全文获取类型
收费全文 | 16902篇 |
免费 | 1509篇 |
国内免费 | 1058篇 |
专业分类
电工技术 | 524篇 |
技术理论 | 1篇 |
综合类 | 1186篇 |
化学工业 | 1710篇 |
金属工艺 | 1916篇 |
机械仪表 | 1439篇 |
建筑科学 | 1836篇 |
矿业工程 | 1333篇 |
能源动力 | 515篇 |
轻工业 | 281篇 |
水利工程 | 731篇 |
石油天然气 | 1776篇 |
武器工业 | 172篇 |
无线电 | 1634篇 |
一般工业技术 | 2639篇 |
冶金工业 | 752篇 |
原子能技术 | 239篇 |
自动化技术 | 785篇 |
出版年
2024年 | 44篇 |
2023年 | 209篇 |
2022年 | 414篇 |
2021年 | 530篇 |
2020年 | 523篇 |
2019年 | 467篇 |
2018年 | 430篇 |
2017年 | 517篇 |
2016年 | 588篇 |
2015年 | 630篇 |
2014年 | 992篇 |
2013年 | 955篇 |
2012年 | 1055篇 |
2011年 | 1232篇 |
2010年 | 869篇 |
2009年 | 1007篇 |
2008年 | 951篇 |
2007年 | 1022篇 |
2006年 | 1015篇 |
2005年 | 837篇 |
2004年 | 712篇 |
2003年 | 621篇 |
2002年 | 596篇 |
2001年 | 442篇 |
2000年 | 395篇 |
1999年 | 394篇 |
1998年 | 352篇 |
1997年 | 320篇 |
1996年 | 278篇 |
1995年 | 217篇 |
1994年 | 194篇 |
1993年 | 139篇 |
1992年 | 121篇 |
1991年 | 93篇 |
1990年 | 96篇 |
1989年 | 64篇 |
1988年 | 44篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
测量刚体位移的非接触式光电系统 总被引:2,自引:0,他引:2
首次提出用标定法测量刚体的线位移和角位移的方法,该方法具有结构简单,性能可靠,非接触性,集成化高,工业上易实现和价格便宜等优点。本文同时还采用了一个小功率激光器为光源,CCD为光电转换器件。最后通过相关分析法和数据拟合技术等图象处理技术,提高了整套系统的分辨率。 相似文献
72.
Chih-Chun Hsieh Tao-Chih Chang Dong-Yih Lin Ming-Che Chen Weite Wu 《Metals and Materials International》2007,13(5):411-416
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel
welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition
of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD),
scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS),
respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless
steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding.
The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in
the fusion zone of the third pass welds during multi-pass welding. 相似文献
73.
矫直状态下钢管弹塑性变形区的研究 总被引:2,自引:0,他引:2
根据钢管矫直时的变形规律,通过对矫直中钢管的力学状态及矫直前后的状态参数分析,建立了一种适于现场应用的确定钢管弹、塑性变形区的新方法。 相似文献
74.
75.
全断面双护盾掘进机在引黄工程断层破碎带的卡机处理 总被引:1,自引:0,他引:1
万家寨引黄工程国际Ⅱ、Ⅲ标已查明的断层有34条,隐伏断层可能还有一些,除了利民堡区域性大断层(F32)外,较大的集中于7#洞北段59+700—68+820,主要有F65、F70、F90、F74。全断面双护盾掘进机适应于较复杂的地质条件,因此在通过断层破碎带时一般都较正常。但在通过引黄工程区域性大断层F65时,发生了卡机事故,处理用了3个月时间。该文对处理TBM卡机事故的施工进行了总结。 相似文献
76.
Using airborne laser scanning to monitor tree migration in the boreal-alpine transition zone 总被引:1,自引:0,他引:1
The boreal tree line is expected to advance upwards into the mountains and northwards into the tundra due to global warming. The major objective of this study was to find out if it is possible to use high-resolution airborne laser scanner data to detect very small trees — the pioneers that are pushing the tree line up into the mountains and out onto the tundra. The study was conducted in a sub-alpine/alpine environment in southeast Norway. A total of 342 small trees of Norway spruce, Scots pine, and downy birch with tree heights ranging from 0.11 to 5.20 m were precisely georeferenced and measured in field. Laser data were collected with a pulse density of 7.7 m− 2. Three different terrain models were used to process the airborne laser point cloud in order to assess the effects of different pre-processing parameters on small tree detection. Greater than 91% of all trees > 1 m tall registered positive laser height values regardless of terrain model. For smaller trees (< 1 m), positive height values were found in 5-73% of the cases, depending on the terrain model considered. For this group of trees, the highest rate of trees with positive height values was found for spruce. The more smoothed the terrain model was, the larger the portion of the trees that had positive laser height values. The accuracy of tree height derived from the laser data indicated a systematic underestimation of true tree height by 0.40 to 1.01 m. The standard deviation for the differences between laser-derived and field-measured tree heights was 0.11-0.73 m. Commission errors, i.e., the detection of terrain objects — rocks, hummocks — as trees, increased significantly as terrain smoothing increased. Thus, if no classification of objects into classes like small trees and terrain objects is possible, many non-tree objects with a positive height value cannot be separated from those actually being trees. In a monitoring context, i.e., repeated measurements over time, we argue that most other objects like terrain structures, rocks, and hummocks will remain stable over time while the trees will change as they grow and new trees are established. Thus, this study indicates that, given a high laser pulse density and a certain density of newly established trees, it would be possible to detect a sufficient portion of newly established trees over a 10 years period to claim that tree migration is taking place. 相似文献
77.
介绍了标准型直燃机的分类、原理及长庆至呼和浩特输气管道工程冷冻供热站的设计实例 ,重点论述了标准型直燃机在严寒地区使用的利弊 相似文献
78.
高功率二极管泵浦固体激光技术和应用前景的分析 总被引:2,自引:1,他引:1
文章对高功率二极管泵浦固体激光器的若干关键技术,包括激光二极管和增益介质,泵浦,耦合和冷却技术,以及光学谐振腔等作了详细的分析。 相似文献
79.
The twinning of YBa2Cu3O7 (YBCO) thin films with c-axis orientation on (001) MgO, (001) SrTiO3, (012) LaAlO3, (110) NdGaO3 and (001) NdGaO3 substrates, prepared by laser ablation, has been examined using a combination of and θ/2θ scans at a four-circle diffractometer. On all substrates, except for (001) NdGaO3, the tetragonal to orthorhombal phase transition results in four different orientations of YBCO twins relating to the substrate. On (001) NdGaO3 only two different twin orientations, accompanied by a slight lattice monoclinization, has been observed. 相似文献
80.