收费全文 | 1292篇 |
免费 | 77篇 |
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 29篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 35篇 |
2017年 | 27篇 |
2016年 | 51篇 |
2015年 | 45篇 |
2014年 | 59篇 |
2013年 | 69篇 |
2012年 | 111篇 |
2011年 | 107篇 |
2010年 | 70篇 |
2009年 | 56篇 |
2008年 | 89篇 |
2007年 | 68篇 |
2006年 | 92篇 |
2005年 | 67篇 |
2004年 | 46篇 |
2003年 | 47篇 |
2002年 | 38篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1967年 | 4篇 |
1965年 | 4篇 |
1963年 | 4篇 |
1958年 | 5篇 |
1957年 | 4篇 |
Naturalistic grazing by large herbivores is an increasingly practiced way of managing habitats with conservational value. It has the potential to restore and enhance biodiversity, creating self-sustainable environments vital for organisms requiring regular disturbances to moderate and/or reverse successional changes. European bison, Exmoor pony, and Tauros cattle were introduced in 2015 to a former military training area in Milovice, Czech Republic. The prevailing vegetation type is a forest-steppe savanna with Bromus erectus-dominated xeric grasslands mixed with deciduous shrubs and trees. After the cessation of military use, the area was abandoned which led to successional changes, including the dominance of tall grasses, litter accumulation, and bush encroachment. In 2017–2021, we monitored grassland vegetation in 30 grazed permanent plots (2?×?2 m) and 5 control plots representative of ungrazed, abandoned vegetation adjacent to the grazed areas. Naturalistic grazing increased species richness and the cover of forbs, while the cover of grasses and legumes was minimally affected. Grazing increased functional diversity of plant community, promoted a compositional change to small statured species and an increased incidence of red-list species. Seven years of continuous grazing increased the conservation value of this forest-steppe vegetation, a habitat type rapidly declining in Europe.
相似文献We evaluated the effect of different watering regimes on the growth, chlorophyll fluorescence, phytohormones, and phenolic acids in Ceratotheca triloba (Bernh.) Hook.f., a commonly consumed African indigenous leafy vegetable. The study was conducted in the greenhouse under different watering regimes [seven (daily); three (thrice); two (twice); one (once) day(s) per week] for a period of 2 and 4-months. In each pot (7.5 cm diameter; 150 ml volume), 50 ml of water was applied per treatment. At the end of the experiment, plant growth, chlorophyll fluorescence, phytohormones, and phenolic acids were determined. A decrease in water availability resulted in a consistent decline in plant growth after a 4-month growth period. The severity of reduced water availability was more noticeable in plants watered once a week with a 1.4-fold reduction in growth and quantum efficiency of PSII (Fv/Fm) value of 0.80. The significant decline in growth and chlorophyll fluorescence was probably due to the increased production of abscisic acid (ABA) and cytokinin (CK) content together with the detected phytohormones in plants with restricted water supply. Furthermore, plants watered once a week had a trade-off between growth and phenolic acid production, with significantly higher (threefolds) concentrations of vanillic, ferulic, caffeic, and 4-coumaric acids in 4-month-old plants. Even though C. triloba grew best in well-watered soil, the plant had the potential to adapt and survive in soils with limited water supply for longer periods of growth. These findings suggest that regulation of phytohormones and phenolic acids played an important role in improving the growth of C. triloba under limited water conditions.
相似文献