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   105篇
  免费   0篇
林业   9篇
农学   4篇
  23篇
综合类   20篇
农作物   10篇
水产渔业   2篇
畜牧兽医   34篇
园艺   1篇
植物保护   2篇
  2023年   3篇
  2022年   2篇
  2021年   5篇
  2020年   3篇
  2019年   6篇
  2018年   4篇
  2017年   5篇
  2016年   5篇
  2015年   6篇
  2014年   4篇
  2013年   3篇
  2012年   6篇
  2011年   7篇
  2010年   2篇
  2009年   4篇
  2008年   3篇
  2007年   6篇
  2006年   1篇
  2005年   1篇
  2004年   2篇
  2003年   2篇
  2002年   1篇
  2001年   1篇
  2000年   1篇
  1998年   1篇
  1997年   1篇
  1986年   1篇
  1979年   1篇
  1978年   1篇
  1976年   1篇
  1975年   4篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1969年   1篇
  1968年   1篇
  1967年   3篇
  1966年   2篇
  1965年   2篇
排序方式: 共有105条查询结果,搜索用时 15 毫秒
31.
The presence of aggregates of various sizes in the soil is an important condition for soil carbon sequestration. In this system, microbial biomass is a key link. This work was devoted to the study of the influence of land use systems on the distribution of SOС, MB-SIR, microbial activity and eco-physiological indices (qCO2, QR, MB-SIR/SOС and qCO2/SOС) in relation to the size of soil aggregates. The distribution of SOС, MB-SIR and mineralization activity among the aggregates was heterogeneous. In the soil of crop rotation, high mineralization activity and MB-SIR were found in the aggregates 0.5–0.1 mm, in the monoculture soil in aggregates <0.1 mm and in the control soil in the aggregates 1–0.25 mm. There was a general trend towards a decrease in microbial activity, MB-SIR and SOС availability with an increase in aggregate size. In agricultural soils, microbial activity was determined by large aggregates (>5 mm), while in the control soil, by the aggregates 5–1 mm. Depending on the type of site and the size of aggregates, the differences in microbial metabolism were revealed. The qCO2 and QR values decreased, and the MB-SIR/SOС and qCO2/SOС increased in the series: control soil > crop rotation > monoculture. In the control soil, the values of the eco-physiological indices decreased with decreasing aggregate size. And vice versa, in agricultural soils, these parameters were the highest in the microaggregates (<0.25 mm). The monoculture soil, in contrast to the control soil and crop rotation soil, turned out to be more energy efficient.  相似文献   
32.
Three structurally different fucoidans from the brown seaweeds Saccharina latissima (SL), Fucus vesiculosus (FV), and Cladosiphon okamuranus (CO), two chemically modified fucoidans with a higher degree of sulfation (SL-S, CO-S), and a synthetic totally sulfated octasaccharide (OS), related to fucoidans, were assessed on anticoagulant and antithrombotic activities in different in vitro experiments. The effects were shown to depend on the structural features of the compounds tested. Native fucoidan SL with a degree of sulfation (DS) of 1.3 was found to be the most active sample, fucoidan FV (DS 0.9) demonstrated moderate activity, while the polysaccharide CO (DS 0.4) was inactive in all performed experiments, even at high concentrations. Additional introduction of sulfate groups into fucoidan SL slightly decreased the anticoagulant effect of SL-S, while sulfation of CO, giving rise to the preparation CO-S, increased the activity dramatically. The high level of anticoagulant activity of polysaccharides SL, SL-S, and CO-S was explained by their ability to form ternary complexes with ATIII-Xa and ATIII-IIa, as well as to bind directly to thrombin. Synthetic per-O-sulfated octasaccharide OS showed moderate anticoagulant effect, determined mainly by the interaction of OS with the factor Xa in the presence of ATIII. Comparable tendencies were observed in the antithrombotic properties of the compounds tested.  相似文献   
33.
Bayesian MCMC calibration and uncertainty analysis for computationally expensive models is implemented using the SOARS (Statistical and Optimization Analysis using Response Surfaces) methodology. SOARS uses a radial basis function interpolator as a surrogate, also known as an emulator or meta-model, for the logarithm of the posterior density. To prevent wasteful evaluations of the expensive model, the emulator is built only on a high posterior density region (HPDR), which is located by a global optimization algorithm. The set of points in the HPDR where the expensive model is evaluated is determined sequentially by the GRIMA algorithm described in detail in another paper but outlined here. Enhancements of the GRIMA algorithm were introduced to improve efficiency. A case study uses an eight-parameter SWAT2005 (Soil and Water Assessment Tool) model where daily stream flows and phosphorus concentrations are modeled for the Town Brook watershed which is part of the New York City water supply. A Supplemental Material file available online contains additional technical details and additional analysis of the Town Brook application.  相似文献   
34.
 采用SMART RACE 方法,从东方山羊豆盐诱导抑制性差减杂交cDNA 文库中分离到了一个脱水蛋白(GoDHN)基因。该基因cDNA 全长1169bp,开放阅读框843bp,编码281 个氨基酸,编码的蛋白质分子量为28.71kDa。经实时荧光定量PCR 分析,GoDHN 基因在东方山羊豆的茎和叶中表达量明显高于根中表达量,并且基因表达受ABA、NaCl和PEG 的诱导,随着诱导时间的增加,表达量呈持续增长趋势。这些结果表明,DHN 基因在东方山羊豆的抗逆性中可能起到重要的调控作用。本研究成功构建了pCAMBIA1302-DHN 植物表达载体,为下一步转基因研究奠定了基础。  相似文献   
35.
Natural anionic polysaccharides fucosylated chondroitin sulfates (FCS) from sea cucumbers attract great attention nowadays due to their ability to influence various biological processes, such as blood coagulation, thrombosis, angiogenesis, inflammation, bacterial and viral adhesion. To determine pharmacophore fragments in FCS we have started systematic synthesis of oligosaccharides with well-defined structure related to various fragments of these polysaccharides. In this communication, the synthesis of non-sulfated and selectively O-sulfated di- and trisaccharides structurally related to branching sites of FCS is described. The target compounds are built up of propyl β-d-glucuronic acid residue bearing at O-3 α-l-fucosyl or α-l-fucosyl-(1→3)-α-l-fucosyl substituents. O-Sulfation pattern in the fucose units of the synthetic targets was selected according to the known to date holothurian FCS structures. Stereospecific α-glycoside bond formation was achieved using 2-O-benzyl-3,4-di-O-chloroacetyl-α-l-fucosyl trichloroacetimidate as a donor. Stereochemical outcome of the glycosylation was explained by the remote participation of the chloroacetyl groups with the formation of the stabilized glycosyl cations, which could be attacked by the glycosyl acceptor only from the α-side. The experimental results were in good agreement with the SCF/MP2 calculated energies of such participation. The synthesized oligosaccharides are regarded as model compounds for the determination of a structure-activity relationship in FCS.  相似文献   
36.
On the postnatal development of the skeletal muscle cells in the pig Skeletal muscle cells of pigs up to ten years old were examined histologically and histometrically for age-related changes. Also examined was the relationship between the changes of the average muscle cell diameter and the age-related weight changes of the muscles. It was found that, during the entire postnatal period, skeletal muscle cells, despite their high differentiation, continued to develop and developed anew. The two muscle celltypes, red and white, could be differentiated by the end of the first month. The white cells formed the periphery of the muscle cell bundle. They developed from the red muscle cells and can be regarded as more highly differentiated than the latter. The red muscle cells, which retained many postnatal reatures, after the first month formed a group of cells in the center of a muscle cell bundle. Growth of muscle therefore does not only occur by enlargement of the muscle cells (hypertrophy) buy also by their increase in numbre (hyperplasia). The average diameter of the muscle cells in thus related in addition to age, breed, sex, diet and husbandry, also to mitotic intensity and the formation of new muscle cells.  相似文献   
37.
38.
39.
Criteria and indices of the degree of degradation of the vegetation cover are established. The limiting effect of abiotic factors on productivity of degraded pastures is determined.  相似文献   
40.
There is limited regeneration of lost tissue after central nervous system injury, and the lesion is sealed with a scar. The role of the scar, which often is referred to as the glial scar because of its abundance of astrocytes, is complex and has been discussed for more than a century. Here we show that a specific pericyte subtype gives rise to scar-forming stromal cells, which outnumber astrocytes, in the injured spinal cord. Blocking the generation of progeny by this pericyte subtype results in failure to seal the injured tissue. The formation of connective tissue is common to many injuries and pathologies, and here we demonstrate a cellular origin of fibrosis.  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