全文获取类型
收费全文 | 6865篇 |
免费 | 460篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 80篇 |
综合类 | 2篇 |
化学工业 | 1990篇 |
金属工艺 | 116篇 |
机械仪表 | 211篇 |
建筑科学 | 296篇 |
矿业工程 | 25篇 |
能源动力 | 266篇 |
轻工业 | 1000篇 |
水利工程 | 60篇 |
石油天然气 | 37篇 |
无线电 | 424篇 |
一般工业技术 | 1058篇 |
冶金工业 | 331篇 |
原子能技术 | 47篇 |
自动化技术 | 1394篇 |
出版年
2024年 | 24篇 |
2023年 | 99篇 |
2022年 | 281篇 |
2021年 | 324篇 |
2020年 | 216篇 |
2019年 | 241篇 |
2018年 | 291篇 |
2017年 | 301篇 |
2016年 | 287篇 |
2015年 | 237篇 |
2014年 | 320篇 |
2013年 | 594篇 |
2012年 | 454篇 |
2011年 | 555篇 |
2010年 | 381篇 |
2009年 | 408篇 |
2008年 | 349篇 |
2007年 | 314篇 |
2006年 | 271篇 |
2005年 | 199篇 |
2004年 | 145篇 |
2003年 | 166篇 |
2002年 | 137篇 |
2001年 | 77篇 |
2000年 | 85篇 |
1999年 | 66篇 |
1998年 | 55篇 |
1997年 | 60篇 |
1996年 | 53篇 |
1995年 | 43篇 |
1994年 | 35篇 |
1993年 | 28篇 |
1992年 | 16篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有7337条查询结果,搜索用时 15 毫秒
131.
Yulong Li Hassan Karim Bang Wang Carlos Guzmn Wendy Harwood Qiang Xu Yazhou Zhang Huaping Tang Yunfeng Jiang Pengfei Qi Mei Deng Jian Ma Jingyu Lan Jirui Wang Guoyue Chen Xiujin Lan Yuming Wei Youliang Zheng Qiantao Jiang 《International journal of molecular sciences》2022,23(15)
The granule-bound starch synthase I (GBSSI) encoded by the waxy gene is responsible for amylose synthesis in the endosperm of wheat grains. In the present study, a novel Wx-B1 null mutant line, M3-415, was identified from an ethyl methanesulfonate-mutagenized population of Chinese tetraploid wheat landrace Jianyangailanmai (LM47). The gene sequence indicated that the mutated Wx-B1 encoded a complete protein; this protein was incompatible with the protein profile obtained using sodium dodecyl sulfate–polyacrylamide gel electrophoresis, which showed the lack of Wx-B1 protein in the mutant line. The prediction of the protein structure showed an amino acid substitution (G470D) at the edge of the ADPG binding pocket, which might affect the binding of Wx-B1 to starch granules. Site-directed mutagenesis was further performed to artificially change the amino acid at the sequence position 469 from alanine (A) to threonine (T) (A469T) downstream of the mutated site in M3-415. Our results indicated that a single amino acid mutation in Wx-B1 reduces its activity by impairing its starch-binding capacity. The present study is the first to report the novel mechanism underlying Wx-1 deletion in wheat; moreover, it provided new insights into the inactivation of the waxy gene and revealed that fine regulation of wheat amylose content is possible by modifying the GBSSI activity. 相似文献
132.
Marta Abrantes Maria Salete Balula Anabela A. Valente Filipe A. Almeida Paz Martyn Pillinger Carlos C. Romão João Rocha Isabel S. Gonçalves 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):215-222
The organotin vanadate [Me3SnVO3] (1) has been prepared and characterised in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis, multinuclear
magic-angle spinning (MAS) NMR, IR and Raman spectroscopy. The phase purity and structure of microcrystalline 1 were confirmed by carrying out a full Rietveld structural refinement at ambient temperature and from conventional powder
XRD. 51V and 119Sn MAS NMR data for compound 1 were in agreement with the predicted structure, showing two equally-abundant, nonequivalent Me3Sn groups and two equally-abundant, nonequivalent vanadium atoms. The compound was applied as a catalyst for the liquid-phase
epoxidation of olefins at 55 °C using tert-butyl hydroperoxide (tBuOOH) as the oxidant. The reaction rate for the different substrates followed the order cis-cyclooctene > (R)-(+)-limonene ≅ trans-2-octene > cyclododecene > styrene > 1-octene; the corresponding epoxides were the
only observed products. Leaching tests indicated that the catalytic epoxidation of cyclooctene was mainly heterogeneous in
nature.
This paper is dedicated to Professor Ian Manners and his scientific accomplishments. 相似文献
133.
Relative effect of particle size on the physical properties of corn meal extrudates: Effect of particle size on the extrusion of corn meal 总被引:1,自引:0,他引:1
Carlos W.P. Carvalho Cristina Y. Takeiti Charles I. Onwulata Lester O. Pordesimo 《Journal of food engineering》2010
Corn meal of various particle sizes ranging from 180 to 710 μm were processed in a twin-screw extruder to produce directly expanded extrudates. The extrusion process effects on the specific mechanical energy (SME), expansion indexes (radial, longitudinal and volumetric), pasting viscosity, water absorption index (WAI) texture properties, and microstructure were determined. Increasing the particle size decreased the SME input. Extrudates produced with corn meal of higher particle sizes expanded more than extrudates produced with smaller particle sizes. For all treatments there was no peak viscosity at 95 °C. But expanded corn meal extrudate from the 180 μm fraction showed a discontinuous gel matrix phase. Increasing corn meal particle size decreased WAI values. The mechanical resistance of the extrudates from the smallest particle size was significantly higher (p < 0.05) than that of the largest particle size. The microstructure of raw corn meal revealed large fractured particles with small rounded particles adhering to the surface. 相似文献
134.
Merlin Itsel Cruz-De la Rosa Hilda Jimnez-Wences Judit Alarcn-Milln Manuel Joaquín Romero-Lpez Carlos Alberto Castan-Snchez Eric Genaro Salmern-Brcenas Gloria Fernndez-Tilapa 《International journal of molecular sciences》2022,23(13)
The overexpression of miR-218-5p in cervical cancer (CC) cell lines decreases migration, invasion and proliferation. The objective was to identify target genes of miR-218-5p and the signaling pathways and cellular processes that they regulate. The relationship between the expression of miR-218-5p and RUNX2 and overall survival in CC as well as the effect of the exogenous overexpression of miR-218-5p on the level of RUNX2 were analyzed. The target gene prediction of miR-218-5p was performed in TargetScan, miRTarBase and miRDB. Predicted target genes were subjected to gene ontology (GO) and pathway enrichment analysis using the Kyoto Encyclopaedia of Genes and Genomes (KEGG). The miR-218-5p mimetic was transfected into C-33A and CaSki cells, and the miR-218-5p and RUNX2 levels were determined by RT–qPCR. Of the 118 predicted targets for miR-218-5p, 86 are involved in protein binding, and 10, including RUNX2, are involved in the upregulation of proliferation. Low miR-218-5p expression and a high level of RUNX2 are related to poor prognosis in CC. miR-218-5p overexpression is related to decreased RUNX2 expression in C-33A and CaSki cells. miR-218-5p may regulate RUNX2, and both molecules may be prognostic markers in CC. 相似文献
135.
Lucía Fernández-Espada Carlos Bengoechea José Alberto Sandía Felipe Cordobés Antonio Guerrero 《应用聚合物科学杂志》2019,136(5):47012
The addition of salts, like sodium bicarbonate (SB) or carbonate (SC), into the formulation of bioplastic materials may alter their hydrophilic character to a significant extent. Soy protein isolate (SPI) is a byproduct of the soybean oil industry, which, when properly blended with glycerol (GL), can be further processed through a lab-scale injection molding device. A maximum in the water uptake around 2250 or 2500% is obtained for bioplastics obtained when either SB or SC content is around 1 wt %, respectively. Thus, they exceed the limit to be considered superabsorbent materials (SAMs). Regarding their mechanical properties, a higher presence of SB within the SPI/GL matrix provides materials with a higher extensibility and lower Young's modulus. A higher water uptake is observed after replacing SB for SC in the formulation, probably related to a higher alkalinization of the material as well as to the high hydrophilicity of the carbonate. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47012. 相似文献
136.
Rodrigo Battisti Eduardo Hafemann Carlos Alberto Claumann Ricardo Antonio Francisco Machado Cintia Marangoni 《Polymer Engineering and Science》2019,59(5):891-898
This study provides a novel value‐added utilization of the agroindustrial waste of royal palm tree leaf sheath to produce cellulose acetate. One of the motivations of this work was the fact that Brazil is one of the largest heart of palm producers in the world. However, as a result of extraction and processing, tons of waste are generated and discharged to the environment. Such waste is rich in lignocellulosic material, which could be reused to obtain derivatives of interest and commercial value. The synthesis of cellulose acetate was performed through a homogeneous acetylation reaction. Three different conditions were tested for delignification of the raw material, which resulted in a reduction in lignin content from 17.75 to 7.72%. The highest yield of cellulose acetate reached 99.5%, with degree of substitutions ranging between 2.08 and 2.82, which indicates satisfactory conversion. The Fourier transform infrared spectrum showed that practically all hydroxyl groups were replaced by acetate groups; this was also confirmed by nuclear magnetic resonance analysis. X‐ray diffraction analysis showed that the cellulose acetate crystallinity index was 8.9%. This demonstrates the viable potential of cellulose acetate production with low cost and use of highly available agroindustrial waste. POLYM. ENG. SCI., 59:891–898, 2019. © 2018 Society of Plastics Engineers 相似文献
137.
Campos E Façanha AR Costa EP Fraga A Moraes J da Silva Vaz I Masuda A Logullo C 《International journal of molecular sciences》2011,12(6):3525-3535
The physiological roles of polyphosphates (polyP) recently found in arthropod mitochondria remain obscure. Here, the relationship between the mitochondrial membrane exopolyphosphatase (PPX) and the energy metabolism of hard tick Rhipicephalus microplus embryos are investigated. Mitochondrial respiration was activated by adenosine diphosphate using polyP as the only source of inorganic phosphate (P(i)) and this activation was much greater using polyP(3) than polyP(15). After mitochondrial subfractionation, most of the PPX activity was recovered in the membrane fraction and its kinetic analysis revealed that the affinity for polyP(3) was 10 times stronger than that for polyP(15). Membrane PPX activity was also increased in the presence of the respiratory substrate pyruvic acid and after addition of the protonophore carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. Furthermore, these stimulatory effects disappeared upon addition of the cytochrome oxidase inhibitor potassium cyanide and the activity was completely inhibited by 20 μg/mL heparin. The activity was either increased or decreased by 50% upon addition of dithiothreitol or hydrogen peroxide, respectively, suggesting redox regulation. These results indicate a PPX activity that is regulated during mitochondrial respiration and that plays a role in adenosine-5'-triphosphate synthesis in hard tick embryos. 相似文献
138.
Carlos Plana Sabino Armenise Antonio Monz��n Enrique Garc��a-Bordej�� 《Topics in Catalysis》2011,54(13-15):914-921
A catalyst of Ni supported on alumina coated monolith has been prepared, characterized and tested in NH3 decomposition. The characterization of the catalyst by XPS and TPR showed that there is no formation of aluminates after catalyst use. It is studied the effect of the space velocity, by varying the feed flow rate and the catalyst??s length. Some evidences are shown about the reaction inhibition by produced H2 and about the reasons for the better performance of the monolith than packed bed catalyst. 相似文献
139.
Córdova MO Flores Ramírez CI Bejarano BV Arroyo Razo GA Pérez Flores FJ Tellez VC Ruvalcaba RM 《International journal of molecular sciences》2011,12(12):8575-8580
In this work, the results of a study comparing the use of irradiation from different regions of the infrared spectrum for the promotion of several organic reactions, are presented and discussed. This use of eco-conditions provides a green approach to chemical synthesis. A set of ten different organic reactions were evaluated, including the Knoevenagel, Hantzsch, Biginelli and Meldrum reactions. It is important to highlight the use of a commercial device that produces infrared irradiation in the near infrared region and its distribution by convection providing heating uniformity, significantly reducing reaction times, achieving good yields and proceeding in the absence of solvent. It is also worth noting that a variety of different reactions may be performed at the same time. Finally, the products obtained were identified using TLC, together with corresponding MS-data, complementarily in comparison of NMR (1)H and (13)C data with literature information. 相似文献
140.
Carlos Enrique Daza Oscar A. Gamba Yesid Hernández Miguel A. Centeno Fanor Mondragón Sonia Moreno Rafael Molina 《Catalysis Letters》2011,141(7):1037-1046