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991.
Kaj Heydorn 《Accreditation and quality assurance》2006,10(9):479-484
Proficiency data with stated uncertainties represent a unique opportunity for testing that the reported uncertainties are consistent with the Guide to the expression of uncertainty in measurement (GUM). In most proficiency tests, however, this opportunity is forfeited, because proficiency data are processed without regard to their uncertainties. In this paper we present alternative approaches for determining a reference value as the weighted mean of all mutually consistent results and their stated uncertainties. Using an accepted reference value each reported uncertainty estimate can be expressed as an E
n
number, but a value of confirms its validity only if the uncertainty of the reference value is negligible in comparison.Reference values calculated for results from an International Measurement Evaluation Programme (IMEP-9) by “bottom up” as well as “top down” methods were practically identical, although the first strategy yielded the lowest uncertainty. A plot of individual coefficients of variation (CV) versus E
n
numbers helps interpretation of the proficiency data, which could be used to validate relative uncertainties down to <1%. 相似文献
992.
Jianmin Dou Daopeng Zhang Dacheng Li Daqi Wang 《Journal of organometallic chemistry》2006,691(26):5673-5679
Three nickel(II) carborane complexes, [Ni2(μ-Cl)2{7,8-(PPh2)2-7,8-C2B9H10}2] (1), [Ni{7-(OPPh2)-8-(PPh2)-7,8-C2B9H10}{7,8-(PPh2)2-7,8-C2B9H10}] (2) and [NiBr2{1,2-(PPh2)2-1,2-C2B10H10}] · CH2Cl2 (3), have been synthesized by the reactions of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane with NiCl2 · 6H2O or NiBr2 · 6H2O in ethanol under different conditions, respectively. For complex 1, it could also be obtained under the solvothermal condition. All the three complexes were characterized by elemental analysis, FT-IR, 1H and 13C NMR spectroscopy and X-ray structure determination. Single crystal analysis shows that the molecular symmetry of complex 1 is centrosymmetric, containing two same structure units - Ni(7,8-(PPh2)2-7,8-C2B9H10) linked by two bridged-Cl atoms. The central square plane formed by the [Ni2Cl2] unit is almost parallel to the two side NiPP planes. For complex 2, the coordination environment of the Ni atom is a seriously distorted square-planar, in which two positions come from the chelating diphosphine ligand [7,8-(PPh2)2-7,8-C2B9H10]− degraded from the closo species, while the other two are occupied by an unsymmetrical chelating phosphine oxide ligand [7-(OPPh2)-8-(PPh2)-7,8-C2B9H10]−. As for complex 3, the geometry at the Ni atom is a slightly distorted square-planar. The closo carborane diphosphine ligand 1,2-(PPh2)2-1,2-C2B10H10 was coordinated bidentately to the metal ion through the two phosphorus atoms, and the two Br atoms are at cis position which can fulfill the four coordination mode of the metal. 相似文献
993.
The complexes of the type (ArCH2)2SnO were catalytic-oxygenated by Ag+ and yielded mixed-ligand organotin(IV) complexes (ArCH2)(2-C5H4NCO2)2(ArCOO)tin(IV) (Ar = C6H5 (1), 2-ClC6H4 (2), 2-CNC6H4 (3), 4-ClC6H4 (4), 4-CNC6H4 (5), 2-FC6H4 (6)). The complexes 1-6 are characterized by elemental analyses, IR and NMR (1H, 13C, 119Sn) spectroscopies. Single X-ray crystal structure analysis has been determined, which reveals that the center tin atom of complex 2 is seven-coordinated geometry. 相似文献
994.
R.M.G. Roberts 《Journal of organometallic chemistry》2006,691(12):2641-2647
A series of reactions have been used to introduce oxygen substituents into (η-arene)(η-cyclopentadienyl) iron (II) complexes. Photochemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species. Using microwave techniques, reaction times for SNAr displacement reactions of halobenzene complexes by phenols were reduced from several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also reported.The Nef reaction has been adapted to convert (η6-α-nitroalkylarene)(η5-Cp) iron (II) salts to corresponding aldehyde and ketone complexes. The α-nitroalkyl arene complexes were synthesised in good yields from (η6-halobenzene)(η5-Cp) iron (II) complexes using NaOtBu in DMSO. H/D exchange reactions with 2[H]6-DMSO in the presence of K2CO3 showed partial D incorporation in the methyl group for the unreacted α-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion of the α-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three methods:
- (A)
- H2O2 and NaOtBu in DMSO followed by reaction with CF3CO2H.
- (B)
- SnCl2/aq. HCl.
- (C)
- K2CO3 in DMF using microwave-mediated reactions.
995.
Kang Min Ok 《Journal of solid state chemistry》2006,179(5):1345-1350
A new one-dimensional tellurite phosphate, Ba2TeO(PO4)2 has been synthesized by standard solid-state reaction techniques using BaCO3, TeO2, and (NH4)H2PO4 as reagents. The structure of Ba2TeO(PO4)2 was determined by single-crystal X-ray diffraction. Ba2TeO(PO4)2 crystallizes in the triclinic space group P-1 (No. 2), with , , , α=76.843(4)°, β=79.933(4)°, γ=75.688(4)°, , and Z=2. Ba2TeO(PO4)2 has a novel one-dimensional chain structure that is composed of PO4 tetrahedra and TeO5 polyhedra. Te4+ cations are in asymmetric coordination environments attributable to their lone pairs. The lone pairs on the Te4+ cations point in the [100] and [−100] direction and interact with the Ba2+ cations. Infrared, Raman, and UV-Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are also presented. 相似文献
996.
Leonid N. Bochkarev Vladislav I. Scherbakov Irina P. Malysheva Galina V. Basova Natalia E. Stolyarova Irina K. Grigorieva Andrey L. Bochkarev Georgii K. Fukin Yurii A. Kurskii Gleb A. Abakumov 《Journal of organometallic chemistry》2006,691(5):983-986
The novel silicon-, germanium- and tin-containing imido alkyl complexes of tungsten of the type (ArN)2W(CH2EMe3)2 (; E = Si (1), Ge (2), Sn (3)) have been prepared by the reactions of (ArN)2WCl2(dme) (dme = 1,2-dimethoxyethane) with heteroelement-containing alkyllithium or Grignard reagents Me3ECH2Li (E = Si, Ge), Me3ECH2MgCl (E = Ge, Sn). The title compounds were isolated in high yields as crystalline solids and characterized by elemental analysis, IR, 1H, 13C, 29Si and 119Sn NMR spectroscopy and X-ray diffraction studies. The geometry of the W atoms in the compounds can be described as a distorted tetrahedron. 相似文献
997.
A number of new, layered nitride mixed halides have been synthesised in the quaternary phase systems Sr-N-Cl-Br and Sr-N-Br-I. The variation in structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques and the structure of strontium nitride iodide, Sr2NI, has been determined for the first time (rhombohedral space group R-3m, , , Z=3). A continuous solid solution exists between Sr2NCl and Sr2NBr with intermediate compounds adopting the same anti-α-NaFeO2 structure (rhombohedral space group R-3m) as the ternary end members. A similar smooth and linear relationship between structure and composition is seen from Sr2NBr to Sr2NI and hence cubic close packing of metal-nitrogen layers is adopted regardless of halide, X (X′). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of the halides in the quaternary materials irrespective of stoichiometry or temperature (between 3 and 673 K). 相似文献
998.
A.M. Alekseeva A.M. Abakumov A. Leithe-Jasper Yu. Prots G. Van Tendeloo Yu. Grin 《Journal of solid state chemistry》2006,179(9):2751-2760
The new magnesium rhodium boron compound Mg8Rh4B has been synthesized by reaction of the metal powders with crystalline or amorphous boron or the RhB precursor. The crystal structure of Mg8Rh4B was solved using single-crystal X-ray diffraction data (space group , , Z=8, 174 reflections, RF=0.016). The crystal structure can be described as a filled Ti2Ni type where the interstitial sites 8b (), located at the center of two nested Mg4Rh4 tetrahedra, are occupied by boron atoms. Taking into account the absence of the Ti2Ni-type phase in the binary Mg-Rh system, the boron atoms can be considered as stabilizing this structural motif. From the bonding analysis with the electron localization function the crystal structure is described as covalently bonded [Rh4B]3− anions, embedded in a cationic magnesium matrix. 相似文献
999.
Two sets of ancient roman Egyptian blue (EB) samples and one set of EB samples synthesised in our lab, were analysed by EPR spectroscopy, a technique not commonly used in this field. The spectroscopic parameters obtained were used to attempt the discrimination of the provenance and of the manufacturing techniques of the investigated samples.The results obtained show that EPR technique could be very useful for this purpose.Furthermore, the similarity of the obtained parameters between the ancient and new samples testify the successful attempt to reproduce the EB according to the chemical knowledge. 相似文献
1000.
New β,β′-aryl/heteroaryl 2,3-divinylfuran derivatives (9a-d) in which a hexatriene system is a part of heteroaromatic ring have been synthesized and their photochemical properties were investigated. The primary process observed was the isomerization to trans,trans-isomers 9a-d followed by photochemical rearrangement of the furan ring giving the phototransposition products (I-IV). Stilbenes (20, 21) and phenanthrenes (22, 25, and 26), formed as secondary products from the competitive intermolecular cycloadditions, were also observed. 相似文献