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51.
Loline alkaloids exhibit a strained ether-bridged pyrrolizidine skeleton and possess insecticidal and insect antifeedant properties. The synthesis of acetylnorloline, a prototypical member of the alkaloid family, is described. Central to the route is a stereoselective tethered aminohydroxylation (TA) of a homoallylic carbamate. Allylic (A1,3) strain is exploited to enforce diastereofacial selectivity during the aminohydroxylation. 相似文献
52.
Trost BM Breder A O'Keefe BM Rao M Franz AW 《Journal of the American Chemical Society》2011,133(13):4766-4769
An atom-economical method for the direct synthesis of [3.1.0]- and [4.1.0]-bicyclic frameworks via Ru-catalyzed redox bicycloisomerization of enynols is reported. The presented results highlight the unique reactivity profile of propargyl alcohols, which function as β-oxocarbene precursors, in the presence of a ruthenium(II) complex. Furthermore, a rare case of a formal vinylic C-H insertion reaction is described. 相似文献
53.
Yogendra Kumar Sanjay Kumar Saxena Meera Venkatesh Ashutosh Dash 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):109-114
This article presents the development, the testing and the efficiency estimation of a system for the monitoring of the atmospheric
concentration of radon using a detector ionization chamber type in pulse mode for environmental measurements in which the
measurement of the average value of the ionization current is completed with the recording of the impulses of the ionization
current caused by the alpha disintegrations from the sensible volume of the detector. 相似文献
54.
Meera KM Sankar RM Jaisankar SN Mandal AB 《Colloids and surfaces. B, Biointerfaces》2011,86(2):292-297
In this paper, we report the preparation and characterization of mesoporous and biocompatible transparent silica aerogel by the sol-gel polymerization of tetraethyl orthosilicate using ionic liquid. Choline cation based ionic liquid allows the silica framework to form in a non collapsing environment and controls the pore size of the gel. FT-IR spectra reveal the interaction of ionic liquid with surface -OH of the gel. DSC thermogram giving the evidence of confinement of ionic liquid within the silica matrix, which helps to avoid the shrinkage of the gel during the aging process. Nitrogen sorption measurements of gel prepared with ionic liquid exhibit a low surface area of 100.53 m2/g and high average pore size of 3.74 nm. MTT assay proves the biocompatibility and cell viability of the prepared gels. This new nanoporous silica material can be applied to immobilize biological molecules, which may retain their stability over a longer period. 相似文献
55.
C. R. Jejurkar Jayrang S. Dave Pratik R. Patel Meera R. Menon 《Molecular Crystals and Liquid Crystals》2013,570(1):753-758
Abstract Four macrocyclic liquid crystalline ligands derived from 1,8 dihydroxy ethyl 1,3,6,8,10,13 hexa aza cyclotetradecane(DHAT) and trans-4-n-alkoxy cinnamoyl chloride have been synthesised and their metal complexes using Cu(II),Ni(II),Pb(II), V(V) and U(VI) metal ions have been isolated. The ligands and their metal complexes were characterised by elemental analysis, FTIR,NMR,X-Ray and DSC studies. Polarising microscope was used to identify mesomorphic textures of the ligands and the complexes. The transition temperature and mesophase textures of the ligands and complexes have been compared. The effect of presence of different metal ions on mesomorphic properties has been discussed. 相似文献
56.
The dielectric response in a magnetic field is routinely used to probe the existence of coupled magnetic and elastic order in the multiferroics. However, here we demonstrate that magnetism is not necessary to produce a magnetocapacitance when the material is inhomogeneous. By considering a two-dimensional, two-component composite medium, we find a characteristic dielectric resonance that depends on magnetic field. We propose this as a possible signature of inhomogeneities and we argue that this behavior has already been observed in nanoporous silicon and some manganites. 相似文献
57.
pH and temperature play critical roles in multistep enzymatic conversions. In such conversions, the optimal pH for individual
steps differs greatly. In this article, we describe the production of glucoamylase (from Aspergillus oryzae MTCC152 in solid-state fermentation) and glucose isomerase (from Streptomyces griseus NCIM2020 in submerged fermentation), used in industries for producing high-fructose syrup. Optimum pH for glucoamylase was
found to be 5.0. For glucose isomerase, the optimum pH ranged between 7.0 and 8.5, depending on the type of buffer used. Optimum
temperature for glucoamylase and glucose isomerase was 50 and 60°C, respectively. When both the enzymatic conversions were
performed simultaneously at a compromised pH of 6.5, both the enzymes showed lowered activity. We also studied the kinetics
at different pHs, which allows the two-step reaction to take place simultaneously. This was done by separating two steps by
a thin layer of urease. Ammonia generated by the hydrolysis of urea consumed the hydrogen ions, thereby allowing optimal activity
of glucose isomerase at an acidic pH of 5.0. 相似文献
58.
We calculate the zero-temperature (T=0) phase diagram of a polarized two-component Fermi gas in an array of weakly coupled parallel one-dimensional (1D) "tubes" produced by a two-dimensional optical lattice. Increasing the lattice strength drives a crossover from three-dimensional (3D) to 1D behavior, stabilizing the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulated superfluid phase. We argue that the most promising regime for observing the FFLO phase is in the quasi-1D regime, where the atomic motion is largely 1D but there is weak tunneling in the other directions that stabilizes long-range order. In the FFLO phase, we describe a phase transition where the quasiparticle spectrum changes from gapless near the 3D regime to gapped in quasi-1D. 相似文献
59.
A novel method has been found to enhance the metastable zone width of solutions in their supersaturated region in order to grow large size crystals. In which, the incorporation of a small quantity of Ethylenediamine tetra acetic acid (EDTA), a well‐known chelating agent, enhances the zone width significantly due to its chelating action. Also this incorporation reduces the nucleation rate and enhances the growth rate of the crystal. X‐ray rocking curve experiment for the grown crystals reveals that EDTA addition does not affect the crystalline quality. This concept was first realized with Potassium acid phthalate (KAP) solutions and then confirmed with Potassium dihydrogen phosphate (KDP) and Triglycine Sulphate (TGS). 相似文献
60.
B. P. Chandra Yuvaraj Rahangdale Meera Ramrakhiani M. H. Aansari Y. K. Sharma 《Crystal Research and Technology》1992,27(4):561-568
The present paper reports on a statistical model of the mechanoluminescence (ML) excitation in crystals where attempts have been made to explain stress, temperature-, strain rate-, activator concentration dependence and several other aspects of ML. It is found that ML emission should take place only during the period at which stress will change with time. The total ML intensity should be directly proportional to the square of the stress and there should be phase difference between the ML pulse and the applied stress pulse. It is found that the ML intensity should decrease faster with temperature as compared to the corresponding photoluminescence intensity. within the limit of concentration quenching the ML intensity should increase directly with the defect centre concentration. The ML intensity should increase with the stress rate or strain rate of the solids. Furthermore, the concept of mechanoluminescent and non-mechanoluminescent materials is explored. 相似文献