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   78篇
  免费   1篇
林业   19篇
农学   4篇
  15篇
综合类   3篇
农作物   3篇
水产渔业   9篇
畜牧兽医   16篇
园艺   1篇
植物保护   9篇
  2022年   1篇
  2021年   1篇
  2020年   3篇
  2019年   2篇
  2017年   4篇
  2016年   5篇
  2015年   5篇
  2014年   2篇
  2013年   8篇
  2012年   4篇
  2011年   8篇
  2010年   7篇
  2009年   1篇
  2008年   4篇
  2007年   2篇
  2006年   2篇
  2005年   2篇
  2004年   1篇
  2003年   2篇
  2001年   2篇
  2000年   2篇
  1998年   1篇
  1991年   1篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1980年   1篇
  1972年   1篇
  1971年   1篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
排序方式: 共有79条查询结果,搜索用时 31 毫秒
1.
2.
3.
Fish Physiology and Biochemistry - Yolk processing pathways vary in the oocytes of benthophil and pelagophil teleosts. The present study investigated the yolk processing pattern in the oocytes of...  相似文献   
4.
Multifunctional applications of textiles have been limited by the inability to spin important materials into yarns. Generically applicable methods are demonstrated for producing weavable yarns comprising up to 95 weight percent of otherwise unspinnable particulate or nanofiber powders that remain highly functional. Scrolled 50-nanometer-thick carbon nanotube sheets confine these powders in the galleries of irregular scroll sacks whose observed complex structures are related to twist-dependent extension of Archimedean spirals, Fermat spirals, or spiral pairs into scrolls. The strength and electronic connectivity of a small weight fraction of scrolled carbon nanotube sheet enables yarn weaving, sewing, knotting, braiding, and charge collection. This technology is used to make yarns of superconductors, lithium-ion battery materials, graphene ribbons, catalytic nanofibers for fuel cells, and titanium dioxide for photocatalysis.  相似文献   
5.
6.
A cross sectional study was conducted to assess the prevalence of synthetic pyrethroids (SP) resistance in Rhipicephalus (Boophilus) microplus in India. Twenty-seven areas located in six agro-climatic regions were selected for the collection of engorged ticks using two stage stratified sampling procedure. Adult immersion test (AIT) and larval packet test (LPT) were optimized using laboratory reared susceptible line of R.(B.) microplus (IVRI-I) for determination of 95% lethal concentration (LC(95)) of deltamethrin (29.6 ppm in AIT and 35.5 ppm in LPT) and cypermethrin (349.1 ppm in AIT and 350.7 ppm in LPT). The AIT with a discriminating dose (2 × LC(95)) was used to detect deltamethrin and cypermethrin resistance in the field isolates of R.(B.) microplus. On the basis of the data generated on three variables viz., mortality, egg masses and reproductive index, the resistance level was categorized as I, II, III and IV. The overall prevalence of SP-resistant R.(B.) microplus among the sampled farms was 66.6% (18/27). Out of these 18 areas, resistance to deltamethrin at level I was detected in 08 areas (resistance factor=2.0-4.9), at level II in 09 areas (RF=5.2-11.8), at level III in 01 area (RF=34.9) and at level IV in 01 area (RF=95.7). The resistance to cypermethrin was detected in 16 areas and level of resistance was detected at level I in 10 areas (RF=2.06-4.64) and at level II in 06 areas (RF=5.13-9.88). The middle-gangetic and trans-gangetic plains revealed higher density of resistant ticks where intensive cross bred cattle population are reared and the SP compounds are commonly used. The data generated on acaricide resistant status in ticks will help in formulating tick control strategy for the country.  相似文献   
7.
Climate is a critical factor affecting forest ecosystems and their capacity to produce goods and services. Effects of climate change on forests depend on ecosystem-specific factors including dimensions of climate (temperature, precipitation, drought, wind etc.). Available information is not sufficient to support a quantitative assessment of the ecological, social and economic consequences. The present study assessed shifts in forest cover types of Western Himalayan Eco-region (700?4500 m). 100 randomly selected samples (75 for training and 25 for testing the model), genetic algorithm of rule set parameters and climatic envelopes were used to assess the distribution of five prominent forest cover types (Temperate evergreen, Tropical semi-evergreen, Temperate conifer, Subtropical conifer, and Tropical moist deciduous forests). Modelling was conducted for four different scenarios, current scenario, changed precipitation (8% increase), changed temperature (1.07°C increase), and both changed temperature and precipitation. On increasing precipitation a downward shift in the temperate evergreen and tropical semi-evergreen was observed, while sub-tropical conifer and tropical moist-deciduous forests showed a slight upward shift and temperate conifer showed no shift. On increasing temperature, an upward shift in all forest types was observed except sub-tropical conifer forests without significant changes. When both temperature and precipitation were changed, the actual distribution was maintained and slight upward shift was observed in all the forest types except sub-tropical conifer. It is important to understand the likely impacts of the projected climate change on the forest ecosystems, so that better management and conservation strategies can be adopted for the biodiversity and forest dependent community. Knowledge of impact mechanisms also enables identification and mitigation of some of the conditions that increase vulnerability to climate change in the forest sector.  相似文献   
8.
Plant biomass, species diversity and net primary productivity are presented for herb layer of banj oak (Quercus leucotrichophora A. Camus)-chir pine (Pinus roxburghii Sarg.) mixed forest in Kumaun, central Himalaya, India. The species diversity declined from a maximum (3.56) in September to a minimum (2.11) in December. The monthly live shoots biomass exhibited a single peak growth pattern with highest live shoot biomass of 185 g·m-2 in August. The seasonal pattern showed that the maximum above-ground production (131 g·m-2) occurred during the rainy season and the minimum (1 g·m-2) during winter season. The below-ground production was maximum during winter season (84 g·m-2) and minimum during summer season (34 g·m-2). The annual net shoot production was 171 g·m-2 and total below-ground production was 165 g·m-2. Of the total input 61% was channeled to above-ground parts and 39% to below-ground parts. Transfer of live shoots to dead shoots compartments and that of dead shoots to litter compartments was 61% and 66%, respectively. The total dry matter disappearance was 61% of the total input within annual cycle. The herb layer showed a net accumulation of organic matter, indicating the seral nature of the community.  相似文献   
9.
10.
The population of the freshwater animal was declined day by day due to the degradation of habitat and use of illegal fishing methods, which cause a great threat to these aquatic animals. The main purpose of this study was to scrutinize the wild population and fecundity of freshwater prawn Macrobrachium assamense peninsulare in Rawasan stream to assess the health status of prawn. Fecundity was estimated by a random sampling of prawn from five selected sites of Rawasan stream. A wild collection of a total of 35 ovigerous females was collected for an interval of 2 years (August 2013–July 2015) from May to September month, that is breeding session. The maximum number of eggs was 102 eggs in an individual having 52 mm total length and 2.66 g body weight. It was concluded that fecundity of Macrobrachium assamense peninsulare was low, and egg dimension was larger than other closely related species of freshwater prawn. Fecundity of Macrobrachium assamense peninsulare showed a positive relationship with a total weight (R2 = .71) and moderate with the total length (R2 = .38). A strong correlation exists between egg mass and total weight, and between egg mass and total length of female (R2 = .849 and R2 = .77 at p < .05) respectively. The numbers of eggs, that is fecundity, in a female were increased with the body growth of an individual, which results in a linear graph.  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