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   2764篇
  免费   143篇
  国内免费   84篇
电工技术   23篇
综合类   168篇
化学工业   1324篇
金属工艺   29篇
机械仪表   49篇
建筑科学   199篇
矿业工程   13篇
能源动力   76篇
轻工业   72篇
水利工程   31篇
石油天然气   10篇
武器工业   7篇
无线电   76篇
一般工业技术   175篇
冶金工业   60篇
原子能技术   16篇
自动化技术   663篇
  2023年   9篇
  2022年   9篇
  2021年   7篇
  2020年   23篇
  2019年   19篇
  2018年   24篇
  2017年   19篇
  2016年   25篇
  2015年   23篇
  2014年   32篇
  2013年   48篇
  2012年   68篇
  2011年   69篇
  2010年   62篇
  2009年   69篇
  2008年   60篇
  2007年   83篇
  2006年   62篇
  2005年   53篇
  2004年   54篇
  2003年   51篇
  2002年   35篇
  2001年   30篇
  2000年   42篇
  1999年   19篇
  1998年   15篇
  1997年   12篇
  1996年   9篇
  1995年   56篇
  1994年   40篇
  1993年   10篇
  1992年   10篇
  1991年   6篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1986年   2篇
  1985年   159篇
  1984年   292篇
  1983年   346篇
  1982年   264篇
  1981年   347篇
  1980年   155篇
  1979年   66篇
  1978年   82篇
  1977年   37篇
  1976年   19篇
  1975年   34篇
  1974年   14篇
  1973年   7篇
排序方式: 共有2991条查询结果,搜索用时 15 毫秒
1.
This research supports the cross-modal correspondence between the shape of the bottle and consumers’ perception of sweetness and price using physical measures of beverage bottles. Images that add visual weight to the lower section of a package increase the perception of attributes associated with sweetness. In terms of price, the shape of the bottle is informative about its volume, which is the cue predictor of price. Through a within-subject experiment, we evaluated consumers’ perceptions of sweetness and price for a sample of 15 soft drink bottle silhouettes. These perceptions were correlated with the psychophysical characteristics of the silhouettes. Results reveal that sweetness has a negative correlation with height and the visual weight towards the bottom of the bottle. Instead, the price has a positive correlation with the area, width, height, lid, and variance of the bottle shape. Practical implications support having a package design that is consistent with product positioning and attributes.  相似文献   
2.
A comprehensive study of the macrobenthic communities in the Kodungallur–Azhikode Estuary (KAE) was conducted during 2009–2011 period. A total of 18,846 organisms were collected, with 60% being malacostracans, followed by polychaetes (20%), molluscs (9%) and ‘others’ group (11%). A total of 79 species in 71 genera belonging to 49 families were identified, with 33 spp. being polychaetes, 26 spp. being malacostracans, 11 spp. being molluscs and 9 spp. being in the ‘others’ group. A single species of opportunistic amphipod (Americorophium triaeonyx) comprised more than 62.05% of the total numerical abundance of macrobenthos. The other dominant species were Obelia bidentata, Arcuatula senhousia, Cirolana fluviatilis, Prionospio cirrifera and Capitella sp. Canonical correspondence analysis (CCA) results indicated environmental parameters such as water column salinity, turbidity, sediment Eh, substratum type, chlorophyll‐a concentration, depth and organic matter in sediment were the significant factors influencing the distribution of macrobenthic species in the KAE. The present study provides baseline information for future KAE benthic studies.  相似文献   
3.
Women might experience modulation in their perception and cognition of colours and odours during the menstrual cycle, but how women's impressions of and correspondence between colours and odours differ according to the cycle changes remains unknown. Here, we experimentally examined women's performance of several tasks, including evaluation of impressions of colours and odours, matching/nonmatching of colours with odours, and identification of odours, comparing two phases: the beginning of menstruation and ovulation. The results showed that participants had similar impressions of colours and odours and made similar colour choices for odours in both the menstrual and ovulation phases, while “pleasant-unpleasant” impressions of colour and odour might vary according to the menstrual cycle. We found no significant differences in odour identification between the phases. The findings imply that hormonal changes during the menstrual cycle might affect “pleasant-unpleasant” impressions of colour and odour but not other features regarding impressions or crossmodal correspondence. In future studies, examination with a large number of participants is necessary.  相似文献   
4.
张再 《润滑与密封》2018,43(7):78-82
为提高水性液体磁性磨具的稳定性,制备以六偏磷酸钠与聚丙烯酸(PAA)为表面活性剂、纳米二氧化硅为辅助剂的复合分散剂。通过Minitab软件的DOE实验设计模块,以水基液体磁性磨具的沉淀率和零场黏度为评价指标,采用极端形顶点设计复合分散剂的配方并实验研究复合分散剂各组分对沉淀率和零场黏度的影响。结果表明:六偏磷酸钠与PAA之间存在协同作用,纳米二氧化硅对水基液体磁性磨具的零场黏度起到重要作用,三者能够很好地提高水基液体磁性磨具的稳定性。综合考虑沉降率和零场黏度,确定复合分散剂的最佳配比,并通过实验验证了预测值的准确性。  相似文献   
5.
PurposeTo measure the refractive index (RI) of commonly available soft contact lens (CL) materials, their packaging solutions and compare to the manufacturers’ nominal RI. The relationship between RI versus water content, and the effect of inaccurate RI when converting lens power measured in solution to in-air back vertex power were examined.MethodsThe RI of 18 single vision soft CL materials were measured using CLR 12–70 digital refractometer. Three lenses of each material were measured, in their packaging solution and then after soaking in standard phosphate buffered saline (PBS). The RIs of packaging solution were also measured. Accuracy requirements for correct wet to dry power conversion based on thick lens formula were projected.ResultsThe standard deviation between three samples was less than 0.005. The measured RI ranged from 1.3744 ± 0.001–1.4265 ± 0.0004 for PBS soaked and from 1.3739 ± 0.0003–1.4264 ± 0.0024 for packaging solution soaked materials. Comparing nominal with mean measured PBS and packaging solution RIs, 5 and 3 lens materials, respectively, fell outside ISO tolerance. The packaging solution RI of DailiesAquaComfortPlus had the largest difference of 0.0040, compared to RI of standard PBS. For converting lens power measured in PBS to in-air power, the difference between measured and nominal RI of 0.0104 would result in wrongly calculated in-air power 0.99 D for a -6.00 D lens.ConclusionThe CLR 12–70 is reliable and accurate refractometer for the measurement of soft CL materials. Accurate RI measurements are of relevance with increased use of wavefront sensors to measure lens power while they are immersed in solution. Even small errors in solution or material RI can lead to significant errors in converted in-air power. To obtain valid in-air lens power results, measurement conditions must match the material and solution RIs used for the conversion.  相似文献   
6.
Dry weight concentrations of cadmium, lead, copper and zinc were measured in clams, submerged aquatic macrophytes and sediments from several locations in the Chesapeake Bay region. Clam species included Macoma balthica, Mya arenaria, and Rangia cuneata; plant taxa included Najas spp., Potamogeton spp., Ruppia maritima, Vallisneria americana, and Zostera marina. Cadmium and lead concentrations were generally greater in whole plants than in soft tissues of clams, while the reverse was true for zinc; no marked trend was observed in copper concentrations. These results suggest that the changes occurring in the food habits of some Chesapeake Bay waterfowl towards increased clam utilization as a result of declining submerged plant abundances is not increasing ingestion of the nonessential metals cadmium and lead. Highest lead, copper and zinc concentrations were observed in sediments from the Patapsco River, which is probably due to the proximity of Baltimore Harbor. Highest cadmium concentrations were observed in sediments in the Port Tobacco River, a tributary of the Potomac River. These observations were generally consistent with high concentrations of the respective metal(s) in biota from these locations. Concentrations of the four metals in sediments were highly correlated to organic matter content.  相似文献   
7.
The effects of lithium (Li) in growth media on Phaseolus vulgaris L. ‘Bush Blue Lake 290’ (snap bean) were studied under controlled environmental conditions. Concentrations of 4 to 12 ppm Li in the substrate produced toxic symptoms. The development of these symptoms is described and measurements of selected growth parameters presented. At 4 ppm Li, plant height, first trifoliate fresh weight and leaf area increased. At concentrations greater than 4 ppm stomatal diffusive resistance increased temporarily, indicating partial stomatal closure. It can be concluded that Li interferes with biomass accumulation and plant water relations.  相似文献   
8.
Three filter media were evaluated for their suitability in recovering seeded poliovirus type 2 from tap and river water. The importance of the presence of aluminium cations was also examined. Fibreglass filters gave best recoveries in this evaluation when used with 0.0005 M AlCl36H2O, being up to 4 × more efficient than filters used without Al3+. No such Al3+ requirement was found for cellulose nitrate membrane filters. A procedure was arrived at suitable for the recovery of enteroviruses from tap and river water. The efficiency of the organic flocculation procedure as a secondary concentration method varied with viral serotype.  相似文献   
9.
The biodegradation of pentachlorophenol (PCP) was tested in a three phase protocol. Phase I involved acclimation; phase II allowed determintion of biodegradation kinetics through use of continuous stirred tank reactors (CSTR) operated at solids retention times of 3.2, 7.8, 12.8 and 18.3 days; phase III assessed the importance of volatilization and sorption in PCP removal and evaluated the extent of biodegradation. Over the range of SRT's studied, PCP was found to be biodegradable with first order kinetics; the rate constant (μm/Ks) had a value of 0.0017 l μg−1d−1. The minimum concentration of PCP attainable in a CSTR was found to be 27 μg l−1. Additional studies suggested that the full relationship between the PCP degradation rate and the PCP concentration followed an inhibition-type function, with the maximum rate occurring at a PCP concentration of around 350 μg l−1. Radioisotopic studies revealed that PCP was mineralized by the culture, with the liberation of CO2 and the incorporation of carbon into cell material. Neither volatilization nor sorption removed significant amounts of PCP from the reactors.  相似文献   
10.
Concentrations of Co, Cu, Fe, Hg, Mn, Sb, Se and Zn in IAEA milk (dry) standard A-11 were re-evaluated with the help of instrumental and radiochemical neutron activation analysis (NAA). The results show reasonably good agreement for Co (5.1 ± 0.55 ng/g) and Zn (34 ± 2.5 μg/g), in relation to the recommended values. For Cu (374 ± 15 ng/g), Fe (2.4 ± 0.34 μg/g) and Mn (250 ± 20 ng/g); the results obtained are lower than the reported values.Cu, Mn, and Zn were cross-checked by atomic absorption spectrophotometry (AAS). The results, Cu = 331 ± 27 ng/g, Mn = 302 ± 62 ng/g, and Zn = 35 ± 1 μg/g, fall within the range of mean values obtained by NAA.For Hg and Se, using instrumental NAA, only upper limits could be indicated; because of the low levels of concentrations of Hg and Se on one hand, and high content of P (9100 μg/g) in A-11 milk standard on the other, NAA coupled with radiochemistry is to be preferred for these two elements.In pooled human milk, in addition to Cu and Mn (radiochemical) and Co, Fe, Sb and Zn (instrumental), Hg and Se could also be determined non-destructively because of the favourable Hg/P and Se/P ratios in this matrix.  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