全文获取类型
收费全文 | 1179篇 |
免费 | 63篇 |
国内免费 | 2篇 |
专业分类
林业 | 135篇 |
农学 | 88篇 |
基础科学 | 15篇 |
291篇 | |
综合类 | 85篇 |
农作物 | 101篇 |
水产渔业 | 91篇 |
畜牧兽医 | 304篇 |
园艺 | 18篇 |
植物保护 | 116篇 |
出版年
2023年 | 8篇 |
2022年 | 23篇 |
2021年 | 34篇 |
2020年 | 37篇 |
2019年 | 34篇 |
2018年 | 46篇 |
2017年 | 53篇 |
2016年 | 42篇 |
2015年 | 29篇 |
2014年 | 47篇 |
2013年 | 111篇 |
2012年 | 69篇 |
2011年 | 77篇 |
2010年 | 62篇 |
2009年 | 52篇 |
2008年 | 56篇 |
2007年 | 24篇 |
2006年 | 40篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 33篇 |
2002年 | 32篇 |
2001年 | 35篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 7篇 |
1968年 | 7篇 |
排序方式: 共有1244条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Mohammad Nakib Dad Khan Takao Yoshimatsu Alok Kalla Toshiyoshi Araki Shuichi Sakamoto 《Fisheries Science》2008,74(2):397-404
ABSTRACT: A 56-day feeding trial was conducted to evaluate the effects of Porphyra spheroplasts (PS) as a feed additive on growth, carcass composition and feed utilization of black sea bream. Four experimental diets with or without PS (0, 1, 3, 5% inclusion level) were formulated to determine the proper incorporation level for best growth and utilization using white fishmeal as the principal protein source. Three replicate groups of fish averaging 1.28 ± 0.05 g (mean ± SD) were maintained in flow-through thermo-controlled sea water (32–34 psu, 25°C) aquaria (100 L) under the laboratory conditions (L12 : D12) and fed three times a day at 09:00, 13:00 and 17:00 hours by hand at approximately 3% body weight on each diet. The rearing trial revealed that growth performance (in terms of weight gain, specific growth rate) are almost the same level in all the dietary groups, nevertheless the survival, nutrient utilizations and retentions (feed efficiency, protein efficiency ratio, protein retention rate, lipid retention rate) were significantly higher ( P < 0.05) in a group fed on the diet containing 3% spheroplasts. Further, the fish fed on the diet containing PS had significantly higher ( P < 0.05) crude lipid level in their dorsal muscles and viscera. The fish fed a PS-based diet showed higher level of eicosapentaenoic acid and docosahexaenoic acid (DHA) in viscera and DHA in dorsal muscles. The results obtained in this feeding trial suggest that the optimum dietary PS supplementation level up to 3% for black sea bream can be considered as improved consequence on growth performance, nutrient utilization or body composition were noticed. 相似文献
995.
Muhammad Arif Salman Ali Muhammad Ilyas Muhammad Riaz Kashif Akhtar Kawsar Ali Muhammad Adnan Shah Fahad Imran Khan Shahen Shah Haiyan Wang 《Soil Use and Management》2021,37(1):104-119
Biochar amendments offer promising potential to improve soil fertility, soil organic carbon (SOC) and crop yields; however, a limited research has explored these benefits of biochar in the arid and semi‐arid regions. This two‐year field study investigated the effects of Acacia tree biomass‐derived biochar, applied at 0 and 10 t ha?1 rates with farmyard manure (FYM) or poultry manure (PM) and mineral phosphorus (P) fertilizer combinations (100 kg P ha‐1), on maize (Zea mays L.) productivity, P use efficiency (PUE) and farm profitability. The application of biochar with organic–inorganic P fertilizers significantly increased soil P and SOC contents than the sole organic or inorganic P fertilizers. Addition of biochar and PM as 100% P source resulted in the highest soil P (104% increase over control) and SOC contents (203% higher than control). However, maize productivity and PUE were significantly higher under balanced P fertilizer (50% organic + 50% mineral fertilizer) with biochar and the increase was 110%, 94% and 170% than 100%‐FYM, 100%‐PM and 100% mineral fertilizer, respectively. Maize productivity and yield correlated significantly positively with soil P and SOC contents These positive effects were possibly due to the ability of biochar to improve soil properties, P availability from organic–inorganic fertilizers and SOC which resulted in higher PUE and maize productivity. Despite the significant positive relationship of PUE with net economic returns, biochar incorporation with PM and mineral fertilizer combination was economically profitable, whereas FYM along biochar was not profitable due to short duration of the field experiments. 相似文献
996.
Continuous rise in the atmospheric CO2 concentration upshots the genesis of cataclysmic planetary problems such as global warming and climate change. Another critical issue which is environmentally challenging is land degradation. When productive land is poorly managed, it turns to marginal land. And further degradation of marginal land ends up to being unproductive land. On the Contrary, considerable part of depleted soil C pool can be restored through the adoption of conservation agricultural practices, unproductive land could be converted to marginal land and by its further restoration, into productive land. Aromatic plants can sustain various adverse conditions prevailing on the marginal lands. Aromatic plants require low input but the output is quite high due to the production of highvalue essential oil. The pivotal perspective of utilization of marginal lands of India for the production of aromatic plants would explore factors such as land availability, aromatic plants adaptability, C sequestration potential and economic feasibility. India is the largest exporter of essential oils and produces huge amount of aromatic spent residues, which could be converted into several valueadded products. Proficient recycle of distillation waste of aromatic plants in marginal lands will aid to sequester C in soil and enhance the biomass yield. Improvement in the livelihood of farmers especially in developing nations through rise in production and income diversification would encourage farmers to reclaim their marginal lands and accelerate their transition to aromatically cultivable lands. 相似文献
997.
Waqas–ud–Din Khan Tariq Aziz Imran Hussain Pia Muhammad Adnan Ramzani Thomas G. Reichenauer 《Archives of Agronomy and Soil Science》2017,63(5):599-611
Soil salinity imposes an unprecedented risk to the soil fertility and availability of plant nutrients. The present proposal is designed to address the effect of salt stress on photosynthetic apparatus of maize including chlorophyll a fluorescence and how silicon nutrition helps to overcome this issue. In a sand culture experiment, two maize cultivars were sown in small pots with two levels of silicon (0 and 2 mM H2SiO3) and two levels of salinity stress (0 and 60 mM NaCl). Salinity stress reduced dry matter yield and potassium (K) concentration in both maize cultivars and also induced inefficient working of photosynthetic apparatus including photochemical efficiency of photosystem II. Silicon addition alleviated NaCl stress on maize crop by improving the dry matter yield and water use efficiency (WUE). It decreased shoot Na concentration by increasing root and shoot K concentration of maize plants. It enhanced maximum quantum yield of primary photochemistry which leads to smooth electron transport chain. It also significantly enhanced shoot silicon concentration and has a significant positive correlation with WUE. Therefore, silicon-treated maize plants have better chance to survive under salt stress conditions as their photosynthetic apparatus is working far better than non-silicon-treated plants. 相似文献
998.
Xu Xiaoli Mao Xiali Van Zwieten Lukas Niazi Nabeel Khan Lu Kouping Bolan Nanthi S. Wang Hailong 《Journal of Soils and Sediments》2020,20(11):3921-3930
Journal of Soils and Sediments - The residual phosphorus (P) in Hedley’s sequential fractionation procedure is considered to be a relatively stable soil P pool and unavailable for plant... 相似文献
999.
Dietary phosphorus requirement of fingerling Labeo rohita (6.1 ± 0.13 cm; 1.88 ± 0.05 g) was quantified by feeding seven isonitrogenous (350 g/kg crude protein) and isocaloric (16.72 kJ/g gross energy) purified diets with different levels of phosphorus as 3.5 (basal diet), 4.6, 5.7, 6.5, 7.8, 8.9, and 10.1 g/kg. Triplicate groups of fish were fed at 0800, 1200, and 1600 h to apparent satiation for 8 wk. Live weight gain (LWG; 494.68%), specific growth rate (3.18%/d), feed conversion ratio (1.54), feed efficiency (0.65), protein gain (PG; 1.26 g/fish), protein efficiency ratio (1.86), and phosphorus utilization efficiency (98.78%) improved significantly (P < 0.05), with increasing dietary phosphorus level up to 6.5 g/kg. However, phosphorus contents of vertebrae and scale increased significantly up to 7.8 g/kg. Dietary phosphorus levels significantly affected serum phosphorus concentration and alkaline phosphatase activity. Broken‐line analysis based on LWG; PG; and whole‐body, vertebrae, and scale phosphorus against dietary phosphorus indicated the optimal phosphorus requirement of fingerling L. rohita at 6.56, 6.58, 6.56, 8.02, and 8.44 g/kg diet, respectively. In order to restrict superfluous phosphorus in the diet, inclusion of 6.56 g/kg phosphorus is recommended for optimal growth of fingerling L. rohita. 相似文献
1000.
Quantification of the impacts of climate warming and crop management on canola phenology in Punjab,Pakistan
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S. Ahmad G. Abbas Z. Fatima R. J. Khan M. A. Anjum M. Ahmed M. A. Khan C. H. Porter G. Hoogenboom 《Journal of Agronomy and Crop Science》2017,203(5):442-452
Yield is influenced by the length of the growing season, which is affected by weather conditions and management practices of a crop, including sowing dates and shifting of cultivars. It is necessary to understand the effects of agronomic management practices and weather variables on phenological stages and crop phases in order to develop strategies for adaptation of agricultural systems to changes in climatic conditions. The goal of this study was to determine the impact of warming trends on phenology of canola from 1980 to 2014 for central and southern Punjab, Pakistan. Sowing, emergence, anthesis and physiological maturity dates were delayed by an average of 6.02, 3.14, 3.31 and 1.89 days per decade, respectively. The duration of sowing to anthesis, sowing to physiological maturity and anthesis to physiological maturity phases decreased an average 2.71, 4.13 and 1.42 days per decade, respectively, for all 10 locations that were analysed in this study. The sowing, emergence, anthesis and physiological maturity dates were positively correlated with an increase in temperature by an average 2.71, 1.41, 1.49 and 0.85 days per °C, respectively. However, the phenological phases such as sowing to anthesis, anthesis to maturity and sowing to maturity were negatively correlated with an increase in temperature by an average of 1.22, 0.64 and 1.86 days per °C, respectively, for all 10 locations. Applying a process‐based CSM‐CROPGRO‐Canola model using a standard cultivar (field tested) for all locations and years indicated that the simulated phenological stages occurred earlier due to the warming trend compared to the observed phenological stages. One‐quarter of the negative effects of this thermal trend was compensated by growing new cultivars that had higher thermal time requirements. Therefore, new canola genotypes with a higher number of growing degree day requirement and high temperature tolerance should be a priority for evolving new cultivars. 相似文献