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排序方式: 共有387条查询结果,搜索用时 15 毫秒
31.
GC–MS Studies of Thiophenes in the Supercritical Fluid CO2 and Solvent Extracts of Tagetes patula L.
Szabolcs Szarka István Gyurján Miklós László Éva Héthelyi Inna N. Kuzovkina Éva Lemberkovics Éva Szőke 《Chromatographia》2010,71(11-12):1039-1047
The intact plant parts and genetically modified hairy root clone #TpA6 of Tagetes patula were extracted with supercritical fluid CO2 extraction (SFE) and a conventional solvent extraction. SFE optimization included the variation of fluid CO2 pressure, dynamic time, and the addition of methanol modifier co-solvent. The four characteristic thiophene metabolites, 5-(3-buten-1-ynyl)-2,2′-bithienyl (BBT), 2,2′:5′,2″-terthiophene (α-T), 5-(4-acetoxy-1-butynyl)-2,2′-bithienyl (BBTOAc), and 5-(3,4-diacetoxy-1-butynyl)-2,2′-bithienyl [BBT(OAc)2], were analysed by GC–MS. The proposed SFE method allowed the selective extraction of thiophenes in 60 min dynamic time with supercritical CO2 without modifier co-solvent, at 30 MPa and 40 °C. The SFE and the reference solvent extraction yielded similar results. The SFE of intact roots and flowers yielded 717 ± 31.3 and 480 ± 26.6 μg g?1 α-T, respectively, while the leaves did not contain considerable amounts of thiophenes. Remarkable amounts of BBT, BBTOAc, and BBT(OAc)2 were characteristic of the SFE of hairy root cultures. 相似文献
32.
Gy?rgy Székely Viktor Farkas László Párkányi Tünde Tóth Miklós Hollósi Péter Huszthy 《Structural chemistry》2010,21(1):277-282
This paper describes the structures of pseudo-18-crown-6 compounds (2, R,R-4 and 5) in the crystals together with theoretical calculations of the electronic circular dichroism (ECD) spectra. The achiral macrocyclic
phosphinic acid 5 forms hydrogen-bonded dimers in the crystal. The O1–O2 distance (2.489 Ǻ) indicates strong H-bondings. The conformations
of the macrorings of the achiral phosphinate 2 and the monomers of the achiral phosphinic acid 5 are chiral. A comparison of the torsion angles of the achiral methyl phosphinate 2 and the monomeric units of achiral 5 indicates a similar geometry. The torsion angles of the chiral methyl phosphinate (R,R)-4 differ more significantly from those in achiral methyl phosphinate 2. A negative 1Bb exciton couplet was observed in the ECD spectrum of monomeric (R,R)-6 in MeOH and H2O as in the spectra of (R,R)-4 in all solvents. To support the idea that (R,R)-4 has basically the same conformation in the crystal and in solution, the ECD spectrum of (R,R)-4 was calculated using the geometry of the molecule in the crystal. The calculated ECD spectrum shows a reasonable agreement
with the ECD spectra obtained in solution. This shows that the steric structure observed in the crystal is predominant in
solution as well. 相似文献
33.
Ákos Kuki Miklós Nagy Lajos Nagy Miklós Zsuga Sándor Kéki 《Journal of the American Society for Mass Spectrometry》2010,21(9):1561-1564
The complex formation in solution, and the gas-phase dissociation of a phenanthrolineterminated poly(ethylene glycol) with
Fe2+ ions were investigated. The size distribution of poly(ethylene glycol)-α-monomethyl-ω-5-[1,10]phenanthroline (mPEG_phen)
was determined by electrospray ionization mass spectrometry (ESI-MS). Based on the measured ligand size distribution of mPEG_phen
by ESI-MS, the 1:3 complex formation (Fe2+/mPEG_Phen) was computer-simulated as a pure random assembly process. The simulated distribution fits excellently to that
of the complex Fe(mPEG_phen)32+ determined from the ESI-MS intensities. In addition, the collision-induced dissociation (CID) of the Fe(mPEG_phen)32+ complex was also studied by tandem mass spectrometry (ESI-MS/MS) and by computer simulation, as well. The ESI-MS/MS intensity
distribution of the Fe(mPEG_phen)22+ formed from Fe(mPEG_phen)32+ by the loss of an mPEG_phen ligand under CID conditions fits quite well to the calculated one. 相似文献
34.
Line-scanning tomographic optical microscopy (LSTOM) requires precise rotation of the scanning line. We demonstrate a method that applies translation-invariant optical elements (polarizer and birefringent plate) to minimize the rotation error. An astigmatic line produced by means of a focused beam through a birefringent plate is used as line illumination. A comparative theoretical and experimental study is presented using an LSTOM system. 相似文献
35.
36.
Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes 下载免费PDF全文
Lajos Nagy Tibor Nagy György Deák Ákos Kuki Borbála Antal Miklós Zsuga Sándor Kéki 《Journal of mass spectrometry : JMS》2015,50(9):1071-1078
Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH4Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH4]+, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]? into a Cl? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH4]+ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
37.
Veronika Takács-Kollár Miklós Nyitrai Dénes Lőrinczy Gábor Hild 《Journal of Thermal Analysis and Calorimetry》2017,127(2):1261-1266
Differential scanning calorimetry was applied to compare the effects of mammalian twinfilin-1 or toxofilin on the thermodynamic properties of actin monomer. Although twinfilin and toxofilin have different structure and actin-binding sites, they similarly increased the thermodynamic stability of monomeric actin. The mammalian twinfilin increased, while the toxofilin did not significantly change the T1/2 value (the width at half-height of the transition peak) during the complex formation between the actin and the monomer binding proteins. In case of toxofilin, the EA value (activation energy) significantly increased compared to twinfilin where the activation energy was nearly insensitive to the complex formation. It seems that toxofilin can achieve its main function as an actin monomer sequestering protein by more effectively and consistently modifying the basic thermodynamic properties of the monomeric actin. 相似文献
38.
This paper presents a matrix-analytic solution for second-order Markov fluid models (also known as Markov-modulated Brownian motion) with level-dependent behavior. A set of thresholds is given that divide the fluid buffer into homogeneous regimes. The generator matrix of the background Markov chain, the fluid rates (drifts) and the variances can be regime dependent. The model allows the mixing of second-order states (with positive variance) and first-order states (with zero variance) and states with zero drift. The behavior at the upper and lower boundary can be reflecting, absorbing, or a combination of them. In every regime, the solution is expressed as a matrix-exponential combination, whose matrix parameters are given by the minimal nonnegative solution of matrix quadratic equations that can be obtained by any of the well-known solution methods available for quasi birth death processes. The probability masses and the initial vectors of the matrix-exponential terms are the solutions of a set of linear equations. However, to have the necessary number of equations, new relations are required for the level boundary behavior, relations that were not needed in first-order level dependent and in homogeneous (non-level-dependent) second-order fluid models. The method presented can solve systems with hundreds of states and hundreds of thresholds without numerical issues. 相似文献
39.
Albrow VE Ponder EL Fasci D Békés M Deu E Salvesen GS Bogyo M 《Chemistry & biology》2011,18(6):722-732
Sentrin specific proteases (SENPs) are responsible for activating and deconjugating SUMO (Small Ubiquitin like MOdifier) from target proteins. It remains difficult to study this posttranslational modification due to the lack of reagents that can be used to block the removal of SUMO from substrates. Here, we describe the identification of small molecule SENP inhibitors and active site probes containing aza-epoxide and acyloxymethyl ketone (AOMK) reactive groups. Both classes of compounds are effective inhibitors of hSENPs 1, 2, 5, and 7 while only the AOMKs efficiently inhibit hSENP6. Unlike previous reported peptide vinyl sulfones, these compounds covalently labeled the active site cysteine of multiple recombinantly expressed SENP proteases and the AOMK probe showed selective labeling of these SENPs when added to complex protein mixtures. The AOMK compound therefore represents promising new reagents to study the process of SUMO deconjugation. 相似文献
40.
Imre Miklós Szilágyi Eero Santala Mikko Heikkilä Marianna Kemell Timur Nikitin Leonid Khriachtchev Markku Räsänen Mikko Ritala Markku Leskelä 《Journal of Thermal Analysis and Calorimetry》2011,105(1):73-81
This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite
fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and
to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C6H9NO)
n
] and ammonium metatungstate [AMT, (NH4)6[H2W12O40]·nH2O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were
characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT
fibers decomposed thermally in air in four steps, and pure monoclinic WO3 nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min−1, 600 °C) were used, the WO3 nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min−1, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min−1, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and
temperature (1 °C min−1, 550 °C) were applied, WO3 nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles)
and crystallinity (monoclinic WO3) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively
removed from the nanofibers and monoclinic WO3 was present in a highly crystalline and ordered form. 相似文献