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81.
Reaction of [Mo(CO)4(diene)] with 4,4′-bipyridine (44′B), trans-1,2-bis(2-pyridyl)ethene (2-bpe) and trans-1,2-bis(4-pyridyl)-ethene (4-bpe) gives polymeric [Mo(CO)4(44′B)]n, mononuclear cis-[Mo(CO)4(2-bpe)2] and binuclear [Mo(CO)4(4-bpe)]2 respectively. Reaction of the same ligands with [Mo(CO)4(bpy)] (bpy is 2,2′-bipyridine) produces the bridged binuclear complexes [{Mo(CO)3(bpy)}2(44′B)] and [{Mo(CO)3(bpy)}2(4-bpe)]. Products are characterised by microanalysis and spectroscopy (IR, 1H NMR, UV/vis). Reduction of [{Mo(CO)3(bpy)}2(44′B)] produces an anion in which the unpaired electron is localised on the chelating bpy ligand. 相似文献
82.
MS -Xα calculations have been performed for the neutral species and the transition states for the positive and negative ions of the heavy metal atoms Mo, W, Re, Ir, Pt, and U and their diatomic hydrides and fluorides. Both nonspin-polarized and spin-polarized calculations were performed. The main purpose of this study was to gain insight into which negative ion species might be preferable to try to prepare for use in ion sources for tandem accelerators. 相似文献
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A novel method for calculation of Hele-Shaw flows with receding free boundaries is presented. The method is applied to flows with suction from a point sink and to flow in a channel with parallel walls. In each case the unknown fluid region is mapped conformally onto the unit disc, the free boundary being mapped onto the unit circle. This mapping, which is a function of position and time, is calculated numerically at points on the unit circle using a version of the boundary integral method. The free boundary is thus found without explicit calculation of the pressure at internal points, and the computation times are much less than those for other numerical methods for this problem. Numerical results are compared with explicit analytic solutions for several test problems. 相似文献
86.
J. H. Neave P. J. Dobson J. J. Harris P. Dawson B. A. Joyce 《Applied Physics A: Materials Science & Processing》1983,32(4):195-200
Two concentration ranges of silicon doping in MBE-grown GaAs films have been investigated in some detail. In lightly doped films, with a free-electron concentration of ≈1016cm?3, low-temperature photoluminescence spectra have been analysed to develop a model to account for spectral features previously attributed to Ge and Si acceptor levels. In heavily doped films, a maximum free-electron concentration of ≈7×1018 cm?3 has been obtained, which is only rather weakly dependent on growth conditions and the nature of the arsenic species (As2 or As4). Transmission electron microscopy has shown that no significant precipitation effects occur when higher Si fluxes are used but there is evidence for autocompensation. The maximum PL intensity (300 K) is found at a lower free electron concentration then with Sn-doped films, and is more sharply peaked, but there is no evidence for an anomalous Moss-Burstein shift. 相似文献
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The surge of information generated by the Human Genome Project has left many health professionals and their patients struggling to understand the role of genetics in health and disease. To aid the lay public and health professionals, the US National Library of Medicine developed an online resource called 'Genetics Home Reference' (GHR), located at http://ghr.nlm.nih.gov/. Launched in April 2003, GHR's goal is to help the public interpret the health implications of the Human Genome Project. It bridges the clinical questions of consumers and the rich technical data emerging from the sequenced human genome. The GHR web site is designed for easy navigation among summaries for genetic conditions and the related gene(s) and chromosome(s). This design strategy enhances the user's appreciation of how genes, chromosomes, and conditions are interrelated. 相似文献
90.
Danni Wu Kathleen Joyce D. Carillo Shen‐Long Tsai Jiun‐Jie Shie Der‐Lii M. Tzou 《中国化学会会志》2019,66(10):1318-1326
The neurosteroid trans‐dehydroandrosterone (DHEA) and its analogs with slightly different modifications in the side chain attached to C17, that is, (3S)‐acetoxypregn‐5‐en‐20‐one ( 1 ) and (3S,20R)‐acetoxypregn‐5‐en‐20‐ol ( 2 ), have been synthesized to investigate DHEA–cation interactions. In this study, we applied solid‐state 1H/13C cross‐polarization/magic‐angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy to a series of DHEA analog/Mg2+ mixtures at different Mg2+ concentrations. The high‐resolution 13C NMR spectra of 1 /Mg2+ mixtures exhibit two distinct 13C spectral patterns, one attributable to 1 free from Mg2+, and the other attributable to 1 with bound Mg2+. For 2 , the 13C NMR spectra exhibit three distinct spectral patterns; besides that of the free form, the other two can be assigned to Mg2+‐bound forms. Based on the analysis of the chemical shift deviations (CSDs), we conclude that both 1 and 2 might be subject to a cation–π interaction via the C5–C6 double bond, in contrast to that observed previously for DHEA. As demonstrated, DHEA possesses two Mg2+ binding sites, that is, C17–O and C5–C6 double bond, in which the binding affinity of the former is at least three times stronger than that of the latter. The solid‐state 13C NMR investigation allows better understanding of the underlying cation binding effects of neurosteroid molecules in vitro. 相似文献