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排序方式: 共有359条查询结果,搜索用时 234 毫秒
1.
Condeixa Lucas Dias Silva Pierry Moah Diego Farias Brenda Leiras Adriana 《Central European Journal of Operations Research》2022,30(3):921-940
Central European Journal of Operations Research - Societal awareness and legislation changes concerning sustainability have affected how organizations generate value for stakeholders, as well as... 相似文献
2.
Arthur G. Maki John C. Grecu Brenda Winnewisser Manfred Winnewisser 《Journal of Molecular Spectroscopy》2003,222(2):198-212
High-resolution spectra of 15N12C12C15N and 14N13C13C14N have been measured and analyzed from 200 to 3600 cm−1. All the vibrational levels below 900 cm−1 have been observed and characterized. The Fermi resonance between ν2 and 2ν4 has been studied and the resonance constant has been determined for several cases. Several Σ− states have been directly observed for the first time for each isotopomer, the (0001111)0f, (0011111)0f, and (0002222)0f states. The pattern of the energy levels for clusters of l-type resonance coupled levels, such as 0001131,3, has been determined for cyanogen for the first time. Among other things this involved the determination of the vibrational l-type resonance constant, r45. Many of the power series constants, αi and xij, and higher order constants have been determined. 相似文献
3.
Brenda J. Latka 《Journal of Graph Theory》2003,42(3):165-192
A finite tournament T is tight if the class of finite tournaments omitting T is well‐quasi‐ordered. We show here that a certain tournament N5 on five vertices is tight. This is one of the main steps in an exact classification of the tight tournaments, as explained in [10]; the third and final step is carried out in [11]. The proof involves an encoding of the indecomposable tournaments omitting N5 by a finite alphabet, followed by an application of Kruskal's Tree Theorem. This problem arises in model theory and in computational complexity in a more general form, which remains open: the problem is to give an effective criterion for a finite set {T1,…,Tk} of finite tournaments to be tight in the sense that the class of all finite tournaments omitting each of T1,…,Tk is well‐quasi‐ordered. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 165–192, 2003 相似文献
4.
Ghandi K Addison-Jones B Brodovitch JC McCollum BM McKenzie I Percival PW 《Journal of the American Chemical Society》2003,125(32):9594-9595
Muoniated free radicals have been detected in muon-irradiated aqueous solutions of acetone at high temperatures and pressures. At temperatures below 250 degrees C, the radical product is consistent with muonium addition to the keto form of acetone. However, at higher temperatures, a different radical was detected, which is attributed to muonium addition to the enol form. Muon hyperfine coupling constants have been determined for both radicals over a wide range of temperatures, significantly extending the range of conditions under which these radicals and the keto-enol equilibrium have been studied. 相似文献
5.
M. A. B. Pougnet M. Peisach A. L. Rodgers C. A. Pineda 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(6):441-448
25 human stone samples previously analyzed by inductively coupled plasma atomic emission spectroscopy /ICP-AES/ and the IAEA Animal Bone Standard Reference Material were used to evaluate trace element analysis by PIXE. Bombardment with 4 MeV protons was used for the determination of Mn, Fe, Cu, Pb, Br, Rb, Sr as well as Ca. PIXE and ICP-AES data gave correlation factors better than 0.97 for the elements Ca, Fe, Zn, Sr and Pb. 相似文献
6.
G. Rauret R. Rubio L. Pineda J. F. López Sanchez J. L. Beltran 《Fresenius' Journal of Analytical Chemistry》1991,341(10):631-635
Summary For studying the mechanisms of trace metal mobilization in sediments several strategies have been employed, such as single extraction, sequential extractions, ion exchange, or progressive acidification. Several authors assert that sequential extraction is the best option. In this study two procedures are used in order to assess the mobility of copper and lead in heavily polluted river sediments: sequential extraction using a modified Tessier procedure, and progressive acidification, using an automated method. Six heavily polluted sediment samples are studied by applying the two procedures. The amount of metal released at different pH-values (pH 5 and pH 2) is compared with the resulting distribution when the sequential extraction procedure is applied. The information obtained from the two different approaches is discussed. For both metals a different behaviour is observed when applying each of the two procedures. Thus, copper is more easily released than lead when progressive acidification is followed, whereas an inverse situation is observed when sequential extraction is applied. 相似文献
7.
Guy Guelachvili K. Narahari Rao Richard H. Tipping Brenda P. Winnewisser Manfred Winnewisser 《Mikrochimica acta》1988,95(1-6):339-343
This paper reports the observation of the far infrared absorption spectrum of a single crystal of N2, measured over absorption paths of 4 cm (lengthwise) and 2 cm (across the crystal). The crystal chamber, with quartz windows, was immersed in a flow of cold helium gas. The spectrum from 20 to 120 cm–1 was recorded in the liquid phase, the-phase, and over the full temperature range of the-phase (35.6–2.0 K) with a Fourier transform spectrometer. The spectral resolution, which was not instrument-limited, and the large path allowed the observation of more detailed multiphonon-transition structure in the spectrum of the-phase than has previously been observed. 相似文献
8.
Brenda J. Postnikova 《Tetrahedron letters》2004,45(3):501-504
C3-Symmetric chiral receptors have been developed for enantioselective alkylation of sodium enolates of active methylene compounds. It has been demonstrated that a 1:1 binding complex forms between these receptors and sodium enolates in THF-d8/CD3CN by 1H NMR titration experiments. Moderate enantiomeric enrichment of the benzylation product of 2-acetylcyclohexanone has been demonstrated using this strategy. Templation of enolate alkylation by synthetic receptors represents a new approach to asymmetric induction. 相似文献
9.
Feng Ji Paul W. Percival Jean-Claude Brodovitch Brenda Addison-Jones Stanislaw Wlodek 《Hyperfine Interactions》1994,87(1):853-858
Muonium adds to allyl chloride, CH2=CHCH2Cl, to form two radicals: MuCH2CHCH2Cl (main product) and CH2CHMuCH2Cl (minor product). Both radicals were fully characterized bySR andLCR. In the main product, the LCR lines due to the35Cl and37Cl nuclei were observed. Also, the temperature dependence of various hyperfine coupling constants (hfc) indicates that both Mu and Cl eclipse the unpaired electronp
2-orbital in the minimum energy conformation. For the fragment-CH2Cl, the presence of Mu in the-position is found to affect significantly the hfc of Cl in the-position; an internal rotational barrier of 12 kJ mol–1 was estimated using a simpleV
2 torsional potential. 相似文献
10.
Photoproducts of pyridoxal-5-P, i.e., 4-pyridoxic-5-P and bis-pyridoxal-5-P, have been studied by spectroscopic methods. The spectroscopic properties of bis-pyridoxal-5-P (bis-PLP) resemble those of pyridoxal-5-P (PLP) under similar experimental conditions. The coupling of methylen hydrogens to the phosphorus atom has been shown by NMR spectroscopy. The singlet in the31P-NMR spectra and the triplet in1H-undecoupled experiments confirm the presence of the phosphate group in the 5 position of the structure of the vitamin. The effect of pH and solvent composition on the relative distribution of species of bis-pyridoxine-5-P (bis-PNP) has been investigated by absorption and fluorescence spectroscopy. The acid-base dissociation of the phosphate group is easily detected by emission spectroscopy. Bis-PNP and bis-PLP bind to the enzyme RNase A and they behave as competitive inhibitors with respect to the substrate cytidine-2-3-cyclic phosphate. The natural forms of vitamin B6, pyridoxine, and pyridoxine-5-P have no effect on the catalytic activity of the protein. Experimental evidence derived from fluorescence and inhibition experiments is consistent with the hypothesis that bis-PNP recognizes the catalytic site of RNase A. 相似文献