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   296篇
  免费   21篇
林业   27篇
农学   8篇
基础科学   3篇
  85篇
综合类   5篇
农作物   44篇
水产渔业   45篇
畜牧兽医   56篇
园艺   8篇
植物保护   36篇
  2023年   1篇
  2022年   9篇
  2021年   13篇
  2020年   11篇
  2019年   21篇
  2018年   23篇
  2017年   31篇
  2016年   24篇
  2015年   18篇
  2014年   14篇
  2013年   49篇
  2012年   15篇
  2011年   18篇
  2010年   15篇
  2009年   10篇
  2008年   12篇
  2007年   9篇
  2006年   2篇
  2005年   2篇
  2004年   2篇
  1998年   1篇
  1992年   2篇
  1990年   3篇
  1989年   1篇
  1988年   2篇
  1983年   4篇
  1981年   1篇
  1980年   1篇
  1976年   1篇
  1973年   2篇
排序方式: 共有317条查询结果,搜索用时 46 毫秒
81.
Aquaculture International - Astaxanthin (AX) is one of the commonly used feed supplements to enhance the growth performance and provide antioxidant and immune functions of several aquatic animals....  相似文献   
82.
In order to investigate the effects of different iron (Fe) sources (nano iron (Fe)-chelate, Fe- ethylenediamine-di(o-hydroxy phenyl acetic acid (EDDHA) and iron (II) sulfate (FeSO4)) on lettuce (Lactuca sativa) growth in alkaline solutions, an experiment was arranged in hydroponic system. This study showed that leaf Fe content and overall plant growth was significantly increased by Fe-chelate application, and the highest values of leaf Fe, plant pigments and vegetative growth were recorded in plants treated with nano Fe-chelate. The lowest Fe, chlorophyll, carotenoids and soluble sugars in leaves were observed in FeSO4 treatment. There were no difference in soluble sugars contents of plants between nano Fe-chelate and Fe-EDDHA treatments. Fertilization of lettuce plants with different Fe-chelate sources had a beneficial effect on the manganese (Mn) and zinc (Zn) uptake in plants. It is concluded that application of chelated form of Fe (especially nano Fe-chelate) must be performed in hydroponic system with alkaline water, to overcome Fe deficiencies and to make better nutritional status.  相似文献   
83.
84.
Column experiments were conducted over 45 d to determine the degree of P mobility. The sandy loam soil was spiked with 200 mg P kg–1 and 5% organic residues. The treatments included: control without any water‐soluble P and plant residues, potato, wheat, water‐soluble P fertilizer, wheat + water‐soluble P, and potato + water‐soluble P. Each column was leached with distilled water, and leachates were collected and analyzed for P, K+, Ca2+, Mg2+, along with pH and EC. Sequential extraction was performed on soil samples at the end of leaching column experiments. The relatively high initial concentration of P in the leachates decreased to more stable values after 15 d which can be attributed to the colloid‐bound P. The P concentrations in the leachates fluctuated between 8 and 220 mg L–1 in the water‐soluble–P fertilizer treatment, between 0.80 and 230 mg L–1 in the potato + water‐soluble‐P treatment, and between 0.90 and 214 mg L–1 in the wheat + water‐soluble P treatment. Leaching loss of P mainly occurred in the 15 d of leaching, accounting for 94%, 88%, and 65% of total P leached in wheat + water‐soluble‐P, potato + water‐soluble‐P, and water‐soluble‐P treatments, respectively. Maximum amount of P leached was found from an exponential kind model and was in the range 0.45 mg kg–1 to 125.4 mg kg–1 in control and potato + water‐soluble‐P treatments, respectively. Sequential extraction results showed that in control and amended soils the major proportion of P was associated with Ca. The leachate samples in all treatments were saturated with respect to hydroxyapatite, β‐tricalcium phosphate, and octacalcium phosphate up to 20 d of leaching, whereas they were undersaturated with respect to Mg‐P minerals through the entire leaching experiment.  相似文献   
85.
We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl2‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.  相似文献   
86.
An investigation was made of the action of the juvenile hormone analogues (JHAs) methoprene (ZR-515) and 3-[5-(4-ethylphenoxy)-3-methylpent-3-enyl]-2, 2-dimethyloxirane (R-20458), and the insecticides chlorpyrifos and methomyl, when applied, separately or in combination, to the late insect stages of susceptible (S) and aminocarb-resistant (Rm) strains of Spodoptera littoralis Boisd. Sixth-instar larvae of the Rm strain showed detectable levels of cross-resistance to chlorpyrifos, methomyl and R-20458. However, cross-resistance to methoprene was less pronounced in the Rm strain. Treatment of the same instar with the ED50 of methoprene produced an appreciable level of sterility in the S strain, but this level decreased in the Rm strain. Similar treatment with R-20458 caused a lower level of sterility in the S strain and the Rm strain was less affected. In the S strain, the ED25 of either chlorpyrifos or methomyl when applied simultaneously with the ED25 of R-20458, produced an antagonistic effect and the Rm strain was more capable of resisting the joint action of these compounds. The treatment, ED25 chlorpyrifos + ED25 methoprene produced an additive effect on the S strain, while the Rm strain tolerated their combined action. Nevertheless, the treatment, ED25 methomyl + ED25 methoprene produced additive effects on both the S and Rm strains. The prepupae of the Rm strain tolerated the action of the insecticides methomyl and chlorpyrifos. A similar pattern of cross-resistance was also detected against the action of the two hormones at the ED25 level, while at the ED25 level, both the S and Rm strains were almost equally sensitive to the action of the two juvenoids. Chlorpyrifos-JHA combinations produced additive effects on prepupae of the S strain while the Rm strain completely resisted their joint action. Methomyl-JHA combinations produced high potentiation in the S strain, but the Rm strain remained insensitive to their joint action. Detectable levels of tolerance to the action of chlorpyrifos and methomyl at the ED25 and ED50 levels were indicated in 2-day-old pupae of the Rm strain. This was less evident in the case of JHAs, particularly methoprene, which was to some extent equally effective on both strains; the reproductive ability of the S and Rm strains was highly affected by this compound. The pupae of the Rm strains were equally as affected as those of the S strain by the combination ED25 chlorpyrifos+ ED25 R-20458. Nevertheless, the two strains showed antagonism to the action of chlorpyrifos with methoprene. A high level of potentiation was produced in the S strain to the combination of methomyl and R-20458 but the Rm strain was able to withstand their combined action. Of interest in this respect was the action of the combination of methomyl and methoprene, for which high levels of potentiation were detected in pupae of the S and Rm strains. This combination also Produced a high percentage of sterility in mated females of the Rm strain.  相似文献   
87.
Veterinary Research Communications - Industrial chemical solutions are widely used as a method to disinfection of aquaculture water and environments. The aim of the present study was to evaluate...  相似文献   
88.
A field experiment was conducted on Indian mustard (Brassica juncea) with five levels of sulfur (S), 0, 15, 30, 45, and 60 kg S ha?1 in sub-tropical Inceptisol of Jammu, North India. The residual effect of S on rice crop was evaluated. The seed and stover yield of mustard increased in the linear order up to 60 kg S ha?1 but significant yield increase was obtained up to 30 S kg ha?1 which was 21.4 percent higher in comparison to the yield obtained in control. The uptake of S at maturity was significantly affected with all the levels of S application. The seed S uptake increased significantly up to 30 kg S ha?1 and stover 45 kg S ha?1. The residual effect of S was convincing in enhancing the rice yield to the tune of 5.3% over control, but was statistically non-significant. The S uptake was also favourably influenced by the residual S which was evidenced through increased S use efficiency. Agronomic and physiological efficiency as well as S recovery were all greatly influenced by direct and residual effect of S. Apparent S recovery was higher at 30 kg S ha?1 in mustard (12.06%).  相似文献   
89.
Chu  Demiao  Yao  Tao  Zhou  Liang  Yan  Hanwei  Yu  Min  Liu  Yamei  You  Yunfei  Bahmani  Mohsen  Lu  Changqing  Ding  Zhenhao  Liu  Shengquan 《European Journal of Forest Research》2022,141(1):59-69

This work focuses on the genetic variation of Chinese fir clones in the radial direction. Four 20-year-old Chinese fir clones were selected in Kaihua Forest Farm, Zhejiang, China, and the differences and genetic characteristics were studied. Clonal repeatability, genotype coefficient of variable, and phenotypical coefficient of variable were calculated to light on the genetic variation on the radial direction. Results showed significant differences (P?<?0.05) between the clones and annual rings of the same clone. The clonal repeatability of the ten wood properties is ranged from 0.5 to 0.8, wherein the fiber length, elastic modulus, and total dry density are higher than 0.7. For all the measured traits, the phenotypic variation of clones is greater than that of the genetic variation. Overall, the measured wood traits, especially the mechanical and physical properties, are strongly controlled by heredity, which means they are potentially helpful for genetic improvement of wood properties and optimal breeding. Furthermore, the clonal repeatability of the measured traits varies between annual rings, and the physical and mechanical properties are relatively stable. The principal component analysis results reveal that the clone of Kai 13 has the highest score.

  相似文献   
90.
The objectives of this study were to determine the effects of nitrogen (N) forms and deficient and toxic rates of boron (B) on the growth, NO3 accumulation, membrane permeability, mineral nutrition, and nitrogen use efficiency (NUE) of bunch onion (Allium cepa L. var. Radar) plants. Therefore, 20% of NO3 in reference nutrient solution was replaced by NH4, urea, or mixed amino acids (AA). To each of these solutions 3, 30, or 300 mmol m?3 B was added. Fresh and dry weights were the same in the reference and mixed AA treatments, but NH4 and urea decreased these growth parameters as compared to the reference. Mixed AA decreased the NO3-N content while urea increased it, and NH4 treatment yielded similar NO3-N content as compared to the reference. The nitrogen content of plants was increased by NO3 replacement with either NH4 and, urea or mixed AA. At the 300 mmol m?3 B rate, B content of plants was decreased by NH4 and urea, but increased by the mixed AA treatment. Membrane permeability was increased by NH4?replacement of NO3. Nitrogen use efficiency was found the highest in the reference treatment. Nitrogen and NO3-N contents were increased by the 300 mmol m?3 B rate. Increasing B in nutrient solution increased the B contents of plants. Mixed AA treatment decreased the phosphorus (P) content of plants. Potassium (K) and chloride (Cl) contents of plants were decreased in the NH4 treatment where B was applied at the 3 mmol m?3 rate. These results suggest that bunch onion growers may reduce NO3 content in onion tops by partially replacing NO3 with amino acids without reducing yield.  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