全文获取类型
收费全文 | 571775篇 |
免费 | 49608篇 |
国内免费 | 29582篇 |
专业分类
电工技术 | 56849篇 |
技术理论 | 72篇 |
综合类 | 66933篇 |
化学工业 | 57557篇 |
金属工艺 | 22216篇 |
机械仪表 | 40386篇 |
建筑科学 | 60338篇 |
矿业工程 | 26716篇 |
能源动力 | 18006篇 |
轻工业 | 28292篇 |
水利工程 | 21534篇 |
石油天然气 | 20698篇 |
武器工业 | 7996篇 |
无线电 | 52074篇 |
一般工业技术 | 40929篇 |
冶金工业 | 26603篇 |
原子能技术 | 5966篇 |
自动化技术 | 97800篇 |
出版年
2024年 | 1291篇 |
2023年 | 5946篇 |
2022年 | 11144篇 |
2021年 | 15511篇 |
2020年 | 14325篇 |
2019年 | 11266篇 |
2018年 | 10985篇 |
2017年 | 14509篇 |
2016年 | 17982篇 |
2015年 | 20486篇 |
2014年 | 35271篇 |
2013年 | 31316篇 |
2012年 | 40055篇 |
2011年 | 41442篇 |
2010年 | 32022篇 |
2009年 | 32788篇 |
2008年 | 31676篇 |
2007年 | 41754篇 |
2006年 | 38959篇 |
2005年 | 34096篇 |
2004年 | 28056篇 |
2003年 | 25552篇 |
2002年 | 20213篇 |
2001年 | 16953篇 |
2000年 | 14297篇 |
1999年 | 11447篇 |
1998年 | 8552篇 |
1997年 | 7267篇 |
1996年 | 6561篇 |
1995年 | 5551篇 |
1994年 | 4820篇 |
1993年 | 3458篇 |
1992年 | 2992篇 |
1991年 | 2225篇 |
1990年 | 1942篇 |
1989年 | 1649篇 |
1988年 | 1263篇 |
1987年 | 832篇 |
1986年 | 610篇 |
1985年 | 555篇 |
1984年 | 531篇 |
1983年 | 400篇 |
1982年 | 348篇 |
1981年 | 277篇 |
1980年 | 236篇 |
1979年 | 172篇 |
1978年 | 108篇 |
1977年 | 120篇 |
1976年 | 93篇 |
1962年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
52.
53.
Zachary Zander Deirdre Newton Heather Scaglione Averie Reiber Parminder Agarwal 《Polymer Engineering and Science》2021,61(12):3029-3036
The incursion of microbial growth on polymeric products can deteriorate their performance and lead to the development of undesirable staining and odors. A growing trend in the industry has aimed to reduce microbial populations on high-touch surfaces via the use of antimicrobials to protect material aesthetics and durability or to prevent the spread of pathogenic microorganisms. In this study, a variety of plastic substrates (30 unique polymer compounds), including poly(acrylonitrile-co-butadiene-co-styrene), poly(butylene terephthalate), poly(etherimide), various thermoplastic elastomers (TPEs), poly(carbonates), and poly(amides), were screened for susceptibility to microbial attack using American Society for Testing and Materials (ASTM) G21 (fungi susceptibility), Japanese Industrial Standard (JIS) Z2801, and modified ASTM E1428-15a (bacterial susceptibility) test standards. TPEs were determined to be most susceptible to microbial attack under the appropriate environmental conditions. Subsequent studies assessed the use of an antimicrobial additive, zinc pyrithione (ZPT), for potential efficacy in a variety of TPE blends for diverse target market applications. ZPT proved to be very effective in protecting TPEs, reducing Staphylococcus aureus and Escherichia coli populations by 99.9% or more in JIS Z2801 testing and inhibiting fungal growth (rating = 0) according to the ASTM G21 standard. 相似文献
54.
Xiaojun Chen Hongyang Liu Dechao Hu Huaqing Liu Wenshi Ma 《Ceramics International》2021,47(17):23749-23761
With the blossom of information industry, electromagnetic wave technology shows increasingly potential in many fields. Nevertheless, the trouble caused by electromagnetic waves has also drawn extensive attention. For instance, electromagnetic pollution can threaten information safety in vital fields and the normal function of delicate electronic devices. Consequently, electromagnetic pollution and interference become an urgent issue that needs to be addressed. Carbon nanotubes (CNTs) have become a potential candidate to deal with these problems due to many advantages, such as high dielectric loss, remarkable thermodynamic stability, and low density. With the appearance of climbing demands, however, the carbon nanotubes combining various composites have shown greater prospects than the single CNTs in microwave absorbing materials. In this short review, recent advances in CNTs-based microwave absorbing materials were comprehensively discussed. Typically, we introduced the electromagnetic wave absorption mechanism of CNTs-based microwave absorbing materials and generalized the development of CNTs-based microwave absorbers, including CNTs-based magnetic metal composites, CNTs-based ferrite composites, and CNTs-based polymer composites. Ultimately, the growing trend and bottleneck of CNTs-based composites for microwave absorption were analyzed to provide some available ideas to more scientific workers. 相似文献
55.
56.
57.
Guglielmina Chimienti Anna Picca Flavio Fracasso Francesco Russo Antonella Orlando Giuseppe Riezzo Christiaan Leeuwenburgh Vito Pesce Angela Maria Serena Lezza 《International journal of molecular sciences》2021,22(4)
Calorie restriction (CR) is the most efficacious treatment to delay the onset of age-related changes such as mitochondrial dysfunction. However, the sensitivity of mitochondrial markers to CR and the age-related boundaries of CR efficacy are not fully elucidated. We used liver samples from ad libitum-fed (AL) rats divided in: 18-month-old (AL-18), 28-month-old (AL-28), and 32-month-old (AL-32) groups, and from CR-treated (CR) 28-month-old (CR-28) and 32-month-old (CR-32) counterparts to assay the effect of CR on several mitochondrial markers. The age-related decreases in citrate synthase activity, in TFAM, MFN2, and DRP1 protein amounts and in the mtDNA content in the AL-28 group were prevented in CR-28 counterparts. Accordingly, CR reduced oxidative mtDNA damage assessed through the incidence of oxidized purines at specific mtDNA regions in CR-28 animals. These findings support the anti-aging effect of CR up to 28 months. Conversely, the protein amounts of LonP1, Cyt c, OGG1, and APE1 and the 4.8 Kb mtDNA deletion content were not affected in CR-28 rats. The absence of significant differences between the AL-32 values and the CR-32 counterparts suggests an age-related boundary of CR efficacy at this age. However, this only partially curtails the CR benefits in counteracting the generalized aging decline and the related mitochondrial involvement. 相似文献
58.
59.
目的:研究抗坏血酸(ascorbic acid,AsA)-还原型谷胱甘肽(reduced glutathione,GSH)循环代谢在水杨酸处理采后甜瓜诱导的过量H2O2清除过程中的作用。方法:用4 mmol/L水杨酸浸泡‘玉金香’厚皮甜瓜10 min,测定处理后果实常温贮藏过程中丙二醛(malondialdehyde,MDA)含量,分析活性氧的积累水平、超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活力,以及AsA-GSH循环过程相关酶活力及产物和底物含量。结果:水杨酸处理降低了果实MDA含量,第10天处理组MDA含量较对照组降低14.6%;显著提高了果实O2-·的产生速率和H2O2含量(P<0.05),其中处理后第2天O2-·的产生速率高出同期对照组的1.9 倍,第6天H2O2含量高出对照组果实29.7%;提高了果实SOD活力,但抑制了CAT活力,说明H2O2的清除可能是依赖于除酶促系统外的其他系统。此外,水杨酸处理提高了果实抗坏血酸过氧化物酶、单脱氢抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶的活力,增加了AsA和氧化型谷胱甘肽的含量,降低了脱氢抗坏血酸和GSH的含量。结论:水杨酸处理诱导了厚皮甜瓜果实的氧爆,抑制了MDA产生,由水杨酸诱导产生的过量H2O2主要依靠AsA-GSH循环系统清除。 相似文献
60.