全文获取类型
收费全文 | 436595篇 |
免费 | 73938篇 |
国内免费 | 49005篇 |
专业分类
电工技术 | 34432篇 |
综合类 | 24020篇 |
化学工业 | 63385篇 |
金属工艺 | 35460篇 |
机械仪表 | 15067篇 |
建筑科学 | 18619篇 |
矿业工程 | 15323篇 |
能源动力 | 13788篇 |
轻工业 | 47274篇 |
水利工程 | 10534篇 |
石油天然气 | 17700篇 |
武器工业 | 3977篇 |
无线电 | 56026篇 |
一般工业技术 | 73978篇 |
冶金工业 | 52028篇 |
原子能技术 | 7583篇 |
自动化技术 | 70344篇 |
出版年
2024年 | 2855篇 |
2023年 | 4904篇 |
2022年 | 6926篇 |
2021年 | 8431篇 |
2020年 | 10600篇 |
2019年 | 20269篇 |
2018年 | 23136篇 |
2017年 | 24491篇 |
2016年 | 24398篇 |
2015年 | 22172篇 |
2014年 | 22772篇 |
2013年 | 28369篇 |
2012年 | 24051篇 |
2011年 | 22621篇 |
2010年 | 19585篇 |
2009年 | 17338篇 |
2008年 | 15876篇 |
2007年 | 15638篇 |
2006年 | 13532篇 |
2005年 | 12029篇 |
2004年 | 14312篇 |
2003年 | 12227篇 |
2002年 | 11988篇 |
2001年 | 10987篇 |
2000年 | 10273篇 |
1999年 | 9637篇 |
1998年 | 16373篇 |
1997年 | 12289篇 |
1996年 | 10074篇 |
1995年 | 8577篇 |
1994年 | 7451篇 |
1993年 | 7136篇 |
1992年 | 6101篇 |
1991年 | 5161篇 |
1990年 | 4975篇 |
1989年 | 4750篇 |
1988年 | 4264篇 |
1987年 | 3178篇 |
1986年 | 3182篇 |
1985年 | 3565篇 |
1984年 | 3347篇 |
1983年 | 2991篇 |
1982年 | 2873篇 |
1981年 | 2968篇 |
1980年 | 2812篇 |
1979年 | 2687篇 |
1978年 | 2769篇 |
1977年 | 2976篇 |
1976年 | 4002篇 |
1975年 | 2544篇 |
排序方式: 共有10000条查询结果,搜索用时 4 毫秒
1.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
2.
采用异佛尔酮二异氰酸酯(IPDI)、聚乙二醇200、400、600、800(PEG200、PEG400、PEG600、PEG800)、2,2-二羟甲基丙酸(DMPA)、1-苯基-1,2-乙二醇、中和剂三乙胺(TEA)、甲乙酮肟等为原料,制备了一种阴离子聚氨酯分散剂.通过FTIR、GPC、TG表征了分散剂的结构与性能.利用自制的分散剂采用研磨法制备了液体靛蓝分散液,以液体靛蓝分散液粒径、离心稳定性、储存稳定性为指标,探讨了分散剂链长、用量对分散液性能的影响.结果表明,研磨1 h后,以PEG400为软段合成的聚氨酯分散剂用量为染料质量的60%时制备的液体靛蓝粒径为277.1 nm,1000 r/min离心稳定性达到93.98%,3000 r/min离心稳定性为51.13%,常温放置7 d后粒径变化在20 nm以内,染色后织物的颜色深度(K/S)为10左右,约是粉状靛蓝染色K/S的2倍,染色织物的颜色性能并未改变,SEM显示分散体颗粒大小分布均匀,与分散剂甲基萘磺酸钠的甲醛缩合物(MF)和木质素85A相比,其分散体系稳定性差别不大. 相似文献
3.
4.
The tracer methods developed to assess exfiltration from sewers in the European project APUSS (assessment of the performance of sewer systems) have a high degree of freedom with regard to the choice of tracer and the dosing strategy. These can lead to very different degrees of uncertainty in the measured exfiltration ratio. In this study, we demonstrate how to select an optimal experimental design using decision analysis, which accounts for this uncertainty and its associated costs. Although the results are site-specific, we can conclude generally that, when NaCl is used as the tracer, the accuracy of the exfiltration estimate is most sensitive to the amount of tracer used and the starting time of the experiment. 相似文献
5.
A GIS-based one-dimensional flood simulation model is presented and applied to the centre of the city of N?mes (Gard, France), for mapping flow depths or velocities in the streets network. The geometry of the one-dimensional elements is derived from the Digital Elevation Model (DEM). The flow is routed from one element to the next using the kinematic wave approximation. At the crossroads, the flows in the downstream branches are computed using a conceptual scheme. This scheme was previously designed to fit Y-shaped pipes junctions, and has been modified here to fit X-shaped crossroads. The results were compared with the results of a two-dimensional hydrodynamic model based on the full shallow water equations. The comparison shows that good agreements can be found in the steepest streets of the study zone, but differences may be important in the other streets. Some reasons that can explain the differences between the two models are given and some research possibilities are proposed. 相似文献
6.
论精神损害的国家赔偿责任 总被引:1,自引:0,他引:1
姚曙明 《湖南冶金职业技术学院学报》2006,6(3):313-316
国家的侵权行为造成相对人的精神损害应当承担赔偿责任是当今世界国家赔偿制度的发展潮流与趋势.确立精神损害的国家赔偿责任对社会公平正义的实现、人权的保护及促使国家公职人员依法行使职权具有重大的意义,因而应在基于我国国情的基础上,构建我国的精神损害国家赔偿制度. 相似文献
7.
Over tensile stress ranges giving creep lives up to 2000 hours at 373 to 463 K, the creep and creep fracture properties of
7010 are compared with results recorded for 7075 and other precipitation-hardened aluminum alloys. Using the ϕ methodology
to quantify the systematic variations in creep curve shape with changing test conditions, the behavior patterns displayed
by the different alloys are shown to depend on the extent to which precipitate coarsening causes a progressive loss of creep
strength with increasing test duration and temperature. The ϕ relationships also introduce new approaches for rationalization
and interpretation of creep data sets, based on the activation energy for lattice diffusion in the alloy matrices and the
yield stress or UTS at the creep temperatures. 相似文献
8.
D. A. Mirzaev N. I. Vorob’ev O. K. Tokovi D. V. Shaburov E. A. Fominykh 《Russian Metallurgy (Metally)》2006,(1):38-41
The solutions to a differential equation for the problem of heating of a cylinder in a medium with a fixed temperature are used to obtain equations for estimating the change in the hydrogen concentration in forgings from data on the hydrogen concentration at the cylinder axis or on the average bulk hydrogen concentration. Similar equations are also obtained for forgings having square cross sections. The calculation demonstrates that, for the case of a twofold decrease in the hydrogen concentration in a forging, the calculated times of annealing of a cylindrical forging differ by three times. 相似文献
9.
Finite element analysis of problems in structural and geotechnical engineering results in linear systems where the unknowns are displacements and rotations at nodes. Although the solution of these systems can be carried out using either direct or iterative methods, in practice the matrices involved are usually very large and sparse (particularly for 3D problems) so an iterative approach is often advantageous in terms of both computational time and memory requirements. This memory saving can be further enhanced if the method used does not require assembly of the full coefficient matrix during the solution procedure. One disadvantage of iterative methods is the need to apply preconditioning to improve convergence. In this paper, we review a range of established element-based preconditioning methods for linear elastic problems and compare their performance with a new method based on preconditioning with element displacement components. This new method appears to offer a significant improvement in performance. 相似文献
10.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献