首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   92篇
  免费   18篇
  国内免费   1篇
林业   3篇
农学   6篇
基础科学   1篇
  17篇
综合类   23篇
农作物   2篇
水产渔业   5篇
畜牧兽医   54篇
  2023年   2篇
  2022年   2篇
  2021年   4篇
  2019年   1篇
  2017年   1篇
  2016年   2篇
  2015年   5篇
  2014年   2篇
  2013年   4篇
  2012年   3篇
  2011年   5篇
  2010年   6篇
  2009年   6篇
  2008年   4篇
  2007年   6篇
  2006年   1篇
  2005年   4篇
  2004年   1篇
  2003年   1篇
  2001年   1篇
  2000年   3篇
  1999年   3篇
  1996年   1篇
  1995年   1篇
  1992年   5篇
  1991年   6篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1978年   2篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1970年   2篇
  1968年   1篇
  1967年   2篇
  1961年   1篇
  1959年   1篇
  1958年   1篇
  1956年   2篇
  1955年   1篇
  1945年   1篇
  1944年   1篇
  1943年   1篇
  1939年   1篇
排序方式: 共有111条查询结果,搜索用时 15 毫秒
61.
During the annual period of bamboo shoot growth in spring, free‐ranging giant pandas feed almost exclusively on the shoots while ignoring the leaves and full‐ height culm. Little is known about the nutritional changes that occur during bamboo shoot growth, if nutritional changes differ among species, or how these changes might influence forage selection. Our objective was to examine the nutrient and mineral composition during three phases of shoot growth (<60, 90–150 and >180 cm) for seven species of bamboo (Phyllostachys (P.) aurea, P. aureosulcata, P. bissetii, P. glauca, P. nuda, P. rubromarginata, Pseudosasa japonica) fed to captive giant pandas at the Memphis Zoo. Total dietary fiber content of bamboo shoots increased (p < 0.0001) from an overall species average of 61% dry matter (DM) at < 60 cm to 75% DM at shoot heights > 180 cm, while crude protein, fat and ash exhibited significant declines (p < 0.05). Phyllostachys nuda had the overall greatest (p = 0.007) crude protein (21% DM) and fat (4% DM) content, and lowest overall total fibre (61% DM) content compared to the other species examined. In contrast, Pseudosasa japonica had the overall lowest crude protein and fat, and relatively higher fibre content (9%, 3% and 74% respectively). Concentrations of Zn and Fe were highest in shoots <60 cm (10–50 μg/g DM) and decreased (p < 0.05) during growth in all species examined. Concentrations of Ca, Cu, Mn, Na and K varied among species and were largely unaffected by growth stage. Due to their higher concentrations of nutrients and lower fibre content in comparison to culm and leaf, bamboo shoots should be a major component of captive giant panda diets when available.  相似文献   
62.
Using radioactive tags, we recorded movements of salamanders (Plethodon jordani) in their home areas and during homing. Males occupied home areas about three times larger than those of females and made occasional excursions into outlying regions. Homing after 22-to 60-meter displacements was direct and rapid, once initiated. Course headings at 1 meter from release were random; those at 2 meters and more were home-oriented. Males initiated homing movements sooner than females, although both sexes traveled at similar rates. Increased incidence of climbing on vegetation after displacement suggests olfactory mechanisms of orientation. These observations give direct evidence of homing orientation in caudate amphibians.  相似文献   
63.
64.
Black spot disease, incited by the fungus Diplocarpon rosae Wolf, is the most important disease of roses (Rosa hybrida L.) in the outdoor landscape. Though partial resistance exists in cultivated germplasm, the genetic basis of this trait has not yet been elucidated. Six diploid and six tetraploid rose cultivars were crossed in two factorial combining ability arrays. Whole plant and detached leaf inoculation methods were used to assess partial resistance under two different disease pressures using a characterized single-spore isolate. Parents from both arrays had significant general combining ability effects across multiple inoculation methods and environments. Specific combining ability was not significant for either array. Parent per se performance was highly correlated with progeny performance on a family mean basis. High positive correlations among whole plant and detached leaf inoculation methods indicate that detached leaf assays can substitute for whole plant assays. Based on these results, a breeding strategy including parental selection and early, among-family selection is proposed. To our knowledge, this is the first investigation of combining ability for disease resistance in rose.  相似文献   
65.
Water quality is one of the potential concerns associated with the development of coalbed natural gas (CBNG) in the Powder River Basin (PRB) of Wyoming and Montana. Large quantities of water (hereafter referred to as CBNG water) are being co-produced and often discharged in the process of exploring natural gas from coal seams. Use of CBNG water for irrigating croplands may be beneficial if factors associated with soil salinity and sodicity are controlled. This study evaluated effects of five water and three soil treatments applied to a mixed-hay cropland on selected soil chemical properties using a split plot design. Water treatments consisted of Piney Creek water (PC or control), direct irrigation with CBNG water (electrical conductivity or EC of 1.38 dS m−1 and sodium adsorption ratio or SAR of 24.3 mmol1/2 L−1/2) with no amendments (NT), CBNG water mixed with solution grade gypsum (G), CBNG water acidified using sulfur burner and mixed with gypsum (GSB) and CBNG water mixed with Piney Creek water (PC/CBNG). Soil treatments consisted of gypsum (G), elemental sulfur (S), combination of these two (GS) and no treatment or the control (NT). Pre (Summer 2003) and post treatment (Fall 2004) soil samples were collected to a depth of 60 cm (top three horizons: A, Bt1 and Bt2) to evaluate the effects of treatments on soil pH, EC, SAR, and sulfate (SO42−) concentrations. Comparisons between pre and post irrigation soil chemistry data indicated CBNG water with no amendments significantly increased (P ≤ 0.05) Na+ concentration within the soil profile. Plots treated with a combination of the GSB water treatment and the GS soil amendments were most effective in maintaining the low SAR values at surface soil layer. In all treatment combinations, both EC and SAR increased significantly in the top two sampling depths (A and Bt1 horizons). Further studies are required to evaluate applications of leaching fractions at the end of each irrigation season for its effectiveness at moving Na+ below the rooting zone.  相似文献   
66.
Perennial ryegrass is an important turf and forage grass in temperate regions worldwide. Limited genetic gains have been made with current breeding strategies compared with other grass crops, such as rice and maize, which benefit from Filial 1 (F1) hybrid breeding. One of the largest constraints on hybrid breeding in ryegrass is self-incompatibility preventing inbreeding, as homozygous parental lines are required to develop hybrids with maximal hybrid vigour. Obligate outcrossing in ryegrass has resulted in cultivars with high levels of heterozygosity, lacking trait uniformity across the population. A naturally occurring self-fertile (SF) locus that overcomes the self-incompatibility system has been identified in a European perennial ryegrass population. This study crossed the SF locus into an elite cultivar, producing a self-compatible population that was inbred for several generations. Genotyping-by-sequencing (GBS) was used to assess the population structure and degree of inbreeding in the self-compatible population. Phenotypic analysis indicated that increased homozygosity did not necessarily affect growth and performance. This study concludes that self-compatible ryegrass is a promising tool for hybrid breeding and agronomic improvement of perennial ryegrass.  相似文献   
67.
Climate‐driven warming has both social and ecological effects on marine fisheries. While recent changes due to anthropogenic global warming have been documented, similar basin‐wide changes have occurred in the past due to natural temperature fluctuations. Here, we document the effects of rapidly changing water temperatures along the United States’ east coast using observations from fisheries newspapers during a warming phase (1945–1951) and subsequent cooling phase (1952–1960) of the Atlantic Multidecadal Oscillation, which we compared to similar recent observations of warming waters (1998–2017). Historical warming and cooling events affected the abundance of species targeted by fishing, the prevalence of novel and invasive species, and physical access to targeted species. Fishing communities viewed historical cooling waters twice as negatively as they did warming waters (72% vs. 35% of observations). Colder waters were associated with a decrease in fishing opportunity due to storminess, while warming waters were associated with the potential for new fisheries. In contrast, recent warming waters were viewed as strongly negative by fishing communities (72% of observations), associated with disease, reductions in abundances of target species, and shifts in distributions across jurisdictional lines. This increasing perception that warming negatively affects local fisheries may be due to an overall reduction of opportunity in fisheries over the past half century, an awareness of the relative severity of warming today, larger changes in American culture, or a combination of these factors. Negative perceptions of recent warming waters’ effects on fisheries suggest that fishing communities are currently finding the prospect of climate adaptation difficult.  相似文献   
68.
A free-ranging juvenile male black bear (Ursus americanus), found dead in Alberta, Canada, had severe nonsuppurative encephalitis. Lesions in the brain were most severe in the gray matter of the cerebral cortex, and included perivascular cuffs of lymphocytes and plasma cells, areas of gliosis that disrupted the neuropil, and intralesional protozoan schizonts. The left hindlimb had suppurative myositis associated with Streptococcus halichoeri. Immunohistochemistry and molecular analyses (PCR and sequencing of 4 discriminatory loci: 18S rDNA, ITS-1 rDNA, cox1, rpoB) identified Sarcocystis canis or a very closely related Sarcocystis sp. in the affected muscle and brain tissues. The main lesion described in previously reported cases of fatal sarcocystosis in bears was necrotizing hepatitis. Fatal encephalitis associated with this parasite represents a novel presentation of sarcocystosis in bears. Sarcocystosis should be considered a differential diagnosis for nonsuppurative encephalitis in bears.  相似文献   
69.
This retrospective study was conducted to identify hemodynamic alterations associated with the administration of an ionic iodinated contrast media in dogs. Case records of 49 dogs that were anesthetized for computed tomography scanning were reviewed. Values for heart rate (HR) and direct arterial pressure were obtained. Overall, 37% of dogs had a ≥20% change in either HR or systolic arterial pressure from baseline values. Four dogs (8%) became tachycardic and two dogs (4%) became bradycardic. Eight dogs (16%) became hypertensive and two dogs (4%) became hypotensive. A significant proportion of dogs experienced changes in HR and blood pressure following IV administration of an ionic iodinated contrast media under general anesthesia.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号