全文获取类型
收费全文 | 1300篇 |
免费 | 153篇 |
国内免费 | 145篇 |
专业分类
电工技术 | 16篇 |
综合类 | 67篇 |
化学工业 | 159篇 |
金属工艺 | 45篇 |
机械仪表 | 20篇 |
建筑科学 | 135篇 |
矿业工程 | 26篇 |
能源动力 | 21篇 |
轻工业 | 50篇 |
水利工程 | 82篇 |
石油天然气 | 552篇 |
武器工业 | 1篇 |
无线电 | 36篇 |
一般工业技术 | 121篇 |
冶金工业 | 32篇 |
原子能技术 | 28篇 |
自动化技术 | 207篇 |
出版年
2024年 | 5篇 |
2023年 | 30篇 |
2022年 | 42篇 |
2021年 | 89篇 |
2020年 | 65篇 |
2019年 | 40篇 |
2018年 | 44篇 |
2017年 | 50篇 |
2016年 | 75篇 |
2015年 | 45篇 |
2014年 | 56篇 |
2013年 | 126篇 |
2012年 | 72篇 |
2011年 | 94篇 |
2010年 | 70篇 |
2009年 | 65篇 |
2008年 | 67篇 |
2007年 | 92篇 |
2006年 | 72篇 |
2005年 | 88篇 |
2004年 | 69篇 |
2003年 | 50篇 |
2002年 | 49篇 |
2001年 | 24篇 |
2000年 | 28篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1959年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1598条查询结果,搜索用时 31 毫秒
1.
While the challenges associated with the stability of metal halide perovskites are well known and intensely studied, variability in electronic properties represents an equally significant, yet seldom studied, challenge that could potentially slow or inhibit the commercial viability of these systems. In this work, the contactless characterization technique time-resolved microwave conductivity (TRMC) is used to quantify the variability in electronic properties of the prototypical perovskite, methylammonium lead iodide (MAPbI3) both between different samples, and at different locations within the same sample. Using scanning electron microscopy (SEM) and a quasi-automated image-analysis strategy, it is possible to evaluate the metrics of heterogeneity in surface microstructure and correlate them with the electronic properties as obtained by TRMC. Substantial intra-sample and inter-sample variation is observed in the mobility-yield product in samples prepared following differing protocols, and in samples prepared following identical protocols. 相似文献
2.
针对超高强钢在机械行业的广泛使用,焊接接头易出现淬硬脆化、裂纹等缺陷的情况,采用焊条电弧焊(SMAW)和药芯气体保护焊(FCAW-GS)组合的焊接方法,对API X52管线钢与Corus RQT 701超高强钢的焊接进行了工艺试验,并进行常规力学性能试验。结果表明,通过合理匹配焊接工艺参数,严格控制低热输入量及层间温度,实现了小熔合比的异种钢焊接,且焊接接头具有良好的力学性能,达到了标准和规格书的要求;异种高强钢焊接,采用SMAW打底焊接和FCAWGS填充并盖面的方法,焊接效率较单纯采用焊条电弧焊工艺提高2倍以上。 相似文献
3.
With the circulation of misinformation about the COVID-19 pandemic, the World Health Organization has raised concerns about an “infodemic,” which exacerbates people’s misperceptions and deters preventive measures. Against this backdrop, this study examined the conditional indirect effect of social media use and discussion heterogeneity preference on COVID-19-related misinformation beliefs in the United States, using a national survey. Findings suggested that social media use was positively associated with misinformation beliefs, while discussion heterogeneity preference was negatively associated with misinformation beliefs. Furthermore, worry of COVID-19 was found to be a significant mediator as both associations became more significant when mediated through worry. In addition, faith in scientists served as a moderator that mitigated the indirect effect of discussion heterogeneity preference on misinformation beliefs. That is, among those who had stronger faiths in scientists, the indirect effect of discussion heterogeneity preference on misinformation belief became more negative. The findings revealed communication and psychological factors associated with COVID-19-related misinformation beliefs and provided insights into coping strategies during the pandemic. 相似文献
4.
Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs. 相似文献
5.
Acceptance of a product by a consumer may result from a convoluted interplay between product attributes and individual characteristics of that consumer. Different methods that systematically combine product properties with consumer groups segmented on such characteristics have provided unprecedented insight, but ignore heterogeneity in acceptance within each consumer group. Although such knowledge is invaluable for targeted marketing, dedicated methods for consumer group heterogeneity are lacking. The authors aim to fill this gap by the Individual Differences (InD) method, which models differences between consumers within the same target group. The method scores the ‘diffusion’ within each group, shows how much each consumer contributes to that, and relates this information to product properties. Thereby also novel groups may be discovered, with attributes not covered in the consumer segmentation. The illustrative consumer study on apple juice reveals how young women differ in their price-consciousness and their acceptance on specific preparation technologies more than older women. Although men exhibit heterogeneity on the same product attributes, their mutual variability is considerably lower and they thereby form more homogeneous target groups. 相似文献
6.
Burhan Can Karahasan 《Papers in Regional Science》2020,99(3):603-644
This paper investigates spatial variability of regional convergence for the 2004-2017 period in Turkey. Results from neoclassical convergence model which are robust to inclusion of a spatial battery points out the existence of convergence. However, additional results highlight that regional convergence is spatially heterogeneous. While underdeveloped regions exhibit higher convergence, convergence speed is not distributed evenly among these underdeveloped eastern regions. These findings point out that, last epoch of Turkish transformation fails to have equity enhancing effects at local level, rather there are winners and losers of the rapid growth of 2000s. 相似文献
7.
Ahlam Ammar Sharif 《建筑学研究前沿(英文版)》2020,9(4):837-857
Urban researchers have maintained a constant interest in the complexity and continuity of urban space usage. Some have applied actor–network theory (ANT) to investigate the heterogeneity of spaces and present them through the networks of their users’ activities. However, these accounts are predominantly limited in examining the extent to which these spaces may be heterogeneous when exploring such networks. This paper draws on recent ANT scholarship, which employs an ethnographic research conducted in a main park in a housing project at Dahiyat Al Hussein in Amman, Jordan. The findings describe the complex and unpredictable negotiations that occur within spaces by documenting the varieties and interrelations among user activity networks within this common and shared urban space. This research reveals the extent to which spaces, parks in this case, may be heterogeneous by unpacking their usage. The conclusions and insights assert the necessity of paying attention to design detail and creating designs that are responsive to evolving user activities. 相似文献
8.
9.
Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Despite numerous efforts to target epidermal growth factor receptor (EGFR), commonly dysregulated in GBM, approaches directed against EGFR have not achieved the same degree of success as seen in other tumor types, particularly as compared to non-small cell lung cancer (NSCLC). EGFR alterations in glioblastoma lie primarily in the extracellular domain, unlike the kinase domain alterations seen in NSCLC. Small molecule inhibitors are difficult to develop for the extracellular domain. Monoclonal antibodies can be developed to target the extracellular domain but must contend with the blood brain barrier (BBB). We review the role of EGFR in GBM, the history of trialed treatments, and the potential paths forward to target the pathway that may have greater success. 相似文献
10.
综合利用岩心观察、粒度分析、岩石薄片鉴定、扫描电镜分析及测井资料综合解释成果,对尚店油田东部沙四段储层非均质性进行了系统研究。综合分析认为,引起储层非均质性的主要原因是沉积环境的变化。在此基础上建立了滨浅湖沉积环境下不同沉积微相的储层非均质性模式,为油田开发方案的编制和调整打下基础。 相似文献