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   382篇
  免费   12篇
林业   18篇
农学   15篇
  50篇
综合类   23篇
农作物   3篇
水产渔业   14篇
畜牧兽医   249篇
园艺   2篇
植物保护   20篇
  2024年   1篇
  2023年   3篇
  2022年   6篇
  2021年   17篇
  2019年   5篇
  2018年   3篇
  2017年   9篇
  2016年   9篇
  2015年   7篇
  2014年   11篇
  2013年   19篇
  2012年   13篇
  2011年   20篇
  2010年   4篇
  2009年   9篇
  2008年   20篇
  2007年   18篇
  2006年   27篇
  2005年   8篇
  2004年   17篇
  2003年   15篇
  2002年   12篇
  2001年   11篇
  2000年   7篇
  1999年   7篇
  1998年   3篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   8篇
  1991年   11篇
  1990年   14篇
  1989年   4篇
  1988年   11篇
  1987年   14篇
  1986年   11篇
  1985年   12篇
  1984年   4篇
  1983年   1篇
  1980年   1篇
  1979年   3篇
  1977年   1篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1971年   1篇
  1965年   2篇
  1963年   1篇
排序方式: 共有394条查询结果,搜索用时 15 毫秒
141.
Tsujimoto  Kumiko  Ono  Kotaro  Ohta  Tetsu  Chea  Koemorn  Muth  E-Nieng  Hor  Sanara  Hok  Lyda 《Paddy and Water Environment》2021,19(4):635-648

The dependencies of the planting date on rainfall and soil moisture in paddy fields in Cambodia were analyzed to quantify farmers’ empirical knowledge regarding their decision of the planting date. Remote sensing data from multiple satellites covering the 2003–2019 period were analyzed. The planting dates in rain-fed paddies ranged from April to August, with large spatial variations and year-to-year fluctuations. In years when planting was suppressed in April and May, planting was extensively enhanced in June and August compared to normal years, and vice versa. Over the northeastern side of Tonle Sap Lake and south of Phnom Penh city, the areas planted in April and May were found to have positive correlations with rainfall and soil moisture, suggesting that wetter-than-average conditions encouraged farmers to plant earlier in the season. In contrast, this relationship was unclear on the western side of Tonle Sap Lake, where the rainfall amounts were larger throughout the year than in other areas in Cambodia. In this region, the relationship between the planting area and soil water availability was either unclear or was even slightly negative from June to August. Since more frequent dry spells have been detected after the onset of the rainy season in recent years, further studies and disseminations of potential changes in dry spells are important for the agronomic adaptation of planting dates under climate change.

  相似文献   
142.
Three-week iron (Fe) deficiency stress experiments were conducted using two citrus root stocks, Fe-deficiency tolerant Orange Jasmine (OJ, Murraya exotica L.) and the sensitive Flying Dragon [FD, Poncirus trifoliata var. monstrosa (T. Ito) Swingle]. Root ferric chelate reductase activity and proton extrusion increased in OJ between 12 and 18 d of stress, whereas there was no change in FD. Dry weight of OJ roots increased in contrast to FD which decreased. The Mn content in OJ remained the same even under Fe stress. Zn content in OJ roots doubled while that of FD increased 4-folds. The shoot/root Fe accumulation ratio increased in OJ while it decreased in FD. OJ apparently has mechanisms for increasing root biomass, controlling Fe reutilization and regulating manganese (Mn) and zinc (Zn) absorption in response to Fe deficiency. These mechanisms could help maintain homeostasis under heavy metal stress, which would be useful for improved growth of economically important citrus species.  相似文献   
143.
144.
Genes and proteins of human origin are often administered to monkeys for research purposes, however, it can be difficult to obtain sufficient levels of the products in vivo due to immunological clearance. In this study, we showed that human erythropoietin (hEPO) induces generation of anti-hEPO antibody in cynomolgus macaques (n=2), although 92% of amino acid residues are common between the human and macaque EPO. The administered hEPO was thus eliminated from the animals. On the other hand, when an immunosuppressant, cyclosporin A (CyA), was administered (6 mg/kg) intramuscularly every other day in combination with hEPO (n=2), no anti-hEPO antibody was generated and high serum levels of hEPO were obtained during administration of hEPO, resulting in an increase in serum hemoglobin levels. No adverse effects associated with CyA were observed. Thus, CyA treatment is useful for prevention of immune responses associated with the administration of human proteins in monkeys.  相似文献   
145.
We report atomic-scale characterization of the pseudogap state in a high-Tc superconductor, Bi2Sr2CaCu2O(8+delta). The electronic states at low energies within the pseudogap exhibit spatial modulations having an energy-independent incommensurate periodicity. These patterns, which are oriented along the copper-oxygen bond directions, appear to be a consequence of an electronic ordering phenomenon, the observation of which correlates with the pseudogap in the density of electronic states. Our results provide a stringent test for various ordering scenarios in the cuprates, which have been central in the debate on the nature of the pseudogap and the complex electronic phase diagram of these compounds.  相似文献   
146.
147.
Canine lymphoma is a disease with high morbidity and poor long-term prognosis, despite a high response rate to chemotherapy. In this study, we focused on liquid biopsy, in which small amounts of substances from body fluids were analysed, to determine whether cell-free DNA (cfDNA) in the plasma can be used as a biomarker for lymphoma in dogs. We found that 23 patients with lymphoma had significantly higher cfDNA concentrations than the 12 healthy dogs (median 2360 ng/mL versus 299 ng/mL, p < .0001). Polymerase chain reaction for antigen receptor rearrangement (PARR) was also employed using cfDNA from the lymphoma group to investigate whether cfDNA could be used for the detection of genetic clonality of lymphomas, as well as the genomic DNA (gDNA) extracted from an original lesion in each case. The correlation of the PARR results between cfDNA and gDNA was observed in 100% of B-cell lymphomas (10/10), 77.8% of T-cell lymphomas (7/9), and 100% of other types of lymphomas (4/4), respectively. These results indicate that plasma cfDNA levels are increasing in canine lymphoma patients, that cfDNA concentration can be a novel diagnostic tool, and that it can be used as a diagnostic tool for PARR.  相似文献   
148.
Effect of temperature on the development of eggs of round herring Etrumeus teres was experimentally examined to construct a temperature-dependent egg development model. Mature fish were collected in the field and their eggs were artificially fertilized onboard. The eggs were incubated at nine temperatures set between 14.0 and 25.0°C. All eggs at the lowest three temperatures, 14.0°C, 15.0°C, and 16.0°C, ceased development and died at various stages before hatching. Durations required to hatching after fertilization ranged from 38.0 h at 25.0°C to 90.0 h at 17.5°C. The temperature-dependent egg development model, i.e., egg age in hours (y i,t ) at the ith stage and temperature t (°C), was expressed as: y i,t  = 4.604 × exp(−0.100 × t −0.129 × i) × i 2.593. From the application of the model to early-stage eggs collected in the field, it is concluded that round herring starts spawning immediately after sunset and almost completes spawning by midnight. The temperature-dependent egg development model and the daily pattern of spawning presented in this study are essential tools for developing the daily egg production method to estimate the spawning stock biomass.  相似文献   
149.
We recently developed a Landrace line that is resistant to mycoplasmal pneumonia of swine (MPS) infection by genetic selection for five generations, and we reported that the immunophenotype of this line is different from that of the non‐selected line in terms of changes in peripheral blood leukocyte population after MPS vaccination. This study followed up previous findings demonstrating changes in soluble factors in blood, namely, hormones, Mycoplasma hyopneumoniae‐specific immunoglobulin G (IgG), and cytokines. These two lines were injected with MPS vaccine on days ?7 and 0 after blood sampling on those days, and blood samples were collected on days ?14, ?7, 0, 2, 7 and 14. We found changes in the levels of many hormones and cytokines in both lines. However, we found that only growth hormone (GH) and interferon (IFN)‐γ levels were statistically different between these two lines. GH concentration was reduced (day 0) and IFN‐γ concentration was increased (day 14) in the MPS‐selected line compared with the non‐selected line, despite unchanged IFN‐γ messenger RNA expression in blood cells. Although detailed mechanisms underlying these phenotypes remain unsolved, these traits would be useful to improve MPS resistance in pig production and provide an insight into MPS infection.  相似文献   
150.
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