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   5768篇
  免费   241篇
  国内免费   8篇
林业   492篇
农学   209篇
基础科学   52篇
  1343篇
综合类   739篇
农作物   273篇
水产渔业   365篇
畜牧兽医   1928篇
园艺   176篇
植物保护   440篇
  2023年   28篇
  2022年   57篇
  2021年   103篇
  2020年   115篇
  2019年   140篇
  2018年   107篇
  2017年   128篇
  2016年   132篇
  2015年   99篇
  2014年   158篇
  2013年   271篇
  2012年   330篇
  2011年   404篇
  2010年   254篇
  2009年   205篇
  2008年   347篇
  2007年   349篇
  2006年   362篇
  2005年   373篇
  2004年   322篇
  2003年   297篇
  2002年   310篇
  2001年   77篇
  2000年   72篇
  1999年   86篇
  1998年   66篇
  1997年   54篇
  1996年   55篇
  1995年   45篇
  1994年   29篇
  1993年   44篇
  1992年   36篇
  1991年   35篇
  1990年   39篇
  1989年   43篇
  1988年   37篇
  1987年   26篇
  1986年   19篇
  1985年   33篇
  1984年   22篇
  1983年   35篇
  1982年   22篇
  1981年   20篇
  1980年   21篇
  1978年   18篇
  1977年   17篇
  1976年   14篇
  1974年   16篇
  1973年   18篇
  1972年   14篇
排序方式: 共有6017条查询结果,搜索用时 15 毫秒
941.
Improving the protein content and composition of cereal grain   总被引:4,自引:0,他引:4  
Cereals are important sources of protein for human nutrition but have low quality due to limitations in the amounts of essential amino acids, notably lysine. These deficiencies result from the low levels of these amino acids in the prolamin storage proteins and hence are exacerbated when high levels of nitrogen fertiliser are used to increase yield and total protein content.Genetic and genetic engineering strategies to increase both total protein content and the composition of essential amino acids have been employed. These include the exploitation of mutant high lysine genes and the use of transformation to either express additional proteins which are rich in lysine and/or methionine or to increase the free pools of these amino acids.  相似文献   
942.

Background  

The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting.  相似文献   
943.
944.
A juvenile free-ranging raccoon (Procyon lotor) was presented for acute onset of abnormal mentation and seizures. Ethylene glycol toxicosis was diagnosed on postmortem examination. This report highlights the importance of including ethylene glycol toxicosis on the list of differential diagnoses for abnormal mentation and seizures in free-ranging raccoons.  相似文献   
945.
Single-photon emission computed tomography (SPECT) can be used to study the regional distribution of the cerebral blood flow in the feline brain without interference of anesthetics. When the tracer, 99mtechnetium-ethyl cysteinate dimer (99mTc-ECD), is injected in the awake animal, the acquisition can be performed afterward under general anesthesia, whereas the tracer distribution still represents the regional cerebral blood flow (rCBF) in the awake animal. The aim of this study was to look at the in vivo stability of 99mTc-ECD in the feline brain. For this purpose, 6 cats (n = 6) were used, and 3 serial acquisitions were performed starting at 40 (T40), 60 (T60), and 85 (T85) minutes after tracer injection. Total counts and perfusion indices (PIs), normalized to the total brain and to the cerebellum, were calculated. When T85 was compared with T40, total counts decreased, depending on the brain region, with 29% (left thalamus) to 51% (bulbus olfactorius). These regional differences in tracer clearance resulted in significantly altered PIs at T85 as compared with T40. This study shows that 99mTc-ECD SPECT can be used in cats for studying the rCBF and that the clearance of 99mTc-ECD in the feline brain is region dependent. As a result, the acquisition should be started between 40 and 60 minutes after tracer injection.  相似文献   
946.
947.
948.
949.
950.
Oat bran muffins, containing 4 or 8 g of β‐glucan per two‐muffin serving, were prepared with or without β‐glucanase treatment to produce a range of β‐glucan molecular weights from 130,000 to just over 2 million. Following an overnight fast, the glycemic responses elicited by the untreated and treated muffins was measured in 10 healthy subjects and compared with a control whole wheat muffin. Taken all together, the 4‐g β‐glucan/serving muffins reduced blood glucose peak rise (PBGR) by 15 ± 6% compared with the control. The 8‐g β‐glucan/serving muffins had a significantly greater effect (44 ± 5% reduction compared with the control, P < 0.05). The efficacy of the muffins decreased as the molecular weight was reduced from a 45 ± 6% reduction in PBGR (P < 0.05) for the untreated muffins (averaged of both serving sizes) to 15 ± 6% (P < 0.05) for muffins with the lowest molecular weight. As the molecular weight was reduced from 2,200,000 to 400,000, the solubility of the β‐glucan increased from a mean of 44 to 57%, but as the molecular weight was further decreased to 120,000, solubility fell to 26%. There was a significant correlation (r2 = 0.729, P < 0.001) between the peak blood glucose and the product of the extractable β‐glucan content and the molecular weight of the β‐glucan extracted.  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