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   360篇
  免费   11篇
  国内免费   3篇
林业   30篇
农学   6篇
基础科学   1篇
  69篇
综合类   23篇
农作物   10篇
水产渔业   66篇
畜牧兽医   149篇
园艺   7篇
植物保护   13篇
  2023年   1篇
  2022年   1篇
  2021年   8篇
  2020年   3篇
  2019年   3篇
  2018年   5篇
  2017年   5篇
  2016年   4篇
  2015年   14篇
  2014年   22篇
  2013年   39篇
  2012年   23篇
  2011年   20篇
  2010年   12篇
  2009年   14篇
  2008年   16篇
  2007年   34篇
  2006年   25篇
  2005年   17篇
  2004年   21篇
  2003年   29篇
  2002年   13篇
  2001年   8篇
  2000年   9篇
  1999年   1篇
  1998年   4篇
  1997年   4篇
  1996年   1篇
  1995年   3篇
  1994年   4篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1988年   1篇
  1987年   3篇
  1984年   1篇
  1980年   1篇
  1979年   1篇
排序方式: 共有374条查询结果,搜索用时 15 毫秒
31.
Blood total antioxidant capacity (TAC) has become a key bio‐marker for animal health. Forest‐grazing cattle are known to forage various native plants that have high TAC. This study evaluated differences of plasma TAC between forest‐grazing (FG) and pasture‐grazing cattle (PG). Experiment 1 monitored the plasma TAC levels of 32 Japanese Black cattle. The level in PG did not change throughout the grazing period. However, that in FG, which increased from summer, was significantly higher than that in PG through fall (P < 0.05). In experiment 2, we used nine Japanese Black heifers and investigated their blood antioxidant parameters and the TAC in plants that the cattle consumed in late June and September. The plasma TAC levels in FG were significantly higher than those in PG in both periods (P < 0.05). Plasma levels of lipid peroxidation in FG tended to be lower than that in PG (P = 0.098). Furthermore, the TAC levels in various species of shrubs and trees consumed by FG were higher than those in pasture grasses. Results of this study show that plasma TAC of grazing Japanese Black cattle in forestland increase from summer through fall.  相似文献   
32.
We attempted to elucidate seasonal variations in fossil-fuel-derived carbon (FC) and biomass-derived carbon (BC) in urban atmospheric aerosols. We undertook continuous measurements of the composition of fine particle (PM2.1) in central Tokyo, including the 14C/12C ratio. The percent modern carbon (pMC) contained in all samples averaged 43, and the highest was 54 in late December and the lowest was 31 in early August. From the observed carbonaceous component concentrations and the pMC we could calculate the content ratio of FC and BC in PM2.1 and investigate their seasonal variations. Although there was almost no seasonal variation in the ratio of FC, the ratio of BC was observed to rise in early winter. This indicates that FC is influenced by the emission sources without seasonal variations (such as automobiles driven in urban areas). Furthermore, there is significant correlation between BC and organic carbon (OC), and even for urban areas, it is considered that the contribution of biomass carbon to OC in PM2.1 is high.  相似文献   
33.
Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein.  相似文献   
34.
Iran supports five different vegetation zones. One of those is the Irano-Touranian zone that is located in the northeast of Iran. This vegetation zone includes arid and semi-arid lands, and its area is about 3.5 million hm2. It supports growth of pistachio (Pistacia vera), a deciduous-broadleaved species, which is one of the ecologically and economically most important native species. In this study, we analyzed three images acquired by ALOS satellite, including 10m resolution multispectral band (AVNIR-2), 2.5 m resolution “Backward” PRISM image, and 2.5 m resolution “Nadir” PRISM image, based on a provided rational polynomial coefficient (RPC). Using the “Backward” and “Nadir” images, a 2.5 m resolution digital elevation model (DEM) was produced. Four methods with AVNIR-2 and PRISM data were used to produce pan-sharpening images and conduct an object-based feature extraction process. Normalized Difference Vegetation Index (NDVI) was used to determine the maximum distribution of pistachio in related elevation. The accuracy of the DEM was tested on 28 ground control points in the pair image as tie points, with the value of parallax error of 0.9027 m. The created elevation map indicated that pistachio trees grow up at 650m above sea level (a.s.l.). The result from NDVI in the related elevation showed the maximum density of pistachio at 800m a.s.l. In addition, the result of feature extraction in the forest showed the area of each target element calculated. The results of this research will improve decision-making and lead to sustainable management in general.  相似文献   
35.
Functional brain organization of macaque monkeys and humans was directly compared by functional magnetic resonance imaging. Subjects of both species performed a modified Wisconsin Card Sorting Test that required behavioral flexibility in the form of cognitive set shifting. Equivalent visual stimuli and task sequence were used for the two species. We found transient activation related to cognitive set shifting in focal regions of prefrontal cortex in both monkeys and humans. These functional homologs were located in cytoarchitectonically equivalent regions in the posterior part of ventrolateral prefrontal cortex. This comparative imaging provides insights into the evolution of cognition in primates.  相似文献   
36.
To decrease the age at first calving in Holsteins, the effects of average daily body weight gain (ADG) and crude protein (CP) level until first insemination on growth performance and milk production were examined. The MM group had a target ADG of 0.75 kg and received a diet with a CP level of 14%. The HM and HH groups had a target ADG of 1 kg; both these groups received a diet with CP levels 14% and 16%, respectively. The ADG in the HM and HH groups was 1.1 kg, whereas in the MM group it was 0.97 kg (P < 0.01). The HM and HH groups showed no differences in withers height at body weight 350 kg. The ages at first calving in MM, HM and HH groups were 23.1, 21.0 and 21.8 months, respectively. The HM and HH groups had lower milk yield at day 305 than the MM group (P < 0.01). These results suggest that growth performance until first insemination should be maintained at an ADG of 0.97 kg or less with a CP level of approximately 14%, to shorten time until first insemination and prevent the decrease of milk yield.  相似文献   
37.
(pp. 59–66)
In order to understand the detailed soil distribution of a terrace with a diluvial deposit, the method to draw a large-scale soil map was studied in Urausu Town of Sorachi district by combinig soil survey and digital elevation data for a 10 m grid.
The results are summarized as follows:
  • 1) 

    From a soil survey, soils in the research area were classified into 3 soil series groups according to Classification of Cultivated Soils in Japan, Third Approximation, which were Skeletal Terrace Brown Forest Soils, Fine-textured Aquic Brown Forest Soils and Fine-textured Haplic Gray Upland Soils. In addition, Fine-textured Haplic Gray Upland Soils · were classified into 2 categories based on the abundance of gravel in the subsoil.

      相似文献   
38.
39.
Summary The biomass of newborn snails was higher in paddy soil without rice plants than in the soil with rice plants. There was an inverse correlation between shell width and concentratins of Zn and Cu in snail flesh. The Zn and Cu concentrations in snail flesh were extremely high compared with those in the paddy soil surrounding the snails, possibly because snails ingest sludge, one of the main components of the composts. These results suggest that this type of snail may be used to eliminate Zn and Cu from paddy soil when composted sewage sludge has been applied.  相似文献   
40.
The sexual preferences of Japanese isolates of Phytophthora infestans were determined by mating on agar, in broth, or in plants. The influence of their sexual preference was confirmed in the host tissues. Three wild-type isolates and a -glucuronidase (GUS) transformant were co-cultured to identify the origin of antheridia and oogonia. Japanese A1 isolate had a unique sexual preference compared with foreign isolates. It produced self-fertile oospores with about 40% of total gametangia but tended to form antheridia on V-8 agar medium. In addition, oospores were formed in plants, but their sexual preference could not be reflected in vitro.  相似文献   
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