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851.
Zhao RS Cheng CG Yuan JP Jiang T Wang X Lin JM 《Analytical and bioanalytical chemistry》2007,387(2):687-694
A novel purge-and-trap method coupled with gas chromatography-mass spectrometry (GC-MS) is developed for the analysis of trace
and ultratrace phenols based on their derivatization with acetic anhydride. Parameters affecting the extraction efficiency,
such as purge temperature, concentration of sodium chloride, purge time, and volume of derivatization reagent, were investigated.
The optimized conditions were addition of 150 μL acetic anhydride, purge time of 25 min at the purge temperature of 60 °C
with 30% NaCl. The linear range was 0.2–100 μg L−1 for phenols. The limits of detection (LODs) ranged from 0.08 to 0.15 μg L−1 and the relative standard deviations (RSDs) for most of the phenols at the 10 μg L−1level were below 10%. Natural water samples collected from a pool were successfully analyzed using the proposed method. The
recovery of spiked water samples was 72.9–84.2%. 相似文献
852.
Schmitt-Jansen M Bartels P Adler N Altenburger R 《Analytical and bioanalytical chemistry》2007,387(4):1389-1396
The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the non-steroidal
anti-inflammatory drug diclofenac is ubiquitously present in most of the surveyed surface waters, worldwide. Phototransformation
of diclofenac was reported from laboratory assays as well as in natural water systems, raising the question of possible adverse
effects of the phototransformation products of diclofenac to aquatic organisms. In this study the phytotoxicity of diclofenac
exposed to natural sunlight was evaluated using synchronized cultures of the unicellular chlorophyte Scenedesmus vacuolatus. Diclofenac dissolved in ultra-pure water at 50 mg L−1 was exposed to natural midsummer sunlight for a maximum of 145 h. Twice a day subsamples were taken for chromatography and
parallel phytotoxicity assessment. Inhibition of algal reproduction of the initial diclofenac solution was in the mg L−1 range indicating no specific toxicity of diclofenac towards S. vacuolatus. Fast degradation of diclofenac was observed with half lives between 3.3 and 6.4 h during the first and the third day of
exposure, respectively. Phytotoxicity increased after 3.5 h of exposure of diclofenac to sunlight and showed a maximum of
sixfold enhanced toxicity after 53 h of exposure to sunlight. Several phototransformation products were found during the experiment.
The time courses of the relative concentration of three transformation products significantly correlated with enhanced phytotoxicity
during the experiment. This indicates a high toxicity potential of phototransformation products of diclofenac at concentration
levels that may come close to environmental concentrations of residual diclofenac after degradation. We conclude that toxicity
assessment of phototransformation products should be included in the risk assessment of pharmaceuticals in the environment. 相似文献
853.
Contribution of UV light to the decomposition of toluene in dielectric barrier discharge plasma/photocatalysis system 总被引:1,自引:0,他引:1
Hai Bao Huang Dai Qi Ye Ming Li Fu Fa Da Feng 《Plasma Chemistry and Plasma Processing》2007,27(5):577-588
The contribution of UV light from plasma and an external UV lamp to the decomposition of toluene in a dielectric barrier discharge
(DBD) plasma/UV system, as well as in a plasma/photocatalysis system was investigated. It was found that UV light from the
DBD reactor was very weak. Its contribution to the removal of toluene in the plasma/photocatalysis system could be ignored.
Whereas, the introduction of external UV light to the plasma significantly improves the removal efficiency of toluene by 20%.
The removal efficiency of toluene in the plasma/photocatalysis system increased about 22% and 16% when compared with a plasma
only system and plasma driven photocatalyst system, respectively. The increased toluene removal efficiency was mostly attributed
to the contribution of the synergy between plasma and UV light, but not to the synergy between plasma and photocatalysis.
The synergetic effect between plasma and photocatalysis was not significant. 相似文献
854.
A chemo-electro-mechanical multi-field model, termed the multi-effect-coupling pH-electric-stimuli (MECpHe) model, has been
developed to simulate the response behavior of smart hydrogels subject to pH and electric voltage coupled stimuli when the
hydrogels are immersed in a pH buffer solution subject to an externally applied electric field. The MECpHe model developed
considers multiphysics effects and formulates the fixed charge density with the coupled buffer solution pH and electric voltage
effects, expressed by a set of nonlinear partial differential governing equations. The model can be used to predict the hydrogel
displacement and the distributive profiles of the concentrations of diffusive ionic species and the electric potential and
the fixed charge density in both the hydrogels and surrounding solution. After validation of the model by comparison of current
numerical results with experiment data extracted from the literature, one-dimensional steady-state simulations were carried
out for equilibrium of the smart hydrogels subject to pH and electric coupled stimuli. The effects of several important physical
conditions, including the externally applied electric voltage, on the distributions of the concentrations of diffusive ionic
species, the electric potential, the fixed charge density, and the displacement of the hydrogel strip were studied in detail.
The effects of the ionic strength on the bending deformation of the hydrogels under the solution pH and electric voltage coupled
stimuli are also discussed. 相似文献
855.
We determined the gas-phase acidities of two cysteine-polyalanine peptides, HSCA3 and HSCA4, using a triple-quadrupole mass spectrometer through application of the extended kinetic method with full entropy analysis. Five halogenated carboxylic acids were used as the reference acids. The negatively charged proton-bound dimers of the deprotonated peptides with the conjugate bases of the reference acids were generated by electrospray ionization. Collision-induced dissociation (CID) experiments were carried out at three collision energies. The enthalpies of deprotonation (Delta(acid)H) of the peptides were derived according to the linear relationship between the logarithms of the CID product ion branching ratios and the differences of the gas-phase acidities. The values were determined to be Delta(acid)H(HSCA3) = 317.3 +/- 2.4 kcal/mol and Delta(acid)H (HSCA4) = 316.2 +/- 3.9 kcal/mol. Large entropy effects (Delta(DeltaS) = 13-16 cal/mol K) were observed for these systems. Combining the enthalpies of deprotonation with the entropy term yielded the apparent gas-phase acidities (Delta(acid)G(app)) of 322.1 +/- 2.4 kcal/mol (HSCA3) and 320.1 +/- 3.9 kcal/mol (HSCA4), in agreement with the results obtained from the CID-bracketing experiments. Compared with that in the isolated cysteine residue, the thiol group in HSCA3,4 has a stronger gas-phase acidity by about 20 kcal/mol. This increased acidity is likely due to the stabilization of the negatively charged thiolate group through internal solvation. 相似文献
856.
Two new ruthenium(II) polypyridyl complexes
(1) (dtmi = 3-(pyrazin-2-yl)-as-triazino[5,6-f]-5-methoxylisatin) and
(2) (dtni = 3-(pyrazin-2-yl)-as-triazino[5,6-f]-5-nitroisatin) have been synthesized and characterized by elemental analysis,
FAB-MS, ES-MS and 1H-n.m.r. The DNA-binding patterns of complexes were investigated by spectroscopic titration, viscosity measurements and thermal
denaturation. The results indicate that the complexes (1) and (2) interact with calf thymus DNA (CT-DNA) by intercalative mode. Due to the withdrawing electronic substitutent in the intercalative
ligand, ptni, the DNA-binding affinity of the complexes (2) is larger than that complex (1) does. 相似文献
857.
Absalon C Fabre S Tarascou I Fouquet E Pianet I 《Analytical and bioanalytical chemistry》2011,401(5):1489-1499
Tannins represent a key element in red wine flavors, so researchers have made a lot of effort to try to understand the role
of their structure in wine taste in recent decades. We report some new routes to achieve a true structure–taste relationship
for the major tannins found in wine, which are procyanidins in their monomeric or oligomeric state. All these routes use synthetic
standards. New advances in their synthesis and their analyses using chromatographic methods, NMR spectroscopy, and mass spectrometry
to obtain more precise information about their chemical structure, including their stereochemistry and their precise degree
of polymerization and galloylation, are described. 相似文献
858.
Jian-fu Xu Fu-shuang Li Zi-ming Feng Jian-shuang Jiang Pei-cheng Zhang 《Chemistry of Natural Compounds》2011,47(2):218-219
A new sesquiterpenoid, malloapelin D (1), and a known schizandriside (2) were isolated from the roots of Mallotus apelta. Their structures were elucidated on the basis of spectroscopic methods including IR, MS, and 1D and 2D NMR. 相似文献
859.
Thermophysical properties and material modelling of acrylic bone cements used in vertebroplasty 总被引:1,自引:0,他引:1
Sebastian Kolmeder Alexander Lion Ralf Landgraf Jörn Ihlemann 《Journal of Thermal Analysis and Calorimetry》2011,105(2):705-718
The stabilization of osteoporotic vertebrae with acrylic bone cement, called vertebroplasty, is a common procedure in modern
surgery. However, the thermomechanical-chemically coupled material behaviour of curing bone cements makes the application
even for experienced surgeons difficult and can lead to potential complications like heat necrosis, leaking bone cement, embolisms
and postoperative load shifting. In order to reduce these potential complications, to minimize the risks and to better understand
the occurring effects, the thermophysical properties of a commercial acrylic bone cement were investigated in detail using
differential scanning calorimetry, volumetric dilatometry and temperature controlled rheometry. More specifically, the reaction
kinetics, the specific heat, the thermal conductivity, the thermal expansion, the chemical shrinkage as well as the mechanical
behaviour was studied during the reaction process of the bone cement. Furthermore, the explored material behaviour is described
by a customized material model that takes into account all observed effects. With the aid of this model the inhomogeneous
chemical, thermal and mechanical states that appear during the application and curing of acrylic bone cements, can be studied
by finite element treatment. 相似文献
860.
Köcher T Pichler P Mazanek M Swart R Mechtler K 《Analytical and bioanalytical chemistry》2011,400(8):2339-2347
The Mascot search algorithm is one of the most commonly used tools for protein identification. Tandem mass spectrometry data
searched against a protein sequence database is utilized for identifying peptides and proteins, each reported with a score.
Higher Mascot scores are associated with lower chances of random hits. The process of peak selection performed by the search
engine prior to the search is a critical aspect of the process. Here, we show that Mascot divides the MS/MS spectrum into
fixed m/z regions for peak selection, starting at the lowest m/z value of the peak list. Therefore, modifying the m/z range of the peak lists by insertion of a dummy peak with low m/z value changes the ensemble of peaks used for searching. As a consequence, Mascot peptide scores and search results are altered
significantly and a different subset of the peptides present in the sample is identified after processing. We further show
that the effect can be exploited and additional proteins and peptides can be identified by repeating the search with a combined
set of differently processed files, even when applying identical false-positive rates. 相似文献