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21.
MavroudisA. Demertzis SotirisK. Hadjikakou Dimitra Kovala‐Demertzi Aglaia Koutsodimou Maciej Kubicki 《Helvetica chimica acta》2000,83(10):2787-2801
The synthesis and spectral characterization of the novel organotin complexes [SnBu2(ten)] ( 1 ) and [SnBu2(Hten)2] ( 2 ) of the potent and widely used anti‐inflammatory drug tenoxicam (H2ten) are reported. A crystal‐structure determination of 1 showed that, in this complex, the ligand is doubly deprotonated at the hydroxy O‐atom and the amide N‐atom and is coordinated to the SnBu2 fragment via four‐ and six‐membered chelate rings. An extended network of Sn−O−Sn, C−H⋅⋅⋅O and C−H⋅⋅⋅π contacts lead to aggregation and a supramolecular assembly. Potentiometric titrations in nonaqueous solutions support the ionization of the drug by removal of the second H‐atom, the amide H‐atom, in the presence of the diorganotin(IV) fragment. The Ka values of the poorly H2O‐soluble drug tenoxicam were obtained spectrophotometrically in aqueous solutions of constant ionic strength. 相似文献
22.
Marina A. Tzani Dimitra K. Gioftsidou Michael G. Kallitsakis Nikolaos V. Pliatsios Natasa P. Kalogiouri Panagiotis A. Angaridis Ioannis N. Lykakis Michael A. Terzidis 《Molecules (Basel, Switzerland)》2021,26(24)
Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (1O2) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date. 相似文献
23.
24.
Dr. Ignacio Vayá Dr. Johanna Brazard Dr. Miquel Huix‐Rotllant Dr. Arun K. Thazhathveetil Prof. Frederick D. Lewis Dr. Thomas Gustavsson Prof. Dr. Irene Burghardt Dr. Roberto Improta Dr. Dimitra Markovitsi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4904-4914
The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)n. Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)n structures with those reported previously for alternating (GC)n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence. 相似文献
25.
Dimitra Kosta 《Proceedings of the Steklov Institute of Mathematics》2009,264(1):102-109
Let X be a complete intersection of two hypersurfaces F
n
and F
k
in ℙ5 of degree n and k, respectively, with n ≥ k, such that the singularities of X are nodal and F
k
is smooth. We prove that if the threefold X has at most (n + k − 2)(n − 1) − 1 singular points, then it is factorial. 相似文献
26.
The interaction of diphosphonates with calcitic surfaces: understanding the inhibition activity in marble dissolution 总被引:1,自引:0,他引:1
Spanos N Kanellopoulou DG Koutsoukos PG 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2074-2081
The rates of dissolution of calcitic Carrara marble have been reported to be significantly reduced in alkaline pH (pH 8.25) at 25 degrees C in the presence of (1-hydroxyethylidene)-1,1 diphosphonic acid (HEDP). The adsorption takes place at the calcite/water interface at the double layer through the interaction of charged surface species with the charged solution species of the adsorbate. The present work focused on obtaining a better understanding of the interaction of the calcite surface with HEDP. Calculations were performed according to the triple layer model, assuming the formation of surface complexes between the charged surface species of calcite and the species of HEDP dominant at pH 8.25. According to the model, the adsorbed species are located at the inner Helmholtz plane of the electrical double layer. Strong lateral interactions between the adsorbed species were suggested and were corroborated from the calculation of the respective energy, which was equal to 69 kJ mol(-1). The adsorption isotherm was consistent with the proposed model at low surface coverage values, while discrepancies between the values experimentally measured and the predicted were found at higher adsorbate concentrations. The deviations from the predicted values were attributed to the fact that HEDP adsorption on calcite resulted in the formation of multiple layers. The model explained adequately the changes in the zeta-potential values of calcite in the presence of HEDP in the solution which resulted in charge reversal upon adsorption. 相似文献
27.
Yumrutas O Sokmen A Akpulat HA Ozturk N Daferera D Sokmen M Tepe B 《Natural product research》2012,26(19):1848-1851
This study was designed to evaluate the in vitro antioxidant activities of n-hexane (Hex), dichloromethane (DCM), methanol (MeOH) and essential oils (EO) extracts obtained from Salvia euphratica var. euphratica and Salvia euphratica var. leiocalycina and to determine their essential oil and phenolic acid compositions. The samples were screened for their antioxidant activity by using DPPH and β-carotene/linoleic acid assays. Methanol extracts of both varieties exhibited strong antioxidant activities. Our results showed that rosmarinic acid was dominant phenolic acid of MeOH extracts (39.4 and 55.8?μg?mg?1, respectively). The chemical compositions of essential oils of two varieties were analysed and their main components were determined as eucalyptol (18.4%) and trans-pinocarvyl acetate (24.9%), respectively. It can be said that these varieties could be used as natural antioxidant. 相似文献
28.
Dimitra Papadimitriou Efthymios Liarokapis Wolfgang Richter 《Mikrochimica acta》2001,136(3-4):165-169
Strain effects on semiconductor layers were studied by means of optical spectroscopic techniques with a device developed
especially for the study of layered structures and microstructures. Raman, modulated photoreflectance and reflectance anisotropy
spectroscopy (RAS) were applied. Measurements were performed on elemental semiconductors (Si), semiconductor alloys (Si–Ge)
and III–V semiconductor compounds (GaAs). By application of RAS, strains lower than 10−4 could be resolved, which is at least one order of magnitude lower than those observable with Raman and modulated reflectance
techniques. The RAS spectra of layers strained along either the [010] or [011] direction showed a derivative-like structure
at E1-gap energies, which increased linearly and very quickly with increasing strain. The dependence of this spectral feature on
applied strain was used to evaluate strain-dependent effects. This behaviour strongly suggests that RAS can be applied for
the optical characterisation of strain in semiconductor microstructures and devices, with a higher efficiency and accuracy
than that achieved by previously established optical methods such as Raman and modulation spectroscopy. In addition, the compactness
and ease of operation of the instrumentation of RAS provides considerable potential for in situ monitoring/control of semiconductor fabrication conditions. 相似文献
29.
The development of a new type of microsensors based on chemically sensitive field-effect transistors (CHEMFETs) covered with
polymeric bulk ion-partitioning membranes is presented. For the construction of the microsensor, a PVC plasticized membrane
containing two ionophores, one selective to protons and the other to the analyte cation of interest, is placed on the gate
of a pH sensitive field-effect transistor which acts as the transducer. With the use of thin (5–10 μm) ion-partitioning membranes
onto the pH-sensitive ISFET gate, the proton displacement out of the membrane and to the pH sensitive gate is fast and reversible.
This displacement generates a signal that is directly related to the analyte concentration found in the test solution. Comparing
the performance of CHEMFETs and ISEs selective to the monovalent potassium cation and the divalent calcium ion validates this
novel CHEMFET response mechanism. 相似文献
30.
S. M. Angel Dimitra N. Stratis Kristine L. Eland Tianshu Lai Mark A. Berg David M. Gold 《Analytical and bioanalytical chemistry》2001,369(3-4):320-327
Pre-ablation dual-pulse LIBS enhancement data for copper, brass and steel using ns laser excitation are reported. Although
large enhancements are observed for all samples, the magnitude of the enhancement is matrix dependent. Whereas all of the
dual-pulse studies used ns laser excitation we see interesting effects when using ps and fs laser excitation for single-pulse
LIBS. LIBS spectra of copper using 1.3 ps and 140 fs laser pulses show much lower background signals compared to ns pulse
excitation. Also, the atomic emission decays much more rapidly with time. Because of relatively low backgrounds when using
ps and fs pulses, non-gated detection of LIBS is shown to be very effective. The plasma dissipates quickly enough using ps
and fs laser pulses, that high pulse rates, up to 1000 Hz, are effective for increasing the LIBS signal, for a given measurement
time. Finally, a simple near-collinear dual-pulse fiber-optic LIBS probe is shown to be useful for enhanced LIBS measurements.
Received: 1 August 2000 / Revised: 2 November 2000 / Accepted: 8 November 2000 相似文献