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41.
Frederik Detobel Veronika Fekete Wim De Malsche Selm De Bruyne Han Gardeniers Gert Desmet 《Analytical and bioanalytical chemistry》2009,394(2):399-411
The present paper provides a detailed analysis of the analyte-wall adsorption effects in nanochannels, including a random
walk study of the analyte-wall collision frequency, and uses these insights to estimate wall desorption times from chromatographic
experiments in nanochannels. Using coumarin dye analytes and using a methanol/water mixture buffered at pH 3 in 120-nm deep
channels, the surface desorption times on naked fused-silica glass were found to be maximally of the order of 60 to 150 μs,
while they were found to be on the order of 100 to 500 μs on a hydrophobically coated wall. These nonzero adsorption and desorption
times lead to an additional band broadening when conducting chromatographic separations. Shear-driven flows, requiring a noncoated
moving wall and a stationary coated wall, intrinsically turn out to be more prone to this effect than pressure-driven or electro-driven
flows for example. The present study also shows that, interestingly, the number of analyte-wall collisions increases with
the inverse of the channel depth and not with its second power, as would be expected from the Einstein–Smoluchowski relationship
for molecular diffusion. 相似文献
42.
Veronika Gemmer-olos und Rolf Neeb 《Fresenius' Journal of Analytical Chemistry》1987,326(8):766-769
Zusammenfassung Mikrogramm-Mengen von Arsen(III) können nach Ausschütteln mit Benzol aus salzsauren Lösungen mit der differentiellen Pulse-Polarographie bestimmt werden. Die polarographische Bestimmung kann entweder direkt im organischen Extrakt nach Zusatz einer nichtwäßrigen Grundlösung oder nach Verdampfen der organischen Phase über einer wäßrigen Grundlösung durchgeführt werden. Die Bedingungen für die Reduktion des Arsens(V) in schwefelsauren Aufschlußlösungen zum anschließenden Ausschütteln und für die polarographische Bestimmung werden angegeben.
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbandes der Chemie-Fonds der Chemie unterstützt. 相似文献
Differential-pulse-polarographic determination of arsenic after extraction of arsenic(III) chloride
Summary After extraction with benzene from hydrochloric acid solutions microgram amounts of arsenic(III) can be determined by differential-pulse-polarography. The polarographic determination can be performed either in the organic extract after addition of a non-aqueous supporting electrolyte or after evaporation of the organic solvent over a suitable aqueous electrolyte. Conditions for the reduction of arsenic (V) in sulfuric acid decomposition solutions prior to extraction and further polarographic determination are dealt with.
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbandes der Chemie-Fonds der Chemie unterstützt. 相似文献
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Interaction between similarly charged surfaces can be attractive at high electrostatic coupling constants Ξ = l(B)Z(2)/μ(GC), where l(B) is the Bjerrum length, μ(GC) the Gouy-Chapman length, and Z the valency of counterions. While this effect has been studied previously in detail, as a function of surface charge density and valency of the pointlike counterions, much less is known about the effect of counterion size. We apply the Wang-Landau sampling Monte Carlo (MC) simulation method to compute the free energy F as a function of the scaled distance between the plates D?=D/μ(GC) for a range of Ξ and scaled counterion radii R?=R/μ(GC). We find that for large Ξ and small ion radius, there is a global equilibrium distance D?=D?(eq)=2(1+R?), correctly giving the expected value at the point counterion limit. With increasing R? the global minimum in F(D?) changes to a metastable state and finally this minimum vanishes when R? reaches a critical value, which depends on Ξ. We present a state diagram indicating approximate boundaries between these three regimes. The Wang-Landau MC method, as it is applied here, offers a possibility to study a wide spectrum of extended problems, which cannot be treated by the use of contact value theorem. 相似文献
46.
Niculina D. Bogdan Dr. Mihaela Matache Veronika M. Meier Dr. Cristian Dobrotă Dr. Ioana Dumitru Gheorghe D. Roiban Dr. Daniel P. Funeriu Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2170-2180
Herein we describe the design and synthesis of the first series of di‐functional ligands for the directed construction of inorganic‐protein frameworks. The synthesized ligands are composed of a metal‐ion binding moiety (terpyridine‐based) conjugated to an epoxysuccinyl peptide, known to covalently bind active cysteine proteases through the active‐site cysteine. We explore and optimize two different conjugation chemistries between the di‐functionalized metal‐ion ligand and the epoxysuccinyl‐containing peptide moiety: peptide‐bond formation (with limited success) and CuI‐catalysed click chemistry (with good results). Further, the complexation of the synthesized ligands with FeII and NiII ions is investigated: the di‐functional ligands are confirmed to behave similarly to the parent terpyridine. As designed, the peptidic moiety does not interfere with the complexation reaction, in spite of the presence of two triazole rings that result from the click reaction. ES‐MS together with NMR and UV/Vis studies establish the structure, the stoichiometry of the complexation reactions, as well as the conditions under which chemically sensitive peptide‐containing polypyridine ligands can undergo the self‐assembly process. These results establish the versatility of our approach and open the way to the synthesis of di‐functional ligands containing more elaborated polypyridine ligands as well as affinity labels for different enzyme families. As such, this paper is the first step towards the construction of robust supramolecular species that cover a size‐regime and organization level previously unexplored. 相似文献
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48.
Pavel Jandera Jiří Urban Veronika Škeříková Pavel Langmaier Romana Kubíčková Josef Planeta 《Journal of chromatography. A》2010,1217(1):22-33
We prepared hybrid particle-monolithic polymethacrylate columns for micro-HPLC by in situ polymerization in fused silica capillaries pre-packed with 3–5 μm C18 and aminopropyl silica bonded particles, using polymerization mixtures based on laurylmethacrylate–ethylene dimethacrylate (co)polymers for the reversed-phase (RP) mode and [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl) zwitterionic (co)polymers for the hydrophilic interaction (HILIC) mode. The hybrid particle-monolithic columns showed reduced porosity and hold-up volumes, approximately 2–2.5 times lower in comparison to the pure monolithic columns prepared in the whole volume of empty capillaries. The elution volumes of sample compounds are also generally lower in comparison to packed or pure monolithic columns. The efficiency and permeability of the hybrid columns are intermediate in between the properties of the reference pure monolithic and particle-packed columns. The chemistries of the embedded solid particles and of the interparticle monolithic moiety in the hybrid capillary columns contribute to the retention to various degrees, affecting the selectivity of separation. Some hybrid columns provided improved separations of proteins in comparison to the reference particle-packed columns in the reversed-phase mode. Zwitterionic hybrid particle-monolithic columns show dual mode retention HILIC/RP behaviour depending on the composition of the mobile phase and allow separations of polar compounds such as phenolic acids in the HILIC mode at lower concentrations of acetonitrile and, often in shorter analysis time in comparison to particle-packed and full-volume monolithic columns. 相似文献
49.
Simone Göttlich Simon Hoher Patrick Schindler Veronika Schleper Alexander Verl 《Applied Mathematical Modelling》2014
In this paper a model comparison approach based on material flow systems is investigated that is divided into a microscopic and a macroscopic model scale. On the microscopic model scale particles are simulated using a model based on Newton dynamics borrowed from the engineering literature. Phenomenological observations lead to a hyperbolic partial differential equation on the macroscopic model scale. Suitable numerical algorithms are presented and both models are compared numerically and validated against real-data test settings. 相似文献
50.
Boris Remenec Silvia Dulanská Veronika Gardoňová Ľubomír Mátel 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):907-910
This paper describes a rapid method of 94Nb pre-concentration, separation and purification by using cation and anion exchange resins. The method is suitable for analyzing highly contaminated radioactive waste samples in a relatively short time and high decontamination factors. The use and effectiveness of the method was successfully tested by analysis of samples from nuclear reactor parts such as control rod drive shaft, shielding cassettes, neutron in-core measurement channels (KNI), pressure vessel construction material and fuel cassette construction material samples. 相似文献