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   261篇
  免费   31篇
  国内免费   5篇
林业   8篇
农学   9篇
基础科学   1篇
  11篇
综合类   37篇
农作物   5篇
水产渔业   48篇
畜牧兽医   163篇
园艺   2篇
植物保护   13篇
  2024年   1篇
  2023年   7篇
  2022年   4篇
  2021年   11篇
  2020年   13篇
  2019年   17篇
  2018年   10篇
  2017年   10篇
  2016年   13篇
  2015年   19篇
  2014年   13篇
  2013年   9篇
  2012年   11篇
  2011年   15篇
  2010年   13篇
  2009年   9篇
  2008年   15篇
  2007年   21篇
  2006年   7篇
  2005年   10篇
  2004年   8篇
  2003年   7篇
  2002年   6篇
  2001年   5篇
  2000年   7篇
  1999年   4篇
  1998年   8篇
  1997年   6篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1978年   2篇
  1956年   1篇
排序方式: 共有297条查询结果,搜索用时 12 毫秒
21.
22.
23.
The effects of diverse phenylaminopyrimidines (PAP), namely PAP-pyridines (type A), PAP-pyrazoles (type B) and PAP-thiazoles (type C), on Neurospora crassa Shear & Dodge has been investigated. The results revealed that type A strongly inhibit the in vitro growth of N crassa, whereas types B and C are much less active. A significant correlation was observed between the Neurospora growth inhibition and the intrinsic activity of type A compounds on the cyclin-dependent protein kinase p34(CDC2) of starfish, suggesting that the target of phenylaminopyrimidines in fungi is a cyclin-dependent protein kinase (CDK). The phenylaminopyrimidine-binding CDKs Phoss (major band) and CDC2 (minor band) involved in phosphorus uptake, glycogen synthesis and the cell cycle were identified from N crassa by affinity chromatography on phenylaminopyrimidine-sepharose. Comparative experiments with different protein kinases revealed the importance of the side chain of phenylaminopyrimidines for their target selectivity. A type B compound was found to selectively inhibit the MAP-kinase OS-2 involved in the osmoregulatory pathway of Neurospora.  相似文献   
24.
Optimized nitrogen(N)management can increase N-use efficiency in intercropping systems.Legume-nonlegume intercropping systems can reduce N input by exploiting biological N fixation by legumes.Measurement of N utilization can help in dissecting the mechanisms underlying N uptake and utilization in legume-nonlegume intercropping systems.An experiment was performed with three planting patterns:monoculture maize(MM),monoculture soybean(SS),and maize-soybean relay intercropping(IMS),and three N application levels:zero N(NN),reduced N(RN),and conventional N(CN)to investigate crop N uptake and utilization characteristics.N recovery efficiency and 15N recovery rate of crops were higher under RN than under CN,and those under RN were higher under intercropping than under the corresponding monocultures.Compared with MM,IMS showed a lower soil N-dependent rate(SNDR)in 2012.However,the SNDR of MM rapidly declined from 86.8%in 2012 to 49.4%in 2014,whereas that of IMS declined slowly from 75.4%in 2012 to 69.4%in 2014.The interspecific N competition rate(NCRms)was higher under RN than under CN,and increased yearly.Soybean nodule dry weight and nitrogenase activities were respectively 34.2%and 12.5%higher under intercropping than in monoculture at the beginning seed stage.The amount(Ndfa)and ratio(%Ndfa)of soybean N2 fixation were significantly greater under IS than under SS.In conclusion,N fertilizer was more efficiently used under RN than under CN;in particular,the relay intercropping system promoted N fertilizer utilization in comparison with the corresponding monocultures.An intercropping system helps to maintain soil fertility because interspecific N competition promotes biological N fixation by soybean by reducing N input.Thus,a maize-soybean relay intercropping system with reduced N application is sustainable and environmentally friendly.  相似文献   
25.
Two hypotheses related to effects of juvenile pink salmon (Oncorhynchus gorbuscha) foraging behaviour and size on their predation risk were evaluated using field data collected in Prince William Sound, Alaska 1 995–97. My results supported the hypothesis that low macrozooplankton density leads to dispersion of juvenile salmon from shallow nearshore habitats and greater predation risk, but zooplankton type was an important factor. When the biomass of large copepods (primarily Neocalanus spp.) declined, salmon dispersed from shallow nearshore habitats, and mean daily individual predator consumption of salmon increased by a factor of 5. A concomitant five‐fold increase in the probability of occurrence of salmon in predator stomachs supported the notion that increased predation on salmon was caused by a greater overlap between predator and prey when salmon dispersed offshore, not an increase in the number of salmon consumed per feeding bout. The results also generally supported the hypothesis that the timing of predation events modifies the nature of size‐dependent predation losses of salmon to different predator groups (small and large planktivores and piscivores). Size‐dependent vulnerabilities of salmon to predators were a function of both predator and prey sizes. When simulated predation was shifted from May to June, the vulnerability of salmon became more dependent on their growth than initial size. But, the size‐ and growth‐dependent vulnerabilities of salmon differed more among predator groups than between May and June, suggesting that changes in the composition of predator fields could more strongly affect the nature of size‐dependent predation than changes in the timing of predation losses.  相似文献   
26.
本项试验以酯酶染色法和E-玫瑰花环形成试验,对兔抢风、百会穴灸前及灸后不同时间(3、6、12、24、48、72、96小时)测定淋巴细胞值%,经148只次的测定结果表明:艾灸对T淋巴细胞表现有明显的激励作用(P<0.01),并呈现一定的规律性;灸后3小时T淋巴细胞值%开始升高,至24小时达高峰,然后逐渐下降.艾灸对T淋巴细胞的激励作用,可能是艾灸治病的机理之一。预示着,测定T淋巴细胞值有可能作为判定艾灸疗效的一种手段。  相似文献   
27.
Hus和Robbin于1947年提出了完全收敛性的概念,完全收敛比几乎处处收敛条件更严格。本文通过构造收敛鞅,证明了相依随机变量序列的完全收敛性。作为推论,证明了负相依随机变量序列的完全收敛性。  相似文献   
28.
探讨了由于汇率的随机波动而面临着收益风险的风险厌恶竞争性出口企业的行为,这类企业可进入无偏差的外汇无期市场,在那里对外汇风险进行无成本套期保值。通过引入状态依赖效用拓展了标准方法并考察了众所周知的分离理论和全套期理论在这种一般化框架中是否仍然成立。  相似文献   
29.
30.
Irisin, a novel peptide, was initially been shown to be expressed explicitly in the muscle tissues. We studied the presence of irisin immunoreactivity in porcupine adrenal glands and kidneys. Immunocytochemistry showed that irisin was localised both in the adrenal cortex and adrenal medulla. In organs, irisin immunoreactivity was found in the tubular and collecting system of the nephron. The functional role of irisin in the adrenal gland and kidney has not been precisely yet. However, irisin might have a paracrine and autocrine function as do other locally produced peptides.  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