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61.
Frazier BA Bartholomew ER Wolczanski PT DeBeer S Santiago-Berrios M Abruña HD Lobkovsky EB Bart SC Mossin S Meyer K Cundari TR 《Inorganic chemistry》2011,50(24):12414-12436
A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru). Metathesis of VCl(3)(THF)(3) with 2 Li(smif) with a reducing equiv of Na/Hg present afforded 1-V, while 2 Na(smif) and IrCl(3)(THF)(3) in the presence of NaBPh(4) gave [(smif)(2)Ir]BPh(4) (1(+)-Ir). Electrochemical experiments led to the oxidation of 1-M (M = Cr, Mn, Co) by AgOTf to produce [(smif)(2)M]OTf (1(+)-M), and treatment of Rh(2)(O(2)CCF(3))(4) with 4 equiv Na(smif) and 2 AgOTf gave 1(+)-Rh. Characterizations by NMR, EPR, and UV-vis spectroscopies, SQUID magnetometry, X-ray crystallography, and DFT calculations are presented. Intraligand (IL) transitions derived from promotion of electrons from the unique CNC(nb) (nonbonding) orbitals of the smif backbone to ligand π*-type orbitals are intense (ε ≈ 10,000-60,000 M(-1)cm(-1)), dominate the UV-visible spectra, and give crystals a metallic-looking appearance. High energy K-edge spectroscopy was used to show that the smif in 1-Cr is redox noninnocent, and its electron configuration is best described as (smif(-))(smif(2-))Cr(III); an unusual S = 1 EPR spectrum (X-band) was obtained for 1-Cr. 相似文献
62.
Márquez JM Martínez-Castro E Gabrielli S López Ó Maya I Angulo M Álvarez E Fernández-Bolaños JG 《Chemical communications (Cambridge, England)》2011,47(19):5617-5619
We report the synthesis of the hitherto unknown zwitterionic alkoxyamino cyanoboranes by reduction of O-alkyloximes with sodium cyanoborohydride; unprecedented cyanoboronated N-alkoxyformamidines were also isolated as by-products. Boronated alkoxyamines were found to be efficient cyanoborane transfer agents towards more basic amines, including aminosugars; they were also successfully transformed into neoglycoconjugates by the neoglycorandomization reaction with reducing sugars. 相似文献
63.
J.L. Costa-Krämer M. Díaz P.A. Serena 《Applied Physics A: Materials Science & Processing》2005,81(8):1539-1543
Conductance histograms have become a powerful tool for studying transport properties of metallic nanowires. However, the
individual conductance curves display a very rich structure that might be concealed by the statistical procedure of finding
preferred conductance values by building conductance occurrence histograms using consecutive nanocontact breakage experiments.
This is particularly true when it comes to discerning 1/2G0=e2/hquantization in magnetic nanowires. The effect of disorder, added to possible magnetic sources of scattering, and different
magnetic states of different nanowires, might hide its appearance as histogram peaks. This work analyzes and compares Ni and
Cu nanowire experimental histograms at room temperature (RT). Those obtained with no curve selection criteria are basically
unaffected by the presence of a magnetic field. A selection of particular sets of conductance curves shows that conductance
quantization could occur in steps of e2/h and 2e2/h in Ni as well as in Cu in the presence or absence of a magnetic field. Sorting out curves in sets that present conductance
plateaus at half integer and integer values, and compiling statistics on the number of such curves that appear, depending
on the applied magnetic field, results in differences between the behaviour of Cu and Ni. While for Cu, the magnetic field
keeps the ratio of curves that present plateaus at 1/2G0with respect those presenting G0 plateaus unchanged; for Ni, the number of curves which exhibit plateaus at just G0 almost disappears with the applied field. This experimental fact might indicate that the magnetic field removes spin degeneracy
in these magnetic nanowires.
PACS 72.25.Ba; 73.40.Jn; 73.63.Rt; 75.75.+a 相似文献
64.
Kretz T Bats JW Losi S Wolf B Lerner HW Lang M Zanello P Wagner M 《Dalton transactions (Cambridge, England : 2003)》2006,(41):4914-4921
Cationic dinuclear Cu(II) complexes 3 and 4 have been prepared using the novel hydroquinone-based imine chelators 2,5-((i)Pr(2)NCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (1) and 2,5-(pyCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (2), respectively (py = 2-pyridyl). X-Ray quality crystals of both complexes were grown from their DMF solutions. The sterically more encumbered compound crystallizes in the form of discrete dinuclear entities with Cu(II) centres in a distorted square-planar ligand environment (one coordination site is occupied by a DMF molecule). The pyridyl derivative 4 features dinuclear hydroquinone-bridged subunits similar to 3. However, the Cu(II) ions are now six-coordinate with two DMF molecules at an axial and an equatorial position of a Jahn-Teller-distorted octahedron. Moreover, the dinuclear subunits are no longer isolated but linked with each other via bridging hydroquinone oxygen atoms which occupy the second apical position of each octahedron. The structure suggests that the magnetic properties of the resulting coordination polymer of 4 could be described by a model valid for dimerized spin chains. As a result of this analysis the antiferromagnetic coupling constants J(1)/k(B) = 9.9 K (intradimer) and J(2)/k(B) = 0.9 K (interdimer) are obtained. Both in 3 and in 4, the hydroquinone --> semiquinone transition of the central bridging unit (E degrees ' = + 0.57 V, 3; E degrees ' = + 0.51 V, 4; DMF; vs. SCE) displays features of chemical reversibility. In the case of , reduction of Cu(II) centres requires a peak potential of E(p) = - 0.42 V. 相似文献
65.
Tebben L Neumann M Kehr G Fröhlich R Erker G Losi S Zanello P 《Dalton transactions (Cambridge, England : 2003)》2006,(14):1715-1720
[3]Ferrocenophanone rac-8 was prepared by several non-Friedel-Crafts pathways starting from a Mannich-type coupling of 1,1'-diacetylferrocene followed by catalytic hydrogenation. Hydride abstraction from the resulting alpha-dimethylamino[3]ferrocenophane rac-14 with B(C6F5)3 followed by hydrolysis gave the ketone rac-8. Several variants of the Sommelet reaction, using ethylglyoxylate, formaldehyde or hexamethylenetetramine (urotropine) as the "oxidizing" reagent gave the alpha-[3]ferrocenophanone 8 in good to excellent yield. Some variants of these reactions were also used for the preparation of the pure enantiomer (R)-8. The electrochemical behaviour of 8 has been investigated and compared with related derivatives. 相似文献
66.
Corr SA O'Byrne A Gun'ko YK Ghosh S Brougham DF Mitchell S Volkov Y Prina-Mello A 《Chemical communications (Cambridge, England)》2006,(43):4474-4476
Fluorescent magnetite nanocomposites based on magnetic nanoparticles, a polyhedral octaaminopropylsilsesquioxane and a porphyrin derivative have been prepared. The intracellular uptake of the nanocomposites by macrophage and bone osteoblast cells, and their potential as MRI contrast agents, has been demonstrated. 相似文献
67.
Valli L Casilli S Giotta L Pignataro B Conoci S Borovkov VV Inoue Y Sortino S 《The journal of physical chemistry. B》2006,110(10):4691-4698
This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin dimers (1) in Langmuir-Sch?fer (LS) thin films by combining scanning force microscopy (SFM) with film balance, UV-vis absorption, fluorescence, and nanosecond laser flash photolysis measurements. Results show that depending on the surface pressure the Langmuir films of pure 1 can be arranged in two different condensed phases, whereas SFM of the LS films shows characteristic fractal networks constituted by nanoscopic aggregates. The spectral findings agree with a picture in which 1 is apparently present in the anti conformation but aggregated in a sort of H-type structure whose optical features resemble those of the syn conformer. This type of structure is not responsive to light stimuli. By diluting 1 in arachidic acid the porphyrin aggregation is significantly minimized with 1 exhibiting almost exclusively the anti conformation. As a result the LS films become photoresponsive, showing fluorescence emission and triplet-triplet transient absorption. 相似文献
68.
John Bargar Serena DeBeer George Hendrik Ohldag Gordon Brown 《Synchrotron Radiation News》2013,26(2):22-24
Scanning transmission X-ray microscopy (STXM) has emerged as an important technique for chemical imaging and spectromicroscopy on the <100nm spatial scale in the environmental, geological, and biomedical sciences. Much has transpired technologically and scientifically in the 20-plus year interval that zone-plate STXM technology has been in development. Yet STXM/nanoprobe facilities are few in number, beam time remains exceedingly tight, and numerous scientific, technical, and infrastructure challenges continue to present significant barriers to the widespread use of these techniques in these three areas of science. 相似文献
69.
Marco Mazzucchelli 《Mathematische Zeitschrift》2013,275(3-4):715-739
We provide a simple proof of a theorem due to Nancy Hingston, asserting that symplectically degenerate maxima of any Hamiltonian diffeomorphism $\phi $ of the standard symplectic $2d$ -torus are non-isolated contractible periodic points or their action is a non-isolated point of the average-action spectrum of $\phi $ . Our argument is based on generating functions. 相似文献
70.
In this article a class of subgroups of a finite group G, called Q-injectors, is introduced. If G is soluble, the Q-injectors are precisely the injectors of the Fitting sets. A characterization of nilpotent Q-injectors is given as well as a sufficient condition for the solubility of a finite group G, in terms of Q-injectors, which generalizes a well known result. 相似文献