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991.
Stevens JF Miranda CL Wolthers KR Schimerlik M Deinzer ML Buhler DR 《Journal of agricultural and food chemistry》2002,50(12):3435-3443
Oligomeric proanthocyanidins constitute a group of water-soluble polyphenolic tannins that are present in the female inflorescences (up to 5% dry wt) of the hop plant (Humulus lupulus). Humans are exposed to hop proanthocyanidins through consumption of beer. Proanthocyanidins from hops were characterized for their chemical structure and their in vitro biological activities. Chemically, they consist mainly of oligomeric catechins ranging from dimers to octamers, with minor amounts of catechin oligomers containing one or two gallocatechin units. The chemical structures of four procyanidin dimers (B1, B2, B3, and B4) and one trimer, epicatechin-(4beta-->8)-catechin-(4alpha-->8)-catechin (TR), were elucidated using mass spectrometry, NMR spectroscopy, and chemical degradation. When tested as a mixture, the hop oligomeric proanthocyanidins (PC) were found to be potent inhibitors of neuronal nitric oxide synthase (nNOS) activity. Among the oligomers tested, procyanidin B2 was most inhibitory against nNOS activity. Procyanidin B3, catechin, and epicatechin were noninhibitory against nNOS activity. PC and the individual oligomers were all strong inhibitors of 3-morpholinosydnonimine (SIN-1)-induced oxidation of LDL, with procyanidin B3 showing the highest antioxidant activity at 0.1 microg/mL. The catechin trimer (TR) exhibited antioxidant activity more than 1 order of magnitude greater than that of alpha-tocopherol or ascorbic acid on a molar basis. 相似文献
992.
Prediction of wetting front stability in dry field soils using soil and precipitation data 总被引:1,自引:0,他引:1
A need exists for information regarding the stability of wetting fronts in field soils because they increase the vulnerability for groundwater contamination. In this study, we develop a simple approach for the evaluation of wetting front stability in dry soils. We show that the stability of wetting fronts in the top layer of a soil depends both on the type of soil and the intensity of the precipitation. Our approach distinguishes stability criteria for wetting events that are different for a high, intermediate, and low infiltration rate. At high infiltration rates, wetting fronts are stable if the infiltration rate exceeds or equals the saturated hydraulic conductivity of the soil. The stability criterion for low infiltration rates (less than approximately 0.2 cm/h for sand soils) is based on two characteristics times[ a gravitational time and an infiltration time. The gravitational time, tgrav, indicates when gravity and capillarity each contribute equally to the process of infiltration. The infiltration time, tinfil, is the duration of the infiltration event. Experimental and literature data show that in well-sorted laboratory sands, wetting fronts are stable when tinfil < 0.002 tgrav. This expression can also be expressed as Wi < 0.002 S2 with W the total amount of precipitation, i its intensity, and S the sorptivity at a slightly positive soil-water pressure. For intermediate infiltration rates, wetting fronts remain stable as long as W is smaller than the amount of water needed to wet a distribution layer near the surface. The application of the stability criteria is demonstrated with a case study from the Sevilleta dunes near Socorro, NM. 相似文献
993.
Antioxidant capacity manipulation in transgenic potato tuber by changes in phenolic compounds content 总被引:1,自引:0,他引:1
Lukaszewicz M Matysiak-Kata I Skala J Fecka I Cisowski W Szopa J 《Journal of agricultural and food chemistry》2004,52(6):1526-1533
The main goal of this study was to generate potato tubers with increased levels of flavonoids and thus modified antioxidant capacities. To accomplish this, the vector carrying multigene construct was prepared and several transgenic plants were generated, all overexpressing key biosynthesis pathway enzymes. The single-gene overexpression or simultaneous expression of genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) resulted in a significant increase of measured phenolic acids and anthocyanins. The increase in phenolic compounds synthesis is accompanied by decreases in starch and glucose levels in transgenic plants. The flavonoids-enriched plants showed improved antioxidant capacity; however, there is a complex relationship between antioxidant capacity and flavonoids content, suggesting the great participation of other compounds in the antioxidant potential of the plants. These other compounds are not yet recognized. 相似文献
994.
Miguel . A. Pinheiro de Carvalho Jan J. Slaski Ivo Abreu Filipe T. Ganana Teresa M. M. dos Santos Lurdes Freitas Maria R. Clemente Vieira Antonieta Nunes Ana Domingues Gregory J. Taylor 《植物养料与土壤学杂志》2004,167(1):93-98
Forty genotypes representing maize genetic diversity from the Island of Madeira were screened for resistance to aluminum (Al) in nutrient solution. Seeds of maize were obtained from local farmers from field plots spread around the island in a range of altitudes from 99 to 1000 m above sea level. The content of ionic aluminum and the pH of soils cultivated with maize were determined. The mean pH value of all examined soils was 4.9, while the mean ionic Al content was 0.76 cmol kg–1. Seventy‐two hours (h) exposure to 100 and 200 μM Al followed by a 48 h recovery period of 4‐day old seedlings revealed significant differences in Al resistance in the Madeiran maize germplasm. Root survival and regrowth exceeding 80 % of the seedlings were observed in 22 and 8 of the tested genotypes screened at 100 and 200 μM Al in nutrient solution. High Al resistance among Madeiran maize genotypes appeared not to be associated with the lower pH of soil, and did not correlate with the amount of soil Al3+ or the altitude at the site of collection. The high level of Al resistance of the maize cultivars indicates an initial genetic trait enhanced by open pollination of maize. 相似文献
995.
TAXI type endoxylanase inhibitors in different cereals 总被引:2,自引:0,他引:2
Goesaert H Gebruers K Brijs K Courtin CM Delcour JA 《Journal of agricultural and food chemistry》2003,51(13):3770-3775
An affinity-based purification procedure with the immobilized family 11 Bacillus subtilis endoxylanase XynA allowed us to obtain high yields of highly pure endoxylanase inhibitor fractions from rye, barley, and durum wheat. In contrast, no inhibitors interacting with the B. subtilis endoxylanase affinity column are present in corn, buckwheat, rice, and oats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis and inhibitor specificity showed that the isolated inhibitors belonged to the TAXI endoxylanase inhibitor family, thus providing a view on the diversity of this cereal inhibitor family. The isolated inhibitors are basic proteins of ca. 40 kDa, occurring in two molecular forms, with pI values of ca. 8.5 (durum wheat) and ca. 9.0 (rye, barley). They are, in general, strong inhibitors of family 11 endoxylanases but not of family 10 endoxylanases. Because cereal endogenous endoxylanases belong to the latter family, this probably indicates that they do not influence cereal metabolic processes. For the first time, endoxylanase inhibitors, similar to TAXI I and TAXI II from wheat, were isolated from durum wheat and characterized. For each cereal, high-resolution cation exchange chromatography revealed the presence of multiple isoinhibitors, each of which occurs in two molecular forms. However, in durum wheat and barley, a single isoform is predominantly present. 相似文献
996.
Lorenc-Kukuła K Amarowicz R Oszmiański J Doermann P Starzycki M Skała J Zuk M Kulma A Szopa J 《Journal of agricultural and food chemistry》2005,53(9):3685-3692
The principal goal of this paper was to generate flax (Linum usitatissimum L.) plants with increased antioxidant properties. To accomplish this a vector containing a multigene construct was prepared, and transgenic plants overexpressing essential flavonoid biosynthesis pathway enzymes were generated and analyzed. The simultaneous expression of genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) resulted in a significant increase of flax antioxidant capacity. To investigate the determinants of higher antioxidant properties of transgenic plants, the phenolic acids and lignans compound contents were measured. In both green part and seed extracts from transgenic plants, the phenolic acids level was increased when compared to the control. The calculated correlation coefficient between phenolic acids content and antioxidant capacity (0.82 and 0.70 for green part and flaxseed, respectively) perfectly reflects their strong relationship. The increase in yield of transgenic plants and their higher resistance to Fusarium culmorum and Fusarium oxysporum when compared to the control plants was a characteristic feature. It was assessed a very high correlation (correlation coefficient = 0.9) between phenolic acids level in flaxseed extract and resistance to F. culmorum. The flowering date of transgenic plants was approximately 3 weeks earlier than that of the control plants. Interestingly, a significant increase in monounsaturated fatty acids and a slight increase in lignans content accompanied the increase in antioxidant properties of flaxseeds. 相似文献
997.
Improving nutritional quality of maize proteins by expressing sense and antisense zein genes 总被引:8,自引:0,他引:8
Huang S Adams WR Zhou Q Malloy KP Voyles DA Anthony J Kriz AL Luethy MH 《Journal of agricultural and food chemistry》2004,52(7):1958-1964
The predominant proteins in maize grain are a family of alcohol-soluble prolamin storage proteins called zeins. They account for >50% of total seed proteins but are deficient in several essential amino acids. As a result, the corn grain is considered to be nutritionally poor for monogastric animals with respect to key essential amino acids, most notably lysine, tryptophan, and methionine. Thus, corn mutants with reduced levels of zeins, such as opaque-2 (o2), have been demonstrated to possess grain with improved nutritional quality characteristics. The o2 mutant has a superior amino acid composition and has been used through conventional breeding to develop Quality Protein Maize (QPM) for human and animal consumption in developing countries. With the understanding of molecular genetics of zeins and progress in biotechnology, an alternative approach to zein reduction is explored here. Through the targeted reduction of the 19-kDa alpha-zeins, increased levels of lysine, tryptophan, and methionine have been engineered in grain of transgenic hybrids. Currently, the agronomic properties and nutritional values of these transgenic lines are being evaluated. 相似文献
998.
999.
Krzeminski R Gorinstein S Leontowicz H Leontowicz M Gralak M Czerwinski J Lojek A Cíz M Martin-Belloso O Gligelmo-Miguel N Trakhtenberg S 《Journal of agricultural and food chemistry》2003,51(19):5774-5779
The mechanism of the hypocholesterolemic effect of olive oils was investigated in 60 Wistar rats adapted to cholesterol-containing and cholesterol-free diets. The rats were divided in six diet groups of 10. The control group was fed only basal diet (BD), which contained wheat starch, casein, cellulose, and mineral and vitamin mixtures. For the five other groups, 10 g/100 g virgin (virgin group) or lampante (lampante group) olive oils, 1 g/100 g cholesterol (chol group), or both cholesterol and oil (chol/virgin and chol/lampante groups) were added to the BD. The experiment lasted 4 weeks. Before and after the experiment the bile was collected, and its flow and biliary bile acids and cholesterol concentrations were registered. Plasma lipids, liver cholesterol, plasma antioxidative potential (TRAP), fecal output, fecal bile acids, and fecal cholesterol excretion were measured. Groups did not differ before the experiment. After the experiment significant hypocholesterolemic and antioxidant effects were registered mainly in groups of rats fed cholesterol-containing diets supplemented with both olive oils (chol/virgin and chol/lampante). Significant increases in the bile flow and in the bile cholesterol and bile acids concentrations were observed (19.2% and 16.9%, 30.5% and 18.2%, and 79.6% and 45.6% for the chol/virgin and chol/lampante groups, respectively). Also, significant increases of the fecal output and fecal excretion of bile acids and cholesterol in rats of these groups were found. In conclusion, olive oils positively affect plasma lipid metabolism. The hypocholesterolemic effect of olive oils is genuine and is most likely mediated through increases in bile flow and biliary cholesterol and bile acids concentrations and subsequent increases in their fecal excretion. 相似文献
1000.