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601.
S. Chithra B. Jasim C. Anisha Jyothis Mathew E. K. Radhakrishnan 《Applied biochemistry and biotechnology》2014,173(1):30-35
Piper nigrum is very remarkable for its medicinal properties due to the presence of metabolites like piperine. Emerging understanding on the biosynthetic potential of endophytic fungi suggests the possibility to have piperine producing fungi in P. nigrum. In the current study, endophytic fungi isolated from P. nigrum were screened for the presence of piperine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This resulted in the identification of a Mycosphaerella sp. with the ability to produce piperine extracellularly. The biosynthesis of piperine (C17H19NO3) by the endophytic fungal isolate was confirmed by the presence of m/z 286.1 (M + H+) in the LC-MS/MS analysis using positive mode ionization. This was further supported by the presence of specific fragment ions with masses 135, 143, 171 and 201 formed due to the fragmentation of piperine present in the fungal extract. 相似文献
602.
Investigation of chloromethane complexes of cryptophane‐A analogue with butoxy groups using 13C NMR in the solid state and solution along with single crystal X‐ray diffraction
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Emilie Steiner Renny Mathew Iwan Zimmermann Thierry Brotin Mattias Edén Jozef Kowalewski 《Magnetic resonance in chemistry : MRC》2015,53(8):596-602
Host‐guest complexes between cryptophane‐A analogue with butoxy groups (cryptophane‐But) and chloromethanes (chloroform, dichloromethane) were investigated in the solid state by means of magic‐angle spinning 13C NMR spectroscopy. The separated local fields method with 13C‐1H dipolar recoupling was used to determine the residual dipolar coupling for the guest molecules encaged in the host cavity. In the case of chloroform guest, the residual dipolar interaction was estimated to be about 19 kHz, consistent with a strongly restricted mobility of the guest in the cavity, while no residual interaction was observed for encaged dichloromethane. In order to rationalize this unexpected result, we performed single crystal X‐ray diffraction studies, which confirmed that both guest molecules indeed were present inside the cryptophane cavity, with a certain level of disorder. To improve the insight in the dynamics, we performed a 13C NMR spin‐lattice relaxation study for the dichloromethane guest in solution. The system was characterized by chemical exchange, which was slow on the chemical shift time scale but fast with respect to the relaxation rates. Despite these disadvantageous conditions, we demonstrated that the data could be analyzed and that the results were consistent with an isotropic reorientation of dichloromethane within the cryptophane cavity. Copyright © 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd. 相似文献
603.
S. Bürger K. J. Mathew P. Mason U. Narayanan 《Journal of Radioanalytical and Nuclear Chemistry》2009,279(2):659-673
The characterized concentrations of 24 impurity elements in New Brunswick Laboratory (NBL) Certified Reference Material (CRM)
124 were reevaluated. A provisional certificate of analysis was issued in September 1983 based upon the “as prepared” values
(gravimetric mixing). The provisional certificate does not state uncertainties for the characterized values, or estimate the
degree of homogeneity. Since release of the provisional certificate of analysis various laboratories have reported analytical
results for CRM 124. Based upon the reported data a re-evaluation of the characterized values with an estimate of their uncertainties
was performed in this work. An assessment of the degree of homogeneity was included. The overall difference between the re-evaluated
values for the 24 impurity elements and the “as prepared” values from the provisional certificate of analysis is negligible
compared to the uncertainties. Therefore, NBL will establish the “as prepared” values as the certified values and use the
derived uncertainties from this work for the uncertainties of the certified values. The traceability of the “as prepared”
values was established by the gravimetric mixing procedure employed during the preparation of the CRM. NBL further recommends
a minimum sample size of 1 g of the CRM material to ensure homogeneity. Samples should be dried by heating up to 110 °C for
one hour before use. 相似文献
604.
Novel catalysts for dimethyl ether (DME) steam reforming (SR) were designed based on catalysis database on-demand. A catalyst library consisting of precious metals loaded on various metal oxides was tested for DME SR and its elemental reactions of DME hydrolysis and MeOH SR. Platinum loaded on alumina, Pt/Al2O3, shows high activity for DME SR as reported previously. The drawback of the catalyst was also confirmed; the formation of methane leading to the reduction of hydrogen formation. From the fact database for DME hydrolysis and MeOH SR built up with high-throughput experimentation tools, the high activity of Pt/Al2O3 for DME SR is owing to its high activity on DME hydrolysis because its activity on MeOH steam reforming is not remarkable. Based on these facts, novel catalysts were designed and achieved by physical mixing of Pt/Al2O3 which reveals high activity on DME hydrolysis with an active catalyst on MeOH steam reforming. By mixing of Pt/Al2O3 with Pd/Al2O3, methane formation was suppressed without loss of hydrogen production activity. 相似文献
605.
We prove several identities relating three-variable Mahler measures to integrals of inverse trigonometric functions. After deriving closed forms for most of these integrals, we obtain ten explicit formulas for three-variable Mahler measures. Several of these results generalize formulas due to Condon and Lalín. As a corollary, we also obtain three q-series expansions for the dilogarithm. 相似文献
606.
K. M. Mathew S. Ravi T. K. Subramanian 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(3):697-699
Copper activated zinc sulphide phosphor was coated with tritiated polystyrene to give self-sustained light sources. The stability
of the zinc sulphide phosphor coated with polystyrene was studied. It is suggested that the drastic reduction in light output
over a period of two years may be due to the phosphor damage rather than loss of radioactivity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
607.
Control over Electrochemical Water Oxidation Catalysis by Preorganization of Molecular Ruthenium Catalysts in Self‐Assembled Nanospheres
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Dr. Fengshou Yu David Poole III Dr. Simon Mathew Dr. Ning Yan Joeri Hessels Nicole Orth Prof. Ivana Ivanović‐Burmazović Prof. Joost N. H. Reek 《Angewandte Chemie (International ed. in English)》2018,57(35):11247-11251
Oxygen formation through water oxidation catalysis is a key reaction in the context of fuel generation from renewable energies. The number of homogeneous catalysts that catalyze water oxidation at high rate with low overpotential is limited. Ruthenium complexes can be particularly active, especially if they facilitate a dinuclear pathway for oxygen bond formation step. A supramolecular encapsulation strategy is reported that involves preorganization of dilute solutions (10?5 m ) of ruthenium complexes to yield high local catalyst concentrations (up to 0.54 m ). The preorganization strategy enhances the water oxidation rate by two‐orders of magnitude to 125 s?1, as it facilitates the diffusion‐controlled rate‐limiting dinuclear coupling step. Moreover, it modulates reaction rates, enabling comprehensive elucidation of electrocatalytic reaction mechanisms. 相似文献
608.
Highly efficient implementation of pseudospectral time‐dependent density‐functional theory for the calculation of excitation energies of large molecules
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Yixiang Cao Thomas Hughes Dave Giesen Mathew D. Halls Alexander Goldberg Tati Reddy Vadicherla Madhavi Sastry Bhargav Patel Woody Sherman Andrew L. Weisman Richard A. Friesner 《Journal of computational chemistry》2016,37(16):1425-1441
We have developed and implemented pseudospectral time‐dependent density‐functional theory (TDDFT) in the quantum mechanics package Jaguar to calculate restricted singlet and restricted triplet, as well as unrestricted excitation energies with either full linear response (FLR) or the Tamm–Dancoff approximation (TDA) with the pseudospectral length scales, pseudospectral atomic corrections, and pseudospectral multigrid strategy included in the implementations to improve the chemical accuracy and to speed the pseudospectral calculations. The calculations based on pseudospectral time‐dependent density‐functional theory with full linear response (PS‐FLR‐TDDFT) and within the Tamm–Dancoff approximation (PS‐TDA‐TDDFT) for G2 set molecules using B3LYP/6‐31G** show mean and maximum absolute deviations of 0.0015 eV and 0.0081 eV, 0.0007 eV and 0.0064 eV, 0.0004 eV and 0.0022 eV for restricted singlet excitation energies, restricted triplet excitation energies, and unrestricted excitation energies, respectively; compared with the results calculated from the conventional spectral method. The application of PS‐FLR‐TDDFT to OLED molecules and organic dyes, as well as the comparisons for results calculated from PS‐FLR‐TDDFT and best estimations demonstrate that the accuracy of both PS‐FLR‐TDDFT and PS‐TDA‐TDDFT. Calculations for a set of medium‐sized molecules, including Cn fullerenes and nanotubes, using the B3LYP functional and 6‐31G** basis set show PS‐TDA‐TDDFT provides 19‐ to 34‐fold speedups for Cn fullerenes with 450–1470 basis functions, 11‐ to 32‐fold speedups for nanotubes with 660–3180 basis functions, and 9‐ to 16‐fold speedups for organic molecules with 540–1340 basis functions compared to fully analytic calculations without sacrificing chemical accuracy. The calculations on a set of larger molecules, including the antibiotic drug Ramoplanin, the 46‐residue crambin protein, fullerenes up to C540 and nanotubes up to 14×(6,6), using the B3LYP functional and 6‐31G** basis set with up to 8100 basis functions show that PS‐FLR‐TDDFT CPU time scales as N2.05 with the number of basis functions. © 2016 Wiley Periodicals, Inc. 相似文献
609.