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991.
Yaimara Solís Natalia Davidenko Raúl G. Carrodeguas Jeny Cruz Andy Hernández Miriela Tomás Ruth E. Cameron Carlos Peniche 《Journal of Materials Science》2013,48(2):841-849
Chitosan/apatite (CHI/Ap) composites are attracting great attention as biomaterials for bone repair and regeneration procedures. The reason is their unique set of properties: bioactivity and osteoconductivity provided by Ap and resorbability supplied by CHI among others. Thus, in this study, CHI/Ap and CHI/Si-doped Ap composites were prepared and characterized. Particle size, surface area, in vitro physiological stability, enzymatic biodegradation, and bioactivity were evaluated. Unimodal particle size distribution was obtained for composites with high CHI/Ap ratios while bimodal distribution was present in composites with low CHI/Ap ratio. Physiological stability decreased with Si doping and with the CHI content. Acetylation degree and molecular weight of CHI did not affect in vitro stability. Rate of enzymatic degradation increased with the CHI content in composites. Si-doped Ap composites also showed increased degradation with respect to non-doped ones. The bioactivity of the composites was evidenced by the deposition on their surface of a calcium phosphate layer with Ap morphology after immersion in simulated body fluid. Both, biodegradation and bioactivity were dependent on the molecular weight of the polymeric CHI matrix. These results suggest that the CHI/Ap composites obtained are promising materials for bone regeneration applications. 相似文献
992.
Hybrid organic–inorganic materials based on polypyrrole and 1,3-dithiole-2-thione-4,5-dithiolate (DMIT) containing dianions 总被引:1,自引:0,他引:1
Antonio Gerson Bernardo da Cruz James Lewis Wardell Ana M. Rocco 《Journal of Materials Science》2008,43(17):5823-5836
The synthesis of hybrid materials by electropolymerization of pyrrole and inorganic complexes based on the DMIT ligand (1,3-dithiole-2-thione-4,5-dithiolate),
e.g. [NEt4]2[M(DMIT)
n
] (M = Ni, Pd or Pd, n = 2; M = Sn, n = 3], in acetonitrile solution is reported. Spectroscopic data showed that DMIT-containing anions, [M(DMIT)
n
]2−, were inserted into the polypyrrole framework without chemical modification during the electropolymerization process. Cyclic
voltammetry showed that materials obtained were electroactive, undergoing redox processes related to both the conducting polymer
and the counteranions. The electrochemical results also suggest that, in the case of the transition metal containing films,
the counteranions are not trapped in the PPy matrix but undergo anion exchange during the redox cycle of PPy. However, an
opposite behaviour was observed with the film with [M(DMIT)
n
]2−. The films exhibit good thermal stabilities and have conductivity values expected for semiconductors. This study of these
hybrid materials highlights the importance of targeting specific materials for specific applications.
相似文献
Antonio Gerson Bernardo da CruzEmail: |
993.
Steven F. Durrant Nilson C. da Cruz Elidiane C. Rangel Mario A. Bica de Moraes 《Thin solid films》2008,516(15):4940-4945
Thin films were deposited by plasma enhanced chemical vapor deposition from titanium (IV) ethoxide (TEOT)–oxygen–helium mixtures. Actinometric optical emission spectroscopy was used to obtain the relative plasma concentrations of the species H, CH, O and CO as a function of the percentage of oxygen in the feed, Rox. The concentrations of these species rise with increasing Rox and tend to fall for Rox greater than about 45%. As revealed by a strong decline in the emission intensity of the actinometer Ar as Rox was increased, the electron mean energy or density (or both) decreased as greater proportions of oxygen were fed to the chamber. This must tend to reduce gas-phase fragmentation of the monomer by plasma electrons. As the TEOT flow rate was fixed, however, and since the species H and CH do not contain oxygen, the rise in their plasma concentrations with increasing Rox is explained only by intermediate reactions involving oxygen or oxygen-containing species. Transmission infrared (IRS) and X-ray photoelectron (XPS) spectroscopies were employed to investigate film structure and composition. The presence of CH2, CH3, CC, C–O and CO groups was revealed by IRS. In addition, the presence of C–O and CO groups was confirmed by XPS, which also revealed titanium in the + 4 valence state. The Ti content of the films, however, was found to be much less than that of the monomer material itself. 相似文献
994.
Juliana Coatrini SoaresAndré Brisolari Valquíria da Cruz RodriguesEdgar Aparecido Sanches Débora Gonçalves 《Reactive and Functional Polymers》2012,72(2):148-152
Urease (Urs) was immobilized in electrochemically prepared polypyrrole (PPy) and the resulting films were characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet visible spectroscopy (UV-VIS). The enzymatic activity of Urs entrapped in the PPy matrix was confirmed by the catalytic conversion of urea into carbon dioxide and ammonia, when urea was detected amperometrically at different concentrations in standard samples and commercial fertilizers. The PPy/Urs biosensors exhibited selectivity, a relatively high efficiency at urea concentrations below 3.0 mmol L−1, and a sensitivity to urea of 2.41 μA cm−2 mmol−1 L. 相似文献
995.
Carlos Oliveira Cruz Rui Cunha Marques 《Computer-Aided Civil and Infrastructure Engineering》2012,27(10):782-800
Abstract: The use of the public sector comparator (PSC) is gaining momentum as a tool to ensure value for money in public–private partnership (PPP) projects. Several countries have been engaging in the calculation of the PSC, but the methodologies are excessively dependent on deterministic models, as referred to by the existing literature. Alternatives to accommodate uncertainty and forecast bias are required to improve the robustness of the calculations. This article proposes new developments in existing methodologies able to accommodate dynamic analysis to cope with uncertainty in the assumptions. A simulation model was used to compute the variability in the PSC, but the research went a step further in developing a Bayesian network approach. The output of both models is a probability distribution for the PSC, instead of just a single value, therefore, the authors have developed a methodology for comparing the PSC distribution with the PPP value. 相似文献
996.
Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge 总被引:1,自引:0,他引:1
De la Cruz N Giménez J Esplugas S Grandjean D de Alencastro LF Pulgarín C 《Water research》2012,46(6):1947-1957
This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L−1, and a real global quantity of micropollutants of 29.5 μg L−1. The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV254) alone, dark Fenton (Fe2+,3+/H2O2) and photo-Fenton (Fe2+,3+/H2O2/light). Different irradiation sources were used for the photo-Fenton experiences: UV254 and simulated sunlight. Iron and H2O2 concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV254, 50 mg L−1 of H2O2, with and without adding iron (5 mg L−1 of Fe2+ added or 1.48 mg L−1 of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H2O2 concentration increased (10, 25 and 50 mg L−1), best degradations were observed. UV254, Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal.The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations. 相似文献
997.
Herrero-Fresno A Martínez N Sánchez-Llana E Díaz M Fernández M Martin MC Ladero V Alvarez MA 《International journal of food microbiology》2012,157(2):297-304
Tyramine and histamine are the biogenic amines (BAs) most commonly found in cheese, in which they appear as a result of the microbial enzymatic decarboxylation of tyrosine and histidine respectively. Given their toxic effects, their presence in high concentrations in foods should be avoided. In this work, samples of three cheeses (Zamorano, Cabrales and Emmental) with long ripening periods, and that often have high BA concentrations, were screened for the presence of BA-degrading lactic acid bacteria (LAB). Seventeen isolates were found that were able to degrade tyramine and histamine in broth culture. All 17 isolates were identified by 16S rRNA sequencing as belonging to Lactobacillus casei. They were typed by plasmid S1-PFGE and genomic macrorestriction-PFGE analysis. Two strains (L. casei 4a and 5b) associated with high degradation rates for both BAs were selected to test how this ability might affect histamine and tyramine accumulation in a Cabrales-like mini-cheese manufacturing model. The quantification of BAs and the monitoring of the strains' growth over ripening were undertaken by RP-HPLC and qPCR respectively. Both strains were found to reduce histamine and tyramine accumulation. These two strains might be suitable for use as adjunct cultures for reducing the presence of BAs in cheese. 相似文献
998.
Zuzarte M Gonçalves MJ Cruz MT Cavaleiro C Canhoto J Vaz S Pinto E Salgueiro L 《Food chemistry》2012,135(3):1505-1510
This work reports the antifungal activity of Lavandula luisieri essential oils against yeast, dermatophyte and Aspergillus strains responsible for human infections and food contamination. The oil's cytotoxicity and its effect on the yeast-mycelium transition in Candida albicans, an important virulence factor, were also evaluated. Analyses by GC and GC/MS showed a peculiar composition of irregular monoterpenes. Significant differences between the samples occurred in the amounts of 1,8-cineole, fenchone and trans-α-necrodyl acetate. The oil with higher amounts of irregular monoterpenes was the most effective. The influence of the oils on the dimorphic transition in C. albicans was also studied through the germ tube inhibition assay. Filamentation was completely inhibited at concentrations sixteen times lower than the minimal inhibitory concentration. The results support the use of L. luiseiri essential oils in the development of new phytopharmaceuticals and food preservatives and emphasise its antifungal properties at concentrations not cytotoxic or with very low detrimental effects on mammalian cells. 相似文献
999.
S.H.I. Lee C.H. Camargo J.L. Gonçalves A.G. Cruz B.T. Sartori M.B. Machado C.A.F. Oliveira 《Journal of dairy science》2012
This research aimed to evaluate the occurrence of Staphylococcus aureus isolates in milk and in the milking environment of 10 small-scale farms (<400 L/d) located in the regions of Franca and Ribeirão Preto, state of São Paulo, Brazil. Two-hundred twenty samples of milk were collected from individual cows, along with 120 samples from bulk tank milk, 389 samples from milking equipment and utensils (teat cups, buckets, and sieves), and 120 samples from milkers’ hands. Fifty-six Staph. aureus strains were isolated from 849 analyzed samples (6.6%): 12 (5.5%) from milk samples of individual cows, 26 (21.7%) from samples of bulk tank milk, 14 (3.6%) from samples collected from equipment and utensils, and 4 (3.3%) from samples from milkers’ hands. Pulsed-field gel electrophoresis typing of the 56 Staph. aureus isolates by SmaI restriction enzyme resulted in 31 profiles (pulsotypes) arranged in 12 major clusters. Results of this study indicate a low incidence, but wide distribution of Staph. aureus strains isolated from raw milk collected from individual cows and surfaces of milkers’ hands and milking equipment in the small-scale dairy farms evaluated. However, the high percentage of bulk milk samples found with Staph. aureus is of public health concern because raw, unprocessed milk is regularly consumed by the Brazilian population. 相似文献
1000.
Pavón MÁ González I de la Cruz S Martín R Lacarra TG 《Journal of the science of food and agriculture》2012,92(1):74-77
BACKGROUND: Detection and quantification of ochratoxin A (OTA) in dried fig samples purchased in Spain has been carried out using high‐performance liquid chromatography with fluorescence detection after extraction with methanol and sodium bicarbonate, and clean‐up by using an immunoaffinity column. RESULTS: The detection limit of the method was 0.06 ng g?1, and the limit of quantification 0.18 ng g?1. OTA was detected in 31 (88.6%) out of 35 samples of dried figs analysed, with concentrations that ranged from < 0.1 to 277 ng g?1. However, only three samples contained OTA concentrations above the tolerable level set by European Commission regulations for dried vine fruits (10 ng g?1). CONCLUSION: The results of this survey show the value of monitoring OTA in dried figs especially if they are home grown. Copyright © 2011 Society of Chemical Industry 相似文献