全文获取类型
收费全文 | 1219篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
林业 | 94篇 |
农学 | 57篇 |
基础科学 | 16篇 |
217篇 | |
综合类 | 79篇 |
农作物 | 129篇 |
水产渔业 | 132篇 |
畜牧兽医 | 398篇 |
园艺 | 24篇 |
植物保护 | 118篇 |
出版年
2023年 | 14篇 |
2022年 | 42篇 |
2021年 | 55篇 |
2020年 | 71篇 |
2019年 | 61篇 |
2018年 | 46篇 |
2017年 | 51篇 |
2016年 | 48篇 |
2015年 | 50篇 |
2014年 | 51篇 |
2013年 | 102篇 |
2012年 | 79篇 |
2011年 | 93篇 |
2010年 | 43篇 |
2009年 | 24篇 |
2008年 | 54篇 |
2007年 | 49篇 |
2006年 | 29篇 |
2005年 | 26篇 |
2004年 | 32篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1969年 | 4篇 |
1967年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有1264条查询结果,搜索用时 46 毫秒
991.
Ahmed M. Elhendy Abdulaziz A. Alzoom 《Aquaculture Economics & Management (Blackwell Science)》2013,17(3-4):229-238
Abstract Because Saudi Arabia is a substantial importer of fish and its capture fishery is operating beyond maximum sustainable limits, it has a special interest in developing fish farming. It has been encouraging tilapia production. This study examines the costs of tilapia farming in the Central Region of Saudi Arabia using cross sectional data from 23 intensive fish farms. It provides information about the relative importance of different cost items such as variable costs and feed costs in total costs. Also, cost functions are estimated by ordinary least squares and a cubic cost function is found to provide the best fit to the available data. Minimum average cost of production occurs for 201 tonnes of tilapia per year per farm and profit is maximised for a production of 300 tonnes annually per farm. All farms operate at less than profit‐maximising scale and most operate at less than minimum efficient scale. The reasons could be low quality fry, low levels of management expertise in culturing tilapia and the secondary nature of tilapia farming. Lack of water is likely to limit future expansion of tilapia farming in Saudi Arabia. 相似文献
992.
Nesar Ahmed Catherine Lecouffe Edward H. Allison James F. Muir 《Aquaculture Economics & Management (Blackwell Science)》2013,17(3):246-269
A conceptual framework, drawn from an approach to poverty reduction known as the Sustainable Livelihoods Approach (SLA), is applied to understanding the role of freshwater prawn (Macrobrachium rosenbergii) marketing systems in southwest Bangladesh. Freshwater prawn marketing potentially provides economic returns and social benefits to the rural poor. Although the potential benefits are great, a number of constraints were identified for the long-term sustainability of prawn marketing systems. The study used the SLA framework as an analytical tool to identify ways to strengthen livelihoods of prawn traders and associated groups. 相似文献
993.
Ercisli S Tosun M Karlidag H Dzubur A Hadziabulic S Aliman Y 《Plant foods for human nutrition (Dordrecht, Netherlands)》2012,67(3):271-276
Fruit skin color, total phenolics, total anthocyanins, soluble solids content, titratable acidity and total antioxidant capacity in fresh fruits of a number of local and well-known fig (Ficus carica L.) genotypes and cultivars grown in northeastern Turkey were determined. TEAC (Trolox equivalent antioxidant capacity) and FRAP (ferric reducing antioxidant power) assays were used to determine total antioxidant capacity. Fruit skin color of genotypes were found to be very diverse, i.e., light green, light purple, purple, dark purple and black. The content of total phenolics, soluble solids content (SSC) and titratable acidity greatly varied in the range from 24 to 237?mg of gallic acid equivalent per 100?g fresh weight, 18.60 to 26.30?% and 0.16 to 0.47?% in local genotypes and studied cultivars. In general, total antioxidant capacities determined by two methods expressed higher values in the local fig genotypes compared with the cultivars. The results suggested that genotype is the main factor that determines difference in the composition of bioactive compounds in figs and provide information on putative health benefits locally grown genotypes. 相似文献
994.
Ahmed Mediani Faridah Abas Tan Chin Ping Alfi Khatib Nordin H. Lajis 《Plant foods for human nutrition (Dordrecht, Netherlands)》2012,67(4):344-350
The impact of tropical seasons (dry and wet) and growth stages (8, 10 and 12 weeks) of Cosmos caudatus on the antioxidant activity (AA), total phenolic content (TPC) as well as the level of bioactive compounds were evaluated using high performance liquid chromatography (HPLC). The plant morphology (plant height) also showed variation between the two seasons. Samples planted from June to August (during the dry season) exhibited a remarkably higher bioactivity and height than those planted from October to December (during the wet season). The samples that were harvested at eight weeks of age during the dry season showed the highest bioactivity with values of 26.04 g GAE/100 g and 22.1 μg/ml for TPC and IC50, respectively. Identification of phytochemical constituents in the C. caudatus extract was carried out by liquid chromatography coupled with diode array detection and electrospray tandem mass (LC-DAD-ESIMS/MS) technique and the confirmation of constituents was achieved by comparison with literature data and/or co-chromatography with authentic standards. Six compounds were indentified including quercetin 3-O-rhamnoside, quercetin 3-O-glucoside, rutin, quercetin 3-O-arabinofuranoside, quercetin 3-O-galactoside and chlorogenic acid. Their concentrations showed significant variance among the 8, 10 and 12-week-old herbs during both seasons. 相似文献
995.
Farooq Ahmed Arain Anwaruddin Tanwari Tanveer Hussain Zulfiqar Ali Malik 《Fibers and Polymers》2012,13(1):118-122
In this study, a multiple response optimization model based on response surface methodology was developed to determine the best rotor speed and yarn twist level for optimum rotor yarn strength and unevenness, and minimum yarn hairiness and imperfections. Cotton yarn of 30 tex, was produced on rotor spinning machine with different twist levels (i.e. 500, 550, 600 and 700 tpm) at different rotor speeds (i.e. 70000, 80000, 90000 and 100000 rpm). Yarn quality characteristics were determined for all the experiments. Based on the results, multiple response optimization model was developed using response surface regression on MINITAB® 16 statistical tool. Optimization results indicate that with the quality of raw material selected for this study, top 50 % quality level, according to USTER® yarn quality benchmarks, can be achieved with 100 % desirability satisfaction for all the selected yarn quality parameters at rotor speed of 77,800 rpm and yarn twist of 700 twists per meter. 相似文献
996.
The photocatalytic degradation of a commercial azo dye Benzopurpurine 4B (BP4B) in aqueous solution was investigated under
UV-A light at different operating conditions, including irradiation time, pH solution, initial dye concentration, amount of
catalyst, light intensity as well as band gap of other semiconductor groups by UV-spectrophotometric monitoring. The highest
decomposition efficiency was obtained at pH 8 as a result of 97.24 % degradation of BP4B for 80 min of irradiation time. Photodecomposition
reaction of BP4B dye was correlated with pseudo-first-order kinetic model. The degradation data of BP4B dye were satisfactory
described by Langmuir-Hinshelwood (L-H) mechanism. 相似文献
997.
Liaqat Ali Abdul Latif Khan Lubna Al-Kharusi Javid Hussain Ahmed Al-Harrasi 《Marine drugs》2015,13(7):4344-4356
The marine ecosystem has been a key resource for secondary metabolites with promising biological roles. In the current study, bioassay-guided phytochemical investigations were carried out to assess the presence of enzyme inhibitory chemical constituents from the methanolic extract of marine green alga—Codium dwarkense. The bioactive fractions were further subjected to chromatographic separations, which resulted in the isolation of a new triterpenic acid; dwarkenoic acid (1) and the known sterols; androst-5-en-3β-ol (2), stigmasta-5,25-dien-3β,7α-diol (3), ergosta-5,25-dien-3β-ol (4), 7-hydroxystigmasta-4,25-dien-3-one-7-O-β-d-fucopyranoside (5), 7-hydroxystigmasta-4,25-dien-3-one (6), and stigmasta-5,25-dien-3β-ol (7). The structure elucidation of the new compound was carried out by combined mass spectrometry and 1D (1H and 13C) and 2D (HSQC, HMBC, COSY, and NOESY) NMR spectroscopic data. The sub-fractions and pure constituents were assayed for enzymatic inhibition of alpha-glucosidase. Compound 1 showed significant inhibition at all concentrations. Compounds 2, 3, 5, and 7 exhibited a dose-dependent response, whereas compounds 4–6 showed moderate inhibition. Utilizing such marine-derived biological resources could lead to drug discoveries related to anti-diabetics. 相似文献
998.
Mohamed R. Akl Nehad M. Ayoub Hassan Y. Ebrahim Mohamed M. Mohyeldin Khaled Y. Orabi Ahmed I. Foudah Khalid A. El Sayed 《Marine drugs》2015,13(1):288-311
Receptor tyrosine kinases are key regulators of cellular growth and proliferation. Dysregulations of receptor tyrosine kinases in cancer cells may promote tumorigenesis by multiple mechanisms including enhanced cell survival and inhibition of cell death. Araguspongines represent a group of macrocyclic oxaquinolizidine alkaloids isolated from the marine sponge Xestospongia species. This study evaluated the anticancer activity of the known oxaquinolizidine alkaloids araguspongines A, C, K and L, and xestospongin B against breast cancer cells. Araguspongine C inhibited the proliferation of multiple breast cancer cell lines in vitro in a dose-dependent manner. Interestingly, araguspongine C-induced autophagic cell death in HER2-overexpressing BT-474 breast cancer cells was characterized by vacuole formation and upregulation of autophagy markers including LC3A/B, Atg3, Atg7, and Atg16L. Araguspongine C-induced autophagy was associated with suppression of c-Met and HER2 receptor tyrosine kinase activation. Further in-silico docking studies and cell-free Z-LYTE assays indicated the potential of direct interaction between araguspongine C and the receptor tyrosine kinases c-Met and HER2 at their kinase domains. Remarkably, araguspongine C treatment resulted in the suppression of PI3K/Akt/mTOR signaling cascade in breast cancer cells undergoing autophagy. Induction of autophagic death in BT-474 cells was also associated with decreased levels of inositol 1,4,5-trisphosphate receptor upon treatment with effective concentration of araguspongine C. In conclusion, results of this study are the first to reveal the potential of araguspongine C as an inhibitor to receptor tyrosine kinases resulting in the induction of autophagic cell death in breast cancer cells. 相似文献
999.
Bernd Krock Urban Tillmann éric Potvin Hae Jin Jeong Wolfgang Drebing Jane Kilcoyne Ahmed Al-Jorani Michael J. Twiner Qun G?thel Matthias K?ck 《Marine drugs》2015,13(11):6687-6702
Two strains of Azadinium poporum, one from the Korean West coast and the other from the North Sea, were mass cultured for isolation of new azaspiracids. Approximately 0.9 mg of pure AZA-36 (1) and 1.3 mg of pure AZA-37 (2) were isolated from the Korean (870 L) and North Sea (120 L) strains, respectively. The structures were determined to be 3-hydroxy-8-methyl-39-demethyl-azaspiracid-1 (1) and 3-hydroxy-7,8-dihydro-39-demethyl-azaspiracid-1 (2) by 1H- and 13C-NMR. Using the Jurkat T lymphocyte cell toxicity assay, (1) and (2) were found to be 6- and 3-fold less toxic than AZA-1, respectively. 相似文献
1000.