全文获取类型
收费全文 | 298篇 |
免费 | 17篇 |
专业分类
315篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 18篇 |
2013年 | 26篇 |
2012年 | 22篇 |
2011年 | 22篇 |
2010年 | 10篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 9篇 |
2005年 | 14篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有315条查询结果,搜索用时 0 毫秒
21.
22.
Tourniaire R Ferran A Gambier J Giuge L Bouffault F 《Journal of insect physiology》2000,46(5):721-726
To improve the efficiency of the ladybeetle Harmonia axyridis as a biological control agent against aphids, a flightless population was produced by feeding adults with a mutagen and selecting their progeny for non-flying but otherwise morphologically normal individuals. The inability to fly could result from a change in their flying behavior compared with control adults. Flight duration was very much shorter, wing beat frequency and more particularly the amplitude of the wing beats were clearly lower. More time was spent on the other components of flight behavior such as wing rotation, wing immobility and wing folding. The sequence of these patterns differed slightly mainly due to changes in their frequency. The locomotory behavior was not modified by the mutation, which only affected the wing muscles. The searching behavior of mutant adults differed from that of control adults only in that they took longer to encounter and ingest aphids. As this difference is not important, it should be possible to use this flightless population in biological control programs. 相似文献
23.
The brush-tailed porcupine (Atherurus africanus) is a hystricomorph rodent, which frequents the forests of West and Central Africa. With an average weight of 3 kg, it is a favourite source of meat for urban and rural populations of Gabon, Nigeria, Cameroon or Congo. Hunted in large quantities, its price is often higher than that of other game or domestic animals. Although its current productivity in captivity is limited to a single young per birth and two to three births per year per female, this species could be a good candidate for minilivestock programmes in African forest areas if its current reproductive potential in captivity could be improved. Further research should be encouraged on its biology and reproduction since the current level of hunting for this species is probably not sustainable. Captive breeding programmes could play a role in assessing a better knowledge of the species' biology, and in reducing the effects of intensive hunting in areas where this activi ty is no longer sustainable. 相似文献
24.
Lovern B Stroud LA Ferran NA Evans SL Evans RO Holt CA 《Computer methods in biomechanics and biomedical engineering》2010,13(6):803-809
The shoulder complex has a larger range of motion (ROM) than any other joint complex in the human body, leaving it prone to numerous injuries. Objective kinematic analysis could yield useful functional insights that may assist clinical practice. Non-invasive optoelectronic motion analysis techniques have been used to assess the shoulders of five healthy subjects performing ROM tasks and 10 functional tasks of daily living. The four most demanding tasks - touching the side and back of the head, brushing the opposite side of the head, lifting an object to shoulder height and lifting an object to head height, required 78%, 60%, 61% and 71%, respectively, of the glenohumeral elevation necessary for full abduction in the scapular plane for the 10 shoulders. This has implications for clinical practice where maximum arm elevation is commonly used to determine a patient's ability to return to work and other everyday activities. 相似文献
25.
Saissetia oleae (Olivier) (Hemiptera: Coccidae) populations were studied and compared in citrus (Citrus spp.) and olive (Olea europaea L.) groves to determine the number of generations, crawler emergence periods and changes in population density during the year. Ten citrus and four olive groves were sampled regularly between March 2003 and December 2005 in eastern Spain, covering an area of 10,000 km2. Each sample consisted of 16 branches and 64 leaves. Saissetia oleae populations presented a similar trend in both crops during the three years of study. Populations peaked in July, when crawlers emerged after the egg-laying period, and decreased during several months due to mortality of first instars in summer. A second crawler emergence period, with lower numbers and more variability from year to year, occurred between October and March. Populations did not increase during this period, probably because most eggs and crawlers perished during the winter and also because females that gave rise to this fall-winter generation were half as big and fecund as spring females. No differences were found between the size of mature females that had developed on citrus and on olives during the spring. Considering this population pattern, the best seasonal period to apply pesticides to control S. oleae would be at the end of July, when populations are synchronous, all crawlers have already emerged, and first instars predominate. 相似文献
26.
27.
Constant�� Stefanescu Ignasi Torre Jordi Jubany Ferran P��ramo 《Journal of Insect Conservation》2011,15(1-2):83-93
Although butterfly declines have been reported across Europe, no assessment based on detailed quantitative data has ever been made for any extensive area in the Mediterranean Basin. In 1994, a Butterfly Monitoring Scheme was launched in Catalonia (NE Spain), and in 2005 a similar, albeit much smaller, scheme started in the neighbouring Pyrenean country of Andorra. Here we provide a first thorough assessment of butterfly trends in both areas for the last 15 years. Several patterns emerged, above all a worrying decline of a substantial part of the fauna. It was also evident that habitat specialists are experiencing greater declines than habitat generalists, thereby butterfly communities becoming progressively dominated by common species. However, habitat indicators based on characteristic species also revealed that trends are actually associated with habitat types, grassland and scrub specialists declining strongly but woodland specialists showing a marginal increase. These differences are certainly related to profound landscape changes, mainly a dramatic reduction of semi-natural grasslands and open Mediterranean scrub, and a major increase in woodlands. The general effect of climatic warming on butterfly populations was investigated by using the temperature community index (CTI) approach. The thermal structure of butterfly communities remained very stable over time, except in one case where, contrary to the expectations, a significant negative trend in the CTI was noted. However, this surprising result can be explained by taking into account the above-reported pattern of butterfly communities becoming dominated by common species, characterized by low thermal indices in comparison with declining Mediterranean specialists. 相似文献
28.
29.
We studied the expression pattern of the major renal protein Podocalyxin during the development of mouse brain using in situ hybridization. Podocalyxin mRNA was widely expressed at least from E14, the first age we studied, and expression remained high until adulthood. The highest levels of expression were postnatal. Podocalyxin expression was particularly elevated in the cortical plate, the hippocampus and cerebellum, and in several basal forebrain nuclei. 相似文献
30.
Soil microbial carbon and nitrogen transformations at a glacial foreland on Anvers Island, Antarctic Peninsula 总被引:1,自引:0,他引:1
Microbial communities can play a critical role in soil development and succession at glacial forelands through their contribution to soil carbon (C) and nitrogen (N) cycling. Using a combination of molecular fingerprinting techniques and metabolic rate measurements, we examined the soil microbial community composition and key transformations in the C and N cycles at a glacial foreland on Anvers Island along the Antarctic Peninsula. Soils were sampled along transects representing a chronosequence of <1 to approximately 10?years since deglaciation. The soil microbial community was active adjacent to the receding edge of the glacier, where soil had been ice-free for <1?year. A survey of the microbial community composition identified typical soil bacterial species such as Arthrobacter and Sphingomonas, as well as known Antarctic heterotrophs, cyanobacteria and fungi. The soil C cycle over this zone was dominated by phototrophic microbial activity, while the N cycle was dominated by heterotrophic N2-fixation and not cyanobacterial N2-fixation as found at other recently deglaciated forelands. Other N transformations such as ammonia oxidation and denitrification appeared to be of limited relevance. 相似文献