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   339篇
  免费   17篇
林业   32篇
农学   27篇
基础科学   5篇
  99篇
综合类   19篇
农作物   50篇
水产渔业   40篇
畜牧兽医   50篇
园艺   6篇
植物保护   28篇
  2023年   2篇
  2022年   6篇
  2021年   14篇
  2020年   15篇
  2019年   16篇
  2018年   17篇
  2017年   22篇
  2016年   25篇
  2015年   12篇
  2014年   21篇
  2013年   39篇
  2012年   23篇
  2011年   19篇
  2010年   12篇
  2009年   11篇
  2008年   25篇
  2007年   13篇
  2006年   9篇
  2005年   4篇
  2004年   5篇
  2003年   5篇
  2002年   4篇
  2000年   2篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1982年   1篇
  1981年   2篇
  1979年   3篇
  1975年   1篇
  1971年   1篇
  1966年   1篇
  1961年   1篇
排序方式: 共有356条查询结果,搜索用时 15 毫秒
341.
The pharmacokinetics of tripelennamine (T) was compared in horses (n = 6) and camels (n = 5) following intravenous (i.v.) administration of a dose of 0.5 mg/kg body weight. Furthermore, the metabolism and urinary detection time was studied in camels. The data obtained (median and range in brackets) in camels and horses, respectively, were as follows: the terminal elimination half-lives were 2.39 (1.91-6.54) and 2.08 (1.31-5.65) h, total body clearances were 0.97 (0.82-1.42) and 0.84 (0.64-1.17)L/h/kg. The volumes of distribution at steady state were 2.87 (1.59-6.67) and 1.69 (1.18-3.50) L/kg, the volumes of the central compartment of the two compartment pharmacokinetic model were 1.75 (0.68-2.27) and 1.06 (0.91-2.20) L/kg. There was no significant difference (Mann-Whitney) in any parameter between camels and horses. The extent of protein binding (mean +/- SEM) 73.6 + 8.5 and 83.4 +/- 3.6% for horses and camels, respectively, was not significantly statistically different (t-test). Three metabolites of T were identified in urine samples of camels. The first one resulted from N-depyridination of T, with a molecular ion of m/z 178, and was exclusively eliminated in conjugate form. This metabolite was not detected after 6 h of T administration. The second metabolite, resulted from pyridine ring hydroxylation, had a molecular ion of m/z 271, and was also exclusively eliminated in conjugate form. This metabolite could be detected in urine sample for up to 12 h after T administration. The third metabolite has a suspected molecular ion of m/z 285, was eliminated exclusively in conjugate form and could be detected for up to 24 h following T administration. T itself could be detected for up to 27 h after i.v. administration, with about 90% of eliminated T being in the conjugated form.  相似文献   
342.
Growth, photosynthesis and mineral ions accumulation of aromatic small grain, local coarse grain and HYV types of rice were evaluated under saline conditions. Three cultivars from each type were subjected to 0, 50, 100, 150 and 200 mvi NaCl concentrations. After three weeks of 200 mvi NaCl application only Pokkali and Kalobail, both belonging to the local coarse grain type and IPK 37011 of the HYV type were able to survive. Plant height, green leaf area, leaf weight, shoot and root growth were seriously decreased by salinity. However, leaf area was decreased more than other growth parameters. In general aromatic small grain type showed higher salt-sensitiveness in relation to growth than other types of rice. Photosynthesis (Pn) was decreased by salinity and apparently stomatal resistance was partially responsible for the decreased Pn. Kalijira, an aromatic small grain eultivar, showed serious reduction in Pn, especially at the 150mM NaCl level. Na accumulation was increased while K accumulation was decreased by salinity in all types. Salt tolerant eultivars in all types of rice accumulated less Na and more K than susceptible ones. The K/Na ratio was also higher in tolerant eulti-vars. Ca and Mg eoncentrations were decreased by salinity although not all the eultivars showed clear accumulation patterns as observed for Na and K. As HYV and local coarse grain types of rice in general showed high salt tolerance, a comprehensive breeding programme should be of value for the improvement of salt tolerance of aromatic small grain rice which has a high demand in rice importing countries.  相似文献   
343.
Camels have the potential for milk, meat and draught power and can contribute a handsome share of the production of these commodities. The potential of this wonderful animal has never been realized and it could be harnessed as a prospective milk producing animal. The future of animals that can thrive under harsh environmental conditions, the camel being at the top of the list, is bright. The camel is still a neglected species in Pakistan and has not received the proper attention of researchers and scientists. The population explosion, urbanization and industrialization have expanded agricultural activities to produce more food for the rapid growing human population of the country. Cultivated areas are shrinking, thus reducing the fodder production area for buffalo and cattle. Under these circumstances we have to search for other available sources to enhance milk production. The environmental changes occurring on the earth and the water shortage in the region have also adversely affected the production potential of buffalo, cattle, goats and sheep. Under these changing ecological circumstances, rearing camel is the best option for more milk production and the proper utilization of the vast unused lands of this country. Most studies also have named the camel as an animal of great socioeconomic importance in large tracts of the industrializing world. The camel serves as a cheaper source of power for drawing water from wells, plowing and leveling land, working mini extraction mills (extracting from oil seeds), grinding wheat, corn and other grains and crushing sugarcane and pulling carts for the transportation of goods as well as people.  相似文献   
344.
Nineteen agrochemical traits of 20 almond inter-specific backcrosses progenies were evaluated and compared for three consequence years to find out their phenotypic diversity and determine the relationships of fruit quality traits in almond × peach backcrosses breeding progenies. The variation was observed for traits of phenology parameters (blooming time, ripening time), Physical parameters (fruit weight, width, height, shape, thickness, skin pubescences, colour and flower type), chemical parameters (total sugar content, soluble solids content and acidity) and sensory parameters (attractiveness, taste, and flavor) and yield. Many fruit characteristics that are important to breeders are present in this collection. A high variability was found in the evaluated almond progenies and significant differences were found among them in all studied quality attributes. Year-by-year variations were observed for majority of traits. A significant correlation was found among the fruit height, fruit width, skin pubescences and yield. Fruit height showed a significant positive correlation with fruit weight and fruit thickness and some other traits and a negative correlation with the titratable acidity, skin pubescences and fruit flavour. A high negative correlation was found between the fruit weight and titratable acidity (?0.8). Low coefficients were got between the flower colour and skin pubescences. In addition, principal component analysis it possible to established similar groups of genotypes depending on their quality characteristics and to study relationships among pomological traits in almond progenies evaluated.  相似文献   
345.
Osmotic adjustment is the main component for physiological machinery of wheat drought tolerance. Some of parameters implicated in osmotic adjustment in 15 bread wheat cultivars were evaluated at soil water deficits (50% FC) and FC as the control in the greenhouse. For the physiological traits, analysis of variance showed that there are highly significant differences between treatments, i.e. water stress levels and wheat cultivars. Shahpasand and Marvdasht as sensitive wheat cultivars had significantly lower osmotic adjustment, relative water content, K+ content, soluble sugar, proline, and glycine betaine levels than the rest of the cultivars. The results of cluster analysis revealed that all cultivars were grouped into three distinct clusters. Dez, Kavir, Pishtaz, and Maron cultivars which have the highest osmoregulation activity were in cluster I, whereas clusters II (Pishgam, Aflak, Hirmand, Zagros, and Vee/Nac) and III (Ws-89-2, Sardari, Azar2, Shapasand, and Marvdasht) had intermediate activity and the lowest capacities for osmoregulation, respectively. In addition, in wheat flag leaf during the reproductive stage under drought conditions, the changes in gene expression of two key genes namely P5CS (D-Pyrroline-5-carboxylate synthetase) and BADH (Betaine Aldehyde Dehydrogenase) in two selected cultivars including Dez and Marvdasht revealed that water stress can increase the expression level of the genes P5CS and BADH in the resistant cultivar, Dez, compared with Marvdasht, the sensitive one. In general, it seemed that application of the all cultivars in cluster I would enable breeders to acquire more reliable achievements under drought conditions.  相似文献   
346.
Wild pistachio tree (Pistacia mutica) is considered the most important species in the Zagros forests. It can adapt to unfavorable environmental conditions. To find the suitable ecological conditions for pistachio species, we investigated different environmental factors such as gradient, aspect and position of the slopes through the distribution area. Frequency of pistachio trees in the north and northwest of Qalajeh forests was 36.4% and 1%, respectively. Maximum (32%) and minimum (13%) number of wild pistachio trees were in 30%–60% and >120% slope classes, respectively. The most number and least number of pistachio trees were found at elevations of 1100–1200 m and 2200–2300 m, respectively. The percentage of pistachio canopy coverage was 10. The average percentage of herbaceous coverage was 6.5. Pistachio trees of diameter per hectare at breast height (DBH) >20 cm numbered 5 while average number of pistachio trees was 8 per hectare. Pistachio seedlings per hectare averaged 3.5. The number of other species per ha was 7 trees. The effect of aspect on other species was not significant (p=0.151). Slope class and geographical aspect did not affect regeneration (p=0.275 and p=0.111, respectively). Pistachio plays an important economic role in semi-arid areas, therefore it is essential to protect and restore Qalajeh forests through participation by government and local people.  相似文献   
347.
348.
The rice eultivars grown in the tropies and sub-tropics can be broadly categorized as aromatic small grain, local coarse grain and modern high yielding varieties (HYV). The first two categories are traditional rice, and are generally palatable. The aromatic rice has better market value than HYV rice, yet farmers are unwilling to expand its cultivation because of the low yield potential. One possibility to expand the cultivation of traditional rice is o t find stress tolerant cultivars for growing in marginal land. The salinity tolerance of nine rice cultivars representing three from each type of aromatic small grains, local coarse grains and HYV types, was analysed at germination and early seedling stage. Seeds were placed for germination and the seedlings were allowed to grow for nine days at NaCl concentrations of 0, 50, 100, 150 and 200 mM. NaCl decreased the germination index (GI), speed of germination, seedling height and seedling dry matter weight. Seedling characteristics were decreased more than GI. In general aromatic small grain type showed more salt sensitivity than the other two types. Among the nine cultivars Shakkorkhora (aromatic type) showed the least salt tolerance in relation to germination and seedling characters while the other two cultivars of the same group showed tolerance as high as the tolerant cultivars in other types. Generalization of group salt tolerance of rice, therefore, has little value from the agronomic point of view at least at early growth stage. As the number of cultivars employed in this study was only three from each type it is suggested that more cultivars be considered for the purpose of salt tolerant improvement programme of various types of rice.  相似文献   
349.
Journal of Crop Science and Biotechnology - Salinity stress is one of the most important abiotic stresses which reduce crop production worldwide. In this study, 17 morphological and agronomic...  相似文献   
350.
 绿洲农业是依靠灌溉发展起来的生态系统。干旱地区地表水资源共同特点是春、秋季供水紧张,夏季相对富裕;但种植业产业结构上用水又集中在春季,水的利用矛盾重重。本文分析新疆策勒绿洲近50年农业统计资料,结合课题组调查收集的第一手资料,在充分分析干旱区绿洲农业结构与水资源利用特点的基础上,用资源最优分配模型和线性优化模型方法,提出了绿洲农业结构、作物布局和水资源利用最佳方案,为干旱区绿洲水资源合理利用、区域经济发展提供科学依据。  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