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11.
Thierry Astruc Philippe Gatellier Roland Labas Véronique Santé Lhoutellier Penka Marinova 《Meat science》2010
A histological and ultrastructural study was conducted to characterize changes in beef muscle structure after heating. Pieces of rectus abdominis muscle were heated at 100 °C over varying time frames from 15 min to 60 min and at 270 °C for 1 min; samples were then prepared for optical and transmission electron microscopy. After 15 min of heating, at 100 °C, a lateral shrinkage in fibre of 48% and an increase in gaps between the myofibrillar masses of 27% was noted. No more significant evolution was observed as heating duration escalated. The ultrastructure showed strong myofibril to sarcolemma detachments in which granular aggregates, coming in part from myofibrillar proteins, are stored. Neighbouring muscle fibres showed strong heterogeneity in morphological behaviour after thermal treatment, suggesting that differences in composition and structure of the cytoskeleton proteins in the different fibres can cause denaturation/shrinkage of the proteins at different times along the timescale of microstructural changes during heating. Short heating at high temperatures expanded the gaps between myofibrillar mass, but the overall changes in the ultrastructure were similar to those obtained when heating at 100 °C. 相似文献
12.
Deteriorating effects of lichen and microbial colonization of carbonate building rocks in the Romanesque churches of Segovia, Spain 总被引:1,自引:0,他引:1
de Los Ríos A Cámara B García Del Cura MA Rico VJ Galván V Ascaso C 《The Science of the total environment》2009,407(3):1123-1134
In this study, the deterioration effects of lichens and other lithobionts in a temperate mesothermal climate were explored. We examined samples of dolostone and limestone rocks with visible signs of biodeterioration taken from the exterior wall surfaces of four Romanesque churches in Segovia (Spain): San Lorenzo, San Martín, San Millán and La Vera Cruz. Biofilms developing on the lithic substrate were analyzed by scanning electron microscopy. The most common lichen species found in the samples were recorded. Fungal cultures were then obtained from these carbonate rocks and characterized by sequencing Internal Transcribed Spacers (ITS). Through scanning electron microscopy in back-scattered electron mode, fungi (lichenized and non-lichenized) were observed as the most frequent microorganisms occurring at sites showing signs of biodeterioration. The colonization process was especially conditioned by the porosity characteristics of the stone used in these buildings. While in dolostones, microorganisms mainly occupied spaces comprising the rock's intercrystalline porosity, in bioclastic dolomitized limestones, fungal colonization seemed to be more associated with moldic porosity. Microbial biofilms make close contact with the substrate, and thus probably cause significant deterioration of the underlying materials. We describe the different processes of stone alteration induced by fungal colonization and discuss the implications of these processes for the design of treatments to prevent biodeterioration. 相似文献
13.
Transmission electron microscopy, scanning electron microscopy, and ultrastructural cytochemistry were utilized to study megakaryoblastic cells from four patients suffering from megakaryoblastic leukemia. The results show that megakaryoblastic leukemic cells have a unique ultrastructural appearance, surface architecture, and cytochemical activity. The cells are positive for platelet peroxidase cytochemical reaction, which is localized in the perinuclear space and endoplastic reticulum, but not in the Golgi apparatus and cytoplasmic granules. They have a rather smooth surface and display blebs or tuberculi which are different from those in other types of leukemic cells as seen under the scanning electron microscope. The megakaryoblastic leukemic cells also show a special appearance under the transmission electron microscope, such as a cytoplasm which contains numerous small mitochondria, mostly concentrated in one pole of the cell. These ultrastructural and cytochemical characteristics of the megakaryoblastic leukemic cells revealed by the combined techniques are very useful in the diagnosis of megakaryoblastic leukemia. 相似文献
14.
Changes in physiochemical quality and browning related enzyme activity of longkong fruit during four different weeks of on-tree maturation 总被引:3,自引:0,他引:3
Karthikeyan VenkatachalamMutita Meenune 《Food chemistry》2012,131(4):1437-1442
The optimum harvesting period of longkong from 13 to 16 weeks of maturation were used to analyse the changes in physiochemical and browning related enzymes. The colour, such as lightness (L∗) and yellowness (b∗) decreased and conversely redness (a∗) increased. The fruit weight was significantly increased from 21.21 to 24.93 g and the diameter was also increased (p > 0.05). Chemical qualities, such as total soluble solids, pH, total sugar and reducing sugar increased while titratable acidity decreased at the end of maturation period (p < 0.05). The antioxidant activity, such as 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (from 4.73 to 8.97 mg/100 g), ferric reducing antioxidant power (from 5.06 to 6.83 mg/100 g) and total phenolic content increased (from 42.65 to 58.71 mg/100 g) (p < 0.05). The polyphenol oxidase activity significantly increased throughout the maturation; peroxidase and phenyl alanine ammonia lyase enzymes increased at the beginning but after that they decreased at the end of the maturation period. Peel epidermal trichomes losses on the surface and parenchyma cell changes in the cross section were found during these stages. 相似文献
15.
This study investigated the effect of pre-rigor rapid chilling (RC) on the rate of pH and temperature decline, shear force values and ultrastructure of M. longissimus from beef carcasses exposed to electrical stimulation (ES). Chinese bull carcasses were electrically stimulated, and the alternate sides of the carcasses either were chilled conventionally (CC, 0-4°C, air speed 0.5 m/s for 24 h) or they underwent RC (-14±1°C, air speed 3 m/s for 2 h and then cooled under CC conditions until 24 h post-mortem). The results showed that RC increased the rate of temperature decline (P<0.05) and decreased the rate of pH decline (P<0.05). There were no significant differences in the shear force value and sarcomere length of M. longissimus between the two treatments (P>0.05). The results of this study indicate that RC has no detrimental impact on the tenderness of beef carcasses exposed to ES. 相似文献
16.
17.
The effect of the helical wood fiber structure on in-plane composite properties has been analyzed. The used analytical concentric
cylinder model is valid for an arbitrary number of phases with monoclinic material properties in a global coordinate system.
The wood fiber was modeled as a three concentric cylinder assembly with lumen in the middle followed by the S3, S2 and S1
layers. Due to its helical structure the fiber tends to rotate upon loading in axial direction. In most studies on the mechanical
behavior of wood fiber composites this extension-twist coupling is overlooked since it is assumed that the fiber will be restricted
from rotation within the composite. Therefore, two extreme cases, first modeling fiber then modeling composite were examined:
(i) free rotation and (ii) no rotation of the cylinder assembly. It was found that longitudinal fiber modulus depending on
the microfibril angle in S2 layer is very sensitive with respect to restrictions for fiber rotation. In-plane Poisson’s ratio
was also shown to be greatly influenced. The results were compared to a model representing the fiber by its cell wall and
using classical laminate theory to model the fiber. It was found that longitudinal fiber modulus correlates quite well with
results obtained with the concentric cylinder model, whereas Poisson’s ratio gave unsatisfactory matching. Finally using typical
thermoset resin properties the longitudinal modulus and Poisson’s ratio of an aligned softwood fiber composite with varying
fiber content were calculated for various microfibril angles in the S2 layer. 相似文献
18.
Soymilk was prepared from boiled and unboiled comminuted suspensions of dehulled soybean and water using pressurized homogenization (one pass and two pass). Particle size showed significant differences between soymilks homogenized by one pass and two pass. Apparent viscosities and total solid contents showed significant differences between boiled and unboiled treatments. Soymilks exhibited pseudoplastic and thixotropic behavior and Arrhenius model was fitted to express temperature dependence of apparent viscosity. Microscopic images showed hydrated, separated, uniformly distributed, and homogeneous particles in boiled two-pass soymilk as they were disrupted easily and it was selected as the best treatment for processing soymilk containing all of the soybean solids. 相似文献
19.
Amphibian oocytes, arrested in prophase I, are stimulated to progress to metaphase II by progesterone. This process is referred to as meiotic maturation and transforms the oocyte, which cannot support the early events of embryogenesis, into the egg, which can. Meiotic maturation entails global reorganization of cell ultrastructure: In the cell cortex, the plasma membrane flattens and the cortical granules undergo redistribution. In the cell periphery, the annulate lamellae disassemble and the mitochondria become dispersed. In the cell interior, the germinal vesicle becomes disassembled and the meiotic spindles form. Marked changes in the cytoskeleton and mRNA distribution also occur throughout the cell. All of these events are temporally correlated with intracellular signalling events: Fluctuations in cAMP levels, changes in pH, phosphorylation and dephosphorylation, and ion flux changes. Evidence suggests that specific intracellular signals are responsible for specific reorganizations of ultrastructure and mRNA distribution. 相似文献
20.
野蚕黑卵蜂成虫触角化学感器的超微结构和功能 总被引:4,自引:0,他引:4
对野蚕黑卵蜂成虫触角上多侧孔感器和端孔坛形感器超微结构的透射电镜观察表明:在多侧孔感器上,微孔分布于感器的外侧面(迎风面),感器内部具典型的嗅觉感器结构;端孔坛形感器上,微孔分布于感器的顶端,内部神经细胞丰富,具典型的味觉感器(接触化学感器)结构。野蚕黑卵蜂雌蜂触角不同程度切除试验表明:多侧孔感器与寻找寄主栖境(桑树)有关,端孔坛形感器则与对其寄主卵的识别和接受有关。 相似文献