全文获取类型
收费全文 | 1680篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 200篇 |
金属工艺 | 37篇 |
机械仪表 | 41篇 |
建筑科学 | 76篇 |
矿业工程 | 4篇 |
能源动力 | 22篇 |
轻工业 | 189篇 |
水利工程 | 12篇 |
石油天然气 | 3篇 |
无线电 | 100篇 |
一般工业技术 | 201篇 |
冶金工业 | 611篇 |
原子能技术 | 10篇 |
自动化技术 | 208篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 18篇 |
2018年 | 35篇 |
2017年 | 23篇 |
2016年 | 36篇 |
2015年 | 21篇 |
2014年 | 40篇 |
2013年 | 81篇 |
2012年 | 57篇 |
2011年 | 71篇 |
2010年 | 58篇 |
2009年 | 49篇 |
2008年 | 84篇 |
2007年 | 63篇 |
2006年 | 64篇 |
2005年 | 43篇 |
2004年 | 61篇 |
2003年 | 48篇 |
2002年 | 44篇 |
2001年 | 41篇 |
2000年 | 26篇 |
1999年 | 40篇 |
1998年 | 110篇 |
1997年 | 78篇 |
1996年 | 54篇 |
1995年 | 40篇 |
1994年 | 25篇 |
1993年 | 38篇 |
1992年 | 30篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 21篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有1729条查询结果,搜索用时 15 毫秒
1.
De Coster Arnaud Musliu Nysret Schaerf Andrea Schoisswohl Johannes Smith-Miles Kate 《Journal of Scheduling》2022,25(1):35-58
Journal of Scheduling - We propose an algorithm selection approach and an instance space analysis for the well-known curriculum-based course timetabling problem (CB-CTT), which is an important... 相似文献
2.
Zizhan Li Kate Howell Zhongxiang Fang Pangzhen Zhang 《Comprehensive Reviews in Food Science and Food Safety》2020,19(1):247-281
Grapes are an important global horticultural product, and are mainly used for winemaking. Typically, grapes and wines are rich in various phytochemicals, including phenolics, terpenes, pyrazines, and benzenoids, with different compounds responsible for different nutritional and sensory properties. Among these compounds, sesquiterpenes, a subcategory of the terpenes, are attracting increasing interest as they affect aroma and have potential health benefits. The characteristics of sesquiterpenes in grapes and wines in terms of classification, biosynthesis pathway, and active functions have not been extensively reviewed. This paper summarizes 97 different sesquiterpenes reported in grapes and wines and reviews their biosynthesis pathways and relevant bio‐regulation mechanisms. This review further discusses the functionalities of these sesquiterpenes including their aroma contribution to grapes and wines and potential health benefits, as well as how winemaking processes affect sesquiterpene concentrations. 相似文献
3.
4.
Kletzander Lucas Musliu Nysret Smith-Miles Kate 《Annals of Mathematics and Artificial Intelligence》2021,89(7):617-637
Annals of Mathematics and Artificial Intelligence - This paper considers the Rotating Workforce Scheduling Problem, and shows how the strengths and weaknesses of various solution methods can be... 相似文献
5.
Václav Doležal Ladislav Nádherný Kateřina Rubešová Vít Jakeš Alena Michalcová Ondřej Jankovský Morgane Poupon 《Ceramics International》2019,45(9):11233-11240
Polycrystalline LaMgAl11O19 (LMA) was prepared by four different non-hydrolytic sol-gel methods. From stable solutions, four powder precursors containing an amorphous and nanocrystalline phase with specific reactivity were obtained. The particle size, morphology, thermal behaviour, and phase composition of the powder precursors were studied using DLS, TEM, DSC/TG and XRD. Bulk ceramic samples containing LMA were prepared at 1200?°C for 16?h and examined in terms of phase purity and microstructure using XRD, SEM, and TEM. Raman spectroscopy of pure LMA was used to study the structure in detail. A mechanism of LMA formation and a relation between powder precursor properties and final phase composition is proposed. These findings may be useful for designing modern technologies for fabrication of LMA for optical or protective coating applications. 相似文献
6.
Dr. Dae-Shik Kim Dr. Atsushi Endo Dr. Francis G. Fang Dr. Kuan-Chun Huang Dr. Xingfeng Bao Dr. Hyeong-wook Choi Dr. Utpal Majumder Dr. Young Y. Shen Steven Mathieu Xiaojie Zhu Kristen Sanders Dr. Thomas Noland Dr. Ming-Hong Hao Dr. Yu Chen Dr. John Y. Wang So Yasui Karen TenDyke Jiayi Wu Christy Ingersoll Kara A. Loiacono Dr. Janna E. Hutz Dr. Nadeem Sarwar 《ChemMedChem》2021,16(11):1741-1744
A strategy for creating potent and pan-genotypic stimulator of interferon genes (STING) agonists is described. Locking a bioactive U-shaped conformation of cyclic dinucleotides by introducing a transannular macrocyclic bridge between the nucleic acid bases leads to a topologically novel macrocycle-bridged STING agonist (MBSA). In addition to substantially enhanced potency, the newly designed MBSAs, exemplified by clinical candidate E7766 , exhibit broad pan-genotypic activity in all major human STING variants. E7766 is shown to have potent antitumor activity with long lasting immune memory response in a mouse liver metastatic tumor model. Two complementary stereoselective synthetic routes to E7766 are also described. 相似文献
7.
David F. Sanders Ruilan Guo Zachary P. Smith Qiang Liu Kevin A. Stevens James E. McGrath Donald R. Paul Benny D. Freeman 《Polymer》2014
Thermal rearrangement of polyimides with ortho-position groups to polybenzoxazoles and related structures has been of recent interest for producing gas separation membranes. This study explores the influence of synthesis route and ortho-position functional group on the thermal rearrangement process and the fractional free volume of thermally rearranged (TR) polymers produced from polyimides derived from 3,3′-dihydroxy-4,4′-diamino-biphenyl and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB–6FDA). Acetate, propanoate, and pivalate ortho-position functional groups were considered. Thermogravimetric analysis (TGA) was used to study thermal rearrangement at temperatures between 350 and 450 °C, and evolved gases from TGA were analyzed via mass spectrometry to characterize the byproducts of thermal rearrangement and thermal degradation. CO2 was the major byproduct of thermal rearrangement for all samples, and its evolution began well before the onset of thermal degradation. When non-hydroxyl ortho-position groups were present in the polymers, several byproducts other than CO2 were also observed due to the loss of these ortho-position groups before thermal rearrangement. Free volume generally increased with increasing extent of thermal rearrangement, but precise values of free volume could not be accurately determined for polymers with propanoate and pivalate ortho-position functional groups due to uncertainties in the chemical structure of partially converted materials. For polymers with acetate and hydroxyl ortho-position groups, free volume could be determined within the uncertainty of density measurements. Thermal rearrangement behavior and free volume results for acetate containing polymers synthesized via different routes were very similar. Based on these results, the chemical structure of the ortho-position functional group has a larger impact on TR polymer properties than the polyimide precursor synthesis route. 相似文献
8.
Dmytro Savytskii Marisa Sanders Roman Golovchak Brian Knorr Volkmar Dierolf Himanshu Jain 《Journal of the American Ceramic Society》2014,97(1):198-205
Congruent crystallization of antimony sulphoiodide (SbSI) glass of stoichiometric composition, which is prepared successfully for the first time using rapid melt‐quenching, has been investigated using differential scanning calorimetry (DSC). The results for glass powder show a glass transition at 127°C and two separate exothermal peaks with maxima around 140°C and 190°C. The ratio of the intensities of the exothermal peak at ~190°C to the peak at ~140°C increases as the particle size and heating rate are increased, but their total enthalpy remains constant at 62 ± 2 J/g for all DSC runs. Surface heating of the glass induced by a 520 nm CW laser shows two contracted regions: needle‐like crystalline formations at low temperature and bulk crystallization at high temperature. The observed phenomena and DSC results suggest two different kinds of crystallization of the SbSI phase: one‐dimensional crystallization at low temperature which starts from the sample surface and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The origin of the two different crystallizations can be traced to the strong anisotropy of the SbSI crystal structure due to the weak van der Waals interaction between covalent‐ionic chains (Sb2S2I2)n. 相似文献
9.
The Chemistry and Biology of 6‐Hydroxyceramide,the Youngest Member of the Human Sphingolipid Family 下载免费PDF全文
Andrej Kováčik Dr. Jaroslav Roh Prof. Dr. Kateřina Vávrová 《Chembiochem : a European journal of chemical biology》2014,15(11):1555-1562
Sphingolipids are crucial for the life of the cell. In land‐dwelling mammals, they are equally important outside the cell—in the extracellular space of the skin barrier—because they prevent loss of water. Although a large body of research has elucidated many of the functions of sphingolipids, their extensive structural diversity remains intriguing. A new class of sphingolipids based on 6‐hydroxylated sphingosine has recently been identified in human skin. Abnormal levels of these 6‐hydroxylated ceramides have repeatedly been observed in atopic dermatitis; however, neither the biosynthesis nor the roles of these unique ceramide subclasses have been established in the human body. In this Minireview, we summarize the current knowledge of 6‐hydroxyceramides, including their discovery, structure, stereochemistry, occurrence in healthy and diseased human epidermis, and synthetic approaches to 6‐hydroxysphingosine and related ceramides. 相似文献
10.
Specificity of a UDP‐GalNAc Pyranose–Furanose Mutase: A Potential Therapeutic Target for Campylobacter jejuni Infections 下载免费PDF全文
Dr. Myles B. Poulin Yun Shi Carla Protsko Dr. Sean A. Dalrymple Prof. David A. R. Sanders Prof. B. Mario Pinto Prof. Todd L. Lowary 《Chembiochem : a European journal of chemical biology》2014,15(1):47-56
Pyranose–furanose mutases are essential enzymes in the life cycle of a number of microorganisms, but are absent in mammalian systems, and hence represent novel targets for drug development. To date, all such mutases show preferential recognition of a single substrate (e.g., UDP‐Gal). We report here the detailed structural characterization of the first bifunctional pyranose–furanose mutase, which recognizes both UDP‐Gal and UDP‐GalNAc. The enzyme under investigation (cjUNGM) is involved in the biosynthesis of capsular polysaccharides (CPSs) in Campylobacter jejuni 11168. These CPSs are known virulence factors that are required for adhesion and invasion of human epithelial cells. Using a combination of UV/visible spectroscopy, X‐ray crystallography, saturation transfer difference NMR spectroscopy, molecular dynamics and CORCEMA‐ST calculations, we have characterized the binding of the enzyme to both UDP‐Galp and UDP‐GalpNAc, and compared these interactions with those of a homologous monofunctional mutase enzyme from E. coli (ecUGM). These studies reveal that two arginines in cjUNGM, Arg59 and Arg168, play critical roles in the catalytic mechanism of the enzyme and in controlling its specificity to ultimately lead to a GalfNAc‐containing CPS. In ecUGM, these arginines are replaced with histidine and lysine, respectively, and this results in an enzyme that is selective for UDP‐Gal. We propose that these changes in amino acids allow C. jejuni 11168 to produce suitable quantities of the sugar nucleotide substrate required for the assembly of a CPS containing GalfNAc, which is essential for viability. 相似文献