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   347篇
  免费   24篇
  国内免费   3篇
林业   27篇
农学   33篇
基础科学   4篇
  67篇
综合类   41篇
农作物   26篇
水产渔业   41篇
畜牧兽医   107篇
园艺   12篇
植物保护   16篇
  2024年   1篇
  2022年   14篇
  2021年   8篇
  2020年   12篇
  2019年   9篇
  2018年   9篇
  2017年   16篇
  2016年   13篇
  2015年   16篇
  2014年   5篇
  2013年   21篇
  2012年   15篇
  2011年   23篇
  2010年   25篇
  2009年   26篇
  2008年   17篇
  2007年   16篇
  2006年   22篇
  2005年   15篇
  2004年   17篇
  2003年   16篇
  2002年   11篇
  2001年   8篇
  2000年   5篇
  1999年   4篇
  1998年   4篇
  1997年   7篇
  1996年   2篇
  1995年   1篇
  1993年   7篇
  1992年   4篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1983年   1篇
  1980年   1篇
排序方式: 共有374条查询结果,搜索用时 234 毫秒
351.
Complex odontoma from a female Sprague-Dawley rat is described histopathologically. Necropsy revealed a hard (bony), white mass (3.0 x 3.0 x 2.1 cm) on the left mandible. Microscopically, the mass consisted of islands or nests of epithelial and mesenchymal elements that formed abortive tooth structures. In other areas, tooth formation consisted of a pulp cavity lined by layers of odontoblasts, dentin, enamel, and ameloblasts. Concerning all features of normal tooth formation which was differentiated and mineralized yet completely disorganized, the diagnosis of complex odontoma was recommended.  相似文献   
352.
提高绵、山羊颗粒冻精品质的研究   总被引:10,自引:4,他引:6  
用波德代羊和无角陶赛特羊品质良好的鲜精,研制出9个绵羊精液冷冻稀释液配方,同时对稀释、平衡、解冻、授配等方法和步骤进行相庆优化试验研究,获得冻精解冻后活力在0.45以上,冷冻保存409天的冻精解冻后活力在0.5以上,组织300只当地绵羊授配试验,30天的情期不返情率为65.57%。研制出波尔山羊(Boer)冻精的优化的稀释液配方和优化的冷冻工艺,授配试验结果表明母羊情期不返情率为65.77%。  相似文献   
353.
精子活率是评价精液品质的一项重要指标,采用肉眼估测法、加热法、伊红-苯胺黑染色法、中性红染色法,其在光学显微镜下的测定,操作简便、直观,仍为临床常规检查所应用。  相似文献   
354.
The aim of the present study was to improve the penetration during in vitro fertilization (IVF) of a frozen lot of epididymal sperm with a notoriously low fertilization ability of a Ban boar which is a native Vietnamese breed by optimizing different parameters of the IVF system. In Experiment 1, we determined that Pig‐fertilization medium was superior medium to Tyrode's albumin lactate pyruvate‐polyvinyl alcohol medium for IVF and defined the optimum the sperm concentration (1 × 106 sperm/ml). In Experiment 2, we clarified that partial removal of cumulus cells from cumulus‐oocyte complexes by hyaluronidase treatment before IVF enhances sperm penetration, whereas complete cumulus removal reduces penetration. Finally, in Experiment 3 the elevation of concentration of caffeine in Pig‐fertilization medium from 2 to 5 mmol/L and the prolongation of the co‐culture of gametes from 3 to 5 hr significantly increased the total penetration rate from 15.2% to over 50%. In conclusion, the combination of partial oocyte denudation, an elevated caffeine concentration in Pig‐fertilization medium and an extended interval of IVF with using an optimized sperm concentration was a potent way to improve the fertilization results for a frozen epididymal Ban sperm lot with low fertility.  相似文献   
355.
A 10‐wk feeding trial to determine the effect of daily feeding ratio on growth and body composition of subadult olive flounder fed the extruded pellet (EP) was performed during the summer season. Thirteen flounder (an initial body weight of 319 g) per tank were distributed into fifteen 500‐L flow‐through tanks. Five treatments of feeding ratio in 5% decrement were prepared in triplicate: 100 (satiation), 95, 90, 85, and 80% of satiation. Fish in the control group (100% of satiation) were hand‐fed to apparent satiation twice a day. Then, feed allowance in the rest of the four groups was determined based on average feed consumption of fish in the control group. Weight gain of fish fed to 100% of satiation was significantly (P < 0.05) higher than that of fish fed to 85 and 80% of satiation but not significantly (P > 0.05) different from that of fish fed to 95 and 90% of satiation. Serum total protein, glucose, and glutamic pyruvic transaminase were not significantly (P > 0.05) affected by feeding ratio but triglyceride and glutamic oxaloacetic transaminase were. In considering these results, it can be concluded that optimum daily feeding ratio for growth of subadult olive flounder seemed to be 90% of satiation when fish were fed the EP twice a day during the summer season.  相似文献   
356.
The objectives of the present experiment were to determine the effects on growth factors and some haematological parameters in Korean rockfish, Sebastes schlegeil, after dietary 7,12‐dimethylbenz(a)anthracene (DMBA) exposure at 0.6, 1.2, 2.4 and 4.8 mg kg?1 diet for 8 weeks. The specific growth rate of the fish exposed to DMBA (≥1.2 mg kg?1) showed significantly lower performance than the control. Following 8 weeks of exposure, the DMBA‐exposed groups (2.4 and 4.8 mg kg?1) had a significantly higher mean hepatosomatic index. Condition factor of the fish exposed to DMBA did not show any statistically significant deviation from the control (P>0.05), although the mean values were somewhat lower than those of the control group. Observations on haematological parameters indicated DMBA treatment induced a severe anaemia. Total protein, albumin and total cholesterol concentrations decreased following exposure to DMBA at 2.4 and 4.8 mg kg?1. In contrast, serum bilirubin and blood urea nitrogen in fish exposed to DMBA increased. Significant decreases in serum electrolytes, chloride, phosphorus, magnesium and calcium, and osmolality were observed in all DMBA‐treatment groups. All DMBA‐treatment groups showed a significantly higher activity of lactate dehydrogenase and alkaline phosphatase. Serum transaminase activity after the highest level of 4.8 mg kg?1 DMBA was significantly increased. The key finding from this study is that rockfish exposed to dietary DMBA at concentrations of 1.2 and 2.4 mg kg?1 diet are likely to experience adverse impacts in growth and haematological property respectively.  相似文献   
357.
Patient-specific, immune-matched human embryonic stem cells (hESCs) are anticipated to be of great biomedical importance for studies of disease and development and to advance clinical deliberations regarding stem cell transplantation. Eleven hESC lines were established by somatic cell nuclear transfer (SCNT) of skin cells from patients with disease or injury into donated oocytes. These lines, nuclear transfer (NT)-hESCs, grown on human feeders from the same NT donor or from genetically unrelated individuals, were established at high rates, regardless of NT donor sex or age. NT-hESCs were pluripotent, chromosomally normal, and matched the NT patient's DNA. The major histocompatibility complex identity of each NT-hESC when compared to the patient's own showed immunological compatibility, which is important for eventual transplantation. With the generation of these NT-hESCs, evaluations of genetic and epigenetic stability can be made. Additional work remains to be done regarding the development of reliable directed differentiation and the elimination of remaining animal components. Before clinical use of these cells can occur, preclinical evidence is required to prove that transplantation of differentiated NT-hESCs can be safe, effective, and tolerated.  相似文献   
358.

The present study evaluated effects of the degree of hydrolysis and peptide profile of sardine (Sardinella sp.) protein hydrolysates (SPH) from muscle tissue wastes on productive performance, body composition, hematological parameters, biochemical parameters of metabolism, antioxidant response, and intestinal microbiology tilapia (Oreochromis niloticus). Diets containing three SPH with different degrees of hydrolysis (low: 5.5%; intermediate: 27.9%, and high: 62.5%) were compared to a control diet with fish meal. The experimental design was completely randomized with four treatments and five repetitions. One hundred eighty tilapia juveniles (6.16?±?2.0 g) were distributed in 20 polyethylene tanks of 70 l of useful volume and were evaluated during 56 days. No direct relationship was observed between the degree of hydrolysis of SPH and fish productive performance. Feed consumption was reduced in all diets with SPH (means 53.03 g) compared to the control group (65.91 g), which impaired fish growth and metabolic reserves. Feed utilization was affected by the SPH peptide profile. SPH with a more diverse peptide profile (mean 1.40) had a feed efficiency similar to the control diet (1.22). Changes in biochemical and metabolic parameters in tissues, oxidative response, and microbial populations were observed but may be associated with the low consumption of diets containing SPH. Results suggest that it is necessary to properly characterize hydrolysates and understand their composition before applying fish feed.

  相似文献   
359.
The population structure of Hymenoscyphus fraxineus, the causal agent of ash dieback, was assessed at four closely located sites in the Czech Republic. To analyse the genetic variation, one Swiss and one Norwegian population with known population structures were selected as reference points. The analysis was performed using 16 previously published and five newly developed microsatellite markers. The quality of the new markers was assessed by sequencing the flanking region, identifying the type of the mutation and analysing the inheritance and linkage between all pairs of loci. In addition, markers were tested on 45 Japanese strains to confirm their usability on native H. fraxineus populations in Asia. One of the new markers was monomorphic in all European populations and one marker exhibited a high percentage of null alleles in the Japanese samples. Twenty markers in the four Czech populations showed lower average gene diversity than in the other two European populations. One Czech population significantly differed from all the others, with a pairwise GST of approximately 0.2, the lowest allelic richness and very low average gene diversity, likely resulting from a founder effect. The amount of genetic differentiation between the four neighbouring Czech populations exceeds the expected value from previous Europe‐wide population studies and suggests that local population dynamics can affect the population structure of H. fraxineus.  相似文献   
360.
Methods are described for the extraction and analysis of hydrophilic and lipophilic antioxidants, using modifications of the oxygen radical absorbing capacity (ORAC(FL)) procedure. These methods provide, for the first time, the ability to obtain a measure of "total antioxidant capacity" in the protein free plasma, using the same peroxyl radical generator for both lipophilic and hydrophilic antioxidants. Separation of the lipophilic and hydrophilic antioxidant fractions from plasma was accomplished by extracting with hexane after adding water and ethanol to the plasma (hexane/plasma/ethanol/water, 4:1:2:1, v/v). Lipophilic and hydrophilic antioxidants were efficiently partitioned between hexane and aqueous solvents. Conditions for controlling temperature effects and decreasing assay variability using fluorescein as the fluorescent probe were validated in different laboratories. Incubation (37 degrees C for at least 30 min) of the buffer to which AAPH was dissolved was critical in decreasing assay variability. Lipophilic antioxidants represented 33.1 +/- 1.5 and 38.2 +/- 1.9% of the total antioxidant capacity of the protein free plasma in two independent studies of 6 and 10 subjects, respectively. Methods are described for application of the assay techniques to other types of biological and food samples.  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