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   263篇
  免费   24篇
林业   18篇
农学   9篇
  46篇
综合类   9篇
农作物   14篇
水产渔业   35篇
畜牧兽医   124篇
园艺   5篇
植物保护   27篇
  2023年   6篇
  2022年   6篇
  2021年   19篇
  2020年   17篇
  2019年   30篇
  2018年   17篇
  2017年   17篇
  2016年   16篇
  2015年   9篇
  2014年   9篇
  2013年   17篇
  2012年   13篇
  2011年   17篇
  2010年   16篇
  2009年   3篇
  2008年   2篇
  2007年   6篇
  2006年   5篇
  2005年   10篇
  2004年   3篇
  2003年   11篇
  2002年   7篇
  1999年   3篇
  1998年   4篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1993年   4篇
  1992年   1篇
  1991年   2篇
  1990年   3篇
  1988年   1篇
  1986年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1977年   1篇
  1969年   1篇
排序方式: 共有287条查询结果,搜索用时 125 毫秒
11.
Veterinary Research Communications - Propofol is a widely used drug in veterinary medicine to induce anesthesia; as well as the chosen compound for protocols of intravenous anesthesia. The present...  相似文献   
12.
本文研究了大叶桃花心木(Swietenia macrophylla King)一年生幼苗在经过夜温处理后的光响应曲线和在饱和光强下的CO2反应曲线.结果表明:在大气CO2浓度下,叶片的最佳光合作用温度在25-31℃之间,而在饱和CO2浓度下为31-35℃.在25℃以下光合速率开始降低,主要是由于羧化效率的降低,而当温度超过31℃时,光合速率下降,是因为羧化效率的降低和呼吸速率的增加.CO2浓度对光合的促进作用在低温下受到抑制,这意味着未来在CO2浓度增高的情况下,高浓度的CO2对热带常绿植物光合的促进在冬天低温情况下表现不十分明显.图4参23.  相似文献   
13.
A 22‐year‐old Tennessee Walking Horse mare was presented to the Auburn University Large Animal Teaching Hospital with a 3‐day history of lethargy, anorexia, and mild signs of colic. The mare had a several‐month history of weight loss and refractory cough. Physical examination revealed an increased respiratory rate, and crackles and wheezes were heard on thoracic auscultation. Thoracic ultrasonographic examination showed disseminated, minor, bilateral comet tail‐like lesions on the parietal pleural surfaces. Abdominal ultrasonographic examination was unremarkable. Trans‐rectal palpation revealed a firm small colon impaction with concomitant diarrhea. Laboratory data were characterized by a very pronounced acute inflammatory leukogram with severe neutropenia and significant left shift, evidence of hepatocellular damage/necrosis, cholestasis, and possibly mixed metabolic alkalosis and acidosis. On cytologic evaluation of a peritoneal fluid sample, there were many large granular lymphocytes (LGL). Large numbers of LGL were also observed on cytologic examination of a subsequent transtracheal wash. The final cytologic interpretation was disseminated lymphoma with LGL morphology. Due to worsening of the clinical signs and poor prognosis, the mare was euthanized. On necropsy and in histopathologic examination, disseminated lymphoma with LGL morphology was noted in a mesenteric lymph node, lungs, liver, spleen, kidneys, and right dorsal colon. Lymphoma with LGL morphology is rarely diagnosed in the horse. This report provides unique cytologic findings of a case of disseminated lymphoma with LGL morphology in a horse, confirmed with histopathologic evaluation.  相似文献   
14.
Inhibitors of cyclin‐dependent kinases, as roscovitine, have been used to prevent the spontaneous resumption of meiosis in vitro and to improve the oocyte developmental competence. In this study, the interference of oil overlay on the reversible arrest capacity of roscovitine in sheep oocytes as well as its effects on cumulus expansion was evaluated. For this, cumulus‐oocyte complexes (COCs) were cultured for 20 h in TCM 199 with 10% foetal bovine serum (Control) containing 75 μm roscovitine (Rosco). Subsequently, they were in vitro matured (IVM) for further 18 h in inhibitor‐free medium with LH and FSH. The culture was performed in Petri dishes under mineral oil (+) or in 96 well plates without oil overlay (?) at 38.5°C and 5% CO2. At 20 and 38 h, the cumulus expansion and nuclear maturation were evaluated under stereomicroscope and by Hoechst 33342 staining, respectively. No group presented cumulus expansion at 20 h. After additional culture with gonadotrophins, a significant rate of COCs from both Control groups (+/?) exhibited total expansion while in both Rosco groups (+/?) the partial expansion prevailed. Among the oocytes treated with roscovitine, 65.2% were kept at GV in the absence of oil overlay while 40.6% of them reached MII under oil cover (p < 0.05). This meiotic arrest was reversible, and proper meiosis progression also occurred in the Control groups (+/?). So, the culture system without oil overlay improved the meiotic inhibition promoted by roscovitine without affecting the cumulus expansion rate or the subsequent meiosis progression.  相似文献   
15.
Morphological changes and biochemical composition of abdominal muscles over the molt cycle were investigated in juvenile Litopenaeus vannamei. Eight molt stages were characterized and clear uropod images are presented. Molt frequency was highly correlated with the age of the shrimp. Juvenile shrimps appeared to molt faster at one month of age (4.6 ± 0.5 days/cycle), slow to 11.8 ± 1.7 days/cycle at three months of age, and reach a long molt cycle at six months (17.2 ± 2.7 days/cycle). Myofiber cross-sectional images revealed specific morphological changes in abdominal muscle associated with each molt stage. Expanded fiber size was observed during intermolt stages. Water content and total soluble proteins were balanced throughout the molt cycle. Total DNA concentration increased in intermolt and premolt, while total RNA concentration remained stable except in late-premolt stages. SDS-PAGE analysis showed high levels of actin and myosin in postmolt, reaching a plateau in intermolt and declining in premolt. These results suggest the occurrence of muscle fiber rearrangement in both the premolt and postmolt stages. Abdominal muscle buildup occurs mostly during the intermolt stage.  相似文献   
16.
Journal of Soils and Sediments - This study consists of the evaluation of metals acute toxicity levels taking into consideration a hypothetic scenario of dam breaking and land deposition of two...  相似文献   
17.
Environmental problems many times could evolve when manure-containing pathogens are distributed into an open environment with no effort made to reduce the content of pathogens or limit their movement in the environment. Wind, surface flow, and subsurface flow can all carry enough pathogens to receiving waters to exceed water quality standards. This study was conducted to assess the microbiological quality of water associated with animal-based agriculture in the sub-basin of Pinhal River located in the rural area of Concordia, Santa Catarina, Brazil. Six sampling points representing different agricultural land uses (LU1—dairy cattle; LU2—without animals; LU3—dairy + pigs + poultry + crops; LU4—pigs + poultry + crops; LU5—dairy + pigs + poultry + crops + human; and LU6—dairy+pigs+crops) along the Pinhal River sub-basin (north to south) were sampled biweekly from August 2006 to December 2008. Concentrations of fecal coliforms and Escherichia coli varied significantly (p?≤?0.05) with land use (LU), but there was no interaction effect of LU, season, and time. Water samples from the catchment area of LU1 had the highest concentration of fecal coliforms (4,479?±?597 CFU ml?1) when compared with other catchment areas. Catchment area associated with LU2 (no animal) had the lowest concentrations of fecal coliforms (39.2?±?5.2 CFU ml?1). With the exception of LU2 (control site), all the maximum concentrations of E. coli exceeded the single maximum allowable concentration for E. coli (100 CFU ml?1). When LU1 was compared with other catchment areas (LU3, 50%; LU4, 67%; LU5, 58%; and LU6, 44%), it had the lowest counts (39%) of Salmonella sp. Our results suggest that spatial pattern of bacterial water quality is evident, which can be linked to the different land uses and associated practices (present or absent of animal activities). Therefore, varying responses associated with the different land uses would be critical in identifying the importance of different sources of bacteria in the catchment area and the mechanisms transferring them.  相似文献   
18.
19.
20.
Summary Significant advances in increasing tolerance to the leafhopper Empoasca kraemeri Ross & Moore in common bean have been obtained using a new breeding scheme where yield under leafhopper attack is the principal selection criterion in the evaluation of progenies. However, to further refine this breeding scheme, a study was conducted to determine whether selection for nonprotected yield would be more effective in early versus late generations. Two selection strategies were compared. In Strategy I, early generation selections in the F2 and F3 were compared to Strategy II where late generation selections were made in the F4 and F5, with the F2 and F3 generations advanced using single pod descent and bulk practices, respectively. Yield trials of the F6 lines from both selection strategies were conducted under nonprotected and insecticide protected treatments. No significant differences were detected between the two selection strategies. However, Strategy II did produce advanced lines with greater nonprotected yields than did Strategy I, with the best F6 line, in three out of four crosses, coming out of Strategy II. Late generation selection is recommended over early generation selection. Results of the new leafhopper breeding scheme, based on yield, are compared to the old breeding scheme where selections were made using visual selection practices in early generations.  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