全文获取类型
收费全文 | 128444篇 |
免费 | 16453篇 |
国内免费 | 10871篇 |
专业分类
电工技术 | 24230篇 |
技术理论 | 21篇 |
综合类 | 14853篇 |
化学工业 | 4862篇 |
金属工艺 | 2800篇 |
机械仪表 | 6538篇 |
建筑科学 | 13413篇 |
矿业工程 | 3502篇 |
能源动力 | 3296篇 |
轻工业 | 2127篇 |
水利工程 | 3005篇 |
石油天然气 | 2574篇 |
武器工业 | 1231篇 |
无线电 | 21617篇 |
一般工业技术 | 5379篇 |
冶金工业 | 2830篇 |
原子能技术 | 424篇 |
自动化技术 | 43066篇 |
出版年
2024年 | 831篇 |
2023年 | 2482篇 |
2022年 | 4771篇 |
2021年 | 5325篇 |
2020年 | 5388篇 |
2019年 | 3963篇 |
2018年 | 3292篇 |
2017年 | 4066篇 |
2016年 | 4195篇 |
2015年 | 4782篇 |
2014年 | 8800篇 |
2013年 | 7650篇 |
2012年 | 9770篇 |
2011年 | 10145篇 |
2010年 | 7841篇 |
2009年 | 8103篇 |
2008年 | 8368篇 |
2007年 | 9417篇 |
2006年 | 8126篇 |
2005年 | 7150篇 |
2004年 | 5966篇 |
2003年 | 5341篇 |
2002年 | 4152篇 |
2001年 | 3609篇 |
2000年 | 2863篇 |
1999年 | 2289篇 |
1998年 | 1610篇 |
1997年 | 1289篇 |
1996年 | 1050篇 |
1995年 | 821篇 |
1994年 | 629篇 |
1993年 | 408篇 |
1992年 | 316篇 |
1991年 | 190篇 |
1990年 | 153篇 |
1989年 | 147篇 |
1988年 | 101篇 |
1987年 | 59篇 |
1986年 | 47篇 |
1985年 | 44篇 |
1984年 | 48篇 |
1983年 | 55篇 |
1982年 | 47篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1975年 | 4篇 |
1959年 | 5篇 |
1955年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
An interpenetrating polymer network (IPN) hydrogel composed of chitosan and polyallylamine exhibited electric‐sensitive behavior. The chitosan/polyallylamine IPN hydrogel was synthesized by radical polymerization using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The swelling behavior of the IPN was studied by immersion of the gel samples in aqueous NaCl solutions at various concentrations and pHs. The swelling ratio decreased with increasing concentration and pH of electrolyte solution. The stimuli response of the IPN hydrogel in electric fields was also investigated. When a swollen the IPN was placed between a pair of electrodes, the IPN exhibited bending behavior in response to the applied electric field. The IPN also showed stepwise bending behavior depending on the electric stimulus. In addition, thermal properties of the IPN were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2290–2295, 2002 相似文献
993.
Members of health social networks may be susceptible to privacy leaks by the amount of information they leave behind. The threat to privacy increases when members of these networks reuse their pseudonyms in other social networks. The risk of re‐identifying users from such networks requires quantitative estimates to evaluate its magnitude. The estimates will enable managers and members of health social communities to take corrective measures. We introduce a new re‐identification attack, the social network attack, that takes advantage of the fact that users reuse their pseudonyms. To demonstrate the attack, we establish links between MedHelp and Twitter (two popular social networks) based on matching pseudonyms. We used Bayesian networks to model the re‐identification risk and used stylometric techniques to identify the strength of the links. On the basis of our model 7‐11. 8% of the MedHelp members in the sample population who reused their pseudonyms in Twitter were re‐identifiable compared with 1% who did not. The risk estimates were measured at the 5% risk threshold. Our model was able to re‐identify users with a sensitivity of 41% and specificity of 96%. The potential for re‐identification increases as more data is accumulated from these profiles, which makes the threat of re‐identification more serious. 相似文献
994.
995.
文章介绍了PIT Navigator对水泥熟料生产自动化控制的实现,基于神经网络的自学习、自适应控制元件,将相关的过程数据记录下来,随后借助数据关联性进行分析,在预测和自学习过程模型(模型预测控制)中处理这些数据,并计算过程参数的实时预测,使用这些工具,可以实现更稳定的窑况,同时提高产量和降低能耗。 相似文献
996.
王中锋 《南水北调与水利科技(中英文)》2017,15(2):89-94
水华风险不仅是水利工程规划时需要考虑的环境问题,也是水利设施运营时不能忽视的监测项目。为了提高明渠水化风险等级预测的准确率,针对水华成因的不确定性和发展的时序性,基于动态朴素贝叶斯网络分类器提出一种应用于明渠的水华风险评估模型。模型用水华风险等级结点对应藻叶绿素a(Chla)的浓度,并考虑了9项影响水藻生长的因素。采用主成分分析法,处理专家咨询结果,进行参数的设计。在苏州河道北门桥2011年6月初至9月初观测的53例连续监测数据上,与基于朴素贝叶斯网络分类器的评估模型进行比较实验。混淆矩阵显示对中等风险情况的预测识别率提高了15.625%,单尾配对t检验表明在显著性水平0.05时,两模型预测识别率差异显著。考虑了时序特征的基于动态贝叶斯网络分类器的评估模型对明渠中等水化风险的预测识别率提高显著。 相似文献
997.
998.
Occurrence patterns of alien freshwater turtles in a large urban pond ‘Archipelago’ (Rome,Italy): Suggesting hypotheses on root causes 下载免费PDF全文
Maria Paola Di Santo Leonardo Vignoli Giuseppe M. Carpaneto Corrado Battisti 《Lakes & Reservoirs: Research and Management》2017,22(1):56-64
The patterns of the occurrence and distribution of alien freshwater turtle species in an urban pond archipelago (Rome, Italy) were analysed, with the aim of exploring the role of a set of factors (type of ponds, landscape context, size area, distance from the nearest road) with a generalized linear model approach. A total of 311 ponds subdivided in three types (fountains, small basins, lakes) embedded in different landscape contexts (public parks, private parks, urban areas) at differing distances from the nearest road were sampled. Six non‐native freshwater turtle species in 31 sites were recorded (9.97%). Lakes exhibited the highest occurrence rates of alien freshwater turtles, compared to small basins and fountains. Freshwater turtle species in urbanized areas were only observed in parks (both public and private). In both the public and private parks, the lakes exhibited the highest percentage of occupied sites, with fountains being the lowest. A direct and significant relationship was observed between pond size and species richness. The distance from the nearest road did not appear to affect species richness. A first interpretation of the data from this study facilitated the postulation of two a posteriori hypotheses that should be tested, as follows: (i) the causal process of turtle release is random, and the rate of extinction (and recapture) is higher in smaller ponds, thus producing the observed pattern; and (ii) the turtle release is not random, and people actively select the ponds they consider more suitable for their pet animals. In this study, it appears the lakes were perceived by those who abandon their pets as the most ecologically suitable habitats among other pond types to accommodate the different species of turtles. Knowledge of people's attitudes in regard to releasing pet animals also might assist managers of public green spaces to develop strategies aimed to preserve local biodiversity, and to educate the public about the conservation issue represented by the alien species. 相似文献
999.
1000.
针对水面传感器随机部署时网络覆盖率较低的问题,采用了一种面向水环境的无线传感网虚拟距离覆盖算法,在保证连通性的前提下提高网络的覆盖率。在虚拟距离算法中,每个传感器节点的运动受到3个虚拟距离的影响:节点之间的虚拟距离、未被覆盖区域格点与节点的虚拟距离以及边界与节点间的虚拟距离。仿真结果表明:该算法可以有效地提高网络覆盖率。可以得出以下结论:虚拟距离算法通过对节点位置的控制更新有效提高了网络覆盖率,使节点得到优化部署。 相似文献