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   399篇
  免费   28篇
林业   28篇
农学   33篇
基础科学   9篇
  98篇
综合类   21篇
农作物   43篇
水产渔业   26篇
畜牧兽医   135篇
园艺   10篇
植物保护   24篇
  2023年   4篇
  2022年   6篇
  2021年   7篇
  2020年   14篇
  2019年   12篇
  2018年   16篇
  2017年   25篇
  2016年   20篇
  2015年   17篇
  2014年   11篇
  2013年   32篇
  2012年   21篇
  2011年   25篇
  2010年   16篇
  2009年   17篇
  2008年   27篇
  2007年   9篇
  2006年   9篇
  2005年   11篇
  2004年   9篇
  2003年   8篇
  2002年   8篇
  2001年   7篇
  2000年   4篇
  1999年   7篇
  1998年   4篇
  1997年   6篇
  1995年   2篇
  1994年   4篇
  1993年   6篇
  1992年   5篇
  1991年   3篇
  1990年   2篇
  1989年   3篇
  1986年   3篇
  1984年   2篇
  1983年   2篇
  1982年   5篇
  1981年   3篇
  1979年   6篇
  1978年   2篇
  1977年   2篇
  1975年   2篇
  1973年   2篇
  1971年   2篇
  1970年   3篇
  1969年   2篇
  1968年   2篇
  1967年   2篇
  1966年   3篇
排序方式: 共有427条查询结果,搜索用时 15 毫秒
101.
Atmospheric general circulation models used for climate simulation and weather forecasting require the fluxes of radiation, heat, water vapor, and momentum across the land-atmosphere interface to be specified. These fluxes are calculated by submodels called land surface parameterizations. Over the last 20 years, these parameterizations have evolved from simple, unrealistic schemes into credible representations of the global soil-vegetation-atmosphere transfer system as advances in plant physiological and hydrological research, advances in satellite data interpretation, and the results of large-scale field experiments have been exploited. Some modern schemes incorporate biogeochemical and ecological knowledge and, when coupled with advanced climate and ocean models, will be capable of modeling the biological and physical responses of the Earth system to global change, for example, increasing atmospheric carbon dioxide.  相似文献   
102.
Thirteen BVDV isolates collected in four geographic regions of India between 2000 and 2002 were typed in 5'-UTR. To confirm results of genetic typing, selected viruses were also analysed in the N(pro) region. Phylogenetic analysis revealed that all Indian BVDV isolates belong to BVDV-1b (Osloss-like group). Despite a long distance between the farms from which the viruses were isolated there was no correlation between the origin of viral isolates and their position in a phylogenetic tree. Higher genetic similarity of Indian BVDV isolates was observed most probably due to the uncontrolled movement of cattle as well as the uncontrolled use of semen from bulls for breeding of local and farm cattle in different states of India.  相似文献   
103.
Summary Microbial populations were estimated in four different forest stands at different regenerational stages, two each at higher and lower altitudes. The fungal and bacterial populations showed marked seasonal variations at both altitudes. Quantitatively, the bacterial population was higher than the fungal population. Although 25 fungal species were isolated at the lower altitude, only 15 were obtained at the higher altitude. Penicillium chrysogenum and Trichoderma viride were dominant at the lower and higher altitudes, respectively. In the more degraded forest stand at the lower altitude both the fungal and the bacterial population showed a significant positive correlation with organic C (r=0.658 and 0.735, respectively), whereas in the less degraded forest stand there was a significant correlation only between the fungal population and organic C (r=0.835). At the higher altitude, however, a highly significant correlation (P<0.05) was observed between the fungal population, soil moisture and organic C in both the forest stands. Disturbance to the soil and vegetation adversely affected the microbial population, and also affected endogonaceous spores. At the lower altitude, plants in the more degraded forest stand were more mycotrophic compared to those in the less degraded stand. The level of mycorrhizal infection showed a highly positive correlation with soil moisture, organic C, total N, and available P. The spore population, however, was correlated negatively with these parameters. Three different endogonaceous genera, Glomus, Gigaspora, and Acaulospora, were identified during the course of investigation. Glomus, however, was dominant.  相似文献   
104.
A field investigation was conducted at the Indian Agricultural Research Institute's Research Farm during the kharif (wet) seasons of 2002 and 2003 in a split plot design with three replications, consisting of 27 treatments, namely, main plots: three varieties (PRH-10, Pusa Sugandh-3 and Pusa Basmati-1) and three plant spacings (20 × 10, 20 × 15 and 20 × 20 cm2) and sub-plots: three levels of nitrogen (0, 80 and 160 kg N ha?1). The research results indicated that aromatic rice hybrid PRH-10 produced 33 and 6%, respectively, more grain yield than that of Pusa Sugandh-3 and Pusa Basmati-1. The appreciable higher grain yield of PRH-10 over Pusa Sugandh-3 and Pusa Basmati-1 was due to considerable improvement in most of the yield attributing characters. Application of 160 kg N ha?1 recorded 23.7 and 26.1% more grain yield over no nitrogen application whereas it was 6.4 and 6.1% more over 80 kg N ha?1, respectively, during first and second year of the experimentation. Wider plant spacing of 20 × 20 cm2 and application of 160 kg N/ha recorded significantly higher hulling, milling and head rice recovery compared to closer spacing and zero nitrogen application.  相似文献   
105.
The aim of this study was to evaluate dietary dosages of Microcystis on the immune response and disease resistance against infections due to the opportunistic pathogen Aeromonas hydrophila in Labeo rohita fingerlings. Labeo rohita fingerlings were fed diet containing 0 (Control), 0.5, 1.0 and 5 g Microcystis powder kg?1 dry diet for 90 days. Three replicate groups of fish averaging 20 ± 2 g were fed for 3 months daily. At 30 days interval, samples were assayed for different biochemical [serum total protein, albumin, globulin, albumin:globulin (A:G) ratio] and immunological (superoxide anion production, lysozyme and serum bactericidal activity) parameters. The results demonstrate that fish fed Microcystis showed increased levels of lysozyme, serum bactericidal activity, serum protein and albumin (P ≤ 0.05) as compared with the control group. After 90 days, fish were challenged with A. hydrophila and mortality (%) was recorded up to day 10 postchallenge. The group fed 1.0 g Microcystis kg?1 dry diet showed the highest percentage survival (72%). These results indicate that Microcystis aeruginosa stimulates the immunity and makes L. rohita more resistant to infection by A. hydrophila when fed in dried form in feed.  相似文献   
106.
Dietary fiber(DF)was considered an antinutritional factor due to its adverse effects on feed intake and nutrient digestibility.However,with increasing evidence,scientists have found that DF has enormous impacts on the gastrointestinal tract(GIT)development,digestive physiology,including nutrient digestion,fermentation,and absorption processes of poultry.It may help maintain the small and large intestine’s integrity by strengthening mucosal structure and functions and increasing the population and diversity of commensal bacteria in the GIT.Increasing DF content benefits digestive physiology by stimulating GIT development and enzyme production.And the inclusion of fiber at a moderate level in diets also alters poultry growth performance.It improves gut health by modulating beneficial microbiota in the large intestine and enhancing immune functions.However,determining the source,type,form,and level of DF inclusion is of utmost importance to achieve the above-noted benefits.This paper critically reviews the available information on dietary fibers used in poultry and their effects on nutrient utilization,GIT development,gut health,and poultry performance.Understanding these functions will help develop nutrition programs using proper DF at an appropriate inclusion level that will ultimately lead to enhanced DF utilization,overall health,and improved poultry growth performance.Thus,this review will help researchers and industry identify the sources,type,form,and amount of DF to be used in poultry nutrition for healthy,costeffective,and eco-friendly poultry production.  相似文献   
107.
A survey for the parasitic alga. Cephaleuros virescens Künze in relation to its seasonal distribution in different forest types has been done. The alga was absent in gymnosperms and was common in angiosperms. The disease severity was more in summer and the rainy season and absent in winter, Combretum decandrum was found to be most susceptible to this parasite alga. Altogether 49 hosts were recorded out of which 26 were new host records. Healthy leaves contain higher amounts of total nitrogen and total phenol, whereas in algal infected leaves the amounts of total sugar, total amino acid and dry weight were higher.  相似文献   
108.
OBJECTIVE: To examine associations between shopping, food preparation, meal and eating behaviours and fruit and vegetable intake among women. DESIGN: Cross-sectional survey. SETTING: Community-based sample from metropolitan Melbourne, Australia. SUBJECTS: A sample of 1136 women aged 18-65 years, randomly selected from the electoral roll. RESULTS: Food-related behaviours reflecting organisation and forward-planning, as well as enjoyment of and high perceived value of meal shopping, preparation and consumption were associated with healthier intakes of fruits and vegetables. For example, women who more frequently planned meals before they went shopping, wrote a shopping list, enjoyed food shopping, planned in the morning what they will eat for dinner that night, planned what they will eat for lunch, reported they enjoy cooking, liked trying new recipes and who reported they sometimes prepare dishes ahead of time were more likely to consume two or more servings of vegetables daily. Conversely, women who frequently found cooking a chore, spent less than 15 minutes preparing dinner, decided on the night what they will eat for dinner, ate in a fast-food restaurant, ate takeaway meals from a fast-food restaurant, ate dinner and snacks while watching television and who frequently ate on the run were less likely to eat two or more servings of vegetables daily. CONCLUSIONS: Practical strategies based on these behavioural characteristics could be trialled in interventions aimed at promoting fruit and vegetable consumption among women.  相似文献   
109.
The Dig-labeled probe specific to Babesia bigemina generated from monomorphic RAPD fragment of approximately 873 bp size amplified by a 10 mer CGGTGGCGAA, detected up to 100 ng of template DNA. This nonradioactive probe also detected B. bigemina in preparations of larval tick DNA from two of the five samples on dot-blot hybridization.  相似文献   
110.
Madhuca longifolia (Koenig) J. F. Macbride is native to India. Seeds contain 20–50% oil (Mahua oil) and the seed cake is used as manure. Mahua oil is used by rural communities for protection against storage pests. Almost all parts of this tree have medicinal properties. Four explorations and collection missions was conducted during July–October 2007 in Tamil Nadu and the Union Territory of Puducherry. This resulted in the collection of 55 accessions. Characterisation and analysis of 7 seed characters were done. The existence of enormous variability in seed length, thickness and 100 seed weight indicates scope for utilization of these accessions for selection of promising material for extraction of oil. Oil content of kernels has been evaluated. Kernel oil ranged from 44.43 to 61.50%. Three accessions IC556617 with 61.50, IC556632 with 60.80 and IC556632 with 60.55% of kernel oil are superior to the rest. Further collections in the site of these oil rich accessions are promising for more productive Madhuca longifolia genetic resources.  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