全文获取类型
收费全文 | 2581篇 |
免费 | 190篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 25篇 |
综合类 | 5篇 |
化学工业 | 1011篇 |
金属工艺 | 33篇 |
机械仪表 | 44篇 |
建筑科学 | 67篇 |
矿业工程 | 4篇 |
能源动力 | 76篇 |
轻工业 | 447篇 |
水利工程 | 20篇 |
石油天然气 | 13篇 |
无线电 | 132篇 |
一般工业技术 | 375篇 |
冶金工业 | 211篇 |
原子能技术 | 5篇 |
自动化技术 | 306篇 |
出版年
2024年 | 8篇 |
2023年 | 32篇 |
2022年 | 201篇 |
2021年 | 217篇 |
2020年 | 70篇 |
2019年 | 97篇 |
2018年 | 91篇 |
2017年 | 109篇 |
2016年 | 128篇 |
2015年 | 105篇 |
2014年 | 132篇 |
2013年 | 179篇 |
2012年 | 157篇 |
2011年 | 163篇 |
2010年 | 121篇 |
2009年 | 130篇 |
2008年 | 140篇 |
2007年 | 91篇 |
2006年 | 89篇 |
2005年 | 71篇 |
2004年 | 54篇 |
2003年 | 43篇 |
2002年 | 31篇 |
2001年 | 36篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 67篇 |
1997年 | 42篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 8篇 |
1967年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2774条查询结果,搜索用时 0 毫秒
101.
A series of partially aliphatic copolyimides derived from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-diaminodiphenylmethane (DDM) and 1,6-diaminohexane (DAH) was synthesized. Solubility tests and structural characteristics, evaluated by wide-angle X-ray diffraction measurements (WAXD) did not vary steadily with the content of the flexible segment. On the dynamic mechanical analysis (DMA) the evolution of the secondary relaxations (γ and β) suggested an increased chain tightness as more aliphatic component is included. The onset temperature of α-relaxation decreased regularly with the content of aliphatic sequence. During the α-relaxation the trend of E′, E″ and tan δ with temperature, and at multiple frequencies, evidenced the overlapping of phenomena. The increased mobility determines the formation of oriented structures that behave as constraints. Simultaneously, as the flexible content (DAH segment) is more important, orientation relaxations take place with increasing temperature. The equilibrium between stiffening and flowing makes the polyimides with high aliphatic content behave like elastomers. 相似文献
102.
Egg parasitoids are able to find their hosts by exploiting their chemical footprints as host location cues. In nature, the
apolar epicuticular wax layer of plants that consists of several classes of hydrocarbons serves as the substrate that retains
these contact kairomones. However, experiments on chemical footprints generally have used filter paper as substrate to study
insect behavior. Here, we explored the ability of Trissolcus basalis (Scelionidae) females to discriminate between footprint cues left by male and female Nezara viridula (Pentatomidae) on leaves of their host plant Brassica oleracea (broccoli). Furthermore, we analyzed the chemical composition of the outermost wax layer of broccoli leaves to evaluate the
degree of overlap in insect and plant cuticular hydrocarbons that could lead to masking effects in the detection of footprint
cues. Our results showed that B. oleracea epicuticular wax retains the chemical footprints of adult bugs and allows T. basalis females to differentiate hosts of different sex. Traces of female bugs elicited more extensive searching behavior in egg
parasitoids than traces of males. The application of n-nonadecane, a compound specific to male N. viridula, on the tarsi of female bugs prevented parasitoid females from distinguishing between host male and host female footprints.
Analyses of B. oleracea leaves revealed that epicuticular waxes were mainly composed of linear alkanes, ketones, and secondary alcohols. Alkanes
were dominated by n-nonacosane (nC29) and n-hentriacontane (nC31), while male-specific n-nonadecane (nC19) was absent. The ecological significance of these results for parasitoid host location behavior is discussed. 相似文献
103.
Colour assays: An inside look into Alentejo traditional limewash paintings and coloured lime mortars
Milene Gil Jose Aguiar Ana Seruya Rosário Veiga Luisa Carvalho Helena Vargas Jose Mirão Antonio Candeias 《Color research and application》2011,36(1):61-71
A series of colour assays were conducted taking into account old bibliographic recommendations and oral testimony regarding traditional lime painting technology from the Alentejo (South Portugal) region. The main objectives were: (a) the colorimetric analysis of paintings made with different limewash preparation methods; (b) the comparison between natural processed red and yellows ochre pigments (“home made” and from industrial origin) and synthetic iron oxides in different concentrations and lime proportions; (c) the evaluation of the colorimetric CIELAB coordinates during the lime carbonation process in coloured mortars and limewashes. The results shows that the evolution of L*, a*, and b* during the carbonation process is independent of pigment concentration and paint thickness but dependent of pigment composition and finishing technique (lime painting or coloured mortar). They also emphasize the importance of surface appearance attributes and its influence on the colorimetric parameters. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 61–71, 2011 相似文献
104.
Peptide‐Based Fluorescent Probes for Deacetylase and Decrotonylase Activity: Toward a General Platform for Real‐Time Detection of Lysine Deacylation 下载免费PDF全文
Dr. Debra R. Rooker Yuliya Klyubka Dr. Ritika Gautam Prof. Dr. Elisa Tomat Prof. Dr. Daniela Buccella 《Chembiochem : a European journal of chemical biology》2018,19(5):496-504
Histone deacetylases regulate the acetylation levels of numerous proteins and play key roles in physiological processes and disease states. In addition to acetyl groups, deacetylases can remove other acyl modifications on lysines, the roles and regulation of which are far less understood. A peptide‐based fluorescent probe for single‐reagent, real‐time detection of deacetylase activity that can be readily adapted for probing broader lysine deacylation, including decrotonylation, is reported. Following cleavage of the lysine modification, the probe undergoes rapid intramolecular imine formation that results in marked optical changes, thus enabling convenient detection of deacylase activity with good statistical Z′ factors for both absorption and fluorescence modalities. The peptide‐based design offers broader isozyme scope than that of small‐molecule analogues, and is suitable for probing both metal‐ and nicotinamide adenine dinucleotide (NAD+)‐dependent deacetylases. With an effective sirtuin activity assay in hand, it is demonstrated that iron chelation by Sirtinol, a commonly employed sirtuin inhibitor, results in an enhancement in the inhibitory activity of the compound that may affect its performance in vivo. 相似文献
105.
Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method 下载免费PDF全文
María J. Martínez‐Ortiz Miguel A. de la Rosa‐Guzmán Jorge R. Vargas‐García Jorge L. Flores‐Moreno Nancy Castillo Ariel Guzmán‐Vargas Sara Morandi Rosa M. Pérez‐Gutiérrez 《加拿大化工杂志》2018,96(1):297-306
A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N2 sorption experiments. The basic and metal functions were analyzed by CO2‐TPD and H2‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method. 相似文献
106.
Synthesis and Evaluation of the Anticancer and Trypanocidal Activities of Boronic Tyrphostins 下载免费PDF全文
Noemi de J. Hiller Nayane A. A. e Silva Dr. Robson X. Faria Dr. André Luís A. Souza Dr. Jackson A. L. C. Resende André Borges Farias Dr. Nelilma Correia Romeiro Dr. Daniela de Luna Martins 《ChemMedChem》2018,13(14):1395-1404
Molecules containing an (cyanovinyl)arene moiety are known as tyrphostins because of their ability to inhibit proteins from the tyrosine kinase family, an interesting target for the development of anticancer and trypanocidal drugs. In the present work, (E)‐(cyanovinyl)benzeneboronic acids were synthesized by Knoevenagel condensations without the use of any catalysts in water through a simple protocol that completely avoided the use of organic solvents in the synthesis and workup process. The in vitro anticancer and trypanocidal activities of the synthesized boronic acids were also evaluated, and it was discovered that the introduction of the boronic acid functionality improved the activity of the boronic tyrphostins. In silico target fishing with the use of a chemogenomic approach suggested that tyrosine‐phosphorylation‐regulated kinase 1a (DYRK1A) was a potential target for some of the designed compounds. 相似文献
107.
Geta David Ioana Turin-Moleavin Laura-Elena Ursu Dragos Peptanariu Daniela Ailincai 《Iranian Polymer Journal》2018,27(7):517-526
Combining two or more materials for carrier construction is one of the topical approaches to avoid/diminish deficiencies and to increase functionality in delivery systems for bioactive compounds. In this context, here, multilayered nanoparticles comprising both natural (atelocollagen—AteCol; hyaluronic acid derivative—HA) and synthetic [poly(ε-caprolactone)—PCL; polyethylenimine—PEI; poly(l-lysine)—PLL] polymers were prepared and characterized. The combination of a modified double-emulsion method with polymer modification reactions allowed improvement of the polymer particle’s functionality. Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, fluorescence spectroscopy, dynamic light scattering, transmission/scanning electron microscopy and fluorescence microscopy investigations confirmed the obtention of the envisaged nanomaterials with the expected composition and structure. The double-layered biopolymer/PCL-based nanoparticles formed in a first synthesis step could be successfully coated with PEI and PLL. The gel electrophoresis assay attested the DNA packing ability of the formed nano-vehicles involving surface grafting of the former biopolymer/PCL-based nanoparticles in the case of both cationic polymers, for N/P ratios of 10 (PEI coating) and 3.5 (PLL coating), respectively. According to the FTIR registration, the protein’s native form was preserved. Considering the advantage of biocompatibility and high versatility (controlled size, tuned chemistry and biodegradation rate) some of the resulted nanomaterials may appear as potential candidates for biomedical uses (i.e., drug/gene delivery and tissue engineering). 相似文献
108.
A new approach to the modification of azidomethyl polyethersulfones using click reactions with acetylenic derivatives in the presence of CuBr as catalyst is presented. An azidomethyl polyethersulfone was prepared by the reaction of chloromethylated polysulfone with sodium azide in dimethylformamide. By the Cu(I)‐catalysed Huisgen 1,3‐dipolar cycloaddition reaction of the azidomethyl polyethersulfone to acetylenic derivatives, new polyethersulfones containing 1,2,3‐triazole rings were obtained. The structures of the polymers were confirmed using attenuated total reflectance Fourier transform infrared and NMR spectroscopy. The polymers were characterized using dynamic mechanical analysis, thermogravimetric analysis, stress‐strain and water contact angle measurements and solubility tests. The polymers bearing 1,2,3‐triazole rings having OH or COOH as substituents exhibited static contact angles smaller than that of the parent polyethersulfone. Copyright © 2010 Society of Chemical Industry 相似文献
109.
110.
Marius Eugen Ciurea Ada Maria Georgescu Stefana Oana Purcaru Stefan-Alexandru Artene Ghazaleh Hooshyar Emami Mihai Virgil Boldeanu Daniela Elise Tache Anica Dricu 《International journal of molecular sciences》2014,15(5):8169-8185
Almost all tumors are composed of a heterogeneous cell population, making them difficult to treat. A small cancer stem cell population with a low proliferation rate and a high tumorigenic potential is thought to be responsible for cancer development, metastasis and resistance to therapy. Stem cells were reported to be involved in both normal development and carcinogenesis, some molecular mechanisms being common in both processes. No less controversial, stem cells are considered to be important in treatment of malignant diseases both as targets and drug carriers. The efforts to understand the role of different signalling in cancer stem cells requires in depth knowledge about the mechanisms that control their self-renewal, differentiation and malignant potential. The aim of this paper is to discuss insights into cancer stem cells historical background and to provide a brief review of the new therapeutic strategies for targeting cancer stem cells. 相似文献