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   439篇
  免费   37篇
  国内免费   1篇
林业   26篇
农学   20篇
基础科学   1篇
  40篇
综合类   28篇
农作物   98篇
水产渔业   44篇
畜牧兽医   197篇
园艺   6篇
植物保护   17篇
  2023年   7篇
  2022年   9篇
  2021年   25篇
  2020年   11篇
  2019年   10篇
  2018年   15篇
  2017年   19篇
  2016年   20篇
  2015年   23篇
  2014年   33篇
  2013年   37篇
  2012年   35篇
  2011年   29篇
  2010年   25篇
  2009年   17篇
  2008年   16篇
  2007年   35篇
  2006年   27篇
  2005年   24篇
  2004年   5篇
  2003年   12篇
  2002年   10篇
  2001年   3篇
  2000年   7篇
  1999年   4篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1994年   2篇
  1993年   1篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1972年   2篇
  1969年   1篇
排序方式: 共有477条查询结果,搜索用时 531 毫秒
1.
Trace minerals feeding had significant effects on sperm production and fertility with better absorption and proper utilization within the body for optimum reproductive function. Several studies have shown that more influenced trace elements in the diets of animals are copper (Cu) and zinc (Zn). Bucks showing deficiency of this mineral might affect the quality of semen production which in turn would affect the fertility. This experiment was thus designed to test the effects of organic Cu and Zn supplementation on antioxidants enzyme activities and sperm functional attributes in fresh semen of bucks. Forty bucks (n = 40, Aged 5 months) were assigned to ten groups of four animals in each group, supplemented (for a period of 8 months) with different levels of organic Zn: 20 mg (T2), 40 mg (T3) and 60 mg (T4), organic Cu: 12.5 mg (T5), 25 mg (T6), 37.5 mg (T7) and combined organic Zn and Cu: 20 + 12.5 mg (T8), 40 + 25 mg (T9), 60 + 37.5 mg (T10), respectively, per kg dry matter and no additional mineral diet (control; T1). One hundred and sixty semen samples were collected through electro‐ejaculator and analysed for sperm quantity, quality, acrosome intactness and plasma membrane integrity and correlated with the catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase enzyme activities in seminal plasma. The results indicated organic Cu and zinc supplemented bucks produced more sperm cells, had higher sperm concentrations, maintained higher (< .01) sperm livability, plasma membrane and acrosome integrities, more motility and velocity. The increased antioxidant enzyme activities, reduced oxidative stress and lowered lipid peroxidation were positively correlated (< .05) with the sperm functional attributes. In conclusion, organic Cu and Zn supplement to male goats showed protective roles against oxidative damage and maintained better fresh semen characteristics.  相似文献   
2.
3.
4.
Glutathione (GSH) concentrations of oocytes are considered as an important marker of the cytoplasmic maturation. The present study was designed to compare GSH concentrations of in vivo and in vitro matured canine oocytes. In vivo matured oocytes were collected 72 hr after ovulation by flushing fallopian tubes after laparotomy. Ovaries were collected from bitches with different reproductive stages, and collected oocytes were divided into 2 groups according to the size viz. < 120 microm and > 120 microm in diameter and cultured for 72 hr in Tissue Culture Medium-199 supplemented with 10% FBS, 2.2 mg/ml sodium bicarbonate, 2.0 microg/ml estrogen, 0.5 microg/ml FSH, 0.03 IU/ml hCG, and 1% penicillin-streptomycin solution in the presence or absence of 50 microM beta-mercaptoethanol. GSH concentrations were determined by the dithionitrobenzoic acid-glutathione disulfide (DTNB-GSSG) reductase recycling assay. GSH concentrations of immature canine oocytes were 2.9 and 3.8, 3.5 and 6.8, and 3.1 and 6.5 pM/oocyte for < 120 microm and > 120 microm in diameter oocyte groups at anestrous, follicular and luteal stage, respectively (P<0.05). In vivo matured oocytes had significantly higher GSH concentrations compared with in vitro matured oocytes. The GSH content was 19.2 pM/oocyte for in vivo matured oocytes, while 4.1 to 8.1 and 5.7 to 13.2 pM/oocyte for in vitro matured oocytes cultured in the absence or presence of beta-mercaptoethanol, respectively (P<0.05). Presence of beta-mercaptoethanol increased GSH synthesis in canine oocytes cultured in vitro, and oocytes collected from follicular and luteal stage was superior to anestrus oocytes.  相似文献   
5.
Transmissible venereal tumor (TVT) is a well-documented transplantable tumor in dogs, with no breed or sex predilection and a low metastatic rate. In this report, a 2-year-old intact female Mastiff that had numerous, rapidly growing masses throughout the subcutis mainly at the dorsal body plane, the caudal half of the ventral abdomen, and around the vulva was euthanized due to poor prognosis. Neoplastic nodules similar to those seen in the subcutis were also noted in the lung, anterior mediastinum, liver, spleen, kidney, and superficial and deep lymph nodes in both abdominal and thoracic cavities. The neoplastic nodules from the subcutis as well as metastatic foci revealed similar cytologic and histologic features, which were consistent with canine TVT. By immunohistochemical staining, the neoplastic cells were positive for lysozyme and vimentin but were negative for cytokeratin, desmin, CD3, and CD79a. The diagnosis of the TVT was further supported by the identification and analysis of long interspersed nuclear elements (LINE) from paraffin-embedded tumor tissue. This case is a rare example of TVT with multiorgan metastasis. In this case, the polymerase chain reaction technique was useful in differential diagnosis of canine round cell tumors because this technique can be applied in retrospective as well as future study.  相似文献   
6.
Forty peptides were synthesized corresponding to hydrophilic clusters of amino acids within the sequences of foot-and-mouth disease virus (FMDV) nonstructural proteins (NSP). Six peptides were studied in more detail and the most promising, a 2B peptide, was evaluated in enzyme-linked immunosorbent assay (ELISA) using sera from naive, vaccinated, and vaccinated-and-challenged cattle as well as bovine sera from field outbreaks. The performance of the new NSP peptide ELISA was compared to that of 4 commercial NSP ELISA kits. Antibody to 2B was detectable from the end of the first week to the second week after infection in most of the nonvaccinated animals and by the second to third week in vaccinated-and-challenged animals. The sensitivity of the 2B peptide ELISA was comparable to the 3ABC Ceditest (Ceditest FMDV-NS, Cedi Diagnostics B.V.; Chung et al., 2002). With some modification and further validation, this 2B test could be useful as a screening or conformational NSP test in postvaccination surveillance for FMD.  相似文献   
7.
8.
9.
This study was performed to evaluate the effect of beta-tricalcium phosphate and poly L-lactide-co-glycolide-co-epsilon-caprolactone (TCP/PLGC) membrane in the repair of partial bone defects in canine proximal humerus. Three adult mixed-breed dogs were used during the experimental period. The length of the defect was quarter of the full length of humerus, and width of the defect was quarter of middle diameter of the lateral aspect of humerus. The humeri of each dog were divided into treatment (TCP/PLGC) and control groups. The defect was covered with TCP/PLGC membrane in treatment group. To evaluate regeneration of the bone, computerized tomography (CT) and histopathologic examination were performed. The radiopaque lines were appeared at the original defect sites in TCP/PLGC group but below the original site in control at 4th week. Radiopacity and thickness of the defect sites, and radiopaque lines were more increased at 8th week than those of 4th week. Histopathologic findings revealed fibrous connective tissue migration into the defect and the migration inhibited the structure of new cortex to be placed in the original level in control whereas new cortex growth was found in the level of original line in TCP/PLGC group. However, the new cortical bone in the TCP/PLGC group was thinner and less organized than the adjacent intact cortex, and the amount of new cancellous bones were also scanty. The result suggested that TCP/PLGC membrane is a good guided bone regeneration material to restore the original morphology of humerus in partial defect.  相似文献   
10.
To compliment the current subirrigation systems used for production of potted plants, a nutrient-flow wick culture (NFW) system was developed and compared with other subirrigation systems, such as an ebb and flow culture (EBB) system and a nutrient-stagnant wick culture (NSW) system in relation to their system characteristics and plant growth. Kalanchoe (Kalanchoe blossfeldiana cv. New Alter) was cultivated in a 6 cm pot for 10 weeks in each subirrigation system. The water-absorption pattern of the medium, water content of the medium, water loss, algal growth, salt-buildup and plant growth under various culture systems were observed. The water contents of medium under the NFW and EBB systems showed fluctuations from 30 to 40% and from 50 to 60% (by volume), respectively, whereas the water content under the NSW system gradually increased to over 40% without fluctuation. Relative to other systems, the water loss in the NFW system was 50–70% due to the reduction in the evaporation from the surfaces of the trough and medium. Algae appeared in the NSW system because the nutrient solution was always stagnant in the trough, while it was not observed under the NFW system. The dissolved oxygen in the nutrient solution was the highest during the irrigation period and the salinity in the medium was the lowest in the NFW system. With regard to system characteristics, the NFW system was simple, water-saving and efficient. In addition, the growth of kalanchoes in the NFW system was similar to those in the NSW and EBB systems at an irrigation frequency of five times a day.  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