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排序方式: 共有7564条查询结果,搜索用时 0 毫秒
961.
962.
Bird assemblages in forest fragments within Mediterranean mosaics created by wild fires 总被引:1,自引:1,他引:0
The role of habitat heterogeneity as a key factor in determining species pools in habitat mosaics has been acknowledged, but we still know little on the relative importance of the different ecological processes acting within such complex landscapes. We compared species richness and distribution in forest fragments imbedded in shrub-lands to those in continuous forests or in continuous shrublands. We examined the consistency of our data with the predictions of two hypotheses: 1) the Habitat fragmentation hypothesis which states that fragmentation has negative effects on the species from the original continuous habitat; 2) the Habitat supplementation /complementation hypothesis which stipulates that the presence of a matrix habitat around the fragments will mitigate negative effects on the species from the original habitat (supplementation) or allow the presence of species that depend on the presence of both the fragment and matrix habitats (complementation). We show that: 1) species richness in forest fragments did not differ from species richness in segments of continuous forests of equal area; 2) the bird community of forest fragments got impoverished in some forest species but a higher proportion of species common in continuous forests were not affected by fragmentation; 3) fragment communities had a significant proportion of common species that were scarce in, or absent from both continuous forests and shrublands. While, a few forest species supported predictions from the fragmentation hypothesis, occurrence patterns observed in several other species were consistent with either the supplementation or the complementation hypotheses. Our results suggest that there is no single hypothesis that properly captures the consequences of a shift from continuous forests to a mosaic of forest fragments and shrublands and that different ecological mechanisms act in conjunction to determine species pools in habitat mosaics. Habitat heterogeneity at a local scale appears a key factor in maintaining bird diversity in fire driven Mediterranean landscapes. 相似文献
963.
Sabrina?Bertin Simona?Palermo Cristina?Marzachì Domenico?BoscoEmail author 《Phytoparasitica》2004,32(2):141-145
Different molecular procedures were compared for the detection of aster yellows phytoplasmas (AYP) in the leafhopper vectorsMacrosteles quadripunctulatus (Kirschbaum),Euscelidius variegatus (Kirschbaum) andEuscelis incisus (Kirschbaum). Polymerase chain reaction (PCR) with universal and group-specific primers designed on the 16S-rDNA sequence
was most sensitive in nested assays. A dot-blot procedure with an oligoprobe designed on the 16S-rDNA was less sensitive and
consistent to detect phytoplasmas in total insect DNA, but consistently detected amplicons from direct PCR. The dot-blot assay
with a probe based on a phytoplasma plasmid sequence detected AYP in most vector specimens and did not react with DNAs from
leafhoppers infected by flavescence dorée and psyllids infected by apple proliferation phytoplasmas. This last assay is almost
devoid of contamination risks, faster and cheaper compared to PCR, therefore it has to be preferred for field-scale analysis
of leafhopper populations.
http://www.phytoparasitica.org posting Feb. 24, 2004. 相似文献
964.
Eggs and L1 nymphs of the greenhouse whiteflyTrialeurodes vaporariorum (Westwood) (Hem.: Aleyrodidae) on bean leaves were directly sprayed with the fungicides maneb and mancozeb at recommended
rates for practical use. Strong ovicidal and nymphicidal effects were observed. These fungicides may prove to have practical
use for integration in IPM programs for whitefly control, as they also exert low or no toxicity to the whitefly parasitoidEncarsia formosa.
http://www.phytoparasitica.org posting April, 30, 2004. 相似文献
965.
N.?VovlasEmail author N.?J.?O.?Sim?es N.?Sasanelli M.?C.?V.?dos?Santos I.?M.?de?O.?Abrantes 《Phytoparasitica》2004,32(2):167-173
During a nematode survey, severe infections of tobacco feeder roots and heavy soil infestations byMeloidogyne incognita race 1 were found in S. Miguel (Azores islands, Portugal). This is the first record ofM. incognita infection of tobacco in Azores. Morphology of various life stages, analysis of the esterase electrophoretic pattern and differential
host tests were used for nematode characterization and identification. Nematode-induced mature galls were spherical and/or
ellipsoidal and usually contained more than one female, males and egg masses with eggs. Feeding sites were characterized by
the development of giant cells that contained granular cytoplasm and many hypertrophied nuclei. Giant cell cytoplasm was aggregated
along a thickened cell wall. Vascular tissues within galls appeared disorganized. The relationship between the initial nematode
population density and growth of tobacco plants was tested in a glasshouse experiment in which inoculum levels varied from
0 to 512 eggs and juveniles (J2) cm−3 of soil. Seinhorst’s model was fitted to height and top fresh weight data of the inoculated and control plants. Tolerance
limits with respect to plant height and fresh top weight of tobacco cv. ‘Erzegovina’ plants toM. incognita race 1 were estimated as 1.25 eggs and J2 cm−3 of soil. The maximum nematode reproduction rate was 404.7 at an initial population density of 4 eggs and J2 cm−3 of soil.
http://www.phytoparasitica.org posting March 2, 2004. 相似文献
966.
Sathyanarayana?Niranjan?Raj Nandini?Prasad?Shetty Hunthrike?Shekar?ShettyEmail author 《Phytoparasitica》2004,32(5):523-527
In an attempt to find a suitable alternative to the otherwise perilous chemical control strategy of disease management, the
amino acid proline was evaluated for its efficiency to elicit resistance in pearl millet (Pennisetum glaucum (L.) R. Br.) against downy mildew disease caused bySclerospora graminicola (Sacc.) Schroet both under greenhouse and field conditions. Proline treatment to seeds at 50 mM concentration for 3 h, significantly
enhanced the seed germination and seedling vigor of pearl millet in comparison with the control. The same concentration and
duration of seed treatment protected the pearl millet plants from downy mildew by offering 58% protection under greenhouse
and 67% protection under field conditions. Studies revealed that 3 days were required for proline-treated plants to develop
resistance, which was systemic and was sustained throughout the life of the plants. Apart from disease protection, proline
was also found effective in enhancing vegetative and reproductive growth of the plants, as evidenced by the increase in height,
fresh weight, leaf area, tillering capacity, 1000-seed weight and grain yield in comparison with the control plants.
http://www.phytoparasitica.org posting Oct. 3, 2004. 相似文献
967.
968.
Motoo?KoitabashiEmail author Yuuji?Kajitani Keita?Hirashima 《Journal of General Plant Pathology》2004,70(2):124-130
Fungal strain Kyu-W63 from a wheat leaf suppressed the development of wheat powdery mildew caused by Blumeria graminis f. sp. tritici. Nuclear magnetic resonance analysis revealed that Kyu-W63 produced two volatile substances: 5-pentyl-2-furaldehyde and 5-(4-pentenyl)-2-furaldehyde. Although the two are known to be nematicidal substances, the antifungal activity of 5-(4-pentenyl)-2-furaldehyde was first confirmed in the present study. Culture experiments revealed that synthesized 5-pentyl-2-furaldehyde had antifungal activity against three other pathogens – Fusarium oxysporum f. sp. lycopersici, Colletotrichum fragariae, Botrytis cinerea – with a minimum inhibitory concentration of 2–4µg/ml. The two fractionated substances were also inhibitory against C. fragariae. Because the absence of spores in strain Kyu-W63 made its identification difficult, the sequence in the rDNA internal transcribed spacer (ITS) region of Kyu-W63 was compared with that of Irpex lacteus, which is known to produce these substances. Strain Kyu-W63 completely agreed with I. lacteus in terms of the ITS sequences, so strain Kyu-W63 was inferred to be I. lacteus. Two other strains of I. lacteus tested also produced the two furaldehydes and suppressed the growth of F. oxysporum f. sp. lycopersici. Both Kyu-W63 and additional strains produced the two furaldehydes on potato dextrose agar but not on water agar.The nucleotide sequence data reported are available in the DDBJ databases under accession numbers AB079264, AB079265, AB079266, and AB079267 相似文献
969.
970.
Takeshi?Toda Joseph M.?Mghalu Achmadi?Priyatomojo Mitsuro?HyakumachiEmail author 《Journal of General Plant Pathology》2004,70(5):270-272
The rDNA-ITS sequence of Rhizoctonia solani AG 1-ID was determined and compared to those of R. solani AG 1-IA, AG 1-IB, and AG 1-IC. The similarity of the isolates from each AG 1 subgroup was almost identical (99%–100%), whereas it was lower between subgroups (91%–95%) than within subgroups. Phylogenetic analysis indicated that isolates of AG 1-ID and other subgroups were separately clustered. Isolates of R. solani AG 1 were clearly separated from R. solani AG 2-1, AG 4, and binucleate Rhizoctonia AG-Bb and AG-K. These results showed that analysis of the rDNA-ITS sequence is an optimal criterion for differentiating R. solani AG 1-ID from other subgroups of R. solani AG 1. 相似文献