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   314篇
  免费   17篇
  国内免费   1篇
林业   65篇
农学   4篇
  23篇
综合类   9篇
农作物   25篇
水产渔业   45篇
畜牧兽医   146篇
园艺   2篇
植物保护   13篇
  2021年   9篇
  2020年   3篇
  2019年   8篇
  2018年   6篇
  2017年   14篇
  2016年   7篇
  2015年   8篇
  2014年   10篇
  2013年   19篇
  2012年   17篇
  2011年   22篇
  2010年   7篇
  2009年   7篇
  2008年   17篇
  2007年   8篇
  2006年   17篇
  2005年   18篇
  2004年   13篇
  2003年   13篇
  2002年   19篇
  2001年   9篇
  2000年   12篇
  1999年   6篇
  1998年   4篇
  1997年   3篇
  1996年   1篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   5篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1983年   4篇
  1982年   1篇
  1981年   4篇
  1980年   1篇
  1979年   4篇
  1978年   3篇
  1977年   1篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
  1971年   3篇
  1970年   2篇
  1968年   2篇
  1967年   1篇
  1966年   1篇
排序方式: 共有332条查询结果,搜索用时 435 毫秒
61.
Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 106 CFU/g and 1 × 108 CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 108 CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 108 CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 108 CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load.  相似文献   
62.
Diploid gametes generated with tetraploid animals are a stepping stone to improving chromosome manipulation techniques. However, artificially induced tetraploid individuals generally die soon after hatching. Diploid gametes could be induced by in vivo cultures of tetraploid primordial germ cells (PGCs) through germ-line chimera. In the present study, characteristics of PGCs were studied in inviable tetraploid masu salmon, Oncorhynchus masou. Histological observation of tetraploid embryos revealed that the same or smaller numbers of PGCs were observed and they migrate into the genital ridges as did diploid PGCs during gonadogenesis. By whole-mount in situ hybridization using vasa messenger RNA (mRNA), 4–35 vasa-positive signals were detected in a pair of genital ridges of tetraploids. By cytological observation of genital ridge cell suspensions, several large round cells were observed, some of which extended pseudopodia. They also contained large nuclei and round granules in their cytoplasm, characteristics of PGCs. As the results suggest that inviable artificial tetraploids have PGCs, we expect to achieve diploid gamete production through surrogate propagation and tetraploid fish production.  相似文献   
63.
64.
This study evaluated the effects of condensed barley distillers soluble (CBDS) on growth rate, rumen fermentation, plasma metabolite, and myofiber properties, and gene expression related to metabolism in the skeletal muscles of Japanese Black calves, compared with soybean meal and corn. Twenty‐four calves were divided into four groups: fed 5% CBDS based on the hay dry matter weight (low CBDS) and fed soybean meal and corn at the same nutrition level (control); and fed 15% CBDS based on the hay dry matter weight (high CBDS) and fed soybean meal and corn at the same nutrition level (high soy). The daily gain was larger in the low (p = 0.08) and high (< 0.05) CBDS groups compared with the control group. In the CBDS‐fed groups, plasma β‐hydroxybutyric acid concentrations were significantly higher at 6 months of age (< 0.05), the percentage of type I myofibers was significantly lower and their diameters were significantly larger at 9 months of age (< 0.05), and carnitine palmitoyltransferase 1b mRNA expression was significantly lower (< 0.05) and citrate synthase mRNA expression tended to be lower (low; p = 0.06, high; = 0.05) compared with control group. Thus, feeding CBDS promotes growth and leads to animals with more glycolytic and less oxidative muscle metabolism.  相似文献   
65.
This experiment was conducted to clarify the nutritional functions of rice and phytase addition for broiler chicks. Thirty‐six 7‐day‐old male chicks (ROSS 308 strain) were assigned to one of the four treatment groups: corn‐ or rice‐based diet groups and each diet with added phytase (2000 phytase units/kg diet) groups (corn + P or rice + P groups). The non‐phytate phosphorus (npP) content in the diets with added phytase was approximately half of the requirement. Body weight gain and feed intake in the rice group was significantly higher than those in the corn group. Breast and thigh muscle weights and nitrogen retention in the rice group were significantly higher than that in the corn group. Although the efficiency of phosphorus retention (%) in the corn + P group was significantly higher than that in the corn group, no significant difference was observed between the rice and rice + P groups. Liver threonine dehydrogenase activity in the corn group was significantly higher than in the other three groups. These results indicate that rice is superior to corn as a starter diet in broiler chicks, and that phytase action in the rice‐based diet was less than that in the corn‐based diet.  相似文献   
66.

Context

Recent conceptual developments in ecosystem services research have revealed the need to elucidate the complex and unintended relationships between humans and the environment if we are to better understand and manage ecosystem services in practice.

Objectives

This study aimed to develop a model that spatially represents a complex human–environment (H–E) system consisting of heterogeneous social–ecological components and feedback mechanisms at multiple scales, in order to assess multi-dimensional (spatial, temporal, and social) trade-offs in ecosystem services.

Methods

We constructed an agent-based model and empirically calibrated it for a semi-arid region in Northeast China, and examined ecosystem service trade-offs derived from the Sloping Land Conversion Program (SLCP), which is based on payment for ecosystem services. This paper describes our model, named Inner Mongolia Land Use Dynamic Simulator (IM-LUDAS), using the overview, design concepts, and details + decision (ODD + D) protocol and demonstrates the capabilities of IM-LUDAS through simulations.

Results

IM-LUDAS represented typical characteristics of complex H–E systems, such as secondary and cross-scale feedback loops, time lags, and threshold change, revealing the following results: tree plantations expanded by the SLCP facilitated vegetation and soil restoration and household change toward off-farm livelihoods, as expected by the government; conversely, the program caused further land degradation outside the implementation plots; moreover, the livelihood changes were not large enough to compensate for income deterioration by policy-induced reduction in cropland.

Conclusions

IM-LUDAS proved itself to be an advanced empirical model that can recreate essential features of complex H–E systems and assess multi-dimensional trade-offs in ecosystem services.
  相似文献   
67.
68.
Paddy and Water Environment - In recent years, Paddy Field Dams have received recognition as a measure to alleviate flooding due to torrential rains. Paddy Field Dams have been in practice in...  相似文献   
69.
70.
The spectral data of a new triterpene, cucurbita-5,23-diene-3beta,25-diol, isolated from the seeds of Sicana odorifera, are reported.  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