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91.
Growth, mycorrhiza and frost resistance of Picea abies seedlings following fertilization with different levels of nitrogen . NPK fertilization with varying levels of nitrogen causes increased growth of spruce seedlings and faster flushing in spring. During the growing season, the frost resistance of all organs of the plants, especially new needles and shoots is the lower, the more nitrogen the plants have received. Consequently, spruce plantations, especially at high altitudes, may be liable to late frost damage. 相似文献
92.
Matrix models of forest dynamics rely on four hypotheses: independence hypothesis, Markov’s hypothesis, Usher’s hypothesis, and temporal homogeneity hypothesis. We investigate the consequences of relaxing Markov’s hypothesis, allowing the state of the tree at time t to depend on its states at time t−1 and t−2. The methodology for building and testing the relevance of second-order matrix model is thus proposed. The derivation of second-order transition probabilities turns to be sensitive to the width of the diameter classes. A strategy for choosing diameter classes is proposed. A second-order matrix model is then built for a tropical rain-forest in French Guiana. A different behaviour is detected between small (dbh ≤30 cm) and large trees, the smaller trees being more sensitive to their past history: small trees that have well grown have a tendency to grow well again, and small trees that have not grown tend to have a higher probability to die. The widths of the diameter classes that are selected are much less than the widths usually retained, that favour first-order selection. 相似文献
93.
Thierry Koumbi-Mounanga Tony Ung Paul Cooper Brigitte Leblon Kevin Groves 《Wood material science & engineering》2015,10(1):17-26
AbstractThe potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R2 value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test. 相似文献
94.
The impact of human activities on size class distribution and spatial distribution of Vitellaria paradoxa (karité or shea butter tree) in the parklands of sub-Saharan Africa has not been reported in the literature. Two sites (Koumantou and Mperesso) in southern Mali and three treatments (cultivated field, fallow and forest) per site were involved in the present study. Results of a statistical test for random distribution showed that the spatial pattern of Vitellaria paradoxa became progressively aggregated from cultivated field to fallow and then to forest. A permanent aggregated pattern found at Koumantou was not found at Mperesso. A test of the independence of larger and smaller tree locations shows that size classes clump together at Koumantou but not at Mperesso. Results of the third test showed that in the cultivated field, auto-correlation was only observed at large scale. In the fallow the trend was towards negative correlation for both sites. In the forest, negative correlation was observed up to 20 m at Koumantou whereas at Mperesso, positive correlation was observed around 35 m and above 50 m. Site differences may be explained by the intensity of fruit production and recruitment, bound to rainfall and land use pressure. Greater regularity of the spatial pattern in cultivated field, then fallow, may be the result of human intervention.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
95.
Imamura K Yasuda M Riwar B Inui S Ekino S 《Comparative immunology, microbiology and infectious diseases》2009,32(5):419-428
We established the method of isolating individually encapsulated germinal centers (GCs) from immunized spleen and analyzed single cell suspension of GCs by flowcytometry. In GCs, the high frequency of sIgG+ cells (29%) and sIgA+ cells (5%) was detected. Two-color flowcytometry analysis showed that GCs contained 27% of sIgM-IgG+ cells, in which isotype switch from IgM to IgG had occurred, and 5% of Bu1-IgG+ cells, which were differentiating into plasma cells. On the other hand, sIgM-IgG+ and Bu1-IgG+ cells were not detected in the bursa, which contained 95% of B cells and only 1% of T cells. CD4+ but not CD8+ T cells were detected in the light zone of GCs and these CD4+ T cells are supposed to play a key role in isotype switching and differentiation into plasma cells in GCs. These results clearly demonstrate that GCs provide a site for isotype switching and differentiation into plasma cells. 相似文献
96.
Martin S. A. Seewald Wolfgang Singer Brigitte A. Knapp Ingrid H. Franke-Whittle Armin Hansel Heribert Insam 《Biology and Fertility of Soils》2010,46(4):371-382
The agronomic effects of composts, mineral fertiliser and combinations thereof on chemical, biological and physiological soil
properties have been studied in an 18-year field experiment. The present study aimed at tracing treatment effects by evaluating
the volatile organic compound (VOC) emission of the differently treated soils: non-amended control, nitrogen fertilisation
and composts (produced from organic waste and sewage sludge, respectively) in combination with nitrogen fertiliser. Microbial
community structure was determined by denaturing gradient gel electrophoresis (DGGE). Aerobic and anaerobic soil VOC emission
was determined after glucose amendment using proton transfer reaction–mass spectrometry (PTR-MS). After inducing VOC production
by substrate (glucose) addition and at the same time reducing oxygen availability to impair degradation of the produced VOCs,
we were able to differentiate among the treatments. Organic waste compost did not alter the VOC emissions compared to the
untreated control, whilst sewage sludge composts and mineral fertilisation showed distinct effects. This differentiation was
supported by DGGE analysis of fungal 18S rDNA fragments and confirms earlier findings on bacterial communities. Three major
conclusions can be drawn: (1) VOC patterns are able to discriminate among soil treatments. (2) Sewage sludge compost and mineral
fertilisation have not only the strongest impact on microbial community composition but also on VOC emission patterns, but
specific tracer VOCs could not be identified. (3) Future efforts should aim at a PTR-MS-linked identification of the detected
masses. 相似文献
97.
Bos AS Brisson BA Nykamp SG Poma R Foster RA 《Journal of the American Veterinary Medical Association》2012,240(8):969-977
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