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   266篇
  免费   15篇
林业   30篇
农学   7篇
  37篇
综合类   11篇
农作物   11篇
水产渔业   70篇
畜牧兽医   96篇
园艺   4篇
植物保护   15篇
  2023年   1篇
  2022年   2篇
  2021年   6篇
  2020年   5篇
  2019年   3篇
  2018年   10篇
  2017年   7篇
  2016年   12篇
  2015年   11篇
  2014年   20篇
  2013年   20篇
  2012年   15篇
  2011年   15篇
  2010年   5篇
  2009年   13篇
  2008年   13篇
  2007年   16篇
  2006年   15篇
  2005年   11篇
  2004年   13篇
  2003年   12篇
  2002年   13篇
  2001年   8篇
  2000年   5篇
  1999年   2篇
  1998年   5篇
  1997年   4篇
  1996年   6篇
  1992年   2篇
  1991年   1篇
  1990年   2篇
  1987年   2篇
  1979年   1篇
  1975年   3篇
  1974年   1篇
  1971年   1篇
排序方式: 共有281条查询结果,搜索用时 15 毫秒
121.
The effect of addition of Acacia mangium bark powder on the thermosetting processes of two commercial phenol resins, PF-A and PF-B, was examined by bond strength test, torsional braid analysis, and differential scanning calorimetry. When the bark powder was added to PF-A, the bond strength of plywood pressed at 110°C increased and was comparable to that of plywood pressed at 120 and 130°C. However, when the bark powder was added to PF-B, the bond strength of plywood pressed at 110°C was still lower than that of plywood pressed at 120 and 130°C. The relative rigidity and loss tangent of PF-A cured with the bark powder obtained by heating at 100°C were comparable to those at 120 and 140°C, and the reaction enthalpy was increased by bark powder addition. In contrast, chemical reactions for cured PF-B were not enhanced by bark powder addition.  相似文献   
122.
Urinary liver-type fatty acid-binding protein (uL-FABP) is a clinically useful biomarker for monitoring chronic kidney disease (CKD) in humans. However, long-term monitoring of uL-FABP in CKD cats has not been reported. The objective of this preliminary study was to investigate whether the urinary excretion of L-FABP could predict the deterioration of renal function in 2 CKD model cats. Urinary liver-type fatty acid-binding protein (uL-FABP) increased before standard renal biomarkers, including serum creatinine, blood urea nitrogen, and symmetric dimethylarginine, in 1 cat with deteriorating renal function, but remained low and relatively stable in another cat with stable renal function. Our results suggest that uL-FABP is a potential clinical biomarker for predicting the progression of CKD in cats, as it is in humans.  相似文献   
123.
A method of recording the fetal electrocardiogram (ECG) and heart rate (HR) is described. An abdominal lead and a thoracic lead were used to measure the fetal ECG and maternal ECG, respectively. The maternal component in the abdominal lead measurement was estimated by a digital adaptive filter using the thoracic lead measurement as a reference. By suppressing the estimated maternal components in the abdominal lead, the fetal ECG could be detected. The beat‐by‐beat fetal QRS complex peaks were determined by a digital matched filter from the fetal ECG enhanced in this way. The method was trialed in 10 pregnant Holstein cows at gestational periods ranging from 136 to 224 days. The results show that this method can extract the fetal ECG and determine the fetal HR from the raw noisy measurement data. The results suggest that the method would have applicability in monitoring fetal ECG as well as providing a non‐invasive, continuous HR profile during gestation, which will enable better understanding of the development of cattle fetuses before delivery.  相似文献   
124.
Seven miniature pigs were injected intravenously with deoxynivalenol (DON) at 1 mg/kg body weight; afterward, the number of leukocytes in peripheral blood, the luminol-dependent chemiluminescence of neutrophils, the serum or plasma concentration of cytokines and acute-phase proteins were evaluated to determine the effects of acute exposure to DON on inflammatory responses. White blood cell counts were transiently increased at 3, 6, and 12 hr post-injection (PI) due to the increased number of neutrophils. The luminol-dependent chemiluminescence value of neutrophils was significantly elevated at 24 hr PI, indicating the activation of the bactericidal function of neutrophils. Significant increases of interleukin (IL)-8 and tumor necrosis factor-α at 3 hr PI and IL-6 at 6 hr PI were detected in the serum. The concentration of haptoglobin and serum amyloid A was significantly increased at 24 hr PI. These results suggest that acute exposure to DON induced a temporary recruitment of neutrophils in the peripheral blood by IL-8 and subsequent activation of the bactericidal function, and a transient increase of proinflammatory cytokines and acute-phase proteins, indicating the immunomodulatory effects of DON in pigs.  相似文献   
125.
An epidemiological survey on a Theileria parasite infection of cattle in Northeast China was carried out using allele-specific PCR and DNA sequence analysis of the major piroplasm surface protein (MPSP) gene. The results showed that 14 of 104 blood samples were positive for Theileria by PCR. Among the positive cases, co-infection with various combinations of C- and I-type parasites was detected in 12 samples; no B- and Thai-type parasites were detected by allele-specific PCR. Phylogenetic analysis based on the MPSP gene sequences revealed that Theileria parasites with the MPSP types 1, 2, and 4 were distributed in Northeast China.  相似文献   
126.
在发现健康桑蚕幼虫消化道中存在β-溶血性的肠球菌的基础上,首次证实了肠球菌中只在厌氧条件下发生β-溶血反应菌的存在.Craigie试管法和毛细管法进一步确认了分离肠球菌菌株的生物性运动.“0082”分离菌株在接种菌量较多、培养温度较高和碱性较大(pH值9~10)条件下显示了较强的运动性.因此,它也将较容易地附着在桑蚕幼虫的围食膜上  相似文献   
127.
Carotenoids are used commercially for dietary supplements, cosmetics, and pharmaceuticals because of their antioxidant activity. In this study, colored microorganisms were isolated from deep sea sediment that had been collected from Suruga Bay, Shizuoka, Japan. One strain was found to be a pure yellow carotenoid producer, and the strain was identified as Sphingomonas sp. (Proteobacteria) by 16S rRNA gene sequence analysis; members of this genus are commonly isolated from air, the human body, and marine environments. The carotenoid was identified as nostoxanthin ((2,3,2′,3′)-β,β-carotene-2,3,2′,3′-tetrol) by mass spectrometry (MS), MS/MS, and ultraviolet-visible absorption spectroscopy (UV-Vis). Nostoxanthin is a poly-hydroxy yellow carotenoid isolated from some photosynthetic bacteria, including some species of Cyanobacteria. The strain Sphingomonas sp. SG73 produced highly pure nostoxanthin of approximately 97% (area%) of the total carotenoid production, and the strain was halophilic and tolerant to 1.5-fold higher salt concentration as compared with seawater. When grown in 1.8% artificial sea salt, nostoxanthin production increased by 2.5-fold as compared with production without artificial sea salt. These results indicate that Sphingomonas sp. SG73 is an efficient producer of nostoxanthin, and the strain is ideal for carotenoid production using marine water because of its compatibility with sea salt.  相似文献   
128.
Abstract

By applying nitrogen (N) and phosphorus (P) fertilizers at different rates and times to high-yielding rice cultivars, we determined the absorption of N, P, and potassium (K) in relation to the grain yield. The results showed that, at a higher top-dressing rate of N, the grain yield increased and the absorption of N, P, and K was stimulated, whereas top-dressing of P did not significantly increase the grain yield and nutrient absorption. The absorption of N, P, and K differed markedly among the cultivars, even at the same level of grain yield in the same field (for Yangdao 4 and Suweon 258). N absorption in line 9004 was 29.2 g m?2 for a paddy grain yield of 1,250 g m?2 (brown rice: about 1,000 g m?2), being much higher than the value reported in the literature. The ratio of N : P : K absorption at different yield levels revealed that, with the increase of grain yield of the cultivars, the absorption of P and K relative to the absorption of N decreased. The absorption amounts and ratios of N, P, and K depended on the cultivars, yield levels~, and possibly, soils of the field.  相似文献   
129.
Abstract

Soil carbon evolution under the lowest moisture conditions varies considerably among experimental systems/techniques, leading to discrepancies in the estimations from carbon dynamics models under low moisture conditions. We focused our study on clarifying the regulating factors of soil carbon evolution under the lowest moisture conditions by conducting laboratory experiments under precisely controlled conditions. Nanoscale porosity and surface properties of these soils were determined to analyze the role of residual water in the carbon evolution processes in dry soils. Laboratory incubation showed that the carbon evolution from a microporous (D < 2 n m) volcanic soil proceeded even at -100 U kg-1 water potential (INT) in contrast to the carbon evolution from a phyllosilicate alluvial soil. Pore-size estimation and 1H-NMR spectroscopy showed that the carbon evolution at -100 U kg-1 WP proceeded through the utilization of nanopore-water in soils. Batch sorption experiment suggested that the surface affinity of the soils to dissolved organic matter (DOM) had enhanced carbon evolution by attracting DOM into hydrophilic spheres of the soil at -100 U kg-1 MT. Solid-state IIGNMR of organic matter samples (incubated in the absence of soils) suggested that the chemical alteration of the samples was significant for aliphatic components, while the alteration was not observed in the samples incubated at -100 U kg-1 WP. This fact also indicated the contribution of nanoscale pores in the volcanic components to carbon evolution. Application of the experimental results to several biogeochemical models revealed that both volumetric water content and MT are required to estimate carbon evolution under low moisture conditions. A micro habitat model showed that the carbon evolution at -100 U kg-1 WP could be attributed to extracellular enzymatic processes or other abiotic processes rather than to the activities of living microorganisms.  相似文献   
130.
Abstract

Yacon (Polymnia sonchifolia) plants originating from Andean highlands are known to accumulate a large amount of oligofructans in their tubers and tuberous roots (Ohyama et al. 1990; Asami et al. 1992). Asami et al. (1992) have reported that tubers and tuberous roots which were harvested in late fall contained about 57 and 66% respectively (on a dry matter basis) of oligofructans. However, the tubers, tuberous roots and shoots of the yacon contained only a small amount of starch and inulin. The tuberous roots of yacon which resemble those of sweet potato in appearance are usually eaten raw and are expected to become commercially valuable as a source of oligofructans.  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