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971.
Marina Villegas Amador C. Caballero Carlos Moure Pedro Durán José F. Fernández Robert E. Newnham 《Journal of the American Ceramic Society》2000,83(1):141-46
Pb(Zn1/3 Nb2/3 )O3 -based ceramics have been prepared by two different processing methods: conventional (PZN-C) and reaction-sintering (PZN-RS). The conventionally prepared PZN-based ceramics densified at lower temperatures (950°C) than the reaction-sintered samples (1100°C), but the perovskite/pyrochlore ratio was always higher in PZN-RS. The presence of a substantial amount of pyrochlore phase in PZN-C ceramics caused a decrease in the electrical properties. The maximum dielectric constant values in PZN-C ceramics were 10%–15% lower than those of PZN-RS, despite a similar average grain size, 7 ± 0.2 μm. The temperature of the maximum of the dielectric constant ( T max ) was lower than that expected from the mixing rule because of the possible formation of Ba–Nb clusters. The higher chemical homogeneity in PZN-RS ceramics is the main reason for the higher dielectric constant, T max and electromechanical response, as well as for the lower difference between T max and the depolarization temperature ( T d ) and the lower diffusiveness parameter (δ). 相似文献
972.
Robert A. Gibson Mark A. Neumann Sharon L. Burnard Josephine A. Rinaldi Glen S. Patten Edward J. McMurchie 《Lipids》1992,27(3):169-176
Adult male marmoset monkeys were fed eicosapentaenoic acid (20∶5n−3) as the ethyl ester in diets containing either 32% (reference
diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18∶2n−6) for 30 wk. No changes
were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both
the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent
of total n−3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated
(P/M/S) ratio 0.2∶0.6∶1.0) than reference diets (P/M/S ratio 1∶1∶1) and this was true for both PE (33.4±1.0%vs 24.3±1.1%) and PC (9.3±0.5%vs 4.9±0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with
marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20∶5n−3
was preferentially incorporated into PE (10.8±0.2%, 6.0±0.02%) while smaller amounts were incorporated into PC (6.9±0.4%,
3.2±0.2%). The major n−3 polyunsaturated fatty acid found in PE in response to dietary 20∶5n−3 was the elongation metabolite
22∶5n−3 in both the atherogenic (17.7±0.7%) and reference (14.3±1.0%) dietary groups; 22∶6n−3 levels were less affected by
diet (4.7±0.3% and 3.9±0.2%, respectively). The results can be interpreted to indicate an inverse relationship between the
amount of dietary 18∶2n−6 and incorporation of 20∶5n−3 into erythrocyte membrane phospholipids regardless of whether the major
dietary n−3 fatty acid was α-linolenate (18∶3n−3) or 20∶5n−3. This interpretation is supported by theoretical calculations. 相似文献
973.
Fred J. Eller Robert J. Bartelt Baruch S. Shasha David J. Schuster David G. Riley Philip A. Stansly Thomas F. Mueller Kenneth D. Shuler Bruce Johnson James H. Davis Carol A. Sutherland 《Journal of chemical ecology》1994,20(7):1537-1555
This study describes the identification of an aggregation pheromone for the pepper weevil,Anthonomus eugenii and field trials of a synthetic pheromone blend. Volatile collections and gas chromatography revealed the presence of six male-specific compounds. These compounds were identified using chromatographic and spectral techniques as: (Z)-2-(3,3-dimethylcyclohexylidene)ethanol, (E)-2-(3,3-dimethylcyclohexylidene)ethanol, (Z)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-3,7-dimethyl-2,6-octadienoic acid (geranic acid), and (E)-3,7-dimethyl-2,6-octadien-1-ol (geraniol). The emission rates of these compounds from feeding males were determined to be about: 7.2, 4.8, 0.45, 0.30, 2.0, and 0.30µg/male/day, respectively. Sticky traps baited with a synthetic blend of these compounds captured more pepper weevils (both sexes) than did unbaited control traps or pheromone-baited boll weevil traps. Commercial and laboratory formulations of the synthetic pheromone were both attractive. However, the commercial formulation did not release geranic acid properly, and geranic acid is necessary for full activity. The pheromones of the pepper weevil and the boll weevil are compared. Improvements for increasing trap efficiency and possible uses for the pepper weevil pheromone are discussed. A convenient method for purifying geranic acid is also described.The mention of firm names or trade products does not imply endorsement or recommendation by the U.S. Department of Agriculture over other firms or similar products not mentioned. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status or handicap. 相似文献
974.
Wen-yi Lin Jen-Yan Hsu Robert F. Speyer 《Journal of the American Ceramic Society》1994,77(5):1162-1168
The stability of MoSi2 in combustion gas at 1370° and 1600°C was evaluated using SOLGASMIX-PV thermodynamic modeling, periodic weight measurements, and characterization via XRD, SEM, EDS, and image analysis. Passive oxidation occurred at both temperatures. During an initial stage of exposure, specimen surfaces oxidized to form MoO3(g) and amorphous SiO2 via reduction of CO2 and H2 O. After a short time (<6.5 min at 1370°C, <1 min at 1600°C), the oxidation mechanism switched; Mo5 Si3 and amorphous SiO2 formed as oxidation products. The first mechanism esulted in the formation of 46.1 vol% at 1370°C and 42.6 vol% at 1600°C of the amorphous silica surface coating. The attainment of a near-terminal weight gain implied silica formation was limited by H2 O and CO2 diffusion through the silica coating. 相似文献
975.
Selim M. Erhan Robert Kleiman Terry A. Isbell 《Journal of the American Oil Chemists' Society》1993,70(5):461-465
The formation of estolides was detected during the studies on dimerization of meadowfoam oil fatty acids. By adjusting the
reaction conditions, it was possible to produce monoestolides with little dimer or trimer formations. Estolides have potential
use in lubricant, cosmetic and ink formulations and in plasticizers. This paper reports the conditions for production of estolides
from mixed meadow-foam fatty acids, commercial oleic acid, high-oleic sun-flower oil fatty acids,cis-5,cis-13-docosadienoic acid, petroselinic acid and linoleic acid. 相似文献
976.
Reinhold H. Dauskarat David B. Marshall Robert O. Ritchie 《Journal of the American Ceramic Society》1990,73(4):893-903
The subcritical growth of fatigue cracks under (tension-tension) cyclic loading is demonstrated for ceramic materials, based on experiments using compact C(T) specimens of a MgO-partially-stabilized zirconia (PSZ), heat-treated to vary the fracture toughness K c from ∼3 to 16 MPa·m1/2 and tested in inert and moist environments. Analogous to behavior in metals, cyclic fatigue-crack rates (over the range 10−11 to 10−5 m/cycle) are found to be a function of the stress-intensity range, environment, fracture toughness, and load ratio, and to show evidence of fatigue crack closure. Unlike toughness behavior, growth rates are not dependent on through0-thickness constraint. Under variable-amplitude cyclic loading, crack-growth rates show transient accelerations following low-high block overloads and transient retardations following high-low block overloads or single tensile overloads, again analogous to behavior commonly observed in ductile metals. Cyclic crack-growth rates are observed at stress intensities as low as 50% of K c , and are typically some 7 orders of magnitude faster than corresponding stress-corrosion crack-growth rates under sustained-loading conditions. Possible mechanisms for cyclic crack advance in ceramic materials are examined, and the practical implications of such "ceramic fatigue" are briefly discussed. 相似文献
977.
Robert G. Jensen F. A. Dejong R. M. Clark Lisa G. Palmgren Teresa H. Liao Margit Hamosh 《Lipids》1982,17(8):570-572
The lingual lipase in gastric aspirates from premature infants was found to be partially stereospecific forsn-3 esters of synthetic enantiometric triacylglycerols containing 18∶1 and 16∶0. Thesn-3 ester was hydrolyzed about 4 times faster than the acid at thesn-1 position with no difference in rates between 18∶1 and 16∶0. Thesn-2 was also hydrolyzed to some extent.
Scientific contribution no. 949, Storrs Agricultural Experiment Station, University of Connecticut, Storrs, Ct 06268. 相似文献
978.
An extracellular lipase (EC 3.1.1.3) from Geotrichum marimum was purified 76-fold with 46% recovery using Octyl Sepharose 4 Fast Flow and Bio-Gel A 1.5 m chromatography. The purified
enzyme showed a prominent band on SDS-PAGE and a single band on native PAGE based on the activity staining. The molecular
mass of the lipase was estimated to be 62 kDa using SDSPAGE and Bio-Gel A chromatography, indicating that the lipase likely
functions as a monomer. The pl of the lipase was determined to be 4.54. The apparent V
max and K
m were 1000 μmol/min/mg protein and 11.5 mM, respectively, using olive oil emulsified with taurocholic acid as substrate. The
lipase demonstrated a pH optimum at pH 8.0 and a temperature optimum at 40°C. At 6 mM, Na+, K+, Ca2+, and Mg2+ stimulated activity, but Na+, and K+ at 500 mM and Fe2+ and Mn2+ at 6 mM reduced lipase activity. The anionic surfactant, taurocholic acid, and the zwitterionic surfactant, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate,
enhanced the activity at 0.1 mM. Other anionic surfactants such as SDS and sodium dioctyl sulfosuccinate, the cationic surfactants
methylbenzethonium bromide and cetyltriethylammonium bromide, and the nonionic surfactants Tween-20 and Triton X-100 inhibited
the lipase activity to different extents. The lipase was found to have a preference for TG containing cis double bonds in their FA side chains, and the reaction rate increased with an increasing number of double bonds in the side
chain. The lipase had a preference for ester bonds at the sn-1 and sn-3 positions over the ester bond at the sn-2 position. 相似文献
979.
Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect
on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for
4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the
three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However,
the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order
as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading
to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation. 相似文献
980.
The concentrations of CLA isomers were determined by Ag+-HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed),
linoleic acid (sunflower seed), or α-linolenic acid (linseed). Highly significant (P≤0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of α-linolenic acid and the CLA isomers trans-12,trans-14, trans-11,trans-13, cis,trans/trans,cis-12,14, trans-11,cis-13, and cis-11,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600–650 m), the mountains (900–1210
m), and the highlands (1275–2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only
three CLA isomers (cis-9,trans-11, trans-11,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans-11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk
products of Alpine origin. 相似文献