全文获取类型
收费全文 | 10410篇 |
免费 | 954篇 |
国内免费 | 5篇 |
出版年
2023年 | 77篇 |
2022年 | 181篇 |
2021年 | 370篇 |
2020年 | 208篇 |
2019年 | 269篇 |
2018年 | 294篇 |
2017年 | 234篇 |
2016年 | 399篇 |
2015年 | 714篇 |
2014年 | 730篇 |
2013年 | 736篇 |
2012年 | 1036篇 |
2011年 | 939篇 |
2010年 | 521篇 |
2009年 | 386篇 |
2008年 | 550篇 |
2007年 | 584篇 |
2006年 | 452篇 |
2005年 | 403篇 |
2004年 | 405篇 |
2003年 | 314篇 |
2002年 | 301篇 |
2001年 | 57篇 |
2000年 | 47篇 |
1999年 | 49篇 |
1998年 | 75篇 |
1997年 | 37篇 |
1996年 | 38篇 |
1995年 | 28篇 |
1994年 | 31篇 |
1993年 | 36篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 25篇 |
1978年 | 32篇 |
1977年 | 25篇 |
1976年 | 34篇 |
1975年 | 25篇 |
1974年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
361.
Ancillary contributions of heterologous biotin protein ligase and carbonic anhydrase for CO2 incorporation into 3‐hydroxypropionate by metabolically engineered Pyrococcus furiosus
下载免费PDF全文
![点击此处可从《Biotechnology and bioengineering》网站下载免费的PDF全文](/ch/ext_images/free.gif)
362.
363.
Maintained functional diversity in benthic communities in spite of diverging functional identities
下载免费PDF全文
![点击此处可从《Oikos》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ecological studies based on time‐series often investigate community changes centered on species abundance or biomass but rarely expose the consequential functional aspects underlying such changes. Functional diversity measures have proven to be more accurate predictors for ecosystem functioning than traditional taxonomic approaches and hence gained much attention. There are only limited studies available that analyse the functional implications behind decadal changes of entire communities. We studied zoobenthic communities of two habitats, sheltered and exposed, of a coastal system subject to contrasting changes in community composition over the past four decades. Besides eutrophication and climate‐related impacts, the system has been invaded by a non‐native polycheate Marenzelleria spp., adding altered functional properties to the communities. The functional dispersion (FDis) metric was used as a measure for comparing the functional diversity of the contrasting habitats, with special focus on the role of Marenzelleria for the entire communities. We highlight changes in the functional identity of the communities, expressed as community‐weighted means of trait expression (CWM), using multivariate techniques, and investigate the relationship between taxonomic and functional changes. Despite contrasting community developments in the two habitats, with characteristics traditionally suggesting different environmental quality, we found that the FDis in both habitats remained similar and increased with the introduction of Marenzelleria. Although showing maintained functional diversity across time and space, the functional identity (CWM) of communities changed irrespective of taxonomical differences. Examples include inter alia alterations in palatability proxies, feeding position and sediment transportation types, indicating changed functionality of zoobenthos in coastal systems. We show, when focussing on qualitative functional changes of communities, it is important to evaluate the underlying functional identity, and not only rely on measures of the diversity of functions per se, as the quality indication of expressed functional traits can be concealed when using multi‐functionality approaches. 相似文献
364.
365.
366.
367.
Benjamin Wiggins 《Ethnic and racial studies》2016,39(14):2583-2600
In the early 1990s, a new cycle of films emerged that depicted complex portrayals of the lives of African-Americans in the neighbourhoods in which they lived. This so-called ‘hood genre was quite radical in its foregrounding of structural racism and police violence. But Hollywood's marketing of these films muted this radical content by directly contradicting explicit signifiers in the films’ story worlds. While many of the ‘hood films take place on the urban fringe and in suburbs, their promotional materials worked to confine the action, to a mythic ‘inner city'.This essay studies the two most popular films of the genre, Boyz n the Hood and Menace II Society, to illustrate how ‘paratexts' redistricted 'hood films. Through a comparative analysis of the films and their promotional materials, this essay argues Hollywood marketed a racialized ‘imaginative geography' for this important genre of African-American cinema. 相似文献
368.
Rebecca Hendershott Alison Behie Benjamin Rawson 《International journal of primatology》2016,37(4-5):586-604
Primate activity budgets are dictated by food availability and distribution; thus primates living in seasonal environments must adapt their behaviors to accommodate fluctuations in resources. Cat Ba langurs (Trachypithecus poliocephalus), a Critically Endangered Asian colobine and a member of the limestone langur group (francoisi superspecies group within genus Trachypithecus), live only in fragmented and disturbed habitats on Cat Ba Island, northeastern Vietnam. This study aimed to assess the behaviors and diet of Cat Ba langurs by group, age, sex, and season. We predicted they would have high rates of inactivity and foraging, low rates of social behaviors, with seasonal variation that reflects an energy-maximizing strategy. We conducted behavioral observations through scan sampling over an 11-month period and found that Cat Ba langurs spent a significant portion of their day inactive (57 %) followed by foraging (18 %), socializing (13 %), locomoting (10 %), and engaging in “other” behaviors (2 %). Their diet was made up primarily of leaves (83 %) followed by flowers (8 %), fruit (6 %), and stems (3 %). We found groups to differ in diet and activity, which is likely owing to differences in demographics and home range between groups. Seasonally, the animals ate more leaves and spent more time foraging in the dry season than the wet season, suggesting that they are energy maximizers. Cat Ba langurs have activity and dietary budgets similar to those of other limestone langurs, and respond to a presumed seasonal fluctuation in food availability similarly. 相似文献
369.
370.
Adriana Corrales Scott A. Mangan Benjamin L. Turner James W. Dalling 《Ecology letters》2016,19(4):383-392
Tropical forests are renowned for their high diversity, yet in many sites a single tree species accounts for the majority of the individuals in a stand. An explanation for these monodominant forests remains elusive, but may be linked to mycorrhizal symbioses. We tested three hypotheses by which ectomycorrhizas might facilitate the dominance of the tree, Oreomunnea mexicana, in montane tropical forest in Panama. We tested whether access to ectomycorrhizal networks improved growth and survival of seedlings, evaluated whether ectomycorrhizal fungi promote seedling growth via positive plant–soil feedback, and measured whether Oreomunnea reduced inorganic nitrogen availability. We found no evidence that Oreomunnea benefits from ectomycorrhizal networks or plant–soil feedback. However, we found three‐fold higher soil nitrate and ammonium concentrations outside than inside Oreomunnea‐dominated forest and a correlation between soil nitrate and Oreomunnea abundance in plots. Ectomycorrhizal effects on nitrogen cycling might therefore provide an explanation for the monodominance of ectomycorrhizal tree species worldwide. 相似文献