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41.
Grant A. Boyle Hendrik G. Kruger Glenn E. M. Maguire Amith Singh 《Structural chemistry》2007,18(5):633-639
The complete NMR elucidation of four pentacycloundecane (PCU) derived ligands is reported. 2D NMR techniques are used to overcome
the problem of major overlapping of methine signals on the cage skeleton. One of the cage ligands is chiral and the 13C NMR signals of the leucinol side “arms” to the cage appear to be split into two or more peaks indicating either impurities
or conformational differences. Impurities were ruled out and the only logical explanation for this unusual observation appears
to be conformational effects due to different positions of the two relative bulky side chains or “arms”. The rigid cage skeleton
is known for through space deshielding of signals in close proximity to oxygen atoms attached to the cage skeleton. The leucinol
side chains in closer proximity to the cage ether bridge would experience a larger shielding effect causing those carbon atoms
to be shifted upfield with respect to the corresponding atoms in other conformations. The intrinsic chiral nature of the cage
could also play a role in this case to perhaps enhance the observed effect.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
42.
Abbasi Malek Kruger Alexander Y. Théra Michel 《Set-Valued and Variational Analysis》2021,29(3):701-719
Set-Valued and Variational Analysis - This paper proposes three enlargements of the conventional Moreau–Rockafellar subdifferential: the sup-, sup?- and symmetric subdifferentials. They... 相似文献
43.
44.
Oluwatayo F. Ikotun Nadia Marino Paul E. Kruger Miguel Julve Robert P. Doyle 《Coordination chemistry reviews》2010,254(7-8):890-915
Current attention continues to revolve around the chemistry and biochemistry associated with polyphosphate anions because of their importance in biology. A pivotal intermediate within this family is the pyrophosphate tetraanion, P2O74?. Considering its biological relevance and the multidentate nature that makes it an ideal ligand in the field of the coordination chemistry, there is a growing interest in the use of this anion in building new class of molecules/compounds for different purposes. While the total number of characterized structures still remains modest, several new pyrophosphate-containing coordination complexes have been reported in the last decade, as well as different solid-state structures. This review focuses on the structural, magnetic, and biological properties of coordination complexes incorporating the pyrophosphate ligand reported to date. 相似文献
45.
Paul E. Kruger Philip R. Mackie Mark Nieuwenhuyzen 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):e532-e532
The title compound, C6HCl3N2O4, is an intermediate in the synthesis of 1,3,5‐trichloro‐2,4,6‐trinitrobenzene. The crystal structure at 153 K shows no major deviations from the previously reported structure at 295 K other than the expected contraction of the a and c axes and, correspondingly, the β angle. 相似文献
46.
Grant A. Boyle Thavendran Govender Hendrik G. Kruger Glenn E. M. Maguire 《Structural chemistry》2009,20(5):925-932
The complete NMR elucidation of five camphor-derived ligands is reported. 2D NMR techniques such as NOESY are used to assist
in the determination of the orientation of the donor groups in space. The compounds were synthesized as ligands to be used
in asymmetric catalysis. They represent the first instance where both donor groups are pendant on the C3 position of the camphor
skeleton. The single crystal X-ray structure of one of the ligands was obtained and was helpful in determining the potential
NOESY interactions within the molecule. For the other ligands, density functional theory (DFT) optimizations was performed
[B3LYP/6-31+g(d)] to visualize possible NOE interactions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
47.
Roy S Banerjee R Nangia A Kruger GJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(14):3777-3788
4,4-Diphenyl-2,5-cyclohexadienone (1) crystallized as four conformational polymorphs and a record number of 19 crystallographically independent molecules have been characterized by low-temperature X-ray diffraction: form A (P2(1), Z'=1), form B (P1, Z'=4), form C (P1, Z'=12), and form D (Pbca, Z'=2). We have now confirmed by variable-temperature powder X-ray diffraction that form A is the thermodynamic polymorph and B is the kinetic form of the enantiotropic system A-D. Differences in the packing of the molecules in these polymorphs result from different acidic C-H donors approaching the C=O acceptor in C-H...O chains and in synthons I-III, depending on the molecular conformation. The strength of the C-HO interaction in a particular structure correlates with the number of symmetry-independent conformations (Z') in that polymorph, that is, a short C-HO interaction leads to a high Z' value. Molecular conformation (Econf) and lattice energy (Ulatt) contributions compensate each other in crystal structures A, B, and D resulting in very similar total energies: Etotal of the stable form A=1.22 kcal mol(-1), the metastable form B=1.49 kcal mol(-1), and form D=1.98 kcal mol(-1). Disappeared polymorph C is postulated as a high-Z', high-energy precursor of kinetic form B. Thermodynamic form A matches with the third lowest energy frame based on the value of Ulatt determined in the crystal structure prediction (Cerius2, COMPASS) by full-body minimization. Re-ranking the calculated frames on consideration of both Econf (Spartan 04) and Ulatt energies gives a perfect match of frame #1 with stable structure A. Diphenylquinone 1 is an experimental benchmark used to validate accurate crystal structure energies of the kinetic and thermodynamic polymorphs separated by <0.3 kcal mol(-1) (approximately 1.3 kJ mol(-1)). 相似文献
48.
We report a high yield, two-step synthesis of fac-[Ru(bpy)(CH3CN)3NO2]PF6 from the known complex [(p-cym)Ru(bpy)Cl]PF6 (p-cym = eta(6)-p-cymene). [(p-cym)Ru(bpy)NO2]PF6 is prepared by reacting [(p-cymene)Ru(bpy)Cl]PF6 with AgNO3/KNO2 or AgNO2. The 15NO2 analogue is prepared using K15NO2. Displacement of p-cymene from [(p-cym)Ru(bpy)NO2]PF6 by acetonitrile gives [Ru(bpy)(CH3CN)3NO2]PF6. The new complexes [(p-cym)Ru(bpy)NO2]PF6 and fac-[Ru(bpy)(CH3CN)3NO2]PF6 have been fully characterized by 1H and 15N NMR, IR, elemental analysis, and single-crystal structure determination. Reaction of [Ru(bpy)(CH3CN)3NO2]PF6 with the appropriate ligands gives the new complexes [Ru(bpy)(Tp)NO2] (Tp = HB(pz)3-, pz = 1-pyrazolyl), [Ru(bpy)(Tpm)NO2]PF6 (Tpm = HC(pz)3), and the previously prepared [Ru(bpy)(trpy)NO2]PF6 (trpy = 2,2',6',2' '-terpyridine). Reaction of the nitro complexes with HPF6 gives the new nitrosyl complexes [Ru(bpy)TpNO][PF6]2 and [Ru(bpy)(Tpm)NO][PF6]3. All complexes were prepared with 15N-labeled nitro or nitrosyl groups. The nitro and nitrosyl complexes were characterized by 1H and 15N NMR and IR spectroscopy, elemental analysis, cyclic voltammetry, and single-crystal structure determination for [Ru(bpy)TpNO][PF6]2. For the nitro complexes, a linear correlation is observed between the nitro 15N NMR chemical shift and 1/nu(asym), where nu(asym) is the asymmetric stretching frequency of the nitro group. 相似文献
49.
Woods KK Maehigashi T Howerton SB Sines CC Tannenbaum S Williams LD 《Journal of the American Chemical Society》2004,126(47):15330-15331
The crystal structure of [d(CGCAAATTTGCG)]2 has been determined to 1.5 A resolution, representing the first high-resolution structure of this DNA fragment. The ion interactions are novel. A spermine molecule replaces a Mg2+ observed in analogous structures. Unlike lower-resolution structures, the minor groove is narrow and the major groove lacks extra Watson-Crick hydrogen bonds. In addition, a monolayer of solvent sites, including a "spine of hydration", is visible in the minor groove. The crystal of [d(CGCAAATTTGCG)]2 was grown from a solution containing spermine, magnesium, and lithium. The conformation recapitulates that of "monovalent-minus" DNA. 相似文献
50.
This paper addresses the complex chemistry in the boundary later over a substrate in a chemical vapor deposition rector at atmospheric pressure. In this study, a highspeed plasma (140m/s) was created using a radio-frequency inductively coupled plasma torch for the deposition of diamond thin films. Growth rates on the order of 50 m/ h were obtained for well-faceted continuous films grown on molybdenum substrates positioned normal to the plasma flow. The highest growth rates were obtained at substrate temperatures of 1370 K and a feed gas ratio of 2.5% CH4 in H2. Growth rates are compared to predicted results obtained from numerical simulations, based on a one-dimensional stagnation-point flow, and are/mend to be in good agreement. Several other surface analysis techniques were used to characterize the deposited films, inchaling SEA/, Raman spectroscopy, transmission electron microscopy. Rutherfard backscattering spectroscopy, and hydrogen-forward recoil spectroscopy. Optical emission spectroscopy was used to characterize the RF plasma during the deposition process. Results from these studies form an important database for the validation and improvement of current models of the atmospheric-pressure diamond CVD environment. 相似文献