全文获取类型
收费全文 | 27297篇 |
免费 | 586篇 |
国内免费 | 124篇 |
专业分类
电工技术 | 553篇 |
综合类 | 64篇 |
化学工业 | 4350篇 |
金属工艺 | 1076篇 |
机械仪表 | 728篇 |
建筑科学 | 637篇 |
矿业工程 | 79篇 |
能源动力 | 724篇 |
轻工业 | 2356篇 |
水利工程 | 221篇 |
石油天然气 | 188篇 |
武器工业 | 1篇 |
无线电 | 2669篇 |
一般工业技术 | 4712篇 |
冶金工业 | 7168篇 |
原子能技术 | 441篇 |
自动化技术 | 2040篇 |
出版年
2022年 | 184篇 |
2021年 | 417篇 |
2020年 | 211篇 |
2019年 | 239篇 |
2018年 | 378篇 |
2017年 | 376篇 |
2016年 | 412篇 |
2015年 | 294篇 |
2014年 | 455篇 |
2013年 | 1075篇 |
2012年 | 679篇 |
2011年 | 993篇 |
2010年 | 701篇 |
2009年 | 747篇 |
2008年 | 835篇 |
2007年 | 873篇 |
2006年 | 703篇 |
2005年 | 778篇 |
2004年 | 651篇 |
2003年 | 685篇 |
2002年 | 721篇 |
2001年 | 698篇 |
2000年 | 628篇 |
1999年 | 639篇 |
1998年 | 2339篇 |
1997年 | 1602篇 |
1996年 | 1177篇 |
1995年 | 810篇 |
1994年 | 664篇 |
1993年 | 708篇 |
1992年 | 379篇 |
1991年 | 357篇 |
1990年 | 359篇 |
1989年 | 360篇 |
1988年 | 309篇 |
1987年 | 282篇 |
1986年 | 260篇 |
1985年 | 295篇 |
1984年 | 247篇 |
1983年 | 223篇 |
1982年 | 227篇 |
1981年 | 265篇 |
1980年 | 256篇 |
1979年 | 193篇 |
1978年 | 189篇 |
1977年 | 385篇 |
1976年 | 622篇 |
1975年 | 141篇 |
1974年 | 115篇 |
1973年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Can Ercan S. Esra Safran Artuğ Türkmenoğlu Uğur Karabakal 《Journal of surfactants and detergents》2021,24(1):139-147
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated. 相似文献
2.
Prof. Andrea Baier Dr. Anne Kokel Dr. William Horton Ewa Gizińska Dr. Garima Pandey Prof. Ryszard Szyszka Prof. Béla Török Prof. Marianna Török 《ChemMedChem》2021,16(12):1927-1932
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays. 相似文献
3.
Anna Stasiowicz Natalia Rosiak Ewa Tykarska Maciej Kozak Jacek Jenczyk Piotr Szulc Joanna Kobus-Cisowska Kornelia Lewandowska Anita Paziska Wojciech Paziski Judyta Cielecka-Piontek 《International journal of molecular sciences》2021,22(8)
Piperine is an alkaloid that has extensive pharmacological activity and impacts other active substances bioavailability due to inhibition of CYP450 enzymes, stimulation of amino acid transporters and P-glycoprotein inhibition. Low solubility and the associated low bioavailability of piperine limit its potential. The combination of piperine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) causes a significant increase in its solubility and, consequently, an increase in permeability through gastrointestinal tract membranes and the blood–brain barrier. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) were used to characterize interactions between piperine and HP-β-CD. The observed physicochemical changes should be combined with the process of piperine and CD system formation. Importantly, with an increase in solubility and permeability of piperine as a result of interaction with CD, it was proven to maintain its biological activity concerning the antioxidant potential (2,2-diphenyl-1-picryl-hydrazyl-hydrate assay), inhibition of enzymes essential for the inflammatory process and for neurodegenerative changes (hyaluronidase, acetylcholinesterase, butyrylcholinesterase). 相似文献
4.
Lindsey Yue Alicia Bayon Wojciech Lipiński 《American Institute of Chemical Engineers》2021,67(8):e17267
The effects of particle size and carbon dioxide concentration on chemical conversion in engineered spherical particles undergoing calcium oxide looping are investigated. Particles are thermochemically cycled in a furnace under different carbon dioxide concentrations. Changes in composition due to chemical reactions are measured using thermogravimetric analysis. Gas composition at the furnace exit is evaluated with mass spectroscopy. A numerical model of thermal transport phenomena developed previously is adapted to match the physical system investigated in the present study. The model is used to elucidate effects of reacting medium characteristics on particle temperature and reaction extent. Experimental and numerical results show that (1) an increase in particle size results in a decrease in carbonation extent, and (2) the carbonation step consists of fast and slow reaction regimes. The reaction rates in the fast and slow carbonation regimes increase with increasing carbon dioxide concentration. The effect of carbon dioxide concentration and the distinction between the fast and slow regimes become more pronounced with increasing particle size. 相似文献
5.
Ewa Olewnik-Kruszkowska Magdalena Gierszewska Sylwia Grabska-Zieliska Joanna Skopiska-Winiewska Ewelina Jakubowska 《International journal of molecular sciences》2021,22(7)
Hydrogels based on chitosan are very versatile materials which can be used for tissue engineering as well as in controlled drug delivery systems. One of the methods for obtaining a chitosan-based hydrogel is crosslinking by applying different components. The objective of the present study was to obtain a series of new crosslinked chitosan-based films by means of solvent casting method. Squaric acid—3,4-dihydroxy-3-cyclobutene-1,2-dione—was used as a safe crosslinking agent. The effect of the squaric acid on the structural, mechanical, thermal, and swelling properties of the formed films was determined. It was established that the addition of the squaric acid significantly improved Young’s modulus, tensile strength, and thermal stability of the obtained materials. Moreover, it should be stressed that the samples consisting of chitosan and squaric acid were characterized by a higher swelling than pure chitosan. The detailed characterization proved that squaric acid could be used as a new effective crosslinking agent. 相似文献
6.
Babilas R. Łoński W. Młynarek K. Bajorek A. Radoń A. 《Metallurgical and Materials Transactions A》2020,51(8):4215-4227
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y... 相似文献
7.
8.
9.
10.
Bican Osman Bayça Salih Uğur Kuleyin Hamdi Gümrük Recep 《Metal Science and Heat Treatment》2021,63(3-4):156-162
Metal Science and Heat Treatment - The effect of solid boronizing at 950°C for 2 and 4 h on the phase composition, microstructure, hardness and abrasive wear of steel AISI 304L is studied... 相似文献