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   292篇
  免费   15篇
林业   18篇
农学   14篇
基础科学   3篇
  70篇
综合类   7篇
农作物   53篇
水产渔业   49篇
畜牧兽医   73篇
园艺   9篇
植物保护   11篇
  2023年   2篇
  2022年   9篇
  2021年   16篇
  2020年   19篇
  2019年   21篇
  2018年   16篇
  2017年   25篇
  2016年   17篇
  2015年   13篇
  2014年   11篇
  2013年   34篇
  2012年   20篇
  2011年   30篇
  2010年   10篇
  2009年   10篇
  2008年   15篇
  2007年   7篇
  2006年   6篇
  2005年   7篇
  2004年   4篇
  2003年   3篇
  2002年   2篇
  2000年   1篇
  1999年   1篇
  1995年   1篇
  1994年   3篇
  1989年   2篇
  1987年   1篇
  1945年   1篇
排序方式: 共有307条查询结果,搜索用时 15 毫秒
81.
Basalt Weathering and Soil Development since the Middle Tertiary on Lanzarote, Canary Islands - The Profile Malaya Chica A polygenetic soil on tertiary (miocene) basalt in the north of Lanzarote (Canary Islands, Spain) was examined. Soil development was reconstructed, which took place in a semiarid climate since the end of the tertiary period. The interpretation of field and laboratory results (carbonate, grainsize distribution, oxalate and dithionithe soluble oxides, CEC, clay minerals, micromorphology) explained the history of development. Since the miocene at least seven consecutive phases of soil development took place induced by erosion, volcanic and colluvial sedimentation and/or climatic changes.  相似文献   
82.
This paper reports on an experiment to determine growth and survival of blacklip pearl oyster, Pinctada margaritifera (L.), larvae fed a 1:1 mixture of Isochrysis aff. galbana clone T-ISO and Pavlova salina at six different densities (1, 2, 5, 10, 20 and 30 × 103 cells ml-1. Larval growth and survival were assessed every four days over a 20–day period. Exponential and logistic regression models were fitted to the growth and survival responses, respectively. Overall growth of larvae fed 5 × 103 cells ml-1 was significantly greater (p > 0.01) than growth of larvae reared at other algal densities. The optimal food ration for maximum larval growth was 20 × 103 cells ml-1, which resulted in larvae with antero-posterior shell length of 230 m after 20 days. These larvae were significantly larger (p > 0.05) than those in all other treatments at the end of the experiment. Survival of larvae fed 0, 1 and 2 × 103 cells ml-1 was significantly lower than that of larvae in all other treatments at the end of 15 days (p > 0.01). Maximal survival (8%) over the 20 day period was shown by larvae fed 10 × 103 cells ml-1, while lower survival was shown by larvae fed 2 × 103 cells ml-1 (2%) and 1 × 103 cells ml-1 (0%).  相似文献   
83.
Partitioning of the genotypes by environment interaction (GEI) is important in order to determine the nature of the GEI. The objectives of this study were to assess the presence and nature of GEI for nine agronomic traits of rapeseed cultivars, and to identify cultivars with favorable levels of stable oil production. Nine rapeseed cultivars, including seven open pollinated and two hybrids, Hyola308 and Hyola401, were grown in ten environments under rain-fed warm areas of Iran. The GEI was significant for all traits and was partitioned into components representing heterogeneity due to environmental index and the remainder of the GEI. Among the all traits with a highly significant heterogeneity, the largest amount of heterogeneity removed from the GEI was for seeds per pod and seed weight. We found GEIs for both oil content and seed yield were largely influenced by differences in correlations among pairs of cultivars (86.8 and 71.4% of the GEI sum of squares, respectively), suggesting that crossover GEIs (i.e., change in genotype rankings among environments) are present. The mean correlation of each cultivar with all other cultivars ([`(r)]ii \bar{r}_{{ii^{\prime}}} ) ranged from 0.53 to 0.83 for oil content and 0.86 to 0.96 for seed yield. A comparison was done of the significance of Sh-σi2 (stability variance derived from total GEI) and Sh-Si2 (adjusted stability variance derived from residual GEI) assignable to each genotype for oil content and seed and oil yield. Based on Sh-σi2, three cultivars were unstable for oil content, whereas six cultivars were unstable for seed and oil yield. The removal of heterogeneity revealed that one unstable cultivar for oil content and three unstable cultivars for oil yield were judged to be stable. All cultivars with [`(r)]ii \bar{r}_{{ii^{\prime } }}  ≤ 0.63 were labeled unstable for oil content, whereas all with [`(r)]ii \bar{r}_{{ii^{\prime } }}  ≤ 0.94 were considered unstable for seed yield. The relationships between [`(r)]ii \bar{r}_{{ii^{\prime } }} and Sh-σi2 were significant (P < 0.01) for oil content and seed yield. The results of rank correlation coefficients showed significant positive correlations of Yield-Stability statistic (YSi) with oil content and oil yield. Cultivars such as Option500 and Hyola401 were identified as having stable, high levels to seed yield and oil content.  相似文献   
84.
Yield and fruit quality in fig (Ficus carica L.) are highly dependent on cultural practices especially caprification (pollination). However, this technique remains not well controlled in Tunisia. This study was conducted during two successive years, 2009 and 2010, to investigate different pollination conditions, i.e. number of caprifigs and repetitions of caprification on fruiting of two cultivars Bouhouli (San Pedro type) and Zidi (Smyrna type). In addition, the efficiency of four pollen sources was evaluated to identify the most effective pollinator for female cultivar Zidi. The following parameters were recorded: fruit number per shoot, fruit set, productivity, fruit characteristics and vegetative growth.  相似文献   
85.
To achieve higher titer of rabies virus higher density of host cells will need. In this study, capability of FibraCel disks packed in 500 mL spinner basket versus Cytodex-1 in 500 mL spinner flask was investigated for propagation of Vero cells and PV rabies virus proliferation. Minimal Essential Medium (MEM) + 10% Foetal Calf Serum (FCS) and Virus Production- Serum Free Medium (VP-SFM) +4 mM L-glutamine were used in growth phase and MEM+ 0.2% Bovine Serum Albumin (BSA) and VP-SFM were used in virus production phase. Adapted Vero cells grown in VP-SFM were used in all SFM experiments while batch and stepwise perfusion modes were applied and compared in growth stage. The highest Vero cell density were achieved in the trials with 10 g FibraCel disk in stepwise perfusion mode equal to 6.12 x 10(6) and 5.87 x 10(6) cells mL(-1) in MEM and VP-SFM, respectively while with 2.73 g Cytodex-1 lower density equal to 4.2 x 10(6) and 4.0 x 10(6) cells mL(-1) were achieved. The highest titer of rabies virus and overall virus production rate were resulted in VP-SFM and on 10 g disks equal to 2.9 x 10(7) Fluorescent Focus Unit (FFU) mL(-1) and 0.14 FFU/Cell/h, respectively versus 1.7 x 10(7) FFU mL(-1) and 0.08 FFU/cell/h on cytodex-1 in similar conditions. The second harvest of virus was also satisfactory in experiment with 10 g disks (1.7 x 10(7) FFU mL(-1)) in compare to Cytodex-1 (0.51 x 10(7) FFU mL(-1)). An equal surface area at 6600 and 12000 cm(-2) were provided in all comparable trials with seeding density of 12.5 x 10(3) cells cm(-2). Adapted Vero cells grown in VP-SFM were used in all SFM experiments while batch and stepwise perfusion modes were applied and compared in growth stage.  相似文献   
86.
We carried out a study to see the effect of contaminated water of Nullah Dek on fine rice paddy and straw yields and trace elements accumulation in different parts of rice plants and soil. A site was selected near the bank of Nullah Dek at Kot Pindi Das in the District of Sheikhupura, Pakistan. The water of this nullah is contaminated by industrial effluents carrying different micronutrients. This water was employed to grow rice crop. Water samples were collected before transplanting and during the season with 15 days interval for analysis from 20 July to 1 November 2002 from a spot near village Shamke. Three fine rice varieties, viz. Super Basmati, Shaheen Basmati and Basmati 2000 were transplanted. These rice varieties were grown up to maturity. Paddy and straw yields data were recorded. Six composite soil samples from three random spots were collected from the experimental site before the start of the study to see the status of trace elements in soil. After the harvest of rice crop, soil, paddy and straw samples were analysed for Zn, Cu, Fe and Mn. The chemical analysis of Nullah Dek water showed that total salts concentration was greater than the safe limit, i.e. electric conductance (EC) > 1.0 dS m−1. Even sodium adsorption ratio (SAR) was very high, but there was no problem of high residual sodium carbonate (RSC). Zn, Cu, Fe and Mn were present but within safe limits. The water of Nullah Dek remained within permissible limits of irrigation from onset of rainy season till 15 October. There was an increase in EC, SAR and trace elements concentrations after 15 October but within safe limits. Soil analysis revealed its saline nature, devoid of sodicity. Among trace elements, the zinc ranged between deficiency (<0.5 mg kg−1) and adequate limits (>1.0 mg kg−1). Copper, Mn and Fe were present in adequate amounts. After the harvest of rice crop there was a slight decrease in pH, ECe and SAR at both the depths, while the concentrations of all trace elements were slightly increased with more in upper layer than the lower layer. Shaheen Basmati produced the maximum paddy yield followed by Basmati 2000 and then Super Basmati. The chemical analysis of paddy samples indicated a sufficient accumulation of zinc (1.68–1.78 mg kg−1), copper (1.38–1.45 mg kg−1), iron (6.12–6.37 mg kg−1) and manganese (2.22–2.42 mg kg−1). Analysis of rice straw also showed sufficient accumulation of zinc (27.50–28.50 mg kg−1), copper (20.0–20.50 mg kg−1), iron (270–280 mg kg−1) and manganese (2.38–2.41 mg kg−1).  相似文献   
87.
Genetic Resources and Crop Evolution - Marrubium L., is a problematic genus of Lamiaceae family with approximately 40 taxa that some of its species grow in Iran. In the current study, we studied...  相似文献   
88.

Lack of control options for cool-season broadleaf weeds is a major deterrent to autumn-sown chickpea. Weed control and chickpea tolerance to PRE (pre-emergence) and POST (post-emergence) application of isoxaflutole and oxyflurofen, PRE metribuzin, POST pyridate, and flumetsulam were investigated at three locations, including Kermanshah, Kurdistan, and Hamedan provinces during 2017–2018. Untreated and weed-free checks were added for comparison. Pyridate and PRE oxyflurofen 125?g ai ha?1 caused the minor visual crop injury according to EWRS score (1–1.8), while the highest crop injury occurred with metribuzin (EWRS score 3.5–8.5) in whole locations. The most effective herbicides for weed reduction were pyridate (70–75%), PRE oxyfluorfen (69–76%), and POST oxyfluorfen (65–73%) at Kermanshah, PRE oxyfluorfen at 125 and 175?g ai ha?1 (70–78%), POST oxyfluorfen (70–76%) and pyridate (70–78%) at Kurdistan, PRE oxyfluorfen at 125 and 175?g ai ha?1 (88–96%), metribuzin (91–100%) and Pyridate (80–97%) at Hamedan. Pyridate and PRE oxyfluorfen at 125?g ai ha?1 resulted in the highest chickpea grain yield at the three locations. In general, PRE oxyfluorfen (125?g ai ha?1) was similar to pyridate in terms of efficacy in weed control and grain yield enhancement.

  相似文献   
89.
The Common Carotid artery Intima-Media Thickness (CCIMT) can reflect systemic atherosclerosis in renal patients on hemodialysis. This study aimed to compare CCIMT measured by color Doppler ultrasonography between two groups including dialytic patients and normal subjects. In this case-control setting, 48 patients with Chronic Kidney Disease (CKD) on hemodialysis (case group) and 46 age and sex-matched healthy subjects (control group) were enrolled in this study. Color Doppler ultrasound was used to measure CCIMT and determine presence of atherosclerotic plaques in carotid bulb in both groups. Various laboratory parameters were also determined. Serum levels of triglyceride, total cholesterol, low-density lipoprotein, fasting sugar, ionized calcium, inorganic phosphorus and magnesium were comparable between the two groups. Hypertension and elevated levels of serum C-reactive protein, as well as the mean levels of serum non-fasting homocysteine and phosphate were significantly higher in the case group. Mean levels of serum high-density lipoprotein and albumin were significantly higher in the controls. Mean maximum CCIMT was significantly higher in the case group than in controls (0.73 +/- 0.15 vs. 0.68 +/- 0.08 mm, p = 0.01) even after adjusting for other confounding variables. Frequency of patients with atherosclerotic plaques in carotid bulbs was not significantly different between case and controls. In conclusion, this study showed that CCIMT is significantly higher in CKD patients on hemodialysis comparing with matched normal counterparts. Furthermore, this difference was independent of other conventional risk factors for atherosclerosis.  相似文献   
90.
A laboratory study was performed to investigate the influence of soil texture (sandy loam vs. clay loam), Pb supply (as Pb(NO3)2 without or with compost) and Pb levels on the extraction of available Pb by diethylene triamine pentaacetic acid (DTPA) and its desorption patterns at ten shaking periods. The soils were polluted with five Pb levels without or with compost and incubated for 1 month. Kinetic models commonly used to study the release of the nutrients were used in this study. Results showed that Power function model described the pattern of Pb desorption better than other models. The amount of extracted Pb increased as the Pb levels increased and was found to be higher in sandy loam soil treated with Pb without compost than that of clay loam soil treated with Pb with compost. The a value (Pb desorption constant) was the highest in sandy loam soil amended with Pb without compost. The lowest value of a, however, was observed in clay loam soil amended with Pb with compost. The ab coefficient (initial desorption rate of Pb) was higher in sandy loam than clay loam soil, demonstrating higher initial release rates of Pb in the coarser-textured soil. Addition of Pb without compost resulted in a higher increase in ab value in comparison with Pb with compost, in both the 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