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   307篇
  免费   10篇
  国内免费   24篇
林业   8篇
农学   37篇
基础科学   8篇
  32篇
综合类   146篇
农作物   36篇
水产渔业   6篇
畜牧兽医   32篇
园艺   25篇
植物保护   11篇
  2024年   1篇
  2023年   2篇
  2022年   5篇
  2021年   10篇
  2020年   3篇
  2019年   3篇
  2018年   5篇
  2017年   7篇
  2016年   10篇
  2015年   19篇
  2014年   24篇
  2013年   18篇
  2012年   29篇
  2011年   31篇
  2010年   26篇
  2009年   26篇
  2008年   25篇
  2007年   22篇
  2006年   19篇
  2005年   9篇
  2004年   9篇
  2003年   7篇
  2002年   3篇
  2001年   7篇
  2000年   1篇
  1999年   5篇
  1998年   1篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
排序方式: 共有341条查询结果,搜索用时 31 毫秒
31.
吲唑酯是一种新的植物生长调节剂,对于它的分析国内尚未见报道.为了探讨吲唑酯的稳定性和残留量,我们对分析方法进行了研究,发现吲唑酯有明显的荧光现象,测定了它的标准激发光谱和荧光光谱谱图,并由此鉴定了我院合成的吲唑酯。利用高效液相色谱紫外、荧光双检测器双通道检测,对吲唑酯及乳剂进行了定量分析,同一样品紫外和荧光检测结果基本一致,由此确立了一套从固体样品、乳剂到极低浓度溶液的色谱、光谱测定条件。方法优越性:样品不需预处理,用量极少(几微毫),快速(几分钟),干扰很少(尤其荧光检测),线性范围宽(可达10~5),检测下限很低(荧光可达1ppb)。分析结果表明,吲唑酯乳剂存放3年含量稍有下降。  相似文献   
32.
肉鸡心脏热应激损伤和热休克蛋白mRNA转录水平的相关性   总被引:7,自引:1,他引:7  
 通过分光光度计、组织病理学和荧光定量反转录PCR检测技术,研究肉鸡心脏热应激损伤和热休克蛋白mRNA 变化的相关性。试验结果显示,热应激过程中肌酸激酶和谷丙转氨酶的活性呈现波动性变化,肌酸激酶的变化更明显;心脏的组织病理学变化主要表现为心肌纤维变性和坏死;热应激过程中HSC70 mRNA也呈现波动性变化,而 HSP70 mRNA水平呈现上升趋势。结果提示,HSC70 mRNA与肌酸激酶活性变化呈现一定负相关,HSC70有可能作为心脏热应激损伤的标志物。  相似文献   
33.
 采用荧光显微镜技术观察转基因水稻花粉在药用野生稻柱头上的萌发及在花柱内的生长过程,以明确两者之间不亲和性发生的阶段,为判断其能否发生基因漂流提供依据。结果表明,两种转基因栽培稻(Y003和99t)的花粉在药用野生稻柱头上的萌发率均比药用野生稻自花授粉的低,花粉管在花柱中的生长速度较慢,且分别在到达花柱中部(Y003)或花柱基部(99t)时停止生长,顶端异常膨大,杂交子房逐渐萎缩,结实率为0。药用野生稻与栽培稻杂交不亲和的原因是花粉管在花柱中停止生长、不能进入胚囊完成受精,在自然条件下转基因栽培稻中的外源基因  相似文献   
34.
以无损检测为前提,采用激光为激发光源,对杨树活体叶片进行荧光光谱采集,对采集到的光谱数据进行处理分析得到水分利用效率的荧光光谱敏感波段,建立基于叶片温度修正下的植物水分利用效率与荧光光谱的数学回归模型,模型的复相关系数R2=0.975.并对建立的数学回归模型进行效果检验,相关系数r=0.8746,模型的检测效果较好.  相似文献   
35.
The biodegradation of polycyclic aromatic hydrocarbons (PAHs) via free-living and attached micro-organisms in soil/water systems was observed in order to examine the variability in the community dynamics and physiological profiles of the micro-organisms. As determined by fluorescence in situ hybridization (FISH), the Domain Bacteria, consisting of three phyla α-, β- and γ-Proteobacteria, reached 41.27–56.05% of all organisms in the soil/water system for PAH biodegradation. Among the free-living species, Proteobacteria, including Brevundimonas (Pseudomonas) diminuta, Caulobacter spp., Mycoplana bullata, Acidovorax spp. and Pseudomonas aeruginosa were found to be dominant—making up 93.51–99.80% of the population—and therefore seem to be associated with PAH biodegradation. Total plate count numbers and the count of Pseudomonas sp. present in the free-living population increased to between 103 and 106 CFU ml−1 when clay with very low organic matter content was used as the matrix for PAH degradation. However, total plate count microbial numbers increased to only 101–102 CFU ml−1 using natural soil from Taichung containing 1.883% organic matter. The soil organic content (SOM) seemed to affect the mass transfer of PAH in soil, leading to the difference in PAH biodegradation. Two different approaches, which included community-level physiological profiling (CLPP) and ectoenzymatic activities, were used to explain the functional diversity between free-living and attached bacteria. The free-living and attached bacterial communities from the clay system showed proportionately greater differences using CLPP. Relatively high levels of esterases, aminopeptidases and some specific glycolysis-gluconeogenesis enzymes gave an identifiable correlation with PAH biodegradation. The differences in bacterial composition, numbers and physiological characteristics show that free-living and attached micro-organisms may play different biochemical roles in PAH degradation in soil.  相似文献   
36.
Litter is one of the main sources of dissolved organic carbon (DOC) in forest soils and litter decomposition is an important control of carbon storage and DOC dynamics. The aim of our study was to evaluate (i) effects of tree species on DOC production and (ii) relationships between litter decomposition and the amount and quality of DOC. Five different types of leaves and needles were exposed in litterbags at two neighboring forest sites. Within 12 months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory. In the collected litter percolates we measured DOC concentrations and recorded UV and fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules. Furthermore, we investigated the biodegradability of DOC from fresh and decomposed litter during 6 weeks incubations. Fresh sycamore maple litter released the largest amounts of DOC reaching about 6.2% of litter C after applying precipitation of 94 mm. We leached 3.9, 1.6, 1.0 and 3.3% carbon from fresh mountain ash, beech, spruce and pine litter, respectively. In the initial phase of litter decomposition significantly decreasing DOC amounts were released with increasing litter mass loss. However, after mass loss exceeds 20% DOC production from needle litter tended to increase. UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter. However, for deciduous litter the relationship was less obvious. We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds. Biodegradability of DOC from fresh litter was very high, ranging from 30 to 95% mineralized C. DOC from degraded litter was on average 34% less mineralizable than DOC from fresh litter. Taking into account the large DOC production from decomposed needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.  相似文献   
37.
The aim of the present article is to show the possibilities of chemometric tools and the parallel factor analysis (PARAFAC) model, as well as to understand the complexities of the fluorescence emission-excitation matrix (EEM) of water-soluble organic matter (WSOM) extracted from sewage sludge samples obtained with different origins and stabilization procedures. The variation in the composition of WSOM in the different sewage sludge samples could be correlated with the conditions of stabilization; therefore, the use of fluorescence spectroscopy to monitor these changes can be a useful tool to optimize the management of this residual flux, avoiding environmental pollution. However, the “contour density” EEM maps obtained with fluorescence present continuous spectra with different peaks, valleys, and shoulders where manual peak picking can be complicated and subjective, especially in complex matrixes such as sewage sludge. With the PARAFAC algorithm, it is possible to resolve the emission and excitation spectra of the different fluorescence components present in the samples and their contribution to the total fluorescence. Also, the contribution (scores) of the different fluorophors can be coupled with another chemometric tool to provide an effective classification method using the stabilization conditions of sewage sludge as main criterion. In this study, a wide survey of sewage sludge samples (287) was characterized by fluorescence emission-excitation matrix. The final molecular composition of the sewage sludge samples was not related to the stabilization (aerobic vs anaerobic) treatments. However, a sewage sludge classification based on a combined spectroscopic-chemometric approach was obtained, which could be used for the optimization of sewage sludge use in agriculture, minimizing the environmental risks.  相似文献   
38.
为了深入探讨转基因的整合位置对基因表达的影响,对转绿色荧光蛋白基因(gfp)大麦的荧光表达和gfp基因的染色体位置进行了研究。结果表明,绿色荧光蛋白(gfp)在大麦的根尖和花粉中均有表达,四倍体的荧光表达强度大于二倍体,表现出基因的剂量效应。gfp基因插入到第6染色体(6H)短臂和另一染色体的短臂近末端。  相似文献   
39.
AIM:To examine the effect of compound salvae-dropping-pill (CSDP) on intracellular free calcium in cultured rat myocardial cells subjected to hypoxia and reoxygenation.METHODS:The Fluo- 3/AM was applied to probe intracellular calcium concentration and the fluorescent intensity was detected using laser confocal microscopy technique.RESULTS:Fluorescent intensity in hypoxia plus CSDP group was significantly lower (1 217.78±312.07) than that of hypoxia group (1 509±508.48), and the Fluorescent intensity of hypoxia/reoxygenation plus CSDP group was also markedly lower (1 567.91±577.61) than that of hypoxia/reoxygenation group (1 617.60±477.53).CONCLUSION:The cultured rat myocardial cells could be effectively protected by administration of CSDP in case of hypoxia and reoxygenation through decreasing the intracellular calcium concentration.  相似文献   
40.
Association of Helicobacter with cholangiohepatitis in cats   总被引:1,自引:0,他引:1  
Infection with Helicobacter spp. is increasingly linked with hepatobiliary inflammation and neoplasia in people and in a variety of animals. We sought to determine if Helicobacter species infection is associated with cholangiohepatitis in cats. Deoxyribonucleic acid was extracted from tissue blocks from cats with cholangiohepatitis (32), noninflammatory liver disease (13), and cats with normal liver histology (4). Deoxyribonucleic acid was polymerase chain reaction-amplified with 2 sets of Helicobacter genus-specific primers, gel purified, and sequenced. Polymerase chain reaction-positive hepatic tissue was further examined with Steiner's stain, immunocytochemistry for Helicobacter species, and eubacterial fluorescent in situ hybridization. Gastric tissues of cats with known Helicobacter infection status served as controls for deoxyribonucleic acid extraction and sequence comparison. Helicobacter species were detected in 2/32 cats with cholangiohepatitis, and 1/17 controls. Sequences had 100% identity with Helicobacter species liver, Helicobacter pylori, and Helicobacter fenelliae/cinaedii in a cat with suppurative cholangitis, Helicobacter species liver, Helicobacter pylori, and Helicobacter nemistrineae in a cat with mild lymphocytic portal hepatitis, and Helicobacter bilis in a cat with portosystemic vascular anomaly. In contrast, sequences from gastric biopsies showed highest homology (99-100%) to "Helicobacter heilmannii," Helicobacter bizzozeronii, Helicobacter felis, and Helicobacter salomonis. Fluorescent in situ hybridization revealed a semicurved bacterium, with Helicobacter-like morphology, in an intrahepatic bile duct of the cat with suppurative cholangitis. This study has identified Helicobacter deoxyribonucleic acid in 2/32 cats with cholangiohepatitis and 1/13 cats with noninflammatory liver disease. Deoxyribonucleic acid sequences of hepatic Helicobacter species were distinct from those found in the stomach and are broadly consistent with those identified in cat intestine and bile, and hepatobiliary disease in people and rodents.  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