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   220篇
  免费   12篇
  国内免费   2篇
林业   18篇
农学   20篇
基础科学   2篇
  69篇
综合类   24篇
农作物   26篇
水产渔业   1篇
畜牧兽医   47篇
园艺   7篇
植物保护   20篇
  2023年   2篇
  2022年   10篇
  2021年   11篇
  2020年   11篇
  2019年   9篇
  2018年   17篇
  2017年   11篇
  2016年   11篇
  2015年   8篇
  2014年   15篇
  2013年   25篇
  2012年   14篇
  2011年   13篇
  2010年   17篇
  2009年   8篇
  2008年   7篇
  2007年   10篇
  2006年   10篇
  2005年   5篇
  2004年   1篇
  2003年   1篇
  2002年   3篇
  2001年   2篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1994年   2篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1987年   1篇
  1978年   1篇
  1971年   1篇
排序方式: 共有234条查询结果,搜索用时 109 毫秒
141.
In a 1-year study, quantification of nitrous oxide (N2O) emission was made from a flood-irrigated cotton field fertilized with urea at 100kg N ha−1 a−1. Measurements were made during the cotton-growing season (May–November) and the fallow period (December–April). Of the total 95 sampling dates, 77 showed positive N2O fluxes (range, 0.1 to 33.3g N ha−1 d−1), whereas negative fluxes (i.e., N2O sink activity) were recorded on 18 occasions (range, −0.1 to −2.2g N ha−1 d−1). Nitrous oxide sink activity was more frequently observed during the growing season (15 out of 57 sampling dates) as compared to the fallow period (3 out of 38 sampling dates). During the growing season, contribution of N2O to the denitrification gaseous N products was much less (average, 4%) as compared to that during the fallow period (average, 21%). Nitrous oxide emission integrated over the 6-month growing period amounted 324g N ha−1, whereas the corresponding figure for the 6-month fallow period was 648g N ha−1. Subtracting the N2O sink activity (30.3g N ha−1 and 3.8g N ha−1 during the growing season and fallow period, respectively), the net N2O emission amounted 938g N ha−1 a−1. Results suggested that high soil moisture and temperature prevailing under flood-irrigated cotton in the Central Punjab region of Pakistan though favor high denitrification rates, but are also conducive to N2O reduction thus leading to relatively low N2O emission.  相似文献   
142.
Salinity stress can be mitigated by using the physiological seed enhancements. Kharchia 65 (salt tolerant) and PI.94341 (salt sensitive) genotypes were evaluated under salt stress (20 dS/m) by various priming treatments, that is hydropriming and halopriming (50?mmol, KCl and NaCl) in a pot study. Experiment was conducted in completely randomized design under factorial arrangements with three replications. Priming agents improved the final emergence percentage (FEP), emergence index (EI) and reduced the mean emergence time of both wheat genotypes under normal and saline conditions as compared to non-primed seed. Priming treatments elicited the efficiency of wheat seedlings by increasing both Fv/Fm and Ft under both normal and salt stress conditions which were strongly linked with low Na+ and high K+. In conclusion, all three priming agents effectively nullified the deleterious effects of salt stress by improving seed emergence and triggering the physiological attributes of wheat.  相似文献   
143.
144.
OBJECTIVE: To compare the electrophoretic pattern of serum proteins in clinically healthy adult camels (between 3 and 8 years of age) and camel calves (less than 3 months of age). DESIGN: Laboratory analysis of serum from healthy camels. PROCEDURE: Blood was collected from 30 healthy adult camels and 30 camel calves and the serum separated. Total protein of each serum sample was estimated by automated chemistry analyser. The proteins were fractionated by automated electrophoresis on agarose gel. RESULTS: Serum proteins migrated on the agarose gel as one albumin, two alpha (alpha1 and alpha2-globulins), two beta (beta1 and beta2-globulins) and one gamma-globulin fractions. In adult camels the mean concentration of total protein, albumin alpha1, alpha2, beta1, beta2 and gamma-globulins was 56.8 +/- 1.5, 30.7 +/- 0.8, 2.4 +/- 0.1, 3.2 +/- 0.1, 9.7 +/- 0.3, 3.4 +/- 0.2 and 8.6 +/- 0.3 g/L, respectively. These values in calves were 49.7 +/- 1.8, 23.7 +/- 0.8, 3.2 +/- 0.2, 3.1 +/- 0.2, 14.2 +/- 0.2, 4.0 +/- 0.2 and 4.1 +/- 0.2 g/L, respectively. CONCLUSION: The concentration of total proteins, albumin and gamma-globulins was higher (P < 0.05) in the adult camels than in camel calves. The concentrations of beta1 globulins was higher (P < 0.05) in calves as compared to adult camels.  相似文献   
145.
Cyanobacteria are essential for the vast number of compounds they produce and the possible applications in the pharmaceutical, cosmetical, and food industries. As Lyngbya species’ characterization is limited in the literature, we characterize this cyanobacterium’s growth and biomass. L. purpureum was grown and analyzed under different salinities, culture media, and incubation times to determine the best conditions that favor its cell growth and the general production of proteins, carbohydrates, lipids, and some pigments as phycocyanin and chlorophyll a. In this study, each analyzed biomolecule’s highest content was proteins 431.69 mg g−1, carbohydrates 301.45 mg g−1, lipids 131.5 mg g−1, chlorophyll a 4.09 mg g−1, and phycocyanin 40.4 mg g−1. These results can provide a general context of the possible uses that can be given to biomass and give an opening to investigate possible biocompounds or bio metabolites that can be obtained from it.  相似文献   
146.
Consistent climatic perturbations have increased global environmental concerns, especially the impacts of abiotic stresses on crop productivity. Rice is a staple food crop for the majority of the world’s population. Abiotic stresses, including salt, drought, heat, cold and heavy metals, are potential inhibitors of rice growth and yield. Abiotic stresses elicit various acclimation responses that facilitate in stress mitigation. Plant hormones play an important role in mediating the growth and development of rice plants under optimal and stressful environments by activating a multitude of signalling cascades to elicit the rice plant’s adaptive responses. The current review describes the role of plant hormone-mediated abiotic stress tolerance in rice, potential crosstalk between plant hormones involved in rice abiotic stress tolerance and significant advancements in biotechnological initiatives including genetic engineering approach to provide a step forward in making rice resistance to abiotic stress.  相似文献   
147.
Gynoecism has been used on a large scale in heterosis breeding of cucumber. Production of hybrid seeds in bitter gourd is highly expensive because it is done mainly through hand pollination. But utilization of a gynoecious line would be more economical and easier method. Since gynoecious parent has only female flowers, the open pollinated seeds it produces will be F1 hybrid. It will reduce the cost of male flower pinching and hand pollination. Two gynoecious lines, DBGY-201 and DBGY-202 were crossed with two monoecious cultivars, “Pusa Do Mausami” and “Pusa Vishesh” and their F2 populations were observed to determine the inheritance pattern of gynoecious sex form. Another experiment was conducted to determine magnitude of heterosis by utilizing nine inbred lines including one gynoecious line, DBGY-201 in diallel (without reciprocal) mating system. All the gynoecious hybrids showed significant heterosis in a desirable direction for traits like sex ratio (male:female), days to first picking, number of fruits per plant, yield per plant, and vine length. The segregation pattern in F2 suggested that gynoecious sex form in bitter gourd was governed by single recessive gene. The gynoecious hybrids DBGY-201 × “Pusa Vishesh” and DBGY-201 × “Pusa Do Mausami” were important for early harvest (~50 days after sowing) whereas DBGY-201 × “Priya” and DBGY-201 × “Arka Harit” were promising for higher yield.  相似文献   
148.
Plasma concentrations of thyroxine (T4) and triiodothyronine (T3) were profoundly depressed both in chick embryos and growing chickens after methimazole (MMI) treatment. There was no response of T4 and T3 levels to TRH or TSH injections in the MMI group, either in embryos or growing chickens.

Peroxidase activity measured in the thyroid gland was significantly higher in embryos and growing chickens treated with MMI. However, neither TRH nor TSH affected this activity 2 hr after injection in either control or the MMI-treated group.

Hepatic 5′-monodeiodinase activity was significantly stimulated in the MMI-treated groups of embryos and growing chickens but only when additional sulphydryl groups (DTT) were provided. In embryos, monodeiodination activity 2 hr after TSH injection was not significantly different from control values for either DTT-stimulated or unstimulated conditions within the control and MMI-infused groups. However, in both control and MMI-treated embryos monodeiodination activity significantly increased 2 hr after TRH injection. In the growing chickens, monodeiodination activity 2 hr after TRH or TSH injection was not significantly different from control values in either stimulated or unstimulated conditions of each group.  相似文献   

149.
1. The objective of this study was to investigate the effect of range type, multi-enzyme applications, and a combination of benzoic acid (BA) and essential oils (EO) on the productive performance, organ weight and egg quality of free-range laying hens.

2. Three hundred laying hens were evaluated for the short-term (6 weeks) and long-term (12 weeks) effects of range type (G = no pasture, P = pasture) and feed additives (T1 = control; T2 = betaglucanase/pectinase/protease; T3 = BA/EO). Body weight, feed intake (FI), feed conversion ratio (FCR), egg production (EP), digestive organ weight, and egg quality (EQ) were evaluated. Data were analysed using SPSS 2.2 in a 2×2×3 factorial arrangement.

3. Hens that ranged on pasture were significantly heavier (2043 g vs. 1996 g; p < 0.001), laid heavier eggs (61.9 g vs. 60.3 g; p < 0.001) and produced darker yolk colour (4.3 vs. 7.0; p < 0.001) compared to hens ranged on gravel. Hens fed T2 were significantly heavier (2050 g) compared to hens fed T1 (2005 g) or T3 (2008 g). Organ weights (gizzard, liver and pancreas) were significantly heavier in hens ranged on pasture (16.8 g/kg BW, 22.3 g/kg BW and 1.89 g/kg BW, respectively) compared to hens ranged on gravel (14.2 g/kg BW, 21.7 g/kg BW and 1.83 g/kg BW, respectively). Over time, body weight (1970–2070 g; p < 0.001) and egg weight (59.5–62.8 g; p < 0.001) increased, FI (123–120 g; p = 0.024) was reduced and FCR (2.36–2.10; p = 0.002) improved

4. In conclusion, hens housed on pasture and fed multi-enzyme supplemented diets had significantly heavier body weight and produced heavier eggs with darker yolk colour. Pasture intake and enzyme supplementation increased digestive organ weight significantly.  相似文献   

150.
Quinoa (Chenopodium quinoa Willd.) is a facultative halophyte of great value, and World Health Organization has selected this crop, which may assure future food and nutritional security under changing climate scenarios. However, germination is the main critical stage of quinoa plant phenology affected by salinity. Therefore, two experiments were conducted to improve its performance under salinity by use of saponin seed priming. Seeds of cv. Titicaca were primed in seven different solutions with varying saponin concentrations (i.e. 0%, 0.5%, 2%, 5%, 10%, 15%, 25% and 35%), and then, performances of primed seeds were evaluated based on mean germination time and final germination percentage in germination assays (0 and 400 mM NaCl stress). Saponin solutions of 10%, 15% and 25% concentration were found most effective priming tools for alleviating adverse effects of salt stress during seed germination. Performances of these primed seeds were further evaluated in pot study. At six‐leaf stage, plants were irrigated with saline water having either 0 or 400 mM NaCl. The results indicated that saline irrigation significantly decreased the growth, physiology and yield of quinoa, whereas saponin priming found operative in mitigating the negative effects of salt stress. Improved growth, physiology and yield performance were linked with low ABA concentration, better plant water (osmotic and water potential) and gas relations (leaf photosynthetic rate, stomatal conductance), low Na+ and high K+ contents in leaves. Our results suggest that saponin priming could be used as an easy‐operated and cost‐effective technology for sustaining quinoa crop growth on salt‐affected soils.  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