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21.
A high-performance liquid chromatography (HPLC) method was established using an analytical reversed-phase column and gradient
elution to achieve chromatographic separation of typical compounds in essential oils. For detection, a diode array detector
monitoring different wavelengths simultaneously as well as a mass spectrometer (MS) were used. Atmospheric pressure chemical
ionization operating in the positive mode turned out to be a suitable tool to detect volatiles of different chemical classes
and to identify them in essential oil matrices. Characteristic fingerprints of eucalyptus, lavender, may chang, pine, rosemary,
thyme, and turpentine essential oils monitored at a representative wavelength (220 nm) demonstrated the suitability of HPLC
in essential oil analysis. Additional monitoring wavelengths (210, 250, and 280 nm) provided useful information about the
identity of the specific component and opened the possibility to differentiate presumably coeluting compounds by means of
their distinct absorption behavior. Finally, peak assignment in seven essential oils was performed on the basis of characteristic
retention times and UV and MS data of a broad set of reference volatiles. 相似文献
22.
The main objective of our work was to investigate the possibility and usefulness of indirect methods in X-ray microanalysis
for the quantification of biologically important compounds. Metallothionein-like proteins (MT-like proteins) from kidney and
liver, rich in sulfur were chosen as an indicator of heavy metal presence in cells and their environment. Tissues from goldfish
(Carassius auratus gibelio) were sampled after short and prolonged periods of exposure to Co+2, CrO4
−2, Pb+2, Cu+2 and control treatment and prepared for histochemical staining for peroxidated thiolate groups. Commonly used –S–S– bonds
dye (Nitro Red) was replaced with iodine atoms and they were quantified at L line by means of X-ray microanalysis combined
with SEM. After fish treatments with heavy metal solutions changes in MT-like proteins and in I atom contents were expected.
There was statistically significant decrease in MT-like proteins level in kidney after lead treatment (Pb/C = 0.62). In liver
a statistically significant increase in MT-like proteins concentration was observed after chromium, cobalt and lead ions treatment
in comparison to control animals. The following ratios were noted: 3.04 for Cr/C, 2.18 for Co/C and 2.10 for Pb/C. Our finding
indicates that the method of indirect measurement of MT-like proteins in fish and other animal tissues is possible. The concentration
of iodine atoms is above their detection level by EDS and their changes are possible to identify. During histochemical procedures
it is worth taking into account sample preparation methods which might disturb the quality and quantity of the analysed material. 相似文献
23.
Track etch detectors CR-39 irradiated with relativistic heavy ions (C, Ne, Si and Fe, ) and high-energy protons (35–230 MeV) were etched both chemically and electrochemically. To determine an angular dependence of response in detail (step 1), an arrangement of a single detector bent into a semi-cylindrical form was used. Experimental data were fitted by polynomic functions and the detection efficiencies for isotropic irradiation were calculated. Critical angles of registration were also determined for heavy ions. The possible influence of additional absorbers and radiators was also estimated. 相似文献
24.
We study the localization length lc of a pair of two attractively bound particles moving in a one-dimensional random potential. We show in which way it depends on the interaction potential between the constituents of this composite particle. For a pair with many bound states N the localization length is proportional to N, independently of the form of the two particle interaction. For the case of two bound states, we present an exact solution for the corresponding Fokker–Planck equation and demonstrate that lc depends sensitively on the shape of the interaction potential and the symmetry of the bound state wave functions. 相似文献
25.
The 50,52Cr(d, 6Li) 46,48Ti reactions have been studied at Ed = 65 MeV bombarding energy. Angular distributions of outgoing Li particles were measured for final states in 46,48Ti nuclei from 15° to 50° (lab). These were compared with zero-range and finite-range DWBA calculations in an α-cluster pick-up approximation to obtain relative α-spectroscopic factors. 相似文献
26.
Stefan Turek 《国际流体数值方法杂志》1994,18(1):71-105
We develop simulation tools for the non-stationary incompressible 2D Navier--Stokes equations. The most important components of the finite element code are: the fractional step ?-scheme, which is of second-order accuracy and strongly A-stable, for the time discretization; a fixed point defect correction method with adaptive step length control for the non-linear problems (stationary Navier-Stokes equations); a modified upwind discretization of higher-order accuracy for the convective terms. Finally, the resulting nonsymmetric linear subproblems are treated by a special multigrid algorithm which is adapted to the quadrilateral non-conforming discretely divergence-free finite elements. For the graphical postprocess we use a fully non-stationary and interactive particle-tracing method. With extensive test calculations we show that our method is a candidate for a ‘black box’ solver. 相似文献
27.
A spacer-equipped tetrasaccharide, p-aminocyclohexylethyl alpha-l-Colp-(1-->2)-beta-d-Galp-(1-->3)-[alpha-l-Colp-(1-->4)]-beta-D-GlcpNAc, containing a 4,6-cyclic phosphate in the galactose residue, has been synthesised. The structure corresponds to a part of the repeating unit of the capsular (and lipo-) polysaccharide of the endemic bacteria Vibrio cholerae type O139 synonym Bengal. The synthetic strategy allows continuous syntheses of the complete O139 hexasaccharide repeating unit as well as of the structurally related repeating unit of serotype O22. Starting from ethyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-beta-D-glucopyranoside, a thioglycoside tetrasaccharide donor block was constructed through two orthogonal glycosylations with glycosyl bromide donors. First, a properly protected galactose moiety was introduced using silver triflate as promoter and subsequently the two colitose residues, carrying electron-withdrawing protecting groups for stability reasons, under halide-assisted conditions. The tetrasaccharide block was then linked to the spacer in a NIS-TMSOTf-promoted coupling. Transformation of the azido group into an acetamido group using H2S followed by removal of temporary protecting acetyl groups gave a 4',6'-diol, which was next phosphorylated with methyl dichlorophosphate and deprotected to yield the 4,6-cyclic phosphate tetrasaccharide target structure. 相似文献
28.
We examine scale invariant Fulop-Tsutsui couplings in a quantum vertex of a general degree n. We demonstrate that essentially same scattering amplitudes as for the free coupling can be achieved for two (n−1)-parameter Fulop-Tsutsui subfamilies if n is odd, and for three (n−1)-parameter Fulop-Tsutsui subfamilies if n is even. We also work up an approximation scheme for a general Fulop-Tsutsui vertex, using only n δ function potentials. 相似文献
29.
This contribution reviews an ab initio two-step procedure to determine exchange interactions, spin-wave spectra, and thermodynamic properties of itinerant magnets. In the first step, the self-consistent electronic structure of a system is calculated for a collinear spin structure at zero temperature. In the second step, parameters of an effective classical Heisenberg Hamiltonian are determined using the magnetic force theorem and the one-electron Green functions. The Heisenberg Hamiltonian and methods of statistical physics are employed in subsequent evaluation of magnon dispersion laws, spin-wave stiffness constants, and Curie/Néel temperatures. The applicability of the developed scheme is illustrated by selected properties of various systems such as transition and rare-earth metals, disordered alloys including diluted magnetic semiconductors, ultrathin films, and surfaces. A comparison to other ab initio approaches is presented as well. 相似文献
30.