全文获取类型
收费全文 | 41751篇 |
免费 | 4270篇 |
国内免费 | 11篇 |
出版年
2022年 | 355篇 |
2021年 | 693篇 |
2020年 | 490篇 |
2019年 | 584篇 |
2018年 | 720篇 |
2017年 | 644篇 |
2016年 | 1067篇 |
2015年 | 1768篇 |
2014年 | 1940篇 |
2013年 | 2397篇 |
2012年 | 2943篇 |
2011年 | 2854篇 |
2010年 | 1883篇 |
2009年 | 1662篇 |
2008年 | 2309篇 |
2007年 | 2320篇 |
2006年 | 2190篇 |
2005年 | 1964篇 |
2004年 | 1962篇 |
2003年 | 1734篇 |
2002年 | 1701篇 |
2001年 | 708篇 |
2000年 | 669篇 |
1999年 | 674篇 |
1998年 | 466篇 |
1997年 | 393篇 |
1996年 | 369篇 |
1995年 | 383篇 |
1994年 | 328篇 |
1993年 | 338篇 |
1992年 | 447篇 |
1991年 | 383篇 |
1990年 | 382篇 |
1989年 | 398篇 |
1988年 | 402篇 |
1987年 | 368篇 |
1986年 | 315篇 |
1985年 | 330篇 |
1984年 | 334篇 |
1983年 | 285篇 |
1982年 | 273篇 |
1981年 | 254篇 |
1980年 | 224篇 |
1979年 | 251篇 |
1978年 | 204篇 |
1977年 | 202篇 |
1976年 | 206篇 |
1975年 | 219篇 |
1974年 | 191篇 |
1973年 | 181篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
1. Ecosystem processes depend on the biomass of the involved organisms, but their functional diversity may play an additional role. In particular, the exclusion of key functional groups through habitat disturbance may lead to the breakdown of ecosystem functions. Dung removal is an important process contributing to nutrient cycling and thus productivity in grazed ecosystems. 2. This study investigated the role of different functional groups of dung beetles in dung removal in different habitats within a wood-pasture in two different seasons. An experimental setting with 12 blocks and 108 dung pads was used to investigate short-term dung removal over 1 week of exposure. 3. Dung removal was most strongly affected by habitat type, with almost 40% lower levels in grassland than in adjacent forest and forest gaps. Of all assemblage characteristics, total biomass of tunneller species was the strongest predictor of dung removal, whereas functional diversity showed no significant effect. In accordance with the dung removal pattern at habitat type level, densities of large tunnellers were suppressed in grassland compared with forest. 4. It is concluded that dung removal is habitat-specific and large tunnellers play a disproportionate role in this important ecosystem function in temperate forests. 相似文献
102.
The environmental conditions to which juvenile barnacle geese (Branta leucopsis) were exposed during growth were found to affect their body size at fledging as well as their final adult body size. Small juveniles showed compensatory growth from the time of fledging up to one year of age, but this did not fully compensate the differences in body size that were established before fledging. The variation in protein content in plants eaten during growth could probably explain the observed body size differences, sometimes of more than 10%, between different categories of adult geese. Our results imply that one cannot infer selection on morphological characters from differences between samples of adult birds from different localities or from different cohorts within a population, without first showing that environmental conditions during growth do not affect the development of the characters under study. 相似文献
103.
104.
Xu Zhang Wei Zhang Santosh L. Saraf Mehdi Nouraie Jin Han Michel Gowhari Johara Hassan Galina Miasnikova Adelina Sergueeva Sergei Nekhai Rick Kittles Roberto F. Machado Joe G. N. Garcia Mark T. Gladwin Martin H. Steinberg Paola Sebastiani Donald A. McClain Victor R. Gordeuk 《Human genetics》2015,134(8):895-904
105.
Samuel M. Imathiu Rumiana V. Ray Matthew I. Back Martin C. Hare Simon G. Edwards 《Journal of Phytopathology》2013,161(7-8):553-561
Fusarium langsethiae is a toxigenic fungal species that has been reported in European small‐grain cereal crops such as oats, wheat and barley. Although its relative contribution to fusarium head blight (FHB) symptoms is not well understood, it is reported to contaminate these cereals with high levels of HT‐2 and T‐2 trichothecenes mycotoxins that are currently under consideration for legislation by the European Commission. Ten commercial oat fields in Shropshire and Staffordshire (two adjacent counties in the Midlands) in the UK were surveyed in the 2006/2007 growing season. Samples were taken from predetermined field locations at Zadoks growth stages 32/33, 69, 77‐85 and 90‐92 for F. langsethiae biomass and HT‐2 and T‐2 toxins quantification. The results from this study showed that oats can be heavily infected with F. langsethiae and have high concentrations of HT‐2 and T‐2 toxins with no apparent FHB symptoms. The regression of HT‐2 + T‐2 toxins on F. langsethiae DNA concentration was highly significant (P < 0.001, r2 = 0.55). The results indicated that although F. langsethiae had no direct effect on crop yield, it may result in indirect economic losses where the grain can be rejected or downgraded as a result of intolerable levels of HT‐2 and T‐2 toxins, which are of human food and animal feed safety concern. The influence of cultural field practices on the infection and HT‐2 and T‐2 toxins accumulation in oats was not clear and warrants further studies to identify the sources of F. langsethiae inoculum and conditions favourable for infection and mycotoxin production. 相似文献
106.
107.
Crosses between monokaryotic isolates of two strains of Lentodium squamulosum and one strain of Panus tigrinus showed complete intercompatibility. Hybrid fruits from crosses between monokaryotic isolates of L. squamulosum and P. tigrinus were uniformly like the P. tigrinus parent. Though both isolates of L. squamulosum showed considerable variability in form, merging toward P. tigrinus, L. squamulosum could always be distinguished from P. tigrinus from hand sections of the hymenophore. The significance of these results as they bear on the problem of inter-relationships between hymenomycetes and gasteromycetes is discussed. L. squamulosum is recognized as variety squamulosus of P. tigrinus. 相似文献
108.
109.
110.