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141.
M. Gra?a Dias M. Filomena Cam?es Luísa Oliveira 《Accreditation and quality assurance》2012,17(2):183-189
For consistent interpretation of an analytical method result it is necessary to evaluate the confidence that can be placed
in it, in the form of a measurement uncertainty estimate. The Guide to the expression of Uncertainty in Measurement issued
by ISO establishes rules for evaluating and expressing uncertainty. Carotenoid determination in food is a complex analytical
process involving several mass transfer steps (extraction, evaporation, saponification, etc.), making difficult the application
of these guidelines. The ISO guide was interpreted for analytical chemistry by EURACHEM, which includes the possibility of
using intra- and interlaboratory information. Measurement uncertainty was estimated based on laboratory validation data, including
precision and method performance studies, and also, based on laboratory participation in proficiency tests. These methods
of uncertainty estimation were applied to analytical results of different food matrices of fruits and vegetables. Measurement
uncertainty of food carotenoid determination was 10–30% of the composition value in the great majority of cases. Higher values
were found for measurements near instrumental quantification limits (e.g. 75% for β-cryptoxanthin, and 99% for lutein, in
pear) or when sample chromatograms presented interferences with the analyte peak (e.g. 44% for α-carotene in orange). Lower
relative expanded measurement uncertainty values (3–13%) were obtained for food matrices/analytes not requiring the saponification
step. Based on these results, the saponification step should be avoided if food carotenoids are not present in the ester form.
Food carotenoid content should be expressed taking into account the measurement uncertainty; therefore the maximum number
of significant figures of a result should be 2. 相似文献
142.
Daniel M. Silveira Pedro A. S. Salgueiro M. Filomena G. F. C. Cam?es Ricardo J. N. Bettencourt da Silva 《Accreditation and quality assurance》2012,17(2):115-127
Tear gases are the most widely used non-lethal weapons, both by security forces and by the general public. The pepper spray,
whose active agent is capsaicin, is the only self-defence aerosol allowed in Portugal, where capsaicin concentration must
be below 5 g/100 mL. The cost-effective evaluation of the compliance of self-defence weapons with legislation involves the
use of two measurement procedures with increasing quantitative capability. Samples are first assessed by preliminary measurement
procedure based on single-point GC–MS calibration. Whenever the measurement uncertainty from this assessment makes evaluation
inconclusive, the evaluation of sample compliance using multi-point GC–MS calibration is performed. Metrological models including
sound criteria for the evaluation of sample compliance with legislation were developed for both measurement procedures. Such
models include the evaluation of the impact of instrumental performance, calibration model, sample dilution and standards
preparation on measurement uncertainty. The relative expanded uncertainty, in the studied range (capsaicin 3–7 g/100 mL),
of measurements supported in single-point calibrations ranged from 10 to 22% and the ones supported on multi-point calibrations
from 8 to 12% depending on capsaicin concentration and daily GC–MS repeatability. Measurements are fit for the intended use
since they present a relative expanded uncertainty smaller than a target value of 30, or 15%, for measurements supported in
single- or multi-point calibrations, respectively. 相似文献
143.
144.
Aguilar GH Farías OJ Maziero J Serra RM Ribeiro PH Walborn SP 《Physical review letters》2012,108(6):063601
The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system's state and numerical optimization procedures. Thus, it is natural to seek methods involving fewer measurements that indicate the nature of the correlations in a system. Here we propose a classicality witness that can be accurately estimated via statistics from a single measurement and perform an experiment to explore the utility of this witness for quantum states with different types of correlations. 相似文献
145.
Serra S 《Natural product communications》2012,7(4):455-458
The enantioselective synthesis of (S)-1-hydroxy-1,3,5-bisabolatrien-10-one 1 is here described. This sesquiterpene was prepared using (S)-3-(2-methoxy-4-methyl-phenyl)butan-1-ol as a chiral building block. Two different pathways were employed and both turned out to be high yielding, affording 1 in good chemical purity and without any racemization of the existing stereocenter. The spectroscopic data of the synthetic (S)-1 were in very good agreement with those reported for the natural compound, which was extracted from Juniperus formosana heartwood and from the leaves of J. chinensis. The positive sign of the measured optical rotation value of synthetic (S)-1 allows the unambiguous assignment of the absolute configuration of (+)-1 as the (S)-enantiomer. This finding corrects the previous configuration determination which indicated the opposite result. At last, since even (R)-3-(2-methoxy-4-methyl-phenyl)butan-1-ol is preparable in high enantiomer purity by mean of a different biocatalytic process, the formal synthesis of natural (R)-1 was also accomplished. 相似文献
146.
J. A. Paixo A. Matos Beja M. Ramos Silva L. Alte da Veiga A. C. Serra 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1501-1502
In the title compound, C8H5Br2NO4, the endocyclic angles of the ring deviate significantly from the ideal value of 120°. The substituents deviate from the plane of the ring, with large twist angles for the aldehyde, nitro and methoxy groups. The geometry of the molecule in the crystal is compared with that of the isolated molecule, as given by a self‐consistent field molecular‐orbital Hartree–Fock calculation. Only weak hydrogen bonds of the C—H?Br and C—H?O types are present in the crystal structure. 相似文献
147.
Elena Bosetto Enrico Serra 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2000,17(6):673
We prove that a class of problems containing the classical periodically forced pendulum equation displays the main features of chaotic dynamics. The approach is based on the construction of multibump type heteroclinic solutions to periodic orbits by the use of global variational methods. 相似文献
148.
Rafael Ortega Enrico Serra Massimo Tarallo 《Proceedings of the American Mathematical Society》2000,128(9):2659-2665
A well known theorem says that the forced pendulum equation has periodic solutions if there is no friction and the external force has mean value zero. In this paper we show that this result cannot be extended to the case of linear friction.
149.
Ana Ruas Angelica Graa Joana Marto Lídia Gonalves Ana Oliveira Alexandra Nogueira da Silva Madalena Pimentel Artur Mendes Moura Ana Teresa Serra Ana Cristina Figueiredo Helena M. Ribeiro 《Molecules (Basel, Switzerland)》2022,27(11)
Essential oils (EOs) and hydrolates (Hds) are natural sources of biologically active ingredients with broad applications in the cosmetic industry. In this study, nationally produced (mainland Portugal and Azores archipelago) EOs (11) and Hds (7) obtained from forest logging and thinning of Eucalyptus globulus, Pinus pinaster, Pinus pinea and Cryptomeria japonica, were chemically evaluated, and their bioactivity and sensorial properties were assessed. EOs and Hd volatiles (HdVs) were analyzed by GC-FID and GC-MS. 1,8-Cineole was dominant in E. globulus EOs and HdVs, and α- and β-pinene in P. pinaster EOs. Limonene and α-pinene led in P. pinea and C. japonica EOs, respectively. P. pinaster and C. japonica HVs were dominated by α-terpineol and terpinen-4-ol, respectively. The antioxidant activity was determined by DPPH, ORAC and ROS. C. japonica EO showed the highest antioxidant activity, whereas one of the E. globulus EOs showed the lowest. Antimicrobial activity results revealed different levels of efficacy for Eucalyptus and Pinus EOs while C. japonica EO showed no antimicrobial activity against the selected strains. The perception and applicability of emulsions with 0.5% of EOs were evaluated through an in vivo sensory study. C. japonica emulsion, which has a fresh and earthy odour, was chosen as the most pleasant fragrance (60%), followed by P. pinea emulsion (53%). In summary, some of the studied EOs and Hds showed antioxidant and antimicrobial activities and they are possible candidates to address the consumers demand for more sustainable and responsibly sourced ingredients. 相似文献
150.
Natlia Aniceto Vanda Marques Joana D. Amaral Patrícia A. Serra Rui Moreira Cecília M. P. Rodrigues Rita C. Guedes 《Molecules (Basel, Switzerland)》2022,27(15)
Necroptosis has emerged as an exciting target in oncological, inflammatory, neurodegenerative, and autoimmune diseases, in addition to acute ischemic injuries. It is known to play a role in innate immune response, as well as in antiviral cellular response. Here we devised a concerted in silico and experimental framework to identify novel RIPK1 inhibitors, a key necroptosis factor. We propose the first in silico model for the prediction of new RIPK1 inhibitor scaffolds by combining docking and machine learning methodologies. Through the data analysis of patterns in docking results, we derived two rules, where rule #1 consisted of a four-residue signature filter, and rule #2 consisted of a six-residue similarity filter based on docking calculations. These were used in consensus with a machine learning QSAR model from data collated from ChEMBL, the literature, in patents, and from PubChem data. The models allowed for good prediction of actives of >90, 92, and 96.4% precision, respectively. As a proof-of-concept, we selected 50 compounds from the ChemBridge database, using a consensus of both molecular docking and machine learning methods, and tested them in a phenotypic necroptosis assay and a biochemical RIPK1 inhibition assay. A total of 7 of the 47 tested compounds demonstrated around 20–25% inhibition of RIPK1’s kinase activity but, more importantly, these compounds were discovered to occupy new areas of chemical space. Although no strong actives were found, they could be candidates for further optimization, particularly because they have new scaffolds. In conclusion, this screening method may prove valuable for future screening efforts as it allows for the exploration of new areas of the chemical space in a very fast and inexpensive manner, therefore providing efficient starting points amenable to further hit-optimization campaigns. 相似文献