全文获取类型
收费全文 | 264篇 |
免费 | 18篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 12篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 19篇 |
2011年 | 16篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有282条查询结果,搜索用时 234 毫秒
1.
Nitrate induced iron deficiency chlorosis in Juncus acutiflorus 总被引:1,自引:0,他引:1
Chlorosis caused by iron deficiency is commonly associated with high bicarbonate levels in the soil. However, in rare cases such chlorosis has been observed in soils with high nitrate levels. In a dutch rich-fen, chlorosis has been noted in stands of Juncus acutiflorus at locations where groundwater containing high levels of nitrate reached the surface. Experiments revealed that the chlorosis could be attributed to iron deficiency although iron levels in the shoots were well above the known physiological threshold values for iron deficiency. It is postulated that increased nitrate assimilation leads to an increased apoplastic pH and to a concomitant immobilisation of iron and/or lower iron (III) reduction. Moreover free amino acid levels were markedly higher in the iron deficient plants in the field. It was found, however, that the percentage of nitrogen present as free amino acids was not influenced directly by low iron levels but mainly by the C/N ratios in the shoots. Nowadays, nitrate concentrations in ground water as high 1000 µM are no longer an exception in the Netherlands. We propose that strongly increased nitrate inputs may cause iron stress in natural vegetations, especially in wet habitats. 相似文献
2.
To prepare sections of undecalcified bone suitable both for autoradiography with short-lived radionuclides such as 99m-technetium (t 1/2 = 6 hr) and for normal histology, rapid processing is necessary. By modifying the routine technique of embedding in plastic, sections can be obtained within 6 hours. The most important modification concerns the temperature used for the different steps in the process. The procedure has been used to localize 99mTc labeled methylene diphosphonate for skeletal scintigraphy. 相似文献
3.
4.
C J Persoons A K Minks S Voerman W L Roelofs F J Ritter 《Journal of insect physiology》1974,20(7):1181-1188
By means of analytical and electroantennogram methods, cis-11-and trans-11-tetradecenyl acetate have been isolated and identified as the sex pheromones of the fruit tree tortrix moth, Archips podana. In contrast to the single compounds, mixtures in a ratio of about 1 : 1 are highly attractive to male moths in field experiments. 相似文献
5.
Valeria Agamennone Joeri van Straalen Abraham Brouwer Tjalf E. de Boer Paul J. Hensbergen Niels Zaagman Martin Braster Nico M. van Straalen Dick Roelofs Thierry K.S. Janssens 《Entomologia Experimentalis et Applicata》2019,167(3):269-285
Antibiotic resistance necessitates the search for new bioactive compounds with novel mechanisms of action. Natural products derived from bacteria and fungi are widely used in the field of medicine and new environments can be explored as sources of antimicrobials. Bacteria associated with springtails have shown high inhibitory activity against pathogens. Here, we characterized a bacterial strain with high potential for antimicrobial activity, isolated from the gut of the springtail Folsomia candida Willem (Collembola: Isotomidae). The strain was characterized using the ‘analytical profile index’ and the ‘minimal inhibitory concentration’ assay to test for antibiotic resistance. Agar overlay and agar disk diffusion assays were used to test the inhibitory activity of the strain and its extract against a variety of pathogens, and reporter assays were used to investigate the mode of action. High‐performance liquid chromatography was used to analyze and fractionate the extract of bacterial culture, followed by additional assays on the fractions. The genome of the strain was screened for presence of antibiotic resistance genes and secondary metabolite gene clusters. The isolate was identified as Bacillus toyonensis Jiménez et al., but it displayed differences in metabolic profile when compared to the type species. The isolate was highly resistant to penicillin and inhibited the growth of a variety of pathogenic microorganisms. Genome analysis revealed an enrichment of resistance genes for β‐lactam antibiotics compared to the type isolate. Also, secondary metabolite clusters involved in the production of siderophores, bacteriocins, and nonribosomal peptide synthetases were identified. In conclusion, a unique Bacillus strain was isolated from the gut of F. candida, for which we provide evidence of inhibitory activity against an array of pathogens. This, coupled with high resistance to penicillin as substantiated by the presence of resistance genes, points to the potential of B. toyonensis VU‐DES13 to provide a new source of antimicrobial compounds. 相似文献
6.
Ecological restoration of rich fens in Europe and North America: from trial and error to an evidence‐based approach 下载免费PDF全文
Leon P. M. Lamers Melanie A. Vile Ab P. Grootjans Mike C. Acreman Rudy van Diggelen Martin G. Evans Curtis J. Richardson Line Rochefort Annemieke M. Kooijman Jan G. M. Roelofs Alfons J. P. Smolders 《Biological reviews of the Cambridge Philosophical Society》2015,90(1):182-203
Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land‐use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial‐and‐error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions. 相似文献
7.
8.
9.