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141.
Corbellini F Fiammengo R Timmerman P Crego-Calama M Versluis K Heck AJ Luyten I Reinhoudt DN 《Journal of the American Chemical Society》2002,124(23):6569-6575
Herein we report the formation and characterization of a novel type of capsules resulting from the self-association between oppositely charged complementary building blocks in MeOH/H2O. The assembly is based on the interaction between tetraamidinium calix[4]arenes 1a-d and tetrasulfonato calix[4]arene 2. Evidence for the formation of the expected 1:1 assemblies is provided by proton NMR, ESI-MS, and ITC. The association process is fast on the NMR time scale and strongly entropy driven, with association constants in the range of 10(6) M-1. The system 1a.2 shows binding affinity toward acetylcholine, tetramethylammonium, and N-methylquinuclidinium cations. 相似文献
142.
Summary Reaction of (PPh3)2Cl2CoII with TlC5H5 gave the new (
5-C5H5)(PPh3)ClCoII complex. This complex reacted with Ag(RN3R) or Cu(RN3R) (R=p-MeC6H4,p-ClC6H4 or 3,5-Cl2C6H3) to give the novel compounds (
5-C5H5)(PPh3)(RN3R)CoII, with a spin state of one half, which are representatives of the very small class of paramagnetic monocyclopentadienyl transition metal complexes. The structural conclusions are based on comparison with the isostructural [
5-C5H5)(PPh3)(RN3R)CoIII]PF6 complex, on the i.r. spectra and on the observed redox behaviour. The e.p.r. spectra are reported, but are not well enough resolved for the determination of the hyperfine interactions. The orbital scheme of the new complex is discussed in terms of a distorted octahedral crystal field in relation to the series of isostructural (
5-C5H5)(PPh3)(RN3R)MII (M = Fe, Co or Ni) complexes. 相似文献
143.
DirkJ.A. DeRidder Kees Goubitz Henk Schenk Bert Krijnen JanW. Verhoeven 《Helvetica chimica acta》2003,86(3):799-811
The crystal structures of five N‐arylpiperidin‐4‐one derivatives 2P2, 3P2, 5P2, 1P3 , and 2P3 are presented (Fig. 2 and Tables 1–5) and discussed together with the derivatives 1P2 and 4P2 published previously. In all but one structure, 1P2 , the aryl group is in an equatorial position. The piperidine ring adopts a normal chair conformation. In 1P2 , the piperidine ring central C? C bonds are significantly elongated, which is consistent with the idea that through‐bond interaction is more pronounced in the axial conformation. Through‐bond interaction also influences the pyramidalization at the piperidine C(4)‐atom in such a way that a strong interaction is directing the ethylene C‐atom C(9) into the axial direction. 相似文献
144.
Katrien Monsieurs Kristof T.J. Loones J.A. Dirk De Ridder Kees Goubitz Roger A. Dommisse Bert U.W. Maes 《Tetrahedron》2007,63(18):3870-3881
In search for the structural elucidation of samoquasine A, a natural product isolated from the seeds of Annona squamosa L., two benzo[f]phthalazinone isomers have been synthesized. The synthetic pathway followed to build up these skeletons is based on the combination of two Suzuki reactions on a pyridazinone precursor and a ring closure reaction via a condensation reaction. 1H NMR data of the synthesized compound allowed to establish that the structure of the natural product samoquasine A is not benzo[f]phthalazin-4(3H)-one, as previously suggested. 相似文献
145.
Frank van Mourik Kees J. Visscher Jan M. Mulder Rienk van Grondelle 《Photochemistry and photobiology》1993,57(1):19-23
–Triplet-minus-singlet (T-S) spectra and singlet-triplet annihilation was measured on Rhodospirillum rub-rum chromatophores at low temperatures (4–77K). The T-S spectrum of the LH-1 antenna was dependent on the wavelength of excitation and thus indicative of site-inhomogeneous broadening. The data cannot be understood adequately using the two pigment pool model (B880 + B896) but, in contrast, support a model for LH-1, in which the spectral properties are determined by site-inhomogeneous broadening. Consequently, the 4 K antenna domain for singlet-triplet annihilation in LH-1 is rather small. If the temperature is raised to 77 K the annihilation domain increases, and a fit of the fluorescence quenching and triplet yield data suggests that at 77 K the connectivity is between the extreme cases of the “lake” and the isolated “puddles” models. The implications of the observed antenna inhomogeneity on low temperature annihilation and fluorescence measurements are discussed. 相似文献
146.
Kaletas BK Joshi HC van der Zwan G Fanti M Zerbetto F Goubitz K De Cola L König B Williams RM 《The journal of physical chemistry. A》2005,109(42):9443-9455
The spectroscopic properties of two asymmetric indolylmaleimide derivatives, 4-bromo-3-(1'H-indol-3'-yl)maleimide and 4-methyl-3-(1'H-indol-3'-yl)maleimide, are investigated. The bromo derivative was crystallized and its X-ray structure was determined. Both compounds are strongly colored while their separate components (indole and maleimide) absorb in the UV region only. To understand the ground- and excited-state behavior, the photophysical properties of the two compounds were studied in detail by steady state and time-resolved absorption and emission spectroscopy. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach, which indicates some charge transfer (CT) character in the excited state. Nano- and femtosecond transient absorption spectroscopy was used for the identification and investigation of the CT state. Furthermore, the effect of the complexation with zinc(II) 1,4,7,11-tetraazacyclododecane (Zn-cyclen) on the photophysical properties of these two compounds was studied. An enhancement of the fluorescence intensity upon self-assembly (up to 90 times) and high association constants were observed, which illustrate the potential use of these compounds as luminescent sensors. DFT calculations indicate that HOMO-1 to LUMO excitation is mainly responsible for the charge transfer character and that this transition changes its character drastically when Zn-cyclen complexation occurs, thus giving it sensor properties. 相似文献
147.
The formation of carbon tetrachloride‐benzene charge transfer complex was confirmed by UV and NMR spectrometric studies. A change in UV spectrum of benzene is observed upon addition of carbon tetrachloride. Whereas the appearance of new bands supports the formation of charge transfer complex. NMR study shows that, chemical shift of benzene pmr signal depends on the CCl4‐C6H6 molar ratio. This observation is another criterion for the formation of benzene‐carbon tetrachloride charge transfer complex. Job's Continuous Variation method indicates that a 2:1 CCl4‐C6H6 charge transfer complex (2:1 CTC) is formed. The association constants (K2:1) of (2:1 CTC) was found to be 0.0197 M?2. The maximum concentration of (2:1 CTC) was found to be in samples with 2:1 CCl4‐C6H6 molar ratio (33% benzene mole). On the other hand the maximum yield of chlorobenzene was obtained, also, upon radiolysis of CCl4‐C6H6 samples at a 2:1 molar ratio (33% benzene mole). Therefore, it could be concluded that (2:1 CTC) participates in the formation of chlorobenzene upon radiolysis of the benzene‐carbon tetrachloride system. This conclusion was supported by the dependence of the chlorobenzene yield of a γ‐irradiated carbon tetrachloride‐benzene system (2:1 molar ratio) on irradiation time according to a third order kinetic equation with a very good linearity (R2 = 0.9977). Accordingly, the rate constant for the chlorobenzene formation under this condition was found to be ≈ 5.5 × 10?7 L2.mol?2.h?1. We propose a radiation chemical mechanism in which the 2:1 CTC plays a role in the formation of chlorobenzene. 相似文献
148.
Johan W. Gosselink Gerard van Koten Kees Vrieze Binne Zwanenburg Ben H.M. Lammerink 《Journal of organometallic chemistry》1979,179(4):411-419
Reactions of Pt(PPh3)4 with the sulfines, XYCSO, (X, Y = aryl, S-aryl, S-alkyl, Cl) yield coordination compounds of the type Pt(PPh3)2(XYCSO). Infrared, 31P and 1H NMR spectra reveal that in all cases the sulfine ligand is coordinated side-on via the CS π-bond (Pt—η2-CS). Reactions of Pt(PPh3)4 with either the E- or Z-isomer of (p-CH3C6H4)(CH3S)CSO yields the corresponding E- or Z-coordination compound, Pt(PPh3)2[E-(p-CH3C6H4)(CH3S)CSO] or Pt(PPh3)2[Z-(p-CH3C6H4)(CH3S)CSO], indicating that the configuration of the sulfine ligand is retained upon coordination to the Pt(PPh3)2 unit. The compounds Pt(PPh3)2(XYCSO), containing reactive CX and/or CY bonds (X, Y = S-aryl, S-alkyl, Cl), undergo a rearrangement in solution to give complexes of the type PtX(PPh3)2(YCSO). 相似文献
149.
Kees de Jager 《Progress in Particle and Nuclear Physics》2008,61(1):311-324
Preliminary results of a selected few recent experiments at JLab are presented. 相似文献
150.
Brookman Brian Butler Owen Ciaralli Laura Horsky Monika Laurent Caroline Noblett Tracey Örnemark Ulf Patriarca Marina Sibbesen Lorens P. Tiikkainen Ulla van Putten Kees Robouch Piotr 《Accreditation and quality assurance》2019,24(1):93-101
Accreditation and Quality Assurance - A summary of the working group discussions on proficiency testing (PT) and external quality assessment (EQA) held at the Eurachem Workshop, Portorož,... 相似文献