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   10038篇
  免费   524篇
  国内免费   738篇
林业   643篇
农学   732篇
基础科学   453篇
  1139篇
综合类   3466篇
农作物   635篇
水产渔业   570篇
畜牧兽医   2098篇
园艺   980篇
植物保护   584篇
  2024年   49篇
  2023年   146篇
  2022年   294篇
  2021年   349篇
  2020年   366篇
  2019年   481篇
  2018年   301篇
  2017年   429篇
  2016年   493篇
  2015年   465篇
  2014年   508篇
  2013年   566篇
  2012年   761篇
  2011年   872篇
  2010年   655篇
  2009年   607篇
  2008年   618篇
  2007年   657篇
  2006年   529篇
  2005年   378篇
  2004年   286篇
  2003年   242篇
  2002年   187篇
  2001年   157篇
  2000年   156篇
  1999年   127篇
  1998年   85篇
  1997年   87篇
  1996年   64篇
  1995年   67篇
  1994年   56篇
  1993年   51篇
  1992年   40篇
  1991年   33篇
  1990年   28篇
  1989年   22篇
  1988年   15篇
  1987年   15篇
  1986年   13篇
  1985年   12篇
  1984年   2篇
  1983年   6篇
  1982年   2篇
  1981年   4篇
  1980年   6篇
  1978年   2篇
  1977年   2篇
  1973年   1篇
  1956年   4篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
虚拟现实技术在园林中应用的领域日趋广阔,对园林设计的影响也越来越大。Quest3D是虚拟现实技术得以实现的重要软件之一。文章以一个古典庭院的园林设计为例,结合Quest3D技术制作开发了一个园林漫游展示系统,并从Quest3D技术的选择、软硬件选择及建立的基本流程等方面阐述了园林景观设计中应用Quest3D技术的优缺点。  相似文献   
992.
993.
This article presents a validation of a method, proposed in Podlaski (2003), for estimating the degree of tree damage. This method belongs to a group of small-area methods. To estimate the degree of tree damage in individual P3 sub-blocks of the SINUS system of information on the natural environment, a classification based on the degree of defoliation was used. Spatial distribution of the degree of tree damage was estimated through unrestricted simple random sampling. The maximum total estimation error for proportions of fir and beech with a damage degree of zero, and also with second and third degrees jointly, reached a maximum of 35.6% for fir, and 33.8% for beech. P3 sub-blocks characterised by the highest proportion of the healthiest trees (at least 15% being undamaged trees) occurred in patches in the case of fir, and in larger, compact areas in the case of beech. Because spatial diversification in the health of fir, and to a smaller degree in the case of beech, occurs at small scales, small-area methods for estimating tree condition are necessary. An analogous scheme, combining small-area with large-area methods (utilising sub-blocks of the network of large-area systems in a small-area inventory, and establishing a common database), could be used on a wider scale; for example, by supplementing the program of estimating tree health carried out by the United Nations Economic Commission for Europe (Lorenz et al. 2002) with local inventories.  相似文献   
994.
尾叶香茶菜种子发芽特性研究   总被引:2,自引:1,他引:2  
叶景学  孙桂波  王为  姚方杰  张广臣 《种子》2006,25(11):75-77
研究温度、光照、贮藏时间及GA3处理对尾叶香茶菜种子发芽特性的影响。结果表明:尾叶香茶菜种子存在休眠期,度过休眠期后发芽率迅速增加,到达峰值后如果不采取科学的贮藏手段,发芽率将迅速下降;GA3处理可以提高种子的发芽率,其适宜的浸种浓度为50mg/L;光线对尾叶香茶菜种子萌发没有影响;其适宜发芽温度为20~30℃。  相似文献   
995.
异黄酮是大豆的重要次生代谢物,参与植物与微生物互作。2-羟基异黄酮脱水酶(hydroxyisoflavanone dehydratase,HID)催化2-羟基异黄酮形成稳定的异黄酮。HID属于Abhydrolase_3基因家族,该基因家族具有多种功能,但该基因家族在大豆中的进化模式尚待研究。为了研究Abhydrolase_3基因家族在大豆中的进化模式,本文在大豆基因组中鉴定了62个Abhydrolase_3基因,串联和片段复制是该基因家族主要扩增方式。根据系统进化关系,将大豆Abhydrolase_3基因家族划分为8个亚家族,其中HID所在的亚家族I基因数量最多,并发生多次基因扩增事件。对大豆Abhydrolase_3基因家族结构分析表明,不同亚家族具有不同的基序。多态性分析表明,亚家族Ⅰ、Ⅲ和Ⅴ具有较高的核苷酸差异,并受到放松的自然选择。基因表达分析表明,除了亚家族II和IV外,其它亚家族的基因在大豆不同组织中有较高表达;亚家族Ⅰ、Ⅲ、Ⅳ、Ⅴ和Ⅵ基因受病原菌诱导表达。结果说明HID所在的亚家族I存在基因扩增和功能分化,与病原菌互作相关的基因具有较高的遗传多样性并受病原菌诱导表达。  相似文献   
996.
为获得针对番鸭细小病毒VP3蛋白的多克隆抗体,根据已发表的该病毒基因序列设计一对引物,利用PCR扩增出VP3基因,将其克隆到原核表达载体p ET-32a,转化感受态细胞BL21(DE3)。经IPTG诱导后,SDS-PAGE检测重组蛋白。将重组蛋白切胶免疫BALB/c小鼠,制备抗番鸭细小病毒部分结构蛋白的多克隆抗体。结果显示成功获得VP3基因,构建的原核表达重组质粒成功表达预期的重组蛋白,免疫小鼠获得的多克隆抗体能与番鸭细小病毒及VP3蛋白反应。表明制备的多克隆抗体可用于MDPV的检测,并为进一步研究MDPV奠定了基础。  相似文献   
997.
目的:探讨PC机辅助三维表面覆盖法诊断颞骨茎突骨折的临床价值。方法:对45例颌面及颅底外伤的患者进行多层螺旋CT薄层扫描后,经PC机辅助三维表面覆盖法成像。结果:45例患者中发现颞骨茎突骨折9例,其中双侧骨折2例,单侧骨折7例,均合并有不同程度的颌面部及颅底骨折。结论:PC机辅助三维表面覆盖法可直观地了解颞骨茎突骨折在三维立体空间的实际大小、形态、位置及周围结构的解剖关系,对诊断和治疗有重要的指导作用,同时具有实用、方便、经济诸多优点,值得在颞骨茎突、颌面、骨与关节疾病诊断应用领域推广。  相似文献   
998.
AIM To investigate the effects of bortezomib (BTZ) on microRNA-223 (miR-223)/nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) signaling pathway and lipopolysaccharide (LPS)-induced inflammatory response of human monocytes. METHODS Monocytes were isolated and purified from peripheral blood of rheumatodid arthritis (RA) patients. The levels of interleukin-6 (IL-6), IL-1β and tumor necrosis factor-α (TNF-α) in supernatants of the monocytes were determined by ELISA, and the optimal induction time of LPS and the optimal treatment concentration of BTZ were selected according to the levels of IL-6, IL-1β and TNF-α. The monocytes were divided into control group, LPS induced group and BTZ group. The level of miR-223 in the monocytes was measured by RT-qPCR, and the protein levels of NLRP3, caspase-1, suppressor of cytokine signaling 1 (SOCS1) and SH2 domain-containing inositol phosphatase-1 (SHIP-1) in the monocytes were determined by Western blot. RESULTS The monocytes successfully isolated and purified from the peripheral blood of RA patients were spherical, evenly distributed and regular in shape.And after LPS induction for 24 h, the cells were mostly spindle-shaped and aggregated. According to the levels of IL-6, IL-1β and TNF-α, the optimal induction time of LPS was 24 h, and the optimal concentration of BTZ was 50 nmol/L. Compared with control group, the levels of miR-223, SOCS1 and SHIP-1 in LPS induction group were significantly decreased (P<0.05), and the levels of NLRP3 and caspase-1 were significantly increased (P<0.05). Compared with LPS induction group, the levels of miR-223, SOCS1 and SHIP-1 in BTZ group were significantly increased (P< 0.05), and the levels of NLRP3 and caspase-1 were significantly lowered (P<0.05). CONCLUSION Bortezomib may block the activation of miR-223/NLRP3 signaling pathway, thus reducing the secretion of inflammatory factors in LPS-induced human monocytes.  相似文献   
999.
In the future, UK summers are likely to be warmer and drier. Modelling differential water redistribution and uptake, we assessed the impact of future drier climates on sugar beet yields. Weather was generated for 1961–1990 (BASE) and predictions based on low‐ and high‐emission scenarios (LO, HI) described in the most recent global climate simulations by the Hadley Centre, UK. Distributions and variability of relative soil moisture deficit (rSMD) and yield gap (drought‐related yield loss, YGdr = 1?actual yield/potential yield), and sugar yield were calculated for different time‐lines using regional weather, soil texture and management inputs. The rSMD is estimated to exceed the senescence threshold with a probability of 75% (2050sLO) to 95% (2080sHI) compared with 65% (BASE). The potential yield loss, YGdr, is likely to increase from 17% (BASE) to 22% (2050sLO) to 35% (2080sHI). However, increasing potential growth rates (CO2 × temperature) cause average sugar yields to rise by between 1.4 and 2 t ha?1 (2050sLO and 2050sHI respectively). Yield variation (CV%) may increase from 15–18% (BASE) to 18–23% (2050s) and 19–25% (2080s). Differences are small between regions but large within regions because of soil variability. In future, sugar yields on sands (8 t ha?1) are likely to increase by little (0.5–1.5 t ha?1), but on loams yields are likely to increase from 11 to 13 t ha?1 (2050sHI) and 15 t ha?1 (2080sHI). Earlier sowing and later harvest are potential tools to compensate for drought‐related losses on sandy soils.  相似文献   
1000.
IAA and GA3 had increased the stem thickness by increasing that of cortex, phloem fibers and xylem. Each had increased straw and fiber yield/plant, but the effect was more pronounced with GA3 than IAA. The percentage of long fibers, strength and fineness increased significantly with GA3. The latter two properties decreased with IAA.  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