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   51篇
  免费   7篇
林业   3篇
农学   4篇
  10篇
综合类   10篇
农作物   1篇
水产渔业   4篇
畜牧兽医   24篇
园艺   1篇
植物保护   1篇
  2018年   1篇
  2016年   1篇
  2015年   1篇
  2014年   2篇
  2013年   2篇
  2012年   3篇
  2011年   6篇
  2010年   6篇
  2009年   1篇
  2008年   5篇
  2007年   4篇
  2006年   2篇
  2005年   1篇
  2004年   6篇
  2003年   1篇
  2002年   2篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1996年   2篇
  1994年   2篇
  1993年   1篇
  1991年   1篇
  1978年   1篇
  1945年   1篇
排序方式: 共有58条查询结果,搜索用时 31 毫秒
1.
Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.  相似文献   
2.
The study compared response to prostaglandin F2α (PG), synchrony of ovulation and pregnancy per AI (P/AI) in a 5‐ vs a 7‐day Ovsynch + PRID protocol and investigated whether the initial GnRH affects P/AI in lactating dairy cows. Two hundred and seventy‐six cows (500 inseminations) were assigned to one of four timed‐AI (TAI) protocols: (i) PRID‐7G; 100 μg GnRH im, and a progesterone‐releasing intravaginal device (PRID) for 7 days. At PRID removal, PG (500 μg of cloprostenol) was given im. Cows received the second GnRH treatment at 60 h after PRID removal and TAI 12 h later. (ii) PRID‐5G; as PRID‐7G except the duration of PRID, treatment was 5 days and PG was given twice (12 h apart). (iii) PRID‐7NoG; as PRID‐7G except the initial GnRH, treatment was omitted. (iv) PRID‐5NoG; as PRID‐7NoG except the duration of PRID, treatment was 5 days. Response to treatments and pregnancy status at 32 and 60 days after TAI was determined by ultrasonography. The percentage of cows ovulating before TAI was greatest in PRID‐7G (17.1%), and the percentage of cows that did not have luteal regression was greatest in PRID‐5G (9.5%). The overall P/AI at 32 and 60 days did not differ among TAI protocols. However, during resynchronization, cows subjected to the 5‐day protocols had greater (p < 0.05) P/AI (45.3% vs 33.6%) than cows subjected to the 7‐day protocols. Pregnancy loss between 32 and 60 days tended (p = 0.10) to be greater in cows that did not receive initial GnRH (14.8%) compared to those that received GnRH (8.2%). In conclusion, the PRID‐5G protocol resulted in fewer cows responding to PG, but P/AI did not differ among TAI protocols. A 5‐day protocol resulted in more P/AI in resynchronized cows, and cows that did not receive initial GnRH tended to experience more pregnancy losses.  相似文献   
3.
The similarity in gene order between closely related taxa suggests that genomic information from model systems should facilitate gene isolation and characterization in target crops. If this is the case, a great deal of effort and investment can be saved by focusing attention on a few model systems that have appropriate applicability. Pea (Pisura sativum) provides a good test case: its genome is large and the insertion sites for repetitive elements, which comprise the bulk of its genome, are highly polymorphic (Jing et al., 2005; Vershinin et al., 2003), so we expect a great deal of structural polymorphism between the genomes of Pisum lines. Yet the genetic map of Pisum is essentially coUinear with Medicago (Choi et al., 2004; Kalo et al., 2004).  相似文献   
4.
Vavilovia (Vavilovia Fed.) is one of the five genera in tribe Fabeae and consists of only one species, ‘beautiful’ vavilovia (Vavilovia formosa (Stev.) Fed.). The main centre of distribution is the Central and Eastern Caucasus, with a disjunct distribution among high alpine areas in the region, extending as far as West Turkey, Lebanon and Iran. In Armenia, in situ studies on Vavilovia started in the late 1930s. In July and August 2009, three expeditions were conducted to two locations: two to the Ughtasar Mountain and one to the Geghama Mountains. The first expedition to Ughtasar resulted in fresh plant collections and soil analysis for one of the sites. The expedition to Geghama established the existence of Vavilovia in the region of Lake Aknalitch. The second expedition to Ughtasar provided immature fruits and seeds. Collected plant material was transplanted into the Flora and Vegetation of Armenia plot of the Yerevan Botanic Garden established in 1940. Today, along with other plants the plot contains more than 200 species of wild relatives of cultural plants from 130 genera, including indiginous species of tribe Fabeae such as Vavilovia. The transplanted plants will continue to be monitored to see if the plants go on to successfully flower and set seed or whether further sites, possibly at higher altitudes might need to be tested to meet the long term conservation requirements of this iconic legume. These co-ordinated efforts provide a good example of an ex situ conservation strategy for Vavilovia formosa, which, if successful will improve access and utility for the whole legume research community.  相似文献   
5.
Understanding genetic relationships among the three most important Agrostis species will be important in breeding and genomic studies aimed at cultivar improvement. Creeping, colonial, and velvet bentgrasses (Agrostis stolonifera L., A. capillaris L., and A. canina L., respectively) are commercially important turfgrass species often used on golf courses. Velvet bentgrass is a diploid and creeping and colonial bentgrasses are both allotetraploids. A model for the genomic relationships among these species was previously developed from cytological evidence. The genome designations were A1A1 for velvet bentgrass, A1A1A2A2 for colonial bentgrass, and A2A2A3A3 for creeping bentgrass. Here we used phylogenetic analysis based on DNA sequences of nuclear ITS and protein coding genes and the plastid trnK intron and matK gene to reexamine these relationships. In contrast to the previous model, the DNA sequence analysis suggested that velvet bentgrass was closely related to creeping bentgrass and it is likely the maternal parent of creeping bentgrass. Phylogenetic analysis of some conserved nuclear genes revealed a close relationship of the velvet bentgrass sequences with the A2 subgenome sequences of creeping bentgrass. We therefore propose that velvet bentgrass be designated as having the A2 genome, rather than the A1 genome as in the previous model.  相似文献   
6.
We hypothesized that the inclusion of flaxseed in the diets of lactating dairy cows will increase urinary and fecal concentrations of the lignans, secoisolariciresinol diglycoside (SDG), enterolactone and enterodiol, reduce intrafollicular concentrations of IGF-I and estradiol, and subsequently reduce estradiol and oxytocin receptor expression in the endometrium. To test this hypothesis, 27 cycling, lactating Holstein cows were assigned to 1 of 3 diets supplemented with saturated fatty acids (SAT), flax (FLX), or sunflower (SUN) seed. Rations were formulated to provide 750 g supplemental fat/cow/d in all dietary groups. Ovulation (Day 0) was synchronized, and 5 d later, follicles>8 mm were ablated by an ultrasound-guided procedure in all cows. Samples of blood (Days 0 to 14), follicular fluid (Day 5 and 15), endometrium (Day 15), as well as urine and feces were collected in a subset of the animals. The fecal concentrations of SDG and enterodiol were higher (P<0.05) in cows fed FLX than in those fed SAT or SUN. Enterodiol increased (P<0.05) in urine samples of cows fed FLX, compared to those of cows fed SUN. However, follicular estradiol concentrations on Day 5 and 15 and endometrial concentrations of estradiol and oxytocin receptors on Day 15 did not differ among the dietary groups. Mean plasma progesterone concentrations were higher (P<0.05) in cows fed FLX and SUN than in those fed SAT. In summary, a diet supplemented with flaxseed increased the concentrations of SDG and enterodiol in feces, as hypothesized, but did not alter intrafollicular concentrations of IGF-I or estradiol, or endometrial populations of oxytocin or estrogen receptors in lactating dairy cows.  相似文献   
7.
The extent and frequency of bloodworm digging in northeast North America has never been investigated, making bloodworm fishery management difficult and an assessment of ecological impact impossible. We examined the spatial and temporal patterns of bloodworm digging by surveying 13 mudflats in mid-coast Maine using monthly aerial photography. We used ArcGIS to “georeference” spatial information into the photographs, allowing us to quantify the area of the mudflat disturbed by digging. Of the 122 ha of flats we monitored, almost 48% was dug in 2006, and 24% was dug in 2007, corresponding to 57.9 ha and 24.8 ha, respectively. Individual flats in this study were dug as much as 155% and as little as 0% annually, but rarely were they dug more than once a year as studies assessing the impact of digging on soft-sediment communities have assumed. Digging activity peaked in early spring with a smaller peak in August. On average, 3% of the visual evidence of digging faded each month. Except for those erased by winter storms and ice scour, no dug strip faded before 5 months of age, therefore flats could be monitored every 4–5 months for an accurate estimate of digging activity. Our results allow us, for the first time, to estimate the impact of digging on the bloodworm resource and to design realistic experiments to measure the impact of digging on the soft-sediment community and non-target species.  相似文献   
8.
The objectives were to investigate the relationships between endometrial cytology (EC) and interval from calving to first ovulation, and pregnancy in dairy cows, and that between uterine fluid and EC. On day 25 postpartum, 39 dairy cows were grouped based on EC, as having low (?8%) or high (>8%) polymorphonuclear cells (PMN), and the quantity of uterine fluid was assessed by ultrasound. The interval from calving to first ovulation was shorter in low, than in high PMN cows (32 vs. 45 d). A greater proportion of cows with uterine fluid had high PMN (64% vs. 21%), and the PMN increased from 14% to 34% as the quantity of uterine fluid increased. The mean interval from calving to ovulation was longer in primiparous cows with high PMN (49 d) compared to that of primiparous and multiparous cows with low PMN (28 and 29 d, respectively). Although the conception rate to first service at 92 d postpartum was not different between PMN groups, the cumulative pregnancy at 270 d tended to be higher in low than in high PMN (80% vs. 58%) multiparous cows. Also, cows that had uterine fluid on day 25 postpartum had a shorter interval from calving to pregnancy than those with no uterine fluid (161 vs. 208 d). In conclusion, combining transrectal ultrasonography with endometrial cytology on day 25 postpartum has diagnostic value in the assessment of uterine inflammation.  相似文献   
9.
One of the options for achieving an adequate food supply in tropical Africa is by bringing more land into production. This often requires clearing and developing new vegetation areas for agricultural production. In sub-Saharan Africa, large areas of forest are being cleared for cultivation without adequate knowledge as to the consequences of the clearing method employed. This study was therefore initiated to, among other objectives, assess the effects of some forest clearing methods on soil compaction, texture, and micronutrients. Treatments were the following five clearing methods: (1) mechanical (MC), (2) semi-mechanical (SMC), (3) slash and burn (manual) (SB), (4) mechanical – no planting (MCNP), and (5) slash and burn – no planting (SBNP). After clearing, we planted maize and cowpea in every other row during the first year, and planted maize and cassava during the second year in the plots of treatments 1–3. Changes in soil texture, bulk density, and exchangeable Fe, Zn, Mn, and Cu were determined. Soil bulk density increased (with depth) in all treatments from the intitial (0–15cm) level of 1.1gcm–3 to between 1.27 and 1.39gcm–3 2 years after clearing, with the highest levels occurring in the MC plots. This indicated that clearing was accompanied by soil compaction. Some changes were noted in soil textural composition, but these were not of practical significance. Exchangeable Mn, Fe, and Cu (0–15cm) decreased markedly after clearing, especially under MC in the first year. Zinc levels changed little during the study period. The decline in micronutrient levels was paralleled by a decline in soil organic carbon.  相似文献   
10.
Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced.  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