全文获取类型
收费全文 | 5807篇 |
免费 | 555篇 |
国内免费 | 5篇 |
专业分类
6367篇 |
出版年
2023年 | 33篇 |
2022年 | 64篇 |
2021年 | 150篇 |
2020年 | 87篇 |
2019年 | 110篇 |
2018年 | 148篇 |
2017年 | 125篇 |
2016年 | 219篇 |
2015年 | 303篇 |
2014年 | 348篇 |
2013年 | 376篇 |
2012年 | 523篇 |
2011年 | 520篇 |
2010年 | 308篇 |
2009年 | 267篇 |
2008年 | 373篇 |
2007年 | 365篇 |
2006年 | 343篇 |
2005年 | 266篇 |
2004年 | 282篇 |
2003年 | 225篇 |
2002年 | 251篇 |
2001年 | 65篇 |
2000年 | 60篇 |
1999年 | 49篇 |
1998年 | 69篇 |
1997年 | 39篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 22篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有6367条查询结果,搜索用时 15 毫秒
51.
52.
Katrin Schmidt Antony J. Birchill Angus Atkinson Robert J. W. Brewin James R. Clark Anna E. Hickman David G. Johns Maeve C. Lohan Angela Milne Silvia Pardo Luca Polimene Tim J. Smyth Glen A. Tarran Claire E. Widdicombe E. Malcolm S. Woodward Simon J. Ussher 《Global Change Biology》2020,26(10):5574-5587
Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota—large diatoms, dinoflagellates and copepods—that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico‐ and nanophytoplankton biomass in coastal areas. Among the pico‐fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico‐ and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light‐harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega‐3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition‐related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters. 相似文献
53.
54.
Daniele Novarina Georges E. Janssens Koen Bokern Tim Schut Noor C. van Oerle Hinke G. Kazemier Liesbeth M. Veenhoff Michael Chang 《Aging cell》2020,19(2)
To ensure proper transmission of genetic information, cells need to preserve and faithfully replicate their genome, and failure to do so leads to genome instability, a hallmark of both cancer and aging. Defects in genes involved in guarding genome stability cause several human progeroid syndromes, and an age‐dependent accumulation of mutations has been observed in different organisms, from yeast to mammals. However, it is unclear whether the spontaneous mutation rate changes during aging and whether specific pathways are important for genome maintenance in old cells. We developed a high‐throughput replica‐pinning approach to screen for genes important to suppress the accumulation of spontaneous mutations during yeast replicative aging. We found 13 known mutation suppression genes, and 31 genes that had no previous link to spontaneous mutagenesis, and all acted independently of age. Importantly, we identified PEX19, encoding an evolutionarily conserved peroxisome biogenesis factor, as an age‐specific mutation suppression gene. While wild‐type and pex19Δ young cells have similar spontaneous mutation rates, aged cells lacking PEX19 display an elevated mutation rate. This finding suggests that functional peroxisomes may be important to preserve genome integrity specifically in old cells. 相似文献
55.
Annette Menzel Ye Yuan Michael Matiu Tim Sparks Helfried Scheifinger Regula Gehrig Nicole Estrella 《Global Change Biology》2020,26(4):2599-2612
A paper published in Global Change Biology in 2006 revealed that phenological responses in 1971–2000 matched the warming pattern in Europe, but a lack of chilling and adaptation in farming may have reversed these findings. Therefore, for 1951–2018 in a corresponding data set, we determined changes as linear trends and analysed their variation by plant traits/groups, across season and time as well as their attribution to warming following IPCC methodology. Although spring and summer phases in wild plants advanced less (maximum advances in 1978–2007), more (~90%) and more significant (~60%) negative trends were present, being stronger in early spring, at higher elevations, but smaller for nonwoody insect‐pollinated species. These trends were strongly attributable to winter and spring warming. Findings for crop spring phases were similar, but were less pronounced. There were clearer and attributable signs for a delayed senescence in response to winter and spring warming. These changes resulted in a longer growing season, but a constant generative period in wild plants and a shortened one in agricultural crops. Phenology determined by farmers’ decisions differed noticeably from the purely climatic driven phases with smaller percentages of advancing (~75%) trends, but farmers’ spring activities were the only group with reinforced advancement, suggesting adaptation. Trends in farmers’ spring and summer activities were very likely/likely associated with the warming pattern. In contrast, the advance in autumn farming phases was significantly associated with below average summer warming. Thus, under ongoing climate change with decreased chilling the advancing phenology in spring and summer is still attributable to warming; even the farmers’ activities in these seasons mirror, to a lesser extent, the warming. Our findings point to adaptation to climate change in agriculture and reveal diverse implications for terrestrial ecosystems; the strong attribution supports the necessary mediation of warming impacts to the general public. 相似文献
56.
Benjamin Feit Tim Dempster Tim S. Jessop Jonathan K. Webb Mike Letnic 《Global Change Biology》2020,26(5):2829-2840
Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidence that invasive vertebrates trigger such trophic cascades and alter community structure in terrestrial ecosystems remains rare. Here, we ask how the cane toad, a vertebrate invader that is toxic to many of Australia's vertebrate predators, influences lizard assemblages in a semi‐arid rangeland. In our study area, the density of cane toads is influenced by the availability of water accessible to toads. We compared an index of the abundance of sand goannas, a large predatory lizard that is susceptible to poisoning by cane toads and the abundances of four lizard families preyed upon by goannas (skinks, pygopods, agamid lizards and geckos) in areas where cane toads were common or rare. Consistent with the idea that suppression of sand goannas by cane toads initiates a trophic cascade, goanna activity was lower and small lizards were more abundant where toads were common. The hypothesis that suppression of sand goannas by cane toads triggers a trophic cascade was further supported by our findings that small terrestrial lizards that are frequently preyed upon by goannas were more affected by toad abundance than arboreal geckos, which are rarely consumed by goannas. Furthermore, the abundance of at least one genus of terrestrial skinks benefitted from allogenic ecosystem engineering by goannas where toads were rare. Overall, our study provides evidence that the invasion of ecosystems by non‐native species can have important effects on the structure and integrity of native communities extending beyond their often most obvious and frequently documented direct ecological effects. 相似文献
57.
Alessia Visconti Simone Ribero Marianna Sanna Tim D. Spector Veronique Bataille Mario Falchi 《Pigment cell & melanoma research》2020,33(2):326-333
Body site is highly relevant for melanoma: it affects prognosis and varies according to the patient's sex. The distribution of naevi, a major risk factor for melanoma, at different body sites also varies according to sex in childhood. Using naevus counts at different body sites in 492 unrelated adults from both sexes, we observed that women have an increased number of naevi on the lower limbs compared to men (p = 8.5 × 10?5), showing that a high naevus count on this site persists from childhood throughout life. Then, using data from 3,232 twins, we observed, in women, the lowest naevus count heritability on the trunk (26%), and the highest on the lower limbs (69%). Finally, we showed that, in 2,864 women, six genomic loci previously associated with both naevus count and melanoma risk (IRF4, DOCK8, MTAP, 9q31.2, KITLG and PLA2G6) have an effect on naevus count that is body site‐specific, but whose effect sizes are predominantly stronger on the lower limbs. Sex‐specific genetic influence on naevus count at different sites may explain differences in site‐specific melanoma incidence as well as prognosis between sexes. 相似文献
58.
Judith M. Stahl Dirk Babendreier Maria Cristina Foti Stefano Colazza Tim Haye 《Journal of Applied Entomology》2020,144(8):669-677
Following the accidental introduction and spread of the invasive polyphagous agricultural pest Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), the two European egg parasitoids Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) have been investigated for inundative biological control. Since the competititve outcome between the two generalist parasitoids is difficult to predict, intrinsic competition was investigated with a time-course development study. Both species readily oviposited in H. halys eggs containing eggs and early instar larvae of the competitor, but oviposition decreased when eggs contained late instar larvae and pupae. Ooencyrtus telenomicida offspring emergence from multiparasitized eggs was significantly lower than that from rearing controls, independent of the order of parasitization. Anastatus bifasciatus offspring emergence was not influenced by the presence of O. telenomicida when it parasitized as the first species, but emergence was decreased after oviposition in eggs containing O. telenomicida larvae and pupae. There was no indication that O. telenomicida can act as a facultative hyperparasitoid of A. bifasciatus. These results suggest that A. bifasciatus is the superior intrinsic competitor and no or minor negative implications for A. bifasciatus are expected if released in combination with O. telenomicida. 相似文献
59.
Pavel Pipek Tim M. Blackburn Steven Delean Phillip Cassey aan H. ekerciolu Petr Pyek 《Ecology and evolution》2020,10(9):3944-3953
Invasive alien species are a major threat to biodiversity and human activities, providing a strong incentive to understand the processes by which alien invasion occurs. While it is important to understand the determinants of success at each of several invasion stages—transport, introduction, establishment, and spread—few studies have explored the first of these stages. Here, we quantify and analyze variation in the success of individual animals in surviving the transport stage, based on shipping records of European passerines destined for New Zealand. We mined the original documents of Acclimatisation Societies, established in New Zealand for the purpose of introducing supposedly beneficial alien species, in combination with recently digitized newspaper archives, to produce a unique dataset of 122 ships that carried passerines from Europe to New Zealand between 1850 and 1885. For 37 of these shipments, data on the survival of individual species were available. Using generalized linear mixed models, we explored how survival was related to characteristics of the shipments and the species. We show that species differed greatly in their survival, but none of the tested traits accounted for these differences. Yet, survival increased over time, which mirrors the switch from early haphazard shipments to larger organized shipments. Our results imply that it was the quality of care received by the birds that most affected success at this stage of the invasion process. 相似文献
60.
Bontinck Paul-Antoine Grant Tim Kaewmai Roihatai Musikavong Charongpun 《The International Journal of Life Cycle Assessment》2021,26(8):1687-1701
The International Journal of Life Cycle Assessment - Quantifying the impacts of water consumption on available water resources forms one of the core indicators of many life cycle assessments... 相似文献