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101.
In this paper, we construct an invariant metric in the space of homogeneous polynomials of a given degree (≥3). The homogeneous
polynomials specify a nonlinear symplectic map which in turn represents a Hamiltonian system. By minimizing the norm constructed
out of this metric as a function of system parameters, we demonstrate that the performance of a nonlinear Hamiltonian system
is enhanced. 相似文献
102.
Thermal rearrangement of diethylamino-5-(m-methoxyphenoxy)-pent-2-yne (3) gives 1-(m-methexyphenoxy)-pent-3,4-diene (14) in about 8% yield. Hydration of the latter yields 1-(m-methoxyphenoxy)-pentan-4-one (6), which has been synthesised by an unambiguous route. A mechanism of formation of the allene (14) from the amine (3) has been suggested. 相似文献
103.
The question whether the human cardiac system is chaotic or not has been an open one. Recent results in chaos theory have shown that the usual methods, such as saturation of correlation dimension D(2) or the existence of positive Lyapunov exponent, alone do not provide sufficient evidence to confirm the presence of deterministic chaos in an experimental system. The results of surrogate data analysis together with the short-term prediction analysis can be used to check whether a given time series is consistent with the hypothesis of deterministic chaos. In this work nonlinear dynamical tools such as surrogate data analysis, short-term prediction, saturation of D(2) and positive Lyapunov exponent have been applied to measured ECG data for several normal and pathological cases. The pathology presently studied are PVC (Premature Ventricular Contraction), VTA (Ventricular Tachy Arrhythmia), AV (Atrio-Ventricular) block and VF (Ventricular Fibrillation). While these results do not prove that ECG time series is definitely chaotic, they are found to be consistent with the hypothesis of chaotic dynamics. (c) 1998 American Institute of Physics. 相似文献
104.
Kannan Govindan Martin Brandt Jepsen 《The Journal of the Operational Research Society》2016,67(2):339-376
Many companies today have embraced the concept of risk management, usually in the form of enterprise risk management or supply chain risk management. Both are based on a holistic view of risks. Hence, risks related to specific functions within a company must be considered more broadly than previously. Risks, however, involve uncertainty, and the less specific the context in which risks are viewed, the more uncertainty will be involved. One particular way to express uncertainty is through trapezoidal intuitionistic fuzzy numbers (TrIFNs). In this paper, risks that are relevant for supplier risk assessments are first collected from the literature. Then it is illustrated how the multi-criteria decision analysis method ELECTRE TRI-C can be used for sorting suppliers into risk categories, when the risks as well as some of the method’s parameters are expressed with TrIFNs. In order to do this, we make use of a small modification of an existing method for converting TrIFNs into crisp values. The approach is illustrated in a case problem based on a company that is looking for service providers (suppliers) of electrical maintenance. The problem involves 20 suppliers that are sorted into three risk categories based on evaluations from 27 criteria. Results from the case study point to two low risk suppliers. A further ad-hoc analysis suggests one of these to be less risky than the other. 相似文献
105.
106.
Thamarath SS Bode BE Prakash S Sai Sankar Gupta KB Alia A Jeschke G Matysik J 《Journal of the American Chemical Society》2012,134(13):5921-5930
Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80,000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch. 相似文献
107.
Mo Y Subramanian G Gao J Ferguson DM 《Journal of the American Chemical Society》2002,124(17):4832-4837
The nature and strength of the cation-pi interaction in protein-ligand binding are modeled by considering a series of nonbonded complexes involving N-substituted piperidines and substituted monocylic aromatics that mimic the delta-opioid receptor-ligand binding. High-level ab initio quantum mechanical calculations confirm the importance of such cation-pi interactions, whose intermolecular interaction energy ranges from -6 to -12 kcal/mol. A better understanding of the electrostatics, polarization, and other intermolecular interactions is obtained by appropriately decomposing the total interaction energy into their individual components. The energy decomposition analysis is also useful for parametrizing existing molecular mechanics force fields that could then account for energetic contributions arising out of cation-pi interactions in biomolecules. The present results further provide a framework for interpreting experimental results from point mutation reported for the delta-opioid receptor. 相似文献
108.
Preeti Chauhan Kavya Gupta Govindan Ravikumar Deepak K. Saini Harinath Chakrapani 《化学:亚洲杂志》2019,14(24):4717-4724
The emergence of hydrogen sulfide (H2S) as an important signalling molecule in redox biology with therapeutic potential has triggered interest in generating this molecule within cells. One strategy that has been proposed is to use carbonyl sulfide (COS) as a surrogate for hydrogen sulfide. Small molecules that generate COS have been shown to produce hydrogen sulfide in the presence of carbonic anhydrase, a widely prevalent enzyme. However, other studies have indicated that COS may have biological effects which are distinct from H2S. Thus, it would be useful to develop tools to compare (and contrast) effects of COS and H2S. Here we report enzyme‐activated COS donors that are capable of inducing protein persulfidation, which is symptomatic of generation of hydrogen sulfide. The COS donors are also capable of mitigating stress induced by elevated reactive oxygen species. Together, our data suggests that the effects of COS parallel that of hydrogen sulfide, laying the foundation for further development of these donors as possible therapeutic agents. 相似文献
109.
Rubin Dasgupta Dr. Karthick B. S. S. Gupta Prof. Dr. Huub J. M. de Groot Prof. Dr. Marcellus Ubbink 《Chemphyschem》2021,22(8):733-740
The enzyme laccase catalyzes the reduction of dioxygen to water at the trinuclear copper center (TNC). The TNC comprises a type-3 (T3) and a type-2 (T2) copper site. The paramagnetic NMR spectrum of the small laccase from Streptomyces coelicolor (SLAC) without the substrate shows a mixture of two catalytic states, the resting oxidized (RO) state and the native intermediate (NI) state. An analysis of the resonances of the RO state is reported. In this state, hydrogen resonances only of the T3 copper ligands can be found, in the region of 12–22 ppm. Signals from all six histidine ligands are found and can be attributed to Hδ1, Hβ or backbone amide HN nuclei. Two sequence-specific assignments are proposed on the basis of a second-coordination shell variant that also lacks the copper ion at the T1 site, SLAC−T1D/Q291E. This double mutant is found to be exclusively in the RO state, revealing a subtle balance between the RO and the NI states. 相似文献
110.
P. Govindan A. Palamalai K. S. Vijayan S. Subbuthai S. Murugesan S. V. Mohan R. V. Subba Rao 《Journal of Radioanalytical and Nuclear Chemistry》2002,254(1):65-70
Ammonium uranyl carbonate (AUC) precipitation is developed for the conversion of uranyl nitrate to oxide in the uranium reconversion step of reprocessing of irradiated fuel by the addition of ammonium carbonate salt. Different precipitation conditions of AUC are studied. The solubility of AUC as a function of uranium concentration in the feed at different temperatures using ammonium carbonate salt as precipitant is studied. This study indicates that 95-99.8% of uranium is recovered as AUC by precipitating 5-125 g/l of uranium with loss of uranium (250-10 ppm) in the filtrate by adding ammonium carbonate salt. It is also observed that the solubility of AUC increased as the concentration of uranium decreased. Thermal decomposition is carried out by thermogravimetry/differential thermal analysis (TG/DTA) and evolved gas analysis-mass spectrometry (EGA-MS) to find out AUC decomposition and gases evolved during decomposition. Studies are also carried out to characterize AUC by using X-ray diffraction (XRD). The data show that AUC obtained by the above conditions is very much consistent with published information. 相似文献