首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3863篇
  免费   188篇
  国内免费   9篇
电工技术   55篇
综合类   2篇
化学工业   1075篇
金属工艺   57篇
机械仪表   95篇
建筑科学   194篇
矿业工程   4篇
能源动力   157篇
轻工业   567篇
水利工程   44篇
石油天然气   43篇
无线电   267篇
一般工业技术   535篇
冶金工业   161篇
原子能技术   14篇
自动化技术   790篇
  2024年   11篇
  2023年   47篇
  2022年   117篇
  2021年   174篇
  2020年   104篇
  2019年   137篇
  2018年   144篇
  2017年   122篇
  2016年   189篇
  2015年   90篇
  2014年   173篇
  2013年   326篇
  2012年   260篇
  2011年   320篇
  2010年   237篇
  2009年   249篇
  2008年   220篇
  2007年   172篇
  2006年   125篇
  2005年   94篇
  2004年   99篇
  2003年   76篇
  2002年   83篇
  2001年   47篇
  2000年   35篇
  1999年   43篇
  1998年   44篇
  1997年   46篇
  1996年   31篇
  1995年   33篇
  1994年   27篇
  1993年   17篇
  1992年   26篇
  1991年   14篇
  1990年   15篇
  1989年   16篇
  1988年   18篇
  1987年   8篇
  1986年   5篇
  1985年   9篇
  1984年   9篇
  1983年   8篇
  1982年   4篇
  1981年   7篇
  1980年   7篇
  1979年   3篇
  1978年   3篇
  1977年   6篇
  1976年   5篇
  1962年   1篇
排序方式: 共有4060条查询结果,搜索用时 0 毫秒
71.
72.
Hyperspectral imaging is useful for detecting internal defects of pickling cucumbers. The technique, however, is not yet suitable for high-speed online implementation due to the challenges in analyzing large-scale hyperspectral images. This research aimed to select the optimal wavebands from the hyperspectral image data, so that they can be deployed in either a hyperspectral or multispectral imaging-based inspection system for the automatic detection of internal defects of pickling cucumbers. Hyperspectral reflectance (400–700 nm) and transmittance (700–1,000 nm) images were acquired, using an in-house developed hyperspectral imaging system running at two conveyor speeds of 85 and 165 mm/s, for 300 “Journey” pickling cucumbers before and after internal damage was induced by mechanical load. Minimum redundancy–maximum relevance (MRMR) was used for optimal wavebands selection, and the loadings of principal component analysis (PCA) were also applied for qualitatively identifying the important wavebands that are related to the specific features. Discriminant analysis with Mahalanobis distance classifier was performed for the two-class (i.e., normal and defective) and three-class (i.e., normal, slightly defective, and severely defective) classifications using the mean spectra and textural features (energy and variance) from the regions of interest in the spectral images at selected waveband ratios. The classification results based on MRMR wavebands selection were generally better than those from PCA-based classifications. The two-band ratio of 887/837 nm from MRMR gave the best overall classification results, with the accuracy of 95.1 and 94.2 % at the conveyor speeds of 85 and 165 mm/s, respectively, for the two-class classification. The highest classification accuracies for the three-class classification based on the optimal two-band ratio of 887/837 nm were 82.8 and 81.3 % at the conveyor speeds of 85 and 165 mm/s, respectively. The mean spectra-based classification achieved better results than the textural feature-based classification, except in the three-class classification for the higher conveyor speed. The overall classification accuracies for all selected waveband ratios at the low conveyor speed were slightly higher than those at the higher conveyor speed, since the low speed resulted in more scan lines, thus higher spatial resolution hyperspectral images. The identified two-band ratio of 887/837 nm in transmittance mode could be applied for fast real-time internal defect detection of pickling cucumbers.  相似文献   
73.
Goldenberry is a wild fruit that has been widely used for centuries, mainly in folk medicine. Most studies of goldenberry have focused on the fruit, but new research has studied its byproducts, which were considered to be waste until recently. The main objective of our study was to systematize the published information regarding the composition of goldenberry byproducts (calyces, leaves, seeds, and pomace) and their effects on biological systems. Goldenberry byproducts contain minerals, amino acids, withanolides, flavonoids, and essential fatty acids, thus representing good sources of these compounds. Some of their major biological effects include anti-inflammatory, antioxidant, antidiabetic, and antiproliferative effects. Information regarding their toxicity is also presented here. To determine the optimal dosage, further safety studies would be recommended to ensure the best health benefits of these compounds. The available evidence has demonstrated the nutritional value of different byproducts of goldenberry, suggesting them to be potential candidates for use in the cosmetic industry, in the preparation of functional foods, and in phytomedicine for the prevention and adjuvant treatment of some diseases. © 2020 Society of Chemical Industry  相似文献   
74.
Thirty-two lambs were finished on a total mixed ration (TMR) pelleted alone (00SS) or including sunflower soap stock (SS): 15SS (15 g SS per kg TMR), 30SS (30 g SS per kg TMR) and 60SS (60 g SS per kg TMR). Lambs (8 per group) were slaughtered at 27 kg live weight. Colour evolution, lipid oxidation, microbial growth and detection of diarrhoeagenic Escherichia coli were studied in meat samples. SS in the diet reduced meat lipid oxidation (< 0.05), but had no significant effect (P > 0.05) on the cholesterol oxidation products. Meat from 60SS and control animals (00SS) revealed greater discoloration (< 0.05) than 15SS. SS supplementation did not affect the microbiological populations, whereas high doses of SS seemed to increase the proliferation of diarrhoeagenic E. coli on day 14 (< 0.10). These results suggest that the rate of SS inclusion in the diet of fattening lambs should not be above 15 g SS per kg TMR.  相似文献   
75.
Debittered trub (brewing waste) is an important source of protein source (70.26%). Trub and whey protein were used for 5% protein enrichment of ice cream frozen by liquid nitrogen. Three formulations were elaborated: ice cream standard (ICS), ice cream with whey protein (ICW) and ice cream with trub (ICT). Chemical composition, rheological properties, texture, overrun, melting rate, scanning electron microscopy and a sensorial test were performed. Results showed that ICT presented a higher viscosity, obtained on the upward curve up to 6.76 Pa s−1, consistency index (22.96 (Pa s−1)n), hysteresis area (140.40 mPa s−1) and hardness (31113.33 g) but a lower melting rate (0.38 g min−1), overrun (13.92%) and sensorial acceptability than the other formulations. The addition of trub debittered for protein enrichment improved ice cream properties and demonstrated that it could be used as a food ingredient.  相似文献   
76.
Evidence suggests that diets rich in antioxidants reduce the risk factors of Alzheimer’s disease (AD). Hippophae rhamnoides, commonly known as sea buckthorn (SB), is rich in antioxidants which could have direct effects on amyloid-beta (Aβ) levels and consequently influence AD pathogenesis. In this study, sea buckthorn powder (SBP) was administered at varying concentrations (0.6, 0.9, 1.2, 1.5 and 1.8 µg mL−1) to cell cultures (BE(2)-M17) with 20 mm Aβ for 72 h. MTS test indicated that SB significantly increased cell viability in Aβ-induced cells up to 95%. Results of Western blot showed maximum 38% inhibition of Aβ compared to the control (Aβ only). ELISA demonstrated significantly lower amyloid-β level (6672 pg mL−1) than the control (10189 pg mL−1). Images of AFM further confirmed the presence of low quantity of amyloid beta in SBP-treated cells. These findings suggest that SB warrants further investigation as potential therapeutic agent in the treatment of AD.  相似文献   
77.
78.
79.
Pichia sorbitophila grows rapidly in the presence of very high NaCl concentrations. Under these conditions, even when the K(+) concentration is low, P. sorbitophila cells can maintain low Na(+) and high K(+) contents. This remarkable capacity of P. sorbitophila fails when the external pH is not acidic. This indicates that Na(+) efflux is mediated by an electroneutral Na(+)/H(+) antiporter. We have cloned and sequenced two genes designated as PsNHA1 and PsNHA2, which probably encode two antiporters of this type. The genes present high similarity with the corresponding genes from other yeasts. The heterologous expression of PsNHA1 or PsNHA2 in a Saccharomyces cerevisiae mutant lacking the Na(+) efflux systems and sensitive to high concentrations of Na(+) and K(+) rescued the tolerance and the ability to extrude both cations. The Accession Nos of the sequenced DNA fragments are: PsNHA1, AJ496431; PsNHA2, AJ496432. (TC 2.A.36) Copyright 2002 John Wiley & Sons, Ltd.  相似文献   
80.
The Candida albicans orthologue of the SPC3 gene, which encodes one of the subunits essential for the activity of the signal peptidase complex in Saccharomyces cerevisiae, was isolated by complementation of a thermosensitive mutation in the S. cerevisiae SEC61 gene. The cloned gene (CaSPC3) encodes a putative protein of 192 amino acids that contains one potential membrane-spanning region and shares significant homology with the corresponding products from mammalian (Spc22/23p) and yeast (Spc3p) cells. CaSPC3 is essential for cell viability, since a hemizygous strain containing a single copy of CaSPC3 under control of the methionine-repressible MET3 promoter did not grow in the presence of methionine and cysteine. The cloned gene could rescue the phenotype associated with a spc3 mutation in S. cerevisiae, indicating that it is the true C. albicans orthologue of SPC3. However, in contrast with results previously described for its S. cerevisiae orthologue, CaSPC3 was not able to complement the thermosensitive growth associated with a mutation in the SEC11 gene. The heterologous complementation of the sec61 mutant suggests that Spc3p could play a role in the interaction that it is known to occur between the translocon (Sec61 complex) and the signal peptidase complex, at the endoplasmic reticulum membrane.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号