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581.
582.
Gösta Brunow Pirkko Karhunen Knut Lundquist Solveig Olson Rolf Stomberg 《Journal of chemical crystallography》1995,25(1):1-10
Lignin models of the biphenyl type have been synthesized and crystal structures of two of them have been determined. The tetraacetate of 5,5-bis(hydroxymethyl)-3,3-dimethoxy-2,2-biphenyldiol crystallizes in space group
witha=11.319(2),b=12.232(6),c=9.242(3) Å, =101.66(3)°, =108.14(2)°, =79.08(2)° andZ=2.R=0.036 (2720 observed [I>3(I)] reflections). The acetate of 5,5-di-tert-butyl-2,3,3-trimethoxy-2-biphenylol crystallizes in space group
witha=11.972(2),b=21.621(3),c=9.834(1) Å, =91.18(1)°, =113.13(1)°. =98.42(1)°, andZ=4.R=0.050 (8129 observed [I>3(I)] reflections).1H NMR and13C NMR data for the above-mentioned compounds and a third model, the diacetate of 5,5-bis(1-hydroxyethyl)-2,2,3,3-tetramethoxybiphenyl, are reported. Observed signal positions are compared with those calculated on the basis of crystal structure data. The possibilities to obtain structural information about biphenyl structures in lignins from NMR spectra are discussed. 相似文献
583.
Gary S. Groenewold Marnie M. Cortez Anita K. Gianotto Garold L. Gresham John E. Olson Robert V. Fox Byron M. White William F. Bauer Recep Avci Muhammedin Deliorman Eric Williams 《Surface and interface analysis : SIA》2007,39(6):547-553
Particulate samples collected from a laboratory ventilation manifold during routine maintenance were analyzed to determine if particulate composition had changed as a result of changes in the laboratory's atmosphere. This ventilation manifold exhausts more than 100 fume hoods. The particulate samples were analyzed using static secondary ion mass spectrometry (SIMS). The negative SIMS spectra showed abundant Cl?, NO3?, and HSO4?, consistent with the use of mineral acids in the laboratory. Cluster anions containing primarily Zn (but also other transition metals) were detected, which signaled corrosion of the manifold's galvanized steel by the volatilized acids. The most abundant ions in the cation SIMS spectra were derived from cyclohexylamine (CHA), which had been used as an antiscaling agent in the facility's boiler. Steam from the boiler, which contained CHA, was used to humidify the building air; this practice stopped in 1997. The abundances of the CHA‐derived ions were significantly lower in the samples collected in 2004 and 2006 than in the 1992 samples, indicating that the CHA is being slowly depleted. Changes in the relative abundances suggest exponential depletion from the manifold with rate constants that are on the order of 0.01 to 0.04 month?1. Published in 2007 John Wiley & Sons, Ltd. 相似文献
584.
Tressia A.P. Paulose Jeremy A. Olson J. Wilson Quail Stephen R. Foley 《Journal of organometallic chemistry》2008,693(21-22):3405-3410
The synthesis and characterization of non-symmetric di-N-heterocyclic carbene (diNHC) silver(I) and palladium(II) complexes are described. The activity of the Pd(II) complexes in the Suzuki–Miyaura coupling reaction of bulky substrates was investigated. This synthetic route represents a possible general pathway into a wide variety of non-symmetrically substituted diNHC ligands. 相似文献
585.
As a result of the cochlea's nonlinear mechanics, stimulation by two tones results in the generation of distortion products (DPs) at frequencies flanking the primary tones. DPs are measurable in the ear canal as oto-acoustic emissions, and are used to noninvasively explore cochlear mechanics and diagnose hearing loss. Theories of DP emissions generally include both forward and reverse cochlear traveling waves. However, a recent experiment failed to detect the reverse-traveling wave and concluded that the dominant emission path was directly through the fluid as a compression pressure [Ren, 2004, Nat. Neurosc.7, 333-334]. To explore this further, we measured intracochlear DPs simultaneously with emissions over a wide frequency range, both close to and remote from the basilar membrane. Our results support the existence of the reverse-traveling wave: (1) They show spatial variation in DPs that is at odds with a compression pressure. (2) Although they confirm a forward-traveling character of intraocochlear DPs in a broad frequency region of the best frequency, this behavior does not refute the existence of reverse-traveling waves. (3) Finally, the results show that, in cases in which it can be expected, the DP emission is delayed relative to the DP in a way that supports reverse-traveling-wave theory. 相似文献
586.
We study how the number of numerically determining modes in the Navier–Stokes equations depends on the Grashof number. Consider
the two-dimensional incompressible Navier–Stokes equations in a periodic domain with a fixed time-independent forcing function.
We increase the Grashof number by rescaling the forcing and observe through numerical computation that the number of numerically
determining modes stabilizes at some finite value as the Grashof number increases. This unexpected result implies that our
theoretical understanding of continuous data assimilation is incomplete until an analytic proof which makes use of the non-linear
term in the Navier–Stokes equations is found.
相似文献
587.
The Parallel Plate Avalanche Counter (PPAC) has been used mostly for measuring the energy loss of single, heavily ionizing particles. A PPAC is even more effective with high-energy showers for which a single event causes hundreds of electrons to pass through it. For operation at reduced pressures, the alkanes such as isobutane, C4H10 are excellent PPAC gasses with the quality of performance increasing with the size of the molecule. Under some circumstances the perfluoroalkanes such as perfluoropropane, C3F8, may be preferred. For operation at atmospheric pressure, CF4 and mixtures containing Ar and CO2 work well. 相似文献
588.
We propose an experiment for directly constructing and locally probing topologically entangled states of superconducting vortices which can be performed with present-day technology. Calculations using an elastic string vortex model indicate that as the pitch (the winding angle divided by the vertical distance) increases, the vortices approach each other. At values of the pitch higher than a maximum value the entangled state becomes unstable to collapse via a singularity of the model. We provide predicted experimental signatures for both vortex entanglement and vortex cutting. The local probe we propose can also be used to explore a wide range of other quantities. 相似文献
589.
Anthony PL Arnold RG Arroyo C Baird K Bega K Biesiada J Bosted PE Breuer M Carr R Cates GD Chen JP Chudakov E Cooke M Decker FJ Decowski P Deur A Emam W Erickson R Fieguth T Field C Gao J Gustafsson K Hicks RS Holmes R Hughes EW Humensky TB Jones GM Kaufman LJ Kolomensky YG Kumar KS Lhuillier D Lombard-Nelsen R Mastromarino P Mayer B McKeown RD Michaels R Olson M Paschke KD Peterson GA Pitthan R Pope K Relyea D Rock SE Saxton O Shapiro G Singh J Souder PA Szalata ZM Tobias WA Tonguc BT Turner J 《Physical review letters》2004,92(18):181602
We report a measurement of the parity-violating asymmetry in fixed target electron-electron (M?ller) scattering: A(PV)=[-175+/-30(stat)+/-20(syst)] x 10(-9). This first direct observation of parity nonconservation in M?ller scattering leads to a measurement of the electron's weak charge at low energy Q(e)(W)=-0.053+/-0.011. This is consistent with the standard model expectation at the current level of precision: sin((2)theta(W)(M(Z))((-)MS)=0.2293+/-0.0024(stat)+/-0.0016(syst)+/-0.0006(theory). 相似文献
590.
Heavy-particle cross sections differential in the momentum transferred to the target are investigated using the classical trajectory Monte Carlo method. With the 3.6 MeV/mu Au(53+) + He system as a test case, it is shown that these cross sections are extremely sensitive to the initial target temperature. In particular, when thermal motion is varied for one of the target's initial momentum components between 0 and 25 K the absolute cross sections vary by orders of magnitude and, in addition, their relative shapes undergo major changes. We find that by setting one of the target's transverse momenta to a temperature of 16 K, previously reported major discrepancies between theory and experiment are removed. 相似文献