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71.
C.S. YangD.Z. Jeng Yaw-Jou YangHong-Rong Chen C. Gau 《Experimental Thermal and Fluid Science》2011,35(1):73-81
Experiments have been performed to study the heat transfer process of swirling flow issued into a heated convergent pipe with a convergent angle of 5° with respect to the pipe axis. A flat vane swirler situated at the entrance of the pipe is used to generate the swirling flow. During the experiments, the Reynolds number ranges from 7970 to 47,820, and the swirl number from 0 to 1.2. It is found that the convergence of the pipe can accelerate the flow which has an effect to suppress the turbulence generated in the flow and reduce the heat transfer. However, in the region of weak swirl (S = 0-0.65), the Nusselt numbers increase with increasing swirl numbers until S = 0.65, where turbulence intensity is expected to be large enough and not suppressible. In the region of strong swirl (S > 0.65), where recirculation flow is expected to be generated in the core of the swirling flow, the heat transfer characteristic can be altered significantly. At very high swirl (S ? 1.0), the accelerated flow in the circumferential direction is expected to be dominant, which leads to suppress the turbulence and reduce the heat transfer. The Nusselt number is found proportional to the swirl number. Correlations of the Nusselt numbers in terms of the swirl number, the Reynolds number and the dimensionless distance are attempted and are very successful in both the weak and the strong swirl regions. 相似文献
72.
This paper uses a development technique to estimate the loss reserve in a classical run-off triangle setting. Closed-form solutions for unbiased estimates of reserves and their corresponding standard errors can be obtained by assuming lognormal distributions of the development factors. The technique is applied to the Bornhuetter-Ferguson method [Bornhuetter, R.L., Ferguson, R.E., 1972. The actuary and IBNR. Proc. Casualty Actuarial Soc. 59, 181-195] and to two previously studied data sets. 相似文献
73.
This paper studies the dynamic stability of a pretwisted cantilever beam spinning along its longitudinal axis and subjected to an axial random force at the free end. The axial force is assumed as the sum of a constant force and a random process with a zero mean. Due to this axial force, the beam may experience parametric random instability. In this work, the finite element method is first applied to yield discretized system equations. The stochastic averaging method is then adopted to obtain Ito's equations for the response amplitudes of the system. Finally the mean-square stability criterion is utilized to determine the stability condition of the system. Numerical results show that the stability boundary of the system converges as the first three modes are taken into calculation. Before the convergence is reached, the stability condition predicted is not conservative enough. 相似文献
74.
Oxovanadium(V) complexes and with general formula VO(L3*)(OR5) were prepared in quantitative yields in alcohol (R5OH) from reactions of VO(O-i-Pr)3 and tridentate Schiff bases of beta-amino alcohols having one or two stereogenic centers, (HO)C*(R1)(R2)C*H(R3)N[double bond, length as m-dash]CH(2-OH-3,5-R4(2)-C6H2) (H2L3*). The alkoxy OR5 ligand exchanges readily with the alcoholic molecule in the solvent. Crystal structures of and were determined to be five-coordinate square pyramidal monomers. However, 1H NMR spectra of the complexes reveal two sets of signals, indicating the presence of two isomers in solution. The two isomers are suggested to be the endo/exo pair or the monomer/dimer pair. Asymmetric oxidations of methyl phenyl sulfide catalyzed by catalyst precursors were demonstrated to afford the chiral sulfoxide in yields and ee values similar to those obtained from the in situ-formed catalytic systems of VO(acac)2 and corresponding Schiff base ligands. Complexes and are also good catalysts for asymmetric alkynyl additions to aldehydes. Structural differences between the oxovanadium complexes, for inducing high stereoselectivities in the asymmetric oxidation of organic sulfides and the asymmetric alkynyl addition to aldehydes, are rationalized. 相似文献
75.
Ku SL Hui XP Chen CA Kuo YY Gau HM 《Chemical communications (Cambridge, England)》2007,(37):3847-3849
Novel and highly efficient cross couplings of aryl bromides and chlorides with AlAr3(THF) (Ar = Ph, 2,4,6-Me3C6H2, 2-naphthyl or 4-Me3SiC6H4) catalyzed by the economic palladium catalyst of PCy3 are reported without the use of a base and under mild reaction conditions at room temperature or temperatures < or = 60 degrees C even for couplings of bulky aryl halides and the Al(2,4,6-Me3C6H2)3(THF) reagent. 相似文献
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79.
Shuangliu Zhou Da-Wei Chuang Shih-Ju Chang Han-Mou Gau 《Tetrahedron: Asymmetry》2009,20(12):1407-1412
A series of phenylaluminum reagents AlPhxEt3?x(L) (x = 1–3) containing adduct ligand L [Et2O, THF, OPPh3, or 4-dimethylaminopyridine (DMAP)] were synthesized and characterized. NMR studies showed that AlPhxEt3?x(L) (x = 1 or 2) exists as an equilibrium mixture of 3–4 species in solution. Solid-state structures of the phenylaluminum reagents reveal a distorted tetrahedral geometry. Asymmetric additions of phenylaluminum to 2-chlorobenzaldehyde were examined employing a titanium(IV) complex [TiL1(OPri)2]2 10 (H2L1 = (1R,2S)-2-(p-tolylsulfonylamino)-1,3-diphenyl-1-propanol) as a catalyst precursor. It was found that the adduct ligand L had a strong influence on the reactivity and the enantioselectivity in asymmetric phenyl additions to aldehydes. The phenylaluminum reagents with OPPh3 or DMAP were unreactive toward aldehydes, and AlPh3(THF) was found to be superior to AlPh3(OEt2) or AlPhEt2(THF). Asymmetric aryl additions of AlAr3(THF) to aldehydes employing a loading of 5 mol % titanium(IV) complex 10 with a strategy of a slow addition of the aldehydes over 20 min were conducted, and the reactions produced optically active secondary alcohols in high yields with excellent enantioselectivities of up to 94% ee. 相似文献
80.
This work presents a novel mathematical model to evaluate the effect of pumped well bore mixing volume on formation decontamination. The model equation is solved by the Laplace transform finite difference method. The developed model is applied to assess the effect of well bore mixing volume on contaminant remediation. The simulated results indicated that the well bore volume effect is pronounced for initial plumes with a small maximum contaminated radius, and in media such as bedrock formation where aquifer porosity and longitudinal dispersivity are small. In such systems, the pumped well bore mixing effect reduces the early contaminant concentrations, shifts the peak breakthrough curves to the right and spreading the breakthrough curve, and thus increases the decontamination time. If such a system does not account for pumped well mixing bore effect, estimates of decontamination time required to the regulatory level will be inaccurate. 相似文献