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排序方式: 共有188条查询结果,搜索用时 15 毫秒
91.
92.
The terminal phase of the migration of Trichobilharzia regenti Horák, Kolárová et Dvorák, 1998 in the definitive host (Anas platyrhynchos f. domestica) was studied 12-27 days post infection (p.i.). Brain meninges were the last part of the nervous system where the worms were detected before their occurrence in the nasal cavity. In meninges, the parasites started to feed on red blood cells. Then the worms occurred in the nasal mucosa 14-25 days p.i. and the first immature eggs appeared 15 days p.i. The fully developed miracidia were recorded in the eggs from 17 days p.i. and freely in the nasal mucosa 19 days p.i. Infiltrates of lymphocytes, later also eosinophils and heterophils around the eggs and free miracidia, were observed from 15 and 19 days p.i., respectively. The haemorrhages occurring from 17 days p.i., and the granulomas with lymphocytes, eosinophils and heterophils forming around the eggs from 22 days p.i. were the most apparent pathological changes of nasal tissue. 相似文献
93.
The aim of this study was to investigate how potato yield, the concentrations of elements (N, P, K, Ca, Mg, S, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in tubers and their uptake are affected by mineral N, P and K fertilizers, straw and pig slurry application. 相似文献
94.
Petr Hlavinka Miroslav Trnka Daniela Semerádová Martin Dubrovský Zdeněk Žalud Martin Možný 《Agricultural and Forest Meteorology》2009,149(3-4):431-442
The relationship between seasonal agricultural drought and detrended yields (within a period from 1961 to 2000) of selected crops was assessed in the conditions of the Czech Republic, which are to some extent representative of a wider area of Central Europe. Impact of water stress was analyzed using time series of yields for 8 crops (spring barley, winter wheat, grain maize, potato, winter rape, oats, winter rye and hay from permanent meadows) for 77 districts in the Czech Republic (average district area is 1025 km2). Relative version of Palmer’s Z-index (rZ-index or rZ-i) was used as a tool for quantification of agricultural drought. The monthly values of the rZ-index for each individual district were calculated as the spatial average (only for the grids of arable land). The study showed that severe droughts (e.g., in 1981 and 2000) are linked with significant reduction in yields of the main cereals and majority of other crops through the most drought prone regions. We found a statistically significant correlation (p ≤ 0.05) between the sum of the rZ-index for the main growing period of each crop and the yield departures of spring barley within 81% (winter wheat in 57%, maize in 48%, potato in 89%, oats in 79%, winter rye in 52%, rape in 39%, hay in 79%) of the analyzed districts. This study also defined the crop-specific thresholds under which a soil moisture deficit (expressed in terms of rZ-index) leads to severe impact at the district level. This can be expressed as the sum of the monthly rZ-index during the period of high crop sensitivity to drought; for spring barley it is ?5, winter wheat ?5, maize ?9, rape ?12, winter rye ?10, oat ?4, potato ?6 and for hay ?3. The length of the sensitive period is also crop-specific and includes the months that are important for the yield formation. The results show that yields of spring barley (and spring crops in general) are significantly more affected by seasonal water stress than yields of winter crops and hay from permanent meadows. The study proved that a severe drought spell during the sensitive period of vegetative season does have a quantifiable negative effect, even within more humid regions. These results demonstrate that, at least in some areas of the CR (and probably most of Central Europe), drought is one of the key causes of interannual yield variability. 相似文献
95.
Water use efficiency (WUE) was compared in three upland South Moravian forested microwatersheds in the light of effects of global climate change on forest ecosystems (GCC). The experimental catchments were characterized as upland headwater forested microwatersheds of similar size and morphology and silvicultural system, but each with different dominant tree species in the stands (over 50% of forest stand composition in living stock): Norway spruce, European beech and mixed forest. WUE was evaluated according to mean daily streamflow reduction, measured at the discharge points of the recipients of the individual catchments in precipitation-free periods lasting more than 5 days. During these times, streamflow dynamics are mainly influenced by evapotranspiration processes occurring in the forest stands. Four precipitation-free periods were observed, two in the middle of the growing season and two at its end. Two of these periods were long (15 days or more), and two were shorter (6 days). The results indicated that WUE of upland forested catchments can be very different, depending upon the dominant tree species and the seasonal phase. Highest WUE at the catchment scale (never decreasing below 80%) was exhibited by beech predominating site. WUE of mixed forest was high as well, never decreasing below 69%. The lowest WUE was exhibited by spruce predominating site, especially during a long precipitation-free period in the summer where it decreased down to 39%. In the context of the landscape, upland microwatersheds with pure spruce stands could cause its accelerated dry out in the summer and pose a significant threat to sustainable water and forest management of these areas. In comparison, mixed forests stands where spruce is not the dominant species or beech stands should still be a viable option even under the effects of GCC. 相似文献
96.
Enzyme activities and microbial biomass in topsoil layer during spontaneous succession in spoil heaps after brown coal mining 总被引:1,自引:0,他引:1
Petr Baldrian Josef Trgl Jan Frouz Jaroslav najdr Vendula Valkov Vra Merhautov Tom Cajthaml Jana Herinkov 《Soil biology & biochemistry》2008,40(9):2107-2115
Changes in the activity of extracellular enzymes (cellobiohydrolase, β-glucosidase, β-xylosidase, chitinase, arylsulfatase and phosphatases) and the changes in microbial community and abiotic properties in the topsoil layer, as well as soil abiotic properties during primary succession were investigated in a brown coal mine deposit area near Sokolov, Czech Republic. The study considered the chronosequence of 4 post-mining plots, 4-, 12-, 21- and 45-year old. The 4-year old site had no vegetation cover. Herbs and grasses (mainly Calamagrostis epigeios) were present on the 12-year old plot, shrubs (Salix caprea) occurred on the 21-year old plot and tree cover (Betula spp. and Populus tremuloides) developed on the 45-year old plot. Soil pH gradually decreased with site age, while the content of P, K, C and N peaked in the 21-year old site, being significantly lower in the 45-year old site and much lower in the 4- and 12-year old sites. Phosphatase activities were strongly affected by seasonality while the activities of all the other enzymes measured were more influenced by the effects of succession age and soil layer than by seasonality. Succession age was also the most important factor affecting the total and bacterial PLFA contents, followed by the effects of soil layer and season while for the fungal biomass content-related properties (ergosterol, fungal PLFA and the fungal/bacterial PLFA ratio), season was the most important. Activities of individual enzymes in the topsoil (0–5 cm depth) were significantly affected by both site age and season. Cellobiohydrolase and β-xylosidase were more affected by site age while chitinase and phosphatases were more affected by season. Enzyme activity increased with succession age. Comparison of the effect of site and season on enzyme activity showed that season played a principal role in the enzyme activity of the entire 0–5 cm component of topsoil, as well the soil layers when evaluated separately. 相似文献
97.
Wheat genetic resources enhancement by the International Maize and Wheat Improvement Center (CIMMYT) 总被引:1,自引:0,他引:1
Rodomiro Ortiz Hans-Joachim Braun José Crossa Jonathan H. Crouch Guy Davenport John Dixon Susanne Dreisigacker Etienne Duveiller Zhonghu He Julio Huerta Arun K. Joshi Masahiro Kishii Petr Kosina Yann Manes Monica Mezzalama Alexei Morgounov Jiro Murakami Julie Nicol Guillermo Ortiz Ferrara J. Iván Ortiz-Monasterio Thomas S. Payne R. Javier Peña Matthew P. Reynolds Kenneth D. Sayre Ram C. Sharma Ravi P. Singh Jiankang Wang Marilyn Warburton Huixia Wu Masa Iwanaga 《Genetic Resources and Crop Evolution》2008,55(7):1095-1140
The International Maize and Wheat Improvement Center (CIMMYT) acts as a catalyst and leader in a global maize and wheat innovation
network that serves the poor in the developing world. Drawing on strong science and effective partnerships, CIMMYT researchers
create, share, and use knowledge and technology to increase food security, improve the productivity and profitability of farming
systems and sustain natural resources. This people-centered mission does not ignore the fact that CIMMYT’s unique niche is
as a genetic resources enhancement center for the developing world, as shown by this review article focusing on wheat. CIMMYT’s
value proposition resides therefore in its use of crop genetic diversity: conserving it, studying it, adding value to it,
and sharing it in enhanced form with clients worldwide. The main undertakings include: long-term safe conservation of world
heritage of both crop resources for future generations, in line with formal agreements under the 2004 International Treaty
on Plant Genetic Resources for Food and Agriculture, understanding the rich genetic diversity of two of the most important
staples worldwide, exploiting the untapped value of crop genetic resources through discovery of specific, strategically-important
traits required for current and future generations of target beneficiaries, and development of strategic germplasm through
innovative genetic enhancement. Finally, the Center needs to ensure that its main products reach end-users and improve their
livelihoods. In this regard, CIMMYT is the main international, public source of wheat seed-embedded technology to reduce vulnerability
and alleviate poverty, helping farmers move from subsistence to income-generating production systems. Beyond a focus on higher
grain yields and value-added germplasm, CIMMYT plays an “integrative” role in crop and natural resource management research,
promoting the efficient use of water and other inputs, lower production costs, better management of biotic stresses, and enhanced
system diversity and resilience. 相似文献
98.
Tůmová Štěpánka Hrubešová Diana Vorm Petr Hošek Michal Grygar Tomáš Matys 《Journal of Soils and Sediments》2019,19(4):2020-2033
Journal of Soils and Sediments - River channel sediments have been widely used to trace current and historical pollution in fluvial systems, although they are not the only media employed for that... 相似文献
99.
100.
Liquid extraction method for determination of myoglobin in muscle is not suitable because of changes in the derivatives and time required. Optical reflectance method is useful as a non‐destructive and real‐time measurement. However, the base line of reflectance method, the muscular reflectance background (MRB) imagined as colorless structural elements, has been unknown because of non‐existence. The spectrum of the base line was analyzed as the analogy of bleached meat. A formula was derived for reflectance that had a linear relationship to the reciprocal of wavelength to the power 4. The reflectance characteristic of the MRB was not constant and the curve tended to rise with increasing wavelength. The reflectance at 700 nm was estimated to be 50%. By the characteristic analysis on Commission Internationale l’Eclairage color values and reciprocal reflectance, it was concluded that the reflectance spectrum of the muscular background obtained in this research was fitted as a base line for the reflectance spectrometry. 相似文献