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111.
Abstract The detection and mapping of canopy disturbance caused by natural events such as cyclones in tropical rainforests is important for monitoring and understanding rainforest dynamics and recovery. In February 1999 tropical cyclone Rona crossed the coastline of Far North Queensland, Australia, causing significant damage to the rainforest canopy in some areas. This paper examines the application of multitemporal canopy digital elevation models (DEMs) generated by a NASA‐operated airborne radar mapping system called TOPSAR in 1996 and 2000, for detection of canopy disturbance caused by cyclone damage. Canopy damage was mapped here by identifying areas with a significant decrease in canopy height estimated from the difference of the 1996 and 2000 TOPSAR DEMs. Conventional aerial photographs, flown shortly after the cyclone (March 1999), were used to validate the resulting map of cyclone damaged rainforest canopy. The results showed that the DEM‐derived canopy damage map performed reasonably well when comparing the spatial distribution and size of damaged areas, while taking into account the time difference between cyclone damage and the second radar acquisition. Some errors were encountered on the steeper slopes which were related to terrain distortions inherent in radar images of steep terrain. The height accuracy of the DEM was close to the depth of some of the gaps being mapped, which also contributed to errors. Even so, the results demonstrate there may be potential for weather‐independent, regional‐scale mapping of forest canopy change from imaging radar that is not always possible from traditional optical means of measuring canopy elevation, for example, airborne laser data and stereo aerial photography. This may be possible in relatively flat areas, provided the second radar acquisition occurs within months of the damaging event. Further algorithm refinement is required to improve its robustness and the range of topographies where this approach can provide reliable estimates of the extent of canopy disturbance. 相似文献
112.
113.
目的:探讨模拟100 m氦氮氧(Trimix)常规潜水对家兔氧化应激和炎性反应的影响。方法:空白组家兔8只,模拟100 m Trimix;常规潜水组家兔8只。模拟潜水按照Haldane理论计算所得的水下阶段减压表减压。Elisa法检测家兔模拟潜水前、后血清超氧化物歧化酶(SOD)、谷胱甘肽(GSH)、过氧化氢酶(CAT)、丙二醛(MDA)和过氧化脂质(LPO)等氧化/抗氧化指标的变化。同样采用Elisa法检测空白组和潜水组家兔肺、脑组织γ干扰素(IFN-γ)、肿瘤坏死因子-α(TNF-α)、白介素6(IL-6)、白介素8(IL-8)、髓过氧化物酶活力(MPO)和基质金属蛋白酶9(MMP-9)等炎性因子的表达,并比较组织湿干比(Wet/Dry ratio)。结果:家兔潜水后SOD和GSH活性明显降低(P<0.01),CAT、MDA和LPO含量明显升高(P<0.01);潜水组家兔肺、脑组织中IL-8、IL-6、IFN-γ、TNF-α、MMP-9和MPO的表达均较空白组显著升高(P<0.05,P<0.01);潜水组家兔肺、脑组织湿干比与空白组差异不显著。结论:模拟100 m Trimix常规潜水对家兔氧化应激和炎性反应有显著影响。 相似文献
114.
Rainfall seasonality and drought performance shape the distribution of tropical tree species in Ghana
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Lucy Amissah Godefridus M. J. Mohren Boateng Kyereh Victor K. Agyeman Lourens Poorter 《Ecology and evolution》2018,8(16):8582-8597
Tree species distribution in lowland tropical forests is strongly associated with rainfall amount and distribution. Not only plant water availability, but also irradiance, soil fertility, and pest pressure covary along rainfall gradients. To assess the role of water availability in shaping species distribution, we carried out a reciprocal transplanting experiment in gaps in a dry and a wet forest site in Ghana, using 2,670 seedlings of 23 tree species belonging to three contrasting rainfall distributions groups (dry species, ubiquitous species, and wet species). We evaluated seasonal patterns in climatic conditions, seedling physiology and performance (survival and growth) over a 2‐year period and related seedling performance to species distribution along Ghana's rainfall gradient. The dry forest site had, compared to the wet forest, higher irradiance, and soil nutrient availability and experienced stronger atmospheric drought (2.0 vs. 0.6 kPa vapor pressure deficit) and reduced soil water potential (?5.0 vs. ?0.6 MPa soil water potential) during the dry season. In both forests, dry species showed significantly higher stomatal conductance and lower leaf water potential, than wet species, and in the dry forest, dry species also realized higher drought survival and growth rate than wet species. Dry species are therefore more drought tolerant, and unlike the wet forest species, they achieve a home advantage. Species drought performance in the dry forest relative to the wet forest significantly predicted species position on the rainfall gradient in Ghana, indicating that the ability to grow and survive better in dry forests and during dry seasons may allow species to occur in low rainfall areas. Drought is therefore an important environmental filter that influences forest composition and dynamics. Currently, many tropical forests experience increase in frequency and intensity of droughts, and our results suggest that this may lead to reduction in tree productivity and shifts in species distribution. 相似文献
115.
N Connors R Prevoznak T Brix A Seeley K Gbewonyo R Greasham P Salmon 《Journal of industrial microbiology & biotechnology》1995,15(6):503-508
The production of zaragozic acids by fermentation of the fungusLeptodontidium elatius was examined at the 800-L fermentor scale under two different production medium batch sterilization conditions. Low production-medium heat input (R0=33.4 min) resulted in a 4-desacetoxy zaragozic acid C:4-O-desacetyl zaragozic acid C:zaragozic acid C ratio of 0.53:0.60:1.0. At a higher heat input (R0=50.5 min), the ratio shifted to 1.0:0.66:1.0 with a corresponding 26% increase in total zaragozic acid production. This higher total zaragozic acid titer resulted from an increase in the amount of 4-desacetoxy zaragozic acid C produced while the levels of the other two analogues remained unchanged. Batch sterilization conditions also resulted in differences in growth, carbon substrate consumption, and oxygen uptake rates. The structures of the zaragozic acids produced suggest a precursor/end product relationship. A biosynthetic model describing the synthesis of the three zaragozic acids listed above is postulated and used to explain the effects of production-medium heat input during sterilization. 相似文献
116.
Wu Ruifang Wang Zhenhai Lu Lichang Zhang Fenger Ge Xinglin 《Prostaglandins & other lipid mediators》1996,51(2):161-167
Pelvic congestion may cause chronic pelvic pain in women. The aim of the study is to elucidate a possible role in this condition for prostaglandin. Prostaglandin levels in peritoneal fluid were measured in 18 women with pelvic pain caused by pelvic congestion following sterilization, 10 women without pain following sterilization, and 10 normal healthy women. Peritoneal fluid was aspirated by a silastic catheter from the cul-de-sac under laparoscopic direct vision. Concentration of 6-keto-PGF1α, TXB2, PGF2α and PGE2 were measured with the standard radioimmunoassay method in all samples. Results showed that 6-keto-PGF,. levels in peritoneal fluid from patients with pelvic congestion were markedly higher than those from two control women (P < 0.05); 6-keto-PGF1α/TXB2 in pelvic congestion and control groups were markedly different (P < 0.05); the total amounts of peritoneal fluid was higher in pelvic congestion than that in two control groups (P < 0.001). These data suggested that 6-ketoPGF1α is increased in peritoneal fluid of women with pelvic congestion and the change might play an important role in attack of this disease. 相似文献
117.
Wann Steven R. Veazey Robert L. Kaphammer Jacqueline 《Plant Cell, Tissue and Organ Culture》1997,50(3):221-224
Tissue culture media or aqueous sucrose solutions containing activated charcoal buffered to pH 5.5 and autoclaved did not
undergo appreciable sucrose hydrolysis as reported. Rather, the extent of sucrose hydrolysis in media containing activated
charcoal was found to be directly proportional to the hydrogen ion concentration (pH). This finding is consistent with the
known mechanism of acid-catalyzed hydrolysis of acetals such as sucrose. Several types of charcoal were identified that acidified
culture media to the extent that considerable acid-catalyzed sucrose hydrolysis occurred under autoclave conditions, making
it appear as though activated charcoal was responsible for catalyzing sucrose hydrolysis. A simple mathematical expression
was empirically derived that can be used to predict the extent of sucrose hydrolysis based on the post-autoclave pH of the
media.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
118.
Solute concentrations in atmospheric deposition and stream water were measuredfrom 1984 through 1993 to determine the fate and mobility of solutes in twogauged mixed-conifer catchments (Tharp's and Log creeks) located in theSierra Nevada, California. The two catchments contain mature forest standsdominated by Abies concolor (white fir), Sequoiadendron giganteum (giantsequoia), Abies magnifica (red fir) and Pinus lambertiana (sugar pine).Ammonium, Cl-, Ca2+ and NO-
3were highest in concentration of the solutes measured in wet deposition;bulk deposition was highest in SO2-
4, NH+
4,Cl- and H+. Net retention ofH+, NO3
-, NH4
+,SO4
2- and Cl- occurred in both catchments.Discharge was dominated by spring snowmelt with the largest export yieldsfor acid neutralizing capacity (ANC), SiO2, andCa2+. Export yields of H+,NO3
-, NH4
+ and PO4
3-were relatively small (0.5 kg ha-1 y-1).Discharge-concentration relationships for ANC, SiO2,Na+, K+, Ca2+ andMg2+ were inverse and their concentrations in stream waterwere primarily influenced by discharge and annual differences in the relativecontributions of snowmelt and groundwater. The mobility of these solutes iscontrolled by the rates of mineral weathering and ion exchange. The positiverelationship of SO4
2- concentration with increasingdischarge suggests that atmospherically deposited SO4
2-is temporarily stored and that its release is controlled by the extent of soilwater flushing. 相似文献
119.
The adaptive significance of red coloration in tropical forest leaves remains unclear. In vivo assays show that there is a significant negative correlation between anthocyanin pigments in young leaves and fungal pathogen damage. This supports a previous hypothesis that anthocyanins may protect young leaves from fungal damage during the vulnerable period of leaf expansion. 相似文献
120.
The effects of check dams and other erosion control structures on the restoration of Andean bofedal ecosystems
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Restoring degraded lands in rural environments that are heavily managed to meet subsistence needs is a challenge due to high rates of disturbance and resource extraction. This study investigates the efficacy of erosion control structures (ECSs) as restoration tools in the context of a watershed rehabilitation and wet meadow (bofedal) restoration program in the Bolivian Andes. In an effort to enhance water security and increase grazing stability, Aymara indigenous communities built over 15,000 check dams, 9,100 terraces, 5,300 infiltration ditches, and 35 pasture improvement trials. Communities built ECSs at different rates, and we compared vegetation change in the highest restoration management intensity, lowest restoration management intensity, and nonproject control communities. We used line transects to measure changes in vegetation cover and standing water in gullies with check dams and without check dams, and related these ground measurements to a time series (1986–2009) of normalized difference vegetation index derived from Landsat TM5 images. Evidence suggests that check dams increase bofedal vegetation and standing water at a local scale, and lead to increased greenness at a basin scale when combined with other ECSs. Watershed rehabilitation enhances ecosystem services significant to local communities (grazing stability, water security), which creates important synergies when conducting land restoration in rural development settings. 相似文献