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排序方式: 共有141条查询结果,搜索用时 15 毫秒
1.
Ephrath Solel Doron Pappo Ofer Reany Tom Mejuch Renana Gershoni-Poranne Mark Botoshansky Amnon Stanger Ehud Keinan 《Chemical science》2020,11(48):13015
Flat corannulene has been considered so far only as a transition state of the bowl-to-bowl inversion process. This study was driven by the prediction that substituents with strong steric repulsion could destabilize the bowl-shaped conformation of this molecule to such an extent that the highly unstable planar geometry would become an isolable molecule. To examine the substituents'' effect on the corannulene bowl depth, optimized structures for the highly-congested decakis(t-butylsulfido)corannulene were calculated. The computations, performed with both the M06-2X/def2-TZVP and the B3LYP/def2-TZVP methods (the latter with and without Grimme''s D3 dispersion correction), predict that this molecule can achieve two minimum structures: a flat carbon framework and a bowl-shaped structure, which are very close in energy. This rather unusual compound was easily synthesized from decachlorocorannulene under mild reaction conditions, and X-ray crystallographic studies gave similar results to the theoretical predictions. This compound crystallized in two different polymorphs, one exhibiting a completely flat corannulene core and the other having a bowl-shaped conformation.The first flat metal-free corannulene derivative was predicted by computations and achieved by synthesis. 相似文献
2.
3.
Dr. Qigang Zhong Dr. Artur Mardyukov Dr. Ephrath Solel Dr. Daniel Ebeling Prof. André Schirmeisen Prof. Peter R. Schreiner 《Angewandte Chemie (International ed. in English)》2023,62(46):e202310121
On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of unstable or unconventional molecules, which could not be obtained via traditional synthetic methods. A case in point is the on-surface synthesis of the structurally elusive cyclotriphosphazene (P3N3), an inorganic aromatic analogue of benzene. Here, we report the preparation of this fleetingly existing species on Cu(111) and Au(111) surfaces at 5.2 K through molecular manipulation with unprecedented precision, i.e., voltage pulse-induced sextuple dechlorination of an ultra-small (about 6 Å) hexachlorophosphazene P3N3Cl6 precursor by the tip of a scanning probe microscope. Real-space atomic-level imaging of cyclotriphosphazene reveals its planar D3h-symmetric ring structure. Furthermore, this demasking strategy has been expanded to generate cyclotriphosphazene from a hexaazide precursor P3N21 via a different stimulation method (photolysis) for complementary measurements by matrix isolation infrared and ultraviolet spectroscopy. 相似文献
4.
Dr. Mandeep Singh Ephrath Solel Prof. Ehud Keinan Dr. Ofer Reany 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):536-540
Semithiobambusurils, which represent a new family of macrocyclic host molecules, have been prepared by a convenient, scalable synthesis. These new cavitands are double functional: they strongly bind a broad variety of anions in their interiors and metal ions at their sulfur‐edged portals. The solid‐state structure of semithiobambus[4]uril with HgCl2 demonstrates the ability of these compounds to form linear chains of coordination polymers with thiophillic metal ions. The crystal structure of semithiobambus[6]uril with tetraphenylphosphonium bromide exhibits the unique anion‐binding properties of the host cavity and the characteristics of the binding site. 相似文献
5.
Suppose T+(E){\mathcal{T}_{+}(E)} is the tensor algebra of a W*-correspondence E and H
∞(E) is the associated Hardy algebra. We investigate the problem of extending completely contractive representations of T+(E){\mathcal{T}_{+}(E)} on a Hilbert space to ultra-weakly continuous completely contractive representations of H
∞(E) on the same Hilbert space. Our work extends the classical Sz.-Nagy–Foiaş functional calculus and more recent work by Davidson,
Li and Pitts on the representation theory of Popescu’s noncommutative disc algebra. 相似文献
6.
Baruch Karp 《International Journal of Solids and Structures》2011,48(1):126-136
The dynamic response of an elastic, semi-infinite strip with sliding surfaces, subjected to various forms of end excitations, was solved analytically employing the property of bi-orthogonality of wave modes. An explicit relation between the amplitudes of evanescent waves and the form of the excitation was obtained. Quantitative measure for dynamic end effects was suggested, termed Saint-Venant ratio (SVR). It was shown that two qualities of that ratio are useful for monitoring the health of structural joints (SHM): being that ratio not affected by the intensity of the end excitation and its high sensitivity to small variations in the form of the excitation. The axial behavior of the strip subjected to several forms of end excitations was further used to demonstrate the validity of a previously suggested dynamic version of Saint-Venant’s principle. 相似文献
7.
David Levanony Menahem Baruch 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1987,38(6):874-882
The behaviour of a non-uniform beam loaded by a parallel or tangential compressive force respectively is analyzed by exploiting a two-degree-of-freedom dynamic model. The same system has been analyzed previously by Lee and Reissner from a static point of view and by Neer and Baruch by a dynamic approach using a one-degree-of-freedom model. The previous analyses revealed only part of the phenomena by the present approach.Here, for the tangential force a classical flutter instability is obtained and for the parallel force only static instability is possible. 相似文献
8.
Mono-, di- and tri-alkyl-substituted allenes were potentiostatically oxidized in methanol at graphite and Pt anodes. At the former electrode, α-methoxylated ketones (due to 4F/mole electricity consumption) and esters (6F/mole) were the major products. At a Pt anode, intermediate products such as vinyl-ether derivatives (2F/mole) were characterised too. Unlike the anodic oxidation of alkenes and alkynes previously reproted in the literature, dimerisation is not a typical process in the allenes' oxidation, since of all the products obtained only a sole dimer has been observed. The mechanism for the formation of most products is discussed. 相似文献
9.
In this paper we report the results of an experimental study of the vacuum ultraviolet absorption spectra of molecular impurity states of methyl iodide in Ar (density range ? = 0–1.4 g cm?3) and in Kr (? = 0–2.3 g cm?3), of carbon disulphide in Ar (? = 0–1.4 g cm?3) and of formaldehyde in Ar (? = 0–1.25 g cm?3). The experimental results provide new information regarding medium perturbations of intravalenc transitions, of the lowest extravalence transitions and of transitions to mixed valence—Rydberg configurations, which serve as a diagnostic tool to distinguish between different types of electronic excitations. All the lowest extravalence molecular excitations exhibit appreciable blue spectral shifts at moderate and at high fluid densities, intravalence transitions are practically insensitive to medium effects, while excitations to mixed valence—Rydberg configurations are characterized by a moderate blue spectral shift. New information has been obtained concerning the energetics of molecular ionization processes in a dense fluid. The high n = 2–5 Rydberg states of CH3l exhibit a large red shift at moderate (? = 0–0.5 cm?3) Ar densities. The ionization potential Eg and the effective Rydberg constant G for CH3I in Ar was found to decrease from G = 13.6 eV and Eg = 9.55 eV at ? = 0 and Eg = 9.08 eV and constant G for CH3l in Ar was found to decrease from G = 13.6 eV and Eg = 9.55eV at ? = 0 and Eg = 9.08 eV and G ≈ 7.15 eV at ? = 0.5 g cm?3. Experimental evidence was obtained for the identification of n = 2 molecular Wannier impurity states of CH3I and of CH2O in liquid Ar. These spectroscopic data result in Eg ≈ 8.6 eV for CH3I in liquid Ar and Eg ≈ 10.2 eV for CH2O in liquid Ar. 相似文献
10.
Baruch Cahlon 《Journal of Differential Equations》1974,15(3):418-428
In this paper a boundary value problem for the heat equation with solution-dependent boundary conditions is examined in the case when the dependence is of stochastic type. 相似文献