全文获取类型
收费全文 | 387篇 |
免费 | 17篇 |
出版年
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 23篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 32篇 |
2011年 | 34篇 |
2010年 | 26篇 |
2009年 | 14篇 |
2008年 | 33篇 |
2007年 | 33篇 |
2006年 | 34篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 20篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1981年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 31 毫秒
331.
Richard O. Carey Kati W. Migliaccio Yuncong Li Bruce Schaffer Gregory A. Kiker Mark T. Brown 《Ecological Indicators》2011,11(5):1093-1104
Rapid land use transformations due to extensive agricultural and urban development in south Florida (USA) threaten water resources such as Biscayne Bay, an oligotrophic estuary draining the Miami metropolitan complex and South Dade Agricultural Area. Biscayne Bay is sensitive to nutrient inputs and this study evaluated watershed land use-water quality relationships from 1995 to 2004. Using eight monitoring sites, three spatial extents were considered: sub-basins, canal buffers, and site buffers. Selected sites represented agricultural, urban, and mixed land use classes. Disturbance indicators (landscape metrics; Landscape Development Intensity (LDI) index; percent imperviousness), nutrient loads (nitrate/nitrite-nitrogen (NOX-N); total ammonia nitrogen (NH3-N); total phosphorus (TP)), and multivariate regression models were used to determine land use factors influencing water quality variability. The sub-basin regression model was the best predictor of annual NOX-N loads in the watershed. Both LDI and largest patch index variables were included in this model, indicating that the relative distribution of dominant land use classes influences NOX-N loads. There were no significant regression models for total inorganic nitrogen (NOX-N plus NH3-N) loads. Total phosphorus loads were more closely related to disturbance indicators at a smaller spatial extent (1000 m canal buffer), which is a function of watershed nutrient transport processes. The relative proportion of directly connected impervious areas (DCIA) was not identified as a significant land use variable for regression models. Positive correlations between LDI and DCIA values suggested both indicators provided similar information regarding the intensity of human disturbance. However, the LDI index incorporates anthropogenic intensity associated with a broad range of land uses while DCIA primarily reflects the impact of watershed urbanization. Watershed managers can use the LDI index with landscape metrics that evaluate spatial patterns to link land use development to water quality parameters. 相似文献
332.
Pamela Donner John T. Randolph Peggy Huang Rolf Wagner Clarence Maring Ben Hock Lim Lynn Colletti Yaya Liu Rubina Mondal Jill Beyer Gennadiy Koev Kennan Marsh David Beno Kenton Longenecker Tami Pilot-Matias Warren Kati Akhter Molla Dale Kempf 《Bioorganic & medicinal chemistry letters》2013,23(15):4367-4369
Described herein is the development of a potent non-nucleoside, small molecule inhibitor of genotype 1 HCV NS5B Polymerase. A 23 μM inhibitor that was active against HCV polymerase was further elaborated into a potent single-digit nanomolar inhibitor of HCV NS5B polymerase by additional manipulation of the R and R1 substituents. Subsequent modifications to improve physical properties were made in an attempt to achieve an acceptable pharmacokinetic profile. 相似文献
333.
Mikael Sallinen Anu Holm Jaana Hiltunen Kati Hirvonen Mikko Härmä Jukka Koskelo 《Chronobiology international》2013,30(2-3):279-296
We studied the recovery of multitask performance and sleepiness from acute partial sleep deprivation through rest pauses embedded in performance sessions and an 8 h recovery sleep opportunity the following night. Sixteen healthy men, aged 19–22 yrs, participated in normal sleep (two successive nights with 8 h sleep) and sleep debt (one 2 h night sleep followed by an 8 h sleep the following night) conditions. In both conditions, the participants performed four 70 min multitask sessions, with every other one containing a 10 min rest pause with light neck‐shoulder exercise. The multitask consisted of four simultaneously active subtasks, with the level of difficulty set in relation to each participant's ability. Physiological sleepiness was assessed with continuous electroencephalography/electro‐oculography recordings during the multitask sessions, and subjective sleepiness was self‐rated with the Karolinska Sleepiness Scale. Results showed that multitask performance and physiological and subjective sleepiness were impaired by the sleep debt (p>.001). The rest pause improved performance and subjective sleepiness for about 15 min, regardless of the amount of prior sleep (p>.01–.05). Following recovery sleep, all outcome measures showed marked improvement (p<.001), but they failed to reach the levels observed in the control condition (p<.001–.05). A correlation analysis showed the participants whose multitask performance deteriorated the most following the night of sleep loss tended to be the same persons whose performance was most impaired following the night of the recovery sleep (p<.001). Taken together, our results suggest that a short rest pause with light exercise is not an effective countermeasure in itself for sleep debt‐induced impairments when long‐term effects are sought. In addition, it seems that shift arrangements that lead to at least a moderate sleep debt should be followed by more than one recovery night to ensure full recovery. Persons whose cognitive performance is most affected by sleep debt are likely to require the most sleep to recover. 相似文献
334.
Ditches as species‐rich secondary habitats and refuge for meadow species in agricultural marsh grasslands 下载免费PDF全文
Questions
Can drainage ditches in agricultural marsh grassland provide a suitable habitat for the persistence of fen meadow species? How does the ditch margin vegetation develop as a function of regular dredging? Is ornithologically oriented management also beneficial for plant biodiversity?Location
Riparian marshes, Eider‐Treene‐Sorge lowland, Schleswig‐Holstein, Germany.Methods
We performed vegetation surveys of drainage ditches along with their water body, slope and margin structures annually for 3 years. The data were analysed with respect to date and means of ditch dredging. In addition, we recorded vegetation of the surrounding agricultural grassland, measured nutrient status of the soil and the water body and sampled seed bank of the ditch slopes. We used ANOVA and multivariate methods to describe the development of the ditch vegetation and the persistence of target meadow species.Results
Vegetation re‐development of ditch margins proceeds quite rapidly after disturbance from dredging. Dominance of mudbank species was observed only in the first year, followed by an increase of reed species and reduction of phytodiversity. Target species of wet meadow communities reach highest abundance in the second and third year and build a significant seed bank before being suppressed by reeds.Conclusions
In heavily eutrophicated, intensively used marsh grassland, regularly disturbed ditch margins are important secondary habitats for pioneer and subdominant wetland species, which have nearly disappeared in a larger area. Current management cycles of ditch dredging every 3–4 years comply with the successional development, allowing the mudbank and wet meadow species to persist in the vegetation and seed bank. In contrast to the frequency, the form of dredging (ditch profile), which is crucial for bird protection, plays a minor role for plants. We recommend moderate disturbance (mowing of ditch margins) to suppress strong competitors in the years between dredging for additional support to target plant species. 相似文献335.
Katiúscia Kelli Montanari-Coelho Alessandra Tenório Costa Julio Cesar Polonio João Lúcio Azevedo Silvana Regina Rockenbach Marin Renata Fuganti-Pagliarini Yasunari Fujita Kazuko Yamaguchi-Shinozaki Kazuo Nakashima João Alencar Pamphile Alexandre Lima Nepomuceno 《World journal of microbiology & biotechnology》2018,34(4):56
336.
337.
Isaiah Taylor Ying Wang Kati Seitz John Baer Stefan Bennewitz Brian P. Mooney John C. Walker 《PloS one》2016,11(1)
Receptor-like protein kinases (RLKs) are the largest family of plant transmembrane signaling proteins. Here we present functional analysis of HAESA, an RLK that regulates floral organ abscission in Arabidopsis. Through in vitro and in vivo analysis of HAE phosphorylation, we provide evidence that a conserved phosphorylation site on a region of the HAE protein kinase domain known as the activation segment positively regulates HAE activity. Additional analysis has identified another putative activation segment phosphorylation site common to multiple RLKs that potentially modulates HAE activity. Comparative analysis suggests that phosphorylation of this second activation segment residue is an RLK specific adaptation that may regulate protein kinase activity and substrate specificity. A growing number of RLKs have been shown to exhibit biologically relevant dual specificity toward serine/threonine and tyrosine residues, but the mechanisms underlying dual specificity of RLKs are not well understood. We show that a phospho-mimetic mutant of both HAE activation segment residues exhibits enhanced tyrosine auto-phosphorylation in vitro, indicating phosphorylation of this residue may contribute to dual specificity of HAE. These results add to an emerging framework for understanding the mechanisms and evolution of regulation of RLK activity and substrate specificity. 相似文献
338.
Gabriel Alejandro Bonaterra Hanna Then Lisa Oezel Hans Schwarzbach Matthias Ocker Kati Thieme Pietro Di Fazio Ralf Kinscherf 《PloS one》2016,11(3)
Background
Fibromyalgia (FM) is a chronic musculoskeletal pain disorder, characterized by chronic widespread pain and bodily tenderness and is often accompanied by affective disturbances, however often with unknown etiology. According to recent reports, physical and psychological stress trigger FM. To develop new treatments for FM, experimental animal models for FM are needed to be development and characterized. Using a mouse model for FM including intermittent cold stress (ICS), we hypothesized that ICS leads to morphological alterations in skeletal muscles in mice.Methods
Male and female ICS mice were kept under alternating temperature (4°C/room temperature [22°C]); mice constantly kept at room temperature served as control. After scarification, gastrocnemius and soleus muscles were removed and snap-frozen in liquid nitrogen–cooled isopentane or fixed for electron microscopy.Results
In gastrocnemius/soleus muscles of male ICS mice, we found a 21.6% and 33.2% decrease of fiber cross sectional area (FCSA), which in soleus muscle concerns the loss of type IIa and IIx FCSA. This phenomenon was not seen in muscles of female ICS mice. However, this loss in male ICS mice was associated with an increase in gastrocnemius of the density of MIF+ (8.6%)-, MuRF+ (14.7%)-, Fbxo32+ (17.8%)-cells, a 12.1% loss of capillary contacts/muscle fiber as well as a 30.7% increase of damaged mitochondria in comparison with male control mice. Moreover, significant positive correlations exist among densities (n/mm2) of MIF+, MuRF+, Fbxo32+-cells in gastrocnemius/ soleus muscles of male ICS mice; these cell densities inversely correlate with FCSA especially in gastrocnemius muscle of male ICS mice.Conclusion
The ICS-induced decrease of FCSA mainly concerns gastrocnemius muscle of male mice due to an increase of inflammatory and atrogenic cells. In soleus muscle of male ICS and soleus/gastrocnemius muscles of female ICS mice morphological alterations seem to occur not at all or delayed. The sex-specificity of findings, which is not easily reconciled with the epidemiology of FM (female predominance), implicate that gastrocnemius muscle of male ICS mice should preferentially be used for future investigations with FM. Moreover, we suggest to investigate morphological and/or molecular alterations at different time-points (up to two weeks) after ICS. 相似文献339.
Gi-Bang Koo Michael J Morgan Da-Gyum Lee Woo-Jung Kim Jung-Ho Yoon Ja Seung Koo Seung Il Kim Soo Jung Kim Mi Kwon Son Soon Sun Hong Jean M Mulcahy Levy Daniel A Pollyea Craig T Jordan Pearlly Yan David Frankhouser Deedra Nicolet Kati Maharry Guido Marcucci Kyeong Sook Choi Hyeseong Cho Andrew Thorburn You-Sun Kim 《Cell research》2015,25(6):707-725
340.