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   16162篇
  免费   1017篇
  国内免费   1302篇
林业   1220篇
农学   1194篇
基础科学   191篇
  2209篇
综合类   6811篇
农作物   1352篇
水产渔业   1094篇
畜牧兽医   1961篇
园艺   548篇
植物保护   1901篇
  2024年   144篇
  2023年   362篇
  2022年   607篇
  2021年   648篇
  2020年   603篇
  2019年   747篇
  2018年   449篇
  2017年   729篇
  2016年   889篇
  2015年   717篇
  2014年   883篇
  2013年   1010篇
  2012年   1243篇
  2011年   1258篇
  2010年   1117篇
  2009年   995篇
  2008年   930篇
  2007年   1002篇
  2006年   816篇
  2005年   599篇
  2004年   481篇
  2003年   353篇
  2002年   271篇
  2001年   236篇
  2000年   187篇
  1999年   203篇
  1998年   136篇
  1997年   122篇
  1996年   119篇
  1995年   91篇
  1994年   86篇
  1993年   84篇
  1992年   82篇
  1991年   79篇
  1990年   55篇
  1989年   42篇
  1988年   41篇
  1987年   29篇
  1986年   11篇
  1985年   6篇
  1984年   2篇
  1981年   3篇
  1980年   3篇
  1979年   4篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1963年   1篇
  1962年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
An enriched environment is widely used to improve domestic animals’ welfare and promote their natural behaviors. Music can reduce abnormal behavior in humans, nonhuman primates, and rodents. However, little is known about the effects of music on pigs. This study aims to explore the effects of repeated music stimulation on the behavior, physiology, and immunity of growing pigs. A total of 72 hybrid piglets (Large White × Duroc × Minpig) were randomly divided into three groups, including music (Mozart K.448, 60 to 70 dB), noise (recorded mechanical noise, 80 to 85 dB), and control (natural background sound, <40 dB), and 6 h sound stimulation was given per day (1000 to 1600 hours) from 40 to 100 d of age. The behavioral activities of the pigs were observed during the music stimulation, and their serum cortisol, salivary cortisol, and serum immune indices were also measured. Compared with the control group, the music group and noise group increased activity but decreased lying of pigs (P < 0.05). A significant increase in tail-wagging, playing, and exploring behaviors of pigs was found in the music group (P < 0.05), and the noise significantly increased the aggressive behavior of the pigs (P < 0.05). Tail-wagging, playing, exploring, manipulating, and aggressive behaviors decreased over time. Short-term (8 d) music stimulus had a lower cortisol level than that of the noise and control groups (P < 0.05), whereas long-term (60 d) music stimulus increased immunoglobulin G (IgG), interleukin-2 (IL-2), and interferon-gamma (IFN-γ) levels (P < 0.05) and decreased interleukin-4 (IL-4) level (P < 0.05). Long-term noise stimulus significantly reduced the level of IgG (P < 0.05) but did not affect the level of IL-2, IL-4, and IFN-γ levels (P > 0.05). In conclusion, short-term music stimulus (8 d) reduced the stress response, whereas long-term music stimulus (60 d) enhanced the immune responses. In addition, the noise increased the aggressive behavior, and long-term noise reduced the immunity of the growing pigs.  相似文献   
2.
为探究同期排卵处理母牛体温和活动量变化规律及不同同期排卵技术处理效果,指导同期排卵技术优化。本研究自动监测了18头20月龄左右同期排卵(GnRH-PG-GnRH)处理荷斯坦母牛和17头产后40~60 d预同期排卵(PG-PG-GnRH-PG-GnRH)处理荷斯坦母牛的体温和活动量,应用自动检测系统进行母牛发情监测。结果发现,同期排卵处理母牛发情时阴道温度平均升高(0.43±0.20)℃,持续(12.37±2.73)h;活动量平均升高(18.28±18.61)倍,持续(11.00±1.68)h;排卵时阴道温度平均下降(0.20±0.10)℃,持续(11.00±1.68)h。自动化发情监测显示,同期排卵处理母牛7头发情并排卵;预同期排卵母牛GnRH处理前全部发情排卵。两种同期排卵处理,虽可改变母牛性周期进程,促进母牛性周期同步化,但均难以使母牛性周期完全同步。因此,将同期排卵-定时输精和发情鉴定技术科学结合才能取得更好的繁殖效果。  相似文献   
3.
对异硫氰酸丙烯酯毒杀松材线虫作用机制进行了初步研究。测定了其对线虫虫体形态、运动行为、体内总糖和蛋白质含量的影响,以及处理前后线虫体内过氧化氢酶(CAT)、乙酰胆碱酯酶(AChE)和谷胱甘肽-S-转移酶(GST)活性变化。结果表明:经异硫氰酸丙烯酯处理后的松材线虫虫体形态严重扭曲,运动形态出现由正常的S形变化为多节弯曲和螺旋状卷曲等异常状况,线虫行动随时间的推移变得迟缓,最终呈C形、新月形或直接死亡。随着异硫氰酸丙烯酯处理质量浓度的增大,线虫体内总糖和蛋白质含量显著上升,糖和蛋白质的代谢发生紊乱;线虫体内CAT、AChE和GST活性显著降低,且均低于对照组,表明线虫体内氧化和抗氧化作用失衡;细胞受到极大的影响,神经系统遭到破坏,解毒能力明显降低。研究结果可为研究利用异硫氰酸丙烯酯作为植物源杀线虫剂提供依据。  相似文献   
4.
5.
SUMMARY: Behavioral experiments concerning a releaser pheromone in the urine of female rainbow trout were performed using immature fish administered orally with 17α-methyltestosterone (MT) during the non-spawning season. The urine was collected by catheter. The frequency of entries of test fish was recorded in each channel scented by test and control solutions in a Y-maze trough. The behavior of both MT-treated and control fish demonstrated that they could not discriminate the differences between distilled and environmental water as control solutions. There was also no difference between MT-treated and control fish when distilled and environmental water were introduced. The MT-treated immature fish were attracted to the channel scented by ovulated female urine. Neither coelomic fluid nor the immature female urine had any effect on the behavioral responses of MT-treated fish, while immature control fish had no preference for the urine of ovulated females. These results suggest in rainbow trout that ovulated female urine contains a releaser pheromone to attract mature males, and that androgens are involved in the sensory mechanisms detecting the releaser pheromone in fish.  相似文献   
6.
灵芝硒多糖SeGLP—1抑制小鼠肝腹水癌作用的研究   总被引:8,自引:0,他引:8  
灵芝硒多糖SeGLP-1由葡萄糖、甘露糖、木糖、半乳糖和鼠李糖组成,与灵芝多糖一样是由α-糖苷键连接的吡喃多糖,硒在多糖内极可能是以O=Se=O的形式结合。给移杆肝腹水癌HCa-f的小鼠每日注射50mg/kg的SeGLP-1,15d后抑癌率可达80%,说明SeGLP-1的抑癌作用与其分子组成和分子结构的变化有关。  相似文献   
7.
合成了14个含有 N-莰-2-基的磷酰胺和硫代磷酰胺类化合物,用红外、核磁及元素分析确定其结构,并探讨了~(31)Pδ值的规律性变化。初步生物试验表明,磷酰胺类化合物对水稻发芽具有明显的抑制作用,其中化合物Ⅱ1的活性大于对照药剂抗倒胺但低于多效唑。  相似文献   
8.
Industrial animal agriculture is grounded in the concept of maximizing productivity and profit. Selective breeding for maximum productivity in one characteristic of the animal (e.g. milk yield in cows, or breast meat in broiler chickens) has resulted in genotypes and phenotypes that may predispose the animals to poor health and welfare. The conditions in which these individuals are kept may also frustrate many inherited behaviors that they are strongly motivated to perform. In order to curb the resulting harmful aberrant behaviors, such as feather‐pecking in chickens, we sometimes resort to mutilating the animals. In many places chickens are routinely de‐beaked by means of a hot metal guillotine. Compassion in World Farming (an international organization that promotes the humane treatment of farm animals) believes that it is unethical to treat sentient beings in such ways. We have a duty to respect farm animals' sentience by providing them with housing conditions that take their needs and wants into account, and by reverting to the use of dual‐purpose, slower‐growing breeds that have the potential for good welfare. Alternatives to current farming practices are available, and we owe it to the animals, and to our consciences, to pursue them.  相似文献   
9.
本文讨论一类三阶时滞泛函微分方程解的渐近性质,给出了若干解的有界性及解趋于零的判定准则.  相似文献   
10.
3种农药的微核效应研究   总被引:6,自引:0,他引:6  
运用蚕豆根尖微核技术研究3种农药(甲胺磷、甲基硫菌灵和盐酸吗啉胍)在不同浓度下的诱变效应。结果表明,3种农药诱发蚕豆根尖细胞微核率与对照组相比均有不同程度的上升(P<0.05或P<0.01),农药浓度与微核率呈剂量-效应关系,盐酸吗啉胍的诱变效应大于其他2种农药。  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