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11.
M R Winchester W R Kelly J L Mann W F Guthrie B S MacDonald G C Turk 《Fresenius' Journal of Analytical Chemistry》2001,370(2-3):234-240
The S mass fractions of coal SRMs 2682b, 2684b, and 2685b are certified by direct comparison with coal SRMs 2682a, 2684a, and 2685a, respectively, using high-temperature combustion analysis with infrared (IR) absorption detection. The S mass fractions of the "a" materials used for calibration were previously determined by means of isotope-dilution thermal-ionization mass spectrometry (ID-TIMS). Therefore, the comparisons performed with the combustion-IR absorption method establish direct traceability links to accurate and precise ID-TIMS measurements. The expanded uncertainties associated with the certified S mass fractions are of approximately the same magnitude as would be expected for the ID-TIMS methodology. An important aspect of these certifications is that each "b" material is essentially identical with the corresponding "a" material, because both were produced from the same bulk, homogenized coal. As a test of the efficacy of the new certification approach when calibrant and unknown are not identical, the S mass fraction of coal SRM 2683b has been determined by direct comparison to coal SRM 2683a. These two coals, which have both previously been analyzed with ID-TIMS, are different in terms of S content and other properties. Whereas the S mass fraction for SRM 2683b determined with the new methodology agrees statistically with the ID-TIMS value, there is reason for caution in such cases. In addition to the usefulness of the alternative approach for certification activities within NIST, this approach might also be an excellent way of establishing NIST traceability during the value assignment process for reference materials not issued by NIST. Further research is needed, however, to understand better the scope of applicability. 相似文献
12.
Abe K Ahrens LA Amako K Aronson SH Beier EW Callas JL Cutts D Diwan M Durkin LS Gibbard BG Heagy SM Hedin D Hoftun JS Hurley M Kabe S Kurihara Y Lanou RE Mann AK Marx MD Murtagh MJ Nagashima Y Newcomer FM Shinkawa T Stern E Suzuki Y Terada S White DH Williams HH Yamaguchi Y 《Physical review letters》1987,58(7):636-639
13.
D. E. Vance V. F. Belt T. J. Oatts D. K. Mann 《Journal of Radioanalytical and Nuclear Chemistry》1998,234(1-2):143-147
The determination of neptunium-237 (237Np) traditionally has been performed by alpha spectrometry or neutron activation analysis. These methods are labor intensive
and require several days for completion. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a possible alternative for237Np determinations. This paper describes the analytical method developed for samples that have significant levels of uranium
present. The lower reporting limits achievable by ICP-MS are competitive with the counting methods, but the real advantage
for this laboratory lies in the lower cost and faster turnaround time provided by ICP-MS. 相似文献
14.
Studies on Alkyl Metal Alkoxides of Aluminium, Gallium, and Indium. III. Properties and Vibrational Spectra of Dialkylgallium- and Indium Alkoxides The preparation and the properties of dialkyl metal alkoxides R2MOR′ (with R = CH3, CD3, C2H5; R′ = CH3, CD3 and M = Ga, In) are described. The vibrational data (IR and Raman) of the trimeric methyl derivatives point to puckered six-membered M3O3-ring systems. 相似文献
15.
We describe a five-step synthesis of a PGH2 analogue from (R)-glyceraldehyde acetonide via formation of 1,2(S)-0-isopropylidene-hex-3(E)-en-5-one, conjugate addition of prostanoid C13- C20 side-chain as the cuprate with C1-C7 side-chain used to quench the resultant enolate, and finaily acid-catalysed ketal exchange to provide the desired analogue. 相似文献
16.
The mass spectra of 10 isomeric trimethylcyclohexanes and six cis–trans isomeric 1,2,3,5-tetramethylcyclohexanes are discussed. The thermochemically stable isomers show a higher abundance of the [M? CH3]+ ions and a lower abundance of the [M? C2H5]+ ions than the strained isomers. The log of the intensity ratio for loss of methyl and ethyl from the molecular ions correlates well with the strain energies and with the mean number of gauche arrangements of the stereoisomers. 相似文献
17.
Fourier transform near-infrared (FT-NIR) spectroscopy was used to quantify rapidly the ethanol (34-49% v/v), propylene glycol (20-35% v/v) and water (11-20% m/m) contents within a multi-component pharmaceutical oral liquid by measurement directly through the amber plastic bottle packaging. Spectra were collected in the range 7302-12,000 cm-1 and calibration models set-up using partial least-squares regression (PLSR) and multiple linear regression. Reference values for the three components were measured using capillary gas chromatography (ethanol and propylene glycol) and Karl Fischer (water) assay procedures. The calibration and test sets consisted of production as well as laboratory batches that were made to extend the concentration ranges beyond the natural production variation. The PLSR models developed gave standard errors of prediction (SEP) of 1.1% v/v for ethanol, 0.9% v/v for propylene glycol and 0.3% m/m for water. For each component the calibration model was validated in terms of: linearity, repeatability, intermediate precision and robustness. All the methods produced statistically favourable outcomes. Ten production batches independent of the calibration and test sets were also challenged against the PLSR models, giving SEP values of 1.3% v/v (ethanol), 1.0% v/v (propylene glycol) and 0.2% m/m (water). NIR transmission spectroscopy allowed all three liquid constituents to be non-invasively measured in under 1 min. 相似文献
18.
Molybdenum-95 NMR spectra have been measured for a selection of molybdenum carbonyl compounds and Mo(Σ-C5H5)(η-C5H5)(NO)(S2CNMe2). A chemical shift range of more than 1500 ppm is found. The chemical shifts and linewidths are discussed. 相似文献
19.
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