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991.
Reda Fleet J.B. McLeary V. Grumel W.G. Weber H. Matahwa R.D. Sanderson 《European Polymer Journal》2008,44(9):2899-2911
Graft copolymers were prepared using the RAFT process via a Z-group approach, where xanthate esters were formed directly on a cellulosic substrate. Grafting of vinyl acetate onto the modified cellulosic materials was then carried out via the reversible addition fragmentation chain transfer (RAFT) process. The xanthate RAFT agents on the backbone of the cellulosic materials were identified by Fourier-transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectroscopy (UV-vis). The number average molar masses of the graft copolymers were determined using size exclusion chromatography (SEC) and further characterization was conducted via liquid adsorption chromatography (LAC). The chromatographic results showed that the modified cellulosic materials were successfully grafted with polyvinyl acetate in a controlled manner. Grafted polyvinyl acetate (on the surface) and nongrafted polyvinyl acetate (in the solution) have almost the same molar mass and polydispersity index. 相似文献
992.
993.
《印度化学会志》2021,98(1):100018
Biomass is considered as the most sustainable and renewable resource for the synthesis of value added potential platform chemicals. Various techniques are utilized to extract or to pre-treat or to isolate various value added chemicals from biomass. Pre-treatment of the biomass is a very essential aspect to enhance the biomass processing yield which is attributed to reduced lignin content/delignification, cellulose crystallinity and hemi-cellulose hydration. In search of efficient extraction and processing for biomass treatment, supercritical fluid (SCF) has been considered as the green technique to obtain the value added chemicals with higher efficiency than conventional technique. The use of the supercritical carbon dioxide (SC–CO2) pre-treatment on biomass not only enhances glucose yield effectively but also delignify, hydrolyse hemi-cellulose component and allows extraction of various compounds from the biomass. However, very limited research articles are available for the use of SC-CO2 for biomass processing to obtain value-added chemicals. In view of this, the present review article focus on the recent advances of applications of SC-CO2 in (i) extraction of value added chemicals from biomass processing, (ii) biomass pre-treatment, (iii) factors affecting SC-CO2 processing efficiency, (iv) scale-up scenario (v) challenges and opportunities in this field. 相似文献
994.
《中国化学快报》2021,32(10):3105-3108
Lightweight, highly strong and bio-based structural materials remain a long-lasting challenge. Here, inspired by nacre, a lightweight and high mechanical performance cellulosic material was fabricated via a facile and effective top-down approach and the resulting material has a high tensile strength of 149.21 MPa and toughness of 1.91 MJ/m3. More specifically, the natural balsawood (NW) was subjected to a simple chemical treatment, removing most lignin and partial hemicellulose, follow by freeze-drying, forming wood aerogel (WA). The delignification process produced many pores and exposed numerous aligned cellulose nanofibers. Afterwards, the WA absorbed a quantity of moisture and was directly densified to form above high-performance cellulosic material. Such treatment imitates highly ordered “brick-and-mortar” arrangement of nacre, in which water molecules plays the role of mortar and cellulose nanofibrils make the brick part. The lightweight and good mechanical properties make this material promising for new energy car, aerospace, etc. This paper also explains the strengthening mechanism for making biomimetic materials by water molecules-induced hydrogen bonding and will open a new path for designing high-performance bio-based structural materials. 相似文献
995.
Hibi K Ushio H Fukuda H Mitsubayashi K Hayashi T Ren H Endo H 《Analytical and bioanalytical chemistry》2008,391(4):1147-1152
Bacterial cold water disease, caused by Flavobacterium psychrophilum, is a serious problem in the aquaculture industry worldwide. Several methods to prevent and treat cold water disease have
been studied. Although detection at the early stage of F. psychrophilum infection is very important for the prevention and treatment of cold water disease, an effective detection method has not
yet been developed. The use of flow cytometry (FCM) for the rapid determination of bacterial cell numbers with high sensitivity
is beginning to attract attention. Immunomagnetic separation (IMS) has also been used to detect F. psychrophilum. The purpose of the present study was to develop a method to quickly determine the number of bacterial cells by combining
the FCM and IMS methods. Because samples can be more effectively concentrated using smaller magnetic beads and stronger magnetism,
we used carbonyl iron powder as the magnetic beads for the IMS. The detection level of F. psychrophilum using FCM combined with IMS was 5 orders lower than that using FCM without IMS. The values determined using FCM combined
with IMS strongly correlated with those obtained using the colony-counting method, in the range of approximately 10–108 colony-forming units per milliliter. One FCM assay could be completed within 60 s and the total assay time, including sample
preparation, was less than 2 h. The combined method of FCM with IMS developed in this study can be used reliably for the rapid
detection of F. psychrophilum. 相似文献
996.
An intermediate product that was yellow, soluble, and solid was obtained in a high-radiation flash pyrolysis reactor. Under two different radiant heat fluxes, the yields tended to both increase initially until achieving a steady state, and then increase again with the progress of reaction. The compositional analysis of the yellow product was performed on high performance liquid chromatography (HPLC). It was indicated that the product mainly consisted of oligosaccharides, glucose, levoglucosan, methylglyoxal and so on. The compounds including oligosaccharides such as cellobiose and cellotriose, and monosaccharides such as glucose were regarded as active cellulose. Under the higher heat flux, the relative yield of the active cellulose increased initially, followed by a decreasing trend, and achieved a maximum mass fraction of 68% (w) in the soluble yellow product. The oligosaccharides with higher degree of polymerization (DP) were the primary components. Under the lower heat flux the yield of active cellulose was relatively lower, achieving a maximum of about 57% (w), and more saccharides with lower DP were contained. It was suggested that active cellulose was quite unstable at high temperature, and easily decomposed into saccharides with lower DP, even char, volatiles, and gaseous products. Finally an improved mechanism was proposed to describe the reaction route of formation and consequent evolution of active cellulose during cellulose pyrolysis. 相似文献
997.
Spectrophotometric determination of inorganic mercury (II) after preconcentration of its diphenylthiocarbazone complex on a cellulose column 总被引:1,自引:0,他引:1
Rajesh N Hari MS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(5):1104-1108
A simple and a relatively green methodology have been developed for the preconcentration of mercury based on the adsorption of its diphenylthiocarbazone complex on a cellulose column. The effects of various parameters such as effect of acidity, eluting agents, stability of the column, sample volume, interfering ions, etc. have been studied in detail. The adsorbed complex could be easily desorbed using environmentally benign polyethylene glycol-400 and the concentration of mercury was determined using visible spectrophotometry. The calibration graph was linear in the range 0-2mugmL(-1) of mercury with a detection limit of 2mugL(-1) and the validity of the proposed method was checked by studying the recovery of mercury in spiked tap water, well water and sea water samples. The highest preconcentration factor achieved for quantitative recovery (>95%) of mercury (II) was 33 for a 500mL sample volume. The method was also applied to the analysis of mercury content in city waste incineration ash (CRM176). The relative standard deviation of the method was found to be 3.5%. 相似文献
998.
Terhi Saarinen Monika
sterberg Janne Laine 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,330(2-3):134-142
The adsorption of polyelectrolyte (PE) multilayers and complexes, obtained from both high- and low-charge polyelectrolytes, was studied on silica and on cellulose model surfaces by quartz crystal microbalance with dissipation (QCM-D). The film properties acquired with the different strategies were compared. When polyelectrolytes were added on an oppositely charged surface in sequence to form multilayers both the change in frequency and dissipation increased. The changes in frequency and dissipation were clearly higher if low-charge PEs were used in the multilayer formation. The substrate, silica or cellulose, did not affect the adsorption behaviour of low-charge PEs and only minor differences were seen in the adsorbed amounts and changes in dissipation of high-charge PEs between SiO2 and cellulose. The complexes formed by low-charge PEs had higher changes in frequency and dissipation at low ionic strength on both surfaces, while the complexes formed from high-charge polyelectrolytes adsorbed more at high salt concentration. The complexes of low-charge polyelectrolytes adsorbed more on silica, while the complexes formed by high-charge PEs formed thicker layers on cellulose. The charge ratio had a significant effect on the adsorption and the highest changes in frequency and dissipation were obtained in the anionic/cationic charge ratio of 0.5–0.6. Generally, the multilayers and complexes formed by low-charge polyacrylamides adsorbed highly and formed rather thick layers on both surfaces, unlike the high-charge PEs which formed thin layers using either one of the addition techniques. 相似文献
999.
Linghao Zhong James F. Matthews Michael F. Crowley Tauna Rignall César Talón Joseph M. Cleary Ross C. Walker Giridhar Chukkapalli Clare McCabe Mark R. Nimlos Charles L. Brooks III Michael E. Himmel John W. Brady 《Cellulose (London, England)》2008,15(2):261-273
We describe the construction of a model complex of the cellobiohydrolase I (CBH I) cellulase from Trichoderma reesei bound to a cellulose microfibril in an aqueous environment for use in molecular dynamics (MD) simulations. Preliminary characterization
from the initial phases of an MD simulation of this complex is also described. The linker sequence between the two globular
domains was found to be quite flexible, and the oligosaccharides bound to this linker were found to prefer to be splayed like
the spokes in a wheel due to their hydration requirements. The overall conformations of the two globular domains remained
stable in the simulations, although both underwent changes in their orientations. 相似文献
1000.
Degrees of polymerization (DP) and DP distribution of dilute acid-hydrolyzed products of alkali-treated native and regenerated celluloses 总被引:1,自引:1,他引:0
Three groups of cellulose II samples, 20% NaOH-treated native celluloses (M-native celluloses), commercial regenerated celluloses
and those treated with 20% NaOH (M-regenerated celluloses), were subjected to dilute acid hydrolysis at 105 °C to obtain so-called
leveling-off degrees of polymerization (LODP). Molecular mass parameters of the acid-hydrolyzed products were analyzed by
SEC-MALLS using 1% LiCl/DMAc as an eluent. The LODP values were in the order of M-native celluloses ≅ M-regenerated celluloses > regenerated
celluloses. The LODP values of M-regenerated celluloses are 1.5–1.7 times as much as those of the regenerated celluloses;
the cellulose II crystallites in regenerated celluloses increase in size to the longitudinal direction by the alkali treatment
and the successive acid hydrolysis at 105 °C. This increase in the longitudinal crystal sizes might primarily occur during
acid hydrolysis. All the acid-hydrolyzed products had bimodal SEC elution patterns, i.e. the predominant high-molecular-mass
and minor low-molecular-mass components, the latter of which corresponded to DP 20. 相似文献