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   349篇
  免费   16篇
林业   31篇
农学   3篇
基础科学   1篇
  82篇
综合类   18篇
农作物   21篇
水产渔业   13篇
畜牧兽医   170篇
园艺   7篇
植物保护   19篇
  2024年   1篇
  2023年   4篇
  2022年   5篇
  2021年   15篇
  2020年   11篇
  2019年   13篇
  2018年   11篇
  2017年   18篇
  2016年   14篇
  2015年   12篇
  2014年   15篇
  2013年   11篇
  2012年   28篇
  2011年   34篇
  2010年   20篇
  2009年   20篇
  2008年   21篇
  2007年   21篇
  2006年   20篇
  2005年   13篇
  2004年   11篇
  2003年   8篇
  2002年   7篇
  2001年   4篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1992年   1篇
  1990年   1篇
  1989年   2篇
  1987年   2篇
  1983年   1篇
  1981年   1篇
  1976年   1篇
  1972年   1篇
排序方式: 共有365条查询结果,搜索用时 15 毫秒
61.
Background: Two neutrophilic indices reported by the ADVIA 120 Hematology Analyzer, neutrophilic myeloperoxidase index (MPXI), and mean light absorbance (neutrophil X mean [NXM]) have been proposed as indicators of systemic inflammatory disease in horses and of neutrophil activation in coronary ischemic syndromes in people. Objective: The aim of this study was to evaluate NXM and MPXI in healthy, sick nonseptic, and sick septic foals to determine whether conditions likely associated with neutrophil activation result in decreases in these variables. Methods: In this retrospective study, CBC data from 61 neonatal foals presented to the Equine Teaching Hospital of Barcelona were evaluated for correlations between MPXI, NXM, percentage of large unstained cells, neutrophil count, and percentage of band neutrophils. Results obtained in septic (n=32), sick nonseptic (n=22), and healthy foals (n=7) were compared. In addition, results recorded in septic/neutropenic (n=12), septic/non‐neutropenic (n=20), nonseptic/neutropenic (n=8), nonseptic/non‐neutropenic (n=14), and healthy foals (n=7) were also compared. Results: A weak negative correlation was found between MPXI and neutrophil count and between NXM and percentage of band neutrophils. Septic/neutropenic foals had significantly higher MPXI values (median 17.9, minimum–maximum 4.7–42.5) than did septic/non‐neutropenic (1.5, ?24.4 to 22.3), nonseptic/neutropenic (6.6, 0.6–17.9), and nonseptic/non‐neutropenic foals (8.8, ?10.1 to 16.8) but did not differ significantly from controls (12.8, ?8.5 to 20.4). Conclusions: Significant differences in NXM or MPXI were not found when disease groups were compared with controls; however, septic/neutropenic foals had significantly higher median MPXI than other groups of sick foals. Further prospective studies are needed to clarify if this finding is related to decreased neutrophil function or activation in septic/neutropenic foals.  相似文献   
62.
63.
Ethnobotanical survey was conducted in 101 randomly selected home gardens of Phong My commune, central Vietnam, situated in the buffer-zone of Natural Reserve. Data were collected through semi-structured questionnaires and direct observation. Sixty-seven species belonging to 35 families were identified to be used for various purposes. For each species the botanical and vernacular names, plant parts used and main purposes of use are given. The major use categories reported for plant species were food (86%), medicine (32%) and firewood (32%), however, seventy-seven percent of all inventoried plants have multiple uses. The species Artocarpus heterophyllus Lam., Citrus grandis Osbeck, Citrus reticulata Blanco, Ipomoea batatas (L.) Lam. and Musa spp. were identified as the main sources of plant foods consumed within the households. Statistical analyses indicated by Shannon-Wiener and Margalef indices have shown that local species diversity and richness is affected by home garden size. On the contrary, no relationship between diversity and home garden age was found. On the basis of a cluster analysis of plant species diversity, five home garden types were differentiated. In comparison to previously reported studies on tropical home gardens, the diversity in Phong My is lower, probably due to market-oriented strategy. Nevertheless, based on the results achieved, we can conclude that useful plants cultivated in local home gardens provide valuable foods complementing daily diet and subsequently contributing to socioeconomic status of the households.  相似文献   
64.
Urban and periurban agriculture (UPA) contributes significantly to meeting increasing food demand of rapidly growing urban populations in West African cities. The often intensive high‐input vegetable production within UPA results in large positive nutrient balances, being presumably linked to strong nutrient leaching which needs quantification. This study aimed at estimating leaching losses of mineral N and P in three representative urban gardens of Niamey, Niger, using ion‐exchange‐resin cartridges installed below the crop rooting zone at 0.6 m soil depth. In 2007, a year with below‐average annual rainfall (425 mm as compared to 542 mm), mean leaching of mineral N amounted to 5.9 and 7.3 kg N ha–1 for two gardens with > 80% sand fraction and only 2.2 kg N ha–1 for a garden with 40% silt and clay. Apparent annual P leaching was 0.7 kg P ha–1 in all three gardens. Additional multiannual studies are necessary to assess the effect of inter‐ and intraannual variation in precipitation on nutrient leaching in intensive UPA vegetable production of semiarid West Africa.  相似文献   
65.
Little is known about nutrient fluxes and nutrient‐use efficiencies in urban and peri‐urban agriculture (UPA) of rapidly expanding cities in developing countries. Therefore, horizontal flows of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) as well as leaching losses of mineral N and P were measured over 2 years in three representative agricultural production systems of Kabul. These comprised 21 gardens and 18 fields dedicated to vegetable farming, cereal farming, and table‐grape production (vineyards). Across sites (fields and gardens) biennial inputs averaged 375 kg N ha–1, 155 kg P ha–1, 145 kg K ha–1, and 15 kg C ha–1 while with harvests 305 kg N ha–1, 40 kg P ha–1, 330 kg K ha–1, and 7 kg C ha–1 were removed. In vegetable gardens, biennial net balances were 80 kg N ha–1, 75 kg P ha–1, –205 kg K ha–1, and 4 kg C ha–1, whereas in cereal farming biennial horizontal balances amounted to –155 kg N ha–1, 20 kg P ha–1, –355 kg K ha–1, and 5 kg C ha–1. In vineyards, corresponding values were 295 kg N ha–1, 235 kg P ha–1, 5 kg K ha–1, and 3 kg C ha–1. Annual leaching losses in two selected vegetable gardens varied from 70 to 205 kg N ha–1 and from 5 to 10 kg P ha–1. Night soil and irrigation water were the major sources among the applied nutrient inputs in all studied farming systems, contributing on average 12% and 25% to total N, 22% and 12% to total P, 41% and 53% to total K, and 79% and 10% to total C, respectively. The results suggest that soils in extensive cereal fields are at risk of N and K depletion and in vegetable gardens of K depletion, while vineyards may be oversupplied with nutrients possibly contributing to groundwater contamination. This merits verification.  相似文献   
66.
Closed‐chamber systems are commonly used to determine gaseous C and N emissions from agricultural soils. We investigated the effects of eight cuvette surfaces on two standard gas concentrations of NH3, N2O, CO2, and CH4 under laboratory conditions. Cuvette surface materials differentially affected gas adhesion or recovery as a function of the type and the concentration of the gases. Given the strong effects on results of gas measurements in closed‐chamber systems, both the type and the concentration of the measured gases need to be considered in selecting cuvette surface materials.  相似文献   
67.
The difference in the frequency of the occurrence of reflexes/reactions in 355 cows (average weight 505.5 ± 7.9 kg) and 262 bulls (average weight 735.6 ± 8.4 kg) following stunning with a Matador SS 3,000 B trigger‐activated captive bolt gun (Termet) was determined. The stun shot more than 2 cm from the ideal position was found in 79.6% of animals. Vocalization, corneal reflex, rhythmic breathing, blinking, eyeball rotation and the absence of tongue protrusion occurred more frequently in bulls (p < .05). Spontaneous limb movements and nystagmus occurred more frequently in cows (p < .05). No difference between bulls and cows was determined in the occurrence of a response to painful stimuli or attempts to regain normal posture. No dependency was determined between the frequency of the occurrence of a reflex/reaction and the distance of the stun shot from the ideal point on the skull for any of the monitored signs. This study shows that the occurrence of reflexes/reactions following the stunning of cattle with a captive bolt is not only dependent on the position of the shot if placed within a 9 cm radius from the ideal point on the cattle skull.  相似文献   
68.
The activity of glycosidases is crucial for the function and biological activity of proteins conjugated with sugar moieties, which play an important role in adhesion of cells during attachment and detachment of the foetal membranes. The aim of study was to describe the ability of bovine placental tissues to break down O-glycosidic bonds in different glycoproteins by the determination of activity of β-galactosidase, α-l-fucosidase, β-N-acetyl-hexosaminidase and sialidase in early–mid-pregnancy as well as at parturition with released and retained foetal membranes. Moreover, the availability of substrates for these glycosidases in placental homogenates was evaluated. Placental samples were collected from pregnant (2–4 months) cows in slaughterhouse (n = 8) as well as during Caesarean section and divided into released foetal membranes (n = 8) and retained foetal membranes (n = 8). Tissue homogenates were subjected to spectrofluorimetric and spectrophotometric determinations of enzyme activities as well as electrophoretic separations. Enzyme activities expressed changes within examined time with significant (p < .05) differences between pregnancy and physiological parturition in β-N-acetyl-hexosaminidase and α-l-fucosidase in foetal part of placenta while in maternal part only in the latter one. Decreasing tendency in enzyme activity was noticed in foetal part of retained samples in comparison with released ones with significant (p < .05) differences in α-l-fucosidase activity. The analysis of staining of sugar moieties attached to selected proteins depicted availability of sugar molecules in examined tissues, but their patterns differed between samples. In conclusion, sugar moieties in conjugated proteins express changes in the course of pregnancy which is reflected by the alterations in activities of placental glycosidases.  相似文献   
69.
70.
Phoma macdonaldii, the causal agent of black stem disease of sunflower (Helianthus annuus), also attacks roots and collars of the plants, resulting in early death. Totally resistant lines do not exist for infection of the aerial parts, but tolerant lines have been characterised. This paper presents a study on colonisation of a partially resistant and a susceptible sunflower line by P. macdonaldii. The fungus was transformed with a constitutively expressed reporter gene encoding the jellyfish green fluorescent protein via Agrobacterium tumefaciens, and colonisation of sunflower roots by this transformed strain was studied by various microscopy techniques including confocal and scanning electron microscopy. The results show that penetration of the fungus into the root occurred through natural fissures or through the epidermis and was similar in both lines. In contrast, the colonisation rate of the stele was reduced in the partially resistant line, and the morphology of the fungal hyphae was also affected. The effect on hyphal morphology was strongest in the stele, indicating a localised production of defence compounds in this line.  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