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61.
Antioxidant activity assays on-line with liquid chromatography 总被引:3,自引:0,他引:3
Niederländer HA van Beek TA Bartasiute A Koleva II 《Journal of chromatography. A》2008,1210(2):121-134
Screening for antioxidants requires simple in vitro model systems to investigate antioxidant activity. High resolution screening (HRS), combining a separation technique like HPLC with fast post-column (bio)chemical detection can rapidly pinpoint active compounds in complex mixtures. In this paper both electrochemical and chemistry-based assays are reviewed and discussed. The focus is on the mechanisms involved and differences between the assays, rather than on the matrix or analytes. With 45 applications high resolution antioxidant screening has now become an almost routine tool for the rapid identification of antioxidants in plant extracts, foods and beverages. The methods based on true reactive oxygen species (ROS) provide the most realistic measure of antioxidant activity. Unfortunately these methods are difficult to set up and control and have not been applied since they were reported. The methods based on electrochemical detection are more practical, but have still received only limited attention for practical screening purposes. The methods based on a single relatively stable reagent such as DPPH and ABTS(+) have become most popular, because of their simple set-up and ease of control. The methods have been combined with on-line DAD, MS and NMR detection for rapid identification of active constituents. 相似文献
62.
Raleigh W. Parrott II Christopher G. Hamaker Shawn R. Hitchcock 《Journal of heterocyclic chemistry》2008,45(3):873-878
63.
B. B. Koleva R. D. Nikolova S. Zareva T. Kolev A. G. Bojilova H. Mayer-Figge W. S. Sheldrick 《Structural chemistry》2008,19(6):975-982
IR-spectroscopic characterization of the coumarin-3-phosphonic acid and 1,2-benzoxaphosphorine-3-carboxylic acid ethyl esters has been carried out by means of linear-polarized IR (IR-LD) spectroscopy of oriented colloid suspensions in a nematic host. Quantum chemical DFT calculations at the B3LYP level of theory and 6-311++G** basis set were performed. The electronic structure and vibrational properties of both compounds are discussed. The spectroscopic data for 2-benzoxaphosphorine-3-carboxylic acid ethyl ester are in accordance with the crystal structure determined by single crystal X-ray diffraction. The compound C13H15O5P crystallizes in the noncentrosymmetric space group P212121, and its structure consists of a 3D network formed by short contacts of the type P=O···HC(Ar) with distances of 3.420 and 2.467 Å. The geometry of the PO3C fragment exhibits a pseudo T d symmetry. 相似文献
64.
Crystal structure and spectroscopic properties of ammonium hydrogensquarate squaric acid monohydrate
Tsonko Kolev Rüdiger W. Seidel Bojidarka B. Koleva Michael Spiteller Heike Mayer-Figge William S. Sheldrick 《Structural chemistry》2008,19(1):101-107
The structure of ammonium hydrogensquarate squaric acid monohydrate has been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group C2/c and exhibits a 3D network with molecules linked by intermolecular interactions with participation of the H2Sq, HSq?, NH4 +, and H2O species. The HSq? anion and the neutral H2Sq form a strong head-to-tail dimer through O–H···O hydrogen bonding with lengths of 2.587 and 2.494 Å (protected space between numeral and unit). The layers are connected by ammonium cations and water molecules in a plane through the O···N (2.950, 2.978, 3.036 Å) and O···O (2.953, 2.781 Å) bonds. Another such layer is connected to the NH4 + cation in the adjacent plane through bifurcated N–H···O hydrogen-bonding to form a double layer (NH···O bond lengths are 3.036, 2.978, 2.857, 2.909, 2.958, and 2.742 Å, respectively). The IR-band assignment of the compound was achieved using the polarized IR-spectroscopy of oriented colloids in a nematic host. Theoretical ab initio calculations were performed and achieved with a view to explain the IR-bands of the H2Sq.HSq? motif. 相似文献
65.
Bojidarka B. Koleva Tsonko Kolev Marc Lamshöft Michael Spiteller 《Transition Metal Chemistry》2008,33(7):911-919
The coordination behaviour of the tripeptide glycyl-l-phenylalanyl-glycine (H-Gly-Phe-Gly-OH) with Au(III), Pd(II), and Pt(II) in both solution and in the solid state has been
investigated experimentally. In addition, quantum chemical calculations have been carried out with a view to obtain the structures
and spectroscopic properties of the ligand and its complexes. Both in solution and in the solid state the tripeptide interacts
in a tetradentate manner with the Au(III) and Pd(II) ions through the NH2, two deprotonated amide N atoms and the COO−group, forming [Au(H-Gly-Phe-Gly-OH)H−2)] × H2O and [Pd(H-Gly-l-Phe-Gly-OH)H−2)]Na × H2O complexes. The MN3O chromophores are calculated to be near planar. Interaction with cisplatin leads to the formation of a mononuclear complex
with tridentate coordination of the ligand by NH2 and two N- atoms from the deprotonated amide groups ([Pt(H-Gly-l-Phe-Gly-OH)H−2)NH3] × 2H2O). The fourth coordination position of the Pt(II) is occupied by an NH3 ligand. The PtN4 chromophore is flat with a deviation from planarity of 0.3°.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
66.
Tesia V. Chciuk William R. Anderson Jr. Prof. Robert A. Flowers II 《Angewandte Chemie (International ed. in English)》2016,55(20):6033-6036
The relationship between proton‐donor affinity for SmII ions and the reduction of two substrates (anthracene and benzyl chloride) was examined. A combination of spectroscopic, thermochemical, and kinetic studies show that only those proton donors that coordinate or chelate strongly to SmII promote anthracene reduction through a PCET process. These studies demonstrate that the combination of SmII ions and water does not provide a unique reagent system for formal hydrogen atom transfer to substrates. 相似文献
67.
Pictet–Spengler Synthesis of Quinoline‐Fused Porphyrins and Phenanthroline‐Fused Diporphyrins
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Dr. Ke Gao Norihito Fukui Seok II Jung Prof. Dr. Hideki Yorimitsu Prof. Dr. Dongho Kim Prof. Dr. Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2016,55(42):13038-13042
Doubly and quadruply quinoline‐fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki–Miyaura coupling of β‐borylated porphyrins with 2‐iodoaniline and subsequent Pictet–Spengler cyclization. These quinoline‐fused porphyrins display red‐shifted absorption bands and higher electron‐accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline‐fused porphyrin dimers, which bound either a NiII or ZnII cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins. 相似文献
68.
Kolev T Koleva BB Spiteller M Mayer-Figge H Sheldrick WS 《The journal of physical chemistry. A》2007,111(40):10084-10089
2-amino-4-nitroaniline crystallizes in a noncentrosymmetric space group, which gives it significant potential for second-order nonlinear optical properties (NLO) in the bulk. Crystallographic and linear-polarized IR-spectrocopic data in the solid state unambiguously confirm a quinoide-like structure in the ground state in contrast to UV and theoretical data, which indicate an aromatic one for the excited state. UV-vis spectral elucidations in solutions with different polarities indicate a significant charge-transfer band with shifts of up to 100 nm, corresponding to a large value for the molecular first hyperpolarizability. Calculations of the UV- and IR-spectroscopic properties confirm the stabilization of the quinoide-like structure in the ground state, as well as the theoretically predicted NLO properties at the molecular level and provide a value of beta(tot), which is some 3.6 times higher than the analogous parameter for p-nitroaniline, a classical compound with experimentally confirmed NLO properties. 相似文献
69.
Koleva BB Kolev TM Spiteller M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(5):1187-1196
L-Tyrosine-containing dipeptides valyl-tyrosine (H-Val-Tyr-OH) and tyrosyl-alanine (H-Tyr-Ala-OH) are characterized structurally by means of quantum chemical ab initio calculations and solid-state linear-dichroic infrared (IR-LD) spectroscopy. The IR-characteristic bands are assigned by application of reducing-difference procedure for polarized IR-spectra interpretation. Infrared data obtained are supported as well by the made vibrational analysis. The structures of both peptides are predicted on the basis of conformational analysis and structural information, obtained by the shown IR-spectroscopic tool. 相似文献
70.
We present EQCM study for the electrochemical behavior of various 1-methyl-1'-alkylvilogen (C1CnV:n=1, 7-10, 12, 14,16, 18). In some viologens, we discussed the mechanism of CD-induced comproportionation reaction as well as electrodeposition pathway based on the EQCM and the spectroelectrochemical experimental results. 相似文献