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   2222篇
  免费   66篇
  国内免费   83篇
林业   10篇
农学   506篇
基础科学   47篇
  258篇
综合类   913篇
农作物   158篇
水产渔业   33篇
畜牧兽医   71篇
园艺   160篇
植物保护   215篇
  2024年   12篇
  2023年   29篇
  2022年   60篇
  2021年   56篇
  2020年   76篇
  2019年   75篇
  2018年   61篇
  2017年   77篇
  2016年   90篇
  2015年   84篇
  2014年   105篇
  2013年   133篇
  2012年   140篇
  2011年   147篇
  2010年   108篇
  2009年   96篇
  2008年   90篇
  2007年   116篇
  2006年   94篇
  2005年   88篇
  2004年   49篇
  2003年   66篇
  2002年   39篇
  2001年   34篇
  2000年   37篇
  1999年   34篇
  1998年   26篇
  1997年   34篇
  1996年   25篇
  1995年   32篇
  1994年   19篇
  1993年   27篇
  1992年   30篇
  1991年   26篇
  1990年   19篇
  1989年   28篇
  1988年   20篇
  1987年   18篇
  1986年   20篇
  1985年   9篇
  1984年   12篇
  1982年   4篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1978年   3篇
  1977年   8篇
  1976年   3篇
  1963年   1篇
  1955年   1篇
排序方式: 共有2371条查询结果,搜索用时 0 毫秒
1.
The plants of field bean var. Nadwiślaνski were detopped after about 1 month since the beginning of flowering and after that all flower buds were removed from some plants. The effect of a change in the trophic balance on the setting and subsequent growth of root nodules was studied.
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production.  相似文献   
2.
尖镰孢菜豆专化型(Fusarium oxysporum f. sp. phaseoli)引起的菜豆枯萎病是菜豆生产中最严重的维管束类病害之一, 防治该病害有效方法是利用抗病品种。因此, 一种能够从菜豆受侵染组织中准确鉴定并定量检测枯萎病原菌含量的方法将有助于筛选抗性品种, 应用于普通菜豆枯萎病抗病育种。本研究基于荧光定量PCR技术开发出一种能够对定殖于菜豆组织中的枯萎病原菌准确定量的新方法。该技术对根、茎组织中病原菌DNA的最低检测量为1 pg, 能在接种病原菌6 d后明显区分抗病性不同的品种, 可在菜豆植株表现出明显发病症状前准确鉴定不同品种抗性水平的差异。经验证参试的感病品种BRB-130和A0640-1根、茎组织中定殖的病原菌DNA量显著高于抗病品种260205和黑芸豆, 与表型鉴定的结果完全符合。利用荧光定量PCR技术能够在病原菌侵染早期快速、准确、高效定量菜豆组织中定殖的病原菌, 这对指导菜豆抗病育种和植物病害传播的研究都具有非常重要价值。  相似文献   
3.
Summary Twenty isolates taken at random from indigenous populations of Rhizobium leguminosarum sampled near Aberystwyth were each inoculated into plants of a standard Vicia faba variety grown aseptically under conditions free of combined nitrogen. Plants in association with the individual rhizobium isolates exhibited large differences in dry matter yield, nitrogen content, efficiency of nitrogen utilization and date of first flower. The implications of these differences to the productivity and reliability of varieties of field beans are discussed.  相似文献   
4.
Summary The effects of bulk breeding on yield and its components in two high-yeilding and two low-yielding bean populations when grown at crop densities are interpreted in terms of gene action and selection. There was considerable additive variation in the crosses, dominance effects were variable but tended to be negative. The results were compared with results obtained at low density by another worker with the same populations, and this showed that interpretations of gene action in hybrid vigour depend on the test environment used. The interpretations were also compared with plant breeding interpretations made on the same material (Hamblin, 1977), and it was found that a single pattern of response to natural selection, in plant breeding terms, may be explained by more than one genetic interpretation and, conversely, a single genetic interpretation may result in different patterns of response in plant breeding terms. The value of composite crosses in plant breeding are discussed and it is concluded that there is a greater chance of producing improved lines from a large number of simple crosses than from a smaller number of composite crosses.  相似文献   
5.
为探讨烯效唑(S3307)在寒地红小豆生长中缓解低温伤害、保护根系的作用,建立红小豆抗冷生产技术体系,达到保产增产的目的,在盆栽条件下,以两个红小豆品种宝清红(耐冷型品种)和天津红(冷敏型品种)为材料,于苗期在人工气候室进行低温(15℃,分别持续1,2,3,4,5d)和叶面喷施20mg·L^-1S3307处理,对红小豆根系抗寒生理指标、产量及不同温度敏感性红小豆品种的S3307响应差异进行测定和分析。结果表明,幼苗期低温导致红小豆根系逆境生理指标发生变化,低温诱导SOD、POD和CAT活性的增强,引起可溶性糖和脯氨酸含量的提高,同时也促使MDA含量上升,最终导致红小豆产量下降。与常温条件相比,喷施清水的宝清红和天津红,低温处理3d时,可溶性糖含量分别提高了59.21%和52.57%;脯氨酸含量分别提高了10.12%和25.39%;SOD、POD和CAT活性分别提高了14.92%和11.01%、5.93%和0.75%、53.33%和13.33%。低温处理5d时,可溶性蛋白含量分别提高了6.27%和3.15%;MDA含量分别显著提高了45.41%和51.08%、产量分别显著下降了19.39%和41.69%。低温条件下,喷施S3307与喷施清水的宝清红和天津红相比较,处理3d时,可溶性糖和脯氨酸含量分别提高了22.01%和0.46%、8.55%和1.40%;SOD活性分别提高了13.45%和24.06%、POD活性分别显著提高了23.60%和15.95%,CAT活性分别提高了4.35%和5.88%。处理5d时,MDA含量分别降低了9.05%和4.37%;产量分别显著提高23.06%和43.88%。综上,S3307通过增加可溶性物质和脯氨酸的含量,提高保护酶活性,降低MDA含量,从而缓解低温伤害,进而降低低温对红小豆造成的产量影响。  相似文献   
6.
为探讨光、温、水等气象因子对夏播小豆产量的影响,达到合理利用气象资源、进一步挖掘小豆增产潜力的目的,以中晚熟小豆品种花小豆(V1)和中早熟品系德红5261(V2)为材料,设T1(6月17日)、T2(6月22日)、T3(6月27日)、T4(7月2日)和T5(7月7日)5个播期,形成不同的光、温、水生长环境,对夏播小豆产量...  相似文献   
7.
Soya bean protein concentrate (SPC) with two particle sizes were evaluated on extrusion parameters, kibble formation, digestibility and palatability of dog foods. Eight diets were extruded: PBM—control diet based on poultry by‐product meal (PBM); GM—a diet in which corn gluten meal (GM) replaced 45% of the diet protein; cSPC15%, cSPC30% and cSPC45%—diets in which SPC of coarse particle size (600 μm) replaced 15%, 30% and 45% of the diet protein; and sSPC15%, sSPC30% and sSPC45%—diets in which SPC of small particle size (200 μm) replaced 15%, 30% and 45% of the diet protein. The digestibility of nutrients was evaluated for the PBM, GM, cSPC45% and sSPC45% diets, using six dogs per food. The PBM, GM and cSPC45% diets were compared for palatability. Data were submitted for analysis of variance, and the means were compared by polynomial contrasts or Tukey's test (p < .05). The cSPC increased the specific mechanical energy (SME) application, extrusion temperature and pressure linearly, resulting in lower kibble density and higher expansion and starch gelatinization (SG) (p < .01). When comparing the PBM, GM, cSPC45% and sSPC45% diets, higher SME, extrusion temperature and pressure, SG and kibble expansion were verified for the cSPC45% diet (p < .05). The DM, fat and crude protein digestibility were similar among diets. Faecal pH, ammonia and lactate did not differ, demonstrating that the removal of oligosaccharides and soluble non‐starch polysaccharides of SPC produces an ingredient with mostly non‐fermentable fibre. Dogs preferred the PBM to the GM diet (p < .05), but consumed the PBM and cSPC45% foods equally. In conclusion, SPC exhibited good extrusion functionality, favouring kibble expansion and SG, with high digestibility, similar to that of PBM. The removal of soluble compounds from soya beans resulted in an ingredient with low fermentable fibre content, which did not alter faecal formation or characteristics.  相似文献   
8.
长汀县于2010年引进龙莱1号进行烟后作高山反季节栽培试验示范,表现高产高效。该文介绍龙莱1号的特征特性及高产栽培技术。  相似文献   
9.
以"小明绿"绿豆为材料,采用大田随机区组试验方法,研究了鼓粒期叶施不同质量浓度激动素对绿豆各器官糖分积累及籽粒产量的影响。结果表明:1)激动素处理可以提高喷药后12d绿豆叶片叶绿素含量,30、15和7.5mg/L激动素喷施的叶片叶绿素含量较对照分别增加15.74%、7.01%和16.40%;2)激动素处理组能够减缓喷药后第22~27天叶片可溶性糖含量和蔗糖含量的下降,有效增加喷药后第22天叶片淀粉含量;喷药后第27天,30mg/L激动素的处理茎秆和根系可溶性糖输出量、茎秆和根系蔗糖含量、茎秆淀粉含量均高于其他质量浓度激动素和对照;在喷药后第22天茎秆中的淀粉含量以及喷药后第27天根系淀粉含量均以15mg/L激动素处理为最大;3)激动素处理组能够有效增加绿豆单株粒数,2年试验30、15和7.5mg/L激动素处理绿豆籽粒产量分别较对照平均提高18.23%、10.08%和5.67%。综合分析表明,鼓粒期喷施不同质量浓度激动素能够有效调控叶片叶绿素含量,促进鼓粒后期叶片、茎秆和根系糖分积累,最终提高绿豆籽粒产量。  相似文献   
10.
对造成福建省漳州市东山县的芦笋枯萎病病原菌进行分子鉴定,以期确定病原菌的属、种名,为防治该病害寻求理论依据。试验对分离纯化的病原菌核糖体DNA的ITS区进行测序,在Genbank中搜索其同源性并构建它们的系统发育树,结果表明:引起芦笋枯萎病的病原菌是镰刀属中的尖孢镰刀菌(Fusarium oxysporum),且病原菌之间的同源性高达89%,遗传差异不显著。  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