全文获取类型
收费全文 | 1591篇 |
免费 | 136篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 26篇 |
综合类 | 1篇 |
化学工业 | 196篇 |
金属工艺 | 9篇 |
机械仪表 | 10篇 |
建筑科学 | 25篇 |
能源动力 | 6篇 |
轻工业 | 65篇 |
水利工程 | 1篇 |
无线电 | 171篇 |
一般工业技术 | 231篇 |
冶金工业 | 872篇 |
自动化技术 | 118篇 |
出版年
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 39篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 48篇 |
2015年 | 49篇 |
2014年 | 44篇 |
2013年 | 99篇 |
2012年 | 47篇 |
2011年 | 40篇 |
2010年 | 57篇 |
2009年 | 46篇 |
2008年 | 48篇 |
2007年 | 24篇 |
2006年 | 34篇 |
2005年 | 26篇 |
2004年 | 21篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 4篇 |
1999年 | 34篇 |
1998年 | 279篇 |
1997年 | 147篇 |
1996年 | 93篇 |
1995年 | 52篇 |
1994年 | 43篇 |
1993年 | 62篇 |
1992年 | 14篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1977年 | 25篇 |
1976年 | 39篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1731条查询结果,搜索用时 15 毫秒
51.
Mechanisms of Enhanced Catalysis in Enzyme–DNA Nanostructures Revealed through Molecular Simulations and Experimental Analysis 下载免费PDF全文
Dr. Yingning Gao Christopher C. Roberts Aaron Toop Prof. Chia‐en A. Chang Prof. Ian Wheeldon 《Chembiochem : a European journal of chemical biology》2016,17(15):1430-1436
Understanding and controlling the molecular interactions between enzyme substrates and DNA nanostructures has important implications in the advancement of enzyme–DNA technologies as solutions in biocatalysis. Such hybrid nanostructures can be used to create enzyme systems with enhanced catalysis by controlling the local chemical and physical environments and the spatial organization of enzymes. Here we have used molecular simulations with corresponding experiments to describe a mechanism of enhanced catalysis due to locally increased substrate concentrations. With a series of DNA nanostructures conjugated to horseradish peroxidase, we show that binding interactions between substrates and the DNA structures can increase local substrate concentrations. Increased local substrate concentrations in HRP(DNA) nanostructures resulted in 2.9‐ and 2.4‐fold decreases in the apparent Michaelis constants of tetramethylbenzidine and 4‐aminophenol, substrates of HRP with tunable binding interactions to DNA nanostructures with dissociation constants in the micromolar range. Molecular simulations and kinetic analysis also revealed that increased local substrate concentrations enhanced the rates of substrate association. Identification of the mechanism of increased local concentration of substrates in close proximity to enzymes and their active sites adds to our understanding of nanostructured biocatalysis from which we can develop guidelines for enhancing catalysis in rationally designed systems. 相似文献
52.
Jia‐Wei Li Yu‐Jing Chiu Chia‐Jui Chang Hung‐Chieh He Yi‐Hsuan Tu Kuan‐Ting Lin Yu‐Liang Lin Tzu‐Hsun Kao Hsun‐Hao Hsu Hsiao‐Fan Tseng Tien‐Chang Lu Jiun‐Tai Chen 《大分子材料与工程》2020,305(1)
Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp2 bonding between carbon atoms. 相似文献
53.
Chia En Liu Wen Chieh Lan Hao Ting Yu Han Lin Yang I. Tseng Liu Hsiao Ping Hsu Chung Wen Lan 《International Journal of Applied Ceramic Technology》2020,17(1):146-152
Silicon kerf loss during wafer slicing and the broken quartz crucibles after silicon casting are two major solid wastes from photovoltaic (PV) industry. Especially, the recycle of kerf-loss silicon has become an urgent issue because near 100 000 t of solid wastes are generated every year. One of the most meaningful recycle routes of the kerf-loss silicon is to make silicon nitride crucibles to replace the quartz crucibles. In this study, we demonstrated how this is feasible through acid leaching refining, slip casting, and nitridation. The reaction-bonded silicon nitride (RBSN) crucibles after oxidation were found pure enough for silicon ingot growth. More importantly, they could be reused after ingot growth. With the present examples, the potential of using the kerf-loss silicon for fine ceramics is prominent. 相似文献
54.
Ginseng and lingzhi (Ganoderma lucidum) both are valuable traditional Chinese medicines and have been extensively utilised in functional foods and traditional medicines in many Asian countries. However, massive quantity of ginseng residue is produced after extraction of ginseng which still contains a lot of bioactive compounds such as ginsenosides. The goal of this study was to reuse the American ginseng extraction residue as the fermentation medium of G. lucidum to produce bioactive ginsenoside enriched biotransformation products. The changes of ginsenosides in the fermentation products were analysed during fermentation. Our results showed that after 30 days of fermentation, ginsenoside Rg1, Rd, and compound K (CK) significantly increased, especially Rd, while other ginsenosides (Re, Rb1 and Rc) decreased during fermentation. Ginsenoside Rd is the major ginsenoside in the final fermentation product. Furthermore, the biotransformation of ginsenosides was the major reaction in this fermentation process. 相似文献
55.
Feng‐Yao Tang Yu‐Ching Su Nai‐Chia Chen Hui‐Shan Hsieh Kaun‐Suei Chen 《Molecular nutrition & food research》2008,52(6):683-691
Metastasis is the primary cause of death from breast cancer. Cell migration and invasion play important roles in neoplastic metastasis. The insulin‐like growth factor (IGF‐1) stimulates cell migration through activation of PI‐3K/Akt signaling pathway. IGF‐1 induces the tumorigenicity of many types of cancer cells and is critical for metastatic cell spread in estrogen receptor (ER)‐negative breast‐cancer cells. Matrix metalloproteinase‐2 (MMP‐2) is a key enzyme in the degradation of extracellular matrices and its expression has been dysregulated in breast cancer invasion and metastasis. Resveratrol exhibited potential anticarcinogenic activities in several studies. However, the inhibitory effects of resveratrol on the expression of MMP‐2, migration and invasion of breast‐cancer cell have not been demonstrated yet. In the present study, we investigated the anti‐invasive mechanism of resveratrol in human breast cancer MDA‐MB 435cells. Here, we showed that IGF‐1 is a potent stimulant of the migration of ER‐negative human breast‐cancer cells. Resveratrol could inhibit IGF‐1‐mediated cell migration of MDA‐MB 435 in vitro. The inhibitory effect of resveratrol was mediated in part through the suppression of the activation of PI‐3K/Akt signaling pathway. Furthermore, IGF‐1‐mediated expression of MMP‐2 was significantly inhibited by resveratrol in concomitance with alteration of cell invasion. 相似文献
56.
Weiyi Li Chase Duclos‐Orsello Chia‐Chi Ho 《American Institute of Chemical Engineers》2009,55(6):1434-1446
There is a growing interest in the use of both asymmetric and composite membranes for microfiltration and ultrafiltration processes. This includes particle removal applications in the semiconductor industry and virus clearance in biopharmaceutical applications. Filter fouling plays an important role in these processes. Although flux decline models have been developed for homogeneous membranes, the effects of asymmetric membrane structure on flux decline behavior remain poorly understood on a fundamental level. Here, we develop a theoretical model to describe the effects of asymmetric membrane structure on flux decline. The asymmetric structure was described by the spatial variation in Darcy permeability in the directions normal to and parallel to the membrane surface. The velocity profile and flux decline because of pore blockage were described using Darcy's law and a pore blockage and cake filtration model. Flux decline data were obtained using pseudocomposite membranes with highly interconnected polyvinylidene fluoride membranes (PVDF) and straight through pore polycarbonate track‐etched membranes (PCTE). Model composite membranes were formed by layering PCTE or PVDF membranes with different pore sizes on top of each other. Flux decline data for the composite membrane were in good agreement with model calculations. The results provide important insights into the effects of asymmetric membrane pore structures on flux decline. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
57.
Montmorillonite (MMT) nanoplatelets, fabricated by the exfoliation of MMT during participating in the soap‐free emulsion polymerization of methyl methacrylate, were well‐dispersed in water and performed like a two‐dimensional electrolyte. Their ionic conductivity roughly follows the Manning's limiting law for the conduction of a polyelectrolyte. The dissociated MMT nanoplatelets that carry negative charges in water were able to rapidly adsorb cations, such as tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)) and methylene blue (MB+), and recover into a smectic configuration floating as a separating phase. By using the Langmuir equation, we were able to estimate the occupied surface areas of MMT nanoplatelets by each Ru(bpy) and MB+ cations as 4.708 and 1.806 nm2/ion, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
58.
Chia‐Che Chang Sin‐Ren Li Hung‐Lung Chou Yi‐Cheng Lee Shivaraj Patil Ying‐Sheng Lin Chun‐Chih Chang Yuan Jay Chang Di‐Yan Wang 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(49)
The generation of ammonia, hydrogen production, and nitrogen purification are considered as energy intensive processes accompanied with large amounts of CO2 emission. An electrochemical method assisted by photoenergy is widely utilized for the chemical energy conversion. In this work, earth‐abundant iron pyrite (FeS2) nanocrystals grown on carbon fiber paper (FeS2/CFP) are found to be an electrochemical and photoactive catalyst for nitrogen reduction reaction under ambient temperature and pressure. The electrochemical results reveal that FeS2/CFP achieves a high Faradaic efficiency (FE) of ≈14.14% and NH3 yield rate of ≈0.096 µg min?1 at ?0.6 V versus RHE electrode in 0.25 m LiClO4. During the electrochemical catalytic reaction, the crystal structure of FeS2/CFP remains in the cubic pyrite phase, as analyzed by in situ X‐ray diffraction measurements. With near‐infrared laser irradiation (808 nm), the NH3 yield rate of the FeS2/CFP catalyst can be slightly improved to 0.1 µg min?1 with high FE of 14.57%. Furthermore, density functional theory calculations demonstrate that the N2 molecule has strong chemical adsorption energy on the iron atom of FeS2. Overall, iron pyrite‐based materials have proven to be a potential electrocatalyst with photoactive behavior for ammonia production in practical applications. 相似文献
59.
Ruxiu Liu Chia‐Heng Chu Ningquan Wang Tevhide Ozkaya‐Ahmadov Ozgun Civelekoglu Dohwan Lee A K M Arifuzzman A. Fatih Sarioglu 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(51)
Immunophenotyping is widely used to characterize cell populations in basic research and to diagnose diseases from surface biomarkers in the clinic. This process usually requires complex instruments such as flow cytometers or fluorescence microscopes, which are typically housed in centralized laboratories. Microfluidics are combined with an integrated electrical sensor network to create an antibody microarray for label‐free cell immunophenotyping against multiple antigens. The device works by fractionating the sample via capturing target subpopulations in an array of microfluidic chambers functionalized against different antigens and by electrically quantifying the cell capture statistics through a network of code‐multiplexed electrical sensors. Through a combinatorial arrangement of antibody sequences along different microfluidic paths, the device can measure the prevalence of different cell subpopulations in a sample from computational analysis of the electrical output signal. The device performance is characterized by analyzing heterogeneous samples of mixed tumor cell populations and then the technique is applied to determine leukocyte subpopulations in blood samples and the results are validated against complete blood cell count and flow cytometry results. Label‐free immunophenotyping of cell populations against multiple targets on a disposable electronic chip presents opportunities in global health and telemedicine applications for cell‐based diagnostics and health monitoring. 相似文献