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排序方式: 共有370条查询结果,搜索用时 15 毫秒
81.
82.
The effect of plasma-etching damage on carrier transport properties in GaN has been studied under various plasma conditions
by monitoring the changes in sheet resistivity (ρ
s) and mobility (μ
s) or the resistivity (R). All the etching experiments were performed in an electron cyclotron resonance microwave plasma reactive
ion etching (ECR-RIE) system. Consistent changes in the transport properties have been observed with increasing dc bias (ion
energy) in all plasmas except in those containing chlorine. With noble gas plasmas, the largest change in conductance was
created when Ar, the heaviest ion, was accelerated to its highest voltage. In these Ar sputtering cases, substantial surface
micro-roughening has been observed. These surfaces also display considerable nitrogen deficiency as measured by Auger electron
spectroscopy. These observations suggest that preferential sputtering of nitrogen from the surface of GaN is one form of ion
damage. The other is displacement damage. Both of these forms of ion damage are considered to be the direct cause of the observed
changes in the electrical properties. 相似文献
83.
Persistent halogenated hydrocarbons in consumer fish of China: regional and global implications for human exposure 总被引:3,自引:0,他引:3
Concentrations of persistent halogenated hydrocarbons (PHHs) were determined in 13 consumer fish species (a total of 390 individuals) collected from a major fish-farming region of China. The potential health risks of PHHs associated with consumption of fish from China was also systematically assessed regionally and globally. In all fish samples, DDTs, HCHs, PCBs, and PBDEs were the predominant PHH residues, with the median levels (ranges) being 6.0 (0.14-698.9), 0.50 (0.13-24.06), 0.10 (< 0.02-7.65), and 0.15 (< 0.0012-3.85) ng/g wet weight, respectively. The upper-bound (90th percentile) values of estimated daily intakes of DDT, HCHs, PCBs, and PBDEs via fish consumption were 45.5, 1.35, 0.46, and 0.30 ng/kg bw/d (urban), and 15.9, 0.47, 0.16, and 0.10 ng/kg bw/d (rural). Globally, the upper-bound outflows via fishery exportation of DDT, HCHs, PCBs, and PBDEs were 185, 5.51, 1.86, and 1.22 kg, respectively, in 2005. Japan was the largest recipient of PHHs, followed by Korea and the United States. Fish consumption assessments indicated that consumption of freshwater farmed and wild marine fish generally does not subject consumers to significant health risk as far as PHHs are concerned, while limited consumption of seawater farmed fish is advised. 相似文献
84.
Chen D Mai B Song J Sun Q Luo Y Luo X Zeng EY Hale RC 《Environmental science & technology》2007,41(6):1828-1833
Birds of prey from Northern China (Beijing area) were examined for polybrominated diphenyl ethers (PBDEs). A total of 47 specimens from eight different species were analyzed. Muscle and liver were analyzed separately for each bird. Kidneys were pooled by species. Common kestrels exhibited the highest PBDE levels (mean muscle and liver concentrations of 12300 and 12200 ng/g lipid weight, respectively), with maxima in an individual bird of 31700 in muscle and 40900 ng/g lw in liver. Congener profiles differed between some species, but were generally dominated by the more brominated congeners (e.g., BDE-153, -209, -183, -207). BDE-209 was especially elevated compared to other published reports. Interspecies differences in congener concentrations and profiles may be due to diet, behavior, or biotransformation capacities. BDE-209 was detected in 79.4% of the samples. Common kestrels contained the highest BDE-209 levels (mean/maxima of 2150/6220 in muscle and 2870/12200 ng/g lw in liver). BDE-209 was the dominant congener in tissues from some buzzards, scops owls, and long-eared owls. It was the second most abundant congener in common kestrels. The remarkable levels and dominance of BDE-209 may relate to significant production, usage, or disposal of deca-containing products in China. These observations reinforce the growing view that organisms using terrestrial food chains may have greater exposure to BDE-209. 相似文献
85.
Effects of culturally adapted parent management training on Latino youth behavioral health outcomes.
A randomized experimental test of the implementation feasibility and the efficacy of a culturally adapted Parent Management Training intervention was conducted with a sample of 73 Spanish-speaking Latino parents with middle-school-aged youth at risk for problem behaviors. Intervention feasibility was evaluated through weekly parent satisfaction ratings, intervention participation and attendance, and overall program satisfaction. Intervention effects were evaluated by examining changes in parenting and youth adjustment for the intervention and control groups between baseline and intervention termination approximately 5 months later. Findings provided strong evidence for the feasibility of delivering the intervention in a larger community context. The intervention produced benefits in both parenting outcomes (i.e., general parenting, skill encouragement, overall effective parenting) and youth outcomes (i.e., aggression, externalizing, likelihood of smoking and use of alcohol, marijuana, and other drugs). Differential effects of the intervention were based on youth nativity status. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
86.
A joint investigation of misclassification treatments and imbalanced datasets on neural network performance 总被引:1,自引:1,他引:0
Jyh-shyan Lan Victor L. Berardi B. Eddy Patuwo Michael Hu 《Neural computing & applications》2009,18(7):689-706
Two important factors that impact a classification model’s performance are imbalanced data and unequal misclassification cost
consequences. These are especially important considerations for neural network models developed to estimate the posterior
probabilities of group membership used in classification decisions. This paper explores the issues of asymmetric misclassification
costs and unbalanced group sizes on neural network classification performance using an artificial data approach that is capable
of generating more complex datasets than used in prior studies and which adds new insights to the problem and the results.
A different performance measure, that is capable of directly measuring classification performance consistency with Bayes decision
rule, is used. The results show that both asymmetric misclassification costs and imbalanced group sizes have significant effects
on neural network classification performance both independently and via interaction effects. These are not always intuitive;
they supplement prior findings, and raise issues for the future. 相似文献
87.
Van der Borght Karin; Wallinga Alinde E.; Luiten Paul G. M.; Eggen Bart J. L.; Van der Zee Eddy A. 《Canadian Metallurgical Quarterly》2005,119(4):926
In the current study, the authors investigated whether Morris water maze learning induces alterations in hippocampal neurogenesis or neural cell adhesion molecule (NCAM) polysialylation in the dentate gyrus. Two frequently used rat strains, Wistar and Sprague-Dawley, were trained in the spatial or the nonspatial version of the water maze. Both training paradigms did not have an effect on survival of newly formed cells that were labeled 7-9 days prior to the training or on progenitor proliferation in the subgranular zone. However, the granule cell layer of the spatially trained rats contained significantly more positive cells of the polysialylated form of the NCAM. These data demonstrate that Morris water maze learning causes plastic change in the dentate gyrus without affecting hippocampal neurogenesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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