全文获取类型
收费全文 | 566篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
林业 | 98篇 |
农学 | 43篇 |
基础科学 | 1篇 |
98篇 | |
综合类 | 27篇 |
农作物 | 61篇 |
水产渔业 | 139篇 |
畜牧兽医 | 81篇 |
园艺 | 3篇 |
植物保护 | 49篇 |
出版年
2023年 | 8篇 |
2022年 | 28篇 |
2021年 | 28篇 |
2020年 | 36篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 37篇 |
2015年 | 31篇 |
2014年 | 31篇 |
2013年 | 57篇 |
2012年 | 40篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 8篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1960年 | 2篇 |
排序方式: 共有600条查询结果,搜索用时 218 毫秒
591.
Md SALAHUDDIN Kohzy HIRAMATSU Kento TAMURA Kazumi KITA 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2021,83(6):952
White Leghorn chickens were divided into the control, low-carbohydrate (CHO), and CHO-free groups to investigate dietary CHO’s significance on histological features of chicken ileal mucosa. Paraffin sections of distal ileum from each chicken were stained by periodic acid-Schiff reaction and subjected to morphometrical analysis. Most villi in the control group had a fingerlike shape but those of the experimental groups showed irregular shapes. Villus height, crypt depth and the number of mitotic cells per crypt were significantly lower in the CHO-free group than in the control group. The density of goblet cells also showed a significant decreasing trend with a reduction in dietary CHO level. In conclusion, dietary CHO positively affects the proliferation of epithelial cells in the chicken ileum. 相似文献
592.
The dynamic behavior of water quality and quantity in the Egyptian drains is often viewed as a disruption to the normal operation and performance of the process of water reuse in irrigation. The control of such behavior has been challenging and often elusive in practice. Therefore, this paper presents a framework to advance the understanding and opportunities for improving the reuse process by developing a multivariate process control model. The model starts with preliminary analysis for water quality data that are collected at the reuse site on the examined drain. This phase comprises investigating data distribution and dependency. Then, univariate control charts are used to investigate the state of control for the independent and normally distributed variables. For dependent variables, principal components analysis is used as a method of synthesizing the variables information. In this case, principal component scores are displayed using multivariate control charts. If in-control case existed, process capability index is used to provide a numerical measure of whether or not the reuse process is capable of producing water that satisfies the irrigation quality standards. Since the model will only detect assignable causes if out-of-control or in-capable case existed, management, operational, and/or engineering action will usually be necessary to sustain the reuse process. In these cases, an action plan in response to the model signals will be vital. The main function of the proposed model is to safely manage the reuse practice using statistical quality control techniques. The model was demonstrated using water quality data collected during the period from January 2006 to July 2011 from Hanut (EH02) and El-Salam 3 (ESL03) pump stations along Hadus drain, Eastern Nile Delta-Egypt. The recommended model is automatic, algorithmic, self-tuning, and computerizable. 相似文献
593.
Md. Abul Kashem Bal Ram Singh S M Imamul Huq Shigenao Kawai 《Water, air, and soil pollution》2008,192(1-4):273-279
Selection of a phytoextraction plant with high Cd accumulation potential based on compatibility with mechanized cultivation practice and local environmental conditions may provide more benefits than selection based mainly on high Cd tolerance plants. In this hydroponics study, the potential of Cd accumulation by three plant species; arum (Colocasia antiquorum), radish (Raphanus sativus L.) and water spinach (Ipomoea aquatica) were investigated. Arum (Colocasia antiquorum L.) plants were grown for 60 days in a nutrient solution with 0, 10 or 50 μM Cd, while radish and water spinach plants grew only 12 days in 0, 1.5, 2.5, 5 or 10 μM Cd. Growth of radish and water spinach plants decreased under all Cd treatments (1.5 to 10 μM), while arum growth decreased only at 50 μM Cd. At 10 μM Cd treatment, the growth of arum was similar to the control treatment indicating higher tolerance of arum for Cd than radish and water spinach. Cadmium concentrations in different plant parts of all plant species increased significantly with Cd application in the nutrient solution. Arum and water spinach retained greater proportions of Cd in their roots, while in radish, Cd concentration in leaves was higher than in other plant parts. Cadmium concentrations in arum increased from 158 to 1,060 in the dead leaves, 37 to 280 in the normal leaves, 108 to 715 in the stems, 42 to 290 in the bulbs and 1,195 to 3,840 mg kg?1 in the roots, when the Cd level in the solution was raised from 10 μM Cd to 50 μM Cd. Arum accumulated (dry weight?×?concentration) 25 mg plant?1 at 10 μM, while the corresponding values for radish and water spinach were 0.23 and 0.44 mg plant?1, respectively. With no growth retardation at Cd concentrations as high as 166 mg kg?1 measured in entire plant (including root) of arum at 10 μM Cd in the nutrient solution, arum could be a potential Cd accumulator plant species and could be used for phytoremediation. 相似文献
594.
The importance of demographic niches to tree diversity 总被引:1,自引:0,他引:1
Condit R Ashton P Bunyavejchewin S Dattaraja HS Davies S Esufali S Ewango C Foster R Gunatilleke IA Gunatilleke CV Hall P Harms KE Hart T Hernandez C Hubbell S Itoh A Kiratiprayoon S Lafrankie J de Lao SL Makana JR Noor MN Kassim AR Russo S Sukumar R Samper C Suresh HS Tan S Thomas S Valencia R Vallejo M Villa G Zillio T 《Science (New York, N.Y.)》2006,313(5783):98-101
Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics. 相似文献
595.
596.
597.
598.
Babaee Yassaman Mulligan Catherine N. Rahaman Md. Saifur 《Journal of Soils and Sediments》2018,18(4):1610-1619
Journal of Soils and Sediments - The present study investigates the possible use and effectiveness of starch-stabilized Fe/Cu nanoparticles for in situ immobilization of arsenic in contaminated... 相似文献
599.
Md. Khurshid Alam Bhuiyan Sabrina Qureshi Md. Masum Billah Suresh Varma Kammella Md. Rushna Alam Sunuram Ray Md. Mostafa Monwar Abu Hena M. K. 《Water, air, and soil pollution》2018,229(1):14
Recently, Sancti Petri channel on the southwestern (SW) part of Iberian Peninsula has been experiencing urban, industrial, and vehicular expansion. Until recently, there have been only few published reports documenting the pattern of metal accumulation in this estuarine sediment. In the present study, trace metals such as Cu, Zn, Ni, Mn, Pb, Co, Cd, As, and Hg concentrations were analyzed from 69 sediment samples collected from 23 sampling sites of the Santi Petri channel. The magnitude of trace metal accumulation found as the following trend: Mn > Zn > Cu > Pb > Ni > Co > As > Cd > Hg. Spatial distribution pattern demonstrated overall decreasing trend of trace metal from Cadiz Bay mouth to the open ocean mouth, clearly correlative to the presence of anthropogenic inputs. Results of the principle component analysis (PCA) revealed that sediment metal chemistry of Sancti Petri channel is mainly regulated by the concentrations of Pb, Cu, Zn, and Ni; possible sources of those were from vehicular-related emissions. Pollution load index (PLI) and geo-accumulation index (I geo ) indicated overall low values. The study will stimulate improvement of our understanding regarding the pattern of accumulation of metals in the coastal sediments, and the recorded values of metals in the present study can be used as suitable reference for future studies. 相似文献
600.
Royston Uning Mohd Talib Latif Kai Ling Yu Sze Yin Cheng Fatimah Ahamad Md Firoz Khan Edmand Andrew Bedurus Suhaimi Suratman 《Water, air, and soil pollution》2018,229(9):305
This study aims to determine the composition of surfactants in the sea surface microlayer (SML), underlying water (ULW) and atmospheric particles (AP). Surfactants were determined colorimetrically as methylene blue active substances (MBAS) and disulphine blue active substances (DBAS) for anionic and cationic surfactants, respectively. The concentration of dissolved inorganic nutrients (DIN) in ULW was determined so as to indicate the influence of ULW to the surfactants in SML. The results showed that the concentration of MBAS and DBAS in SML at both stations ranged between 0.05 and 0.31 μmol L?1, and between 0.19 and 0.59 μmol L?1, respectively. Surfactants in ULW influence the concentration of surfactants in SML (r?=?0.65, p?<?0.01, n?=?36). The station influenced by anthropogenic sources showed a higher concentration of surfactants in ULW, SML and AP. This finding suggests fine mode atmospheric particles (FMAP) are the main carrier for anionic surfactants as MBAS in the coastal ecosystem. Anionic surfactants as MBAS were found as better indicator of anthropogenic sources than cationic ones. 相似文献