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61.
Ranjith Jayaweera Richard Petersen Pavel Smejtek 《Pesticide biochemistry and physiology》1982,18(2):197-204
Pentachlorophenol (PCP) decreases the rate of carbon assimilation in the alga Selenastrum capricornutum. In parallel with the reduction of carbon assimilation in this alga there is a decrease of electrical resistance of lipid membranes and development of negative membrane surface charge. The experimental results suggest that PCP toxicity to algae is due to adsorption of negatively charged PCP ions at the membrane surface that act as carriers of hydrogen ion across the membrane. This protonophoretic action of PCP causes the decrease of membrane electrical resistance and the dissipation of hydrogen ion electrochemical potential gradients across cellular and subcellular membranes, which reduces the ability of algae to assimilate carbon. 相似文献
62.
63.
Slavin JA Acuña MH Anderson BJ Baker DN Benna M Gloeckler G Gold RE Ho GC Killen RM Korth H Krimigis SM McNutt RL Nittler LR Raines JM Schriver D Solomon SC Starr RD Trávnícek P Zurbuchen TH 《Science (New York, N.Y.)》2008,321(5885):85-89
Observations by MESSENGER show that Mercury's magnetosphere is immersed in a comet-like cloud of planetary ions. The most abundant, Na+, is broadly distributed but exhibits flux maxima in the magnetosheath, where the local plasma flow speed is high, and near the spacecraft's closest approach, where atmospheric density should peak. The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity. Two outbound current sheet boundaries were observed, across which the magnetic field decreased in a manner suggestive of a double magnetopause. The separation of these current layers, comparable to the gyro-radius of a Na+ pickup ion entering the magnetosphere after being accelerated in the magnetosheath, may indicate a planetary ion boundary layer. 相似文献
64.
Slimak L Svendsen JI Mangerud J Plisson H Heggen HP Brugère A Pavlov PY 《Science (New York, N.Y.)》2011,332(6031):841-845
Palaeolithic sites in Russian high latitudes have been considered as Upper Palaeolithic and thus representing an Arctic expansion of modern humans. Here we show that at Byzovaya, in the western foothills of the Polar Urals, the technological structure of the lithic assemblage makes it directly comparable with Mousterian Middle Palaeolithic industries that so far have been exclusively attributed to the Neandertal populations in Europe. Radiocarbon and optical-stimulated luminescence dates on bones and sand grains indicate that the site was occupied during a short period around 28,500 carbon-14 years before the present (about 31,000 to 34,000 calendar years ago), at the time when only Upper Palaeolithic cultures occupied lower latitudes of Eurasia. Byzovaya may thus represent a late northern refuge for Neandertals, about 1000 km north of earlier known Mousterian sites. 相似文献
65.
The concentration of cellulose in plant material greatly affects the decomposition rate of plant-derived litter and hence carbon availability. The disappearance of pure cellulose in soil was studied as a measure of plant decomposition and carbon turnover. Our objective was to understand the effect of various cellulose concentrations and plant material added to soil and collected during different seasons, on cellulase concentrations under laboratory conditions (e.g. constant soil moisture and incubation temperature). The percentage of recovery of the enzyme in the control soil and in samples amended with known amounts of cellulose powder was estimated. Several methods for estimating soil cellulase concentrations/activity are available, most based on the determination of released reducing sugars. The method used in this study is based on the cleavage of a cellulose-azure substrate by cellulase to spectrophotometrically detectable fragments. Our results showed a significant correlation (p<0.05) between cellulose concentration and cellulase levels in soil, which varied along the study period. When pure cellulose was added to the soil, cellulase was detected after 7 days of incubation, whereas when plant material was added to the soil, cellulase was detected after 14 days. The recovery of cellulase from soil was also found to be seasonally dependent. The method of cellulase determination used in this study was simple, safe and rapid. From the results presented in this study, it can be assumed that there are seasonally dependent factors that affect the existence and concentration of cellulase in soils of the arid Negev Desert, in addition to organic matter, water and temperature. 相似文献
66.
Jana Řepková Antonín Dreiseitl Pavel Lízal Zdeňka Kyjovská Kateřina Teturová Radka Psotková Ahmed Jahoor 《Euphytica》2006,151(1):23-30
Summary Four newly detected accessions of wild barley (Hordeum
vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria
graminis f. sp. hordei were studied with the aim of finding the number of genes/loci conferring the resistance of individual accessions, the type of inheritance of the genes and their relationships to the Mla locus. F2 populations after crosses between the winter variety ‘Tiffany’ and four wild barley accessions and use of microsatellite DNA markers were focused on the identification of individual resistance genes/loci by means of their chromosomal locations. In PI466495, one locus conferring powdery mildew resistance was identified in highly significant linkage with the marker Bmac0213. This location is consistent with the known locus Mla on chromosome 1HS. In the other three accessions the resistance was determined by two independent loci. In PI466197, PI466297 and PI466461, one locus was identified on chromosome 1HS and three new loci were revealed on chromosomes 2HS (highly significant linkage with Bmac0134), 7HS (highly significant linkage with Bmag0021) and 7HL (significant linkage with EBmac0755). Our prospective aim is identification of further linked DNA markers and the exact location of the resistance genes on the barley chromosomes. 相似文献
67.
Identification of species-specific DNA in feedstuffs 总被引:2,自引:0,他引:2
Due to the menace of transmission of spongiform encephalopathies, feed components intended for ruminant nutrition must be checked for the presence of ruminant-derived materials. A sensitive method for the identification of bovine- and ovine- and also swine- and chicken-specific mitochondrial DNA sequences based on Polymerase Chain Reaction (PCR) has been developed. The specificity of the primers for PCR has been tested using samples of DNA of other vertebrate species, which may also be present in rendering plant products intended for feed manufacture. The method allows the detection in concentrate mixtures of 0.01% of the target species derived material. The identity of a sample containing 0.1% of bovine, ovine, swine, and chicken meat-and-bone meal has further been confirmed by sequencing. 相似文献
68.
Tom Navrátil James B. Shanley Petr Skřivan Pavel Krám Martin Mihaljevič Petr Drahota 《Water, air, and soil pollution》2007,186(1-4):149-165
Mn biogeochemistry was studied from 1994 to 2003 in a small forested catchment in the central Czech Republic using the watershed mass balance approach together with measurements of internal stores and fluxes. Mn inputs in bulk deposition were relatively constant during a period of sharply decreasing acidic deposition, suggesting that the Mn source was terrestrial, and not from fossil fuel combustion. Mn inputs in bulk deposition and Mn supplied by weathering each averaged 13 mg m?2 year?1 (26 mg m?2 year?1 total input), whereas Mn export in streamwater and groundwater averaged 43 mg m?2 year?1. Thus an additional Mn source is needed to account for 17 mg m?2 year?1. Internal fluxes and pools of Mn were significantly greater than annual inputs and outputs. Throughfall Mn flux was 70 mg m?2 year?1, litterfall Mn flux was 103 mg m?2 year?1, and Mn net uptake by vegetation was 62 mg m?2 year?1. Large pools of labile or potentially labile Mn were present in biomass and surficial soil horizons. Small leakages from these large pools likely supply the additional Mn needed to close the watershed mass balance. This leakage may reflect an adjustment of the ecosystem to recent changes in atmospheric acidity. 相似文献
69.
This paper focuses on the influence of uranium tailing piles on the contamination of their immediate surroundings. The monitoring was carried out on arable land near Pribram in Central Bohemia, Czech Republic. The monitored arable land is located 600 m northeast of the bottom of the piles. In addition, the high uranium (U) content in the topsoil ranged from 40 to 220 ppm. A former portion of it was found in an exchangeable fraction (49%). Both of these facts make this land unsuitable for agricultural use. The sequential extraction discovered a shift in the U content among sample spots situated in and outside the path of the predominant wind direction. In the first group, uranium binds mainly to Fe/Mn oxides, while in the other samples, U is accumulated in the more mobilizable fractions. 相似文献
70.