首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   203篇
  免费   11篇
林业   18篇
农学   2篇
  12篇
综合类   26篇
农作物   1篇
水产渔业   7篇
畜牧兽医   142篇
园艺   3篇
植物保护   3篇
  2020年   2篇
  2019年   7篇
  2017年   5篇
  2016年   8篇
  2015年   2篇
  2014年   2篇
  2013年   10篇
  2012年   2篇
  2011年   5篇
  2010年   6篇
  2009年   8篇
  2008年   2篇
  2007年   4篇
  2006年   3篇
  2004年   9篇
  2003年   8篇
  2002年   8篇
  2001年   6篇
  2000年   8篇
  1999年   3篇
  1998年   6篇
  1997年   3篇
  1996年   4篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1991年   5篇
  1990年   5篇
  1989年   4篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1985年   3篇
  1984年   7篇
  1983年   1篇
  1982年   1篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1974年   2篇
  1973年   9篇
  1972年   3篇
  1971年   6篇
  1970年   11篇
  1969年   5篇
  1968年   5篇
  1967年   2篇
  1966年   2篇
  1922年   1篇
  1918年   1篇
排序方式: 共有214条查询结果,搜索用时 15 毫秒
101.
Ecological overlap may increase the risks of microbial exchange between humans and wild non-human primates. Escherichia coli bacteria were collected from chimpanzees and humans in Kibale National Park, western Uganda, in May and June 2004, in order to examine whether interaction between humans and apes in the wild might affect gastrointestinal bacterial communities in the two species. Chimpanzees harbored bacteria genetically more similar to those of humans employed in chimpanzee-directed research and tourism than to those of humans from a local village. Most humans (81.6%) and 4.4% of chimpanzees harbored at least one isolate resistant to locally available antibiotics. In isolates from both humans and chimpanzees, resistance was higher to five of these antibiotics than to Ceftiofur, an antibiotic not available in the region. These data indicate that humans and apes interacting in the wild can share genetically and phenotypically similar gastrointestinal bacteria, presumably originating from common environmental sources. Strategies to limit transmission of pathogens between humans and primates, whether that transmission is direct or indirect, would benefit both human health and primate conservation.  相似文献   
102.
The impact of increased-deposited sediment loads on growth and development of tadpoles of the spotted tree frog, Litoria spenceri, in south-eastern Australia was assessed in conjunction with food type and tadpole density. This investigation was conducted in stream enclosures subjected to varying treatments of tadpole density, substrata and deposited-sediment load. Tadpole growth and development were not significantly affected by food type, but there was a trend toward increased performance on periphyton substrata. Tadpole growth and development were significantly reduced by increases in tadpole density and sediment load. These effects were independent, suggesting that increased sediment load reduced food quality rather than quantity. Activities in catchments that increase sediment loads in streams may adversely affect growth and development of tadpoles of L. spenceri. Increased sediment input into streams may therefore reduce tadpole fitness and recruitment to the terrestrial stage. Disturbance processes that increase stream sediment loads, such as forestry activities and associated road construction, may potentially have contributed to the observed declines of L. spenceri and other lotic anurans in south-eastern Australia.  相似文献   
103.
The evaporation from water droplets on artificial soybean leaves was modelled using an energy balance. Observations showed that while droplets were hemispherical initially, they then flattened keeping the base area virtually constant. These observations led to modelling the process as evaporation from a vertical right-circular cylinder which gave excellent agreement with indoor data.  相似文献   
104.
The performance of a commercially available enzyme immunoassay (EIA) for determining the presence of Shiga toxin I and II in human diarrheal stool samples was evaluated for use as a presumptive test for the presence of Escherichia coli O157:H7 in nondiarrheal bovine fecal samples collected from 10 Kansas cow-calf ranches. The prevalence of E. coli O157:H7 in 2,297 samples, as determined by selective bacterial culture, was 1.6%. The sample prevalence of non-E. coli O157:H7 Shiga toxin-producing bacteria, as detected by the Shiga toxin EIA, was 5.8%. Only 2 of 136 samples that tested positive with the Shiga toxin EIA were positive for E. coli O157:H7 by culture. Compared with bacterial culture, the sensitivity of the Shiga toxin EIA was 5.5% and the specificity was 94.1%. Agreement between the 2 tests, as measured by the kappa statistic, was poor (kappa = -0.002). Although the Shiga toxin EIA was not a good presumptive test for the determination of E. coli O157:H7 in bovine fecal samples because of its low sensitivity (5.5%), it might be a useful test for the detection of Shiga toxin producing non-E. coli O157:H7 organisms in bovine feces.  相似文献   
105.
106.
Dating by accelerator mass spectrometry of wooden artifacts, cord, and charcoal samples from Guitarrero Cave, Peru, supports the antiquity of South America's earliest textiles and other perishable remains. The new dates are consistent with those obtained from disintegration counters and leave little doubt about the integrity of the lower Preceramic layers and their early cultivars. Re-evaluation of the mode of deposition suggests that most of the remains resulted from short-term use of the cave in the eighth millennium B.C., with a possible brief human visit as early as 12,560 years ago.  相似文献   
107.
The atmospheres of Jupiter, Saturn, Uranus, and Neptune were modeled as shallow layers of turbulent fluid overlying a smooth, spherical interior. With only the observed values of radius, rotation rate, average wind velocity, and mean layer thickness as model parameters, bands and jets spontaneously emerged from random initial conditions. The number, width, and amplitude of the jets, as well as the dominance of anticyclonic vortices, are in good agreement with observations for all four planets.  相似文献   
108.
Bergner's theoretical analysis of tracer dynamics has important ap plications in biology, not only for the measurement of exchangeable mass (as he demonstrated) but also for elicitation of otherwise inaccessible information on total masses of particular elements in body organs or systems-as well as in Chemical engineering and geophysics.  相似文献   
109.
  1. Tidal energy generators have the potential to injure or kill marine animals, including small cetaceans, through collisions with moving turbine parts. Information on the fine scale behaviour of animals close to operational turbines is required to inform regulators of the likely impact of these new technologies.
  2. Harbour porpoise movements were monitored in three dimensions around a tidal turbine for 451 days between October 2017 and April 2019 with a 12-channel hydrophone array.
  3. Echolocation clicks from 344 porpoise events were localized close to the turbine. The data show that porpoises effectively avoid the turbine rotors, with only a single animal clearly passing through the rotor swept area while the rotors were stationary, and none passing through while rotating.
  4. The results indicate that the risk of collisions between the tidal turbine and porpoises is low; this has important implications for the potential effects and the sustainable development of the tidal energy industry.
  相似文献   
110.
There are several biopesticides based on entomopathogenic fungi available in the market for use against insect pests in greenhouse ecosystems.Although most are compatible for use with predators and parasitoids in greenhouse ecosystems,much more research is needed to determine the intraguild interactions for each combination of host, pathogen, predator, and parasitoid.Our research has demonstrated that, although direct effects on the predators could be demonstrated in laboratory bioassays, different results were found under greenhouse conditions, indicating that results obtained in the laboratory may be a poor predictor of what occurs in the greenhouse.In both cases, additive effects were obtained under greenhouse conditions,demonstrating compatibility. In addition, there is increasing evidence that entomopathogenic fungi have significant potential for dual management of invertebrate pests and plant pathogens.Our studies demonstrated that 3 species of Lecanicillium had significant effects on both aphids and cucumber powdery mildew, Sphaerotheca fuliginea;that the fungus Paecilomyces fumosoroseus was compatible with a mirid predator,Disyphus hesperus,when used concurrently against greenhouse whitefly,Trialeurodes vaporariorum;and that Lecaniciullium longisporum was compatible with a predatory midge,Aphidoletes aphidimyza when used concurrently against green peach aphids.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号