全文获取类型
收费全文 | 7141篇 |
免费 | 717篇 |
国内免费 | 373篇 |
专业分类
电工技术 | 498篇 |
技术理论 | 1篇 |
综合类 | 872篇 |
化学工业 | 751篇 |
金属工艺 | 236篇 |
机械仪表 | 283篇 |
建筑科学 | 1170篇 |
矿业工程 | 489篇 |
能源动力 | 240篇 |
轻工业 | 452篇 |
水利工程 | 521篇 |
石油天然气 | 432篇 |
武器工业 | 58篇 |
无线电 | 322篇 |
一般工业技术 | 541篇 |
冶金工业 | 623篇 |
原子能技术 | 58篇 |
自动化技术 | 684篇 |
出版年
2024年 | 24篇 |
2023年 | 73篇 |
2022年 | 187篇 |
2021年 | 213篇 |
2020年 | 224篇 |
2019年 | 178篇 |
2018年 | 183篇 |
2017年 | 255篇 |
2016年 | 316篇 |
2015年 | 287篇 |
2014年 | 561篇 |
2013年 | 419篇 |
2012年 | 553篇 |
2011年 | 602篇 |
2010年 | 387篇 |
2009年 | 453篇 |
2008年 | 408篇 |
2007年 | 476篇 |
2006年 | 442篇 |
2005年 | 362篇 |
2004年 | 306篇 |
2003年 | 275篇 |
2002年 | 233篇 |
2001年 | 172篇 |
2000年 | 142篇 |
1999年 | 118篇 |
1998年 | 79篇 |
1997年 | 54篇 |
1996年 | 42篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 23篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1985年 | 6篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1964年 | 4篇 |
1963年 | 7篇 |
1962年 | 3篇 |
1961年 | 3篇 |
1960年 | 4篇 |
1959年 | 5篇 |
1958年 | 3篇 |
1957年 | 3篇 |
1956年 | 3篇 |
排序方式: 共有8231条查询结果,搜索用时 0 毫秒
1.
通过对接轨站设置位置和布置图型主要影响因素的分析。按照能够充分反映接轨站作业特点的交接方式。对接轨站所采用的布置图型进行了归纳和分类。 相似文献
2.
Reading requires the orchestration of visual, attentional, language-related, and oculomotor processing constraints. This study replicates previous effects of frequency, predictability, and length of fixated words on fixation durations in natural reading and demonstrates new effects of these variables related to 144 sentences. Such evidence for distributed processing of words across fixation durations challenges psycholinguistic immediacy-of-processing and eye-mind assumptions. Most of the time the mind processes several words in parallel at different perceptual and cognitive levels. Eye movements can help to unravel these processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
4.
5.
林苗 《电气电子教学学报》2002,24(1):43-45
阐述了我校使用“面向21世纪”电工学课程系列教材的实践与探索过程,以及对我校电工学教学所产生的转折性影响和积极的导向作用,最后对教材提出了几点建议。 相似文献
6.
利用2、4和14mm的X60钢紧凑拉伸试样进行同样应力水平、固定应力比(R=0.1)的疲劳裂纹扩展试验,揭示出高韧性管道钢的疲劳裂纹扩展存在显著的厚度效应。由于应力水平低,相应的离面应力也低,不足以导致分层开裂,因此,裂纹端部的三维应力约束随厚度增加而增大。4mm试样的疲劳裂纹速率远高于2mm试样,但厚度再增大,裂纹扩展速率不再有显著变化。进一步对表面裂纹试样进行疲劳裂纹扩展试验,并用勾线法纪录裂纹扩展情况,利用穿透裂纹的da/dN-ΔK曲线预测表面裂纹扩展,用2mm厚试样的数据控制裂纹表面长度的扩展,用14mm厚试样的数据控制裂纹底部沿厚度方面的扩展,得到了与表面裂纹扩展实验吻合很好的预测结果。 相似文献
7.
添加剂组成对通用内燃机油性能的影响 总被引:1,自引:0,他引:1
通过相关模拟试验,分析研究了添加剂组成对通用内燃机油的抗磨性能,抗氧化性能以及清净分散性能的影响。 相似文献
8.
Ignacio Rintoul 《Polymer》2005,46(13):4525-4532
A precise data set describing the kinetics of the free radical copolymerization of acrylamide/acrylic acid (AM/AA) in the range of low total monomer concentration as a function of the pH, total monomer concentration, initiator concentration, and comonomer ratio is presented. Strong impact on the reactivity ratios has been identified for the pH and total monomer concentration. Specifically, at constant total monomer concentration of 0.4 mol/l and T=313 K the reactivity ratio of AM increases from 0.54 at pH 1.8 to 3.04 at pH 12. Contrarily, the reactivity ratio of AA decreases from 1.48 to 0.32. The crossover occurs at pH≈4.2. Electrostatic effects due to the variation of the degree of ionization of AA are primarily suggested to influence the kinetics. When the total monomer concentration increases from 0.2 to 0.6 mol/l at constant pH=12, the reactivity ratios of AM and AA decrease from 4.01 to 2.13 and increase from 0.25 to 0.47, respectively. Reduction of electrostatic repulsion between the ionized monomer AA and partially charged growing polymer chain ends due to higher ionic strength at higher total monomer concentration serves as explanation of the effect. The precise data set is the prerequisite for a novel approach to calculate copolymer compositions in case of variable monomer reactivity. 相似文献
9.
钻杆接头螺纹退刀尺寸是指外螺纹接头的台肩面到螺纹消失前第一个完整螺纹之间的距离。GB9253.1-88规定退刀尺寸应小于或等于12.7mm内螺纹,钻杆接头内螺纹的锤孔尺寸为16±2mm,以保证内、外螺纹啮合良好。经检测发现,从日本NKK公司进口的所有φ127mm钻杆接头外螺纹退刀尺寸都大于12.7mm,镗孔尺寸为16~18mm。而APISpec7K规定钻杆接头内螺纹最小镗孔尺寸为15.9mm。鉴于此,建议对我国的有关标准作相应修改,与API标准保持一致。 相似文献
10.
Quantitative analyses of flow and stage data, remote sensing and geographic information systems analysis, and field studies were used to assess the impact of dams and diversions on the point bar habitat of the Sacramento Valley Tiger Beetle (Cicindela hirticollis abrupta). The reaches of interest include sites of known historic populations of C. h. abrupta along the Sacramento River from approximately 8 km north of Colusa southward to the confluence with the Feather River and along the Feather River between Yuba City and its confluence with the Sacramento River. The results from this study show that construction of two major dams has altered flows such that prolonged and increased flows during summer, fall, and early winter have most likely disrupted life cycles, flooded larvae, drowned overwintering adults and led to high mortality. Additionally, habitat availability has decreased over time because point bars have decreased in number and area causing increased distances between populations and isolation of populations. Moreover, point bar armouring, channel scouring, altered flows, redirected flows through weirs, and lithologic controls have produced a bimodal distribution of mean grain sizes in the Sacramento River in which the more northern bars contain gravel deposits and more southern bars possess fine sands. These conditions negatively alter moisture retention and sediment compaction and, consequently, burrowing conditions needed by this tiger beetle. Additionally, more stabilized flows (reduced variability) and increased fine‐grained deposition have enabled development and encroachment of vegetation onto the sand bars. Finally, human stresses, such as foot traffic and vehicular traffic may have interfered with burrowing, ovipositing, and foraging. The combination of these stress factors has most likely led to a reduction in source populations and, ultimately, the apparent extirpation of the entire metapopulation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献