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   450篇
  免费   18篇
  国内免费   1篇
林业   46篇
农学   53篇
基础科学   6篇
  117篇
综合类   23篇
农作物   38篇
水产渔业   47篇
畜牧兽医   86篇
园艺   5篇
植物保护   48篇
  2023年   12篇
  2022年   9篇
  2021年   11篇
  2020年   16篇
  2019年   19篇
  2018年   19篇
  2017年   17篇
  2016年   23篇
  2015年   7篇
  2014年   17篇
  2013年   46篇
  2012年   24篇
  2011年   20篇
  2010年   20篇
  2009年   22篇
  2008年   22篇
  2007年   18篇
  2006年   17篇
  2005年   10篇
  2004年   12篇
  2003年   7篇
  2002年   9篇
  2001年   14篇
  2000年   3篇
  1999年   10篇
  1998年   5篇
  1997年   2篇
  1994年   3篇
  1993年   3篇
  1992年   2篇
  1990年   5篇
  1989年   4篇
  1988年   7篇
  1987年   5篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   4篇
  1979年   3篇
  1978年   2篇
  1977年   1篇
  1976年   2篇
  1971年   1篇
  1967年   1篇
  1966年   3篇
排序方式: 共有469条查询结果,搜索用时 375 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.
Paddy and Water Environment - Most of the lands of the southern coastal zone of Bangladesh are protected from tidal flooding and storm surges by embankments constructed during the 1960s and 1970s,...  相似文献   
3.
Winter canola (Brassica napus L.) is highly sensitive to increasing temperatures during the reproductive and pod-filling stages. Although the impact of high day-time temperature stress on yield and quality has been documented in canola, similar information under high night-time temperature (HNT) stress is not available. Using six hybrids and four open-pollinated cultivars, we observed a marked shift in peak flowering towards earlier, cooler hours of the morning under HNT. Averaged across two independent experiments, the photochemical efficiency of photosystem II was significantly decreased (3%), with a significant increase in thylakoid membrane damage (13%) in the leaves of susceptible cultivars under HNT stress. Similarly, the susceptible cultivars also recorded significant reduction in biomass (34%), pod number (22%), pod weight (37%) and total seed weight (40%) per plant while the same set of agronomic traits were not affected among the tolerant cultivars. Quantitative impact of heat stress was confirmed with increased sensitivity to HNT exposure from gametogenesis until maturity resulting in a significantly higher yield loss compared to stress exposure from post-flowering till maturity. HNT significantly decreased oil concentration, but increased protein concentration and saturated fatty acid levels in seeds of the susceptible cultivars. However, HNT had no impact on the unsaturated fatty acids in both hybrids and the open-pollinated cultivars. Breeding targets based on fatty acid composition for enhancing canola seed quality may not be easily amenable due to the inconsistency documented with the compositional changes under heat stress. In summary, our findings conclude that canola hybrids are better suited to regions experiencing heat stress, compared to open-pollinated cultivars, indicating the possibility of a complete shift to hybrid canola cultivation under predicted hotter climates in the future.  相似文献   
4.
In rice, pre‐exposure to sublethal treatment followed by harsh lethal treatment is known to improve tolerance of different abiotic stresses at the vegetative stage within and across generations. Our major aim was to test the phenomenon of thermo‐tolerance at flowering across (trans)‐generations and within generation using rice cultivars contrasting for heat stress tolerance at flowering. To test trans‐generational response, plants were exposed to higher temperature at flowering stage and seeds obtained from previous generations were exposed to heat stress during flowering, which recorded significantly lower fertility when exposed to the same degree of stress in their subsequent generations. A pre‐acclimation to moderately high acclimating temperatures imposed over three different durations during the vegetative and initial reproductive stage showed positive response in the tolerant N22, particularly under severe heat stress (40 °C). This finding indicates the possibility of acquiring ameliorative thermo‐tolerant mechanisms at anthesis, restricted to tolerant genetic backgrounds to combat subsequent harsh conditions within the same generation. However, trans‐generational memory was ineffective in mitigating spikelet sterility losses in both tolerant and susceptible backgrounds. Rice is extremely sensitive to heat stress during flowering; hence, similar exercise across other crops of interest needs to be carried out before generalizing conclusions.  相似文献   
5.
6.
The present study reports data on the skull bone morphometry of barking and sambar deer. The skulls of adult barking deer (n = 6) and sambar deer (n = 6) of either sex (n = 3 males and n = 3 females) were collected from the Aizawl Zoological Park, Aizawl, Mizoram, India, with official permission from the Government of Mizoram. Anatomically, barking and sambar deer's skulls were elongated, pyramid-like, dolichocephalic and consisted of thirty-two cranial and facial bones. The cranial bones were eleven (three single and four paired), comprising of occipital, sphenoid, ethmoid, frontal, interparietal, parietal and temporal. The facial bones were twenty-one (one single and ten were paired), consisting of the maxilla, premaxilla (incisive), palatine, pterygoid, nasal, lacrimal, zygomatic (malar), vomer, turbinates, mandible and hyoid. In the present study, altogether 41 different measurements were taken morphologically and 6 different indices were applied. The obtained morphometrical parameters were significantly (p < .01, p < .05) higher in males than females of both species. Species wise, all obtained parameters were higher in sambar deer than barking deer. The obtained 41 different skull parameters and 6 indices showed statistically significant differences (p < .01 and p < .05) between both sexes of barking and sambar deer; however, practically these differences were meagre. The present morphometrical study on the skull of both species can help the wildlife professionals and zoo veterinarians determine the sex of these animals and differentiate it from other domestic and wild small ruminants for solving veterolegal cases. This study's findings will also motivate and assist other comparative studies with various domestic and wild small ruminants.  相似文献   
7.
We screened serum samples of 1024 goats slaughtered for chevon in Bareilly in Northern India for Salmonella antibodies with indirect ELISA, MAT-H (microagglutination test using flagellar antigens e, n, x and 1, 5) and MAT-O (microagglutination test using somatic antigens 4, 12 and 3, 10, 15). Salmonella antibodies were detected in 48, 8 and 40%, goats using Salmonella-cytotoxi-I ELISA, MAT 'H' and MAT 'O', respectively. After adjusting for test accuracy, the seroprevalence were highest for Salmonella-cytotoxi-I ELISA (46%) followed by agglutinins against 'O' 3, 10, 15 (15%) and negligible for other agglutinins. With all 5 tests, prevalence of Salmonella antibodies was significantly higher in females than in males. No significant difference was evident in prevalence of Salmonella antibodies to different antigens in different age groups of male goats except for e, n, x agglutinins that were significantly more prevalent in young adult (<6-18 months) males than in adult (>18 months of age) or young (< or =6 months of age) goats. On the other hand, in females, prevalence of Salmonella-cytotoxin-I antibodies and e, n, x agglutinins differed significantly among three age groups, being the most prevalent in adult goats. As expected, the results of different tests had little or no correlation because the different tests targeted antibodies to different antigens.  相似文献   
8.

BACKGROUND

The potential of weed species to respond to selection forces affecting the evolution of weedy traits such as competitive ability is poorly understood. This research characterized evolutionary growth changes in a single Abutilon theophrasti Medik. population comparing multiple generations collected from 1988 to 2016. A competition study was performed to understand changes in competitive ability, and a herbicide dose–response study was carried out to assess changes in sensitivity to acetolactate synthase-inhibiting herbicides and glyphosate over time.

RESULTS

When grown in monoculture, A. theophrasti biomass production per plant increased steadily across year-lines while leaf number decreased. In replacement experiments, A. theophrasti plants from newer year-lines were more competitive and produced more biomass and leaf area than the oldest year-line. No clear differences in sensitivity to imazamox were observed among year-lines. However, starting in 1995, this A. theophrasti population exhibited a progressive increase in growth in response to a sublethal dose of glyphosate (52 g a.e. ha−1), with the 2009 and 2016 year-lines having more than 50% higher biomass than the nontreated control.

CONCLUSION

This study demonstrates that weeds can rapidly evolve increased competitive ability. Furthermore, the results indicate the possibility of changes in glyphosate hormesis over time. These results highlight the importance of the role that rapid (i.e., subdecadal) evolution of growth traits might have on the sustainability of weed management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
9.
10.
Gilroy DJ, Jensen OP, Allen BC, Chandra S, Ganzorig B, Hogan Z, Maxted JT, Vander Zanden MJ. Home range and seasonal movement of taimen, Hucho taimen, in Mongolia.
Ecology of Freshwater Fish 2010: 19: 545–554. © 2010 John Wiley & Sons A/S Abstract –  Taimen, Hucho taimen, is the world’s largest salmonid and a prized sport fish. We used radio and acoustic telemetry to characterise movements of adult taimen in an extensive river system, the Eg–Uur, in north‐central Mongolia. Forty‐six taimen were tagged with transmitters (27 radio, 17 acoustic and 2 radio‐acoustic combined) and tracked from 2004 to 2008 using mobile surveys and fixed receivers. The mean home range of individual taimen tracked for an average of 2.4 years was 23 km (N = 41, range = 0.5–93.2 km). Of the fish with over 10 relocations (N = 16), 90% remained within a range of 38 km. Four distinct movement patterns were observed: (i) restricted core home range, (ii) core range with seasonal departures, (iii) core range with separate seasonal range and (iv) home range transfer. Movement was greatest in May and June (spawning and postspawning period) with another peak period of movement in September and October (water temperature cooling).  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