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61.
Static pressure usually increases the transition temperatures of polymers by decreasing their free volume. If the pressurizing medium is soluble in the polymer matrix, the opposing effect of increasing the free volume is possible. Those shifts of transition temperatures were monitored with a medium-pressure Differential Scanning Calorimetry (DSC) device. The influences of sorbed and surrounding gas molecules are demonstrated by changes occurring in the transition temperature regions. The results show the severe plasticizing effect of CO2 on poly(p-phenylene sulphide) (PPS). The glass transition temperature TG and the temperature of crystallization TC are influenced by sorbed gas molecules. They decrease due to sorbed CO2 molecules. Glass transition is lowered, but is difficult to interpret, as relaxation phenomena which diminish with increasing pressure occur during DSC runs. In crystallites no gas solution is usually possible, so that the melting point of PPS is mainly affected by influences other than plasticization. 相似文献
62.
Antonio Fernández-Ramos Benjamin A. Ellingson Rubén Meana-Pañeda Jorge M. C. Marques Donald G. Truhlar 《Theoretical chemistry accounts》2007,118(4):813-826
This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them
to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational
symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)
if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers
for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these
four situations are treated systematically and analyzed in detail in the present article. We also include a large number of
examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer. 相似文献
63.
Jacques Barrau Ghassoub Rima Tajani El Amraoui 《Journal of organometallic chemistry》1998,570(2):8645
The reactions of the divalent species (ArO)2M (Ar=2,4,6-[(CH3)2NCH2]3C6H2; M=Ge, Sn) with either Me3SiN3, elemental S8, Se or transition metal complexes M′(CO)n+1 (M′=Fe, n=4; M′=Cr, W; n=5) (Ph3P)2Pt·C2H4 have resulted in the isolation of either the new stable formal metallanimines (ArO)2M=N–SiMe3, germanethione, -selone (ArO)2Ge=E (E=S, Se) (the expected formations of the stannanethione and -selone were not observed), or the (ArO)2M=M′(CO)n, (ArO)2M=Pt(PPh3)2 complexes, respectively. The direct oxidation of the (ArO)2M species with various oxidizing agents led to the formation of the corresponding metalloxanes [(ArO)2M–O–]2. All of the chalcogenido- and transition metal–metal 14 complexes have been physicochemically and chemically characterized. The reactions of the (ArO)2Ge=E (E=S, Se) compounds with 3,5-di-tert-butyl-1,2-benzoquinone produced, by extrusion of sulfur or selenium, the dioxametalloles corresponding to the formal addition of the divalent species (ArO)2M to the benzoquinone. A substitution reaction of chalcogen (S/Se) has been observed permitting to go from germaneselone to germanethione. 相似文献
64.
65.
Daniel Canseco-González 《Journal of organometallic chemistry》2003,679(1):101-109
The complexes cis-[M(Ph2PC6H4-2-S)2] M=Ni, Pd, Pt were stereoselectively synthesized by transmetallation reactions of [M(Cl)2(NCC6H5)2] M=Pd, Pt or NiCl2·6H2O with [Sn(R)2(Ph2PC6H4-2-S)2] R=Ph, nBu or tBu. The conformation of the Pd and Pt derivatives being unequivocally confirmed by single crystal X-ray diffraction studies showing both metal centers to be into a slightly distorted square planar environment, the main distortion being due to the steric hindrance caused by the aromatic rings in the phosphine moiety. 相似文献
66.
Polycrystalline Cu3P was successfully prepared under a wide variety of solvothermal conditions. The reaction of red phosphorus with several copper sources (copper metal, copper (I) iodide, copper (I) chloride and copper (II) chloride) at 150-200 °C for 1-2 days in water produced Cu3P. Products were examined with powder X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Thermal analyses and optical spectroscopy were also performed. A detailed list of reaction conditions, products and impurity phases (where applicable) are reported. 相似文献
67.
A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer trans-[-Pt(PBu3)2CC(p-C6H4)2CC-]n and [HgCC(p-C6H4)2CC-]n were prepared in good yields by Hagihara’s dehydrohalogenation reaction of the corresponding metal chloride precursors with 4,4′-diethynylbiphenyl HCC(p-C6H4)2CCH at room temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model complexes trans-[Pt(Ph)(PEt3)2CC(p-C6H4)2CCPt(Ph)(PEt3)2] and [MeHgCC(p-C6H4)2CCHgMe] as well as the group 11 gold(I) counterpart [(PPh3)AuCC(p-C6H4)2CCAu(PPh3)]. The structural properties of all model complexes have been studied by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) which enables efficient intersystem crossing from the S1 singlet excited state to the T1 triplet excited state. 相似文献
68.
We discuss the impact of density functional electronic structure calculations for understanding the organometallic chemistry of transition metal (TM) surface complexes and clusters. Examples will cover three types of systems, mainly of interest in the context of heterogeneous catalysis: (i) supported carbonyl complexes of rhenium on MgO and of rhodium in zeolites, (ii) TM clusters with CO ligands and adsorbates, and (iii) metal clusters exhibiting chemical bonds with atomic carbon. The first group of case studies promotes the concept that surface groups of oxide supports are bonded to TM complexes in the same way as common (poly-dentate) ligands are bonded in coordination compounds. The second group of examples demonstrates various “ligand effects” of TM clusters. Finally, we illustrate how carbido centers stabilize TM clusters and modify the propensity for adsorption at the surface of such clusters. 相似文献
69.
W. Wasiak 《Chromatographia》1987,23(6):423-426
Summary A column packing containing thiol groups chemically bonded to the silica surface was synthesized. The thiol functional groups were used as ligands capable of forming stable complexes with Cu(II). The prepared material was characterized by gas chromatography using unsaturated linear and branched hydrocarbons as well as cyclic and aromatic hydrocarbons. The occurrence of specific metal—olefin interactions resulting from the formation of -complexes during the chromatographic process was observed.Part IV of a series on transition metal complexes in GC. Part III see ref. [1]. 相似文献
70.
利用abinitio方法对SiH3+O(3P)反应进行了理论研究,在MP2/6-311+G(d,p)水平上优化得到了反应途径上的反应物、中间体、过渡态和产物的几何构型,并在QCISD(T)/6-311+G(d,p)水平上进行单点能计算.计算结果表明,SiH3+O(3P)→IM1→TS3→IM2→TS8→HOSi+H2为主反应通道,其他可能存在的次要产物有HSiOH+H、H2SiO+H和HSiO+H2.HOSi、HSiO和HSiOH(cis)还可能进一步解离生成SiO.另外,计算结果对SiH4+O(3P)反应机理中存在的争议给出了可能的解释,认为Withnall等人在实验中观察到的产物HSiOH、H2SiO和SiO并不是SiH4+O(3P)反应的直接产物,而是来自副反应SiH3+O(3P). 相似文献