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71.
X. D. Chen 《Drying Technology》2013,31(5):1105-1130
ABSTRACT Milk powder manufacture is carried out on large scale and to exacting standards. To date, process control has been largely empirical. Recent advances in the understanding of process mechanisms and product properties is allowing model-based process control strategies to be developed. This review briefly describes the manufacture of milk powder and discusses in detail milk concentrate viscosity and atomization, particle size distribution, the drying mechanism and protein denaturation, in relation to the development of such strategies. 相似文献
72.
Closing forces of the bovine teat canal 总被引:1,自引:0,他引:1
The magnitude of the forces causing closure of the bovine teat canal was estimated by measuring the pressure required to cause retrograde flow of milk into the canal from a manometer attached to the external teat orifice. Before milking, the hydrostatic pressure required to cause retrograde flow was 12 kPa or greater. Retrograde flow occurred at a pressure of 4-6 kPa once the teat canal surface had been wetted. This 2- or 3-fold fall in the closing forces presumably resulted from the combined effects of fracturing the teat canal epithelium and loss of initial resting tension in the smooth muscle fibres surrounding the teat canal. After milking, retrograde flow into any teat canal occurred at a pressure approximately 1 kPa lower than the wetted, pre-milking value. This small drop, and subsequent recovery approximately 30 min after milking, reflects the change in tonicity of the smooth muscle fibres which are stretched during milking. At hydrostatic pressures below 7-9 kPa, retrograde flow could be arrested momentarily by the occurrence of a teat contraction. At 4-7 kPa, the wave of contraction was also capable of expelling 4-14 microliters milk from the teat canal indicating the outwardly directed, peristaltic nature of the phasic muscular activity. 相似文献
73.
Coryneform bacteria and yeasts of 21 brick cheeses from six German dairies, produced by using undefined ripening cultures, were identified. Arthrobacter nicotianae, Brevibacterium linens, Corynebacterium ammoniagenes, Corynebacterium variabilis and Rhodococcus fascians were found in significant numbers. Out of 148 coryneform isolates 36 could not be identified at the species level. With the exception of a large rennet cheese, the coryneform microflora of rennet and acid cured cheeses were similar, but the cheeses had clearly different yeast populations. Debaryomyces hansenii and Galactomyces geotrichum prevailed in rennet cheeses while Kluyveromyces marxianus and Pichia membranaefaciens were the main species found in acid cured cheese. The dominance of Yarrowia lipolytica probably indicates an improper yeast population, resulting in poor cheese quality. Some of the species identified are potential candidates for designing a defined ripening culture for rennet red smear cheese. 相似文献
74.
《International Dairy Journal》2007,17(9):1123-1131
This study reports the antibiotic susceptibility of 203 strains representing human or probiotic associated Bifidobacterium species as determined by the Etest method. Strains showing minimum inhibitory concentration (MIC) for tetracycline ⩾16 μg mL−1 were detected in all studied Bifidobacterium species/groups (prevalence 4–18%). Mostly the high MICs could be associated with a tet gene, although the correspondence between the phenotypic susceptibility and detection of tet determinants was not complete. In addition to tet(W), tet(O), which has not been previously described in bifidobacteria, was detected. Occasional erythromycin (2%) and/or clindamycin (5%) resistant strains were found, while the strains were uniformly susceptible to ampicillin and vancomycin. Bifidobacterium strains displayed generally high MICs for streptomycin and gentamicin suggesting intrinsic resistance. The Etest on lactic acid bacteria susceptibility test medium supplemented with cysteine proved to be an applicable technique for antimicrobial susceptibility testing of bifidobacteria, and is especially useful when susceptibility data of individual strains is needed. 相似文献
75.
A low-cost industrial grade lactase was developed for one-time use in dairy products. The preparation contained the entire biomass of a selected hyperproducing strain of the yeast Kluyveromyces fragilis. Intracellular lactase was made freely accessible to its substrate by permeabilization of the cell membrane with food compatible reagents. In 0.1M phosphate plus 0.4% methyl paraben, permeabilization was complete in 0.5–1 hr at 50°C, with 90% activity recovery from 180 g/L of cells. Whole-cell lactase contained no viable cells and was free of proteolytic activity. Its pH optimum of 5.6–6.0 proved suitable for lactose hydrolysis concurrent with cottage cheese fermentation. Hydrolyzed whey was used in ice cream and bakers' yeast production. 相似文献
76.
An exopolysaccharide (EPS)-producing Streptococcus thermophilus was used to develop an “all-dairy” ingredient with increased EPS content and greater functionality for dairy applications such as Mozzarella cheese. In laboratory-scale trials, milk protein hydrolysate (MPH), whey protein isolate (WPI) and whey protein hydrolysate (WPH) in reconstituted low-heat skim milk powder (LHSMP) were examined as additional dairy protein sources to increase the production of EPS. WPH supplementation resulted in the greatest EPS production. In batch fermentation, a medium based on LHSMP and WPH, combined with optimum conditions of temperature and pH, was used to obtain maximum production of EPS from S. thermophilus. EPS production was growth associated. The fermented biomass was harvested at the end of the exponential phase and freeze-dried. The reduced viable cell count and the retention of ropiness of the powder from the drying process enabled a higher level of EPS inoculation in a preliminary Mozzarella cheese manufacturing trial. 相似文献
77.
《International Dairy Journal》2007,17(9):1028-1033
Thermal stabilities of bovine plasminogen (PG) activators, tissue and urokinase type (t-PA and u-PA), and their impact on activation of PG, were studied after application of various heating conditions (65, 75, 85, or 90 °C for 15, 20, or 30 s), in both milk and buffer systems. Both t-PA and u-PA were thermally stable in milk heated at ⩽75 °C. However, almost half of the t-PA activity and 30% of u-PA activity was lost after heating milk at 85 °C for 30 s. A lower heat stability of both t-PA and u-PA was observed in buffer than in milk. The decrease in level of PG was more pronounced than that of active plasmin in milk heated at ⩾85 °C for 30 s; however, the residual level of PG was considerably higher than the residual level of active PL. Overall, results indicated that u-PA plays a more significant role than t-PA in the activation of PG during storage of heated milk. 相似文献
78.
《Food Control》2005,16(3):227-230
As part of efforts to establish a control program for antimicrobial residues in local Kenyan dairies, a low cost Bacillus calidolactis test plate was evaluated after laboratory standardization. Test parameters studied were: the practicability of the test handling, the test sensitivity in terms of limits of detection (LODs) compared to codex alimentarius maximum residue limits (MRLs) and repeatability within two different laboratories. The observed LODs were: penicillin G (2 μg/kg), ampicillin (2 μg/kg), amoxicillin (2 μg/kg), oxacillin (15 μg/kg), cefalexin (50 μg/kg), cephapirin (30 μg/kg) and ceftiofur (50 μg/kg). These levels were lower than established Codex Alimentarius MRLs. The agreement between the two laboratories was calculated to be 0.83 (83%) with a determined proportion of kappa (κ) ranging between 0.61 and 0.80κ which corresponds to a good agreement strength. The standard error se (k)=0.052 and the confidence intervals at 95% for κ=0.51–0.71 for the two laboratories. The study suggests that raw milk exhibiting inhibition diameters of <19 mm (p<0.05) in the B.calidolactis test plate fulfills the codex alimentarius MRL for the tested β-lactams at their various detection levels. It was concluded that the plate test could be a useful and affordable post screening assay for commonly used β-lactam antimicrobial in the dairy sector within low-income countries. 相似文献
79.
《International Dairy Journal》2007,17(5):448-458
A fluorescent labeling method was developed to determine the effects of heat and β-lactoglobulin (BLG) on the concentration distribution of added fluorescently labeled tissue-type (tPA-647) and urokinase-type (uPA-546) plasminogen activators (PAs) in a model milk system. Prior to heating, the majority of the added PAs (87% of tPA-647, 72% of uPA-546) became associated with casein micelles and could be dissociated by acidification or NaCl. Addition of 0.5% BLG to the unheated system had no significant effect on the distribution of PAs. Heat-induced binding of uPA-546 to micelles was shown by an increase of uPA-546 from 72% to 88% or 95% in the micelle fraction of systems without or with BLG, respectively. Although heat alone had little effect on the total amount of tPA-647 associated with caseins (88%), addition of BLG to a heated system shifted 32% of the tPA-647 to a non-sedimentable casein fraction. After heating, casein–PA interactions became more complex. 相似文献
80.
《International Dairy Journal》2007,17(11):1360-1371
A novel yoghurt process was investigated in which milk proteins were covalently cross-linked by a microbial transglutaminase (TG) preparation containing glutathione (TG+GSH). As unheated milk is normally less reactive towards TG, TG+GSH was applied to enable non-inhibited cross-linking without requiring a pre-heat treatment beyond pasteurisation conditions. After the TG+GSH incubation phase, the enzyme was inactivated by heat treatment of the yoghurt milk prior to fermentation. During yoghurt fermentation, no negative effect of TG+GSH on fermentation time was found. Protein cross-linking by TG+GSH was enhanced, resulting in higher apparent viscosity and a higher degree of protein polymerisation than that given by TG without GSH. Furthermore, different ratios of casein to whey proteins (CWP ratios) were used to investigate the effect of both protein fractions on covalently cross-linked yoghurt gel structures. The results showed a relationship between extent of cross-linking, apparent viscosity and CWP ratio of the yoghurt gels. During storage for up to 6 weeks at 4 °C, no changes in rheological properties and degree of protein polymerisation were measurable for stirred yoghurt gels prepared from cross-linked milk proteins. 相似文献