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311.
Citroni M Datchi F Bini R Di Vaira M Pruzan P Canny B Schettino V 《The journal of physical chemistry. B》2008,112(4):1095-1103
Angle dispersion X-ray diffraction (AXDX) experiments on nitromethane single crystals and powder were performed at room temperature as a function of pressure up to 19.0 and 27.3 GPa, respectively, in a membrane diamond anvil cell (MDAC). The atomic positions were refined at 1.1, 3.2, 7.6, 11.0, and 15.0 GPa using the single-crystal data, while the equation of state (EOS) was extended up to 27.3 GPa, which is close to the nitromethane decomposition threshold pressure at room temperature in static conditions. The crystal structure was found to be orthorhombic, space group P2(1)2(1)2(1), with four molecules per unit cell, up to the highest pressure. In contrast, the molecular geometry undergoes an important change consisting of a gradual blocking of the methyl group libration about the C-N bond axis, starting just above the melting pressure and completed only between 7.6 and 11.0 GPa. Above this pressure, the orientation of the methyl group is quasi-eclipsed with respect to the NO bonds. This conformation allows the buildup of networks of strong intermolecular O...H-C interactions mainly in the bc and ac planes, stabilizing the crystal structure. This structural evolution determines important modifications in the IR and Raman spectra, occurring around 10 GPa. Present measurements of the Raman and IR vibrational spectra as a function of pressure at different temperatures evidence the existence of a kinetic barrier for this internal rearrangement. 相似文献
312.
Maiuri M Polli D Brida D Lüer L LaFountain AM Fuciman M Cogdell RJ Frank HA Cerullo G 《Physical chemistry chemical physics : PCCP》2012,14(18):6312-6319
In carotenoids internal conversion between the allowed (S(2)) and forbidden (S(1)) excited states occurs on a sub-picosecond timescale; the involvement of an intermediate excited state(s) (S(x)) mediating the process is controversial. Here we use high time resolution (sub-20 fs) broadband (1.2-2.5 eV) pump-probe spectroscopy to study the solvent dependence of excited state dynamics of spheroidene, a naturally-occurring carotenoid with ten conjugated double bonds. In the high polarizability solvent, CS(2), we find no evidence of an intermediate state, and the traditional three-level (S(0), S(1), S(2)) model fully accounts for the S(2)→ S(1) process. On the other hand, in the low polarizability solvent, cyclohexane, we find that rapid (~30 fs) relaxation to an intermediate state, S(x), lying between S(1) and S(2) is required to account for the data. We interpret these results as due to a shift of the S(2) energy, which positions the state above or below the energy of S(x) in response to changes in solvent polarizability. 相似文献
313.
Prof. Arturo Arduini Dr. Rocco Bussolati Prof. Alberto Credi Simone Monaco Prof. Andrea Secchi Dr. Serena Silvi Prof. Margherita Venturi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(50):16203-16213
The development of a pseudorotaxane motif capable of performing unidirectional threading and dethreading processes under control of external stimuli is particularly important for the construction of processive linear motors based on rotaxanes and, at least in principle, it discloses the possibility to access to rotary motors based on catenanes. Here, we report a strategy to obtain the solvent‐controlled unidirectional transit of a molecular axle through a molecular wheel. It is based on the use of appropriately designed molecular components, the essential feature of which is their non‐symmetric structure. Specifically they are an axle containing a central electron‐acceptor 4,4′‐bipyridinium core functionalized with a hexanol chain at one side, and a stilbene unit connected through a C6 chain at the other side, and a heteroditopic tris(phenylureido)‐calix[6]arene wheel. In apolar solvents the axle threads into the wheel from its upper rim and with the end carrying the OH group, giving an oriented pseudorotaxane structure. After a stoppering reaction, which replaces the small hydroxy group with a bulky diphenylacetyl moiety, and replacement of the apolar solvent with a polar one, dethreading occurs through the slippage of the stilbene unit from the lower rim of the wheel, that is, in the same direction of the threading process. The essential role played by the stilbene unit to achieve the unidirectional transit of the axle through the wheel, and to tune the dethreading rate by light is also demonstrated. 相似文献
314.
Iacovino R Caso JV Rapuano F Russo A Isidori M Lavorgna M Malgieri G Isernia C 《Molecules (Basel, Switzerland)》2012,17(5):6056-6070
An inclusion complex of hydroxymethylferrocene (FeMeOH) with β-cyclodextrin (β-CD) was prepared in the solid state by different techniques such as physical mixture, coprecipitation, kneading and freeze-drying. The formation of the inclusion complex was confirmed by X-ray Powder Diffractometry and Fourier Transform-Infrared spectroscopy. In aqueous solution, the 1:1 stoichiometry was established by a Job plot. The inclusion complex formation was also investigated by NMR and the stability constant (Kb) of the complex was determined to be 478 M?1, which is in agreement with that obtained with UV-Vis tritation (Kb = 541.3 M?1). The phase solubility study showed a diagram classified as Bs type and that the solubility of FeMeOH was slightly increased in the presence of β-CD. Furthermore, utilizing phase solubility diagram data, the Kb was estimated to be equal to 528.0 M?1. The cytotoxic activity of FeMeOH and its complexation product with β-CD was determined using the MTT-assay on MDA-MB-231 cell line, showing that the inclusion complex has a higher capability of inhibiting cell growth compared to that of pure FeMeOH. 相似文献
315.
Margherita De Rosa 《Tetrahedron letters》2006,47(48):8507-8510
This letter describes the first example of diastereoselective ‘organocatalyzed’ synthesis of the butenolide products substituted at the γ-position by a chain bearing hydroxyl groups. The urea-derivative 4 has proved to be an efficient catalyst for the addition of the commercial TMSOF to carbonyl compounds under solvent-free conditions. The reaction conditions and generality of the procedure have been examined. 相似文献
316.
Cardullo F Donati D Fusillo V Merlo G Paio A Salaris M Solinas A Taddei M 《Journal of combinatorial chemistry》2006,8(6):834-840
One of the still unresolved problems in parallel synthesis is the availability of a general and rapid method for the transformation of a primary amine into the corresponding secondary amine without the issue of polyalkylation. Following the Fukuyama method, which is based on the alkylation of o-nitrobenzenesulfonamides, followed by removal of the sulfonyl group, we have developed a simple protocol which can be easily applied to parallel synthesis making use of supported reagents and scavengers. To verify the robustness of the method, a small representative array of secondary amines have been prepared. Moreover, taking advantage of the possibility to use different supported reagents in the same pot, we also prepared, starting from primary amines, a series of differently substituted tertiary amines. 相似文献
317.
Ciavatta ML Lopez Gresa MP Gavagnin M Manzo E Mollo E D'Souza L Cimino G 《Molecules (Basel, Switzerland)》2006,11(10):808-816
Chemical analysis of the secondary metabolite pattern of the sacoglossan mollusc Elysia cf. expansa, collected along South Indian coasts, showed the presence of the typical Caulerpa-derived sesquiterpene caulerpenyne (1) and two new minor co- occurring metabolites, the compounds dihydrocaulerpenyne (4) and expansinol (5). The chemical characterization of these molecules, structurally related to 1, is reported. 相似文献
318.
Marianna Carbone Antonella Daniele Alessia Ligresti Margherita Gavagnin 《Tetrahedron》2010,66(49):9497-9501
The chemical analysis of a sample of Δ9-THC, which had been stored in an ethanol/propylene glycol solution for 5 years, resulted in the isolation of several hydroxylated Δ9-THC derivatives, the main of which were trans-cannabitriol monoethyl ether (4) and trans-propanediol ethers 7 and 8. cis-Cannabitriol monoethyl ether (5) and the oxidised derivatives 3 and 6 were detected in lesser amounts. The structure elucidation of the unprecedented cannabinoids 3, 5, 7 and 8 was achieved mainly by NMR techniques. Full NMR assignment of compounds 4 and 6 were also made. The detection of cannabitriol (6) and the corresponding solvent-adduct analogues (compounds 4-8) was in agreement with the decomposition mechanisms previously proposed for Δ9-THC. The isolation of the endoperoxide 3 represents indirect evidence of the existence of unstable precursors that were suspected to be intermediates in the non-enzymatic oxidation pathway of Δ9-THC. Both isomers of cannabitriol monoethyl ether exhibited weak affinity at either CB1 (Ki=2.25, 6.30 μM) or CB2 cannabinoid receptors (Ki=1.97, 3.13 μM), the trans isomer always being more potent than the cis isomer. 相似文献
319.
Elena Amico di Meane Margherita Plassa Francesca Rolle Michela Sega 《Accreditation and quality assurance》2009,14(11):607-611
Metrologically traceable measurements are needed, in environmental monitoring, to provide meaningful information on the pollution
level and the possibility to have suitable reference standards is crucial to this purpose to calibrate instruments. The Italian
National Institute of Metrological Research (I.N.Ri.M.), as a primary metrological institute, realizes and maintains primary
standards for the basic and derived units of the International System of Units (SI). In this framework and regarding gas analysis,
in the last few years I.N.Ri.M. has started a research line on the preparation of primary reference mixtures (PRMs) by the
gravimetric method that led to plan and build a facility for evacuating and filling cylinders and a device for high precision
weighing. In the present work the developments in such field at I.N.Ri.M. are reported to underline the relevance, in the
atmospheric pollutants monitoring, of performing accurate and reliable measurements and having reference standards fit for
the calibration of the analytical instrumentation. 相似文献
320.
In this paper we study the Brill–Noether theory of invertible subsheaves of a general, stable rank-two vector bundle on a
curve C with general moduli. We relate this theory to the geometry of unisecant curves on smooth, non-special scrolls with hyperplane
sections isomorphic to C. Most of our results are based on degeneration techniques.
The first three authors are members of G.N.S.A.G.A. at I.N.d.A.M. “Francesco Severi”. 相似文献