE-processed Nb. Quasi-static true stress-strain curves exhibit elastic-nearly perfectly plastic behavior. The quasi-static yield strength is also nearly saturated after eight passes of ECAE. High-strain-rate compressive true stress-strain curves show uniform flow softening. However, the dynamic peak stress keeps rising with an increased number of ECAE passes, suggesting a strong grain boundary contribution to dynamic strengthening. Scanning electron microscopy of post-loaded surfaces displays a morphology of diffuse shear bands accompanying highly compressed grains. In our report, we demonstrate that grain boundaries of severely deformed metals play different roles at low, quasi-static vs. high-strain rates of mechanical loading. The difference is primarily determined by the strength of grain boundaries acting as dislocation barriers at different loading rates. This discovery is significant for the understanding of the effect of the microstructure as a function of the applied loading rate. 相似文献
992.
G. L. Wang J. L. Li J. T. Xiong W. L. Wang P. Y. MA 《Journal of Adhesion Science and Technology》2019,33(10):1033-1046
In this study, evolution characteristics of the friction interface during rotary friction welding of tube were investigated. The friction interface that obtained at different welding stage were observed by confocal laser scanning microscopy. The results show that the friction interface transforms from sliding friction state to visco-plastic deformation state when the welding torque reaches the peak value. In addition, based on the thermodynamic framework extracted from the maximum entropy production principle, an analytical model for transition criterion from sliding friction to visco-plastic deformation was established. The model was verified by the corresponding experimental results of eight alloys, which indicated that the accuracy and generality of the model is satisfactory. 相似文献
993.
N. Sadasivan M. Balasubramanian R. Venkatesh S. Vigneshram T. Sunil 《Materialwissenschaft und Werkstofftechnik》2019,50(2):155-164
Severe plastic deformation improves the strength of a metal by strain hardening. Of the various severe plastic deformation processes, equal channel angular pressing proves to be the right candidate for bulk metal processing. Extensive works were carried out on equal channel angular pressing with channel angle ranging from 90° to 120 ° with or without back pressure on the exit channel. Numerical analyses suggest that reducing the channel angle below 90° would enhance the magnitude of strain imparted and, with prediction of a lesser strain homogeneity in such cases. Hence an acute angled equal channel angular pressing die with a back‐pressure notch sunken into the roof of the exit channel was designed, fabricated and was used for processing pure aluminium. Various mechanical properties of the processed materials were tested and acute angle processing imparted superior tensile strength to the work pieces in a single pass that would require several passes in a conventional equal channel angular pressing die. Substantial improvement in grain refinement and torsional properties was identified. 相似文献
994.
为有效控制动压巷道围岩变形较大、支护控制困难等问题,以山西某矿8102工作面为工程背景,通过现场调研、数值模拟、现场试验等手段,对动载扰动条件下组合锚索的支护效果进行研究分析,并在现场进行了工业性试验。研究结果表明:通过对在动压巷道顶板施加组合锚索的数值模拟得知,巷道顶板应力比较集中,并出现“应力柱”效应,巷道变形较小。结合现场工业性试验,在动压巷道顶板施加组合锚索,巷道变形破坏情况明显好于未施加组合锚索段;组合锚索可以有效控制动压巷道围岩变形破坏情况。 相似文献
995.
针对新疆克州塔日勒嘎水电站泄洪冲沙闸闸室置于不同强度地基基础上的情况,设计了简单易得的扩大回填方案以处理基础,通过三维有限元计算和现场的实际监测,结果表明:这种基础处理方案安全可靠,有一定的实用价值。 相似文献
996.
997.
《Journal of Nuclear Science and Technology》2013,50(11):932-940
To investigate the accuracy of wire mesh tomography (WMT) for gas-liquid flow measurement, the experimental study focused on its intrusive feature has been carried out. The WMT principle is based on the dependency upon electrical conductivity on the local void fraction. The applied wire mesh sensor (WMS) consists of two measuring planes. Each plane has 8x32 crossing points with spatial resolution of2.22x3.03 mm2 and wire diameter of 0.125 mm. The disturbance level is estimated from the deviation of flow properties between each measuring plane of WMT and also from the alternative image processing for low gas intensity range. The results show the dependency of disturbance level on the void fraction shape. Furthermore, the contribution of deceleration and deformation on the flow disturbance related to the flow condition are presented. In addition, the capability of gas velocity evaluation method is confirmed and the intrusive effect becomes only one important parameter for gas velocity measurement. 相似文献
998.
《Thin》2014
This paper summarizes results from an experimental program that investigated the cyclic axial behavior and energy dissipation of cold-formed steel C—sections structural framing members. Fully characterized cyclic axial load–deformation response of individual members is necessary to facilitate performance-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). The cyclic loading protocol was adapted from FEMA 461 with target displacements based on elastic buckling properties. Cyclic response showed large post-buckling deformations, pinching, strength and stiffness degradation. Damage accumulated within one half-wave after buckling. The total hysteretic energy dissipated within the damaged half-wave decreased with increasing cross-section slenderness. More energy dissipation comes at the cost of less cumulative axial deformation before tensile rupture. 相似文献
999.
1000.
应用土力学的基本原理,根据工程实测数据,对竹桩复合地基的承载力、变形和固结特征进行了探讨,认识了其性能的实用性和科学性。 相似文献