全文获取类型
收费全文 | 999篇 |
免费 | 57篇 |
专业分类
1056篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 25篇 |
2015年 | 45篇 |
2014年 | 38篇 |
2013年 | 50篇 |
2012年 | 57篇 |
2011年 | 55篇 |
2010年 | 36篇 |
2009年 | 51篇 |
2008年 | 64篇 |
2007年 | 48篇 |
2006年 | 45篇 |
2005年 | 50篇 |
2004年 | 50篇 |
2003年 | 47篇 |
2002年 | 44篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1972年 | 4篇 |
1970年 | 4篇 |
1969年 | 7篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 4篇 |
1964年 | 6篇 |
1963年 | 9篇 |
1962年 | 8篇 |
1961年 | 5篇 |
1960年 | 7篇 |
1959年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有1056条查询结果,搜索用时 15 毫秒
971.
Attila Hettyey Balázs Vági Tibor Kovács János Ujszegi Patrik Katona Márk Szederkényi Peter B. Pearman Matteo Griggio Herbert Hoi 《Oecologia》2014,176(2):457-464
Experimental evidence suggests that reproductive interference between heterospecifics can seriously affect individual fitness; support from field studies for such an effect has, however, remained scarce. We studied reproductive interference in 25 natural breeding ponds in an area where two ranid frogs, Rana dalmatina and Rana temporaria, co-occur. The breeding seasons of the two species usually overlap and males of both species are often found in amplexus with heterospecific females, even though matings between heterospecifics produce no viable offspring. We estimated species abundance ratios based on the number of clutches laid and evaluated fertilization success. In ponds with low spatial complexity and a species abundance ratio biased towards R. temporaria, the average fertilization success of R. dalmatina eggs decreased, while this relationship was not detectable in spatially more complex ponds. Fertilization success of R. temporaria did not decrease with increasing relative numbers of heterospecifics. This asymmetry in fitness effects of reproductive interference may be attributed to R. temporaria males being more competitive in scramble competition for females than R. dalmatina males. Our study is among the first to demonstrate that in natural breeding populations of vertebrates interference among heterospecifics has the potential to substantially lower reproductive success at the population level, which may in turn affect population dynamics. 相似文献
972.
973.
Szilvia?KovácsEmail author Péter?Fehérvári Krisztina?Nagy Andrea?Harnos Tibor?Cs?rg? 《Central European Journal of Biology》2012,7(1):115-125
Global environmental processes like climate change could severely affect population level migratory behaviour of long range
migrant birds. We analyzed changes in migration phenology and biometrics of three closely-related long-distance migrant Acrocephalus species. We used the records of 12 063 Sedge, 12 913 Reed, and 5 409 Marsh Warblers caught and ringed between 1989–2009,
at a Hungarian stopover site. Quantile regressions were used to analyse the changes in spring and autumn migration phenology.
Median spring arrival date of Sedge and Reed Warblers shifted 6.5 and 7.5 days earlier, respectively. Autumn arrival of all
species shifted one (Reed and Marsh Warblers) or two (Sedge Warbler) weeks later. Mean body mass of adult Reed and Marsh Warblers
decreased in spring (by 0.3 and 0.2 grams, respectively) and in autumn (by 0.8 and 0.2 grams, respectively) while body mass
of adult Sedge Warblers decreased only in autumn (by 0.4 grams). Mean wing length of all species increased significantly (range
of change: 0.6–1 mm). Despite the fact that the studied species are closely related, all three have remarkably different migration
strategies. However, similar patterns can be observed in the studied parameters, indicating that global processes may have
general effects on these species, albeit through markedly different mechanisms. 相似文献
974.
Hans-Christian Siebert Shan-Yun Lu Rainer Wechselberger Karin Born Thomas Eckert Songping Liang Claus-Wilhelm von der Lieth Jesús Jimnez-Barbero Roland Schauer Johannes F.G. Vliegenthart Thomas Lütteke Tibor Kor 《Carbohydrate research》2009,344(12):1515-16285
The affinity to sialic acid-containing oligosaccharides of the small-animal lectin SHL-I isolated from the venom of the Chinese bird-hunting spider Selenocosmia huwena is here described for the first time. By a strategic combination of NMR techniques, molecular modeling, and data mining tools it was possible to identify the crucial amino acid residues that are responsible for SHL-I’s ability to bind sialic acid residues in a specific way. Furthermore, we are able to discuss the role of the functional groups of sialic acid when bound to SHL-I. Also the impact of Pro31 in its cis- or trans-form on SHL-I’s ligand affinity is of special interest, since it answers the question if Trp32 is a crucial amino acid for stabilizing complexes between SHL-I and sialic acid. SHL-I can be considered as a proper model system that provides further insights into the binding mechanisms of small-animal lectins to sialic acid on a sub-molecular level. 相似文献
975.
Roland Horváth Tibor Magura Csaba Szinetár János Eichardt Béla Tóthmérész 《Biodiversity and Conservation》2013,22(10):2139-2150
The role of fragment size, isolation and habitat diversity in the conservation of spider assemblages living in fragmented landscape were studied in dry sandy grasslands (East Hungary, Nyírség). Spiders were collected using pitfall traps at eight dry grassland fragments from 2001 to 2009 from March to October fortnightly. We tested the rules of island biogeography, which suggest that the species richness increases with the size and decreases with the isolation of fragments. The habitat diversity is an important factor for species richness, since large areas usually have more habitats; therefore, the number of species may be higher in these areas. During the 9-year study period, altogether 10,544 individuals belonging to 106 species were collected. Contradicting the classical theory, we found a significant negative relationship between the total number of spider species and the grassland size, while the ratio of sandy grassland specialist spider species increased with fragment size. The relationship between the ratio of generalist species and the fragment size was not significant. The overall species richness and the isolation of studied grasslands did not show a significant relationship. The ratio of sandy grassland specialist species decreased, while the ratio of generalist species increased with the increasing of isolation. The habitat diversity did not show any effect on spider species richness. We concluded that to conserve the habitat specialist species it is recommended to preserve the large and least isolated grassland fragments, furthermore to increase the size of small fragments with the restoration of the adjacent croplands. 相似文献
976.
Szijártó V Pal T Nagy G Nagy E Ghazawi A al-Haj M El Kurdi S Sonnevend A 《FEMS microbiology letters》2012,326(2):131-136
MicroRNAs (miRNAs) are important modulators of gene expression in eukaryotic cells. However RNAs of the same size in bacteria have not been specifically discussed previously. Here, we provide a library of miRNA-size RNAs (msRNAs), which were registered by deep sequencing in Streptococcus mutans. Bioinformatic analysis of the whole set revealed more than 900 individual msRNA species. The cellular content of selected msRNAs was verified by quantitative RT-PCR and Northern blotting. The high abundance and discrete size of the subset of registered msRNAs suggest their functional significance, although the precise biological role of the RNA species revealed in S.?mutans, which is one of the principle causative agents of dental caries, has to be elucidated. 相似文献
977.
Germination responses to aerosol smoke and its aqueous solution (smoke–water) were studied in laboratory for six species common throughout temperate Europe: four annual weeds from the Brassicaceae family (Camelina microcarpa, Capsella bursa-pastoris, Descurainia sophia and Sisymbrium orientale), and two perennial Plantago species (P. lanceolata and P. media) inhabiting natural grasslands. It was hypothesized that smoke enhances germination for these species despite they are not fire-adapted. Both smoke treatments increased the final germination percentage for C. bursa-pastoris and D. sophia by fourfold to fivefold, for C. microcarpa by 73–224 % and for P. lanceolata by 26–41 % compared to the control. S. orientale and P. media showed high (>80 %) germination in the control with no significant response to smoke–water. These results confirm the occurrence of smoke-stimulated germination among species of the European natural flora inhabiting non-fire-prone habitats, suggest more successful seedling recruitment for smoke-responsive species with climate change-driven increase in fire frequency and can be used in the cultivation of the species or in weed control. 相似文献
978.
Background
Fine needle aspiration (FNA) cytology is a well-established diagnostic method based on the microscopic interpretation of often scant cytological material; therefore, experience, good technique and smear quality are equally important in obtaining satisfactory results.Aims of Study
We studied the use of fresh surgical pathology specimens for making so-called mock-FNA smears with the potential of cytohistological correlation. Additionally, we studied how this process aids the improvement of preparation technique and smear quality.Methods
Cytological aspirates from 32 fresh biopsy specimens from various sites: lung (20), lymph nodes (6), and breast (6) were obtained, all with a clinical diagnosis of tumor. Aspiration was performed from grossly palpable tumors. 25G needle and Cameco-type syringe holder was used with minimal or no suction.Results
Unfixed surgical specimens provided sufficient cytological material that resulted in good quality smears. After standard processing of specimens into microscopic sections from paraffin embedded tissues, cytohistological case-series were created. No significant alteration was reported in tissue architecture on hematoxylin-eosin stained sections after the aspiration procedure. A gradual, but steady improvement was observed in smear quality just after a few preparations.Discussions and Conclusions
Our study proved that surgical specimens may be used as a source of cytological material to create cytohistological correlation studies and also to improve FNA cytology skills. The use of very fine gauge needle (25G, 0,6 mm diameter) during the sampling process does not alter tissue architecture therefore the final histopathological diagnosis is not compromised. We conclude that by using fresh surgical specimens useful cytohistological collections can be created both as a teaching resource and as improving experience. 相似文献979.
980.
Regina Lindborg Tibor Hartel Aveliina Helm Elisabeth Prangel Ttriin Reitalu Raimon Ripoll-Bosch 《应用植被学》2023,26(2):e12729