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911.
A new series of amphiphilic β-cyclodextrins were designed and synthesized by grafting peptide chains on to all primary hydroxyl groups via ester bond formation. The desired amphiphilic structures have been produced from ester connection between the C-6 of β-cyclodextrin and the carboxyl group of N-acetylated resides: H2N-Leu-COOH, H2N-Leu-Gly-COOH, H2N-Leu-Gly-Leu-COOH, and H2N-Leu-Gly-Leu-Gly-COOH (3a-d). The synthetic pathway involves selective bromination of all primary hydroxyls of β-cyclodextrins and then substitution with the carboxylate moiety of the mentioned N-acetyl residues in the presence of DBU (1,8-diazabicyclo[5,4,0]undec-7-ene). The ability of the synthetic compounds for extraction and phase transfer of glucosamine, as a hydrophilic organic compound, was then studied. The results showed a considerable ability of these amphiphilic compounds for extraction and a selective tendency of 3c for phase transfer of glucosamine.  相似文献   
912.
An efficient Pd(0)-mediated, base-assisted reaction of phenols with difunctionalised allylic halides results in the formation of coupled products in good yields. The reactions proceed with excellent stereo-, regio- and chemocontrol. An appropriately functionalised Weinreb amide, synthesised by this methodology, undergoes halogen-lithium exchange and subsequent intramolecular 1,2-carbonyl addition/elimination to give an advanced macrocyclic intermediate with potential use in the synthesis of likonide B.  相似文献   
913.
Phase relations have been established in the ternary system Ce-Rh-Si for the isothermal section at 800 0;°C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 0;°C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ7—Ce3RhSi3, (Ba3Al2Ge2-type), τ8—Ce2Rh3−xSi3+x (Ce2Rh1.35Ge4.65-type), τ10—Ce3Rh4−xSi4+x (U3Ni4Si4-type), τ11—CeRh6Si4 (LiCo6P4-type), τ13—Ce6Rh30Si19.3 (U6Co30Si19-type), τ18—Ce4Rh4Si3 (Sm4Pd4Si3-type), τ21—CeRh2Si (CeIr2Si-type), τ22—Ce2Rh3+xSi1−x (Y2Rh3Ge-type) and τ24—Ce8(Rh1−xSix)24Si (Ce8Pd24Sb-type). For τ25—Ce4(Rh1−xSix)12Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ3—CeRhSi2 (CeNiSi2-type) and τ6—Ce2Rh3Si5 (U2Co3Si5-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ4—Ce22Rh22Si56, τ5—Ce20Rh27Si53 and τ23—Ce33.3Rh58.2−55.2Si8.5−11.5 are unknown. High temperature compounds with compositions Ce10Rh51Si33 (U10Co51Si33-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 0;°C.  相似文献   
914.
915.
Two types of chiral stationary phases for HPLC based on π‐acidic or π‐basic perphenylcarbamoylated β‐CDs were synthesized. The relative structural features of the two effective chiral selectors are discussed and compared in both normal‐phase and RP modes. In addition, the nature and concentration of alcoholic modifiers were varied for optimal separation in normal phase and the structural variation of the analytes was also examined. The results showed that hydrogen bonding, steric effect and π‐acidic–π‐basic interaction contributed greatly to enantioseparation. Upon comparison, some of the differences in the separation behavior of the two types of chiral stationary phases might be due to the π‐acidic or π‐basic phenylcarbamate groups.  相似文献   
916.
In this study, a new system for analysis using a dual comprehensive two-dimensional gas chromatography/targeted multidimensional gas chromatography (switchable GC 00;GC/targeted MDGC) analysis was developed. The configuration of this system not only permits the independent operation of GC, GC 00;GC and targeted MDGC analyses in separate analyses, but also allows the mode to be switched from GC 00;GC to targeted MDGC any number of times through a single analysis. By incorporating a Deans switch microfluidics transfer module prior to a cryotrapping device, the flow stream from the first dimension column can be directed to either one of two second dimension columns in a classical heart-cutting operation. Both second columns pass through the cryotrap to allow solute bands to be focused and then rapidly remobilized to the respective second columns. A short second column enables GC 00;GC operation, whilst a longer column is used for targeted MDGC. Validation of the system was performed using a standard mixture of compounds relevant to essential oil analysis, and then using compounds present at different abundances in lavender essential oil. Reproducibility of retention times and peak area responses demonstrated that there was negligible variation in the system over the course of multiple heart-cuts, and proved the reliable operation of the system. An application of the system to lavender oil, as a more complex sample, was carried out to affirm system feasibility, and demonstrate the ability of the system to target multiple components in the oil. The system was proposed to be useful for study of aroma-impact compounds where GC 00;GC can be incorporated with MDGC to permit precise identification of aroma-active compounds, where heart-cut multidimensional GC-olfactometry detection (MDGC-O) is a more appropriate technology for odour assessment.  相似文献   
917.
This study investigates lipophilicity determination by chromatographic measurements using the polar embedded Ascentis RP-Amide stationary phase. As a new generation of amide-functionalized silica stationary phase, the Ascentis RP-Amide column is evaluated as a possible substitution to the n 0;-octanol/water partitioning system for lipophilicity measurements. For this evaluation, extrapolated retention factors, log kwlogkw, of a set of diverse compounds were determined using different methanol contents in the mobile phase. The use of n-octanol enriched mobile phase enhances the relationship between the slope (S 0;) of the extrapolation lines and the extrapolated log kwlogkw (the intercept of the extrapolation), as well as the correlation between log 0;P 0; values and the extrapolated log kwlogkw (1:1 correlation, r2 0;= 0;0.966). In addition, the use of isocratic retention factors, at 40% methanol in the mobile phase, provides a rapid tool for lipophilicity determination. The intermolecular interactions that contribute to the retention process in the Ascentis RP-Amide phase are characterized using the solvation parameter model of Abraham. The LSER system constants for the column are very similar to the LSER constants of the n-octanol/water extraction system. Tanaka radar plots are used for quick visual comparison of the system constants of the Ascentis RP-Amide column and the n-octanol/water extraction system. The results all indicate that the Ascentis RP-Amide stationary phase can provide reliable lipophilic data.  相似文献   
918.
Organic compounds in atmospheric nanoparticles have an effect on human health and the climate. The determination of these particles is challenged by the difficulty of sampling, the complexity of sample composition, and the trace-level concentrations of the compounds. Meeting the challenge requires the development of sophisticated sampling systems for size-resolved particles and the optimization of sensitive, accurate and simple analytical techniques and methods. A new sampling system is proposed where particles are charged with a bipolar charger and size-segregated with a differential mobility analyzer. This system was successfully used to sample particles from wood pyrolysis with particle sizes 30–100 0;nm. Particles were analyzed by four techniques: comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry, gas chromatography–time-of-flight mass spectrometry, gas chromatography–quadrupole mass spectrometry, and aerosol mass spectrometry (aerosol MS). In the chromatographic techniques, particles were collected on a filter and analyzed off-line after sample preparation, whereas in the aerosol MS, particle analysis was performed directly from the particle source. Target compounds of the samples were polyaromatic hydrocarbons and n-alkanes. The analytical techniques were compared and their advantages and disadvantages were evaluated. The sampling system operated well and target compounds were identified in low concentrations.  相似文献   
919.
An image processing approach originating from the proteomics field has been transferred successfully to the processing of data obtained with comprehensive two-dimensional gas chromatographic separations data. The approach described here has proven to be a useful analytical tool for unbiased pattern comparison or profiling analyses, as demonstrated with the differentiation of volatile patterns (“aroma”) from fruits such as apples, pears, and quince fruit. These volatile patterns were generated by headspace solid phase microextraction coupled to comprehensive two-dimensional gas chromatography (HS-SPME-GC 00;GC). The data obtained from GC 00;GC chromatograms were used as contour plots which were then converted to gray-scale images and analyzed utilizing a workflow derived from 2D gel-based proteomics. Run-to-run variations between GC 00;GC chromatograms, respectively their contour plots, have been compensated by image warping. The GC 00;GC images were then merged into a fusion image yielding a defined and project-wide spot (peak) consensus pattern. Within detected spot boundaries of this consensus pattern, relative quantities of the volatiles from each GC 00;GC image have been calculated, resulting in more than 700 gap free volatile profiles over all samples. These profiles have been used for multivariate statistical analysis and allowed clustering of comparable sample origins and prediction of unknown samples. At present state of development, the advantage of using mass spectrometric detection can only be realized by data processing off-line from the identified software packages. However, such information provides a substantial basis for identification of statistically relevant compounds or for a targeted analysis.  相似文献   
920.
An analytical methodology based on headspace solid phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography—time-of-flight mass spectrometry (GC 00;GC–ToFMS) was developed for the identification and quantification of the toxic contaminant ethyl carbamate (EC) directly in fortified wines. The method performance was assessed for dry/medium dry and sweet/medium sweet model wines, and for quantification purposes, calibration plots were performed for both matrices using the ion extraction chromatography (IEC) mode (m/z 62). Good linearity was obtained with a regression coefficient (r2) higher than 0.981. A good precision was attained (R.S.D. <20%) and low detection limits (LOD) were achieved for dry (4.31 0;μg/L) and sweet (2.75 0;μg/L) model wines. The quantification limits (LOQ) and recovery for dry wines were 14.38 0;μg/L and 88.6%, whereas for sweet wines were 9.16 0;μg/L and 99.4%, respectively. The higher performance was attainted with sweet model wine, as increasing of glucose content improves the volatile compound in headspace, and a better linearity, recovery and precision were achieved. The analytical methodology was applied to analyse 20 fortified Madeira wines including different types of wine (dry, medium dry, sweet, and medium sweet) obtained from several harvests in Madeira Island (Portugal). The EC levels ranged from 54.1 0;μg/L (medium dry) to 162.5 0;μg/L (medium sweet).  相似文献   
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