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141.
PB—g—SAN弹性体对SAN树脂的增韧   总被引:2,自引:0,他引:2  
采用种子乳液聚合法在聚丁二烯(PB)乳胶粒上接枝共聚苯乙烯和丙烯腈。合成了PB含量为40%的PB-g-SAN共聚物粉料。将其与SAN树脂熔融共混制得了一系列不同组成的ABS树脂,研究了共混物的力学性能、加工性能和形态结构。结果表明,在SAN树脂中随着PB-g-SAN含量的增加,共混物的冲击韧性和断裂伸长率不断提高,而拉伸强度和熔融指数出现下降的趋势。形态结构研究结果表明,PB橡胶粒子均匀地分散在SAN基体中,其粒径约为0.3μm,在橡胶粒子中含有大量的包容结构-SAN次级粒子。  相似文献   
142.
讨论一类含偏差变元Voherra型积分方程解的存在与渐近问题,利用Banach空间中的非紧性测度和不动点定理,建立了方程有形如z(t)=o(exp(ML(t)))解的充分条件,并给出一个例子说明结论的应用.  相似文献   
143.
《Journal of Natural History》2012,46(15-16):943-954
Non-myrmecophilous lepidopteran larvae using plants bearing ant attractants such as extrafloral nectaries are good models for studying morphological and behavioural mechanisms against ant predation. Udranomia spitzi (Hesperiidae) is a butterfly whose larvae feed on leaves of Ouratea spectabilis (Ochnaceae), a plant with extrafloral nectaries. We described the early stages of U. spitzi, and used field observations and experiments to investigate the defensive strategies of caterpillars against predatory ants. Larvae pass through five instars and pupation occurs inside larval leaf shelters. Ant-exclusion experiments revealed that the presence of ants did not affect significantly caterpillar survival. Predation experiments showed that vulnerability to ant predation decreased with increase in larval size. The present study showed that predatory ants are not as relevant as demonstrated for other systems, and also illustrates how observational data and field experiments can contribute to a better understanding of the biology and ecology of a species of interest.  相似文献   
144.
To observe the behaviour of cymothoid isopods during the infestation process, 30 experiments in aquaria were carried out, using the fish Gymnogeophagus gymnogenys (Hensel, 1870) and Jenynsia multidentata (Jenyns, 1842) as hosts, and Artystone trysibia Schioedte, 1866 as the parasite. All the specimens were collected from Guaíba Lake in Porto Alegre, Rio Grande do Sul. We recorded and analysed the behavioural acts of the parasites and hosts from the moment of encounter to the infestation, which was considered to be completed when the parasite had inserted itself into the fish's body. The behavioural acts are shown as a flow diagram, including the frequencies of occurrence of each act. Positive infestation occurred in 60% of the experiments. No relationship was observed between the sizes of the parasite and host, and the success of the infestation.  相似文献   
145.
《Journal of Natural History》2012,46(31-32):1979-1988
Anurans are known to feign death as a way to avoid or minimize the risk of predation. However, information on this defensive strategy is scattered and we believe that there is more than one behaviour type referred to as thanatosis. Here we review the literature, add original data, and propose definitions and new names that complement the present knowledge on the subject. We collected information on 334 individuals of 99 species in 16 families and grouped the recorded displays into two categories of tonic immobility: (1) thanatosis, death-feigning, or playing possum, and (2) shrinking or contracting. These two categories are treated as different behaviour types because of the display pattern (position of fore- and hindlimbs, eye opening), presence of skin toxins (shrinking is mostly displayed by toxic species, whereas thanatosis is mostly displayed by non-toxic species), social context (interaction with predators), and their putative or actual functions.  相似文献   
146.
147.
《Journal of Natural History》2012,46(4):1015-1027
Males of many bees in the subfamily Nomiinae (Halictidae) have numerous secondary sexual characters, which provide much systematic information. Similarly, the use of these structures by males during sexual behaviour may provide useful characters, but the courtship and copulatory behaviour of most of these bees is not known. Structures and behaviour used for courtship and mating are described for two species of nomiine bees, Dieunomia heteropoda and Nomia tetrazonata, along with brief observations of mating in a parasitic bee, Triepeolus verbesinae (Apidae: Nomadinae). A review of mating behaviour within the Nomiinae shows no obvious phyletic patterns, based upon present limited knowledge. The species-specific nature of the male secondary sexual characters suggests they may have evolved in the context of sexual selection, but behavioural data from populations of additional species are needed to evaluate the hypothesis adequately.  相似文献   
148.
《Journal of Natural History》2012,46(41-42):2623-2632
The present study evaluated the occurrence of thanatosis in freshwater crustaceans. The duration of the thanatosis events was compared with respect to photoperiod and size for Aegla longirostri (Brazil) and Aegla denticulata denticulata (Chile). Adults of A. longirostri did not show thanatosis; juveniles were responsive only when they were out of water. In the two species, thanatosis occurred in both light and dark photophases, and there was no significant difference in the duration of the events between the photophases. For A. d. denticulata, which lives in deep waters and in sympatry with larger decapods, this behaviour seems to represent an adaptation either to the environment or to the biotic community of the species. This behaviour is apparently not necessary for adults of A. longirostri, since this species is mainly nocturnal in its adult phase and its activity rhythms do not coincide with those of its potential predators.  相似文献   
149.
青少年行为偏差问题由于关涉青少年成长、家庭和睦、学校稳定及社会发展,因此成为人们普遍关注的社会问题。青少年行为偏差是家庭、学校、社会等外部因素与青少年自身因素相互交错感染的结果。青少年偏差行为的发生是一个由量变到质变渐次发展的过程,在此过程中,他们经历了“受压产生不适——首度反弹并自我调试——自我调试受挫——二次反弹并背离社会主流规范”四个主要的阶段,四个阶段构成了青少年偏差行为发生的模型。对青少年的偏差行为要进行自助干预和他助干预。要以预防为主,通过养成教育培养青少年良好的行为习惯,以减少偏差行为的发生。  相似文献   
150.
网络表示和网络优化长期以来被用于解决很多工程和科学上的问题.这种应用最早可以追溯到哥尼斯堡七桥问题,然后延伸到各种各样的经典的P类问题和Np-难题,比如最小生成树、最短路及旅行商问题等.为了表述各种子系统之间的关联,在过去几十年里,不同层次的网络扩展被提出来,并对交通和经济这样的复杂系统进行了建模.这些网络扩展被称为超网络,它们可以用统一的方式来描述不同网络上不同选择维度.近年来,多状态的超网络被认为是一种很有潜力的方法来研究基于活动建模领域里的活动和出行行为.本文综述了这方面的研究进展,从最开始的经典交通网络到至今最高层次的一种超网络.这种最高层次的超网络能支持对出行路径和模式选择、活动和停车位置选择、ICT的使用,以及共同出行扣活动的建模.  相似文献   
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