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   522篇
  免费   49篇
  2023年   1篇
  2022年   7篇
  2021年   20篇
  2020年   12篇
  2019年   6篇
  2018年   13篇
  2017年   8篇
  2016年   13篇
  2015年   21篇
  2014年   18篇
  2013年   32篇
  2012年   46篇
  2011年   36篇
  2010年   25篇
  2009年   24篇
  2008年   33篇
  2007年   26篇
  2006年   26篇
  2005年   29篇
  2004年   31篇
  2003年   31篇
  2002年   35篇
  2001年   6篇
  2000年   5篇
  1999年   10篇
  1998年   1篇
  1997年   7篇
  1996年   1篇
  1995年   4篇
  1994年   1篇
  1993年   7篇
  1992年   3篇
  1991年   8篇
  1990年   3篇
  1989年   5篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1981年   2篇
  1979年   2篇
  1978年   3篇
  1974年   1篇
  1973年   1篇
排序方式: 共有571条查询结果,搜索用时 15 毫秒
561.
Applied Psychophysiology and Biofeedback - As the number of diagnosed adults living with autism spectrum disorder (ASD) continues to grow, a lack of resources and lack of available interventions...  相似文献   
562.
Domestication disconnects an animal from its natural environment and diet, imposing changes in the attendant microbial community. We examine these changes in Philornis downsi (Muscidae), an invasive parasitic fly of land birds in the Galapagos Islands. Using a 16S rDNA profiling approach we studied the microbiome of larvae and adults of wild and laboratory-reared populations. These populations diverged in their microbiomes, significantly more so in larval than in adult flies. In field-collected second-instar larvae, Klebsiella (70.3%) was the most abundant taxon, while in the laboratory Ignatzschineria and Providencia made up 89.2% of the community. In adults, Gilliamella and Dysgonomonas were key members of the core microbiome of field-derived females and males but had no or very low representation in the laboratory. Adult flies harbour sex-specific microbial consortia in their gut, as male core microbiomes were significantly dominated by Klebsiella. Thus, P. downsi microbiomes are dynamic and shift correspondingly with life cycle and diet. Sex-specific foraging behaviour of adult flies and nest conditions, which are absent in the laboratory, may contribute to shaping distinct larval, and adult male and female microbiomes. We discuss these findings in the context of microbe–host co-evolution and the implications for control measures.  相似文献   
563.
The mating system of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is based on leks. In field cage choice experiments we examined lek site selection as influenced by the presence of fruit and the presence of conspecific flies. Males were allowed to choose between artificial trees containing fruit and trees without fruit. Males showed a significant preference for the tree baited with fruit. To determine which fruit-related stimuli were important, males were allowed to choose between visual and/or olfactory fruit-derived stimuli. Males preferred to lek on trees presenting both stimuli. To determine the influence of conspecifics on lek site selection, males were allowed to choose between trees containing male and/or female conspecific flies. The presence of pheromone-emitting males was preferred. In addition, both in the field and on artificial trees, we examined the effect of leaf size on lek site selection. In the field, males preferred to lek on leaves of a particular size. Moreover, leaf integrity was important, as males tended to select undamaged leaves as lek sites. In field cage experiments, males consistently chose to lek on trees containing the largest leaves. We conclude that the choice of lek site is influenced by the presence of fruit and of other lekking males, while leaf size and integrity determine male location within a lek.  相似文献   
564.
Comparative studies on tool technologies in extant primates, especially in our closest living relatives, offer a window into the evolutionary foundations of tool use in hominins. Whereas chimpanzee tool technology is well studied across populations, the scarcity of described tool technology in wild populations of our other closest living relative, the bonobo, is a mystery. Here we provide a first report of the tool use repertoire of the Kokolopori bonobos and describe in detail the use of leaf-umbrellas during rainfall, with the aim to improve our knowledge of bonobo tool use capacity in the wild. The tool use repertoire of the Kokolopori bonobos was most similar to that of the nearby population of Wamba and comprised eight behaviors, none in a foraging context. Further, over a 6-month period we documented 44 instances of leaf-umbrella use by 22 individuals from three communities, suggesting that this behavior is habitual. Most leaf-umbrella tool users were adult females, and we observed a nonadult using a leaf-umbrella on only a single occasion. While the study and theory of tool technologies is often based on the use of tools in foraging tasks, tool use in bonobos typically occurs in nonforaging contexts across populations. Therefore, incorporating both foraging and nonforaging contexts into our theoretical framework is essential if we wish to advance our understanding of the evolutionary trajectories of tool technology in humans.  相似文献   
565.
566.
Citizen science has grown rapidly in popularity in recent years due to its potential to educate and engage the public while providing a means to address a myriad of scientific questions. However, the rise in popularity of citizen science has also been accompanied by concerns about the quality of data emerging from citizen science research projects. We assessed data quality in the online citizen scientist platform Chimp&See, which hosts camera trap videos of chimpanzees (Pan troglodytes) and other species across Equatorial Africa. In particular, we compared detection and identification of individual chimpanzees by citizen scientists with that of experts with years of experience studying those chimpanzees. We found that citizen scientists typically detected the same number of individual chimpanzees as experts, but assigned far fewer identifications (IDs) to those individuals. Those IDs assigned, however, were nearly always in agreement with the IDs provided by experts. We applied the data sets of citizen scientists and experts by constructing social networks from each. We found that both social networks were relatively robust and shared a similar structure, as well as having positively correlated individual network positions. Our findings demonstrate that, although citizen scientists produced a smaller data set based on fewer confirmed IDs, the data strongly reflect expert classifications and can be used for meaningful assessments of group structure and dynamics. This approach expands opportunities for social research and conservation monitoring in great apes and many other individually identifiable species.  相似文献   
567.
568.
The metabolism of green algae has been the focus of much research over the last century. These photosynthetic organisms can thrive under various conditions and adapt quickly to changing environments by concomitant usage of several metabolic apparatuses. The main electron coordinator in their chloroplasts, nicotinamide adenine dinucleotide phosphate (NADPH), participates in many enzymatic activities and is also responsible for inter-organellar communication. Under anaerobic conditions, green algae also accumulate molecular hydrogen (H2), a promising alternative for fossil fuels. However, to scale-up its accumulation, a firm understanding of its integration in the photosynthetic apparatus is still required. While it is generally accepted that NADPH metabolism correlates to H2 accumulation, the mechanism of this collaboration is still vague and relies on indirect measurements. Here, we investigated this connection in Chlamydomonas reinhardtii using simultaneous measurements of both dissolved gases concentration, NADPH fluorescence and electrochromic shifts at 520–546 nm. Our results indicate that energy transfer between H2 and NADPH is bi-directional and crucial for the maintenance of redox balance under light fluctuations. At light onset, NADPH consumption initially eventuates in H2 evolution, which initiates the photosynthetic electron flow. Later on, as illumination continues the majority of NADPH is diverted to the Calvin–Benson–Bassham cycle. Dark onset triggers re-assimilation of H2, which produces NADPH and so, enables initiation of dark fermentative metabolism.

Energy transfer between H2 and NADPH is bi-directional and crucial for the maintenance of redox balance under light fluctuations.  相似文献   
569.
Zinc is an essential element in mammalian development. However, little is known about concentrations of zinc in specific regions/organs in the embryo. We have employed selenite autometallography (AMG) and TSQ histofluoroscence to detect histochemically reactive (chelatable) zinc in whole midsagittal embryos and sections from neonatal mice. Chelatable zinc exhibited a broad distribution, being particularly localized to rapidly proliferating tissues, such as skin and gastrointestinal epithelium. Zinc was also observed in various types of tissues such as bone and liver. In the perinatal central nervous system, zinc was present almost exclusively in choroid plexus. The two methods used demonstrated generally similar distributions with some exceptions, e.g., in liver and blood. The ubiquity of zinc in the embryo, particularly in rapidly proliferating tissues, suggests a widespread role in fetal physiology.  相似文献   
570.
We applied the quasi in situ conservation strategy, described in an accompanying paper, to a critically endangered plant species, Iris atrofusca from the Northern Negev, Israel. As the first steps of this strategy implementation we performed habitat and demographic observations; creation of two living collections outside the natural populations, but within the same ecological conditions; and relocation experiments. Plants in the living collections got established and showed high reproductive potential. In the relocation experiments, 3 years after introduction of rhizomes, no firm conclusions could be made about factors limiting species distribution at either large or small scale, but microhabitat was important for relocation success. We conclude that complex conservation approach that includes quasi in situ strategy should be useful for an endangered species that is distributed over variable ecological conditions.  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