全文获取类型
收费全文 | 7898篇 |
免费 | 751篇 |
国内免费 | 7篇 |
出版年
2022年 | 48篇 |
2021年 | 118篇 |
2020年 | 66篇 |
2019年 | 91篇 |
2018年 | 118篇 |
2017年 | 111篇 |
2016年 | 176篇 |
2015年 | 304篇 |
2014年 | 345篇 |
2013年 | 444篇 |
2012年 | 526篇 |
2011年 | 541篇 |
2010年 | 381篇 |
2009年 | 355篇 |
2008年 | 479篇 |
2007年 | 487篇 |
2006年 | 437篇 |
2005年 | 421篇 |
2004年 | 428篇 |
2003年 | 392篇 |
2002年 | 385篇 |
2001年 | 82篇 |
2000年 | 60篇 |
1999年 | 96篇 |
1998年 | 133篇 |
1997年 | 82篇 |
1996年 | 83篇 |
1995年 | 76篇 |
1994年 | 79篇 |
1993年 | 73篇 |
1992年 | 55篇 |
1991年 | 59篇 |
1990年 | 72篇 |
1989年 | 49篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 40篇 |
1985年 | 61篇 |
1984年 | 58篇 |
1983年 | 58篇 |
1982年 | 62篇 |
1981年 | 58篇 |
1980年 | 60篇 |
1979年 | 48篇 |
1978年 | 42篇 |
1977年 | 42篇 |
1976年 | 48篇 |
1974年 | 37篇 |
1973年 | 47篇 |
1970年 | 25篇 |
排序方式: 共有8656条查询结果,搜索用时 15 毫秒
211.
Erika C. Freeman Irena F. Creed Blake Jones Ann‐Kristin Bergstrm 《Global Change Biology》2020,26(9):4966-4987
The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria. 相似文献
212.
213.
Rezende Renan de Souza Kroth Nádia Capitanio Bruna Maria Lima-Rezende Cássia Alves Cassol Angélica Soligo Cozzer Gilberto Dinis Baldissera Ronei Breaux Jennifer Ann Albeny-Simões Daniel 《Limnology》2020,21(3):275-285
Limnology - Aquatic macroinvertebrate communities are dependent on intrinsic environmental characteristics and biological interactions in microhabitat systems. We investigated the... 相似文献
214.
Emmanuel Margolin Youngjun J. Oh Matthew Verbeek Jason Naude Daniel Ponndorf Yulia Alexandrovna Meshcheriakova Hadrien Peyret Michiel T. van Diepen Ros Chapman Ann E. Meyers George Peter Lomonossoff Nobuyuki Matoba Anna‐Lise Williamson Edward P. Rybicki 《Plant biotechnology journal》2020,18(10):2109-2117
215.
Species loss is a global issue. With up to a million species at risk and insufficient protected area to maintain the world's biodiversity, humanity will increasingly need to rely on species re‐introductions to locally restore diversity and function. However, such restoration attempts are bound to fail when ecological communities get locked in a closed state that is resistant to recovery. It is presently unknown how to repair these closed systems. We use mathematical models to identify ways out of this problem. We first show how ecological communities may enter a closed state, to then explain how to open them up again for restoration of their original diversity. We find that restoration is often still possible shortly after initial species loss, as (1) the secondary extinctions that produce closure have not happened yet and (2) mild population fluctuations still allow successful repair during a transient postdisturbance phase. However, after this typically short window of opportunity for restoration, the system enters a new equilibrium, which may be a closed state. Our analysis shows how to take ecological communities out of the closed state: Appropriate management of carrying capacities produces a regime of mild population fluctuations that opens a window for successful species re‐introductions. These windows can be perpetually recurring or permanently open. Such opportunities for repair can be absent under regimes of wild cycles or perfect stability. We conclude that mild cycles may open windows of opportunity for the repair of communities that have become resistant to recovery. 相似文献
216.
Ann Carla Staver Paulo M. Brando Jos Barlow Douglas C. Morton C.E. Timothy Paine Yadvinder Malhi Alejandro Araujo Murakami Jhon del Aguila Pasquel 《Ecology letters》2020,23(1):99-106
Understory fires represent an accelerating threat to Amazonian tropical forests and can, during drought, affect larger areas than deforestation itself. These fires kill trees at rates varying from < 10 to c. 90% depending on fire intensity, forest disturbance history and tree functional traits. Here, we examine variation in bark thickness across the Amazon. Bark can protect trees from fires, but it is often assumed to be consistently thin across tropical forests. Here, we show that investment in bark varies, with thicker bark in dry forests and thinner in wetter forests. We also show that thinner bark translated into higher fire‐driven tree mortality in wetter forests, with between 0.67 and 5.86 gigatonnes CO2 lost in Amazon understory fires between 2001 and 2010. Trait‐enabled global vegetation models that explicitly include variation in bark thickness are likely to improve the predictions of fire effects on carbon cycling in tropical forests. 相似文献
217.
218.
219.
Arianna Martini Ann Huysseune P. Eckhard Witten Clara Boglione 《Journal of fish biology》2021,98(4):971-986
The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studies concerning the effect of rearing density on the skeletal phenotype are lacking. This study analyses the response of the skeleton to different rearing densities and describes the skeletal deformities. Wild-type zebrafish were reared up to 30 dpf (days post-fertilization) in a common environment. From 30 to 90 dpf, animals were reared at three different densities: high density (HD), 32 fish l–1; medium density (MD), 8 fish l–1 and low density (LD), 2 fish l–1. Animals at 30 and 90 dpf were collected and whole-mount stained with Alizarin red S to visualize mineralized tissues. The entire skeleton was analysed for meristic counts and 172 types of deformities. The results showed that the rearing density significantly influenced the specimens’ average standard length, which decreased with the increase in the rearing density. Differences in meristic counts among the three groups were not observed. Rearing density–independent malformations affected the ribs, neural arches and the spines of the abdominal region, as well as vertebrae of the caudal complex. The HD group showed the highest number of deformities per specimen, the highest number of observed types of deformities and, together with the MD group, the highest frequency of specimens affected by severe deformities. In particular, the HD group showed deformities affecting arches, spines and vertebral centra in the caudal region of the vertebral column. This study provides evidence of an effect of the rearing density on the development of different skeletal phenotypes. 相似文献