全文获取类型
收费全文 | 266篇 |
免费 | 28篇 |
国内免费 | 18篇 |
专业分类
安全科学 | 97篇 |
废物处理 | 1篇 |
环保管理 | 14篇 |
综合类 | 83篇 |
基础理论 | 81篇 |
环境理论 | 1篇 |
污染及防治 | 10篇 |
评价与监测 | 8篇 |
社会与环境 | 4篇 |
灾害及防治 | 13篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 3篇 |
2017年 | 13篇 |
2016年 | 8篇 |
2015年 | 12篇 |
2014年 | 6篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 20篇 |
2010年 | 11篇 |
2009年 | 25篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 19篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有312条查询结果,搜索用时 15 毫秒
61.
目的研究电晕放电辐射信号的特征提取和模式识别方法。方法在分析信号特征提取方法的基础上,对实测的电晕放电辐射信号特征提取,利用概率神经网络开展电晕放电辐射信号目标识别,检验特征提取的有效性。结果以奇异值作为输入特征量的PNN在整体上效果更优,稳定性好,对两类不同放电辐射信号的正确识别率均可达到80%以上,并且当输入特征量个数达到10个时,对实测样本的正确识别率均达到了最高值。电晕放电的正确识别率为96.7%,火花放电的正确识别率为93.3%。结论该方法能基本满足实际放电信号的识别应用。 相似文献
62.
湘中锡矿山锑矿田是世界闻名的超大型锑矿田。本文系统地叙述了该矿田该中各矿床蚀变硅化岩及其原岩的稀土元素地球化学特征 ,并在此基础上探讨了稀土元素所反映的地质意义。研究表明 ,尽管硅化岩的稀土元素地球化学特征与原岩相比有所改变 ,但仍可根据硅化岩的稀土元素地球化学特征来恢复原岩 ;根据硅化灰岩的稀土元素地球化学特征可以推测硅质岩的物质来源于地壳上部 ,结合本区硅化岩的硅同位素组成特点 ,可以推测硅质交代中的硅来源于周围地层 ;硅化岩的稀土元素变化特征证明了岩性为石灰岩的层位易于发生硅化 ,从而有利于矿化层的形成。 相似文献
63.
Bruce Lyon 《Behavioral ecology and sociobiology》2007,61(3):455-463
Hosts of avian brood parasites use a variety of defenses based on egg recognition to reduce the costs of parasitism; the most important of which is rejecting the parasitic eggs. Two basic recognition mechanisms are possible: “true recognition”, whereby hosts recognize their own eggs irrespective of their relative frequency in the clutch, and minority recognition (or “recognition by discordancy”), whereby hosts respond to the minority egg type. The mechanism of recognition has been experimentally studied in a handful of species parasitized by interspecific brood parasites, but the mechanism used in defenses against conspecific brood parasitism is unknown. I experimentally determined the mechanism of egg recognition in American coots (Fulica americana), a species with high levels of conspecific brood parasitism, egg recognition, and rejection. I swapped eggs between pairs of nests to alter frequencies of host and “parasite” eggs and then used two criteria for recognition: egg rejection and nonrandom incubation positions in the clutch. Eight of 12 nests (66%) given equal frequencies of host and parasite eggs showed evidence of true recognition. In contrast, only one of eight (12.5%) nests where host eggs were in the minority showed evidence of recognition by discordancy. The nonrandom incubation positions of parasitic eggs indicates that birds sometimes recognize parasitic eggs without rejecting them and provides a means of assessing recognition on a per nest basis in species with large clutches. Adaptive recognition without rejection may also be an important evolutionary stepping stone to the evolution of egg rejection in some taxa. 相似文献
64.
Eldridge S. Adams Lynn Atkinson Mark S. Bulmer 《Behavioral ecology and sociobiology》2007,61(8):1195-1201
Loss of aggression between social groups can have far-reaching effects on the structure of societies and populations. We tested
whether variation in the genetic structure of colonies of the termite Nasutitermes corniger affects the probability of aggression toward non-nestmates and the ability of unrelated colonies to fuse. We determined the
genotypes of workers and soldiers from 120 colonies at seven polymorphic microsatellite loci. Twenty-seven colonies contained
offspring of multiple founding queens or kings, yielding an average within-colony relatedness of 0.33. Genotypes in the remaining
93 colonies were consistent with reproduction by a single queen and king or their progeny, with an average within-colony relatedness
of 0.51. In standardized assays, the probability of aggression between workers and soldiers from different colonies was an
increasing function of within-colony relatedness. The probability of aggression was not affected significantly by the degree
of relatedness between colonies, which was near zero in all cases, or by whether the colonies were neighbors. To test whether
these assays of aggression predict the potential for colony fusion in the field, we transplanted selected nests to new locations.
Workers and soldiers from colonies that were mutually tolerant in laboratory assays joined their nests without fighting, but
workers and soldiers that were mutually aggressive in the assays initiated massive battles. These results suggest that the
presence of multiple unrelated queens or kings promotes recognition errors, which can lead to the formation of more complex
colony structures. 相似文献
65.
One mechanism that permits the maintenance of dominance hierarchies is individual recognition, defined as the ability of an animal to recognize a conspecific on the basis of one or more identifying cues, and to associate it with experiences of victories or defeats that the animal has gained from preceding encounters with that particular individual. We examined whether the long-clawed hermit crab, Pagurus longicarpus, could differentiate between unfamiliar and familiar opponents. The experimental protocol was designed to control in pairs of interacting individuals several factors together, such as status and relative size of the opponent, as well as species, quality, and fit of the inhabited shell. The hermit crabs were more reactive and their agonistic level was higher in unfamiliar than in familiar pairs; in addition, betas were more prone to initiate an interaction with unfamiliar than with familiar alphas. The alternative explanation—that the ability to discriminate between familiar and novel shells can explain our results per se— was tested following, in part, Jackson and Elwoods (1989) protocol for Pagurus bernhardus and was, at least for this species, rejected. This study did not determine whether a true individual recognition occurs, but demonstrated that P. longicarpus categorizes the individuals into two heterogeneous subgroups, thus being capable of a binary discrimination among opponents.Communicated by T. Czeschlik 相似文献
66.
目的 探索建立自然环境试验智能巡检系统,使用机器人替代部分人工巡检工作。方法 通过分析巡检作业环境和巡检任务,确定智能巡检机器人的功能要求和技术参数,进而开展机器人本体结构设计,融合控制后台、远程数据库等设备,实现智能巡检系统构建。结果 开展了智能巡检数据采集的使用验证,巡检机器人采集的样品图像对焦清晰、分辨率高,样品在图像中的位置大小合理,腐蚀特征展示清楚。巡检系统可对样品图像进行自动分割和智能识别,对蚀点、流痕等损伤特征识别准确,精度可达0.1%。结论 智能巡检系统可以满足自然环境试验的巡检要求,替代人工完成部分巡检工作,智能巡检数据便于入库和使用挖掘,对于自然环境试验的数字化转型有积极的推动作用。 相似文献
67.
68.
69.
本文以IT运行维护的故障申报系统为例,介绍如何利用Nuance Recognizer9.0自动语音识别系统和东进D081A模拟中继语音卡电话处理系统设计基于ASR(自动语音识别)的呼叫中心。文中不仅介绍了设计过程中的各个关键环节,而且对该系统的可靠性进行了深入讨论。其中包括如何合理设计语法文件以提高语音识别率;如何在系统运行期间进行同步保障,使系统逐步趋于完善。 相似文献
70.
以特殊互通式立交出口区域主线为研究对象,分析了特殊互通式立交出口交通事故特征,运用汽车制动特性、人机工程学及交通心理学原理获取驾驶员在特殊互通式立交出口处的识别视距,且识别视距均比设计规范值高.以特殊互通式立交出口识别视距为基础,运用几何学及高速公路几何线形原理建立识别视距与立交区域主线圆曲线半径关系模型,运用VB程序开发软件,提出特殊互通式立交出口处满足识别视距不同车道数主线圆曲线半径一般值和最小值.结果表明:对待建高速公路互通式立交出口位置所在主线线形应分析识别视距,并应利用识别视距对主线线形指标验算;对已建成特殊互通式立交出口,应加强其安全保障措施,保证主线及驶离主线车辆行车安全. 相似文献