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排序方式: 共有321条查询结果,搜索用时 13 毫秒
71.
Björn Alriksson Ilona Sárvári Horváth Anders Sjöde Nils-Olof Nilvebrant Leif J. Jönsson 《Applied biochemistry and biotechnology》2005,124(1-3):911-922
When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates
fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several
nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of
NH4OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH4OH compared favorably with Ca(OH)2, Mg(OH)2, Ba(OH)2, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments.
The NH4OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural.
Under the conditions studied, NH4OH treatments gave better results than Ca(OH)2 treatments. The addition of an extra nitrogen source in the form of NH4Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH4OH treatments at alkaline conditions. The addition of CaCl2 or NH4Cl at pH 5.5 after treatment with NH4OH or Ca(OH)2 resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest
that the highly positive effects of NH4OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation. 相似文献
72.
Tomasz Galica Julia Bkowicz Piotr Broda Ilona Turowska-Tyrk 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(7):593-599
Several conditions need to be fulfilled for a photochemical reaction to proceed in crystals. Some of these conditions, for example, geometrical conditions, depend on the particular type of photochemical reaction, but the rest are common for all reactions. The mutual directionality of two neighbouring molecules determines the kind of product obtained. The influence of temperature on the probability of a photochemical reaction occurring varies for different types of photochemical reaction and different compounds. High pressure imposed on crystals also has a big influence on the free space and the reaction cavity. The wavelength of the applied UV light is another factor which can initiate a reaction and sometimes determine the structure of a product. It is possible, to a certain degree, to control the packing of molecules in stacks by using fluoro substituents on benzene rings. The crystal and molecular structure of 2,6‐difluorocinnamic acid [systematic name: 3‐(2,6‐difluorophenyl)prop‐2‐enoic acid], C9H6F2O2, (I), was determined and analysed in terms of a photochemical [2 + 2] dimerization. The molecules are arranged in stacks along the a axis and the values of the intermolecular geometrical parameters indicate that they may undergo this photochemical reaction. The reaction was carried out in situ and the changes of the unit‐cell parameters during crystal irradiation by a UV beam were monitored. The values of the unit‐cell parameters change in a different manner, viz. cell length a after an initial increase starts to decrease, b after a decrease starts to increase, c increases and the unit‐cell volume V after a certain increase starts to decrease. The structure of a partially reacted crystal, i.e. containing both the reactant and the product, namely 2,6‐difluorocinnamic acid–3,4‐bis(2,6‐difluorophenyl)cyclobutane‐1,2‐dicarboxylic acid (0.858/0.071), 0.858C9H6F2O2·0.071C18H12F4O4, obtained in situ, is also presented. The powder of compound (I) was irradiated with UV light and afterwards crystallized [as 3,4‐bis(2,6‐difluorophenyl)cyclobutane‐1,2‐dicarboxylic acid toluene hemisolvate, C18H12F4O4·0.5C7H8] in a space group different from that of the crystal containing the in‐situ dimer. 相似文献
73.
74.
Dr. Jesse V. Gavette Dr. Matthias Stoop Prof. Nicholas V. Hud Prof. Ramanarayanan Krishnamurthy 《Angewandte Chemie (International ed. in English)》2016,55(42):13204-13209
The RNA world hypothesis posits that DNA and proteins were later inventions of early life, or the chemistry that gave rise to life. Most scenarios put forth for the emergence of DNA assume a clean separation of RNA and DNA polymer, and a smooth transition between RNA and DNA. However, based on the reality of “clutter” and lack of sophisticated separation/discrimination mechanisms in a protobiological (and/or prebiological) world, heterogeneous RNA–DNA backbone containing chimeric sequences could have been common—and have not been fully considered in models transitioning from an RNA world to an RNA–DNA world. Herein we show that there is a significant decrease in Watson–Crick duplex stability of the heterogeneous backbone chimeric duplexes that would impede base‐pair mediated interactions (and functions). These results point to the difficulties for the transition from one homogeneous system (RNA) to another (RNA/DNA) in an RNA world with a heterogeneous mixture of ribo‐ and deoxyribonucleotides and sequences, while suggesting an alternative scenario of prebiological accumulation and co‐evolution of homogeneous systems (RNA and DNA). 相似文献
75.
Natural‐Antioxidant‐Inspired Benzo[b]selenophenes: Synthesis,Redox Properties,and Antiproliferative Activity 下载免费PDF全文
Edgars Paegle Dr. Ilona Domracheva Dr. Baiba Turovska Dr. Marina Petrova Dr. Iveta Kanepe‐Lapsa Anita Gulbe Dr. Edvards Liepinsh Dr. Pavel Arsenyan 《化学:亚洲杂志》2016,11(13):1929-1938
The cyclization of arylalkynes under selenobromination conditions, combined with an acid‐induced 3,2‐aryl shift, was elaborated as a general synthetic pathway for the preparation of polyhydroxy‐2‐ and ‐3‐arylbenzo[b]selenophenes from the same starting materials. The redox properties, free‐radical‐scavenging ability, and cytotoxicity against malignant cell lines (MCF‐7, MDA‐MB‐231, HepG2, and 4T1) of the synthesized compounds were explored, and the obtained results were used to consider the structure–activity relationships (SARs) in these compounds. Consequently, the structural features that were responsible for the highly potent peroxyl‐radical‐scavenging activity were established. 相似文献
76.
Josef Kratochvíla Bedřich Friedecký Marek Budina Ilona Šperlingová 《Accreditation and quality assurance》2007,12(3-4):146-150
In this paper, the creation of a certified reference material for urinary creatinine is described. We used the Jaffe method
and HPLC method for establishment of the certified value. Homogeneity tests are also described. We obtained material with
sufficient homogeneity, stability, and with certified value (expanded uncertainty, k=2 for CI 95%) (7.77±0.27) mmol·L−1. This material was consequently used for the interlaboratory comparison (EQA Czech Republic for clinical chemistry). Twenty-nine
percent of the participants obtained measurement results within the interval of the certified value ± expanded uncertainty,
while 85% of the participants obtained values inside the interval of the certified value ± target measurement uncertainty.
Direct use of the certified reference materials for method evaluation in EQA programs means a significant advance for monitoring
and documentation traceability of results in routine measurements. 相似文献
77.
Juraj ?ernák Janusz Lipkowski Ivan Poto?ňák Alexander Hudák 《Monatshefte für Chemie / Chemical Monthly》2001,40(5):193-202
[Cu(tn)2Ni(CN)4]2ċ4H2O and Cu(tn)2Ni(CN)4 (tn = 1,3-diaminopropane) were prepared and characterized. The hydrate is unstable on air and readily dehydrates to Cu(tn)2Ni(CN)4. Crystal structure analysis of the hydrate at 150 K revealed a novel tetranuclear molecular structure of the tetracyanonickellate. The building elements are two [Cu(tn)2]2+ cations (coordination numbers of Cu: 5 and 6, respectively), two [Ni(CN)4)2− anions, and crystal water. The two cations are linked by one tetracyanonickellate anion via bridging cyano groups placed in cis positions. The second anion is bound weakly (Cu-N = 2.82 ?) via one μ2-bridging cyano ligand. The tetranuclear molecules and pairs of solvate water molecules are linked by strong hydrogen bonds, thus forming infinite planes which are linked in the third dimension by considerably weaker hydrogen bonds. 相似文献
78.
The cosmetics industry is currently looking for innovative ingredients with higher bioactivity and bioavailability for the masses of natural and organic cosmetics. Bioferments are innovative ingredients extracted from natural raw materials by carrying out a fermentation process with appropriate strains of microorganisms. The review was conducted using the SciFinder database with the keywords “fermented plant”, “cosmetics”, and “fermentation”. Mainly bioferments are made from plant-based raw materials. The review covers a wide range of fermented raw materials, from waste materials (whey with beet pulp) to plant oils (F-Shiunko, F-Artemisia, F-Glycyrrhiza). The spectrum of applications for bioferments is broad and includes properties such as skin whitening, antioxidant properties (blackberry, soybean, goji berry), anti-aging (red ginseng, black ginseng, Citrus unshiu peel), hydrating, and anti-allergic (aloe vera, skimmed milk). Fermentation increases the biochemical and physiological activity of the substrate by converting high-molecular compounds into low-molecular structures, making fermented raw materials more compatible compared to unfermented raw materials. 相似文献
79.
The use of smart nanocarriers that can modulate therapeutic release aided by biological cues can prevent undesirable cytotoxicity caused by the premature release of cytotoxic drugs during nanocarrier circulation. In this report, degradable nanocarriers based on pH/reduction dual-responsive nanogels were synthesized to encapsulate doxorubicin hydrochloride (DOX) and specifically boost the release of DOX in conditions characteristic of the cancer microenvironment. Nanogels containing anionic monomer 2-carboxyethyl acrylate (CEA) and N,N′-bis(acryloyl)cystamine (CBA) as a degradable crosslinker have been successfully synthesized via photoinitiated free radical polymerization. The loading process was conducted after polymerization by taking advantage of the electrostatic interaction between the negatively charged nanogels and the positively charged DOX. In this case, a high drug loading capacity (DLC) of up to 27.89% was achieved. The entrapment of DOX into a nanogel network could prevent DOX from aggregating in biological media at DOX concentrations up to ~160 µg/mL. Anionic nanogels had an average hydrodynamic diameter (dH) of around 90 nm with a negative zeta (ζ) potential of around −25 mV, making them suitable for targeting cancer tissue via the enhanced permeation effect. DOX-loaded nanogels formed a stable dispersion in different biological media, including serum-enriched cell media. In the presence of glutathione (GSH) and reduced pH, drug release was enhanced, which proves dual responsivity. An in vitro study using the HCT 116 colon cancer cell line demonstrated the enhanced cytotoxic effect of the NG-CBA/DOX-1 nanogel compared to free DOX. Taken together, pH/reduction dual-responsive nanogels show promise as drug delivery systems for anticancer therapy. 相似文献
80.
Ilona Šperlingová Ludmila Dabrowská Miloň Tichý J. Kučera 《Analytical and bioanalytical chemistry》1998,361(8):756-760
Two batches of a reference material (RM) “total protein in human urine” were prepared for quality assurance in the determination of human urinary proteins. The material was prepared by freeze-drying of a pooled urine sample obtained from healthy volunteers. Protein concentrations in both batches were within physiological values, close to their upper limit. Interlaboratory comparisons conducted in 26 laboratories using the standard operation procedures elaborated for six of the most frequently employed methods (biuret, Bradford, Exton, Lowry, Pesce, and Watanabe) revealed that the results obtained by the individual methods were significantly different due to various reaction mechanisms involved. It was therefore necessary to certify the mean values and their uncertainties individually for each method. These operationally defined certified or information values are valid only when the prescribed standard operation procedures are strictly followed. 相似文献