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排序方式: 共有329条查询结果,搜索用时 21 毫秒
1.
2.
Yuen Cheong Tse Dr. Robert Hein Edward J. Mitchell Zongyao Zhang Prof. Paul D. Beer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(58):14550-14559
Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. 1H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P+. redox couple. 相似文献
3.
H. Hein 《Rheologica Acta》1958,1(2-3):286-289
Zusammenfassung Für den Durchfluß der Seifen durch Rohre wird Blockfließen gefunden, wobei der Axial- und der Radialdruck einander proportional sind. Im Bereich kleiner Normaldrucke ist der Zusammenhang zwischen der Gleitgeschwindigkeit an der Wand und der Wandschubspannung abhängig von der in einer dünnen Gleitschicht erfolgenden Temperaturerhöhung mit einer damit verbundenen Herabsetzung des Gleitwiderstandes. Die Dicke der Schicht konnte berechnet werden. Für höhere Normaldrucke zeigen sich beim Rohrdurchfluß Anomalien in der Form, daß mit kleiner werdender Blendenöffnung, d. h. mit steigendem Anpreßdruck, der Durchflußwiderstand geringer wird. Die Ursache ist die nach Überschreiten des Quellungsdruckes bedingte Ausscheidung der flüssigen Phase aus der Seife, was zur Bildung eines Schmierfilmes mit anderen Reibungseigenschaften führt. Trotzdem konnte ein allgemeines Durchflußwiderstandsgesetz angegeben werden.Eine Formel, die es gestattet, für plastische Stoffe den an einer Blende zu erwartenden Druckverlust im voraus zu berechnen, wurde für Seife ebenfalls bestätigt. 相似文献
4.
The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally altemating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces. rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas. 相似文献
5.
6.
The complexation behavior of Aldrich humic acid (AHA) and a modified humic acid (AHA-PB) with blocked phenolic hydroxyl groups for trivalent lanthanides (Ln) is compared, and their influence on the mobility of Ln(III) in an aquifer is analyzed. As speciation technique, capillary electrophoresis (CE) was hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). For metal loading experiments 25 mg L−1 of AHA and different concentrations (cLn(Eu+Gd) = 100–6000 μg L−1) of Eu(III) and Gd(III) in 10 mM NaClO4 at pH 5 were applied. By CE-ICP-MS, three Ln-fractions, assumed to be uncomplexed, weakly and strongly AHA-complexed metal can be detected. For the used Ln/AHA-ratios conservative complex stability constants log βLnAHA decrease from 6.33 (100 μg L−1 Ln3+) to 4.31 (6000 μg L−1 Ln3+) with growing Ln-content. In order to verify the postulated weaker and stronger humic acid binding sites for trivalent Eu and Gd, a modified AHA with blocked functional groups was used. For these experiments 500 μg L−1 Eu and 25 mg L−1 AHA and AHA-PB in 10 mM NaClO4 at pH-values ranging from 3 to 10 have been applied. With AHA-PB, where 84% of the phenolic OH-groups and 40% of the COOH-groups were blocked, Eu complexation was significantly lower, especially at the strong binding sites. The log β-values decrease from 6.11 (pH 10) to 5.61 at pH 3 (AHA) and for AHA-PB from 6.01 (pH 7) to 3.94 at pH 3. As a potential consequence, particularly humic acids with a high amount of strong binding sites (e.g. phenolic OH- and COOH-groups) can be responsible for a higher metal mobility in the aquifer due to the formation of dissolved negatively charged metal-humate species. 相似文献
7.
Nils Helge Schebb David Falck Helene Faber Eva-Maria Hein Uwe Karst Heiko Hayen 《Journal of chromatography. A》2009,1216(27):5249-5255
A new liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS) method for the fast determination of phospholipase A2 (PLA2) activity has been developed. For the first time, the method allows the parallel detection of glycerophosphatidylcholine (GroPCho) as PLA2 substrate as well as of its products fatty acid (FA) and lyso-GroPCho. ESI-MS was carried out in negative ion mode, detecting the FA as [M − H]− ions and the lyso-GroPCho and GroPCho as acetate adducts [M + Ac]−. Utilizing a fast gradient on a short C5-modified silica gel column with 3 μm particles, five GroPChos, five FAs and six lyso-GroPChos could be separated according to their chain length in less than 3 min. A very high average chromatographic efficiency of 41,200 theoretical plates (plate height 0.5 μm) was achieved for the separation of the GroPChos. The method was applied for monitoring the release of arachidonic acid (20:4 FA) and 1-stearoyl-lyso-sn-GroPCho (18:0 GroPCho) from unilamellar vesicles of 1-stearoyl-2-arachidonoyl-sn-GroPCho (18:0/20:4 GroPCho). With a limit of detection of 0.5 pmol (total amount injected on column) for the FAs and lyso-GroPChos and 1.5 pmol for the GroPChos as well as a linear range of 1.5 decades, the method has proven to be suitable for the monitoring of different secretory PLA2 (sPLA2) conversions. Furthermore, it was applied to screen a small library of PLA2 inhibitors for their activity towards sPLA2 type V and snake venom of Bothrops moojeni. In both cases, active samples could be directly identified. With its short analysis time, its high chromatographic efficiency and the parallel detection of substrate and all products, the developed LC–ESI-MS method is well suited for the analysis of PLA2 activity. 相似文献
8.
A proficient etiquette for the stereoselective synthesis of novel 3-methylthio-β-lactams and their Lewis acid mediated functionalization is described. Treatment of 2-methylthioethanoic acid and appropriate imines in the Staudinger reaction leads to the stereocontrolled synthesis of novel trans-3-methylthio-β-lactams in excellent yields. cis-3-Chloro-3-methylthio-β-lactams, obtained from stereoselective chlorination of trans-3-methylthio-β-lactams using N-chlorosuccinimide (NCS) and AIBN, were subjected to Lewis acid (TiCl4 or SnCl4) mediated functionalization using various active aromatic, heterocyclic and aliphatic compounds (nucleophiles). This reaction provides an easy access to novel, stereoselective cis-3-monosubstituted-3-methylthio-β-lactams, which further undergo smooth desulfurization with Raney-nickel to afford C-3 cis- and trans-monosubstituted-β-lactams. The cis or trans configuration of the hydrogen/chloro/nucleophile substituent at C-3 was assigned with respect to C4–H. 相似文献
9.
Anno Hein Ioannis Karatasios Dionysis Mourelatos 《Analytical and bioanalytical chemistry》2009,395(7):2061-2071
The present case study concerns the technology of Byzantine wall paintings from the Mani Peninsula, Greece. An assemblage
of 12 Byzantine churches, constructed in the tenth to fifteenth century, was included in an initial analytical survey. Two
random samples of wall paintings were taken in each monument in order to study their micro stratigraphy and the composition
of pigment and plaster layers. Polished sections were fabricated for examination with optical microscopy and scanning electron
microscopy (SEM). Furthermore, selected samples were powdered and analysed with Fourier-transformed infrared spectroscopy
(FTIR) and X-ray diffraction (XRD). The analytical results achieved in this case study provided general conclusions concerning
painting techniques for wall paintings in a rather provincial area of the Byzantine Empire. The palette comprised mainly earthen
pigments like ochres and carbon black but occasionally also other pigments like cinnabar, minium and ultramarine. In view
of future studies, a portable X-ray fluorescence analysis (XRF) set-up was tested. 相似文献
10.
Jennifer E. Mihalick William P. Griffiths III James E. Muten Travis A. Olson John B. Hein 《Journal of solution chemistry》1999,28(8):1019-1030
Solution calorimetry was used to determine enthalpies and stability constants for binding of lead(II) or cadmium(II) by galacturonic acid and several monosaccharides in aqueous solution. New values for enthalpies of solution in water are reported for galacturonic acid and maltose monohydrate. The interaction of water solvent with the reactants is the largest factor in the binding process. 相似文献