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   1259篇
  免费   71篇
  国内免费   2篇
电工技术   8篇
综合类   5篇
化学工业   415篇
金属工艺   23篇
机械仪表   16篇
建筑科学   56篇
矿业工程   1篇
能源动力   23篇
轻工业   232篇
水利工程   14篇
石油天然气   3篇
无线电   53篇
一般工业技术   160篇
冶金工业   171篇
原子能技术   1篇
自动化技术   151篇
  2023年   13篇
  2022年   77篇
  2021年   92篇
  2020年   37篇
  2019年   35篇
  2018年   43篇
  2017年   32篇
  2016年   37篇
  2015年   36篇
  2014年   46篇
  2013年   78篇
  2012年   61篇
  2011年   111篇
  2010年   52篇
  2009年   57篇
  2008年   58篇
  2007年   59篇
  2006年   57篇
  2005年   56篇
  2004年   47篇
  2003年   18篇
  2002年   28篇
  2001年   16篇
  2000年   24篇
  1999年   11篇
  1998年   8篇
  1997年   7篇
  1996年   20篇
  1995年   14篇
  1994年   16篇
  1993年   8篇
  1992年   7篇
  1991年   2篇
  1990年   10篇
  1989年   5篇
  1988年   2篇
  1987年   6篇
  1986年   7篇
  1985年   3篇
  1984年   2篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1976年   5篇
  1975年   4篇
  1968年   3篇
  1958年   1篇
  1957年   1篇
  1956年   1篇
排序方式: 共有1332条查询结果,搜索用时 46 毫秒
11.
In this paper, two novel methods for facial expression recognition in facial image sequences are presented. The user has to manually place some of Candide grid nodes to face landmarks depicted at the first frame of the image sequence under examination. The grid-tracking and deformation system used, based on deformable models, tracks the grid in consecutive video frames over time, as the facial expression evolves, until the frame that corresponds to the greatest facial expression intensity. The geometrical displacement of certain selected Candide nodes, defined as the difference of the node coordinates between the first and the greatest facial expression intensity frame, is used as an input to a novel multiclass Support Vector Machine (SVM) system of classifiers that are used to recognize either the six basic facial expressions or a set of chosen Facial Action Units (FAUs). The results on the Cohn-Kanade database show a recognition accuracy of 99.7% for facial expression recognition using the proposed multiclass SVMs and 95.1% for facial expression recognition based on FAU detection.  相似文献   
12.
13.
The degradation of the enantiomers of α-, β-, and γ-hexabromocyclododecane (HBCD) by phase I metabolism was investigated using induced rat liver microsomes. HBCD isomers were quantified using HPLC-MS/MS (ESI(-)) after separation on a combination of a reversed phase and a chiral analytical column. The degradation of all six isomers followed first-order kinetics and the estimated half-lives ranged from 6.3 min for both β-HBCD enantiomers to 32.3 min in case of (+)-γ-HBCD. (+)-α- and (-)-γ-HBCD displayed significantly shorter half-lives than their corresponding antipodes. It could be shown that this degradation led to a significant enrichment of the first eluting enantiomers (-)-α- and (+)-γ-HBCD. Individual patterns of mono- and dihydroxylated derivatives obtained from each α- and γ-HBCD enantiomer were seen to be distinctly characteristic. The patterns of monohydroxylated HBCD derivatives detected in liver and muscle tissues of pollack, mackerel and in herring gull eggs were largely similar to those observed in the in vitro experiments with rat liver microsomes. This enabled individual hydroxy-HBCDs to be assigned to their respective parent HBCD enantiomers.  相似文献   
14.
ACE inhibitory activity was studied for different hydrolysates obtained from protein concentrates of two lentil varieties by in vitro gastrointestinal simulation, Alcalase/Flavourzyme, papain and bromelain. Protein/peptide profiles studied by electrophoresis and HPLC-SEC showed a rich composition of the hydrolysates in small peptides ranging in size from 0.244 to 1.06 kDa. ACE inhibitory activity was measured using the HPLC Hippuryl-His-Leu (HHL) substrate method. Significantly different (P < 0.05) IC50 values ranging between 0.053 and 0.190 mg/ml were obtained for different hydrolysates. Furthermore, the inhibition mechanism investigated using Lineweaver–Burk plots revealed a non-competitive inhibition of ACE with inhibitor constants (Ki) between 0.16 and 0.46 mg/ml. These results demonstrate that hydrolysates of lentil proteins obtained by different enzymatic digestions may contain bioactive components.  相似文献   
15.
16.
Tapé is a popular delicacy in Indonesia that is prepared by fermenting starch-rich material. Yeast plays an important role in the making of tapé especially in the aroma and taste of the product. In this study, yeasts were isolated from tapé and subjected to diversity analysis using the restriction fragment length polymorphism (RFLP) technique on 5.8S rRNA encoding gene and the internal transcribed spacer (ITS). A total of 21 yeast isolates were obtained from 3 different types of Indonesian tapé (cassava tapé, white-, and black-glutinous rice tapé). The identified yeast species from cassava tapé were Pichia jadinii, Candida glabrata, and Clavispora lusitaniae. P. fabianii, Rhodotorula mucilaginosa, and Ogataea polymorpha were obtained from white glutinous rice tapé, while Saccharomycopsis fibuligera and Wickerhamomyces anomalus were obtained from black glutinous rice tapé.  相似文献   
17.
There is a gap in knowledge of microbiological quality in raw chicken products produced by nonconventional methods and no studies have reported the microbiological quality of turkeys produced under different rearing environments. Thus, the aim of this study was to compare the microbiological quality of conventionally and organically reared whole chicken and turkey carcasses purchased from 3 retail outlets in Knoxville, Tenn., U.S.A. A total of 100 raw broiler chickens organically (n = 50) and 50 raw turkey carcasses consisting of 3 brands reared either conventionally (n = 25) or organically (n = 25) were evaluated. The FDA BAM protocol for rinsing poultry carcasses was used to enumerate of aerobic bacteria, Campylobacter, and Staphylococcus spp., and for qualitative analysis of Salmonella. Organic chickens from one brand had the highest average counts of aerobic bacteria, Staphylococcus spp. and Campylobacter (4.8, 4.8, and 4.7 Log10 CFU/mL rinsate, respectively) while the other organic brand had the lowest average counts (3.4, 3.3, and 3.1, respectively) of all 4 brands evaluated. The organic turkeys had the highest average counts of these same bacteria (4, 3.9, and 3.8, respectively) compared to the 2 brands of conventional turkeys evaluated. Salmonella (5% prevalence) was isolated only from organic chickens and turkeys. From these data, it appears that the microbiological quality of the raw product was not dependent on rearing conditions and, thus, it cannot be assumed that organic raw poultry is safer than conventionally raised poultry in terms of microbiological quality.  相似文献   
18.
Antiviral activity of Ragusano donkeys' milk proteins was investigated for the effect on echovirus type 5, known to infect the gastrointestinal tract of humans. Three protein fractions were tested; casein (CN), whey protein (WP) and a low molecular whey protein fraction (LWP; <30,000 Da). The antiviral activity of WP and LWP was tested on echovirus type 5 at three concentrations (1, 5 and 10 mg mL?1); CN was assessed only at the lower concentration. All donkey milk protein fractions showed significant inhibition on virus replication at the concentration of 1 mg mL?1, and both WP and LWP fractions showed significant inhibition on the virus replication at all concentrations tested. The strongest antiviral effect was observed for the WP fraction. These findings show that the different whey proteins in donkey milk, probably acting in synergy, exert antiviral activity on echovirus 5 and might contribute to prevent gastrointestinal virus infections in humans.  相似文献   
19.
A multiplex polymerase chain reaction was developed to simultaneously identify Listeria monocytogenes and species of the genus Listeria. Two sets of primers were used, with the first amplifying a 938-bp region of the 16S rRNA gene that is highly conserved in all Listeria species and the second amplifying a 174-bp region of the listeriolysin (hlyA) gene of L. monocytogenes. Thus, isolates of Listeria spp. yield a single 938-bp product, whereas L. monocytogenes isolates yield both the 938-bp product and a 174-bp product. The specificity of the assay was verified with all six Listeria species and 11 serotypes of L. monocytogenes, as well as nonrelated bacteria. The multiplex PCR assay was used to determine the incidence of Listeria spp., especially L. monocytogenes, in mechanically separated turkey samples (n = 150 samples). L. monocytogenes strains were selected by using the University of Vermont two-step enrichment protocol and plating to selective Palcam agar. The multiplex PCR assay was used for verification of presumptive Listeria colonies. Approximately 38% of mechanically separated turkey samples (57 of 150) yielded L. monocytogenes; an additional 18% of these samples (27 of 150) harbored other Listeria spp. Fifty-one percent (29 of 57) of the L. monocytogenes isolates were of serogroup 1, 44% (25 of 57) were of serogroup 4, and 2% (1 of 57) were assigned to serogroups other than 1 and 4.  相似文献   
20.
The anthocyanin composition of Tempranillo, Garnacha and Cabernet Sauvignon grapes over two vintages was studied. Samples were obtained during berry ripening from two vineyards that differed by producing fruit of high and low quality. The proportions of the individual compounds remained practically constant within a single vineyard along the sampling period, the changes in the anthocyanin composition being principally quantitative. Different multivariate statistical methods showed that the anthocyanin profile was primarily determined by variety. This genetic dependence was particularly verified when the sums of the non-acylated glucosides, the acetates and the p-coumaryl derivatives, were analysed. The mean relative content corresponding to these three anthocyanin fractions was always the same within each variety, independently either of the vineyard or the vintage year considered. Relating to the individual compounds, several permanent qualitative differences between vineyards in each variety were also found, although the difference in the total anthocyanin concentration was always much higher.  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