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91.
92.
Gary L. Larson Robert L. Hoffman Bruce R. Hargreaves Robert W. Collier 《Hydrobiologia》2007,574(1):141-148
We addressed potential sources of error in estimating the water clarity of mountain lakes by investigating the use of beam
transmissometer measurements to estimate Secchi disk depth. The optical properties Secchi disk depth (SD) and beam transmissometer
attenuation (BA) were measured in Crater Lake (Crater Lake National Park, Oregon, USA) at a designated sampling station near
the maximum depth of the lake. A standard 20 cm black and white disk was used to measure SD. The transmissometer light source
had a nearly monochromatic wavelength of 660 nm and a path length of 25 cm. We created a SD prediction model by regression
of the inverse SD of 13 measurements recorded on days when environmental conditions were acceptable for disk deployment with
BA averaged over the same depth range as the measured SD. The relationship between inverse SD and averaged BA was significant
and the average 95% confidence interval for predicted SD relative to the measured SD was ±1.6 m (range = −4.6 to 5.5 m) or ±5.0%.
Eleven additional sample dates tested the accuracy of the predictive model. The average 95% confidence interval for these
sample dates was ±0.7 m (range = −3.5 to 3.8 m) or ±2.2%. The 1996–2000 time-series means for measured and predicted SD varied
by 0.1 m, and the medians varied by 0.5 m. The time-series mean annual measured and predicted SD’s also varied little, with
intra-annual differences between measured and predicted mean annual SD ranging from −2.1 to 0.1 m. The results demonstrated
that this prediction model reliably estimated Secchi disk depths and can be used to significantly expand optical observations
in an environment where the conditions for standardized SD deployments are limited. 相似文献
93.
In order to evaluate hydrocarbon inputs to Crater Lake from anthropogenic and natural sources, samples of water, aerosol,
surface slick and sediment were collected and analyzed by gas chromatography-mass spectrometry (GC-MS) for determination of
their aliphatic and aromatic hydrocarbon concentrations and compositions. Results show that hydrocarbons originate from both
natural (terrestrial plant waxes and algae) and anthropogenic (petroleum use) sources and are entering the lake through direct
input and atmospheric transport. The concentrations of petroleum hydrocarbons range from low to undetectable. The distributions
and abundances of n-alkanes, polycyclic aromatic hydrocarbons (PAH) and unresolved complex mixture (UCM) from petroleum are similar for all surface
slick sampling sites. The estimated levels of PAH in surface slicks range from 7–9 ng/m2 which are low. Transport of petroleum-derived hydrocarbons from the lake surface has resulted in their presence in some sediments,
particularly near the boat operations mooring (total petroleum HC = 1440 μg/kg, dry wt. compared to naturally derived n-alkanes, 240 μg/kg, dry wt.). The presence of biomarkers such as the tricyclic terpanes, hopanes and steranes in shallow
sediments further confirms petroleum input from boat traffic. In the deep lake sediments, petroleum hydrocarbon concentrations
were very low (16 μg/kg, dry wt.). Very low concentrations of PAH were detected in shallow sediments (17–40 μg/kg at 5 m depth
near the boat operations) and deep sediments (3–15 μg/kg at 580 m depth). The individual PAH concentrations in sediments (μg/kg
or ppb range) are at least three orders of magnitude less than reported threshold effects levels (mg/kg or ppm range, test
amphipod Hyalella azteca). Therefore, no adverse effects are expected to occur in benthic biota exposed to these sediments. Boating activities are leaving a detectable level of petroleum in surface waters and lake sediments but these concentrations are very low. 相似文献
94.
Seasonal nutrient and plankton dynamics in a physical-biological model of Crater Lake 总被引:1,自引:1,他引:0
Katja Fennel Robert Collier Gary Larson Greg Crawford Emmanuel Boss 《Hydrobiologia》2007,574(1):265-280
A coupled 1D physical-biological model of Crater Lake is presented. The model simulates the seasonal evolution of two functional
phytoplankton groups, total chlorophyll, and zooplankton in good quantitative agreement with observations from a 10-year monitoring
study. During the stratified period in summer and early fall the model displays a marked vertical structure: the phytoplankton
biomass of the functional group 1, which represents diatoms and dinoflagellates, has its highest concentration in the upper
40 m; the phytoplankton biomass of group 2, which represents chlorophyta, chrysophyta, cryptomonads and cyanobacteria, has
its highest concentrations between 50 and 80 m, and phytoplankton chlorophyll has its maximum at 120 m depth. A similar vertical
structure is a reoccurring feature in the available data. In the model the key process allowing a vertical separation between
biomass and chlorophyll is photoacclimation. Vertical light attenuation (i.e., water clarity) and the physiological ability
of phytoplankton to increase their cellular chlorophyll-to-biomass ratio are ultimately determining the location of the chlorophyll
maximum. The location of the particle maxima on the other hand is determined by the balance between growth and losses and
occurs where growth and losses equal. The vertical particle flux simulated by our model agrees well with flux measurements
from a sediment trap. This motivated us to revisit a previously published study by Dymond et al. (1996). Dymond et al. used a box model to estimate the vertical particle flux and found a discrepancy by a factor 2.5–10 between
their model-derived flux and measured fluxes from a sediment trap. Their box model neglected the exchange flux of dissolved
and suspended organic matter, which, as our model and available data suggests is significant for the vertical exchange of
nitrogen. Adjustment of Dymond et al.’s assumptions to account for dissolved and suspended nitrogen yields a flux estimate
that is consistent with sediment trap measurements and our model. 相似文献
95.
Anna CC Aguiar Ananda C Cunha Isabela Penna Ceravolo Regina A Correia Gon?alves Arildo JB Oliveira Antoniana Ursine Krettli 《Memórias do Instituto Oswaldo Cruz》2015,110(7):906-913
Several species of Aspidosperma plants are used to treat diseases in
the tropics, including Aspidosperma ramiflorum, which acts against
leishmaniasis, an activity that is experimentally confirmed. The species, known as
guatambu-yellow, yellow peroba,
coffee-peroba andmatiambu, grows in the Atlantic
Forest of Brazil in the South to the Southeast regions. Through a guided
biofractionation of A. ramiflorum extracts, the plant activity
against Plasmodium falciparum was evaluated in vitro for toxicity
towards human hepatoma G2 cells, normal monkey kidney cells and nonimmortalised human
monocytes isolated from peripheral blood. Six of the seven extracts tested were
active at low doses (half-maximal drug inhibitory concentration < 3.8 µg/mL); the
aqueous extract was inactive. Overall, the plant extracts and the purified compounds
displayed low toxicity in vitro. A nonsoluble extract fraction and one purified
alkaloid isositsirikine (compound 5) displayed high selectivity indexes (SI) (= 56
and 113, respectively), whereas compounds 2 and 3 were toxic (SI < 10). The
structure, activity and low toxicity of isositsirikine in vitro are described here
for the first time in A. ramiflorum, but only the neutral and
precipitate plant fractions were tested for activity, which caused up to 53%
parasitaemia inhibition of Plasmodium berghei in mice with
blood-induced malaria. This plant species is likely to be useful in the further
development of an antimalarial drug, but its pharmacological evaluation is still
required. 相似文献
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100.
Complex genome evolution in Anopheles coluzzii associated with increased insecticide usage in Mali
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Bradley J. Main Yoosook Lee Travis C. Collier Laura C. Norris Katherine Brisco Abdrahamane Fofana Anthony J. Cornel Gregory C. Lanzaro 《Molecular ecology》2015,24(20):5145-5157
In certain cases, a species may have access to important genetic variation present in a related species via adaptive introgression. These novel alleles may interact with their new genetic background, resulting in unexpected phenotypes. In this study, we describe a selective sweep on standing variation on the X chromosome in the mosquito Anopheles coluzzii, a principal malaria vector in West Africa. This event may have been influenced by the recent adaptive introgression of the insecticide resistance gene known as kdr from the sister species Anopheles gambiae. Individuals carrying both kdr and a nearly fixed X‐linked haplotype, encompassing at least four genes including the P450 gene CYP9K1 and the cuticular protein CPR125, have rapidly increased in relative frequency. In parallel, a reproductively isolated insecticide‐susceptible A. gambiae population (Bamako form) has been driven to local extinction, likely due to strong selection from increased insecticide‐treated bed net usage. 相似文献