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1.
Gopa KarAnil K. Saikia Upasana BoraSanjoy K. Dehury Mihir K. Chaudhuri 《Tetrahedron letters》2003,44(24):4503-4505
The bright yellow crystalline cetyltrimethylammonium tribromide (CTMATB) reagent has been synthesized from the reaction of CTMAB and KBr with H2MoO4·H2O, H2O2 and H2SO4 in the molar ratio 1:2:0.01:4:0.93. CTMATB selectively oxidizes a variety of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides in high yields under mild conditions. 相似文献
2.
Anil Saikia 《Tetrahedron letters》2006,47(1):43-46
A novel one-pot synthesis of pyrazoles has been accomplished by the reaction of β-formyl enamides with hydroxylamine hydrochloride catalysed by potassium dihydrogenphosphate in acid medium. 相似文献
3.
Theoretical investigation on local electronic structure and stability of the π–π stacking interaction of pyrazinamide (PZA) with armchair (5,5) and zigzag (9,0) single‐walled carbon nanotubes (SWCNTs) is performed using density functional theory (DFT). PZA is physisorbed onto nanotube sidewall through interaction of π orbitals of PZA and SWCNT and the enhanced structural stability of PZA/SWCNT systems is due to weak side‐on rather than the head‐on π‐interactions. The physisorption of PZA onto SWCNT sidewall is thermodynamically favored; as a consequence, it modulates the electronic properties of pristine nanotube in the vicinity of Fermi region and π–π stacked interactions is stronger in (9,0) SWCNT compared to (5,5) SWCNT. The density of states (DOS) analysis show that PZA contributes toward the enhancement of electronic states. Projected DOS and frontier orbital analysis in the vicinity of Fermi level region suggest the electronic states to be contributed from SWCNT rather than PZA. In addition, hybrid DFT calculation which includes the dispersion correction is employed to explain the non‐covalent π–π stacking interaction between PZA and SWCNT. The local density approximation and GGA results are compared with DFT‐D to explain near about accurately the weak nonbonded van der Waals interactions between PZA and SWCNTs. © 2012 Wiley Periodicals, Inc. 相似文献
4.
The application of graphene and related nanomaterials like boron nitride (BN) nanosheets, BN-graphene hybrid nanomaterials, and graphene oxide (GO) for adsorption of anticancer chemotherapeutic camptothecin (CPT) along with the effect on electronic properties prior to functionalization and after functionalization has been reported using density functional theory (DFT) calculations. The inclusion of dispersion correction to DFT is instrumental in accounting for van der Waals π–π stacking between CPT and the nanomaterial. The adsorption of CPT exhibits significant strain within the nanosheets and noncovalent adsorption of CPT is thermodynamically favoured onto the nanosheets. In case of GO, surface incorporation of functional groups result in significant crumpling along the basal plane and the interaction is basically mediated by H-bonding rather than π–π stacking. Docking studies predict the plausible binding of CPT, CPT functionalized graphene and GO with topoisomerase I (top 1) signifying that CPT interacts through π stacking with AT and GC base pairs of DNA and in presence of nano support, DNA bases preferentially gets bound to the basal plane of graphene and GO rather than the edges. At a theoretical level of understanding, our studies point out the noncovalent interaction of CPT with graphene based nanomaterials and GO for loading and delivery of anticancer chemotherapeutic along with active binding to Top1 protein. 相似文献
5.
Ujwal Pratim Saikia Diganta BaruahPallab Pahari Manash Jyoti Borah Amrit GoswamiDilip Konwar 《Tetrahedron letters》2014
A mild and efficient methodology has been developed for the synthesis of spiro-1,3-oxazine derivatives by the microwave assisted cyclization of N-2-(1′-cyclohexenyl)ethyl-acetamides/benzamides. The reaction was catalyzed by in situ generated trimethylsilyl iodide and featured by its very short reaction time. The starting materials were easily obtained by the condensation of substituted acetic/benzoic acids with 2-(1′-cyclohexenyl)ethyl amine. 相似文献
6.
Nabajyoti Saikia Shigeru Kato Toshinori Kojima 《Journal of Thermal Analysis and Calorimetry》2012,109(1):273-286
Tricalcium aluminate (Ca3Al2O6, C3A) containing 0?C5% of Sn was synthesized by solid-state method, and the products were characterized by XRD technique. Differential thermo-analytical technique (DTA) along with X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were applied to study the hydration behaviour of different C3A samples with and without the presence of gypsum. Results indicate that C3A can accommodate small amount of Sn in its structure and remaining amount forms SnO2. Hydration studies of the synthesized C3A shows that the additions of 0.5 and 1% Sn increase and 2% Sn decrease the reactivity of C3A at the initial period (<3?h) of hydration. Increasing additions of Sn also increase the amounts of amorphous phases and hexagonal calcium aluminate hydrates in the cement pastes. The stabilities of these hydration products also increase with increasing content of Sn in C3A at the experimental conditions. The presence of Sn significantly changes the hydration of C3A and gypsum solid mixture at the initial period of hydration by enhancing the formation of more amounts of AFt and AFm phases. However, at the later stage of hydration (on or after 3?days), the hydration products in C3A and gypsum pastes with and without the presence of Sn are almost similar. 相似文献
7.
It was observed that the reaction of CFCl3 with thiophenoxide gave only 10% of the corresponding thioether. On the other hand, these thioethers could be prepared in excellent yield from diaryl disulfides and CFCl3 in the presence of sodium hydroxymethanesulfinate in aqueous DMF at 4 atm pressure of nitrogen. Dechlorination of the thioether (PhSCFCl2) with different reducing agents were studied. Most of the reducing agents eliminated both fluorine and chlorine functionalities or gave the hydrolyzed products. But its sulfone on treatment with Zinc in methanol gave monochlorofluoromethyl and fluoromethyl phenyl sulfone in good yields. Darzens reaction of these compounds was also studied. 相似文献
8.
We obtain ratchet effect in inertial structureless systems in symmetric periodic potentials where the asymmetry comes from
the non-uniform friction offered by the medium and driven by symmetric periodic forces. In the adiabatic limit the calculations
are done by extending the matrix continued fraction method and also by numerically solving the appropriate Langevin equation.
For finite frequency field drive the ratchet effect is obtained only numerically. In the transient time scales the system
shows dispersionless behaviour as reported earlier when a constant force is applied. In the periodic drive case the dispersion
behaviour is more complex. In this brief communication we report some of the results of our work.
相似文献
9.
Decomposition of clay from Garo Hills of Meghalaya (India) was studied by dynamic thermogravimetry. A fourteen kinetic equation procedure was applied for analysis of non-isothermal weight change upto a temperature of 1223 K. Two stages of decomposition were clearly distinguised i.e. the initial dehydration period at temperature 373 K to 673 K and the dehydroxylation period in the temperature range 723 K to 1073 K. First order decomposition mechanism was found to be applicable to both dehydration and dehydroxylation steps. Activation energies of 67 kJ/mol and 278 kJ/mol are estimated for the first and second steps with frequency factors of 16.3 s–1 and 5.16×106s–1 respectively. The weight loss relating to the steps in TG curves allows determination of the contents of the basic mineral in the clay. Percentages of Al2O3.SiO2 and total volatiles as calculated from weight loss data are in accordance with the results of classical chemical analysis.
Zusammenfassung Mittels DTG wurde die thermische Zersetung von Ton aus der Garo-Hills-Gegend bei Meghalaya (Indien) untersucht. Zur Analyse der nicht-isothermen Gewichtsveränderungen bis zu einer Temperatur von 1223 K wurde ein Verfahren mit vierzehn kinetischen Gleichungen angewendet. Zwei Teilschritte der Zersetzung können eindeutig unterschieden werden, nämlich die anfängliche Dehydratationsperiode bei Temperaturen von 373 bis 673 K und die Dehydroxylierungsperiode bei Temperaturen zwischen 723 K un 1073 K. Für beide Vorgänge konnte als Reaktionsmechanismus eine Zersetzung erster Ordnung angewendet werden. Für den ersten un zweiten Teilschritt konnten Aktivierungsenergien von 67 kJ/mol bzw. 278 kJ/mol un Frequenzfaktoren von 16.3s–1 bzw. 5.16×106s–1 ermittelt werden. Der aus den TG-Kurven hervorgehende Gewichtsverlust läßt auf den Gehalt des Tones an Basismineral schließen. Der prozentuelle Gehalt an Al2O3, SiO2 und der gesamten flüchtigen Bestandteile, berechnet aus den Gewichtsverlusdaten, stimmt mit den Ergebnissen aus herkömmlichen chemischen Analysen überein.相似文献
10.
In this paper, we find new proofs of modular relations for the Göllnitz-Gordon functions established earlier by S.-S. Huang and S.-L. Chen. We use Schröter’s formulas and some simple theta-function identities of Ramanujan to establish the relations. We also find some new modular relations of the same nature. 相似文献