全文获取类型
收费全文 | 1962篇 |
免费 | 155篇 |
国内免费 | 1篇 |
出版年
2022年 | 18篇 |
2021年 | 21篇 |
2019年 | 22篇 |
2016年 | 32篇 |
2015年 | 50篇 |
2014年 | 50篇 |
2013年 | 98篇 |
2012年 | 71篇 |
2011年 | 87篇 |
2010年 | 74篇 |
2009年 | 34篇 |
2008年 | 71篇 |
2007年 | 69篇 |
2006年 | 57篇 |
2005年 | 53篇 |
2004年 | 72篇 |
2003年 | 83篇 |
2002年 | 75篇 |
2001年 | 29篇 |
2000年 | 49篇 |
1999年 | 25篇 |
1997年 | 20篇 |
1996年 | 18篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 34篇 |
1991年 | 18篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 28篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 23篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 21篇 |
1975年 | 26篇 |
1974年 | 44篇 |
1973年 | 28篇 |
1972年 | 32篇 |
1971年 | 28篇 |
1968年 | 24篇 |
1967年 | 23篇 |
1966年 | 24篇 |
1965年 | 17篇 |
1961年 | 19篇 |
排序方式: 共有2118条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
85.
Donato Santovito Virginia Egea Kiril Bidzhekov Lucia Natarelli Andr Mouro Xavier Blanchet Kanin Wichapong Maria Aslani Coy Brunßen Michael Horckmans Michael Hristov Arie Geerlof Esther Lutgens Mat J. A. P. Daemen Tilman Hackeng Christian Ries Triantafyllos Chavakis Henning Morawietz Ronald Naumann Philipp Von Hundelshausen Sabine Steffens Johan Duchêne Remco T. A. Megens Michael Sattler Christian Weber 《Autophagy》2020,16(12):2294
86.
Andrew L. Von Duyke David C. Douglas Jason K. Herreman Justin A. Crawford 《Ecology and evolution》2020,10(12):5595-5616
Continued Arctic warming and sea‐ice loss will have important implications for the conservation of ringed seals, a highly ice‐dependent species. A better understanding of their spatial ecology will help characterize emerging ecological trends and inform management decisions. We deployed satellite transmitters on ringed seals in the summers of 2011, 2014, and 2016 near Utqia?vik (formerly Barrow), Alaska, to monitor their movements, diving, and haul‐out behavior. We present analyses of tracking and dive data provided by 17 seals that were tracked until at least January of the following year. Seals mostly ranged north of Utqia?vik in the Beaufort and Chukchi Seas during summer before moving into the southern Chukchi and Bering Seas during winter. In all seasons, ringed seals occupied a diversity of habitats and spatial distributions, from near shore and localized, to far offshore and wide‐ranging in drifting sea ice. Continental shelf waters were occupied for >96% of tracking days, during which repetitive diving (suggestive of foraging) primarily to the seafloor was the most frequent activity. From mid‐summer to early fall, 12 seals made ~1‐week forays off‐shelf to the deep Arctic Basin, most reaching the retreating pack‐ice, where they spent most of their time hauled out. Diel activity patterns suggested greater allocation of foraging efforts to midday hours. Haul‐out patterns were complementary, occurring mostly at night until April‐May when midday hours were preferred. Ringed seals captured in 2011—concurrent with an unusual mortality event that affected all ice‐seal species—differed morphologically and behaviorally from seals captured in other years. Speculations about the physiology of molting and its role in energetics, habitat use, and behavior are discussed; along with possible evidence of purported ringed seal ecotypes. 相似文献
87.
Robson S. Godoy Vinicius Weber Luis Esteban Krause Lanés Martin Reichard Tanise Gemelli Raquel Von Hohendorff Leonardo Maltchik 《Journal of fish biology》2021,99(4):1476-1484
Annual fish species have evolved complex adaptations to survive in temporary wetlands. The main adaptation of these fish is the ability to produce embryos that survive dry periods. Embryo development of this fish can show variation at multiple levels influenced by many environmental factors, such as photoperiod and temperature. Predator cues are another factor that can influence the embryonic stage. One way in which annual fish could adapt to predators is by using risk-spreading strategies (through bet-hedging). Nonetheless, this strategy depends on the coevolutionary history between predators and preys and on the degree of environmental unpredictability, resulting in different responses across different species. This study investigated the influence of predator cues on the embryonic development and hatching of two Austrolebias species that inhabit ponds that present differences in hydroperiod and the risk of predator presence. The results confirmed a differentiated response between the two annual fish species tested, corroborating the modulation of hatching against the risk of predation by native predatory fish. The authors further showed that development times varied between the two annual fish species, regardless of the presence of predators. They highlight that the variation in embryonic development is strongly affected by different levels of hydroperiod unpredictability faced by the two species. To unravel finer-scale local adaptations in the annual fish embryo development, future studies should focus on a region with greater spatial gradient. 相似文献
88.
Kim Tallaksen Halvorsen Torkel Larsen Howard I. Browman Caroline Durif Nicolai Aasen Leif Asbjørn Vøllestad Alessandro Cresci Tonje Knutsen Sørdalen Reidun M. Bjelland Anne Berit Skiftesvik 《Journal of fish biology》2021,99(4):1513-1518
The movement patterns of three commercially important wrasse (Labridae) species inside a small marine protected area (~ 0.15 km2) on the west coast of Norway were analysed over a period of 21 months. The mean distance between capture and recapture locations varied between 10 and 187 m, and was species and season specific. The extent of movement was not related to body size or sex. These results imply that a network of small strategically located marine protected areas can be used as management tools to protect wrasses from size- and sex-selective fishing mortality. 相似文献
89.
Joana M. Andrade Eva María Domínguez-Martín Marisa Nicolai Clia Faustino Luís Monteiro Rodrigues Patrícia Rijo 《Journal of enzyme inhibition and medicinal chemistry》2021,36(1):258
A series of Plectranthus spp. plant extracts (aqueous, acetonic, methanolic and ethyl acetic) obtained from eight different species, and previously isolated compounds (ranging from polyphenols, diterpenes and triterpenes), were assayed for in vitro inhibition of the skin-related enzymes tyrosinase, collagenase and elastase, and for studying their antioxidant properties. The ethyl acetic extracts of P. grandidentatus and P. ecklonii registered the highest antioxidant activity, whereas acetonic, methanolic and ethyl acetic extracts of P. ecklonii, P. grandidentatus, P. madagascariensis and P. saccatus concerning the enzymatic inhibition assays revealed high anti-tyrosinase and anti-collagenase activities. From the isolated compounds tested, abietane diterpenes and triterpenes were highly active against tyrosinase and elastase activity. Overall, the experimental results showed the powerful antioxidant and inhibitory action on skin-related enzymes tyrosinase, collagenase and elastase of Plectranthus spp. extracts and/or isolated compounds, supporting their further research as bioactive metabolites against skin sagging and hyperpigmentation in cosmetic and pharmaceutical formulations. 相似文献
90.
Land‐use legacies associated with agriculture, such as increased soil fertility and elevated soil pH, promote invasions by non‐native plant species on former agricultural lands. Restoring natural soil conditions (i.e. low fertility and low pH) may be an effective, long‐term method to control and reduce the abundance of non‐native and ruderal species that invade abandoned agricultural lands. In this study, we examined how soil manipulation treatments of lowering soil fertility with carbon additions and lowering soil pH by applying sulfur affect non‐native and ruderal native plant species abundance in two former citrus groves in central Florida. Non‐native plant biomass was removed by one of two methods (tilling or topsoil removal), and was combined with a soil amendment of sulfur, carbon, sulfur + carbon, or none. The biomass removal treatments significantly decreased non‐native abundance, with topsoil removal as the most effective. Carbon additions did not affect soil fertility or vegetation. Sulfur and sulfur + carbon additions significantly decreased soil pH in both groves for at least 1 year post‐treatment; however, we did not see a significant vegetation response. Overall, our results suggest that removing vegetation by tilling and topsoil removal is an effective method for reducing non‐target species cover. Although we did not see a response of vegetation to our treatments, we were able to restore the initial soil characteristics, which can be a first step toward complete restoration. 相似文献