全文获取类型
收费全文 | 368篇 |
免费 | 22篇 |
专业分类
林业 | 32篇 |
农学 | 29篇 |
基础科学 | 5篇 |
105篇 | |
综合类 | 19篇 |
农作物 | 63篇 |
水产渔业 | 42篇 |
畜牧兽医 | 59篇 |
园艺 | 7篇 |
植物保护 | 29篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2017年 | 25篇 |
2016年 | 29篇 |
2015年 | 14篇 |
2014年 | 27篇 |
2013年 | 40篇 |
2012年 | 25篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 13篇 |
2008年 | 25篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2000年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有390条查询结果,搜索用时 31 毫秒
141.
Javad Seyedmohammadi Hamid Reza Matinfar 《Communications in Soil Science and Plant Analysis》2018,49(18):2301-2314
Soil cation exchange capacity (CEC) is a main criterion of soil quality and pollutant sequestration capacity. This research was carried out to evaluate cokriging prediction map of soil CEC spatial variability with the principal components derived from soil physical and chemical properties. Two hundred and forty-seven soil samples were collected that 75% of them were used for training soil CEC and 25% for testing of prediction. The first principal component (PC1) was highly correlated with soil CEC (r = 0.81, P < 0.01), whiles there was no significant correlation between CEC and PC2 (r = -0.19). Then, the PC1 was used as an auxiliary variable for the prediction of soil CEC in cokriging method. The determination coefficient (R2) of cross-validation for the test dataset was 0.47 for kriging and 0.71 for cokriging. Therefore, according to the results, principal components that have the highest positive and significant correlation with the dependent variable have the most potential for cokriging prediction. 相似文献
142.
A metabolic approach to understanding adaptation to sea water by endangered Persian sturgeon,Acipenser persicus fingerlings
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Saeed Hajirezaee Ali Reza Mirvaghefi Hamid Farahmand Naser Agh 《Aquaculture Research》2018,49(1):341-351
In this study, metabolic responses of Persian sturgeon fingerlings to hyperosmotic condition were investigated by NMR‐based metabolomics. Persian sturgeon fingerlings (n = 2010, mean total weight: 3.2 ± 0.6 g; mean total length: 8.5 ± 1.5 cm) were held in freshwater (FW) for 96 hr and then acclimated in brackish water (BW) (12 g/L) for 24 hr. Blood samples were taken before and after salinity acclimation. The major metabolite changes corresponding to salinity acclimation were related to amino acids, osmolytes and energy metabolites. The plasma glucose levels increased significantly after 24 hr acclimation in BW (p < .05). Other energetic metabolites (acetate, acetoacetate, beta‐hydroxybutyrate, phosphocreatine, creatine, glycerol) showed no significant changes after 24 hr salinity challenge (p > .05). The osmolytes (taurine, trimethylamine‐N‐oxide, choline, N,N‐dimethylglycine) and amino acids (aspartate, glutamate, glutamine, leucine, phenylalanine, β‐alanine, histidine, threonine, cysteine) declined significantly after 24 hr acclimation in BW (p < .05). However, the levels of glycine elevated after 24 hr acclimation in BW (p < .05). Other amino acids including aspargine, isoluecine, Tyrosine, Tryptophan, Valine, and Lysine showed no significant changes after salinity challenge (p > .05). The considerable decreases in almost all plasma amino acids and all osmolytes showed specific importance of these metabolites in osmotic adaptation of fish in BW. Also, it seems that Persian sturgeon fingerlings rely more on oxidation of glucose to meet energetic requirements of osmoregulation than oxidation of lipids, as we observed no detectable changes in metabolites associated with lipid oxidation during osmotic acclimation in BW. Our results may help to understand osmoregulation in a chondrostei fish species from a metabolic approach. 相似文献
143.
Saeid Mehdizadeh Hamid Saadatnejadgharahassanlou 《Archives of Agronomy and Soil Science》2017,63(7):942-955
Accurate estimation of reference evapotranspiration (ETo) is essential for water resources management and irrigation systems scheduling, especially in arid and semiarid regions such as Iran. In the present research, constant coefficients of Hargreaves–Samani (CH–S) and Priestley–Taylor (CP–T) equations were locally calibrated to estimate the ETo based on the FAO–Penmen–Monteith (PM) method as standard method. For this purpose, meteorological data of eight synoptic stations located in the northwest of Iran were used during the period of 1997–2008. The outcomes showed that the values of CH–S and CP–T were 0.0026 (instead of 0.0023) and 1.68 (instead of 1.26), respectively. Also, at stations with high wind speed, the values of calibrated coefficients of CH–S and CP–T were maximum. Then, the estimated ETo values using adjusted CH–S and CP–T coefficients were compared to the obtained actual ETo values by PM method using root mean square error and mean bias error indices. The results indicated that the new calibrated H–S and P–T equations have good agreement with the PM method for estimation of the ETo. Moreover, the equation of Ravazzani et al. was calibrated in the studied region. It was concluded that in general, the mentioned equation was shown better performance than original H–S equation. 相似文献
144.
Akram Farshadirad Ali Reza Hosseinpur Hamid Reza Motaghian Shoja Ghorbani Dashtaki 《Archives of Agronomy and Soil Science》2017,63(10):1419-1430
Zinc (Zn) distribution in different soil aggregates can affect Zn availability. In this study, the effect of soil aggregate-size fractions on Zn distribution and availability was determined in some heavy metal-contaminated soils. Air-dried samples were fractionated into four different aggregate-size fractions (2.0–4.0, 0.25–2.0, 0.05–0.25 and <0.05 mm). Extraction efficiency of available Zn determined by using Mehlich-3, DTPA-TEA, Mehlich-1 and H2O methods in different aggregates and relation between extracted Zn and corn indices were studied. Moreover, the Tessier fractionation scheme was applied to determine the partitioning of Zn in different aggregates. Among all the extractants, Mehlich-3 showed better extractability of Zn from soils and the highest amount of extracted Zn was found in the <0.05 (87.65 mg kg?1) and 0.05–0.25 (80.86 mg kg?1) mm fractions. Zn extracted by Mehlich-3 and DTPA-TEA in the <0.05 and 0.05–0.25 mm fractions had significant correlation with the amount of Zn in corn. Also, correlation coefficients between carbonate-bound and Fe–Mn oxide-bound Zn and available Zn in <0.05 and 0.05–0.25 mm aggregates was higher than other aggregates, suggesting that this two fraction of Zn in finer aggregates constituted the major available Zn pools in the studied soils. 相似文献
145.
In this study, the invasive and noninvasive diagnotic tests were compared to choose the appropriate test for diagnostice of H. pylori infection. Helicobacter pylori (H. pylori) is a human pathogen that causes chronic gastritis, has a role in gastric and duodenal ulcer, is involved in gastric carcinogenesis and is regarded as a possible important factor in at least a subset of patients with functional dyspepsia. The diagnosis of H. pylori is an essential element in the management of many common gastrointestinal pathologies. The assessment of each routine invasive and noninvasive test is important. We studied a total of 127 outpatients for the detection of H. pylori infection. The presence of H. pylori infection by invasive tests containing the Rapid Urease Test (RUT), histology (Giemsa staining) and culture in 127 patients. Patients who were positive in culture, or two tests from four tests, invasive and noninvasive, were considered to have H. pylori infection. In noninvasive tests, we evaluated anti-H. pylori IgG and anti-CagA antibodies using commercial Enzyme-Linked Immunoassay (ELISA) and Western blot in dyspeptic patients. Eighty five out of the 127 patients were positive for H. pylori. Helicobacter pylori IgG seropositivity and 35 out of the 127 patients were positive for immunoblot. RUT had sensitivity, specifity and accuracy of 96, 80 and 90.5%, respectively; for Elisa these were 85.2, 33 and 70.5%, respectively and for ELISA with immunoblotting they were 65, 45 and 58.8%, respectively. The results of this study suggest that noninvasive tests (ELISA, immunoblotting) have the lowest and RUT with histology have the highest accuracy. These earlier tests can not be used for accurate infection diagnosis. 相似文献
146.
Zamanian Z Kakooei H Ayattollahi SM Dehghani M 《Pakistan journal of biological sciences: PJBS》2010,13(9):431-436
The aim of this study are to assess, in a hospital setting, the effects of Bright Light (BL) on the rhythms in body temperature, plasma melatonin, plasma cortisol and subjective alertness during shift work. In our experimental design, 34 healthy shift work nurses from a university hospital were exposed to bright light (4500 lux) during two break times (21:15 to 22; 00 and 3:15 to 4:00) for four consecutive weeks. In this survey, the subjects were studied under 24 h of realistic conditions during which their plasma cortisol and plasma melatonin was measured at 3 h intervals. In addition, their body temperatures were measured during and after night shift work. Subjective alertness and fatigue were evaluated with the Karolinska Sleepiness Scale (KSS) and Visual Analog Scale (VOI). It was found that bright light administration significantly suppressed nighttime melatonin levels during night shift, most strongly at 2:00 a.m. A one-way ANOVA, with repeated measurement design, revealed that Bright Light (BL) tended to increase cortisol levels and body temperature and improved alertness significantly during night shift. These results demonstrate that photic stimulation in a hospital setting can have a powerful influence on the adjustment of the circadian system. 相似文献
147.
Improvement in wild endangered Persian sturgeon,Acipenser persicus (Borodin, 1897) semen cryopreservation by 2‐hydroxypropyl‐beta‐cyclodextrin (HβCD)
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ruhollah Rahimi Hamid Farahmand Alireza Mirvaghefi Gholamreza Rafiee Amirreza Abed Elmdoust 《Aquaculture Research》2015,46(10):2452-2456
In this study, cryopreservation feasibility of Persian sturgeon (Acipenser persicus) and the effect of different doses of 2‐hydroxypropyl‐beta‐cyclodextrin on thawed spermatozoa quality (motility duration and motility percentage) were investigated. For freezing, semen of seven male individuals was pooled in equal volumes and diluted with 4°C [Tris‐HCl (100 mM), pH = 8, DMSO 10%] extenders containing 0, 5, 10, 15 mM of HβCD in a ratio of 1:1(semen/extenders). Then semen was filled into 0.5‐mL straws, and was frozen with vapour of liquid nitrogen at 4‐cm above surface of liquid nitrogen. After 3 min, straws were plunged in to liquid nitrogen. Thawing was performed at 40°C water baths for 15 s. Motility duration of the 10 mM HβCD treated spermatozoa at days 14 (228.98 ± 16.39) and 56 (199.66 ±21.78) were longer than other treatments. In day 56, the motility percentage in treatment with 10 mM was significantly higher (16.14 ± 2.54) (P < 0.05) compared with 5 mM treatment (8.75 ± 2.47) (P < 0.05). Therefore, it is recommended that 10 mM of HβCD can be used as an additive cryoprotectant for increasing cryopreserved spermatozoa quality in this species. 相似文献
148.
149.
Because of a number of facilities, the Electrospray (ES) method is gaining ever-increasing popularity among researchers for producing nano-to-micron-sized particles. Microparticles (MPs) of poly lactic-co-glycolic acid (PLGA) were prepared by using the ES technique. The influence of both solution and apparatus parameters on the morphology, size, size distribution, and uniformity of produced MPs were investigated. Results of SEM images and calculations revealed that polymer concentration is a critical parameter in the ES system. In a semi-dilute moderately entangled regime, chain entanglement can easily occur. Solution flow rate is a key factor among apparatus parameters. Vapour pressure is a key parameter affecting MP morphology. The size of the particles tended to reduce with an increase in voltage. The needle gauge did not have an important impact on particle size. The role of the electric field changed at different collecting distances. Using a saturated combination of EtOH/PVA is an acceptable collecting medium for PLGA MPs. It is possible to produce uniform and spherical MPs by using chloroform as a solvent. However, a reduction in particle size is achievable by using a solvent of chloroform/DMF (90/10 w/w). 相似文献
150.
Amin Nobahar Hamid Reza Zakerin Saeed Sayfzadeh Ali Reza Valadabady 《Communications in Soil Science and Plant Analysis》2019,50(6):749-762
Groundnut is an annual legume and important oilseed crop in the world. In order to evaluate the influence of the topping height and application methods of Zinc (Zn) and Calcium (Ca) nano-chelates on quantitative and qualitative characteristics of groundnut, these experiments were carried out during the 2016–2017 cropping seasons on groundnut in Iran. Both foliar and in soil applications of Zn and Ca nano-chelates improved groundnut yield. Foliar application of Zn nano-chelate in combination with topping the main stem 20 cm above the ground produced the highest 100-seed weight (82.19 g), seed yield per unit area (2722.5 kg.h?1), harvest index (57.53%), biological yield (6540.00 kg.h?1), oil yield (1486.76 kg.h?1), protein yield (742.66 kg.h?1), seed Zn content (12.08 ppm) and Ca content (35.86 ppm). The application of Zn nano-chelate had different positive influences on vegetative and reproductive growth of groundnut plants. Generally, optimizing of the nutritional status in groundnut plants with Ca and Zn supplements is recommended to enhance the quantitative and qualitative yield of groundnut. 相似文献