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   649篇
  免费   56篇
林业   82篇
农学   33篇
基础科学   4篇
  118篇
综合类   42篇
农作物   37篇
水产渔业   85篇
畜牧兽医   187篇
园艺   20篇
植物保护   97篇
  2023年   11篇
  2022年   12篇
  2021年   43篇
  2020年   37篇
  2019年   30篇
  2018年   34篇
  2017年   32篇
  2016年   35篇
  2015年   31篇
  2014年   31篇
  2013年   40篇
  2012年   46篇
  2011年   63篇
  2010年   27篇
  2009年   29篇
  2008年   40篇
  2007年   24篇
  2006年   26篇
  2005年   27篇
  2004年   20篇
  2003年   23篇
  2002年   23篇
  2001年   3篇
  2000年   4篇
  1999年   4篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1994年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1975年   1篇
排序方式: 共有705条查询结果,搜索用时 31 毫秒
1.
New Forests - Native trees from the Caribbean were tested for seed desiccation responses, by adapting the “100-seed test” protocol. Ninety-seven seed lots of 91 species were collected...  相似文献   
2.
Development of common bean cultivars with partial white mould resistance through breeding techniques has been a challenge in Brazil. As yet, lines/cultivars from breeding programmes have not been investigated for resistance; therefore, this study screened 107 lines/cultivars for their reactions to white mould in 14 preliminary trials conducted under irrigation. Thirteen resistant lines/cultivars (three of Andean origin) and six Mesoamerican cultivars (three intermediately resistant and three susceptible) were selected for further investigation. These lines/cultivars and the resistant control A195 were evaluated in six advanced trials and two straw tests to assess the effectiveness of the screening procedure. In 11 preliminary trials, screenings were performed under moderate/high or higher disease pressure. These pressures occurred in two advanced trials in which, when yields were averaged across moderate/high and high pressures, 10 Mesoamerican lines/cultivars selected for resistance yielded 14%, 23%, and 38% more than intermediately resistant cultivars, A195, and susceptible cultivars, with median disease ratings (1–9 scale) of 4.5, 5.7, 5.7, and 6.7, respectively. In the straw test, three Andean lines/cultivars (A195 included) and two susceptible cultivars in the field were among those with the highest levels of physiological resistance. Thus, field rating under high disease pressure and greenhouse rating did not correlate significantly, suggesting that field trials are critical to evaluating resistance and to identifying high-yielding beans. Therefore, lines/cultivars from breeding programmes assessed in field trials may provide a low cost and fast way to identify high-yielding bean cultivars with partial resistance to white mould in the subtropical southern hemisphere.  相似文献   
3.
Plant Foods for Human Nutrition - Sorghum is a major cereal crop with various agronomic advantages, contains health-promoting compounds and is gluten-free. There is a growing tendency to use...  相似文献   
4.
5.
6.
ObjectiveTo determine if a nerve stimulation test (NST) could act as a monitoring technique to confirm sacrococcygeal epidural needle placement in cats.Study designProspective experimental trial in a clinical setting.AnimalsTwenty-four adult cats, scheduled for a therapeutic procedure where epidural anesthesia was indicated.MethodsUnder general anesthesia, an insulated needle was inserted through the S3-Cd1 intervertebral space guided by the application of a fixed electrical current (0.7 mA) until a motor response was obtained. The NST was considered positive when the epidural nerve stimulation produced a motor response of the muscles of the tail, whereas it was considered negative when no motor response was evoked. In the NST positive cases, 0.3 mL kg−1 of 0.5% bupivacaine was administrated before needle withdrawal. Ten minutes after injection, epidural blockade was confirmed by the loss of perineal (anal), and pelvic limbs reflexes (patellar and withdrawal).ResultsThe use of a fixed electrical stimulation current of 0.7 mA resulted in correct prediction of sacrococcygeal epidural injection, corroborated by post bupivacaine loss of perineal and pelvic limb reflexes, in 95.8% of the cases.Conclusion and clinical relevanceThis study demonstrates the feasibility of using, in a clinical setting, an electrical stimulation test as an objective and in real-time method to confirm sacrococcygeal epidural needle placement in cats.  相似文献   
7.
8.

Background

There is considerable interest in using goats as models for genetically engineering dairy animals and also for using stem cells as therapeutics for bone and cartilage repair. Mesenchymal stem cells (MSCs) have been isolated and characterized from various species, but are poorly characterized in goats.

Results

Goat MSCs isolated from bone marrow (BM-MSCs) and adipose tissue (ASCs) have the ability to undergo osteogenic, adipogenic and chondrogenic differentiation. Cytochemical staining and gene expression analysis show that ASCs have a greater capacity for adipogenic differentiation compared to BM-MSCs and fibroblasts. Different methods of inducing adipogenesis also affect the extent and profile of adipogenic differentiation in MSCs. Goat fibroblasts were not capable of osteogenesis, hence distinguishing them from the MSCs. Goat MSCs and fibroblasts express CD90, CD105, CD73 but not CD45, and exhibit cytoplasmic localization of OCT4 protein. Goat MSCs can be stably transfected by Nucleofection, but, as evidenced by colony-forming efficiency (CFE), yield significantly different levels of progenitor cells that are robust enough to proliferate into colonies of integrants following G418 selection. BM-MSCs expanded over increasing passages in vitro maintained karyotypic stability up to 20 passages in culture, exhibited an increase in adipogenic differentiation and CFE, but showed altered morphology and amenability to genetic modification by selection.

Conclusions

Our findings provide characterization information on goat MSCs, and show that there can be significant differences between MSCs isolated from different tissues and from within the same tissue. Fibroblasts do not exhibit trilineage differentiation potential at the same capacity as MSCs, making it a more reliable method for distinguishing MSCs from fibroblasts, compared to cell surface marker expression.

Electronic supplementary material

The online version of this article (doi:10.1186/2049-1891-6-1) contains supplementary material, which is available to authorized users.  相似文献   
9.
10.
  1. The rapid degradation of freshwater habitats in southern South America may cause the extinction of the endemic species of Aegla, as well as other freshwater species and components of riverside environments related to them. Information on the distribution of species and their conservation status is essential for developing conservation strategies.
  2. The updated distribution of Aegla in its southernmost distribution was analysed in order to prioritize freshwater ecoregions, applying biogeographical, phylogenetic and conservation status and complementarity approaches.
  3. The distributions of the species of Aegla were delineated on maps and plotted against freshwater ecoregions. A data matrix of areas versus species was constructed and a taxon–area cladogram was created. Ecoregions were ranked, based on their species richness and using a complementarity criterion, to create a list of those considered important for conservation. The conservation status of Aegla species was assessed on the basis of the categories and criteria of the International Union for Conservation of Nature (IUCN) to produce a decreasing order of the risk of species extinction. These assessments were combined to define a consensus ranking of the priority areas for conservation.
  4. The areas of maximum species richness and endemicity, and consequently highest priority of conservation, were the Lower Parana and Patagonia ecoregions. The Cuyan Desaguadero and Mar Chiquita Salinas Grandes ecoregions were the areas of second priority, and the Chaco and Lower Uruguay ecoregions were the areas with the third priority for conservation. Ten out of the 20 species analysed fall within the threat categories of the IUCN. Sixty per cent of the species of Aegla analysed have at least one population contained in protected areas.
  5. The results obtained may be used to design strategies for implementing conservation policies on freshwater species, generate biogeographical atlases and contribute to selecting Ramsar sites.
  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