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   272篇
  免费   32篇
林业   17篇
农学   4篇
  55篇
综合类   16篇
农作物   9篇
水产渔业   14篇
畜牧兽医   162篇
园艺   1篇
植物保护   26篇
  2024年   1篇
  2023年   4篇
  2022年   2篇
  2021年   6篇
  2020年   19篇
  2019年   18篇
  2018年   10篇
  2017年   16篇
  2016年   14篇
  2015年   10篇
  2014年   21篇
  2013年   28篇
  2012年   37篇
  2011年   22篇
  2010年   13篇
  2009年   9篇
  2008年   10篇
  2007年   19篇
  2006年   6篇
  2005年   5篇
  2004年   6篇
  2003年   6篇
  2002年   9篇
  2001年   1篇
  2000年   5篇
  1998年   1篇
  1995年   1篇
  1994年   1篇
  1990年   1篇
  1979年   1篇
  1973年   2篇
排序方式: 共有304条查询结果,搜索用时 31 毫秒
1.
In this study, we evaluated the effects of including cassava wastewater in the diet on the feeding behavior of feedlot lambs in 35 male uncastrated Santa Inês × Dorper crossbred lambs at an approximate age of 3 months, with an average live weight of 20.0?±?3.4 kg. Diets were formulated with hay of cassava shoots (roughage) and a concentrate based on corn and soybean, with a roughage:concentrate ratio of 50:50, plus inclusion of cassava wastewater at the levels of 0, 12, 24, 36, or 48 g/kg of the total diet. Feeding behavior was evaluated between the 46th and 52nd days of the experiment. Increasing cassava wastewater levels in the diet reduced (P?<?0.05) the intakes (kg/day) of dry matter and neutral detergent fiber as well as the efficiency of rumination (g/cud and g/h) of dry matter and neutral detergent fiber. The other behavioral parameters were not affected by wastewater inclusion in the diet. Therefore, the inclusion of up to 48 g/kg of cassava wastewater on fresh matter of diets is not recommended for feedlot lambs.  相似文献   
2.
The objectives of this study were to determine the efficacy of recombinant equine luteinizing hormone (reLH) in shortening the time to ovulation in cycling mares and to determine the effects of treatment on endogenous hormones and inter-ovulatory intervals. In study 1, mares of light horse breeds (3–20 years) were treated with either a vehicle, various doses of reLH, or human chorionic gonadotropin (hCG). Cycling mares were examined by palpation and ultrasound per rectum daily or every 12 h from the time of treatment to ovulation. In studies 2 and 3, jugular blood samples were collected daily or every 12 h from the time of treatment to ovulation for analysis of LH, follicle stimulating hormone (FSH), estradiol-17β (E2), and progesterone (P4) by radioimmunoassays (RIA). Increasing doses of reLH (0.3, 0.6, 0.75, and 0.9 mg) showed increasing effectiveness at inducing ovulation within 48 h of treatment. Treatments with the 0.75 and 0.9 mg doses of reLH resulted in 90% and 80% ovulation rates, which were similar to hCG treatment (85.7%). Except for the early rise in LH after treatment with 0.5, 0.65, and 1.0 mg of reLH, hormone profiles appeared to be similar between control and treated cycles. Inter-ovulatory intervals were similar between control and treatment cycles. In conclusion, reLH is a reliable and effective ovulatory agent that does not significantly alter endogenous hormone profiles or affect inter-ovulatory intervals.  相似文献   
3.
4.
5.
Summary A testing procedure with a new and simple specimen shape is presented which is appropriate to characterize fracturing of inhomogeneous and complex materials like wood. With this, the fracture energy of spruce wood is determined in the TL and RL direction. The size effect, i.e. influences of specimen dimensions on KIC and Gf (specific fracture energy) are investigated. Stress and deformation distribution in the newly developed specimens are analysed with FE methods. The measured load-displacement curves are approximated by bilinear softening diagrams and FE analysis. Based on these results, it is tried to interpret typical deviations from LEFM's behaviour by mechanisms like microcracking, crack branching or crack tip bridging.The authors thank Dr. A. Teischinger for supplying the testing material and Dipl. Ing M. Elser for preparation of the diagrams. Financial support of the Fonds zur Förderung der wissenschaftlichen Forschung, Wien is gratefully acknowledged.  相似文献   
6.
7.
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   
8.
ObjectiveTo compare the effects of propofol and alfaxalone on respiration in cats.Study designRandomized, ‘blinded’, prospective clinical trial.AnimalsTwenty cats undergoing ovariohysterectomy.MethodsAfter premedication with medetomidine 0.01 mg kg−1 intramuscularly and meloxicam 0.3 mg kg−1 subcutaneously, the cats were assigned randomly into two groups: group A (n = 10) were administered alfaxalone 5 mg kg−1 minute−1 followed by 10 mg kg−1 hour−1 intravenously (IV) and group P (n = 10) were administered propofol 6 mg kg−1 minute−1 followed by 12 mg kg−1hour−1 IV for induction and maintenance of anaesthesia, respectively. After endotracheal intubation, the tube was connected to a non-rebreathing system delivering 100% oxygen. The anaesthetic maintenance drug rate was adjusted (± 0.5 mg kg−1 hour−1) every 5 minutes according to a scoring sheet based on physiologic variables and clinical signs. If apnoea > 30 seconds, end-tidal carbon dioxide (Pe′CO2) > 7.3 kPa (55 mmHg) or arterial haemoglobin oxygen saturation (SpO2) < 90% occurred, manual ventilation was provided. Methadone was administered postoperatively. Data were analyzed using independent-samples t-tests, Fisher's exact test, linear mixed-effects models and binomial test.ResultsManual ventilation was required in two and eight of the cats in group A and P, respectively (p = 0.02). Two cats in both groups showed apnoea. Pe′CO2 > 7.3 kPa was recorded in zero versus four and SpO2 < 90% in zero versus six cats in groups A and P respectively. Induction and maintenance dose rates (mean ± SD) were 11.6 ± 0.3 mg kg−1 and 10.7 ± 0.8 mg kg−1 hour−1 for alfaxalone and 11.7 ± 2.7 mg kg−1 and 12.4 ± 0.5 mg kg−1 hour−1 for propofol.Conclusion and clinical relevanceAlfaxalone had less adverse influence on respiration than propofol in cats premedicated with medetomidine. Alfaxalone might be better than propofol for induction and maintenance of anaesthesia when artificial ventilation cannot be provided.  相似文献   
9.
This paper is part of a set of three papers investigating metrological traceability of the quantification of DNA fragments as, for instance, used for quantification of genetic modifications. This paper evaluates the possible impact of several factors on results of real-time Polymerase Chain Reaction (PCR) measurements. It was found that the particle size of the powder samples does not have an influence, whereas the nature of the calibrant (plasmidic or genomic DNA) has a significant effect. Moreover, two real-time PCR detection methods (construct-specific and event-specific) for MON 810 corn were compared. The results obtained in a specifically designed interlaboratory study revealed a significant influence of the DNA extraction method on measurement results when the MON 810 construct-specific real-time PCR detection method was applied. Statistical analyses confirmed the importance of validating DNA extraction methods in conjunction with real-time PCR methods.  相似文献   
10.
The objective of this study was to evaluate the effect of three sources of glycerine (crude glycerine from soya bean oil – CGSO, mixed crude glycerine from frying oil and lard – MCG, and a semipurified glycerine from soya bean oil – SPGSO) in four concentrations in the diet (17.5, 35.0, 52.5 and 70.0 g of each type of glycerine per kg of feed) on the levels of plasmatic glycerol and the activity of the hepatic enzyme glycerol kinase in broilers of 22–35 days old (experiment I) and 33–42 days old (experiment II). The highest (p < 0.05) plasmatic glycerol level was detected in broilers fed diet containing CGSO. Independent of the source, increasing the concentration of glycerine led to a linear increase (p < 0.05) in the plasmatic glycerol concentration. In experiment I, all the diets containing glycerine resulted in increased concentrations of plasmatic glycerol, in relation to the control diet without glycerine. However, in experiment II, only the diet containing 17.5 g of CGSO per kg of feed and the diets formulated with any of the three types of glycerine in the inclusion concentrations of 35, 52.5 and 70 g/kg of feed resulted in higher plasmatic glycerol levels than those observed in the control broilers. The source of glycerine influenced the glycerol kinase activity only in experiment II, where the use of CGSO in the diet increased the enzyme activity. For both experiments, the glycerol kinase activity increased with the inclusion of glycerine in the diet. In conclusion, based on the absence of saturation of the glycerol kinase activity for the three glycerine sources and for both rearing periods evaluated, the broilers can metabolize the glycerol (at the level of the phosphorylation of the glycerol to glycerol‐3‐phosphate in the liver) present in the glycerine when the diet is supplemented with up to 70 g of glycerine per kg of feed.  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