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   16898篇
  免费   1106篇
  国内免费   1492篇
林业   1481篇
农学   1179篇
基础科学   1056篇
  1896篇
综合类   7718篇
农作物   1167篇
水产渔业   1010篇
畜牧兽医   2051篇
园艺   1221篇
植物保护   717篇
  2024年   116篇
  2023年   358篇
  2022年   818篇
  2021年   888篇
  2020年   790篇
  2019年   826篇
  2018年   583篇
  2017年   911篇
  2016年   635篇
  2015年   963篇
  2014年   996篇
  2013年   1131篇
  2012年   1488篇
  2011年   1396篇
  2010年   1341篇
  2009年   1096篇
  2008年   1135篇
  2007年   956篇
  2006年   723篇
  2005年   603篇
  2004年   352篇
  2003年   232篇
  2002年   298篇
  2001年   256篇
  2000年   233篇
  1999年   76篇
  1998年   35篇
  1997年   30篇
  1996年   22篇
  1995年   24篇
  1994年   34篇
  1993年   17篇
  1992年   19篇
  1991年   23篇
  1990年   8篇
  1989年   8篇
  1988年   15篇
  1987年   10篇
  1986年   5篇
  1985年   2篇
  1981年   5篇
  1979年   2篇
  1978年   2篇
  1966年   2篇
  1965年   3篇
  1964年   3篇
  1963年   3篇
  1962年   2篇
  1956年   9篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
为探索不同仿真方法的适用性,对ns=157的单级蜗壳离心泵不同工况的扬程和效率进行定常和非定常计算,并分别分析了定常计算时不同叶片夹角及非定常计算时不同时间步长的影响,通过与实验对比,得到的主要结论有:定常计算仅适用于额定工况外特性仿真,其扬程和效率计算误差分别为4.9%和2.9%,而定常多相位的计算误差分别为7.1%和3.2%;非定常仿真计算时,以4°为时间步长,并间隔20°保存一次计算数据,较好地预测出扬程曲线走势,额定工况扬程和效率计算误差约1.1%和1.8%,但小流量和大流量区间扬程计算误差达到10%左右。因此在水力优化设计时,若只关注高效点位置及其扬程和效率,可采用定常计算,若还关注扬程曲线走势,则应采用非定常计算。  相似文献   
3.
探究氮钾浓度对烟苗生理生化特性的影响,为烟叶苗期氮钾营养平衡提供参考依据.采用水培法,利用基础Hoagland营养液,设置5个不同氮钾浓度处理,分析处理间烟苗的生理生化指标差异.结果表明,氮浓度对烟苗干物质、叶绿素的积累有显著影响,在相同钾浓度下,随着氮浓度的增加,烟苗干物质、叶绿素含量、根系活力显著增加.不同氮水平下,低钾处理间的根系MDA含量、叶片GS活性差异显著.K+对烟苗叶绿素的合成、根系活力、GS活性有一定的促进作用.高氮水平下,高浓度K+会使根系活力、叶片可溶性蛋白含量下降.  相似文献   
4.
以重瓣百合'Thalita'为试材,采用4个不同浓度(10、20、40、80 mg·L-1)的GA4+7+氯吡脲(1∶1),对其进行叶面喷施处理,以清水为对照,测定其株高、茎粗、叶面积等指标,探讨GA4+7+氯吡脲对重瓣百合'Thalita'生长的影响,以期为其推广提供参考.结果 表明:20 mg·L-1 GA4+7+氯吡脲对'Thalita'花苞直径和叶面积促进作用最大,分别比对照高14.18%和55.13%,均达显著差异;茎粗随着GA4+7+氯吡脲的浓度升高表现出一定抑制作用;20 mg·L-1GA4+7+氯吡脲在花苞开放率和花期上综合效果最好;80 mg·L-1 GA4+7+氯吡脲对'Thalita'株高促进效果最好,比对照高2.67%;所有处理组种球鲜质量和根长均比对照低,其中20 mg·L-1 GA4+7+氯吡脲效果最为明显,分别比对照低36.77%和48.18%,均达显著差异.综合比较来看,20 mg·L-1 GA4+7+氯吡脲对重瓣百合'Thalita'生长影响最大,效果更佳.  相似文献   
5.
香蕉新品种‘南天红’由‘南天黄’的自然突变选育而成。假茎平均高度2.59 m,幼树假茎外表面暗红色,抽蕾后转绿。雄花苞片外表面常为深红色,花苞卷曲,常不脱落;从种植到收获11 ~ 13个月,单株产量25 kg,品质好。中高抗香蕉枯萎病4号小种,采用配套的栽培技术可在所有香蕉种植区推广。  相似文献   
6.
大数据环境的变化,不仅改变了用户的信息行为,也使得数字图书馆服务朝着越加个性化、知识化、多元化的角度不断发展,由此带动了数字图书馆资源特征与服务特征的适应性的变化,促使数字图书馆朝着创新服务模式、融合服务元素、拓展服务功能、知识化建设、精确化服务等角度的转型发展,也包括数字图书馆自身对于服务力量的不断强化和服务展现形式的多元化等方面的转型发展,推动数字图书馆不断改变原有的服务范式而朝着更加个性化、知识化和技术化的角度不断发展。  相似文献   
7.
The objective of this study was to investigate the characteristics of ruminal microbial communities of alpacas (Lama pacos) and sheep (Ovis aries) fed three diets with varying ratios of roughage (corn stalk) to concentrate, 3:7 (LS), 5:5 (MS) and 7:3 (HS). Six alpacas (one-year-old and weighing 29.5 ± 7.1 kg) and six sheep (one-year-old and weighing 27.9 ± 2.7 kg) were used in this study, in a replicated 3 × 3 Latin square experiment. Total protozoa concentration was determined under the microscope; total fungi and methanogens were assessed using quantitative polymerase chain reaction and expressed as a percentage of total bacterial 16S rRNA gene copies; bacterial communities were investigated by targeted 16S rRNA gene (V3–V4 region) sequencing. The percentage of fungi was significantly higher in alpacas than in sheep under the LS diet, while the concentration of protozoa was significantly lower in alpacas under HS, MS and LS diets. The alpha diversity including Shannon, Chao l and ACE indices of bacterial communities was higher in alpacas than in sheep, under the LS diet. A total of 299 genera belonging to 22 phyla were observed in the forestomach of alpaca and sheep, with Bacteroidetes and Firmicutes dominating both animal species. Phyla Armatimonadetes and Fusobacteria, as well as 64 genera, were detected only in alpacas, whereas phyla Acidobacteria and Nitrospira, as well as 44 genera, were found only in sheep. The abundance of cellulolytic bacteria, including Butyrivibrio and Pseudobutyrivibrio, was higher in alpacas than in sheep under all three diets. These differences in the forestomach microbial communities partly explained why alpacas displayed a higher poor-quality roughage digestibility, and a lower methane production. Results also revealed that the adverse effects of high-concentrate diets (70%) were lesser in alpacas than in sheep.  相似文献   
8.
一般认为我国南方栗仅宜于菜用,加工极易开瓣和糊化,经过几年的筛选和加工试剂,永荆3号品种可生产B-E级标准的糖水栗子罐头。  相似文献   
9.
AIM: To evaluate the effect of bFGF on the apoptosis and the expression of glucose regulated protein 78 (GRP78) in ovarian cancer CAOV3 cells.METHODS: Starvation induced cell apoptosis was conducted. After treatment with bFGF, the cell cycle and apoptosis were determined by FACS analysis and Annexin V/PI staining, respectively. The expression of protein kinase B (PKB) and GRP78 were detected by Western blotting and RT-PCR. RESULTS: Compared to starvation group, the cells treated with bFGF were still viable and increased activation of PKB and high expression of GRP78 were observed, which were prevented by PKB inhibitor wortmannin effectively (P<0.01). CONCLUSION: bFGF plays a critical role in anti-apoptosis and proliferation in human ovarian cancer through PKB signal transduction pathway, partly by upregulating the expression of GRP78.  相似文献   
10.
国有林场改革路径选择与对策分析   总被引:1,自引:0,他引:1  
贺超 《防护林科技》2009,(5):54-55,72
文章论述了国有林场的建立与发展过程,提出了国有林场面临的主要问题和改革路径选择与对策分析。  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