全文获取类型
收费全文 | 1270篇 |
免费 | 141篇 |
国内免费 | 19篇 |
学科分类
工业技术 | 1430篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 51篇 |
2021年 | 67篇 |
2020年 | 55篇 |
2019年 | 49篇 |
2018年 | 48篇 |
2017年 | 57篇 |
2016年 | 72篇 |
2015年 | 71篇 |
2014年 | 64篇 |
2013年 | 115篇 |
2012年 | 97篇 |
2011年 | 95篇 |
2010年 | 61篇 |
2009年 | 55篇 |
2008年 | 55篇 |
2007年 | 53篇 |
2006年 | 50篇 |
2005年 | 47篇 |
2004年 | 29篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 21篇 |
1997年 | 15篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1430条查询结果,搜索用时 250 毫秒
31.
32.
Dr. Aline Telzerow Dr. Juraj Paris Dr. Maria Håkansson Dr. Javier González-Sabín Dr. Nicolas Ríos-Lombardía Prof. Dr. Harald Gröger Dr. Francisco Morís Dr. Martin Schürmann Prof. Dr. Helmut Schwab Dr. Kerstin Steiner 《Chembiochem : a European journal of chemical biology》2021,22(7):1232-1242
Amine transaminases (ATAs) are used to synthesize enantiomerically pure amines, which are building blocks for pharmaceuticals and agrochemicals. R-selective ATAs belong to the fold type IV PLP-dependent enzymes, and different sequence-, structure- and substrate scope-based features have been identified in the past decade. However, our knowledge is still restricted due to the limited number of characterized (R)-ATAs, with additional bias towards fungal origin. We aimed to expand the toolbox of (R)-ATAs and contribute to the understanding of this enzyme subfamily. We identified and characterized four new (R)-ATAs. The ATA from Exophiala sideris contains a motif characteristic for d -ATAs, which was previously believed to be a disqualifying factor for (R)-ATA activity. The crystal structure of the ATA from Shinella is the first from a Gram-negative bacterium. The ATAs from Pseudonocardia acaciae and Tetrasphaera japonica are the first characterized (R)-ATAs with a shortened/missing N-terminal helix. The active-site charges vary significantly between the new and known ATAs, correlating with their diverging substrate scope. 相似文献
33.
Continuous removal and recovery of palladium in an upflow anaerobic granular sludge bed (UASB) reactor 下载免费PDF全文
34.
《Food Control》2014,35(2):274-282
A survey was carried out on a thousand wines from organic viticulture from different European countries. Analytical data were collected about the most used quality control parameters (e.g. alcoholic strength, reducing sugars, total acidity and pH, volatile acidity, malic and lactic acid, free and total sulfur dioxide), as well as regarding some compounds harmful for human health, such as ochratoxin A and biogenic amines. The results collected on quality control parameters were generally in agreement with the values normally detectable for conventional wines. Total sulfur dioxide was lower than 110–120 mg/L in the most of the samples and no significant correlation was found between sulfite levels and other parameters. Ochratoxin A (OTA) seemed not a generalized problem for organic wine productions: its concentration was below the European legal limit, in the 95% of the samples analyzed; nevertheless, the risk of OTA pollution seemed higher in certain southern European regions. On the other hand, biogenic amines (BA) appeared a serious problem for organic winemaking and high concentrations were found in many of the analyzed wines. They seemed connected with a bad management of malolactic fermentation, being generally associated with high pHs and volatile acidities. 相似文献
35.
With the increased awareness of avoiding residue metals, the field of organocatalysts is attracting more attention. Aliphatic tertiary amines, such as triethylamine (TEA), N, N, N, N‐tetramethylethylenediamine (TMEDA) and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDTA), have low boiling points which allow their easy elimination after a chemical reaction. Here, we used these aliphatic tertiary amines to catalyze ring‐opening polymerizations (ROPs) of trimethylene carbonate (TMC). In the presence of benzyl alcohol, the catalytic activities of the tertiary amines were in the order of TEA < TMEDA < PMDTA. Correlation between the molecular weight of polycarbonates and monomer conversions was linear, suggesting the polymerization was controlled. The polymerization pathway was presumed to follow an alcohol‐activated mechanism according to the end‐group fidelity determined using 1H NMR spectroscopy. The ROP of TMC was also successfully initiated by PEO99‐PPO65‐PEO99 (F127) under the catalysis of the tertiary amines, producing well‐defined PTMCn‐F127‐PTMCn copolymers with narrow dispersity ( ca 1.2) and with thermosensitive properties in aqueous solution. Furthermore, copolymerizations of TMC with acryloyl‐containing cyclic carbonate were catalyzed by the tertiary amines in the presence of F127. No crosslinking reactions were detected. Our results demonstrate that the aliphatic tertiary amines have the potential to catalyze TMC homo‐ or copolymerization featuring controllable structure and composition under mild conditions. Copyright © 2012 Society of Chemical Industry 相似文献
36.
37.
38.
Coastal parts of Croatia are dominated by the SW‐verging Dinaric foldbelt, to the west and SW of which is the Adriatic Basin (the stable foreland). In both areas, the stratigraphic column is dominated by a thick carbonate succession ranging from Carboniferous to Miocene. Four megasequences have been identified: (i) a pre‐platform succession ranging in age from Late Carboniferous (Middle Pennsylvanian: Moscovian) to Early Jurassic (Early Toarcian; Bru?ane and Ba?ke Ostarije Formations); (ii) an Early Jurassic to Late Cretaceous platform megasequence (Mali Alan Formation); (iii) a Paleogene to Neogene post‐platform megasequence (Ra?a Formation); and (iv) a Neogene to Quaternary (Pliocene to Holocene) megasequence (Istra and Ivana Formations). A number of organic‐rich intervals with source rock potential have been identified on‐ and offshore Croatia: Middle and Upper Carboniferous, Upper Permian, Lower and Middle Triassic, Lower and Upper Jurassic, Lower and Upper Cretaceous, Eocene, and Pliocene – Pleistocene. Traps and potential plays have been identified from seismic data in the Dinaric belt and adjacent foreland. Evaporites of Permian, Triassic and Neogene (Messinian) ages form potential regional seals, and carbonates with secondary porosity form potential reservoirs. Oil and gas shows in wells in the Croatian part of the Adriatic Basin have been recorded but no oil accumulations of commercial value have yet been discovered. In the northern Adriatic offshore Croatia, Pliocene hemi‐pelagic marlstones and shales include source rocks which produce commercial volumes of biogenic gas. The gas is reservoired in unconsolidated sands of the Pleistocene Ivana Formation. 相似文献
39.
Mustafa Esen Marti 《分离科学与技术》2016,51(11):1806-1816
Combined use of inert diluents with polar modifiers enables former to be utilized for the recovery of polar value-added chemicals. The results show that polarities of both solvent and modifier are critical for efficient separations. Thus, KD values with 1-octanol were higher than those with 1-decanol; however, those with xylene were superior to those with hexane and toluene. Increasing the amine concentrations increased the KD values, in contrast to the trends with pH and temperature. About 33%, 79% and 67% of acetic acid was recovered using 25% (v/v) Alamine 336 in xylene, 1-octanol and 30% 1-octanol-modified xylene, respectively. Therefore, solvent modification positively affects the extraction power of inert diluents for acetic acid recovery. 相似文献
40.
Matthias F. Groh Alexander Wolff Matthias A. Grasser Michael Ruck 《International journal of molecular sciences》2016,17(9)
Ionic liquids (ILs) have been proven to be valuable reaction media for the synthesis of inorganic materials among an abundance of other applications in different fields of chemistry. Up to now, the syntheses have remained mostly “black boxes”; and researchers have to resort to trial-and-error in order to establish a new synthetic route to a specific compound. This review comprises decisive reaction parameters and techniques for the directed synthesis of polyions of heavy main-group elements (fourth period and beyond) in ILs. Several families of compounds are presented ranging from polyhalides over carbonyl complexes and selenidostannates to homo and heteropolycations. 相似文献