全文获取类型
收费全文 | 11710篇 |
免费 | 815篇 |
国内免费 | 4篇 |
专业分类
林业 | 999篇 |
农学 | 482篇 |
基础科学 | 91篇 |
3078篇 | |
综合类 | 355篇 |
农作物 | 547篇 |
水产渔业 | 1242篇 |
畜牧兽医 | 4503篇 |
园艺 | 215篇 |
植物保护 | 1017篇 |
出版年
2023年 | 90篇 |
2022年 | 145篇 |
2021年 | 287篇 |
2020年 | 286篇 |
2019年 | 254篇 |
2018年 | 584篇 |
2017年 | 539篇 |
2016年 | 538篇 |
2015年 | 423篇 |
2014年 | 484篇 |
2013年 | 730篇 |
2012年 | 849篇 |
2011年 | 801篇 |
2010年 | 487篇 |
2009年 | 432篇 |
2008年 | 681篇 |
2007年 | 678篇 |
2006年 | 531篇 |
2005年 | 540篇 |
2004年 | 466篇 |
2003年 | 400篇 |
2002年 | 354篇 |
2001年 | 254篇 |
2000年 | 264篇 |
1999年 | 215篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 23篇 |
1993年 | 26篇 |
1992年 | 72篇 |
1991年 | 54篇 |
1990年 | 63篇 |
1989年 | 61篇 |
1988年 | 44篇 |
1987年 | 55篇 |
1986年 | 54篇 |
1985年 | 54篇 |
1984年 | 43篇 |
1983年 | 45篇 |
1982年 | 26篇 |
1979年 | 36篇 |
1978年 | 35篇 |
1977年 | 36篇 |
1974年 | 29篇 |
1973年 | 48篇 |
1972年 | 34篇 |
1971年 | 27篇 |
1969年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
981.
Sanz ML del Castillo MD Corzo N Olano A 《Journal of agricultural and food chemistry》2003,51(15):4278-4283
Determination of changes in 2-furoylmethyl amino acids and hydroxymethylfurfural during the storage of four honey samples at 25 and 35 degrees C during 12 months was achieved to assess the potential use of both parameters, singly or in combination, as quality indicators. 2-Furoylmethyl amino acids increased during storage at both temperatures, whereas hydroxymethylfurfural only presented slight variations during storage at 25 degrees C but increased noticeably at 35 degrees C. The study of 2-furoylmethyl amino acids in 49 commercial honeys revealed that 2-furoylmethyl lysine (furosine) was present in all samples, whereas 2-furoylmethyl derivatives of arginine, GABA, and proline were only present in seven samples. Hydroxymethylfurfural can be considered as a good indicator of heat treatments applied to honey samples, whereas 2-furoylmethyl amino acids can be used as suitable markers of the storage period. The use of both parameters can be useful to detect adulteration with invert syrups, excessive heat treatments, or prolonged storage of honey samples. 相似文献
982.
Salas JH González MM Noa M Pérez NA Díaz G Gutiérrez R Zazueta H Osuna I 《Journal of agricultural and food chemistry》2003,51(15):4468-4471
A study was conducted to measure residues of 13 organophosphorus (OP) pesticides, widely used as dairy cattle ectoparasiticides or in crops used for animal feed, in homogenized and pasteurized Mexican milk samples. Four different milk brands with high distribution were collected biweekly during a 12 month period (n = 96) in supermarkets. OP pesticide residues were measured by gas chromatography with a flame photometric detector. Approximately 39.6% of the samples contained detectable levels of OP pesticide residues. Eight samples contained residues exceeding established maximum residue limits (MRL), and the OP pesticides present in these samples were dichlorvos (five samples), phorate, chlorpyrifos, and chlorfenvinphos (one sample, respectively). Average residues of 13 OP pesticides measured were below established MRLs ranging between 0.0051 and 0.0203 ppm. 相似文献
983.
Lezcano M Novo M Al-Soufi W Rodríguez-Núñez E Tato JV 《Journal of agricultural and food chemistry》2003,51(17):5036-5040
The formation of inclusion complexes with beta-cyclodextrin was studied for several popular fungicides of different types: prochloraz, 2-phenylphenol, thiophanate methyl, 8-hydroxyquinoline, and benalaxyl. Phase solubility diagrams showed that in all cases complexation takes place, leading to an important increase of water solubility in prochloraz and benalaxyl. Equilibrium association constants could be determined from the phase solubility data and from NMR titrations in the case of 2-phenylphenol. Because of the low solubility of the complex formed between 8-hydroxyquinoline and beta-cyclodextrin, the corresponding association constant could not be determined. The solid complexes of fungicide-cyclodextrin were prepared and isolated by different methods. The isolation of real complexes and not physical mixtures was confirmed in the cases of prochloraz, 2-phenylphenol, and benalaxyl by differential scanning calorimetry. 相似文献
984.
Soil salinity and its distribution determined by soil sampling and electromagnetic techniques 总被引:3,自引:0,他引:3
Abstract. Diagnosis of soil salinity and its spatial variability is required to establish control measures in irrigated agriculture. This article shows the usefulness of electromagnetic (EM) and soil sampling techniques to map salinity. We analysed the salinity of a 1‐ha plot of surface‐irrigated olive plantation in Aragon, NE Spain, by measuring the electrical conductivity of the saturation extract (ECe) of soil samples taken at 22 points, and by reading the Geonics EM38 sensor at 141 points in the horizontal (EMH) and vertical (EMV) dipole positions. EMH and EMV values had asymmetrical bimodal distributions, with most readings in the non‐saline range and a sharp transition to relatively high readings. Most salinity profiles were uniform (i.e. EMH=EMV), except in areas with high salinity and concurrent shallow water tables, where the profiles were inverted as shown by EMH > EMV, and by ECe being greater in shallow than in deeper layers. The regressions of ECe on EM readings predicted ECe with R2 > 84% for the 0–100 to 0–150 cm soil depths. We then produced salinity contour maps from the 141 ECe values estimated from the electromagnetic readings and the 22 measured values of ECe. Owing to the high soil sampling density, the maps were similar (i.e. mean surface‐weighted ECe values between 3.9 dS m?1 and 4.2 dS m?1), although the electromagnetically estimated ECe improved the mapping of details. Whereas soil sampling is preferred for analysing the vertical distribution of soil salinity, the electromagnetic sensor is ideal for mapping the lateral variability of soil salinity. 相似文献
985.
Estévez M Ventanas S Ramírez R Cava R 《Journal of agricultural and food chemistry》2004,52(16):5168-5174
The effect of the addition of two natural antioxidant extracts (sage and rosemary essential oils) and one synthetic (BHT) on the generation of volatile compounds in liver patés from Iberian and white pigs was analyzed using SPME-GC-MS. Lipid-derived volatiles such as aldehydes [hexanal, octanal, nonanal, hept-(Z)-4-enal, oct-(E)-2-enal, non-(Z)-2-enal, dec-(E)-2-enal, deca-(E,Z)-2,4-dienal] and alcohols (pentan-1-ol, hexan-1-ol, oct-1-en-3-ol) were the most abundant compounds in the headspace of porcine liver patés. Patés from different pig breeds presented different volatiles profiles due to their different oxidation susceptibilities as a probable result of their fatty acid profiles and vitamin E content. Regardless of the origin of the patés, the addition of BHT successfully reduced the amount of volatiles derived from PUFA oxidation. Added essential oils showed a different effect on the generation of volatiles whether they were added in patés from Iberian or white pigs because they inhibited lipid oxidation in the former and enhanced oxidative instability in the latter. SPME successfully allowed the isolation and analysis of 41 volatile terpenes from patés with added sage and rosemary essential oils including alpha-pinene, beta-myrcene, 1-limonene, (E)-caryophyllene, linalool, camphor, and 1,8-cineole, which might contribute to the aroma characteristics of liver patés. 相似文献
986.
Serra-Majem L Ribas L Ngo J Ortega RM García A Pérez-Rodrigo C Aranceta J 《Public health nutrition》2004,7(7):931-935
OBJECTIVE: To evaluate dietary habits in Spanish children and adolescents based on a Mediterranean Diet Quality Index tool, which considers certain principles sustaining and challenging traditional healthy Mediterranean dietary patterns. DESIGN: Observational population-based cross-sectional study. A 16-item Mediterranean Diet Quality Index was included in data gathered for the EnKid study (in which two 24-hour recalls, a quantitative 169-item food-frequency questionnaire and a general questionnaire about socio-economic, demographic and lifestyle items were administered). SETTING: Spain. SUBJECTS: In total, 3850 children and youths aged 2-24 years residing in Spain. RESULTS: Of the sample, 4.2% showed very low KIDMED index results, 49.4% had intermediate values and 46.4% had high index results. Important geographical differences were seen, with subjects from the Northeast showing the most favourable outcomes (52% with elevated scores vs. 37.5% of those from the North). Lower percentages of high diet quality were observed in low socio-economic groups, compared with middle and upper income cohorts (42.8%, 47.6% and 54.9%, respectively). Large cities had more positive results and only slight variations were seen for gender and age. CONCLUSIONS: The KIDMED index, the first to evaluate the adequacy of Mediterranean dietary patterns in children and youth, confirms that this collective is undergoing important changes, which makes them a priority target for nutrition interventions. Results challenge certain commonly perceived notions tied to income level, population size and diet quality. 相似文献
987.
In vivo antifungal activity of the essential oil of Bupleurum gibraltarium against Plasmopara halstedii in sunflower 总被引:1,自引:0,他引:1
Fernández-Ocaña AM Gómez-Rodríguez MV Velasco-Negueruela A Camacho-Simarro AM Fernández-López C Altarejos J 《Journal of agricultural and food chemistry》2004,52(21):6414-6417
The antifungal activity of the essential oil of the aerial parts of Bupleurum gibraltarium was evaluated against Plasmopara halstedii. Fungus spores were inoculated in sunflower seedlings, previously treated with several essential oil solutions, and the sporulation percentage was measured after an 11-day treatment. The oil at a concentration of 5.0 mL/L clearly inhibited the fungus sporulation. The contact between fungus sporangia and essential oil was minimized, so it seems that the oil pretreatment could activate the defense response of the sunflower seedlings against the pathogen invasion. The main compounds in the oil were sabinene (31.1%), alpha-pinene (15.6%), and 2,3,4-trimethylbenzaldehyde (10.9%), among a total of 65 components identified. 相似文献
988.
Patrícia Valent?o Paula B Andrade Eurico Silva Ana Vicente Henrique Santos M Lourdes Bastos Rosa M Seabra 《Journal of agricultural and food chemistry》2002,50(3):460-463
In the course of a phytochemical study of the bitter tonic plant, small centaury (Centaurium erythraea), six methoxylated xanthones (1,5-hydroxy-3-methoxyxanthone, 1-hydroxy-3,5,6-trimethoxyxanthone, 1-hydroxy-3,5,6,7-tetramethoxyxanthone, 1-hydroxy-3,5,6,7,8-pentamethoxyxanthone, 1-hydroxy-3,7,8-trimethoxyxanthone and 1,8-dihydroxy-3,5,6,7-tetramethoxyxanthone) were isolated and identified by spectroscopic means (nuclear magnetic resonance, mass spectroscopy, and UV). Subsequently, a high-performance liquid chromatography/diode array detection method was developed for the determination of these and other methoxylated xanthones occurring in the chloroform extract of small centaury aerial parts. The methodology developed was applied to twelve samples, and in all of them, nine xanthones were identified and quantified. This methodology can be considered complimentary to the one proposed by the European Pharmacopoeia. 相似文献
989.
Darriet P Pons M Henry R Dumont O Findeling V Cartolaro P Calonnec A Dubourdieu D 《Journal of agricultural and food chemistry》2002,50(11):3277-3282
Powdery mildew due to the fungus Uncinula necator is an important disease for the vineyard. The development of the fungus at the surface of the berries leads to the occurrence of a very characteristic and sometimes intense mushroom-type odor cited as an important default for grapes quality. Gas chromatography/olfactometry, gas chromatography, and multidimensional gas chromatogaphy/mass spectrometry techniques were used to investigate the most important odorants of grapes diseased by powdery mildew. Among 22 odorants detected, strongly odorant compounds were identified or tentatively identified in purified extracts obtained from grapes diseased by powdery mildew. Aroma extraction dilution analysis (AEDA) analysis revealed that 1-octen-3-one (mushroom odor), (Z)-1,5-octadien-3-one (geranium-leaf odor), and an unidentified odorous zone (fishy-mushroom like odor) were the most potent volatiles of the diseased grapes. In the presence of nonproliferating Saccharomyces cerevisiae yeast cells, and consequently during alcoholic fermentation, the enzymatic reduction of 1-octen-3-one and (Z)-1,5-octadien-3-one to much less odorant compounds, namely 3-octanone and (Z)-5-octen-3-one, was shown. Those results explain to some extent the disappearance of the fungal aroma specific to powdery mildew grapes during alcoholic fermentation. 相似文献
990.
Hornero-Méndez D Gómez-Ladrón De Guevara R Mínguez-Mosquera MI 《Journal of agricultural and food chemistry》2000,48(9):3857-3864
Changes in the biosynthesis of individual carotenoid pigments have been investigated during fruit ripening of five cultivars of red pepper (Capsicum annuum L.): Mana, Numex, Belrubi, Delfin, and Negral (a chlorophyll-retaining mutant when ripe). The study was carried out throughout the ripening process, and with special emphasis on the ripe stage, to discover possible differences between cultivars and to characterize these by their carotenoid pattern and content for selecting the best varieties for breeding programs. Ripening fruit of the five cultivars showed the typical and characteristic pattern of carotenoid biosynthesis for the Capsicum genus. In the five cultivars, lutein and neoxanthin, both characteristic chloroplast pigments, decreased in concentration with ripening and eventually disappeared. beta-Carotene, antheraxanthin, and violaxanthin increased in concentration, and other pigments were biosynthesized de novo: zeaxanthin, beta-cryptoxanthin, capsanthin, capsorubin, capsanthin-5,6-epoxide, and cucurbitaxanthin A. A pool of zeaxanthin stands out of the rest of pigment during ripening, which reveals the importance of this pigment as a branching point in the carotenoid biosynthesis in Capsicum. Quantitatively, Negral cultivar showed the highest increase in total carotenoid content (48. 39-fold), followed by Mana and Delfin with 38.03- and 36.8-fold, respectively, and by Belrubi and Numex with 28.03- and 23.48-fold, respectively. In all the red varieties, there was an inverse relationship between total carotenoid content and the red to yellow isochromic pigment fraction ratio (R/Y) and the capsanthin-to-zeaxanthin ratio (Caps/Zeax). This seems to be related to the carotenogenic capacity of the cultivar, and thus selection and breeding should not only seek a higher total carotenoid content but also attempt to increase these ratios. In the present study, the cultivar Mana had the highest total carotenoid content (13 208 mg/kg dwt), but the lowest R/Y (1.25) and Caps/Zeax (3.38) ratios, which are therefore the parameters to improve. The cultivar Negral had a high carotenoid content (8797 mg/kg dwt) and high R/Y and Caps/Zeax ratios and could be used for transfer of these characters in direct crosses with the cultivar Mana. The cultivar Numex had the highest Caps/Zeax ratio (7.17) and is thus an ideal progenitor for this character. 相似文献