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181.
Undecanuclear copper clusters, [Cu(11)(micro(9)-Se)(micro(3)-Br)(3)[Se(2)P(OR)(2)](6)] (R = Et, Pr, (i)Pr) (1a-c), were isolated along with closed-shell ion-centered cubes, [Cu(8)(micro(8)-Br)[Se(2)P(OR)(2)](6)] (PF(6)) (2a-c) and [Cu(8)(micro(8)-Se)[Se(2)P(OR)(2)](6)] (3a-c), from the reaction of [Cu(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NBr in a molar ratio of 2:3:2 in CH(2)Br(2). The molecular formulations of these clusters were confirmed by elemental analysis, positive FAB mass spectrometry, and multinuclear NMR ((1)H, (31)P, and (77)Se). (77)Se NMR spectra of Cu(11) clusters (1a-c) are of special interest as two inequivalent selenium nuclei of the diselenophosphate (dsep) ligand exhibit different scalar coupling patterns with the adjacent phosphorus nuclei. X-ray analysis of 1c reveals a Cu(11)Se core stabilized by three bromide and six dsep ligands. The central core adopts the geometry of a 3,3,4,4,4-pentacapped trigonal prism with a selenium atom in the center. The coordination geometry for the nonacoordinate selenium atom is tricapped trigonal prismatic. The X-ray structure 2a or 2c consists of a cationic cluster in which eight copper ions are linked by six diselenophosphate ligands with a central micro(8)-Br ion. The shape of the molecule is a bromide-centered distorted Cu(8) cube. Each diselenophosphate ligand occupies square faces of the cube and adopts a tetrametallic tetraconnective coordination pattern. Each copper atom of the cube is coordinated by three selenium atoms with a strong interaction with the central bromide ion. Molecular orbital calculations at the B3LYP level of the density functional theory have been carried out to study the Cu-micro(9)-Se interactions for clusters [Cu(11)(micro(9)-Se)(micro(3)-X)(3)[Se(2)P(OR)(2)](6)] (X = Br, I). Calculations show that the formal bond order of each Cu-micro(9)-Se bond is slightly smaller than half of those calculated for the terminal Cu-micro(2)-Se bonds. 相似文献
182.
The cytoplasm of a living cell is crowded with several macromolecules of different shapes and sizes. Molecular diffusion in
such a medium becomes anomalous due to the presence of macromolecules and diffusivity is expected to decrease with increase
in macromolecular crowding. Moreover, many cellular processes are dependent on molecular diffusion in the cell cytosol. The
enzymatic reaction rate has been shown to be affected by the presence of such macromolecules. A simple numerical model is
proposed here based on percolation and diffusion in disordered systems to study the effect of macromolecular crowding on the
enzymatic reaction rates. The model qualitatively explains some of the experimental observations.
相似文献
183.
H. W. Wilschut U. Dammalapati D. J. van der Hoek K. Jungmann W. Kruithof C. J. G. Onderwater B. Santra P. D. Shidling L. Willmann 《Pramana》2010,75(1):163-170
One of the greatest successes of the Standard Model of particle physics is the explanation of time-reversal violation (TRV)
in heavy mesons. It also implies that TRV is immeasurably small in normal nuclear matter. However, unifying models beyond
the Standard Model predict TRV to be within reach of measurement in nuclei and atoms, thus opening an important window to
search for new physics. We will discuss two complementary experiments sensitive to TRV: Correlations in the β-decay of 21Na and the search for an electric dipole moment (EDM) in radium. 相似文献
184.
Dr. Shlomy Arava Dr. Sourav K. Santra Dr. Gulab K. Pathe Raja Kapanaiah Prof. Dr. Alex M. Szpilman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15283-15287
Herein we report on the umpolung of Morita–Baylis–Hillman type intermediates and application to the α-functionalization of enone C−H bonds. This reaction gives direct access to α-chloro-enones, 1,2-diketones and α-tosyloxy-enones. The latter are important intermediates for cross-coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way. The proposed mechanism is supported by spectroscopic studies. The key initial step involves conjugate attack of an amine (DABCO or pyridine), likely assisted by hypervalent iodine acting as a Lewis acid leading to formation of an electrophilic β-ammonium-enolonium species. Nucleophilic attack by acetate, tosylate, or chloride anion is followed by base induced elimination of the ammonium species to give the noted products. Hydrolysis of α-acetoxy-enones lead to formation of 1,2-diketones. The α-tosyl-enones participate in Negishi coupling reactions under standard conditions. 相似文献
185.
Doumy G Roedig C Son SK Blaga CI DiChiara AD Santra R Berrah N Bostedt C Bozek JD Bucksbaum PH Cryan JP Fang L Ghimire S Glownia JM Hoener M Kanter EP Krässig B Kuebel M Messerschmidt M Paulus GG Reis DA Rohringer N Young L Agostini P DiMauro LF 《Physical review letters》2011,106(8):083002
The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of Ne(9+) is observed at x-ray frequencies below the Ne(8+), 1s(2) absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of Ne(8+) ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations. 相似文献
186.
Despite widespread discussion, the role of van der Waals dispersion forces in wetting remains unclear. Here we show that nonlocal correlations contribute substantially to the water-metal bond and that this is an important factor in governing the relative stabilities of wetting layers and 3D bulk ice. Because of the greater polarizability of the substrate metal atoms, nonlocal correlations between water and the metal exceed those between water molecules within ice. This sheds light on a long-standing problem, wherein common density functional theory exchange-correlation functionals incorrectly predict that none of the low temperature experimentally characterized icelike wetting layers are thermodynamically stable. 相似文献
187.
O. O. Versolato L. W. Wansbeek G. S. Giri J. E. van den Berg D. J. van der Hoek K. Jungmann W. L. Kruithof C. J. G. Onderwater B. K. Sahoo B. Santra P. D. Shidling R. G. E. Timmermans L. Willmann H. W. Wilschut 《Hyperfine Interactions》2011,199(1-3):9-19
Atomic parity violation (APV) experiments are sensitive probes of the electroweak interaction at low energy. These experiments are competitive with and complementary to high-energy collider experiments. The APV signal is strongly enhanced in heavy atoms and it is measurable by exciting suppressed (M1, E2) transitions. The status of APV experiments and theory are reviewed as well as the prospects of an APV experiment using one single trapped Ra?+? ion. The predicted enhancement factor of the APV effect in Ra?+? is about 50 times larger than in Cs atoms. However, certain spectroscopic information on Ra?+? needed to constrain the required atomic many-body theory, was lacking. Using the AGOR cyclotron and the TRI??P facility at KVI in Groningen, short-lived 212???214Ra?+? ions were produced and trapped. First ever excited-state laser spectroscopy was performed on the trapped ions. These measurements provide a benchmark for the atomic theory required to extract the electroweak mixing angle to sub-1% accuracy and are an important step towards an APV experiment in a single trapped Ra?+? ion. 相似文献
188.
We analyze blow-up phenomena of bounded integrable solutions of a semilinear fourth order elliptic problem with a large exponent
under Dirichlet boundary conditions. We extend the results obtained by Ren-Wei in [26] and [27] to the biharmonic case. 相似文献
189.
In this review we discuss various simulation methods for modeling nanoplasmas created from finite‐size samples after their irradiation with femtosecond, intense X‐ray pulses. Depending on the sample composition and its size, either a particle method or a transport method can be applied. Also, the observables of interest influence the choice of the simulation method. The current status of dedicated methods developed by the CFEL Theory Division at DESY in Hamburg and their possible extensions are presented together with some application examples. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
190.
Sk. Manirul Islam Sumantra Paul Anupam Singha Roy Satabdi Banerjee Kajari Ghosh Ram Chandra Dey S. C. Santra 《Transition Metal Chemistry》2013,38(6):675-682
An iron(III)–ferrocene complex and its heterogeneous analogue bound in a polymer resin have been prepared and employed as catalysts for the oxidation of various organic substrates. Characterization of the heterogeneous and homogeneous complexes was done by SEM, EDAX, TGA, FT-IR, DRS-UV, and spectroscopy. The catalyst’s activity, stability, and reusability were investigated through industrially relevant oxidation reactions. The solid iron(III)–ferrocene Schiff base complex gave more effective results than the solid-supported ferrocene Schiff base ligand. The antimicrobial activities of the molecular complex and free ligand were studied for Gram-positive and Gram-negative bacteria. 相似文献