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101.
Hans H. Becher 《植物养料与土壤学杂志》1991,154(1):3-8
On the bulk density of aggregates and its possible impact on the movement of soil solutions The bulk densities of the aggregate fractions 15-18 mm, 10-15 mm, 5-10 mm, and 3-5 mm from a Typic Hapludalf, an Aquic Hapludalf, and a Typic Chromudert, all used as cropland and grassland, and that of aggregates of the 3-5 mm fraction from a Typic Dystrochrept used for a farm manure and crop residue trial, lay between 1.8 and 2.0 g/cm3. Sampling was done down to depths of 85 cm, 70 cm, 55 cm, and 80 cm. respectively. The bulk density values increase in most cases with decreasing aggregate size and indicate the aggregate pore volumes to generally range from 25 to 35% b.v. This means that either soil aggregates often contain only fine pores or that fine and medium pores also act as inter-aggregate pores. As a consequence, movement and exchange of soil water and soil solution between inter- and intra-aggregate pores is severely restricted. 相似文献
102.
Hans‐Werner Olfs Klaus Blankenau Frank Brentrup Jrg Jasper Axel Link Joachim Lammel 《植物养料与土壤学杂志》2005,168(4):414-431
Under‐ as well as overfertilization with nitrogen (N) will result in economic loss for the farmer due to reduced yields and quality of the products. Also from an ecological perspective, it is important that the grower makes the correct decision on how much and when to apply N for a certain crop to minimize impacts on the environment. To aggravate the situation, N is a substance that is present in many compartments in different forms (nitrate, ammonium, organic N, etc.) in the soil‐plant environment and takes part in various processes (e.g., mineralization, immobilization, leaching, denitrification, etc.). Today, many N‐recommendation systems are mainly based on yield expectation. However, yields are not stable from year to year for a given field. Also the processes that determine the N supply from other sources than fertilizer are not predictable at the start of the growing season. Different methodological approaches are reviewed that have been introduced to improve N‐fertilizer recommendations for arable crops. Many soil‐based methods have been developed to measure soil mineral N (SMN) that is available for plants at a given sampling date. Soil sampling at the start of the growing period and analyzing for the amount of NO ‐N (and NH ‐N) is a widespread approach in Europe and North America. Based on data from field calibrations, the SMN pool is filled up with fertilizer N to a recommended amount. Depending on pre‐crop, use of organic manure, or soil characteristics, the recommendation might be modified (±10–50 kg N ha–1). Another set of soil methods has been established to estimate the amount of N that is mineralized from soil organic matter, plant residues, and/or organic manure. From the huge range of methods proposed so far, simple mild extraction procedures have gained most interest, but introduction into practical recommendation schemes has been rather limited. Plant‐analytical procedures cover the whole range from quantitative laboratory analysis to semiquantitative “quick” tests carried out in the field. The main idea is that the plant itself is the best indicator for the N supply from any source within the growth period. In‐field methods like the nitrate plant sap/petiole test and chlorophyll measurements with hand‐held devices or via remote sensing are regarded as most promising, because with these methods an adequate adjustment of the N‐fertilizer application strategy within the season is feasible. Prerequisite is a fertilization strategy that is based on several N applications and not on a one‐go approach. 相似文献
103.
Wohlmuth H Leach DN Smith MK Myers SP 《Journal of agricultural and food chemistry》2005,53(14):5772-5778
Ginger (Zingiber officinale Roscoe), a monocotyledonous, sterile cultigen, is widely used as a spice, flavoring agent, and herbal medicine. The pungency of fresh ginger is due to a series of homologous phenolic ketones of which [6]-gingerol is the major one. The gingerols are thermally unstable and can be converted to their corresponding shogaols, which are present in dried ginger. Fresh rhizomes of 17 clones of Australian ginger, including commercial cultivars and experimental tetraploid clones, were assayed by HPLC for gingerols and shogaols. [6]-Gingerol was identified as the major pungent phenolic compound in all samples, while [8]- and [10]-gingerol occurred in lower concentrations. One cultivar known as "Jamaican" contained the highest concentrations of all three gingerols and was the most pungent of the clones analyzed. Gingerols were stable in ethanolic solution over a 5-month period when stored at 4 degrees C. Shogaols were not identified in the extracts prepared from fresh rhizomes at ambient temperature, confirming that these compounds are not native constituents of fresh ginger. In contrast to previous findings, this study did not find significant differences in gingerol concentrations between the tetraploid clones and their parent diploid cultivar. 相似文献
104.
Liquid and syrupy dietary saps and juices of plant origin, characterized by the presence of large quantities of saccharides (glucose, fructose, or sucrose) and containing amino acids, were analyzed for the presence of D-amino acids using enantioselective gas chromatography-mass spectrometry. D-amino acids were detected in processed saps and juices of trees (maple, palm, birch), fruits (grape, apple, pear, pomegranate, date), and various other plants (agave, beetroot, sugar cane, carob). D-Ala was detected in all plant products and amounted to approximately 34% D-Ala (relative to L-Ala + D-Ala) in Canadian maple syrups, to approximately 13% in palm saps, and to 48 and 13% D-Ala, respectively, in concentrated grape juices (Spanish Arrope and Turkish Pekmez). Varying amounts and kinds of other D-amino acids were also detected. To test the hypothesis that racemization, that is, partial conversion of L-amino acids into their corresponding D-enantiomers, occurs at reversible stages of the Maillard reaction, the Amadori compound fructose-L-phenylalanine was synthesized. On heating at 200 degrees C for 5 (20) min, release of 10.8% (24.2%) D-Phe was detected. From the data it is concluded that the Amadori compounds formed in the course of the Maillard reaction are pecursors of D-amino acids in foodstuffs. 相似文献
105.
Hans H. Becher 《植物养料与土壤学杂志》1992,155(5):361-366
Relevance of strength distribution within aggregates to the movement of soil water and soil solution Different transport processes exist not only between the total soil and single aggregates, but also within individual aggregates. To clarify the structure of single aggregates without thin-sectioning, resistance to penetration was repeatedly measured on the same aggregate at a predefined soil water tension. The aggregates were sampled from the Go 2 horizon of a Typic Fluvaquent (Φ 15-25mm) and from the Bg 2 horizon of an Aquic Chromudert (Φ 30-50mm) and equilibrated with water tensions ranging from roughly OhPa to 1000hPa. The strength distributions within individual aggregates were calculated using penetration resistance values of all measurements on one aggregate at a single water tension. These distributions, as exemplified by those at 300hPa and 1000hPa. show that the aggregates are surrounded by a thin, but very strong mineral skin which may be discontinuous, especially for aggregates from the Aquic Chromudert soil. In these aggregates, slickenside-like friction planes were found to penetrate through the skin. The deviation in the skin composition from that of the inner-aggregate described in literature, together with the finding of its strength, suggest that the exchange of water and solutes between the inter-aggregate and intra-aggregate pores is strongly impeded. The weaker parts within the skin, however, must be interpreted as preferred pathways, perhaps resulting in some fingering within aggregates at the prevailing matrix potential. The significance of different pathways within aggregates for the general transport of matter in soils is briefly discussed. 相似文献
106.
107.
Bunzel M Ralph J Lu F Hatfield RD Steinhart H 《Journal of agricultural and food chemistry》2004,52(21):6496-6502
Plant cell walls containing suberin or lignin in the human diet are conjectured to protect against colon cancer. To confirm the existence of authentic lignin in cereal grain dietary fibers, the DFRC (derivatization followed by reductive cleavage) method was applied to different cereal grain dietary fibers. By cleavage of diagnostic arylglycerol-beta-aryl (beta-O-4) ether linkages and identification of the liberated monolignols, it was ascertained that lignins are truly present in cereal grains. From the ratios of the liberated monolignols coniferyl alcohol and sinapyl alcohol, it is suggested that lignin compositions vary among cereals. Furthermore, dimeric cross-coupling products, comprising ferulate and coniferyl alcohol, were identified in most cereal fibers investigated. These ferulate 4-O-beta- and 8-beta-coniferyl alcohol cross-coupled structures indicate radical cross-coupling of polysaccharides to lignin precursors via ferulate. 相似文献
108.
Data on atmospheric deposition, transport via run-off water and contents in soil were used to estimate the fluxes of Zn, Cd, Cu, Pb, and Hg to Swedish forest lakes. The calculations refer to a hypothetical lake with a surface area of about 9% of the total catchment area. There are clear differences in the pathways and transport mechanisms for the different elements. The dominating pathway for the input of Zn and Cd to lakes is via run-off from the drainage area. About 60 to 95% of the total load comes from run-off, highest in the acidified areas. The acidification status of the soil is by far the most important factor regulating the mobility of these elements. The amounts of Hg and Pb deposited on the drainage area are mainly accumulating in the surficial soil layers. The transport of these elements is primarily associated with humic substances. About 30 to 50% of the total load of Pb and 25 to 75% of the total load of Hg to lakes originates from run-off. The transport mechanisms for Cu are similar to those of Pb and Hg, but due to the lower anthropogenic airborne load, the direct deposition is of less importance. 相似文献
109.
Ingemar Alenäs B. Ingvar Andersson Hans Hultberg Arno Rosemarin 《Water, air, and soil pollution》1991,59(1-2):55-77
Long-term monitoring, 1973 to 1987, of reactions to liming and reacidification of a forest lake ecosystem near the Swedish west coast is reported in this study. Treatment of Lake Lysevatten with a slag product of limestone in 1974 resulted in neutralization and a positive alkalinity. Prolonged dissolution proceeded for about 7 yr whereby 86% dissolved. During 1984–86 Lake Lysevatten approached maximum reacidification with high Al concentrations and an affected biota. Asellus aquaticus L. decreased and dominance within chironomid groups approached preliming conditions. However, the most obvious biological change was the development of the filamentous algal genus Mougeotia and increased growth of Sphagnum. Populations of both plants increased notably when pH declined to about 5. Our study suggests that extensive reacidification (pH < 6.0) of limed lakes should be avoided by successive treatments to prevent development of destabilized lake ecosystems. 相似文献
110.
The long-term persistence of plant populations may partly depend on pollination processes and seed production. The exact role of pollination in determining plant population viability still remains largely unclear. Orchid species have often been shown to be pollinator limited. Especially, non-rewarding species are characterized by infrequent pollinator visits and low seed set. Therefore, it can be hypothesized that, if overall population fitness of orchid species is influenced by seed production, non-rewarding species should be more prone to local extinction than rewarding species. To study the importance of nectar reward on orchid persistence, we collected historical records about the distribution of 32 orchid species in Flanders (Belgium) and 37 orchid species in the Netherlands. For both regions, present distribution patterns were compared with historical data. Between 1930 (Flanders) or 1950 (the Netherlands) and 2000, 26 (81%) species showed decreases in distribution range in Flanders, eight of which had gone extinct, whereas 29 (78%) species showed declines in distribution area in the Netherlands, five of which went extinct. Contrary to previously reported results, orchid distribution patterns were not related to nectar reward. There was also no significant relationship between nectar reward and extinction for both regions. Orchids typically occurring in wet grasslands and heathlands suffered greater losses than orchids typically confined to forest habitats or calcareous grasslands. We conclude that the production of nectar does not represent a safeguard for local extinction of orchid species. Habitat loss and other deterministic threats associated with habitat fragmentation and deterioration are more important determinants of orchid persistence. 相似文献