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   346篇
  免费   24篇
  国内免费   2篇
林业   18篇
农学   26篇
基础科学   5篇
  80篇
综合类   55篇
农作物   35篇
水产渔业   26篇
畜牧兽医   86篇
园艺   5篇
植物保护   36篇
  2023年   2篇
  2022年   12篇
  2021年   16篇
  2020年   15篇
  2019年   18篇
  2018年   15篇
  2017年   11篇
  2016年   11篇
  2015年   15篇
  2014年   12篇
  2013年   25篇
  2012年   10篇
  2011年   28篇
  2010年   7篇
  2009年   11篇
  2008年   14篇
  2007年   22篇
  2006年   8篇
  2005年   15篇
  2004年   13篇
  2002年   4篇
  2001年   9篇
  2000年   5篇
  1999年   3篇
  1998年   2篇
  1997年   3篇
  1994年   2篇
  1993年   3篇
  1992年   3篇
  1991年   2篇
  1990年   6篇
  1989年   2篇
  1988年   2篇
  1987年   6篇
  1986年   4篇
  1985年   6篇
  1984年   7篇
  1983年   3篇
  1980年   3篇
  1979年   2篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1962年   1篇
排序方式: 共有372条查询结果,搜索用时 31 毫秒
71.
我国油菜根肿病发病面积在66.7万公顷左右,约占总生产面积的10%,已严重威胁到油菜的安全生产。基于此,本研究以含有CRb抗根肿病位点的大白菜材料CR Shinki为供体亲本,以甘蓝型油菜国审杂交种华油杂62的父本Pol.CMS恢复系Bing409为受体亲本,通过杂交、回交及自交等育种程序,结合前景和遗传背景筛选,将CRb抗病位点导入到Bing409中。在BC3F2代获得了遗传背景高度接近Bing409且含CRb抗病位点的抗根肿病新恢复系Bing409R,进而成功选育了我国首个抗根肿病杂交油菜新品种华油杂62R。CRb抗病位点在甘蓝型油菜背景中表现为单基因显性遗传,根肿病抗性遗传改良的同时并未对Bing409R及由其配制的杂交种华油杂62R的产量、品质造成不良影响,Bing409R及华油杂62R对我国四川、湖北、安徽等地区根肿菌生理小种具有免疫抗性。本研究的开展为我国油菜抗根肿病育种提供了宝贵资源,为我国抵抗油菜根肿病的威胁提供了重要保障。  相似文献   
72.
Animal protein in broiler rations was replaced with Barseem Protein Concentrate (BPC). The standard group having blood, meat and fish meal as sources of animal protein showed an average weight gain of 1655 g. Replacement of blood meal with BPC resulted in a slight decrease in the average weight gain (1541 g) of broilers. Average weight gain of broilers increased to 1775 g and 1671 g when fish or meat meal was replaced with BPC in rations. Complete replacement of animal protein with BPC adversely affected growth and average weight gain decreased to 1443 g. Supplementation with lysine or methionine when animal protein was replaced with BPC did not improve growth of the broilers.  相似文献   
73.
Cr3+ sorption on strong acid exchanger Amberlyst-15(H+) is studied as a function of time and temperature using CrCl3.6H2O and [Cr4(SO4)5(OH)2] solutions. The rate is found to be governed by a mixed diffusion for both the solutions and faster for Cl1? solution than SO4 2?. The exchange capacities are found to be higher for Cl1? system than SO4 2?. From the rate constant values, the energies of activation are calculated using the well-known Arrhenius equation. Equilibrium data is explained with the help of the Langmuir equation. The Langmuir parameters are also found to be higher for exchange from the chloride solutions. Various thermodynamic parameters (??Ho, ??So, and ??Go) for Cr3+ exchange on the resin are calculated. The ??Go values are found to be negative while ??Ho and ??So are positive for both the Cr3+/Cl1? and Cr3+/SO4 2? systems. It is suggested that in case of Cl1? solutions, the metal is exchanged as Cr3+, while in case of SO4 2? solutions, the metal exchanging specie is CrSO4 +.  相似文献   
74.
Tropical Animal Health and Production - The current experiment was performed to find the potential effect of inorganic and organic forms of zinc (Zn) on growth, intestinal histomorphology, immune...  相似文献   
75.
Six undescribed polyhydroxy p-terphenyls, namely asperterphenyllins A–F, were isolated from an endophytic fungus Aspergillus candidus LDJ-5. Their structures were determined by NMR and MS data. Differing from the previously reported p-terphenyls, asperterphenyllin A represents the first p-terphenyl dimer connected by a C-C bond. Asperterphenyllin A displayed anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values of 53 μM and 21 μM, respectively. The anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity of p-terphenyls are reported for the first time. Asperterphenyllin G exhibited cytotoxicity against nine cell lines with IC50 values ranging from 0.4 to 1.7 μM. Asperterphenyllin C showed antimicrobial activity against Proteus species with a MIC value of 19 μg/mL.  相似文献   
76.
The use of appropriate source of phosphorus (P) fertilizer at different planting densities has considerable impact on growth, grain yield as well as profitability of maize (Zea mays L). Field experiment was conducted in order to investigate the impact of P sources [(S0 = P not applied, S1 = SSP (single super phosphate) S2 = NP (nitrophos), and S3 = DAP (diammonium phosphate)] on maize growth analysis, yield and economic returns planted at different planting densities (D1 = 40,000, D2 = 60,000, D3 = 80,000, and D4 = 100,000 plants ha?1) at the New Developmental Agricultural Research Farm of Khyber Pakhtunkhwa Agricultural University, Peshawar, Pakistan, during summer 2006. This paper reports the profitability data with two objectives: 1) to compare agronomic efficiency and profitability of P-fertilizers, and 2) to know whether plant densities affect agronomic efficiency and profitability of P-fertilizers. Application of DAP and SSP resulted in higher partial factor productivity (PFP) (63.58 and 61.92 kg grains kg?1 P), agronomic efficiency (AE) (13.01 and 13.71 kg grains kg?1 P) and net returns (NR) (Rs. 16,289 and 16,204 ha?1), respectively, while NP stood at the bottom in the ranking with lower PFP (57.16 kg grains kg?1 P), AE (8.94 kg grains kg?1 P) and NR (Rs. 4,472 ha?1). Among the plant densities, D3 stood first with maximum PFP (69.60 kg grains kg?1 P), AE (18.21 kg grains kg?1 P) and NR (Rs. 21,461 ha?1) as compared to other plant densities. In conclusion, the findings suggest that growing maize at D3 applied with either SSP or DAP is more profitable in the wheat-maize cropping system in the study area.  相似文献   
77.
Abstract

Soil organic carbon (SOC) sequestration is one of the major agronomic measures to mitigate green house gas emission, enhance food security, and improve agriculture sustainability. The study, therefore, aimed to evaluate crop growth (CG) and radiation use efficiency in spring wheat (Triticum aestivum L.) treated soil with residue type (RT), that is, cowpea (Vigna unguiculata) as legume (LR), maize (Zea mays L.) as cereal (CR) and no residue (NR) treatment applied (5 t ha?1) on dry matter basis. The CR was subsequently incorporated with tillage depths (TD), that is, deep (DT?=?35?cm) and shallow (ST?=?15?cm) as main plot treatments. The N was applied in two splits starting from 0 to 160?kg ha?1 as sub plot treatments. Experiment was conducted in two CG seasons 2009–11 at Agronomy Research Farm, the University of Agriculture Peshawar, Pakistan. Results showed the highest CG and RUE with LR incorporated than CR and/or NR with DT. Increasing N-rate resulted an increase in CG, RUE and biomass of wheat. Residue of LR or CR deeply incorporate into the soil has resulted healthy traits (i.e., tillers- and spikes number), which resulted higher biomass. Nitrogen applied 120?kg ha?1 resulted in higher CG, RUE and grain yield for treatment LR, followed by CR and the lowest for the NR. Crop of second year showed higher grain yield, which was due to healthy traits including better CG and RUE. The study suggests that CR of LR or CR nature incorporated deep into the soil can optimize crop N-fertilizer demand for optimum production, which protects environment from the excessive use of N application.  相似文献   
78.
Barley plants were grown hydroponically at two levels of K (3.0 and 30 mm) and Fe (1.0 and 10 μm) in the presence of excess Mn (25 μm) for 14 d in a phytotron. Plants grown under adequate K level (3.0 mm) were characterized by brown spots on old leaves, desiccation of old leaves, interveinal chlorosis on young leaves, browning of roots, and release of phytosiderophores (PS) from roots. These symptoms were more pronounced in the plants grown under suboptimal Fe level (1.0 p,M) than in the plants grown under adequate Fe level (10 μm). Plants grown in 10 μm Fe with additional K (30 mm) produced a larger amount of dry matter and released less PS than the plants grown under adequate K level (3.0 mm), and did not show leaf injury symptoms and root browning. On the other hand, the additional K supply in the presence of 1.0 μM Fe decreased the severity of brown spots, prevented leaf desiccation, and increased the leaf chlorophyll content, which was not sufficient for the regreening of chlorotic leaves. These results suggested that the additional K alleviated the symptoms of Mn toxicity depending on the Fe concentration in the nutrient solution. The concentration (per g dry matter) and accumulation (per plant) of Mn in shoots and roots of plants grown in 10 μm Fe and 30 mm K were much lower than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that additional K repressed the absorption of Mn. The concentration and accumulation of Fe in the shoots and roots of the plants grown in 10 μm Fe and 30 mm K were higher than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that the additional K increased the absorption of Fe under excess Mn level in the nutrient solution. The release of PS, chlorophyll content, and shoot Fe concentration were closely correlated.  相似文献   
79.
The release of phytosiderophore (PS) from roots of Fe-deficient graminaceous plants follows a distinct diurnal rhythm with maximum release rates occurring usually 3 to 4 hours after the onset of light. However, it remains to be determined whether absorption of the PS-Fe3+ complex shows a diurnal rhythmicity similar to that of PS release, Barley plants grown with or without 10 µM FeEDTA for 7 days were fed with ferreted PS (10 µM labelled with 59Fe) at 4-h intervals to study the diurnal variations in the absorption and transloca tion of 59Fe, The absorption of 59Fe, irrespective of the Fe nutritional status of the plants, was higher during the day and lower during the night but did not show any peak throughout the day-night cycle. On the other hand, the translocation of 59Fe into shoots of Fe-deficient plants was lower than that of Fe-sufficient plants, while the Fe nutritional status of the plants did not affect the absorption of 59Fe by roots, The formation of root apoplastic 59Fe was lower during the day and higher during the night, regardless of the Fe nutritional status of plants. Our results showed that the absorption of the PS-Fe3+ complex by roots did not follow the PS release pattern.  相似文献   
80.
The mechanisms of iron (Fe) absorption and translocation in plants have received much study because they are the key processes in the supply of Fe to plants. The objective of this research was to study the effectiveness of phytosiderophore (PS) in the absorption and translocation of 59Fe in Fe-deficient barley (Hordeum vulgare L. cv. ‘Minorimugi’) plants in the presence of plant-borne, synthetic, or microbial chelators. Plants grown under Fe-deficient conditions in a phytotron at pH 5.5 for 7–18 d were fed with Fe3+ (10 μ M labeled with 59Fe) in the presence of 10 μ M of different chelators with or without 10 μ M PS for 4 h starting at 2 p.m. (6 h after the onset of light period). The absorption and translocation of 59Fe in plants treated with PS and Fe3 + were increased relative to plants fed solely with Fe3 + (control). There was no effect found on absorption and translocation of 59Fe in plants treated with EDTA or p-coumarate relative to the control, but a differential increase was observed in 59Fe absorption and translocation in plants treated with EDTA or p-coumarate in the presence of PS. In comparison with the control, a decrease in 59Fe absorption and translocation was observed in plants treated with HEDTA or EDDHA or FOB, but this decrease was avoided in plants treated with HEDTA or EDDHA or FOB in the presence of PS. The enhancement of 59Fe absorption and translocation in plants treated with citrate, and the highest 59Fe absorption and translocation in plants treated with citrate and PS, indicated that citrate had an additive effect on Fe absorption and translocation in plants. Our results showed that PS effectively played a role in Fe absorption and translocation in plants in the presence of other chelators. Plants treated with any chelators had lower extracellular 59Fe in the roots compared with the control.  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