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991.
A pre-concentration method was developed for determination of trace amounts of cadmium, copper and lead in water samples by FAAS after coprecipitation by using potassium 4-methylpiperidinedithiocarbamate (K4-MPDC) as a chelating agent and Bi(III) as a carrier element. This procedure is based on filtration of the solution containing precipitate on a cellulose nitrate membrane filter following Cd(II), Cu(II) and Pb(II) coprecipitation with Bi(III)4-MPDC and then the precipitates together with membrane filter were dissolved in concentrated nitric acid. The metal contents of the final solution were determined by FAAS. Several parameters including pH of sample solution, amount of carrier element and reagent, standing time, sample volume for precipitation and the effects of diverse ions were examined. The accuracy of the method was tested with standard reference material (MBH, C31XB20 and CRM BCR-32) and Cd, Cu and Pb added samples. Determination of Cd, Cu and Pb was carried out in sea water, river water and tap water samples. The recoveries were >95%. The relative standard deviations of determination were less than 10%. 相似文献
992.
Alma Patricia Patiño‐Soto Saúl Sánchez‐Valdes Luis Francisco Ramos‐deValle 《大分子材料与工程》2007,292(3):302-309
Acrylonitrile‐butadiene‐styrene (ABS)/clay nanocomposites have been prepared using two types of ABS with different AN contents and a chemically modified clay, Cloisite 20A. The composites were prepared by melt mixing in a twin‐screw extruder. Their morphological properties were characterized by XRD and TEM. The thermal stability of the polymer nanocomposites was studied using TGA and flammability tests. The results were analyzed in terms of the effect of the clay content and the type of ABS used on the clay dispersion and the thermal stability of the nanocomposites. Experimental results confirmed that better dispersion and intercalation and/or exfoliation can be obtained when using an ABS with a higher AN content. The study using TGA and flammability tests showed that the nanodispersed layers of silicate enhanced the thermal stability of the ABS matrix, and that an ABS with higher AN content was more effective in providing fire retardancy. This suggests that when using higher AN contents, more polar groups are present within the polymer matrix, allowing a more homogeneous dispersion and intercalation of the chain polymers into the organomodified montmorillonite clay (MMT), and even some exfoliation of the nanoclay. <figure> <picture> <source srcset="https://wol-prod-cdn.literatumonline.com/cms/attachment/da7b62bb-9121-4ac1-920d-6b3166631b46/mgra001.jpg" media="(min-width: 1650px)"></source><img class="figure__image-full" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/86290c58-58c1-4fe0-8973-5a8470094357/mgra001.jpg" data-lg-src="https://wol-prod-cdn.literatumonline.com/cms/attachment/da7b62bb-9121-4ac1-920d-6b3166631b46/mgra001.jpg" alt="image" title="image"></picture> <p class="caption-style"> 相似文献
993.
Palmu K Ishida K Mäntsälä P Hertweck C Metsä-Ketelä M 《Chembiochem : a European journal of chemical biology》2007,8(13):1577-1584
Genome-sequencing projects have revealed that Streptomyces bacteria have the genetic potential to produce considerably larger numbers of natural products than can be observed under standard laboratory conditions. Cryptic angucycline-type aromatic polyketide gene clusters are particularly abundant. Sequencing of two such clusters from Streptomyces sp. PGA64 and H021 revealed the presence of several open reading frames that could be involved in processing the basic angucyclic carbon skeleton. The pga gene cluster contains one putative FAD-dependant monooxygenase (pgaE) and a putatively bifunctional monooxygenase/short chain alcohol reductase (pgaM), whereas the cab cluster contains two similar monooxygenases (cabE and cabM) and an independent reductase (cabV). In this study we have reconstructed the biosynthetic pathways for aglycone synthesis by cloning and sequentially expressing the angucycline tailoring genes with genes required for the synthesis of the unmodified angucycline metabolite-UWM6-in Streptomyces lividans TK24. The expression studies unequivocally showed that, after the production of UWM6, the pathways proceed through the action of the similar monooxygenases PgaE and CabE, followed by reactions catalysed by PgaM and CabMV. Analysis of the metabolites produced revealed that addition of pgaE and cabE genes directs both pathways to a known shunt product, rabelomycin, whereas expression of all genes from a given pathway results in the production of the novel angucycline metabolites gaudimycin A and B. However, one of the end products is most probably further modified by endogenous S. lividans TK24 enzymes. These experiments demonstrate that genes that are either inactive or cryptic in their native host can be used as biosynthetic tools to generate new compounds. 相似文献
994.
Poly(propylene) (PP) composites were prepared by using eggshell (ES) as filler and their mechanical properties were compared with those using talc (TA) and calcium carbonate (CC) of different grain sizes (<i>X</i><sub>50</sub>). A decrease in impact strength and deformation at break with increase in filler content was observed. The PP composite with ES (<i>X</i><sub>50</sub> = 8.4 µm) was stiffer than those with CC (<i>X</i><sub>50</sub> = 0.7 µm). The hybrid composite PP‐ES‐TA showed a similar stiffness as the PP‐TA composites due to the similar morphology of TA (<i>X</i><sub>50</sub> = 0.5 µm) and ES, when TA was replaced up to 75 wt.‐% by ES. SEM study revealed evidence of improved interfacial bonding between PP and ES in theirs composites. <figure> <picture> <source srcset="https://wol-prod-cdn.literatumonline.com/cms/attachment/dd387483-44cd-49a1-9948-27328c462499/mgra001.jpg" media="(min-width: 1650px)"></source><img class="figure__image-full" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/dfbe5dab-c674-4333-8a09-aa6494f3dbeb/mgra001.jpg" data-lg-src="https://wol-prod-cdn.literatumonline.com/cms/attachment/dd387483-44cd-49a1-9948-27328c462499/mgra001.jpg" alt="image" title="image"></picture> <p class="caption-style"> 相似文献
995.
Tunnel junctions with multiferroic barriers 总被引:2,自引:0,他引:2
Gajek M Bibes M Fusil S Bouzehouane K Fontcuberta J Barthélémy A Fert A 《Nature materials》2007,6(4):296-302
Multiferroics are singular materials that can exhibit simultaneously electric and magnetic orders. Some are ferroelectric and ferromagnetic and provide the opportunity to encode information in electric polarization and magnetization to obtain four logic states. However, such materials are rare and schemes allowing a simple electrical readout of these states have not been demonstrated in the same device. Here, we show that films of La(0.1)Bi(0.9)MnO(3) (LBMO) are ferromagnetic and ferroelectric, and retain both ferroic properties down to a thickness of 2 nm. We have integrated such ultrathin multiferroic films as barriers in spin-filter-type tunnel junctions that exploit the magnetic and ferroelectric degrees of freedom of LBMO. Whereas ferromagnetism permits read operations reminiscent of magnetic random access memories (MRAM), the electrical switching evokes a ferroelectric RAM write operation. Significantly, our device does not require the destructive ferroelectric readout, and therefore represents an advance over the original four-state memory concept based on multiferroics. 相似文献
996.
Brayner R Barberousse H Hemadi M Djedjat C Yéprémian C Coradin T Livage J Fiévet F Couté A 《Journal of nanoscience and nanotechnology》2007,7(8):2696-2708
Common Anabaena, Calothrix, and Leptolyngbya cyanobacteria are shown to form Au, Ag, Pd, and Pt nanoparticles of well-controlled size. These nanoparticles are synthesized intra-cellularly, and naturally released in the culture medium, where they are stabilized by algal polysaccharides, allowing their easy recovery. The size of the recovered particles as well as the reaction yield is shown to depend on the cyanobacteria genus. Investigations of nanoparticle formation indicate that the intracellular nitrogenase enzyme is responsible for the metal reduction but that the cellular environment is involved in the colloid growth process. 相似文献
997.
BACKGROUND: The free radical theory of aging suggests the oxygen-derived species as the causative agents and free radical scavengers as the defense systems in aging process. The exact role of the free radical scavenging effects of melatonin in aging remains to be clarified. OBJECTIVE: In this experimental study, we investigated the age-related changes of malondialdehyde (MDA), a lipid peroxidation product, and glutathione (GSH) and the effects of exogenous melatonin. METHODS: Plasma, liver, and lung MDA and GSH levels of 9- and 28-month-old rats were measured. RESULTS: Plasma, lung, and liver MDA levels of old rats were significantly higher than those of the young ones (p = 0.024, p = 0.005, and p = 0.0007, respectively). However, while the lung GSH levels were found to be significantly decreased in the control group of old rats as compared with young ones (p = 0.005), the liver GSH levels were unchanged. Plasma MDA levels were found to be significantly lower in the melatonin group of old rats as compared with the control group (p = 0.020) but lung and liver MDA levels were not significantly different. There were no significant differences in the levels of measured parameters between both groups of young rats. CONCLUSION: Our results suggest that increased levels of lipid peroxidation products may have a role in aging, and exogenous melatonin may delay the aging process of tissues by means of its free radical scavenging effects. 相似文献
998.
Raúl Sánchez-Vioque Alfonso Clemente Javier Vioque Juan Bautista Francisco Millán 《Journal of the American Oil Chemists' Society》1998,75(7):851-855
The neutral lipids composition of defatted chickpea flour and two types of protein isolates has been studied. The main compounds
in neutral lipids are triacylglycerols, free fatty acids, and diacylglycerols. Other compounds present are wax esters, free
fatty alcohols, and free sterols. The main fatty acids in neutral lipids are C<sub>18:2</sub> and C<sub>18:1</sub> among the unsaturated, and C<sub>16:0</sub> and C<sub>18:0</sub> among the saturated acids. Free and esterified alcohols range from C<sub>16:0</sub> to C<sub>28:0</sub>, the majority being those with an even number of carbon atoms. Sterols observed are β-sito-sterol, campesterol, stigmasterol,
and δ-5-avenasterol. Triacyl-glycerols are partially hydrolyzed, and the amounts of unsaturated sterols and unsaturated fatty
acids are reduced as a result of the chemical treatment during production of the protein isolates. 相似文献
999.
Marie-Caroline Michalski Stéphane Desobry Marie-Noëlle Pons Joël Hardy 《Journal of the American Oil Chemists' Society》1998,75(4):447-454
Adhesion of oils and fatty food products to packages is an important storage problem, because it increases product-package
interactions that alter quality. Reducing such adhesion would also allow savings in recycling and cleaning processes. The
aim of our work was to test if some thermodynamical adhesion models were correlated to edible oils’ bulk adhesion as measured
experimentally. Food-contact surfaces were low-density polyethylene, polyethylene teraphthalate, stainless steel, and glass.
The Young-Dupré equation and five models of adhesion from the literature were used to calculate solids’ surface tension and
the thermodynamical work of adhesion (Wa). The dispersive, polar, acid-base, and hydrogen surface tension components of oils
and solids were calculated. The experimental adhesion, or amount of edible oils remaining on solid surfaces after contact,
was found to be correlated to Young-Dupré Wa, involving contact angle measured by specially designed image analysis technique.
Two models, involving, respectively, surface tension’s hydrogen component and a linear dependence of Wa<sup>p</sup> on the liquid polar surface tension component, fitted best with oil bulk adhesion as measured experimentally. Our theoretical
approach to fatty food material adhesion seems, so far, consistent to predict global residues of edible oils on solid surfaces. 相似文献
1000.
Franois Ozanam Charlotte Vieillard Marcel Warntjes Thomas Dubois Maxime Pauly Jean-Noël Chazalviel 《加拿大化工杂志》1998,76(6):1020-1026
The hydrogentated surface of silicon exhibits remarkable properties, but poor resistance to oxidation. To improve its stability, surface hydrogen has been replaced by several organic groups. Such grafting can be carried out chemically by a multi-step reaction scheme. However, an electrochemical approach allows direct reaction with the hydrogenated surface. The porous-silicon surface has been partially methoxylated by a controlled anodic dissolution. If has also been methylated using a non-destructive anodic process, with a yield of 80%, limited only by steric hindrance. The methylated surface of porous silicon exhibits a stability against oxidation increased by an order of magnitude. 相似文献