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   369篇
  免费   30篇
林业   13篇
农学   13篇
基础科学   3篇
  60篇
综合类   36篇
农作物   3篇
水产渔业   21篇
畜牧兽医   227篇
园艺   1篇
植物保护   22篇
  2023年   3篇
  2022年   2篇
  2021年   15篇
  2020年   4篇
  2019年   10篇
  2018年   12篇
  2017年   5篇
  2016年   11篇
  2015年   11篇
  2014年   10篇
  2013年   35篇
  2012年   13篇
  2011年   15篇
  2010年   14篇
  2009年   13篇
  2008年   18篇
  2007年   9篇
  2006年   11篇
  2005年   9篇
  2004年   20篇
  2003年   12篇
  2002年   16篇
  2001年   8篇
  2000年   4篇
  1999年   8篇
  1998年   7篇
  1997年   6篇
  1996年   4篇
  1995年   3篇
  1993年   2篇
  1992年   5篇
  1991年   10篇
  1990年   7篇
  1989年   7篇
  1988年   8篇
  1987年   3篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1982年   5篇
  1980年   2篇
  1979年   4篇
  1977年   3篇
  1971年   5篇
  1968年   2篇
  1966年   2篇
  1964年   2篇
  1963年   2篇
  1931年   1篇
  1927年   1篇
排序方式: 共有399条查询结果,搜索用时 31 毫秒
1.
AIMS: To determine if abdominal insufflation with medical air will improve oxygenation and ventilation parameters when compared to insufflation with CO2 in xylazine-sedated sheep undergoing laparoscopic artificial insemination (AI).

METHODS: Forty-seven sheep underwent oestrus synchronisation and were fasted for 24 hours prior to laparoscopic AI. Each animal was randomised to receive either CO2 or medical air for abdominal insufflation. An auricular arterial catheter was placed and utilised for serial blood sampling. Respiratory rates (RR) and arterial blood samples were collected at baseline, after xylazine (0.1?mg/kg I/V) sedation, 2 minutes after Trendelenburg positioning, 5 minutes after abdominal insufflation, and 10 minutes after being returned to a standing position. Blood samples were collected in heparinised syringes, stored on ice, and analysed for arterial pH, partial pressure of arterial O2 (PaO2), and CO2 (PaCO2). The number of ewes conceiving to AI was also determined.

RESULTS: Repeated measures ANOVA demonstrated temporal effects on RR, PaO2, PaCO2 and arterial pH during the laparoscopic AI procedure (p<0.001), but no difference between insufflation groups (p>0.01). No sheep experienced hypercapnia (PaCO2>50?mmHg) or acidaemia (pH<7.35). Hypoxaemia (PaO2<70?mmHg) was diagnosed during the procedure in 14/22 (64%) ewes in the CO2 group compared with 8/23 (35%) ewes in the medical air group (p=0.053). Overall, 15/20 (75%) ewes in the CO2 group conceived to AI compared with 16/22 (72.7%) in the medical air group (p=0.867).

CONCLUSIONS AND CLINICAL RELEVANCE: There were no statistical or clinical differences in RR, PaO2, PaCO2, pH, or conception to AI when comparing the effects of CO2 and medical air as abdominal insufflation gases. None of the sheep experienced hypercapnia or acidaemic, yet 42% (19/45) of sheep developed clinical hypoxaemia, with a higher percentage of ewes in the CO2 group developing hypoxaemia than in the medical air group. Based on the overall analysis, medical air could be utilised as a comparable alternative for abdominal insufflation during laparoscopic AI procedures.  相似文献   
2.
A one-year-old domestic long-haired cat was referred to the New York State College of Veterinary Medicine because of acute onset of paraparesis and hyperesthesia associated with trauma. Myelography and cerebrospinal fluid analysis revealed severe hydromyelia and myelitis, respectively. The definitive diagnosis of feline infectious peritonitis was made by histological examination at necropsy. Lesions were confined exclusively to the brain and spinal cord. Partial occlusion of the third and fourth ventricles with pyogranulomatous debris caused hydrocephalus and subsequent hydromyelia. The hydromyelia may have been the primary means of compensation for the hydrocephalus, thus masking subclinical disease.  相似文献   
3.
4.
Weed:spring barley competition for applied nitrogen in pig slurry   总被引:2,自引:0,他引:2  
Summary The experiments were carried out in the two spring barley fields of the organic six-course cattle:crop rotation at Foulumgaard, Denmark. The weed density was 300 and 1800 plants m−2 respectively. Pig slurry was applied by hand in microplots by four methods: broadcasting followed by incorporation, or injected in bands to depths of 5, 10 or 15 cm. Spring barley and weeds were sampled separately six times during the tillering and elongation phase of the spring barley. The effect of application method on dry-matter (d.m.) production, nitrogen uptake and recovery of applied nitrogen in the spring barley and the weeds is reported. Slurry banding halved the weed d.m. and weed N uptake compared with broadcasting, irrespective of weed density. Weeds recovered up to 12% of the applied nitrogen, which made them a significant competitor when the slurry was broadcast and incorporated. Banding by direct injection reduced the slurry:soil contact and the weed:crop competition balance for applied nitrogen moved in favour of the crop. Thus, the crop recovery of applied nitrogen at the end of the sampling period was increased from approximately 45% for broadcast and incorporated to approximately 50% for injected slurry, and coincidental weed recovery was reduced to a maximum of 5%. As the nitrogen supply normally affects plant d.m. production, banding of slurry might well improve crop competitiveness and its tolerance to mechanical weed control.  相似文献   
5.
AIM: To investigate a possible interaction between lolitrem B and ergovaline by comparing the incidence and severity of ryegrass staggers in sheep grazing ryegrass (Lolium perenne) containing lolitrem B or ryegrass containing both lolitrem B and ergovaline.

METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0–5) weekly during the study. Any animal which was scored ≥4 was removed from the study.

RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41).

CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.  相似文献   

6.
7.
Globally, aquaculture systems with water recirculation experience increasing problems with microbial taste and odor compounds (TOCs) such as geosmin and 2-methylisoborneol (MIB). This study investigated the content of geosmin and MIB in water and the flesh of 200 rainbow trouts from eight recirculated aquaculture systems in Denmark. TOC content in the fish flesh was measured by a dynamic headspace extraction method and was evaluated by a sensory panel. The results showed significant correlations between TOC content in water and fish and between chemical analysis and sensory perception. When geosmin exceeded 20 ng/L in the water, 96% of the fish had an intense muddy flavor, but below 10 ng geosmin/L, 18% of the fish (only 3% in special depuration ponds) had an intense muddy flavor. The results indicate that TOC levels <10 ng/L will ensure that a negligible portion of the fish obtains an unpalatable taste and flavor due to TOCs.  相似文献   
8.
利用常熟市不同时期 (1 966、1 984、1 992、1 999、2 0 0 0、2 0 0 1年 )、不同类型卫星遥感影像 (Corona、TM、SPOT、ETM )进行多波段合成 ,图像增强处理与精校正 ,建立不同影像城镇用地解译标志 ,通过人机交互判读 ,获得不同时期的各乡镇城镇用地矢量图的方法。统计出 35年来常熟市城镇建设用地扩大近 6 .4倍。城镇扩展空间上受到地貌条件和城市经济水平以及政策决策影响 ,城镇多数沿河流或交通线方向扩展 ,各城镇间扩展数量和相对速率有明显差异 ,且存在一定地理分布规律。结合社会经济的统计资料 ,分析发现城镇扩展与不断增加的城镇人口、GDP极显著相关 ,各乡镇单位城镇面积创造的GDP有较大的差异。  相似文献   
9.
Melanin is a widely distributed and striking dark-colored pigment produced by countless living organisms. Although a wide range of bioactivities have been recognized, there are still major constraints in using melanin for biotechnological applications such as its fragmentary known chemical structure and its insolubility in inorganic and organic solvents. In this study, a bacterial culture of Streptomyces cavourensis SV 21 produced two distinct forms of melanin: (1) a particulate, insoluble form as well as (2) a rarely observed water-soluble form. The here presented novel, acid-free purification protocol of purified particulate melanin (PPM) and purified dissolved melanin (PDM) represents the basis for an in-depth comparison of their physicochemical and biological properties, which were compared to the traditional acid-based precipitation of melanin (AM) and to a synthetic melanin standard (SM). Our data show that the differences in solubility between PDM and PPM in aqueous solutions may be a result of different adjoining cation species, since the soluble PDM polymer is largely composed of Mg2+ ions and the insoluble PPM is dominated by Ca2+ ions. Furthermore, AM shared most properties with SM, which is likely attributed to a similar, acid-based production protocol. The here presented gentler approach of purifying melanin facilitates a new perspective of an intact form of soluble and insoluble melanin that is less chemical altered and thus closer to its original biological form.  相似文献   
10.
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