全文获取类型
收费全文 | 19340篇 |
免费 | 1359篇 |
国内免费 | 736篇 |
专业分类
电工技术 | 1185篇 |
综合类 | 1297篇 |
化学工业 | 3186篇 |
金属工艺 | 899篇 |
机械仪表 | 905篇 |
建筑科学 | 1223篇 |
矿业工程 | 401篇 |
能源动力 | 564篇 |
轻工业 | 1244篇 |
水利工程 | 391篇 |
石油天然气 | 712篇 |
武器工业 | 103篇 |
无线电 | 2155篇 |
一般工业技术 | 2382篇 |
冶金工业 | 2032篇 |
原子能技术 | 295篇 |
自动化技术 | 2461篇 |
出版年
2024年 | 71篇 |
2023年 | 220篇 |
2022年 | 383篇 |
2021年 | 579篇 |
2020年 | 417篇 |
2019年 | 378篇 |
2018年 | 411篇 |
2017年 | 437篇 |
2016年 | 411篇 |
2015年 | 551篇 |
2014年 | 733篇 |
2013年 | 902篇 |
2012年 | 962篇 |
2011年 | 996篇 |
2010年 | 938篇 |
2009年 | 924篇 |
2008年 | 1022篇 |
2007年 | 936篇 |
2006年 | 858篇 |
2005年 | 720篇 |
2004年 | 636篇 |
2003年 | 906篇 |
2002年 | 1202篇 |
2001年 | 1051篇 |
2000年 | 613篇 |
1999年 | 499篇 |
1998年 | 788篇 |
1997年 | 534篇 |
1996年 | 375篇 |
1995年 | 310篇 |
1994年 | 275篇 |
1993年 | 229篇 |
1992年 | 129篇 |
1991年 | 113篇 |
1990年 | 74篇 |
1989年 | 71篇 |
1988年 | 80篇 |
1987年 | 61篇 |
1986年 | 77篇 |
1985年 | 50篇 |
1984年 | 66篇 |
1983年 | 50篇 |
1982年 | 56篇 |
1981年 | 53篇 |
1980年 | 47篇 |
1979年 | 27篇 |
1978年 | 39篇 |
1977年 | 37篇 |
1976年 | 66篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
浅谈火灾调查的边缘化趋势 总被引:1,自引:0,他引:1
从火灾调查实际工作状态出发,提出火灾调查存在地位边缘化的趋势,并在分析边缘化趋势原因的基础上提出了相应的对策,供火灾调查同仁探讨。 相似文献
72.
Peter Su Adrian Gerlich Motomichi Yamamoto Thomas H. North 《Journal of Materials Science》2007,42(24):9954-9965
The formation of local melted films during friction stir spot welding of as-cast AZ91D and thixomolded AZ91 material is investigated.
The average temperatures close to the tip of the rotating pin vary from 438 to 454 °C during the dwell period in friction
stir spot welding. These measured temperature values are higher than the melting temperature of α-Mg + Mg17Al12 eutectic (437 °C). It is suggested that the temperature in the stir zone during the dwell period is determined by the relative
proportions of α-Mg and (α-Mg + Mg17Al12) eutectic material, which are incorporated during friction stir spot welding. Based on the stir zone temperature measurements
and a detailed examination of material located at the root of the pin thread it is suggested that material is moved downwards
via the pin thread and into the stir zone during the dwell period in friction stir spot welding. Evidence of local melted
film formation is observed in the stir zone of AZ91 spot welds. It is suggested that melted films are retained since their
dissolution rate is much slower in the high temperature stir zone than it is when melted films is formed in the stir zone
during Al 7075-T6 friction stir spot welding. The spontaneous melting temperature, solute diffusion rate and the thermodynamic
driving force for droplet dissolution are much higher during Al 7075-T6 friction stir spot welding. 相似文献
73.
74.
本分析了山西分公司二期CO2压缩机润滑油消耗高的原因,介绍了采取的针对措施以及2002年取得的节能效果,并进一步指出了CO2压缩机的节能空间。 相似文献
75.
ABSTRACT A purified 160-kDa protein, isolated from the cuticle of kurama prawn and named melanosis collaborating factor (MCF), was a key factor in promoting melanosis by a cooperative reaction with hemocyanin-derived phenoloxidase but hemocyanin itself was incapable of producing black pigment. The enzymatic activity of MCF in the body of the prawn was very stable against the process of freezing and thawing; the enzyme maintained more than 80% of its activity after 3 mo of storage at −2 5 °C. These results indicated that MCF, acting in conjunction with hemocyanin-derived phenoloxidase, played a crucial role in postharvest melanogenesis in prawn. 相似文献
76.
Yukio Sato Tomohito Tanaka Fumiyasu Oba Takahisa Yamamoto Yuichi Ikuhara Taketo Sakuma 《Science and Technology of Advanced Materials》2003,4(6):137
SrTiO3 and ZnO bicrystals with various types of boundaries were fabricated in order to examine their current–voltage characteristics across single grain boundaries. Their grain boundary structures were also investigated by high-resolution transmission electron microscopy. In Nb-doped SrTiO3, electron transport behaviors depend on the type of boundaries. Random type boundaries exhibit highly non-linear current–voltage characteristics, while low angle boundaries show a slight non-linearity. On the contrary, undoped ZnO does not exhibit non-linear current–voltage characteristics in any type of boundaries including random ones. It is suggested that the differences observed in current–voltage properties between the two systems are mainly due to the difference in the accumulation behavior of acceptor-like native defects at grain boundaries. A clear non-linearity is obtained by means of Co-doping even for the highly coherent Σ1 boundary in a ZnO bicrystal. This is considered to result from the production of acceptor-like native defects by Co-doping. 相似文献
77.
N. Karasawa H. Kakehata K. Mishina J. Yamamoto S. Kobayashi 《Photonics Technology Letters, IEEE》2005,17(1):31-33
Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered. 相似文献
78.
79.
空心微珠改性硬质聚氯乙烯复合材料的应用研究 总被引:13,自引:1,他引:12
经过改性的超细空心微珠可以作为填料加入到硬质聚氯乙烯(PVC-U)树脂中,同时改善PVC树脂的流变性、冲击性能和刚性等性能。研究结果表明,超细空心微珠加入到硬质PVC管材中,可以明显改善PVC硬管的加工流动性能,显著缩短塑化时间,降低最大扭矩。而超细空民微珠加入到硬质PVC板材时,可以提高PVC硬板的冲击性能,减小制品的收缩率,赋予PVC硬板优异的耐腐蚀性能,且产品的各项性能均符合PVC板材国家标准GB/T4454-96。 相似文献
80.
J Arikawa M Tokunaga Y Tashiro S Tanaka E Sato K Haraguchi A Yamamoto O Toyohira A Tsuchimochi 《Canadian Metallurgical Quarterly》1997,47(10):730-734
Epstein-Barr virus (EBV) has been implicated as a causal virus of gastric cancer with episomal monoclonality, elevated antibodies and a unique morphologic expression in the early intramucosal stage, but the infection mechanisms have not been demonstrated. EBV has been shown only in the cancerous lesions by the highly sensitive EBV-encoded small RNA in situ hybridization (EBER-ISH) method, not in the dysplastic mucosa adjacent to the cancer. A case is presented of multiple EBV-positive gastric cancer and dysplastic epithelium observed in a 52-year-old man. Serial cut sections of the gastrectomy specimen showed four small cancerous lesions, three of which were EBER-positive, and three EBER-positive, minute, non-cancerous dysplastic lesions. The three cancerous lesions were intramucosal cancer, with one having minimal submucosal invasion forming a lymphoepithelioma-like histology. All of these EBER-positive cancerous and dysplastic lesions showed intense CD8 T-lymphocytic infiltration. There was no such findings in the EBV-negative cancerous lesion. It was concluded that EBV infection may occur in the epithelial cells of atrophic gastric mucosa, and progress to cancer with monoclonal expansion through the EBV-positive dysplastic change. Cytotoxic T-lymphocytic reactions can occur even in the dysplastic lesions. Multifocal EBV infection in the gastric mucosa may occur and, if necessary, total gastrectomy is recommended in such a case. 相似文献