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   701篇
  免费   31篇
  国内免费   1篇
林业   78篇
农学   27篇
基础科学   2篇
  90篇
综合类   57篇
农作物   32篇
水产渔业   67篇
畜牧兽医   312篇
园艺   9篇
植物保护   59篇
  2023年   3篇
  2022年   5篇
  2021年   11篇
  2020年   10篇
  2019年   5篇
  2018年   19篇
  2017年   19篇
  2016年   12篇
  2015年   28篇
  2014年   18篇
  2013年   50篇
  2012年   32篇
  2011年   62篇
  2010年   25篇
  2009年   23篇
  2008年   36篇
  2007年   37篇
  2006年   45篇
  2005年   24篇
  2004年   25篇
  2003年   32篇
  2002年   19篇
  2001年   20篇
  2000年   29篇
  1999年   22篇
  1998年   8篇
  1997年   5篇
  1996年   4篇
  1994年   4篇
  1993年   2篇
  1992年   8篇
  1991年   7篇
  1990年   8篇
  1989年   6篇
  1988年   7篇
  1987年   11篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   3篇
  1979年   5篇
  1978年   4篇
  1977年   3篇
  1975年   2篇
  1974年   4篇
  1973年   3篇
  1971年   4篇
  1970年   3篇
  1966年   1篇
排序方式: 共有733条查询结果,搜索用时 156 毫秒
141.
Six year-old Japanese pear (Pyrus seratina Reheder cv. Kosui) trees grafted on P. serotina cv. Nihonyamanashi were grown in containers filled with Granite Regosol under glasshouse conditions. At different stages of fruit growth, pear trees were exposed to an elevated CO2 concentration (130 Pa CO2 ) along with a control (35 Pa CO2). For one group of plants, CO2 enrichment was applied for 79 d from 52 d after full bloom (DAB) to fruit maturity (long-term CO2 enrichment) and for another group the same treatment was applied for 35 d from 96 DAB to fruit maturity (short-term CO2 enrichment). The effects of the elevated CO2 concentration on vegetative growth, mineral contents, and fruit production and quality were examined. Long-term CO2 enrichment enhanced vegetative growth, without any significant effect on the mineral contents in either flower bud or fruit except for a remarkable increase in the K content. Long-term CO2 enrichment increased the fruit size and fresh weight, but had no significant effect on the fruit quality. On the other hand, the short-term CO2 enrichment did not induce any significant change in the fruit size but increased the fruit sugar concentration. Along with the reduction of the sorbitol concentration in fruit, the fructose and sucrose concentrations increased and these changes occurred earlier at elevated CO2 than at ambient CO2 concentrations. From these results, we concluded that the effect of CO2 enrichment on fruit growth varies depending upon the growth stages of fruit: during the initial and fruitlet stages when fruit expansion occurs, CO2 enrichment increases the fruit size, whereas, during maturation when fruit expansion has slowed down and sugar accumulation in fruit is active, it increases the fruit sugar concentration.  相似文献   
142.
Waimea (Wy-may-ah) is white skinned with round to blocky shaped tubers. It is tolerant to late blight but susceptible to early blight and root knot nematode. In Hawaii, Waimea is adapted to high elevation growing conditions. It is much higher yielding with slightly higher specific gravity when compared to Kennebec. Waimea is comparable to Pele, another Hawaiian cultivar.  相似文献   
143.
Increasing global atmospheric CO2 concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO2 (AMB) or free-air CO2-enrichment (FACE) at CO2 concentrations ranged from 275 to 365 μmol mol−1 above AMB. We supplied 13CO2 to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with 13C at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem 13C content. Furthermore, there were no differences between treatments in whole-plant 13C contents at heading and grain maturity. In contrast, plants supplied with 13C at the grain-filling stage had more 13C in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO2 enrichment might be effectively stored in the grains. Furthermore, regardless of when the 13C was supplied, plants had more 13C in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO2 enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains.  相似文献   
144.
Frequent fishing activities are causing overfishing, destroying the habitat of marine life, and threatening global marine biodiversity. Understanding the dynamics of fishing activities and their drivers is crucial for designing and implementing effective ocean management. The fishing activities in the open sea are reported to be characterized by high spatial variability in local waters; however, it is still unclear whether their high spatial variability is random or regulated by oceanographic variations. Mesoscale eddies are ubiquitous swirling currents that dominate locally biogeochemical processes. Previous case studies presented an ongoing debate regarding how eddies exert impacts on high trophic organisms, which imposes limitations on understanding the dynamics of fishing activities based on the bottom-top control hypothesis from eddies to fish and fishing activities. By combining global fishing activities from deep learning and oceanic eddy atlases from satellite monitoring, we showed that the spatial variations in fishing activities were closely related to mesoscale eddies in the global midlatitude ocean, confirming that fishing activities primarily targeting tuna, were aggregated in (repelled from) anticyclonic (cyclonic) eddy cores. This eddy-fishing activity relationship was opposite to satellite-observed primary production but corresponded well with the temperature and oxygen content in deeper water. By integrating existing evidence, we attribute eddy-related fishing activities to a reasonable hypothesis that warm and oxygen-rich deeper water in anticyclonic eddies relieves the thermal and anoxic constraints for diving predation by tuna while the constraints are aggravated in cold and oxygen-poor cyclonic eddies.  相似文献   
145.
T. Kaneko  M. Kihara  K. Ito 《Plant Breeding》2000,119(3):197-201
β‐Amylase thermostability is one of the major factors affecting fermentability in the brewing process; consequently, it could be used as a selection marker for the trait. In order to clarify what controls its thermostability, the linkage analysis of β‐amylase thermostability and its genotype as restriction fragment length polymorphism patterns was performed in three cross populations. Then, β‐amylase cDNAs cloned from the three varieties which had a different thermostability type were expressed in Escherichia coli. According to the results of the linkage analysis and gene expression test, it was concluded that β‐amylase thermostability resulted from a difference in its structural gene. Furthermore, to construct an STS marker for the gene, the gDNA sequences of β‐amylase were compared among the three varieties, which had different thermostabilities. Although there were many differences in the intron sequence, few nucleotides differed in the exon region. Based on the variation in the intron region, a sequence‐tagged‐site marker was constructed to detect β‐amylase genotypes in breeding material.  相似文献   
146.
杉木促进开花结实方法的探讨   总被引:1,自引:0,他引:1  
试验通过对 1、2、3年生杉木苗施用赤霉素 100 ppm、细胞分裂素、北林激素 10倍水稀释、北林激素20倍水稀释等不同药品的处理,以及与对照的比较,发现以上药品对1年生杉木处理无效果,没有开花现象;对2、3年生杉木苗,北林激素20倍水稀释后对提前雄花开花结实时间效果很明显。  相似文献   
147.
通过对不同年龄的杉木使用截干、斜埋、剪枝等几种不同修剪方法的试验,比较各种不同方法产生穗条的数量及生根情况,确定一种可行的采穗母树剪定方法,为杉木采穗圃的营建与管理提供技术保证。结果表明在使用幼龄苗营建杉木采穗圃时,采用斜埋法产生穗条的数量最多且生根情况最好;如果要从年龄稍大一点的树中获取大量穗条或是建立长期的采穗圃,采用截干法,效果较好。  相似文献   
148.
Increasing food loss and waste (FLW) is a global problem, and efforts are being made to use waste food as potential livestock feed material. The amount of self-supplied feed is lower in Japan than in other countries, and the government recommends FLW use for animal feed. Sake (Japanese rice wine) is a traditional alcoholic beverage. During the sake manufacturing process, large amounts of squeezed solids or “lees” (sake lees) are generated. Sake lees are nutritious and functional, but are prone to spoilage. In this study, we investigated whether sake lees should be mixed with animal feed immediately or after drying. To assess the usefulness of sake lees as a poultry feed ingredient and determine the effect of sake lees on intestinal immunity, we performed a feeding trial with three treatments: a raw sake lees (RSL) diet, dried sake lees (DSL) diet, and control diet. Three-week-old broilers were fed these diets (n=8 per group) for two weeks. We then calculated feed efficiency and performed RT-qPCR to assess the effects of diet on intestinal immunity. The growth performance in the RSL diet group was equivalent to that in the control diet group. The DSL diet became difficult for broilers to eat, resulting in decreased growth performance. In the ileum of RSL-diet broilers, the mRNA expression levels of TGF-β1 and avian β-defensin (AvBD)12 were significantly increased compared to those of control diet broilers (p<0.05), and a significant correlation was observed between the two genes (p<0.05). Our results indicated that sake lees should not be dried and should be mixed immediately with feed, and this sake lees when fed to chicken activates the intestinal immunity. However, sake lees have a lower fat content than corn, and it is thus important to combine sake lees with high-energy feed.  相似文献   
149.
A heterophilic Hanganutziu-Deicher (HD) antigen is present in many animal sera except human and chicken sera. To visualize the antigenic molecules, nine species animal and human sera were analyzed by SDS-PAGE, followed by Western blotting and immunostaining with avain anti-N-glycolylneuraminyl-lactosyl ceramide antibody which recognizes the terminal N-glycolylneuraminic acid moiety of glycoconjugates as an epitope of the HD antigen. Several HD antigen-active glycoprotein bands were detected in the sera of fetal calf, calf, horse, goat, monkey, rabbit, guinea pig, rat and mouse, except for human serum. The HD antigenic proteins showed heterogeneities in their molecular weights and were not identical with any major band visualized with silver-staining, indicating that they are minor components of serum proteins in each animal. Neuraminidase treatment destroyed the antigenicity of all proteins, confirming that N-glycolylneuraminic acid (NeuGc) at the non-reducing terminal of carbohydrate chains is the antigenic epitope in serum glycoprotein molecules as already confirmed in glycosphingolipid (GSL) antigens. The finding of HD-antigenic glycoproteins in animal sera suggests that they also stimulate HD antibody production in patients who received animal antiserum for therapeutic aim.  相似文献   
150.
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