全文获取类型
收费全文 | 1216篇 |
免费 | 54篇 |
专业分类
林业 | 58篇 |
农学 | 45篇 |
基础科学 | 17篇 |
245篇 | |
综合类 | 40篇 |
农作物 | 128篇 |
水产渔业 | 126篇 |
畜牧兽医 | 414篇 |
园艺 | 46篇 |
植物保护 | 151篇 |
出版年
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 58篇 |
2020年 | 56篇 |
2019年 | 82篇 |
2018年 | 52篇 |
2017年 | 78篇 |
2016年 | 59篇 |
2015年 | 42篇 |
2014年 | 48篇 |
2013年 | 90篇 |
2012年 | 78篇 |
2011年 | 77篇 |
2010年 | 52篇 |
2009年 | 40篇 |
2008年 | 47篇 |
2007年 | 36篇 |
2006年 | 42篇 |
2005年 | 46篇 |
2004年 | 31篇 |
2003年 | 21篇 |
2002年 | 31篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有1270条查询结果,搜索用时 31 毫秒
111.
Chemical composition, iron bioavailability, and antioxidant activity of Kappaphycus alvarezzi (Doty)
Fayaz M Namitha KK Murthy KN Swamy MM Sarada R Khanam S Subbarao PV Ravishankar GA 《Journal of agricultural and food chemistry》2005,53(3):792-797
Kappaphycus alvarezzi, an edible seaweed from the west coast of India, was analyzed for its chemical composition. It was found that K. alvarezzi is rich in protein (16.24% w/w) and contains a high amount of fiber (29.40% w/w) and carbohydrates (27.4% w/w). K. alvarezzi showed vitamin A activity of 865 mug retinal equivalents/100 g of sample. It contained a higher quantity of unsaturated fatty acids (44.50% of the total), in which relative percentage of oleic acid was 11%, cis-heptadecanoic acid 13.50%, and linoleic acid 2.3% and 37.0% of saturated fatty acids (mainly heptadecanoic acid). K. alvarezziwas also found to be good source of minerals, viz 0.16% of calcium, 0.033% of iron, and 0.016% of zinc, which are essential for various vital biological activities. Bioavailability of iron by in vitro methods showed a higher efficiency in intestinal conditions than in stomach conditions. Ascorbic acid influenced higher bioavailability of iron. Successive extracts of n-hexane, acetone, ethyl acetate, ethanol, and direct extractables of chloroform/methanol (1:1 and 2:1) were screened for antioxidant activity using a beta-carotene linoleic acid model system (B-CLAMS), DPPH (alpha,alpha-diphenyl-beta-picrylhydrazyl) model system and hydroxyl radical scavenging activity. The chloroform/methanol (2:1) extract has shown 82.5% scavenging activity at 1000 ppm. Acetone fraction extracts at the 1000 ppm level showed 63.31% antioxidant activity in beta-carotene linoleic acid system. The acetone extract showed 46.04% scavenging activity at 1000 ppm concentration. In the case of hydroxyl radical scavenging activity, all the extracts showed better activity at the concentrations of 25 and 50 ppm, where at the 50 ppm level ethyl acetate extract showed 76.0%, acetone 75.12%, and hexane 71.15% activity, respectively. Results of this study suggest the utility of K. alvarezzi (Eucheuma) for various nutritional products, including antioxidant for use as health food or nutraceutical supplement. 相似文献
112.
For the first time the identification and quantification of phenolic compounds of the Olea europaea L. cv. Chemlali olive were carried out to examine their profile during maturation. The phenolic composition was studied by using reverse-phase high-performance liquid chromatography during all steps of fruit development. Oleuropein is the abundant phenolic compound in Chemlali olive, and its concentration increases during maturation. An indirect relationship between oleuropein content in olive fruit and hydroxytyrosol was observed. Weak changes in the amounts of the other phenolic monomers and flavonoids were also observed. The total phenolic content varied from 6 to 16 g/kg expressed as pyrogallol equivalents. Its highest level was found at the last maturation period. The antioxidant capacity of olive extracts was evaluated by measuring the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl. The IC(50) values of the olive extract ranged from 3.2 to 1.5 microg/mL. There was a correlation between antioxidant activity and total phenolic content of samples. The antioxidant activity increased with maturation. This could be attributed to the increase of the tolal phenol level with fruit development. 相似文献
113.
Dellali Mohamed Romeo Michèle Gnassia-Barelli Mauricette Aïssa Patricia 《Water, air, and soil pollution》2004,156(1-4):131-144
Water, Air, & Soil Pollution - From May 1998 to May 1999, the clams Ruditapes decussatus were collected each month at three stations of the Bizerta lagoon. This paper represents a synthesis... 相似文献
114.
Ould El Kebir MV Barnathan G Siau Y Miralles J Gaydou EM 《Journal of agricultural and food chemistry》2003,51(7):1942-1947
If a great number of rays are fished in the Tropical East Atlantic Ocean for their caudal fins, only a small amount of ray flesh is processed. Among them, three species of rays, Dasyatis marmorata, Rhinobatos cemiculus, and Rhinoptera marginata, from the Mauritanian coast have been investigated for the fatty acid composition of their lipids. Gas chromatography and gas chromatography-mass spectrometry allowed identification of 50 molecules from muscles, livers, and gonads of these fishes. Principal component analysis, starting from >50 samples, reveals significant differences in various fatty acid distributions, related to the species and sex of the sampled fish. Some of them are preferentially present in one sex or in both species, whereas the occurrence of others characterizes the male and female of one or two species. The results show that rays are potential resources of polyunsaturated fatty acids (PUFA) and should be used in the diet of local populations. The lipidic fractions contained a high amount of PUFA (up to 30% of the total), mainly composed of docosa-4,7,10,13,16,19-hexaenoic acid, eicosa-5,8,11,14-tetraenoic acid, and eicosa-5,8,11,14,17-pentaenoic acid. 相似文献
115.
Rafi MM Vastano BC Zhu N Ho CT Ghai G Rosen RT Gallo MA DiPaola RS 《Journal of agricultural and food chemistry》2002,50(4):677-684
Herbal therapies are commonly used by patients with cancer, despite little understanding about biologically active chemical derivatives. We recently demonstrated that the herbal combination PC-SPES, which contains licorice root, had anti-prostate cancer activity attributable to estrogen(s) that produced a chemical castration. A recent study also demonstrated that licorice root alone decreased circulating testosterone in men. Other studies demonstrated antitumor activity of PC-SPES in vitro associated with decreased expression of the anti-apoptotic protein Bcl-2 and in patients independent of chemical castration, suggesting that other mechanisms of antitumor activity exist separate from chemical castration. In the present study, we assessed licorice root extract for effects on Bcl-2 to identify novel cytotoxic derivatives. Licorice root extract induced Bcl-2 phosphorylation as demonstrated by immunoblot and G2/M cell cycle arrest, similarly to clinically used antimicrotubule agents such as paclitaxel. Bioassay-directed fractionations resulted in a biologically active fraction for Bcl-2 phosphorylation. HPLC separation followed by mass spectrometry and NMR identified 6 compounds. Only one molecule was responsible for Bcl-2 phosphorylation; it was identified as 1-(2,4-dihydroxyphenyl)-3-hydroxy-3-(4'-hydroxyphenyl) 1-propanone (beta-hydroxy-DHP). The effect on Bcl-2 was structure specific, because alpha-hydroxy-DHP, 1-(2,4-dihydroxyphenyl)-2-hydroxy-3-(4'-hydroxyphenyl) 1-propanone, in contrast to beta-hydroxy-DHP, was not capable of Bcl-2 phosphorylation. Pure beta-hydroxy-DHP induced Bcl-2 phosphorylation in breast and prostate tumor cells, G2/M cell cycle arrest, apoptosis demonstrated by Annexin V and TUNEL assay, decreased cell viability demonstrated by a tetrazolium (MTT) assay, and altered microtubule structure. Therefore, these data demonstrate that licorice root contains beta-hydroxy-DHP, which induced Bcl-2 phosphorylation, apoptosis, and G2/M cell cycle arrest, in breast and prostate tumor cells, similarly to the action of more complex (MW >800) antimicrotubule agents used clinically. 相似文献
116.
M E Hamid G E Mohamed M T Abu Samra A A Hamad 《Revue d'élevage et de médecine vétérinaire des pays tropicaux》1991,44(3):273-275
In a flock of 425 female and male Nubian goats in the Khartoum Province, an outbreak of a disease causing sudden death of 18 apparently healthy goats occurred (11 females and 7 males, 3-6 years old). Adult Fasciola gigantica were found in the livers of all goats and in seven of them Cysticercus tenuicollis cysts. These organs showed necrotic and severe histopathological changes. Clostridium novyi type B was isolated from necrotic areas of all livers and found to be highly pathogenic and toxigenic to laboratory animals. The disease was diagnosed as infectious necrotic hepatitis (black disease). Faecal examination revealed the presence of F. gigantica eggs. Lymnaea natalensis snails were found to be prevalent in the water canals. As the Khartoum Province is regarded as an endemic area for black disease, routine vaccination is highly recommended for its control in goats and sheep. 相似文献
117.
Specific antibody to Pseudomonas pseudomallei exotoxin was detected in sheep sera exposed to natural infection. An enzyme-linked immunosorbent assay (ELISA) was used. Serum antitoxin was present in 49.3% of sera obtained from a flock of sheep naturally exposed to P. pseudomallei infection. Among these sera, 17.0% gave titers of 10,000. In contrast, serum antitoxin was present in only 6.0% of sera collected from sheep kept on a melioidosis-free farm. The ELISA reactivity of all positive sera could be completely absorbed with purified P. pseudomallei exotoxin. Similarly, preincubation of the exotoxin-coated wells with specific antiserum inhibited the ELISA reactivity of sheep sera. The results indicate that exotoxin is produced in vivo during infection by P. pseudomallei. 相似文献
118.
While the respiratory quotient (R.Q.) of Rhinomugil corsula in air-saturated water remains near unity at all levels of random activity, the ammonia quotient (A.Q. = volume or mole: mole relation of ammonia excreted to oxygen consumed) is higher at lower levels of activity, indicating relatively higher protein utilization in less active fish. The mean routine R.Q. values of R. corsula in air-saturated water at temperatures of 30 and 35°C are 0.91 and 0.95 respectively. Assuming that the major sources of ammonia excreted are certain predominant free amino acids, an estimate of caloric break-up of routine meta-bolism of R. corsula suggests that the fish is completely aerobic in air-saturated water and that it derives 14, 44 and 42% of energy from proteins, carbohydrates and fats respectively from a total of 567 cal/kg fish/h at 30°C (15, 55 and 30% at 35°C). At oxygen concentrations below air saturation, R.Q. and A.Q. values of R. corsula increase with decrease in ambient oxygen indicating an increase in anaerobic metabolism and protein utilization. The correlation between the trends of R.Q. and A.Q. levels are similar to that observed earlier in Tilapia mossambica. During hypoxia (1.6 mg O2/l at 30°C) R. corsula derives about half its energy for sustenance and activity anaerobically. The mullet does not appear to accumulate an oxygen debt during hypoxia. 相似文献
119.
A Mohamed Ou Said M G Contrepois M Der Vartanian J P Girardeau 《American journal of veterinary research》1988,49(10):1657-1660
Relative pathogenicity of 151 Escherichia coli isolates from 36 calves with bacteremia after necropsy was studied by measurement of the LD50 after mice were inoculated IP with E coli isolates. Study of virulence factors and markers revealed that the pathogenicity of E coli was associated with the production of hydroxamate siderophores and with resistance to serum bactericidal effects. Production of colicins, including colicin V, and of surface antigen 31A was correlated with virulence. The close association between phenotypic expression of virulence factors and markers was consistent with a hypothesis of a localization of genes coding for virulence factors and markers on the same plasmid. 相似文献
120.
The treatment of synchronized cells of the green alga Chlorella fusca under photoautotrophic conditions with metflurazon (SAN H 6706; 4-chloro-5-dimethylamino-2-(α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone)) induces a bleaching process and results in white-appearing cells. This process of bleaching was followed by quantitative analysis of cell growth and cell division, photosynthetic oxygen evolution, respiratory oxygen consumption, and of pigment pattern at 0, 6, 12, 18, 24, 48, and 72 hr after incubation with different concentrations of metflurazon. Increasing concentrations of metflurazon gradually affected cell growth of Chlorella measured as increase in cell diameter. Cell division was inhibited completely with 1, 10, and 100 μM metflurazon. Photosynthetic oxygen evolution and respiratory oxygen consumption were not inhibited by 1 μM metflurazon during the first 6 hr; after this time a gradually increased inhibition was observed. Both parameters were inhibited by 100 μM metflurazon immediately after herbicide addition. A detailed analysis of the pigment content during the bleaching process revealed that: (a) The bleaching of Chlorella cells by metflurazon is not a simple photochemical process like the photobleaching of boiled cells, but is directed by the active metabolism of Chlorella itself. (b) The bleaching process is characterized by two phases: an accumulation of pigments followed by their degradation. The accumulation phase extends to 6 hr after herbicide addition. (c) During the accumulation phase, chlorophyll is accumulated to 380 and 106% in cells treated with 1 and 100 μM metflurazon, respectively, compared to the initial pigment content. The breakdown of chlorophyll, however, during the degradation phase is 5 times faster in the 1 μM treatment than in the 100 μM treatment. This difference resulted in the faster appearance of white cells with the low metflurazon concentration. (d) During the accumulation phase in the 1 μM treatment, the biosynthesis of chlorophylls, xanthophylls, and carotenes is inhibited by 56, 74, and 78%, respectively, when compared to a nontreated control. When related to the initial amounts, chlorophylls, xanthophylls, and carotenes are accumulated to 380, 230, and 153%, respectively. However, the synthesis of violaxanthin is specifically inhibited, followed by α-carotene. During the degradation phase, violaxanthin and α-carotene again, are the most rapidly disappearing pigments. Continuous culturing of white Chlorella cells resulted in a regeneration to green cells after 96, 240, 384 hr for 1, 10, and 100 μM metflurazone, respectively. The bleaching of Chlorella by metflurazon is evidently dependent on a functioning metabolism and is itself a regulated disassembly of the photosynthetic apparatus, which is reversible and not lethal. 相似文献