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   206篇
  免费   8篇
林业   20篇
农学   6篇
  25篇
综合类   16篇
农作物   4篇
水产渔业   19篇
畜牧兽医   118篇
植物保护   6篇
  2023年   3篇
  2022年   3篇
  2021年   3篇
  2020年   4篇
  2019年   2篇
  2018年   11篇
  2017年   3篇
  2016年   4篇
  2015年   2篇
  2014年   5篇
  2013年   10篇
  2012年   11篇
  2011年   7篇
  2010年   4篇
  2009年   2篇
  2008年   6篇
  2007年   6篇
  2006年   10篇
  2005年   13篇
  2004年   8篇
  2003年   9篇
  2002年   2篇
  2001年   13篇
  2000年   10篇
  1999年   5篇
  1998年   5篇
  1994年   1篇
  1992年   2篇
  1991年   4篇
  1990年   1篇
  1989年   3篇
  1988年   4篇
  1987年   1篇
  1985年   6篇
  1984年   3篇
  1983年   1篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1978年   2篇
  1977年   3篇
  1976年   1篇
  1975年   3篇
  1974年   1篇
  1973年   1篇
  1969年   4篇
  1968年   1篇
  1966年   1篇
  1964年   2篇
  1963年   1篇
排序方式: 共有214条查询结果,搜索用时 15 毫秒
61.
In this study, we examined the effects of reconstructed oocyte–granulosa cell complexes (OGCs) on the development of porcine oocytes derived from early antral follicles (EAFs; 0.5–0.7 mm in diameter). When denuded oocytes were cocultured with granulosa cells derived from other EAFs, the oocytes and granulosa cells aggregated to form OGCs after 2 days of culture. After 14 days of culture, we compared cell number, oocyte diameter, and oocyte chromatin configuration in unmanipulated (natural) OGCs, reconstructed OGCs, and OGCs collected from antral follicles (AFs, 3.0–6.0 mm in diameter). The diameters of oocytes from reconstructed OGCs grown in vitro were not different from those of oocytes from natural OGCs, although they were significantly smaller than those of oocytes from antral follicle (AF) OGCs. Oocyte chromatin configuration did not differ among the 3 OGC groups, but the oocyte nuclear maturation rate was lower in the reconstructed OGCs and higher in the AF OGCs. However, when the in vitro culture period for the reconstructed OGCs was extended by 2 days, the nuclear maturation rate of oocytes from reconstructed OGCs was similar to that of oocytes from natural OGCs. In addition, blastocysts were successfully obtained from oocytes from reconstructed OGCs. In conclusion, we established an innovative culture method that allows oocytes and granulosa cells from EAFs to reaggregate as reconstructed OGCs, which yield oocytes with the ability to develop to the blastocyst stage.  相似文献   
62.

Water management methods regulate water temperature in paddy fields, which affects rice growth and the environment. To understand the effect of irrigation conditions on water temperature in a paddy field, water temperature distribution under 42 different irrigation models including the use of ICT water management, which enables remote and automatic irrigation, was simulated using a physical model of heat balance. The following results were obtained: (1) Irrigation water temperature had a more significant effect on paddy water temperature close to the inlet. As the distance from the inlet increased, the water temperature converged to an equilibrium, which was determined by meteorological conditions and changes in water depth. (2) Increasing the irrigation rate with higher irrigation water amount increased the extent and magnitude of the effects of the irrigation water temperature. (3) When total irrigation water amount was the same, increasing the irrigation rate decreased the time-averaged temperature gradient effect over time across the paddy field. (4) Irrigation during the lowest and highest paddy water temperatures effectively decreased and increased the equilibrium water temperature, respectively. The results indicate that irrigation management can be used to alter and control water temperature in paddy fields, and showed the potential of ICT water management in enhancing the effect of water management in paddy fields. Our results demonstrated that a numerical simulation using a physical model for water temperature distribution is useful for revealing effective water management techniques under various irrigation methods and meteorological conditions.

  相似文献   
63.
Previous studies have shown the physiological significance of dietary conjugated linoleic acid (CLA) in various experimental animals and in human beings. One of the important problems to better elucidate is the difference between triglyceride (TG) and free (FFA) dietary CLA. Here, using splenocytes, this study assesses how TG- and FFA-CLA modulate immunoglobulin and various cytokine productions. In this study, C57BL/6N mice were fed an experimental diet containing 0% CLA, 0.1 or 1% FFA-CLA, or 0.1 or 1% TG-CLA for 3 weeks. The production of immunoglobulin tended to be up-regulated by 1% FFA-CLA. As a result of protein array analysis using the supernatant from splenocytes cultured with no CLA, 1% FFA-CLA, and TG-CLA, some cytokine production was shown to be remarkably regulated by dietary FFA- and TG-CLA. A total of 32 cytokines were examined, and 11-14 produced cytokines that were 2-fold up-regulated as compared with control for FFA- or TG-CLA, respectively. Especially, the production of IL-9 and MCP-5 and other cytokines was remarkably up-regulated by both FFA- and TG-CLA. In addition, seven cytokines were 2-fold down-regulated by TG-CLA. These data show that there is a slight but significant difference between the functionalities of FFA- and TG-CLA.  相似文献   
64.
Mitral valve repair is one of the treatment options for mitral regurgitation. Expanded polytetrafluoroethylene (ePTFE) is a polymer that has been widely used in cardiovascular surgery. In this case series, we report the autopsy and histological findings in 6 dogs that underwent cardiopulmonary bypass for mitral annuloplasty using ePTFE sheets and chordoplasty using ePTFE sutures.From May 2005 to October 2009, 3 female and 3 male dogs with severe mitral regurgitation underwent mitral valve repair. This case series included 3 Cavalier King Charles spaniels, 2 Maltese, and 1 Shih Tzu. The survival period after surgery was 19–72 (35 ± 19) months.In all the cases, autopsy revealed that the ePTFE sheets and sutures were not damaged and well integrated into the surrounding highly differentiated, connective tissues. Low-power microscopy revealed that in all cases, the tissues surrounding the ePTFE sheet in the mitral valve annulus had almost completely been covered by granulation tissue. No inflammatory infiltrate or thrombogenesis was observed around the ePTFE in any of the cases.There was no evidence of reactive changes in the region surrounding the ePTFE. These results suggest that ePTFE has excellent tissue compatibility and durability and can be effectively used for canine mitral valve repair.  相似文献   
65.
Miscanthus ×ogiformis is a hybrid between Miscanthus sacchariflorus and Miscanthus sinensis and its several synonyms indicate the insufficient understanding of the morphological variation of its awn on the spikelet, which is a key characteristic for identifying Miscanthus species. In the present study, all the Miscanthus specimens in 19 herbaria were examined in order to find new localities for Miscanthus ×ogiformis. Thirty‐nine Miscanthus ×ogiformis specimens appeared to be naturally occurring hybrids, as their callus hair length, awn length, and callus‐to‐spikelet ratio differed from those found in the parental species. Therefore, new Miscanthus ×ogiformis individuals with morphological variations are likely to be discovered and these strains might be useful as new genetic resources for this biomass crop.  相似文献   
66.
This study was performed to investigate changes in available soil phosphate associated with temperature under submerged conditions and to explore the possibility for estimating those under submerged conditions during the early growth (tillering) stage of rice plants (Oryza sativa L.). An incubation experiment was conducted under submerged conditions at three temperatures (10°C, 17.5°C and 25°C) using paddy soils collected over a widespread area in Japan. In most soils, significant positive correlations were observed between available soil phosphate and cumulative temperature to 650°C, which corresponded to the tillering stage in Japan. Relationships between the regression formulae of the available phosphate against cumulative temperature to 650°C and soil chemical properties measured in air-dried soil were investigated. The results indicate that the available phosphate of paddy soil against cumulative temperature during tillering stage under submerged conditions can be estimated from the results of air-dried soil analyses which can be conducted before a crop season.  相似文献   
67.
Genomes of animals as different as sponges and humans show conservation of global architecture. Here we show that multiple genomic features including transposon diversity, developmental gene repertoire, physical gene order, and intron-exon organization are shattered in the tunicate Oikopleura, belonging to the sister group of vertebrates and retaining chordate morphology. Ancestral architecture of animal genomes can be deeply modified and may therefore be largely nonadaptive. This rapidly evolving animal lineage thus offers unique perspectives on the level of genome plasticity. It also illuminates issues as fundamental as the mechanisms of intron gain.  相似文献   
68.
Squid Todarodes pacificus suwari gels, set at various temperatures and times, and acid-induced kamaboko gel, which was prepared by soaking suwari gel in 5% acetic acid for 20 h, were studied to evaluate the mechanical properties that are affected by setting conditions. Unset squid meat paste did not form a gel when soaked in acetic acid. The breaking strength of both suwari gel and acid-induced kamaboko gel showed a tendency to increase with setting temperature and time. SDS-PAGE analysis of suwari gel and acid-induced kamaboko gel, which were set at various temperatures and times, showed that myosin heavy chain (MHC) was observed at 30°C only for the first hour. The intensity of the MHC band at 30°C gradually decreased with setting time, while the intensity of the polymer band gradually increased with setting time. These results suggest that the protein-protein bonds in suwari gel affect the final texture of acid-induced kamaboko gel. Based on the analysis of the mechanical properties, and in consideration of the fact that the purpose of this experiment was to reduce energy usage, the best setting condition was determined to be 40°C for 3 h.  相似文献   
69.
Parameter calibration is an important step in the development of rainfall–runoff models. Recently, there has been a significant focus on automatic calibration. In this paper, two evolutionary optimization algorithms were applied to calibration of the long- and short-term runoff model (LST model) to simulate the daily rainfall–runoff process in the Be River catchment located in southern Vietnam. The differential evolution (DE) and evolution strategy (ES) algorithms were employed to optimize three objective functions: the Nash–Sutcliffe efficiency coefficient, root mean square error, and mean absolute error, which are indices for evaluating the simulation accuracy of the LST model. Hydrometeorological data for the periods 1985–1989 and 1990–1991 were used for calibration and validation, respectively. The LST model was calibrated for each objective function using five different parent and offspring population conditions. The results show that both the DE and ES algorithms are efficient methods for automatic calibration of the LST model. After 1000 generations, the best values of the fitness indices found by the DE technique were slightly better and more stable than those found by the ES technique in both calibration and validation. The average computation time for each generation using the DE algorithm was approximately two-thirds as long as that using the ES algorithm.  相似文献   
70.
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