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31.
In the analysis of the constant-time Carr-Purcell-Meiboom-Gill (CT-CPMG) relaxation dispersion experiment, chemical exchange parameters, such as rate of exchange and population of the exchanging species, are typically optimized using equations that predict experimental relaxation rates recorded as a function of effective field strength. In this process, the effect of chemical exchange during the CPMG pulses is typically assumed to be the same as during the free-precession. This approximation may introduce systematic errors into the analysis of data because the number of CPMG pulses is incremented during the constant-time relaxation period, and the total pulse duration therefore varies as a function of the effective field strength. In order to estimate the size of such errors, we simulate the time-dependence of magnetization during the entire constant time period, explicitly taking into account the effect of the CPMG pulses on the spin relaxation rate. We show that in general the difference in the relaxation dispersion profile calculated using a practical pulse width from that calculated using an extremely short pulse width is small, but under certain circumstances can exceed 1 s?1. The difference increases significantly when CPMG pulses are miscalibrated. 相似文献
32.
Spatial and temporal deforestation dynamics in protected and unprotected dry forests: a case study from Myanmar (Burma) 总被引:1,自引:0,他引:1
Melissa Songer Myint Aung Briony Senior Ruth DeFries Peter Leimgruber 《Biodiversity and Conservation》2009,18(4):1001-1018
Tropical dry forests are more threatened, less protected and especially susceptible to deforestation. However, most deforestation
research focuses on tropical rain forests. We analyzed spatial and temporal changes in land cover from 1972 through 2005 at
Chatthin Wildlife Sanctuary (CWS), a tropical dry forest in Myanmar (Burma). CWS is one of the largest protected patches of
tropical dry forest in Southeast Asia and supports over half the remaining wild population of the endangered Eld’s deer. Between
1973 and 2005, 62% of forest was lost at an annual rate of 1.86% in the area, while forest loss inside CWS was only 16% (0.45%
annually). Based on trends found during our study period, dry forests outside CWS would not persist beyond 2019, while forests
inside CWS would persist for at least another 100 years. Analysis of temporal deforestation patterns indicates the highest
rate of loss occurred between 1992 and 2001. Conversion to agriculture, shifting agriculture, and flooding from a hydro-electric
development were the main deforestation drivers. Fragmentation was also severe, halving the area of suitable Eld’s deer habitat
between 1973 and 2001, and increasing its isolation. CWS protection efforts were effective in reducing deforestation rates,
although deforestation effects extended up to 2 km into the sanctuary. Establishing new protected areas for dry forests and
finding ways to mitigate human impacts on existing forests are both needed to protect remaining dry forests and the species
they support. 相似文献
33.
Antony J. Lynam Alan Rabinowitz Than Myint Myint Maung Kyaw T. Latt Saw Htoo T. Po 《Population Ecology》2009,51(1):115-121
As part of a national strategy for recovering tiger populations, the Myanmar Government recently proposed its first and the
world’s largest tiger reserve in the Hukaung Valley, Kachin State. During November 2002–June 2004, camera-traps were used
to record tigers, identify individuals, and, using capture–recapture approaches, estimate density in the reserve. Despite
extensive (203 trap locations, 275–558 km2 sample plots) and intensive (>4,500 trap nights, 9 months of sampling) survey efforts, only 12 independent detections of
six individual tigers were made across three study sites. Due to the sparse data, estimates of tiger abundance generated by
Program CAPTURE could not be made for all survey sites. Other approaches to estimating density, based on numbers of tigers
caught, or derived from borrowed estimates of detection probability, offer an alternative to capture–recapture analysis. Tiger
densities fall in the range of 0.2–2.2 tigers/100 km2, with 7–71 tigers inside a 3,250 km2 area of prime tiger habitat, where efforts to protect tigers are currently focused. Tiger numbers might be stabilized if
strict measures are taken to protect tigers and their prey from seasonal hunting and to suppress illegal trade in wildlife.
Efforts to monitor abundance trends in the tiger population will be expensive given the difficulty with which tiger data can
be obtained and the lack of available surrogate indices of tiger density. Monitoring occupancy patterns, the subject of a
separate ongoing study, may be more efficient. 相似文献
34.
Takeshi Shimogiri George Msalya Si Lhyam Myint Shin Okamoto Kotaro Kawabe Kazuaki Tanaka Hideyuki Mannen Mitsuru Minezawa Takao Namikawa Takashi Amano Yoshio Yamamoto Yoshizane Maeda 《Biochemical genetics》2010,48(9-10):829-839
Six polymorphic sites of the bovine prion protein gene (PRNP) were genotyped in 569 animals of Asian native cattle, Japanese breeds, purebred mythun (Bos frontalis), and mythun × cattle composite animals. At the 23-bp indel site, a deletion (23?) allele was a major allele in all populations except mythun. At the 12-bp indel site, an insertion (12+) allele was a major allele in all populations. The 14-bp indel site was polymorphic in all Asian native cattle. In the octapeptide repeat region, a six-repeat allele was a major allele in all populations, and 5/5 and 4/6 genotypes were detected in Japanese Black and Mongolian cattle and in mythun, respectively. Two nonsynonymous single nucleotide polymorphisms (SNPs) (K3T and S154N) were detected in Asian native cattle and mythun. Haplotype analysis using the genotypes of the six sites estimated 33 different haplotypes. The haplotype 23? 12? K 6 S 14+ was found in all populations. 相似文献
35.
Miller CS Johnson DH Schroeter JP Myint L Glantz RM 《Journal of computational neuroscience》2003,15(2):247-269
Motoneuron responses were elicited by global visual motion and stepwise displacements of an illuminated stripe. Stimulus protocols were identical to those used in previous behavioral studies of compensatory eyestalk reflexes. The firing rates and directional selectivity of the motoneuron responses were measured with respect to four stimulus dimensions (spatial frequency, contrast, angular displacement and velocity). The directional selectivity of the motoneuron response was correlated to the previously measured gain of the reflex for each stimulus dimension. The information theoretical analysis is based upon Kullback-Leibler (K-L) distances which measure the dissimilarity of responses to different stimuli. K-L distances for single neurons are strongly influenced by the mean rate difference of the responses to any pair of stimuli. Because of redundancy, the joint K-L distances of pairs of neurons were less than the sum of the K-L distances of the individual neurons. Furthermore, the joint K-L distances were only weakly influenced by correlations among coactivated neurons. For most of the stimulus dimensions, the K-L distances of single motoneurons were not sufficient to account for the stimulus discriminations exhibited by the eyestalk reflex which typically required the summed output of 2 to 5 motoneurons. Thus the behaviorally relevant information is encoded in the motoneuron ensemble. The minimum time required to discriminate the direction of motion (the encoding window) for a single motoneuron is about 380 to 480 ms (including a 175 ms response latency) for stepwise displacements and up to 1.0 s for global motion. During this period a motoneuron fires 2 to 3 impulses. 相似文献
36.
In this report we show that ubiquinone cytochrome c reductase (complex III) from isolated rat heart mitochondria when inhibited with antimycin A, produces a large amount of superoxide as measured by the chemiluminescent probe coelenterazine. When mitochondria are inhibited with myxothiazol or stigmatellin, there is no detectable formation of superoxide. The antimycin A-sensitive free radical production can be dramatically reduced using either myxothiazol or stigmatellin. This suggests that the antimycin A-sensitive generation of superoxides originates primarily from the Q(o) semiubiquinone. When manganese superoxide dismutase depleted submitochondrial particles (SMP) were inhibited with myxothiazol or stigmatellin, a large superoxide signal was observed. These two inhibitors likely increase the concentration of the Q(i) semiquinone at the N center. The antimycin A-sensitive signal can, in the case of both the mitochondria and the SMP, be dissipated by the addition of copper zinc superoxide dismutase, suggesting that the measured coelenterazine signal was a result of superoxide production. Taken together, this data suggests that free radicals generated from the Q(i) species are more effectively eliminated by MnSOD in intact mitochondria. 相似文献
37.
A sensitive and selective flow injection chemiluminescence method for the determination of cardamonin over the range 1.0 x 10(-8) to 8.0 x 10(-6) g/mL is described. The method is based on the enhancement by cardamonin of the chemiluminescence of the reaction between cerium (IV) and rhodamine 6G in sulphuric acid medium. The optimised flow injection procedure yielded a detection limit for cardamonin of 8.8 x 10(-9) g/mL, whilst the relative standard deviations of intraday and inter-day precision were below 2.5%. The method has the advantages of high sensitivity and a wide linear range. It was successfully applied to the determination of cardamonin in Alpinia katsumadai Hayata. The mechanism of the chemiluminescence reaction is proposed. 相似文献
38.
Miller CS Johnson DH Schroeter JP Myint LL Glantz RM 《Journal of computational neuroscience》2002,13(1):5-21
Compensatory optomotor reflexes were examined in crayfish (Procambarus clarkii) with oscillating sine wave gratings and step displacements of a single stripe. A capacitance transducer was used to measure the rotation of the eyestalk about its longitudinal axis. System studies reveal a spatial frequency response independent of velocity and stimulus amplitude and linear contrast sensitivity similar to that of neurons in the visual pathway. The reflex operates at low temporal frequencies (<0.002 Hz to 0.5 Hz) and exhibits a low-pass temporal frequency response with cut-off frequency of 0.1 Hz. Eyestalk rotation increases as a saturable function of the angular stimulus displacement. When compared to the oscillatory response, transient responses are faster, and they exhibit a lower gain for large stimulus displacements. These differences may reflect system nonlinearity and/or the presence of at least two classes of afferents in the visual pathway. Our metric for information transmission is the Kullback-Leibler (K-L) distance, which is inversely proportional to the probability of an error in distinguishing two stimuli. K-L distances are related to differences in responsiveness for variations in spatial frequency, contrast, and angular displacement. The results are interpreted in terms of the neural filters that shape the system response and the constraints that the K-L distances place on information transmission in the afferent visual pathway. 相似文献
39.
Homeobox gene Hex is essential for onset of mouse embryonic liver development and differentiation of the monocyte lineage 总被引:6,自引:0,他引:6