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   162篇
  免费   3篇
林业   2篇
基础科学   1篇
  10篇
综合类   72篇
农作物   5篇
水产渔业   4篇
畜牧兽医   57篇
园艺   1篇
植物保护   13篇
  2018年   6篇
  2016年   2篇
  2014年   3篇
  2013年   5篇
  2012年   3篇
  2011年   4篇
  2010年   5篇
  2009年   2篇
  2008年   3篇
  2007年   6篇
  2006年   2篇
  2005年   4篇
  2004年   4篇
  2003年   2篇
  2002年   2篇
  1999年   5篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1995年   4篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   4篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   4篇
  1985年   2篇
  1984年   3篇
  1979年   2篇
  1978年   2篇
  1972年   2篇
  1968年   2篇
  1967年   2篇
  1966年   2篇
  1963年   3篇
  1918年   4篇
  1916年   2篇
  1911年   2篇
  1902年   2篇
  1898年   1篇
  1896年   1篇
  1893年   2篇
  1892年   1篇
  1886年   1篇
  1883年   1篇
  1881年   1篇
  1880年   1篇
排序方式: 共有165条查询结果,搜索用时 31 毫秒
61.
Pharmaceuticals and personal care products (PPCPs) can reach soil and aquatic environments through land application of wastewater effluent and agricultural runoff. The objective of this research was to assess the fate of PPCPs at field scale. PPCPs were measured systematically in a wastewater treatment plant (WWTP), and in soil and groundwater receiving treated effluent from the WWTP. A land application site in West Texas was used as the study site; it has received treated wastewater effluent from the WWTP for more than 70 years in order to remove additional nutrients and irrigate non-edible crops. Target compounds (estrone, 17??-estradiol, estriol, 17??-ethynylestradiol, triclosan, caffeine, ibuprofen, and ciprofloxacin) in wastewater, sewage sludge, soil, and groundwater were determined using HPLC/UV with qualitative confirmatory analyses using GC/MS. Samples were collected quarterly over 12 months for wastewater and sludge samples and over 9 months for soil and groundwater samples. Results indicated that concentrations of PPCPs in wastewater influent, effluent, sludge solid phase, and sludge liquid phase were in the range of non-detected (ND)-183 ??g/L, ND-83 ??g/L, ND-19 ??g/g, and ND-50 ??g/L, respectively. Concentrations in soil and groundwater samples were in the range of ND-319 ng/g and ND-1,745 ??g/L, respectively. GC/MS confirmation data were consistent with the results of HPLC/UV analyses. Overall, data indicate that PPCPs in the wastewater effluent from the WWTP transport both vertically and horizontally in the soil, and eventually reach groundwater following land application of the effluent.  相似文献   
62.
Pathology of experimentally-induced, acute toxoplasmosis in macropods   总被引:1,自引:0,他引:1  
SUMMARY Thirteen Tammar wallabies (Macropus eugenii) were dosed orally with 500, 1000 or 10 000 oocysts of Toxoplasma gondii, as part of a vaccination trial. Eleven animals died of acute toxoplasmosis 9 to 15 days after challenge. The lesions were similar in all animals, consisting of foci of necrosis and inflammation in the intestines, lymphoid tissue, adrenal cortex, heart, skeletal muscle and brain, and severe generalised pulmonary congestion and oedema. Free and intracellular tachyzoites of Toxoplasma were associated with the lesions. The remaining 2 animals had shown no signs of disease when euthanased four months after challenge. Small, focal, non-suppurative inflammatory lesions were seen in brain, heart and skeletal muscle of these animals and chronic Toxoplasma infection was confirmed by mouse inoculation.  相似文献   
63.
64.
Objective To provide serological data to support Australia's claim of freedom from porcine reproductive and respiratory syndrome.
Design A national serological survey was designed to provide 99% confidence of detecting at least one infected pig herd in Australia, assuming that at least 5% of herds would have been exposed to porcine reproductive and respiratory syndrome virus and that at least 25% of the 'finisher' pigs in these herds would have antibodies to the virus.
Procedure A two-stage testing regime was used. All samples were tested with a commercially available enzyme-linked immunosorbent assay. If assay reactions were found, all samples from the herd were to be tested using the indirect immunofluorescence antibody assay.
Results Of the 875 samples from 163 herds from all States in Australia, there was some evidence of reactivity in only four samples from four herds on the enzyme-linked immunosorbent assay. Further testing using the indirect immunofluorescence antibody assay according to the study protocol demonstrated that the reactions were not due to the presence of specific porcine reproductive and respiratory syndrome virus antibodies in the sera.
Conclusion The results of this study support the view that Australian pigs are free of porcine reproductive and respiratory syndrome virus.  相似文献   
65.
66.
The quantification of evapotranspiration (ET) from irrigated projects is important for water rights management, water resources planning and water regulation. Traditionally, ET has been estimated by multiplying a weather-based reference ET by crop coefficients (Kc) determined according to the crop type and the crop growth stage. However, there is typically question regarding whether crops grown compare with the conditions represented by the Kc values, especially in water short areas. In addition, it is difficult to estimate the correct crop growth stage dates for large populations of crops and fields. METRIC (Mapping Evapotranspiration at high Resolution and with Internalized Calibration) is an image-processing model for calculating ET as a residual of the surface energy balance. METRIC is a variant of SEBAL, an energy balance process developed in the Netherlands by Bastiaanssen and was extended to provide tighter integration with ground-based reference ET. METRIC was applied with Landsat images in southern Idaho to predict monthly and seasonal ET for water rights accounting and for operation of ground water models. ET “maps” (i.e., images) provide the means to quantify, in terms of both the amount and spatial distribution, the ET on a field by field basis. The ET maps have been used in Idaho to quantify net ground-water pumpage in areas where water extraction from underground is not measured and to estimate recharge from surface-irrigated lands. Application and testing of METRIC indicates substantial promise as an efficient, accurate, and relatively inexpensive procedure to predict the actual evaporation fluxes from irrigated lands throughout a growing season.  相似文献   
67.
68.
Adult bean thrips, Caliothrips fasciatus (Pergande), over-wintering inside the navel of navel oranges in California are an export problem when detected in fruit sent to Australia. At present, a systems approach is used to reduce fruit infestation levels and one component of this approach is to search for thrips inside the navel by cutting 50 fruit per block prior to harvest and 75 fruit per grower lot before packing in the packinghouse with any detection of live bean thrips leading to that grower lot not being eligible for shipment to Australia. Given that bean thrips infestation levels are often 0.5% of the fruit or less, this amount of fruit cutting can lead to shipment of infested lots of citrus to Australia. As an alternative to cutting more fruit, two non-destructive methods of sampling for bean thrips inside the navel of navel oranges were investigated which might be used on larger numbers of fruit and result in fewer infested lots being shipped to Australia. A light trap at the apex of a pyramid-shaped black cloth tent caught 41.1% of adult bean thrips released at the bottom of the tent. When this experiment was repeated with the tent placed over a citrus bin two-thirds full of fruit, however, only 9.3% of thrips released at the bottom of the bin were captured. A second method of sampling, washing bean thrips out of the navel onto a screen, resulted in close to 90% recovery of thrips with each of the five spray rinses evaluated, including distilled water. Regression analysis indicated there was no statistical difference between results with the five rinses. Thus, it might be worthwhile trying to scale-up our laboratory method of rinsing with distilled water to a method that might be used in a commercial packinghouse for detection of bean thrips in large numbers of fruit. Even if one assumes that cutting fruit is 100% efficient in finding bean thrips inside the navel of navel oranges, sampling a much larger number of fruit using a method with 90% efficiency is shown to result in higher odds of finding any bean thrips that are present.  相似文献   
69.
AIM: To obtain an estimate of the incidence of assistance at calving in primiparous (first-calving) beef heifers and the prevalence of breeding heifers at 15 months of age in New Zealand in 2006,and to identify factors contributing to farmers' decisions regarding breeding strategies for heifers, using a survey of beef cattle farmers.

METHODS: A questionnaire was sent to farmers listed in a Massey University database and to members of selected breed societies, as well as published in an industry newspaper; 331 valid responses were received. Information was gathered on the age and number of primiparous heifers, number of heifers assisted, and the importance of various reasons for and against breeding heifers at 15 months of age. Respondents were also required to outline the criteria used for selecting bulls to join with heifers, and the strategies used to manage dystocia in primiparous heifers.

RESULTS: Sixty-five (95% CI=58–71)% of respondents had only 2-year-old primiparous heifers in 2006, whilst a further 11 (95% CI=8–16)% had both 2- and 3-year-old primiparous heifers. The mean reported incidence of assisted calving was 7.0 (95% CI=6.4–7.5)% for 2-year-old primiparous heifers and 1.7 (95% CI=1.2–2.2)% for 3-year-old primiparous heifers. The reported incidence of assistance at calving within individual herdsranged from 0 to 100% for 2-year-old heifers. Respondents with bull-breeding herds most commonly observed their primiparous 2-year-old heifers twice daily, whilst respondents with commercial herds most commonly observed them once daily during calving. The most important reason for breeding heifers at 15 months of age was “increased profit”, whereas the most important reason for not breeding them at that age was “concern about rebreeding performance of 2-year-old heifers”. Estimated breeding value (EBV) for birth weight was the factor considered most frequently when selecting bulls to join with maiden heifers; age of bull and body shape of bull were the next most frequently considered factors. Selection of an appropriate bull was the most common strategy used to manage dystocia in 2-year-old beef heifers.

CONCLUSIONS: The majority of respondents calved their heifers at 2 years of age, and “increased profit” was the primary motivator. Concern about the rebreeding performance of 2-year-old heifers was the most important reason among the remainder of respondents for not breeding heifers at 15 months of age. Dystocia in 2-year-old heifers was “not a problem” or “a minorproblem” in most herds, but there was much variation amongst herds.  相似文献   
70.
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