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The14CH3-lecithins were biosynthesized by normal adult rats injected with14CH3-methionine. About 20% of the dose was incorporated into liver lecithins. The14CH3-lecithins were isolated by thin-layer chromatography. Separation of lecithins on AgNO3-treated silica gel yielded lecithins containing a saturated fatty acid in combination with mainly one unsaturated fatty acid,
namely, oleic, linoleic, eicosatrienoic, or arachidonic acid. These fractions were eluted with methanolic choline chloride,
which prevented elution of AgNO3. The lecithins, after extraction into petroleum ether, were analyzed for radioactivity and for fatty acid composition. Yields
were about 75%, based upon fatty acids or radioactivity applied to the plate.
Specific activities differed sharply between the fractions, and arachidonoyllecithins had the highest specific activity. The
sum of the activities contributed by each of the fractions agreed well with the specific activity of total lecithins, indicating
the recovery of intact lecithin molecules. The recovery of intact molecules allows this procedure to be used with lecithins
containing any isotopic labels.
The high specific activity of arachidonoyl-lecithins relative to the other fractions indicates a high degree of specificity
in the metabolic reactions which lead to the formation of rat liver lecithins. 相似文献
94.
An imporved method for the numerical evaluation of the convolution integral in the relationship between creep compliance and relaxation modulus is discussed. The better approximation is obtained by the assumption that both functions can be assumed to be linear within a series of increasing time intervals which do not change as the calculation progresses. The calculation is carried out on both hypothetical and real examples which substantiates its applicability and accuracy. 相似文献
95.
Iron, iron-0.012 pct C, and iron-0.032 pct C alloys subjected to a multistage rolling-annealing sequence display significantly
different recrystallization textures after a final decarburizing anneal for 100 hours at 870 °C in dry hydrogen. A (110) [001]
texture which developed by primary recrystallization was observed in the 0.012 C alloy. The unalloyed iron and 0.032 C alloy
exhibited major components, respectively,(111〈011〉 and 111–211). Control of the alloy carbon level during the entire processing
is considered to be critical to the development of the various textures. 相似文献
96.
Application of electrical stimulation in the sheep and beef processing industry has been erratic around the world and this may reflect an incomplete knowledge of how to optimise the technology. Although it is well established that stimulation increases the rate of post-mortem glycolysis, other biochemical and biophysical effects have been implicated with the use of this technology. This review seeks to examine the current theories about the effect of stimulation on post-mortem muscle. The classical view that stimulation prevents muscle from shortening excessively during rigor development has been expanded to include the possibility that it also results in physical disruption of muscle structure. The interaction of these effects with the acceleration of the rate of proteolysis through activation of the calpain protease system has not been comprehensively reviewed in the past. Thus there are two mechanisms which could explain the effect of stimulation on tenderisation, reduced 'cold-induced' shortening and alteration of protein structure. A secondary effect is the enhancement of the rate of proteolysis stimulated by release of Ca (2+) at a higher temperature. As a result of this review we highlight several areas that may prove fruitful for further research. The challenge for further development of electrical stimulation systems is optimisation of the activation of the enzyme systems in parallel with manipulation of chilling regimes so as to ensure rigor mortis is achieved at temperatures which minimise shortening. These optimal temperatures largely established at a fixed incubation temperature for detached muscle may be different when measured in intact carcasses. The potential of regional stimulation of sections of the carcass to achieve this outcome is worthy of study given the different fibre composition of muscles and temperature gradients. In addition, to ensure that appropriate amounts of energy are applied to individual carcasses, development of self-response stimulation units, which are able to determine carcass resistance and apply appropriate durations or strengths of stimulation is worthy of future research. This would lead to more effective electrical stimulation practices. 相似文献
97.
The resistance of isolated low density lipoprotein (LDL) to copper-initiated oxidation is often used as a measure of effectiveness
of an antioxidant intervention. Prior to oxidation excess salt and EDTA are removed via dialysis or gel filtration of the
LDL sample. However, there is concern over whether the antioxidant content of dialyzed or gel-filtered LDL is truly representative
of native LDL extracted from a blood sample. Previously, the experiments done after the storage of native and dialyzed LDL
at −80°C showed that the dialysis step can cause a loss of up to 60% in the tocopherol and carotenoid content of LDL. In the
present study, a comparison of the micronutrient concentration in freshly prepared dialyzed and native LDL from 35 subjects
showed that after the correction for cholesterol, only lycopene (13%, P<0.001) and to a lesser extent α-carotene (8%, P<0.02) were significantly decreased, and the absolute fall in concentration was far smaller than previously reported. Other
experiments done with smaller numbers of samples suggested that there were minimal micronutrient losses following gel filtration
and that it was important to include 10 μmol/L EDTA in the dialysis and elution buffer; otherwise micronutrient losses did
occur. In summary, immediate dialysis of freshly isolated LDL in the presence of 10 μmol/L. EDTA does not cause any major
loss in the concentration of tocopherol and most carotenoids. 相似文献
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