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431.
Axel Höhn Michael Sommer Danuta Kaczorek Gisbert Schalitz Jörn Breuer 《植物养料与土壤学杂志》2008,171(3):409-418
The importance of silicon (Si) in nutrition is currently being recognized by its beneficial effects on many crops. Therefore, it is important to determine the soil Si status and to examine different extractants for testing plant‐available Si. Little information is available about the Si status of Histosols and Corg‐rich Gleysols in temperate climate. This study was undertaken (1) to characterize different Si pools in Corg‐rich groundwater soils of an experimental site and (2) to study the influences of small‐scale variability on element distribution. At the experimental site, the thickness of the Corg‐rich layer ranges between 4 and 5 dm overlying fine‐sandy fluvial sediments. Four extractants were evaluated: 0.01 M CaCl2, 0.5 M acetic acid, 0.1 M sodium pyrophosphate, and 0.1 M Tiron (C6H4Na2O8S2 · H2O). Further, total element content was determined following HNO3/HF digestion. Calcium chloride–soluble Si shows no significant relations to other parameters analyzed. On the basis of published data, the soils investigated could be classified as Si‐deficient. The Si fraction extracted with acetic acid displays relations to Corg content of the soil and a weak correlation to CaCl2‐soluble Si, indicating that both solutions extract overlapping but not the same fractions. Sodium pyrophosphate extracts mainly organo‐mineral Fe and Al complexes in the soils studied, which is reflected in a highly positive correlation to Corg. Pyrophosphate‐soluble Si showed a negative relationship to Corg, which means a closer relation of this Si fraction to mineral matter than to Corg. The Tiron solution extracted most Si of all extractants, but this amounts only 1% of the total Si content. Taking into account the element‐specific relationship between pyrophosphate and Tiron‐extractable Fe, Al, and Si, it can be concluded that Tiron dissolves mainly the opaline silica present in Histosols and Corg‐rich Gleysols. The distribution of Corg and ash content shows clear spatial trend at the experimental site, which is correlated to pyrophosphate‐extractable as well as total Si. This small‐scale variability of soil parameters itself is related to a distinct microrelief. 相似文献
432.
Boretti FS Sieber-Ruckstuhl NS Favrot C Lutz H Hofmann-Lehmann R Reusch CE 《American journal of veterinary research》2006,67(12):2012-2016
OBJECTIVE: To evaluate the use of recombinant human (rh) thyroid-stimulating hormone (TSH) in dogs with suspected hypothyroidism. ANIMALS: 64 dogs with clinical signs of hypothyroidism. PROCEDURES: Dogs received rhTSH (75 microg/dog, IV) at a dose independent of their body weight. Blood samples were taken before and 6 hours after rhTSH administration for determination of total serum thyroxine (T(4)) concentration. Dogs were placed into 1 of 3 groups as follows: those with normal (ie, poststimulation values indicative of euthyroidism), unchanged (ie, poststimulation values indicative of hypothyroidism; no thyroid gland stimulation), or intermediate (ie, poststimulation values between unchanged and normal values) post-TSH T(4) concentrations. Serum canine TSH (cTSH) concentration was determined in prestimulation serum (ie, before TSH administration). RESULTS: 14, 35, and 15 dogs had unchanged, normal, and intermediate post-TSH T(4) concentrations, respectively. Basal T(4) and post-TSH T(4) concentrations were significantly different among groups. On the basis of basal serum T(4) and cTSH concentrations alone, 1 euthyroid (normal post-TSH T(4), low basal T(4), and high cTSH concentrations) and 1 hypothyroid dog (unchanged post-TSH T(4) concentration and low to with-in reference range T(4) and cTSH concentrations) would have been misinterpreted as hypothyroid and euthyroid, respectively. Nine of the 15 dogs with intermediate post-TSHT(4) concentrations had received medication known to affect thyroid function prior to the test, and 2 of them had severe nonthyroidal disease. CONCLUSIONS AND CLINICAL RELEVANCE: The TSH-stimulation test with rhTSH is a valuable diagnostic tool to assess thyroid function in selected dogs in which a diagnosis of hypothyroidism cannot be based on basal T(4) and cTSH concentrations alone. 相似文献
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435.
The effect of an enriched methanolic extract ofMelia azedarach L. (Meliaceae) fruits on the size of the corpora allata (CA), the juvenile hormone (JH) titer and the protein content in
the hemolymph of two lepidopteran pests in Egypt,Spodoptera littoralis (Boisd.) andAgrotis ipsilon (Hufn.), was studied. Different concentrations of the extract were incorporated into an artificial diet on which the larvae
were allowed to feed. InS. littoralis, a significant reduction in the CA volume of larvae treated at the 1000 ppm extract levelvs that of control larvae was observed. In A.ipsilon, a reduction was found in the right CA gland only. Larvae of both species that had fed on a diet withMelia extract had a higher mean JH-II titer in the hemolymph than did control larvae. In both species, the content of hemolymph
protein was decreased significantly after feeding for 6 days on a diet treated with concentrations above 50 ppm extract, followed
by 6 days on a normal diet. The results show that aM. azedarach fruit extract has an effect on the neuroendocrine control in the insects. The effect on the hemolymph protein levels is discussed
in connection with changes in the morphology/physiology of the gut. 相似文献