全文获取类型
收费全文 | 8446篇 |
免费 | 837篇 |
国内免费 | 442篇 |
专业分类
电工技术 | 230篇 |
综合类 | 1029篇 |
化学工业 | 573篇 |
金属工艺 | 544篇 |
机械仪表 | 838篇 |
建筑科学 | 732篇 |
矿业工程 | 777篇 |
能源动力 | 219篇 |
轻工业 | 749篇 |
水利工程 | 429篇 |
石油天然气 | 581篇 |
武器工业 | 269篇 |
无线电 | 449篇 |
一般工业技术 | 645篇 |
冶金工业 | 637篇 |
原子能技术 | 64篇 |
自动化技术 | 960篇 |
出版年
2024年 | 12篇 |
2023年 | 105篇 |
2022年 | 238篇 |
2021年 | 276篇 |
2020年 | 309篇 |
2019年 | 222篇 |
2018年 | 199篇 |
2017年 | 247篇 |
2016年 | 283篇 |
2015年 | 334篇 |
2014年 | 526篇 |
2013年 | 456篇 |
2012年 | 594篇 |
2011年 | 687篇 |
2010年 | 508篇 |
2009年 | 505篇 |
2008年 | 417篇 |
2007年 | 526篇 |
2006年 | 510篇 |
2005年 | 458篇 |
2004年 | 376篇 |
2003年 | 341篇 |
2002年 | 282篇 |
2001年 | 242篇 |
2000年 | 218篇 |
1999年 | 151篇 |
1998年 | 114篇 |
1997年 | 111篇 |
1996年 | 80篇 |
1995年 | 66篇 |
1994年 | 71篇 |
1993年 | 50篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1966年 | 2篇 |
1964年 | 4篇 |
1960年 | 4篇 |
1957年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有9725条查询结果,搜索用时 15 毫秒
1.
本文分析了乌兰矿投产前期采矿现状及存在的主要问题,针对该矿所处蒙古国经济落后、投资风险大的现实状况,为避免生产中断、规避投资风险,早日回收前期投资考虑,采取了双斜坡道开拓、全尾胶结充填、高端壁空场嗣后充填采矿、多中段组合式连续开采等系列技术应对方案。大大降低了一次性投资规模及投资风险,前期投资得以快速回笼的同时,矿山产能也充分释放,确保了矿山的持续稳定,取得了较好的经济和社会效益。为海外地下近地表矿体开采矿山规避投资风险提供了很好的技术方案借鉴。 相似文献
2.
3.
The aim of this study was to investigate the structure and corrosion resistance of amorphous, amorphous‐crystalline, and crystalline Mg67Zn29Ca4 alloy for biodegradable applications. This paper presents a preparation method and results of the structural characterization and corrosion resistance analysis of the material. Samples were prepared in the form of 3 mm diameter rods. The structure of the alloy was examined with the use of X‐ray diffractometry and scanning electron microscopy. The thermal properties of the samples were examined with differential scanning calorimetry (DSC). Results of DSC analysis were used to determine heat treatment temperatures, allowing to obtain different fractures of crystalline phase in the material. Corrosion resistance of heat‐treated samples was investigated by immersion tests and electrochemical measurements performed in the simulated body fluid. The X‐ray diffraction results confirmed that the prepared Mg67Zn29Ca4 alloy's structure is fully amorphous. After heat treatment, samples with different fractions of amorphous phase in the structure were obtained. Immersion tests of the samples showed that the structure significantly influenced corrosion resistance in examined materials. It should be pointed out, that certain amounts of crystalline phase in amorphous matrix can greatly improve the corrosion resistance of Mg67Zn29Ca4 alloy. 相似文献
4.
针对人脸识别系统中出现的通过照片或视频“欺诈”解锁问题,提出一种活体检测方法,通过随机指令判断被检测对象是否为真人。利用HOG特征和随机森林算法对摄像头采集的图像进行人脸检测,预测脸部68个特征点位置,把68个特征点位置和脸部位置的相对位置归一化后作为姿态的特征,提取的姿态特征与SVM分类器相结合,训练出分类效果较好的头部姿态估计分类器。通过多次实验,对特征提取方法进行优化,进一步提高检测准确率。最后,使用随机互动式命令序列对被检测人发出指令,实现活体检测。该方法对头部姿态估计具有较高的鲁棒性,并且可以有效地防范照片和视频认证攻击。 相似文献
5.
以宏景塔一矿回采工作面为研究对象,基于切顶卸压无煤柱自动成巷技术原理,采用数值模拟计算和现场实测的方法,对该矿成巷段巷道围岩支承压力分布及围岩变形规律进行分析。研究结果表明:随着工作面向前推进,巷道围岩支承压力呈先增大后减小最后趋于稳定的变化趋势,支承压力稳定值为13.5 MPa;受工作面回采动压的影响,距离工作面70 m以内,锚索受力急剧增大到恒阻值、巷道围岩变形明显;距离工作面70~150 m,锚索受力迅速减小、巷道围岩变形逐渐变缓;在距离工作面150 m之后,锚索受力仅有微量变化、巷道围岩变形趋于稳定。因此确定支护体回撤保守安全位置为工作面后方150 m。工程实践表明:所设支护体回撤距离能够应对巷道围岩变形,成巷效果良好。 相似文献
6.
电力行业是目前国家非常重视与大力发展的行业之一。近些年来,由于接地系统接地电阻不合格引起的电力系统事故逐渐增多,并且接地电阻升高的很大一部分原因是接地体腐蚀造成的,因而人们越来重视接地体的抗腐蚀保护。简要阐述了电力系统目前预防接地体腐蚀所采取的牺牲阳极的阴极保护法,并对接地体新的改造方法提出一些建议。 相似文献
7.
The effects of local body cooling on thermal comfort and sleep quality in a hot environment were investigated in an experiment with 16 male subjects. Sleep quality was evaluated subjectively, using questionnaires completed in the morning, and objectively, by analysis of electroencephalogram (EEG) signals that were continuously monitored during the sleeping period. Compared with no cooling, the largest improvement in thermal comfort and sleep quality was observed when the back and head (neck) were both cooled at a room temperature of 32°C. Back cooling alone also improved thermal comfort and sleep quality, although the effects were less than when cooling both back and head (neck). Mean sleep efficiency was improved from 84.6% in the no cooling condition to 95.3% and 92.8%, respectively, in these conditions, indicating good sleep quality. Head (neck) cooling alone slightly improved thermal comfort and subjective sleep quality and increased Stage N3 sleep, but did not otherwise improve sleep quality. The results show that local cooling applied to large body sections (back and head) could effectively maintain good sleep and improve thermal comfort in a hot environment. 相似文献
8.
Junlei Wang Guoping Li Guifeng Zhao Zunlong Jin Kun Xu 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2018,40(24):2903-2913
The traditional models for VIVPEH (piezoelectric energy harvesting from vortex-induced vibration) are focused on a circular cylinder. In the present paper, a VIVPEH model was built to solve an aero-electromechanical coupling problem during VIVPEH with different cross-sectional shapes. The model was verified by a wind tunnel test. One key benefit of the present model is that the region from the initial position to the threshold of the lock-in region along the voltage time history curve can be calculated quite accurately compared with traditional methods. The present method will significantly contribute to the design and optimization of the key factors of VIVPEH, e.g., the bluff body shape and the electrical circuit. 相似文献
9.
Daisuke Suzuki Yuko Sato Hiroshi Kamasaka Takashi Kuriki 《Journal of Applied Glycoscience》2020,67(3):67
Phosphoryl oligosaccharides of calcium (POs-Ca) is a calcium salt of phosphoryl maltooligosaccharides made from potato starch. POs-Ca is highly water-soluble and can supply both the calcium ion and acidic oligosaccharides in an aqueous solution. In this study, we investigated the effects of POs-Ca on the mycelial growth and fruiting body yield of Pleurotus ostreatus , which is one of the most widely cultivated edible mushrooms in the world. We cultivated the mushroom using both potato dextrose agar (PDA) medium and sawdust-based medium, with added calcium salts. The addition of POs-Ca into the PDA medium with a calcium concentration of 10 mg increased mycelial growth significantly ( p < 0.05, vs . control). POs-Ca addition to the sawdust-based medium at concentrations of 1.0 to 3.0 g/100 g medium increased the amount of calcium in the fruiting bodies but did not affect the length of the cultivation period or the weight of the fruiting body. The calcium content in the fruiting body increased 12-fold when compared to the control. On the other hand, neither the CaHPO 4 ・2H 2 O group nor the CaHPO 4 ・2H 2 O with oligosaccharides group showed changes in the calcium content of the fruiting bodies. Our results indicate that the use of POs-Ca in mushroom cultivation allows for the possibility of developing new functional foods like calcium-enriched edible mushrooms. This is the first report describing the effects of POs-Ca on mushroom cultivation. 相似文献
10.
通过电泳和体积排阻-高效液相色谱探究芝麻内源性蛋白酶的水解性质,在内源性蛋白酶最适的水解条件下,探究水解时间、破乳pH、固形物含量、粒径大小、蛋白质含量对破乳的影响。结果发现,芝麻粗油体中内源性蛋白酶在pH 4、50℃条件下水解速度相对最快,且在此条件下水解4 h后,破乳p H为5时破乳率高达97%。但是综合风味和破乳率的增长速度,发现2 h水解时间为最佳,破乳率可达87%。粗油体固形物含量在50%时破乳率最高。粒径越小、蛋白质含量越高,越难以破乳。实验结果为利用芝麻内源性蛋白酶进行水酶法提油提供了工艺基础。 相似文献