全文获取类型
收费全文 | 1869篇 |
免费 | 118篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 10篇 |
综合类 | 2篇 |
化学工业 | 824篇 |
金属工艺 | 36篇 |
机械仪表 | 21篇 |
建筑科学 | 45篇 |
矿业工程 | 7篇 |
能源动力 | 38篇 |
轻工业 | 312篇 |
水利工程 | 9篇 |
石油天然气 | 9篇 |
无线电 | 71篇 |
一般工业技术 | 313篇 |
冶金工业 | 88篇 |
原子能技术 | 2篇 |
自动化技术 | 203篇 |
出版年
2024年 | 6篇 |
2023年 | 38篇 |
2022年 | 197篇 |
2021年 | 193篇 |
2020年 | 55篇 |
2019年 | 60篇 |
2018年 | 76篇 |
2017年 | 60篇 |
2016年 | 71篇 |
2015年 | 57篇 |
2014年 | 83篇 |
2013年 | 138篇 |
2012年 | 96篇 |
2011年 | 121篇 |
2010年 | 95篇 |
2009年 | 95篇 |
2008年 | 108篇 |
2007年 | 56篇 |
2006年 | 70篇 |
2005年 | 58篇 |
2004年 | 49篇 |
2003年 | 30篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 6篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1964年 | 1篇 |
1911年 | 2篇 |
排序方式: 共有1990条查询结果,搜索用时 15 毫秒
81.
Using polysaccharide-based edible coatings to maintain quality of fresh-cut Fuji apples 总被引:2,自引:0,他引:2
The effect of alginate and gellan-based edible coatings on the shelf-life of fresh-cut Fuji apples packed in trays with a plastic film of a known permeability to oxygen (110 cm3 O2 m−2 bar−1 day−1) was investigated by measuring changes in headspace atmosphere, color, firmness and microbial growth during 23 days of storage at 4 °C. Concentration of O2 and CO2 in the package was measured and no significant differences between coated and uncoated fresh-cut apples were observed. Ethylene concentration in coated apples seemed to be delayed since it remained below 50 μl l−1 throughout the whole refrigerated storage period, while production of this gas was detected in uncoated apples from the very initial days of storage. Coated apple wedges exhibited ethanol and acetaldehyde formation from the second week of storage indicating fermentative metabolism. Polymers were crosslinked with a calcium chloride solution, to which the antibrowning agent N-acetylcysteine was added, being incorporated into the coatings formulation and helping to maintain firmness and color of apple wedges during the entire storage time. The application of the edible coatings also retarded the microbiological deterioration of fresh-cut apples. Alginate and gellan edible coatings effectively prolonged the shelf-life of Fuji apple wedges by 2 weeks of storage compared with the control apple slices which showed a considerable cut surface browning and tissue softening from the very early days of storage, limiting their shelf-life to less than 4 days. 相似文献
82.
Yonglei Liu Yahong Chen Fei Wang Yangjian Cai Chunhao Liang Olga Korotkova 《光电进展(英文版)》2021,4(12):15-24
The degree of coherence (DOC) function that characterizes the second-order correlations at any two points in a light field is shown to provide a new degree of f... 相似文献
83.
Aditi Mehta Stephanie Dobersch Reinhard H. Dammann Saverio Bellusci Olga N. Ilinskaya Thomas Braun Guillermo Barreto 《International journal of molecular sciences》2015,16(3):4492-4511
The expression ratio between the analysed gene and an internal control gene is the most widely used normalization method for quantitative RT-PCR (qRT-PCR) expression analysis. The ideal reference gene for a specific experiment is the one whose expression is not affected by the different experimental conditions tested. In this study, we validate the applicability of five commonly used reference genes during different stages of mouse lung development. The stability of expression of five different reference genes (Tuba1a, Actb Gapdh, Rn18S and Hist4h4) was calculated within five experimental groups using the statistical algorithm of geNorm software. Overall, Tuba1a showed the least variability in expression among the different stages of lung development, while Hist4h4 and Rn18S showed the maximum variability in their expression. Expression analysis of two lung specific markers, surfactant protein C (SftpC) and Clara cell-specific 10 kDA protein (Scgb1a1), normalized to each of the five reference genes tested here, confirmed our results and showed that incorrect reference gene choice can lead to artefacts. Moreover, a combination of two internal controls for normalization of expression analysis during lung development will increase the accuracy and reliability of results. 相似文献
84.
Cover Feature: A Designed Enzyme Promotes Selective Post‐translational Acylation (ChemBioChem 15/2018) 下载免费PDF全文
85.
Olga A. Kladova Olga S. Fedorova Nikita A. Kuznetsov 《International journal of molecular sciences》2022,23(4)
DNA polymerase β (Polβ) is considered the main repair DNA polymerase involved in the base excision repair (BER) pathway, which plays an important part in the repair of damaged DNA bases usually resulting from alkylation or oxidation. In general, BER involves consecutive actions of DNA glycosylases, AP endonucleases, DNA polymerases, and DNA ligases. It is known that protein–protein interactions of Polβ with enzymes from the BER pathway increase the efficiency of damaged base repair in DNA. However natural single-nucleotide polymorphisms can lead to a substitution of functionally significant amino acid residues and therefore affect the catalytic activity of the enzyme and the accuracy of Polβ action. Up-to-date databases contain information about more than 8000 SNPs in the gene of Polβ. This review summarizes data on the in silico prediction of the effects of Polβ SNPs on DNA repair efficacy; available data on cancers associated with SNPs of Polβ; and experimentally tested variants of Polβ. Analysis of the literature indicates that amino acid substitutions could be important for the maintenance of the native structure of Polβ and contacts with DNA; others affect the catalytic activity of the enzyme or play a part in the precise and correct attachment of the required nucleotide triphosphate. Moreover, the amino acid substitutions in Polβ can disturb interactions with enzymes involved in BER, while the enzymatic activity of the polymorphic variant may not differ significantly from that of the wild-type enzyme. Therefore, investigation regarding the effect of Polβ natural variants occurring in the human population on enzymatic activity and protein–protein interactions is an urgent scientific task. 相似文献
86.
Dmitry Oshchepkov Irina Chadaeva Rimma Kozhemyakina Karina Zolotareva Bato Khandaev Ekaterina Sharypova Petr Ponomarenko Anton Bogomolov Natalya V. Klimova Svetlana Shikhevich Olga Redina Nataliya G. Kolosova Maria Nazarenko Nikolay A. Kolchanov Arcady Markel Mikhail Ponomarenko 《International journal of molecular sciences》2022,23(5)
87.
Sanghee Lee Theresa R. Mendoza Danielle N. Burner Michelle T. Muldong Christina C. N. Wu Catalina Arreola-Villanueva Abril Zuniga Olga Greenburg William Y. Zhu Jamillah Murtadha Evodie Koutouan Naomi Pineda Hao Pham Sung-Gu Kang Hyun Tae Kim Gabriel Pineda Kathleen M. Lennon Nicholas A. Cacalano Catriona H. M. Jamieson Christopher J. Kane Anna A. Kulidjian Terry Gaasterland Christina A. M. Jamieson 《International journal of molecular sciences》2022,23(6)
88.
Carina Morando Osvaldo Fornaro Olga Garbellini Hugo Palacio 《Journal of Materials Science: Materials in Electronics》2014,25(8):3440-3447
During last few decades, emerging environmental regulations worldwide, more notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies due to the inherent toxicity of this element. This situation drives to the replacement of the Sn–Pb solder alloy of eutectic composition commonly used as joining material to suitable lead-free solders for microelectronic assembly. Sn-based alloys containing Ag, Cu, Bi, and Zn are potential lead-free solders, usually close to the binary or ternary eutectic composition. For this reason a great effort was directed to establish reliable thermophysical data fundamental to interpret the solidification process and fluidity of alloys belonging to these systems. In this work, an analysis of the solidification process of pure Sn, binary Sn–Ag, Sn–Cu, Sn–Bi, Sn–Zn, Sn–Pb and ternary Sn–Ag–Cu eutectic alloys was carried out using computer aided-cooling curve analysis and differential scanning calorimetry. 相似文献
89.
Minna Puustinen Olga Volckaert-Legrier Danile Coquin Josie Bernicot 《Computers & Education》2009,53(4):1040-1047
This study analyzes middle school students’ spontaneous mathematics-related help-seeking behavior, in view of making ecologically valid recommendations for the design of supporting tools or “help systems”. Our aim was to investigate the content of students’ help-seeking messages – Are there different forms of help-seeking messages and do they evolve with age? We used the archives of a French forum that provides students with free individualized help in mathematics. The data consisted of 206 messages sent by French middle school students over a period of 42 months. The constituent categories of the messages were identified. The results showed that not all middle school students use the same help-seeking “format”. Compared to sixth graders, ninth graders wrote messages containing more constituent categories, i.e., they provided the online expert with more kinds of information. A detailed analysis of the categories further showed that older students’ messages more often contained explicit help requests and contextual information than did younger students’ messages. Thus, the messages of the oldest students (age 15) were both cognitively more understandable and socially more acceptable than those of the youngest students (age 11). The interpretation of these findings and their implications for designing help systems are discussed. 相似文献
90.
Stefania Romeo P. Thomas Vernier Olga Zeni 《Journal of Infrared, Millimeter and Terahertz Waves》2018,39(9):854-862
Electroporation (electropermeabilization) increases the electrical conductivity of biological cell membranes and lowers transport barriers for normally impermeant materials. Molecular simulations suggest that electroporation begins with the reorganization of water and lipid head group dipoles in the phospholipid bilayer interface, driven by an externally applied electric field, and the evolution of the resulting defects into water-filled, lipid pores. The interior of the electroporated membrane thus contains water, which should provide a signature for detection of the electropermeabilized state. In this feasibility study, we use THz time-domain spectroscopy, a powerful tool for investigating biomolecular systems and their interactions with water, to detect electroporation in human cells subjected to permeabilizing pulsed electric fields (PEFs). The time-domain response of electroporated human monocytes was acquired with a commercial THz, time-domain spectrometer. For each sample, frequency spectra were calculated, and the absorption coefficient and refractive index were extracted in the frequency range between 0.2 and 1.5 THz. This analysis reveals a higher absorption of THz radiation by PEF-exposed cells, with respect to sham-exposed ones, consistent with the intrusion of water into the cell through the permeabilized membrane that is presumed to be associated with electroporation. 相似文献