全文获取类型
收费全文 | 390篇 |
免费 | 22篇 |
国内免费 | 58篇 |
专业分类
470篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 17篇 |
2016年 | 15篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 29篇 |
2012年 | 9篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 13篇 |
2008年 | 25篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 26篇 |
2002年 | 14篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 4篇 |
排序方式: 共有470条查询结果,搜索用时 0 毫秒
51.
S. Y. Park Y. W. Kim H. K. Moon H. N. Murthy Y. H. Choi H. M. Cho 《Plant Cell, Tissue and Organ Culture》2008,93(3):341-346
The effect of phytohormones on the breaking of dormancy of axillary buds in Salix pseudolasiogyne and their subsequent proliferation from nodal explants were examined. Nodal explants obtained from a 20–year-old S. pseudolasiogyne tree were cultured either on woody plant basal medium (WPM) or WPM supplemented with benzyladenine (BA, 2.2/4.4 μM), zeatin
(1.1/2.2 μM), gibberillic acid (GA3, 2.9 and 14.5 μM), and GA3 + BA (2.9 + 4.4 μM). Although axillary shoots developed in all the media, a higher percentage bud break occurred on BA supplemented
media. To corroborate the results, endogenous levels of cytokinins [Cks, N
6-isopentenyladenine (iP), zeatin riboside (t-ZR), dihydrozeatinriboside (DHZR)] and abscisic acid (ABA) were determined. On BA supplemented media, the levels of zeatin
type (Z-type) of Cks were higher than those of isopentenyladenine type of Ck in the explants, while the ABA level was low.
Axillary shoots did not grow well and became necrotic upon subculture to fresh basal WPM. In order to improve shoot growth,
they were subcultured twice at a 4-week interval on to WPM supplemented with BA (2.2/4.4 μM), GA3 (1.4 μM), or GA3 + BA (1.4 + 4.4/2.9 + 4.4 μM). Maximal shoot growth (93%) was achieved on WPM supplemented with 2.2 μM BA. Comparative analyses
of endogenous Cks revealed that higher Cks (Z-type Cks) were present in actively growing shoots. Rooting was readily achieved
when the shoots were subcultured to WPM without phytohormones. The rooted plants were acclimatized well upon transplantation. 相似文献
52.
Aboveground disturbances are common in dynamic riparian environments, and Salix nigra is well adapted with a vigorous resprouting response. Soil moisture stresses are also common, and S. nigra is flood tolerant and drought sensitive. The objective of this study was to quantify nonstructural carbohydrate (NSC) reserves
in S. nigra following shoot removal and soil moisture treatments. NSC reserves provide energy for regeneration of shoot tissue until
new functional leaves are developed. Three soil moisture treatments: well-watered (W), periodic flooding (F) and drought (D);
and three shoot removal treatments: no shoots removed (R0), partial shoot removal (R1), and complete shoot removal (R2) were
applied. Plants were harvested when new shoot development was observed (day 13). Statistical significance in the 3 × 3-factorial
design was determined in two-factor ANOVA at P < 0.05. Both roots and cuttings were important reservoirs for NSC during resprouting response, with decreases in root (31%)
and cutting (14%) biomass in R2 compared to R0. Rapid recovery of photosynthetic surface area (from 15 to 37% of R0) was found
in R1. A clear pattern of starch mobilization was found in roots in R0, R1 and R2, with lowest root starch concentration in
W, F higher than W, and D higher than F. Shoot starch concentration was lower in F and D compared to W in R0, however, in
R1 shoot starch was reduced in W compared to F and D, possibly indicating reduced rates of translocation during soil moisture
stress. Evidence of osmotic adjustment was found in roots and shoots with higher total ethanol-soluble carbohydrates (TESC)
during soil moisture stress in F and D treatments. Total plant NSC pool was greater in F and D treatments compared to W, and
progressively reduced from R0 to R1 to R2. Results indicated negative effects of drought, and to a lesser extent periodic
flooding on resprouting response in S. nigra, with implications for reduced survival when exposed to combined stresses of aboveground disturbance and soil moisture. 相似文献
53.
Extension growth of willow (Salix viminalis L.) and changes in soil water were measured in lysimeters containing clay and sandy loam soils with different amendment and watering treatments. No water uptake was found below 0.3 m in the nutritionally poor unamended clay; amendment with organic matter to 0.4 m depth resulted in water extraction down to 0.5 m depth whereas in the sandy loam, there was greater extraction from all depths down to 0.6 m. With water stress, wilting of plants occurred when the volumetric soil water content at 0.1 m was about 31% in the clay and 22% in the sandy loam. Compared with shoots on plants in the amended clay, those in the unamended treatment showed reduced extension growth, little increase in stem basal area (SBA) and a small shoot leaf area, resulting from a reduced number of leaves shoot−1 and a small average area leaf−1. Water stress also reduced shoot extension growth, SBA gain and the leaf area on extension growth. Shoot growth rates were significantly correlated with air temperature and base temperatures between 2.0 and 7.6 °C were indicated for the different treatments. These studies have helped to explain some of the large treatment effects described previously on biomass production and plant leaf area. 相似文献
54.
Plant distribution and dispersal mechanisms at the Hassayampa River Preserve, Arizona, USA 总被引:1,自引:0,他引:1
Taly Dawn Drezner Patricia L. Fall Juliet C. Stromberg† 《Global Ecology and Biogeography》2001,10(2):205-217
This study focuses on the relationships between plant dispersal syndromes and plant distributions at the community scale. Species composition and cover are reported from 29 10 × 20-m vegetation plots along five topographic cross-sections in the riparian zone of the Hassayampa River Preserve, Arizona. We find that spatial patterns of dispersal guilds vary within the flood plain of this semiarid region river. Our main results are: (1) wind-dispersed species are fairly evenly distributed at all elevations and distances from the river, whereas cover of animal-dispersed species increases with elevation above, and at greater distances from, the river; (2) wind-dispersed species are proportionally more abundant in the pioneer Populus–Salix community, whereas plants in the late-seral Prosopis community are predominantly animal-dispersed; (3) most of the species classified as obligate-wetland and facultative-wetland are wind-dispersed, whereas facultative-upland and obligate-upland species are mostly animal-dispersed; and (4) there are significantly fewer wind-dispersed species in areas of high total vegetation cover. These results may reflect successional patterns resulting from periodic flooding. Low areas close to the river flood more frequently and with greater intensity than areas farther from the river. Many pioneer species that establish in disturbed areas are wind-dispersed. Over successional time, pioneer species cede to more drought tolerant species that are predominantly animal-dispersed. 相似文献
55.
Responses of riparian trees to interannual variation in ground water depth in a semi-arid river basin 总被引:14,自引:2,他引:12
We investigated the physiological and growth responses of native (Populus fremontii S. Wats. and Salix gooddingii Ball) and exotic (Tamarix chinensis Lour.) riparian trees to ground water availability at the free‐flowing Hassayampa River, Arizona, during dry (1997) and wet (1998) years. In the drier year, all species experienced considerable water stress, as evidenced by low shoot water potentials, low leaf gas exchange rates and large amounts of canopy dieback. These parameters were significantly related to depth of ground water (DGW) in the native species, but not in T. chinensis, in 1997. Canopy dieback was greater in the native species than in T. chinensis when ground water was deep in 1997, and dieback increased rapidly at DGW > 2·5–3·0 m for the native species. Analysis of combined data from wet and dry years for T. chinensis tentatively suggests a similar physiological sensitivity to water availability and a similar DGW threshold for canopy dieback. In 1998, shoot water potential and leaf gas exchange rates were higher and canopy dieback was lower for all species because of increased water availability. However, T. chinensis showed a much larger increase in leaf gas exchange rates in the wet year than the native species. High leaf gas exchange rates, growth when water is abundant, drought tolerance and the maintenance of a viable canopy under dry conditions are characteristics that help explain the ability of T. chinensis to thrive in riparian ecosystems in the south‐western United States. 相似文献
56.
57.
Soil nutrients and water availability interact to influence willow growth and chemistry but not leaf beetle performance 总被引:2,自引:0,他引:2
We investigated the effects of soil nutrient and water availability on the growth and chemistry of the silky willow (Salix sericea Marshall), and on the performance of the imported willow leaf beetle (Plagiodera versicolora Laichartig). Our major aims were to determine whether there are nutrient–water interactions on plant traits and whether this leads to parallel interactions for herbivore performance. We used a 2 × 3 fully factorial design, which consisted of high and low nutrient treatments crossed with dry, field capacity, and flooded water treatments. We found that nutrient additions increased plant growth, but only in field capacity and flooded conditions (nutrient–water interaction). Leaf nitrogen content also depended on the interaction between soil nutrients and water: nutrient addition resulted in a larger increase in foliar nitrogen in the field capacity treatment than in the flooded and dry treatments. Of the two phenolic glycosides measured, salicortin and 2′‐cinnamoylsalicortin, only one was affected by the treatments. 2′‐cinnamoylsalicortin concentration was lower in the high nutrient–dry treatment compared with the other treatments. In contrast to plant responses, there were no interactions found for larval or pupal weight or development time. Nutrient addition led to an increase in female pupal weight, and foliar N was positively correlated with female pupal weight and negatively correlated with female development time. In addition, leaf water was positively correlated with female development time. The lack of interactions for insect performance may stem from the small absolute differences in foliar nitrogen content associated with the interaction between the nutrients and water. Taken together, our results suggest that nutrient–water interactions influence plant traits that are potentially important for insect performance (leaf nitrogen and water), but these interactions do not produce parallel interactions in beetle performance. 相似文献
58.
59.
Black willow (Salix nigra) uses periodic flood events for dispersal of vegetative propagules, subjecting them to periods of soaking before their deposition along the streambank. It was hypothesized that this life history trait results in optimal conditions for willow growth and survival. To test this hypothesis, a greenhouse experiment was conducted using 1.2‐m‐long black willow cuttings (posts) with a basal diameter of 5 cm. Cuttings were subjected to three soaking treatments (0, 3, and 10 days) and then grown under four soil moisture regimes (control, drought, permanently flooded, and intermittently flooded). Growth, biomass, and survival were recorded. Results showed that soaking posts for 10 days was most beneficial in the control soil moisture regime, enhancing root, shoot, leaf, and total biomass production. Shoot abundance and growth were also enhanced by 10 days of soaking in the control and permanently flooded moisture regimes. Finally, survival increased significantly in control and drought moisture regimes in response to the 10‐day soaking treatment. Results clearly demonstrated that soaking had significant effects on willow post success when evaluated across all soil moisture regimes. Posts subjected to the 10‐day soaking treatment consistently had greatest growth and biomass and displayed a doubling of the survival rate. Therefore, soaking willow cuttings before planting is a simple, inexpensive technique that may be used to bolster streambank restoration success. 相似文献