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1.
Dr. David J. Lurie I. Nicholson J. S. McLay J. R. Mallard 《Applied magnetic resonance》1992,3(5):917-925
The technique of Field-Cycled Dynamic Nuclear Polarization (FC-DNP) involves the EPR irradiation of a free radical solution and the subsequent observation of the NMR signal, the experiment being carried out at a range of magnetic field strengths in order to measure the free radical’s EPR spectrum. In this work FC-DNP has been used to study the EPR spectrum of DMPO spin-trapped hydroxyl free radicals at magnetic field strengths between 0.5 mT and 13.0 mT (5–130 Gauss). The low-field EPR spectrum contains six separate EPR lines, in contrast to the well-known X-band spectrum where only four are seen. Knowledge of the spin-adduct’s EPR spectrum will be of use to workers involved in low-field EPR, especially those conducting biological or in-vivo spin-trapping experiments. 相似文献
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The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid-fluid interaction, sites with varying degree of affinity), (ii) fluid-fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å. 相似文献
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Stephen G. Davies Ian A. Hunter Rebecca L. Nicholson Paul.M. Roberts Edward D. Savory Andrew D. Smith 《Tetrahedron》2004,60(35):7553-7577
α-Dibenzylamino- and α-benzyloxy- derivatives of N-acetyl-(S)-4-benzyl-5,5-dimethyloxazolidin-2-one readily undergo highly stereoselective boron mediated syn-aldol reactions with a range of aromatic and aliphatic aldehydes, generating the syn-aldol products in good to excellent yields as single diastereoisomers after purification. In the α-dibenzylamino series, deprotection of the functionalised aldol fragments to the corresponding α-amino-β-hydroxy methyl ester or α-amino-β-hydroxyaldehyde proved problematic, with a range of N- and O-protecting groups giving mixtures of products arising from endocyclic and exocyclic cleavage pathways. However, in the α-benzyloxy series, O-silyl protection of the aldol products, and subsequent DIBAL reduction gives stereoselectively the corresponding N-1′-hydroxyalkyloxazolidin-2-ones, which undergo base promoted fragmentation to the desired highly functionalised and differentially protected α,β-dihydroxyaldehydes in good yields and without loss of stereochemical integrity. 相似文献
7.
Jensen BP Smith CJ Bailey CJ Rodgers C Wilson ID Nicholson JK 《Rapid communications in mass spectrometry : RCM》2005,19(4):519-524
Inductively coupled plasma mass spectrometry (ICPMS) has been used to determine the rate and routes of excretion of bromine following the intraperitoneal administration (50 mg kg(-1)) of 2-, 3- and 4-bromobenzoic acids to male bile-duct-cannulated rats. Analysis of urine and bile for (79/81)Br using ICPMS showed that all three bromobenzoic acids were rapidly excreted (82-98%) within 48 h of dosing, primarily via the urine. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) was then used to obtain metabolite profiles for bile and urine. These profiles revealed that extensive metabolism had taken place, with the unchanged bromobenzoic acids forming a minor part of the total of compound-related material detected. Concomitant MS studies, supplemented by alkaline hydrolysis, enabled the identification of the major metabolite of all three of the bromobenzoic acids as a glycine conjugate. Ester glucuronide conjugates were also identified, but formed only a small proportion of total. 相似文献
8.
Bailey NJ Stanley PD Hadfield ST Lindon JC Nicholson JK 《Rapid communications in mass spectrometry : RCM》2000,14(8):679-684
Reconstructed ion chromatograms have been used to identify relevant high performance liquid chromatography (HPLC) peaks in a directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry (HPLC/NMR/MS) experiment. This has been applied to a study of the metabolism of a model compound, 5-nitropyridone (2-hydroxy-5-nitropyridine), in maize plants grown hydroponically. By monitoring the on-flow reconstructed ion chromatogram corresponding to the 5-nitropyridone fragment at m/z 143, and additional molecular ions corresponding to metabolites identified as products from similar compounds, relevant peaks were identified rapidly for subsequent stopped-flow 1H NMR spectroscopic analysis. The combination of coupled HPLC/NMR/MS enabled the direct identification of three metabolites, namely the N-glucoside, N-malonylglucoside, and O-malonylglucoside. This work demonstrates the power of HPLC/NMR/MS for the structural elucidation of xenobiotic metabolites in complex biological matrices (such as plant material) with minimal sample preparation. In particular, using mass spectrometry for the initial identification of relevant HPLC peaks allows the analysis of complex samples without the necessity for other spectroscopic markers, such as 19F NMR signal for fluorinated compounds or UV spectroscopy for molecules with strong UV chromophores. 相似文献
9.
Brian K. Nicholson 《Journal of organometallic chemistry》1992,440(3):411-418
The specific additions of one, three or four Ph3PAu groups to [M(CO)5]− (M=Mn, Re) are described. Thus [M(CO)5] − in THF reacts with [(Ph3PAu)3O]BF4 to give [(Ph3PAu)4Mn(CO)4]BF4. An X-ray crystal structure of the M = Mn example shows the cation to have a trigonal bipyramidal Au4Mn core with the Mn in an equatorial site. The previously known neutral (Ph3PAu)3M(CO)4 clusters are formed by addition of two Ph3PAu groups, using the mixed reagent [(Ph3PAu) 3O]BF4/[ppn][Co(CO)4], to Ph3PAuM(CO)5, which itself is readily prepared from [M(CO)5]− and Ph3PAuCl. 相似文献
10.
Michael I. Bruce Omar bin Shawkataly Brian K. Nicholson 《Journal of organometallic chemistry》1985,286(3):427-437
H2Ru3(μ3-S)(CO)9 is deprotonated by K[HBBus3] to give cluster anions which react with [O{Au(PPh3)}3]+ or with AuCl(PPh3)/T1+ to give HRu3Au(μ3-S)(CO)9(PPh3) (1) and Ru3Au2(μ3-S)(CO)9(PPh3)2 (3). A similar sequence with HRu3(μ3-SBut)(CO)9 leads to Ru3Au(μ3-SBut)(CO)9(PPh3) (2) as the main product although some 1 also forms, indicating SC cleavage competes with deprotonation of HRu3(μ3-SBut)(CO)9 by [HBBus3]?. The X-ray crystal structures of 1, 2 and 3 are described; (1) and (2) have “butterfly” AuRu3 cores with markedly different hinge angles of 119 and 148° respectively, while 3 has a trigonal-bipyramidal Au2Ru3 skeleton. All three clusters have the sulphur atom symmetrically bridging the Ru3 triangular face. 相似文献