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排序方式: 共有120条查询结果,搜索用时 15 毫秒
1.
Clayton T Larue Michael Goley Lei Shi Artem G Evdokimov Oscar C Sparks Christine Ellis Andrew M Wollacott Timothy J Rydel Coralie E Halls Brook Van Scoyoc Xiaoran Fu Jeffrey R Nageotte Adewale M Adio Meiying Zheng Eric J Sturman Graeme S Garvey Marguerite J Varagona 《Pest management science》2019,75(8):2086-2094
2.
Niemiec BA 《Journal of veterinary dentistry》2003,20(2):123-126
3.
Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding
landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage)
in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest
derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly
forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the
closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear
models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas.
Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use
of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global
increase in atmospheric CO2 may be changing the competitive balance between savanna and forest by enabling C3 trees to grow fast enough to escape the fire trap presented by flammable C4 grasses. 相似文献
4.
Four two-year-old Thoroughbreds suffered an acute gastrointestinal illness shortly after dosing with mineral oil which was thought to have been contaminated with an organophosphate compound. Three weeks later all four were noted to be dyspnoeic and endoscopic examination showed that they had developed bilateral laryngeal paralysis. Two of the horses died during severe bouts of dyspnoea six and eight months later and the third was killed shortly thereafter. Examination of the left and right recurrent laryngeal nerves from these horses showed a severe loss of myelinated fibres distally, especially in the left nerve. A similar but less severe lesion was seen in other long peripheral nerves, including the phrenic and digital nerves of the third horse. The spinal cord in two horses showed evidence of mild axonal degeneration which was not related to a particular tract or location. The fourth horse had bilateral laryngeal paralysis two years later. The acute clinical signs and delayed neurological sequelae seen in these horses were strongly suggestive of accidental organophosphate toxicity. 相似文献
5.
To ensure both long-term persistence and evolutionary potential, the required number of individuals in a population often greatly exceeds the targets proposed by conservation management. We critically review minimum population size requirements for species based on empirical and theoretical estimates made over the past few decades. This literature collectively shows that thousands (not hundreds) of individuals are required for a population to have an acceptable probability of riding-out environmental fluctuation and catastrophic events, and ensuring the continuation of evolutionary processes. The evidence is clear, yet conservation policy does not appear to reflect these findings, with pragmatic concerns on feasibility over-riding biological risk assessment. As such, we argue that conservation biology faces a dilemma akin to those working on the physical basis of climate change, where scientific recommendations on carbon emission reductions are compromised by policy makers. There is no obvious resolution other than a more explicit acceptance of the trade-offs implied when population viability requirements are ignored. We recommend that conservation planners include demographic and genetic thresholds in their assessments, and recognise implicit triage where these are not met. 相似文献
6.
A computer model was developed to simulate forage systems on dairy farms. The model simulated alfalfa growth, corn silage and corn grain yields, harvest, storage, feeding and ration formulation for a dairy herd. A 26-year series of historical weather data from East Lansing, Michigan, was used to compare management and technological alternatives on the basis of average net return and year-to-year variations. For example, a four-cut alfalfa system was found to be more profitable than a three-cut system 90% of the time. The comparison of a hay system with a silage system was very sensitive to forage intake assumptions; the break-even point shifted from 120 ha to 40 ha when silage intake was increased by 5%. The model can be used to assess the impact of new forage conservation methods under a wide range of climatic and management conditions. 相似文献
7.
Timing of millennial-scale climate change in Antarctica and Greenland during the last glacial period 总被引:2,自引:0,他引:2
A precise relative chronology for Greenland and West Antarctic paleotemperature is extended to 90,000 years ago, based on correlation of atmospheric methane records from the Greenland Ice Sheet Project 2 and Byrd ice cores. Over this period, the onset of seven major millennial-scale warmings in Antarctica preceded the onset of Greenland warmings by 1500 to 3000 years. In general, Antarctic temperatures increased gradually while Greenland temperatures were decreasing or constant, and the termination of Antarctic warming was apparently coincident with the onset of rapid warming in Greenland. This pattern provides further evidence for the operation of a "bipolar see-saw" in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales. 相似文献
8.
Direct estimates of extinction risk are frequently unavailable, so surrogate indicators are used in threatened species categorizations, but there is inadequate information on which best predict vulnerability. We compared the ability of 16 frequently-used factors to predict extinction risk for 45 vertebrate taxa. Median times to extinction were estimated using taxon-specific stochastic population models. Population size (N) and trend were clearly the best correlates of extinction risk in our data set. Stepwise multiple regression with additive and interaction terms identified N, N × trend, plus taxonomic level, number of sub-populations × N × trend, number of offspring (O) and N × O as predictors, and explained 70% of the variation. Trend was important in large, but not in small populations. Population size is the most important data to collect for threatened species and with trend should be the major focus in endangered species categorization and state of the environment reporting. 相似文献
9.
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