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   159篇
  免费   3篇
林业   3篇
农学   3篇
  22篇
综合类   36篇
农作物   13篇
水产渔业   10篇
畜牧兽医   63篇
园艺   4篇
植物保护   8篇
  2024年   1篇
  2022年   1篇
  2021年   4篇
  2020年   3篇
  2019年   1篇
  2018年   3篇
  2017年   2篇
  2016年   1篇
  2015年   2篇
  2014年   1篇
  2013年   3篇
  2012年   8篇
  2011年   8篇
  2010年   2篇
  2009年   8篇
  2008年   9篇
  2007年   18篇
  2006年   4篇
  2005年   4篇
  2004年   8篇
  2003年   3篇
  2002年   8篇
  2001年   4篇
  2000年   3篇
  1999年   4篇
  1996年   1篇
  1995年   2篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1982年   4篇
  1979年   1篇
  1978年   3篇
  1977年   1篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1971年   3篇
  1970年   1篇
  1968年   1篇
  1967年   3篇
  1966年   1篇
  1958年   1篇
  1955年   3篇
  1945年   1篇
排序方式: 共有162条查询结果,搜索用时 14 毫秒
71.
72.
The potential of hyperspectral imaging (HSI) in the visible-near infrared (445-945 nm) wavelength range to discriminate between casing soil, enzymatic browning and undamaged tissue on mushroom (Agaricus bisporus) surfaces was investigated. A calibration set of 108 damage free mushrooms, grown under controlled conditions in a research station, were first tested as undamaged class (U) and then were divided into 2 groups of 54 samples. The first group was smeared with casing soil and designated as casing soil class (C) and the second group was subjected to vibrational damage resulting in enzymatic browning and designated as damaged class (D). Partial least squares discriminant analysis (PLS-DA) models were developed to classify mushroom tissue as one of the three classes investigated (U, C and D) using pixel spectra from each class. Prediction maps were obtained by applying the developed models to the hyperspectral images of candidate mushrooms. Percentages of pixels classified into each class were also calculated for the mushrooms studied in the calibration set. Results obtained showed that the developed models performed satisfactorily to discriminate between the 3 classes studied. Comparison of red-green-blue (RGB) and hyperspectral image analysis showed that HSI was better able to identify the regions containing casing soil. Model validation was performed using 3 different test sets of mushrooms obtained from a commercial producer. It was found that the developed PLS-DA models were satisfactorily capable of identifying undamaged regions, casing soil and enzymatic damaged areas on mushrooms from the validation sets.  相似文献   
73.
74.
Functional corpora lutea (CL) are required for pregnancy establishment and gestational maintenance in swine, and CL function is susceptible to environmental influences. Manganese (Mn) could be critical in regulating CL function since it is a component of the antioxidant enzyme Mn superoxide dismutase (MnSOD) as well as enzymes involved in cholesterol and steroid hormone synthesis. We hypothesized that a more bioavailable dietary Mn source would increase Mn content in the CL thereby influencing luteal function during the mid-luteal phase of the estrous cycle. Postpubertal gilts (n = 32) were assigned to one of four gestation diets. The control diet (CON) met or exceeded National Research Council (2012) requirements and was formulated to contain 20 parts per million (ppm) of added Mn in the form of Mn sulfate. Three additional diets included 20 (treatment [TRT]1), 40 (TRT2), or 60 (TRT3) ppm of added Mn from a Mn–amino acid complex (Availa-Mn; Zinpro Corporation) instead of Mn sulfate. Dietary treatment began at estrus synchronization onset and continued through 12 days post estrus (dpe) of the ensuing estrous cycle. Blood samples were collected at estrus onset, which was assigned as 0 dpe, as well as 4, 8, and 12 dpe. Gilts were euthanized and tissues were collected at 12 dpe. Serum progesterone (P4) increased (P < 0.01) from 0 to 12 dpe but was unaffected by dietary treatment (P = 0.15) and there was no effect of the interaction between day and treatment (P = 0.85). Luteal Mn content increased (P ≤ 0.05) by 19%, 21%, and 24% in gilts fed TRT1, TRT2, and TRT3, respectively, compared to CON. Luteal P4 concentrations decreased (P = 0.03) 25%, 26%, and 32% in gilts fed TRT1, TRT2, and TRT3, respectively, compared to CON. Relative to CON gilts, CL calcium content decreased (P = 0.02) by 36%, 24%, and 34% for TRT1, TRT2, and TRT3 gilts, respectively. Collectively, these data support the hypothesis that feeding a more bioavailable Mn source increases Mn accumulation in CL tissue. If and how this influences CL function may be related to altered luteal P4 concentrations.  相似文献   
75.
An objective method for predicting red meat yield in lamb carcasses is needed to accurately assess true carcass value. This study was performed to evaluate the ability of the lamb vision system (LVS; Research Management Systems USA, Fort Collins, CO) to predict fabrication yields of lamb carcasses. Lamb carcasses (n = 246) were evaluated using LVS and hot carcass weight (HCW), as well as by USDA expert and on-line graders, before fabrication of carcass sides to either bone-in or boneless cuts. On-line whole number, expert whole-number, and expert nearest-tenth USDA yield grades and LVS + HCW estimates accounted for 53, 52, 58, and 60%, respectively, of the observed variability in boneless, saleable meat yields, and accounted for 56, 57, 62, and 62%, respectively, of the variation in bone-in, saleable meat yields. The LVS + HCW system predicted 77, 65, 70, and 87% of the variation in weights of boneless shoulders, racks, loins, and legs, respectively, and 85, 72, 75, and 86% of the variation in weights of bone-in shoulders, racks, loins, and legs, respectively. Addition of longissimus muscle area (REA), adjusted fat thickness (AFT), or both REA and AFT to LVS + HCW models resulted in improved prediction of boneless saleable meat yields by 5, 3, and 5 percentage points, respectively. Bone-in, saleable meat yield estimations were improved in predictive accuracy by 7.7, 6.6, and 10.1 percentage points, and in precision, when REA alone, AFT alone, or both REA and AFT, respectively, were added to the LVS + HCW output models. Use of LVS + HCW to predict boneless red meat yields of lamb carcasses was more accurate than use of current on-line whole-number, expert whole-number, or expert nearest-tenth USDA yield grades. Thus, LVS + HCW output, when used alone or in combination with AFT and/or REA, improved on-line estimation of boneless cut yields from lamb carcasses. The ability of LVS + HCW to predict yields of wholesale cuts suggests that LVS could be used as an objective means for pricing carcasses in a value-based marketing system.  相似文献   
76.
A 12-yr-old intact male red wolf (Canis rufus) diagnosed with bilateral idiopathic dry eye was treated with subconjunctival drug delivery implants designed to release therapeutic levels of cyclosporine from 12-24 mo. Normal tear production and corneal health has been maintained, alleviating the need for daily handling of the animal for topical medication.  相似文献   
77.
OBJECTIVE: To evaluate risk behaviors for transmission of zoonotic diseases at petting zoos during a period without a recognized disease outbreak. DESIGN: Observational survey with environmental microbiologic sampling. SAMPLE POPULATION: 6 petting zoos in Tennessee. PROCEDURES: Attendees were observed for animal and environmental contact, eating or drinking, hand-to-face contact, and use of a hand sanitizer. Hands were examined via bacteriologic culture on some attendees. Environmental samples were collected at three petting zoos. RESULTS: 991 attendees were observed; of these, 74% had direct contact with animals, 87% had contact with potentially contaminated surfaces in animal contact areas, 49% had hand-to-face contact, and 22% ate or drank in animal contact areas. Thirty-eight percent used hand sanitizer; children had better compliance than adults. Results of bacteriologic cultures of hands were negative for Salmonella spp and Escherichia coli O157; Salmonella spp were isolated from 63% and E coli O157 from 6% of the environmental samples. CONCLUSIONS AND CLINICAL RELEVANCE: High risk behaviors were common among petting zoo visitors, and disease prevention guidelines were inconsistently followed. This is an example of the importance of one-medicine, one-health initiatives in protecting the public health. Veterinarians, venue operators, and public health authorities must work together on targeted education to improve implementation of existing disease prevention guidelines.  相似文献   
78.
BACKGROUND: Rat urinary protein concentration is commonly measured during safety assessment studies to evaluate potential drug-induced nephrotoxicity. It has been reported that impregnated reagent test strips (dipsticks) can yield false-positive urinary protein results for alkaline urine samples. OBJECTIVE: The objective of this study was to determine if urinary dipsticks accurately assess protein concentrations, especially in alkaline rat urine. METHODS: Ten male Sprague-Dawley rats were treated with 2% sodium bicarbonate and 2% ammonium chloride to alkalinize and acidify the urine, respectively. Urine pH was measured in treated and control rats using a pH meter and urinary dipsticks with the Clinitek 500. Quantitative urinary protein results were compared to urinary dipstick protein evaluations obtained with the Clinitek 500 and sulfosalicylic acid precipitation test methods. RESULTS: The urinary dipstick pH measurement had a very high correlation (r = .98) with the pH meter technique. Samples with alkaline pH (>or=7.5) analyzed for protein by dipstick analysis were in complete agreement 34.7% of the time with the quantitative technique, which was very similar to the 39.3% agreement for samples with neutral and acidic pH (相似文献   
79.
Six ovine fetal brains were harvested 33 to 35 days postchallenge from 5 ewes, each of which was given 3000 Toxoplasma gondii oocysts on day 90 of pregnancy. Histopathologic examination of transverse sections taken at 13 levels in the fetal brains revealed the presence of toxoplasmosis-related lesions in all 6 brains. However, lesions were not randomly distributed (P = .007); they were most numerous at the level of the optic tract, the rostral margin of the pons, and 4 mm caudal to the ansate sulcus and were absent in all sections at the level of the caudal cerebellum. Lesion distribution may be due to hemodynamic factors, differences in the expression of endothelial surface receptor molecules at the level of the blood-brain barrier, or the presence of localized permissive/inhibitory factors within the brain. The results have implications for the selection of areas of brain from aborted ovine fetuses to be examined histopathologically for laboratory diagnosis.  相似文献   
80.
A Lagrangian experiment was conducted over Iowa during the daytime (9:00–17:30 LT) on June 19, 2007 as part of the North American Carbon Program's Mid-Continent Intensive using a light-weight and operationally flexible aircraft to measure a net drawdown of CO2 concentration within the boundary layer. The drawdown can be related to net ecosystem exchange when anthropogenic emissions are estimated using a combination of the Vulcan fossil fuel emissions inventory coupled with a source contribution analysis using HYSPLIT. Results show a temporally and spatially averaged net CO2 flux of −9.0 ± 2.4 μmol m−2 s−1 measured from the aircraft data. The average flux from anthropogenic emissions over the measurement area was 0.3 ± 0.1 μmol CO2 m−2 s−1. Large-scale subsidence occurred during the experiment, entraining 1.0 ± 0.2 μmol CO2 m−2 s−1 into the boundary layer. Thus, the CO2 flux attributable to the vegetation and soils is −10.3 ± 2.4 μmol m−2 s−1. The magnitude of the calculated daytime biospheric flux is consistent with tower-based eddy covariance fluxes over corn and soybeans given existing land-use estimates for this agricultural region. Flux values are relatively insensitive to the choice of integration height above the boundary layer and emission footprint area. Flux uncertainties are relatively small compared to the biospheric fluxes, though the measurements were conducted at the height of the growing season.  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