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731.
Sulfated tungstate was found to be an effective heterogeneous and reusable catalyst for hydroxy group activation–mediated preparation of benzylic ethers including p-methoxybenzylic ethers of a wide range of alcohols and phenols under mild reaction conditions. 相似文献
732.
Sachin S. Sakate Suhas H. Shinde Gayatri B. Kasar Rajeev C. Chikate Chandrashekhar V. Rode 《Journal of Saudi Chemical Society》2018,22(4):396-404
Dihydrobenzofuran as one of the active ingredients of the naturally occurring motif is synthesized by using in situ generation of ortho allyl phenols. Aryl allyl ethers on reacting with catalytic amounts of non noble metal iron (III) chloride supported on MCM-41 under moderate reaction conditions yield dihydrobenzofuran. First step via Claisen rearrangement gives ortho allyl phenol followed by its in situ cyclization to yield dihydrobenzofuran in very good yields. Both Lewis as well as Brønsted acidity of the catalyst as evidenced by Py-FTIR studies was found to catalyze the cascade synthesis of dihydrobenzofuran. The scope of the present strategy was successfully demonstrated for several substrates with varying electronic effects for the synthesis of corresponding dihydrobenzofuran with high yields in a range of 71–86%. 相似文献
733.
K. T. Poumai S. K. Kaushik 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2016,51(1):41-49
A simple proof of the proposition, stated in ([2], p. 346), asserting that in Hilbert spaces a Riesz basis is greedy, is given. Also, greedy approximant for frames in Hilbert spaces is defined and it is shown that frames satisfy the quasi greedy and almost greedy conditions. Finally, we give the characterizations of approximation spaces As(Ψ), Aqs(Ψ) by means of weak-lp and Lorentz sequence spaces for frames. 相似文献
734.
Sarita D. Gawas Sachin V. Jadhav Virendra K. Rathod 《Applied biochemistry and biotechnology》2016,180(7):1428-1445
The current research work represents solvent free enzymatic synthesis of fatty acid ethyl ester; ethyl laurate. Immobilized lipase Fermase CALB?10,000 was used for the synthesis of ethyl laurate from ethanol and lauric acid. The influence of process parameters such as catalyst loading, speed of agitation, mole ratio, molecular sieves and temperature were studied. Fermase CALB?10,000 offered a conversion of 92.46 % at 60 °C in 4 h at optimized condition. The experimental data was best fitted by the Random Bi-Bi model with inhibition of both the substrates i.e. lauric acid and ethanol. The following kinetic parameters were retrieved from the model: Vmax = 1.243 × 103 mmol/min/g enzyme; KA = 0.1283 mmol; KB = 8.51 mmol; KiA = 5.098 mmol; and SSE = 0.0142. The activation energy for the enzymatic esterification was also determined and calculated to be 28.49 kJ/mol. A maximum conversion of 71 % was obtained after 5 successive reuse of Fermase CALB?10,000 lipase. 相似文献
735.
Ashwani Kumar C. Nayak P. Rajput R. K. Mishra D. Bhattacharyya C. P. Kaushik B. S. Tomar 《Hyperfine Interactions》2016,237(1):143
Gamma radiation induced changes in local structure around the probe atom (Hafnium) were investigated in sodium barium borosilicate (NBS) glass, used for immobilization of high level liquid waste generated from the reprocessing plant at Trombay, Mumbai. The (NBS) glass was doped with 181Hf as a probe for time differential perturbed angular correlation (TDPAC) spectroscopy studies, while for studies using extended X-ray absorption fine structure (EXAFS) spectroscopy, the same was doped with 0.5 and 2 % (mole %) hafnium oxide. The irradiated as well as un-irradiated glass samples were studied by TDPAC and EXAFS techniques to obtain information about the changes (if any) around the probe atom due to gamma irradiation. TDPAC spectra of unirradiated and irradiated glasses were similar and reminescent of amorphous materials, indicating negligible effect of gamma radiation on the microstructure around Hafnium probe atom, though the quaqdrupole interaction frequency (ω Q) and asymmetry parameter (η) did show a marginal decrease in the irradiated glass compared to that in the unirradiated glass. EXAFS measurements showed a slight decrease in the Hf-O bond distance upon gamma irradiation of Hf doped NBS glass indicating densification of the glass matrix, while the cordination number around hafnium remains unchanged. 相似文献
736.
Dr. Gaspard Hedouin Sudripet Sharma Karanjeet Kaur Ramesh Hiralal Choudhary Dr. Jacek B. Jasinski Dr. Fabrice Gallou Dr. Sachin Handa 《Angewandte Chemie (International ed. in English)》2023,62(39):e202312348
Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir0 nanoparticles (NPs) for the first regioselective partial hydrogenation of PV-substituted naphthalenes. Both the isolated and in situ generated NPs are catalytically active. A control nuclear magnetic resonance (NMR) study revealed the presence of metal-surface-bound hydrides, most likely formed from Ir0 species. A control NMR study confirmed that hexafluoroisopropanol as a solvent was accountable for substrate activation via hydrogen bonding. High-resolution transmission electron microscopy of the catalyst supports the formation of ultrasmall NPs, and X-ray photoelectron spectroscopy confirmed the dominance of Ir0 in the NPs. The catalytic activity of NPs is broad as showcased by highly regioselective aromatic ring reduction in various phosphine oxides or phosphonates. The study also showcased a novel pathway toward preparing bis(diphenylphosphino)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl (H8-BINAP) and its derivatives without losing enantioselectivity during catalytic events. 相似文献
737.
Electrooxidation of carbon monoxide and methanol on platinum-overlayer-coated gold nanoparticles: effects of film thickness 总被引:1,自引:0,他引:1
The electrooxidation of carbon monoxide and methanol on Pt-coated Au nanoparticles attached to 3-aminopropyl trimethoxysilane-modified indium tin oxide electrodes was examined as a function of Pt film thickness and Au particle coverage. For the electrodes with medium and high Au particle coverages, the CO stripping peak position shifts to more negative values with increasing Pt film thickness, from ca. 0.8 V (vs Ag/AgCl) at 1 ML to 0.45 V at 10 ML. Accompanying this peak potential shift is the sharpening of the peak width from more than 150 to 65 mV. For the electrode with low Au particle coverage, similar peak width narrowing was also observed, but the peak potential shift is much smaller, from 0.85 V at 1 ML of Pt to 0.65 V at 10 ML. These observations are compared with the CO oxidation on bulk Pt electrodes and on Pt films deposited on bulk Au electrodes. The film-thickness-dependent CO oxidation is explained by d band theory in terms of strain and ligand effects, the particle size effect, and the particle aggregation induced by Pt film growth. Corresponding to the increasing CO oxidation activity, the current density of methanol oxidation grows with the Pt film thickness. The peak potential and current density reach the same values as those obtained on a polycrystalline bulk Pt electrode when more than 4 ML of Pt is deposited on the Au particle electrodes with a particle coverage higher than 0.25. These results suggest that it is feasible to reduce Pt loading in methanol fuel cells by using Pt thin films as the anode catalyst. 相似文献
738.
Kinge SS Crego-Calama M Reinhoudt DN 《Langmuir : the ACS journal of surfaces and colloids》2007,23(17):8772-8777
The synthesis of spherical gold nanoparticle assemblies with multicomponent double rosette molecular boxes as mediators is presented. These nine-component hydrogen-bonded supramolecular structures held together by 36 hydrogen bonds induce gold nanoparticle assembly. The morphologies of the nanoparticle assemblies can be tuned easily by changing the quantity of the building block chemisorbed on the nanoparticle surface. 相似文献
739.
Particles that are partially wetted by oil and water are known to adsorb at oil/water interfaces. By the same mechanism, particles
that are partially wetted by two immiscible polymers should adsorb at the interface between those two polymers. However, since
chemical differences between immiscible polymers are relatively modest, particle adsorption at polymer/polymer interfaces
may be expected to be relatively uncommon. We have conducted experiments with several particle types added to two pairs of
model polymers, polyisoprene/polydimethylsiloxane and polyisoprene/polyisobutylene. Contrary to our expectation, in every
case, particles readily adsorbed at the polymer/polymer interfaces. We evaluated the Girifalco–Good theory as a means to predict
the interfacial activity of the particles. The solid surface energy required by the Girifalco–Good theory was assumed to be
equal to the critical surface tension, which was then found by float/sink tests. Our results suggest that this approach is
not able to predict the observed interfacial activity of particles at polymer/polymer interfaces. 相似文献
740.
The mechanism of 1,4 alkyl group migration in hypervalent halonium ylides: the stereochemical course
Moriarty RM Tyagi S Ivanov D Constantinescu M 《Journal of the American Chemical Society》2008,130(24):7564-7565
Rhodium(II)-acetate-catalyzed decomposition of either 1,3-cyclohexanedione phenyliodonium ylide or 5,5-dimethyl-1,3-cyclohexanedione phenyliodonium ylide in the presence of alkyl halides yields the corresponding 3-alkoxy-2-halocyclohex-2-enones via a 1,4 alkyl group migration shown to be concerted and intramolecular. In the case of (S)-alpha-phenethyl chloride, the rearrangement proceeds with essentially 88.6% retention of configuration. Theoretical calculations at the B3LYP/6-31G level reveal an activation energy of 5.4 kcal/mol for the process. A Claisen-like rearrangement occurs in the case where allylic halides, such as dimethylallyl or methallyl chorides, are used. The mechanistic pathway proposed for these processes involves addition of the halogen atom of the alkyl or allyl halide to the rhodium carbenoid from the iodonium ylide to yield a halonium intermediate that undergoes halogen to oxygen group migration. Aryl halides, such as chloro-, bromo-, iodo-, and fluorobenzene, behave differently under the same reaction conditions, yielding the product of electrophilic aromatic substitution, namely, the 2-(4-halophenyl) 1,3-cyclohexanedione. 相似文献