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   4182篇
  免费   317篇
  国内免费   407篇
林业   510篇
农学   408篇
基础科学   280篇
  513篇
综合类   1634篇
农作物   288篇
水产渔业   229篇
畜牧兽医   651篇
园艺   190篇
植物保护   203篇
  2024年   18篇
  2023年   72篇
  2022年   136篇
  2021年   173篇
  2020年   159篇
  2019年   178篇
  2018年   131篇
  2017年   168篇
  2016年   127篇
  2015年   211篇
  2014年   208篇
  2013年   195篇
  2012年   252篇
  2011年   275篇
  2010年   271篇
  2009年   218篇
  2008年   240篇
  2007年   230篇
  2006年   185篇
  2005年   207篇
  2004年   133篇
  2003年   134篇
  2002年   200篇
  2001年   152篇
  2000年   136篇
  1999年   92篇
  1998年   67篇
  1997年   51篇
  1996年   40篇
  1995年   47篇
  1994年   39篇
  1993年   33篇
  1992年   34篇
  1991年   26篇
  1990年   21篇
  1989年   17篇
  1988年   8篇
  1987年   5篇
  1986年   5篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1965年   1篇
  1964年   1篇
  1956年   3篇
排序方式: 共有4906条查询结果,搜索用时 0 毫秒
71.
内蒙古平原灌区优质高产春玉米综合配套技术浅析   总被引:1,自引:0,他引:1  
本文从品种选择、宽行密株合理密植,科学灌水,平衡施肥,地膜覆盖,土壤条件及培肥,病虫草害防治,精耕细作与机械配套相结合等8个方面,简要分析了公顷产量12.75t~16.50t优质春玉米的综合配套技术.  相似文献   
72.
Weathering of abraded metallic Pb from bullets is a significant source of Pb contamination in shooting range soils. Weathering studies were performed using metallic Pb powder to simulate the fine-size fraction of metallic Pb found in shooting range soils. The effects of soil properties (moisture, organic matter-[OM] and pH) on weathering of abraded metallic Pb were examined by incubating a typical Florida soil for 5 to 12 days at 100% or 80% field capacity (FC) after spiking with 5% metallic Pb, after removal of soil OM at 100% FC, and after adjusting the soil pH to 4.8, 6.1 or 8.5 at 100% FC. The weathering products were examined using X-ray diffraction (XRD). Transformation of metallic Pb to secondary Pb-minerals was more rapid at 100% FC, in the presence of OM, and at lower pH. While little transformation of Pb occurred in the absence of soil OM and mostly litharge (PbO) was found at higher pH, both hydrocerussite and litharge formed at lower pH. A three-step weathering mechanisms of metallic Pb including oxidation, carbonation and dissolution was proposed. Addition of both calcium carbonate and phosphate rock was effective in reducing water-soluble Pb, though the effect was minimal after 11 weeks of incubation, attributing to the liming effect of metallic Pb added to the soil. While reducing soil moisture and organic matter and increasing soil pH slowed weathering of metallic Pb in a soil, the effect of calcium carbonate and phosphate rock on Pb solubility in soils highly contaminated with Pb was limited.  相似文献   
73.
东方杉在宁波沿海不同立地种植特征表现的调查   总被引:3,自引:0,他引:3  
对东方杉与当地耐盐碱树种在宁波沿海地区各种立地条件下种植后的成活率和保存率进行调查和分析,并分析东方杉在宁波沿海地区作为海岸基干林树种栽培和推广应用的可行性.  相似文献   
74.
随着消费信贷业务的迅速发展,有必要对其绩效进行全面评价。为此需要系统、科学地构建评价指标体系,并根据指标特性和AHP原理建立合适的无量纲化评分模型,做出综合评价和分析。  相似文献   
75.
Anthriscus sylvestris, a weed found both in Europe and China, is a kind of representative clustered clonal plant and is a foe on dams and banks. It has been widely investigated in Europe for its powerful progenitive ability and tolerance to severely adverse environments. Our aims were to investigate and quantify its spatial distribution patterns in four types of community habitats, using a clustering method and adjacency lattice established by Greig-Smith. We concluded our environmental interpretation based on canonical correspondence analysis (CCA) appended to a Monte Carlo test with randomized seeding. The results indicate that the buds around the parent roots are in an aggregation distribution pattern in all scales (0.002–5.12 m2), but theoretical distribution fitting, like negative binomial and Poisson distribution, show that some sizes of several sampling locations are out of place. For this, spatial ordination gives a satisfactory answer implying the effect of environmental variables such as depth of humus layer, soil moisture, light condition, disturbance intensity and herb abundance. CCA accounts for 64.7% of the total environmental variation and the remaining variation may be counteracted in those five variances or can be interpreted by other factors like accumulating temperature, annual rainfall and altitude in landscape scale. With the aid of temporal sequencing, the suppressed type II (monodominant) may be the former mode of suppressed type I (stable type), where invasion is done with the help of disturbance from both humans and nature. The abundance of A. sylvestris can add to our cognition in diversity resistance hypothesis and our hypothesis on disturbance before or upon immigration. __________ Translated from Journal of Zhejiang Forestry Science and Technology, 2007, 27(3): 1–7, 11 [译自: 浙江林业科技]  相似文献   
76.
栝楼多糖的超声波辅助提取工艺研究   总被引:2,自引:0,他引:2  
以栝楼为试材,通过单因素试验和响应曲面试验确定栝楼多糖超声波辅助提取工艺的数学模型和最佳条件。结果表明,超声波130 min、乙醇40%、H 浓度3 mol/L、液料比(V/W)20、浸置时间20 min、超声波功率250 W、反应温度40℃,提取1次,超声波辅助提取栝楼多糖的得率高且稳定可行。  相似文献   
77.
沈煜 《湖南农机》2007,(1):134-135
本文阐述了现行增值税的缺点、消费型增值税的优点,并试图对转型中可能会出现的一些问题提出一些建议。  相似文献   
78.
旨在研究小型猪复合麻醉颉颃剂对大鼠不同脑区p-p38蛋白及c-myc mRNA表达的影响,探讨小型猪复合麻醉颉颃剂的催醒机制。将18只大鼠随机分为C组(对照组)、J组(麻醉颉颃剂组)。J组又分为2个亚组,即J1组(注射小型猪专用复合麻醉颉颃剂5min)、J2组(注射小型猪专用复合麻醉颉颃剂1h)。各组大鼠到达相应的时间点后断头处死,分离大脑皮层、小脑、海马、脑干和丘脑,用Western blot的方法检测p-p38蛋白的表达量,实时荧光定量PCR方法检测c-myc基因mRNA的转录量。试验结果显示大鼠大脑皮层、丘脑和脑干的p-p38蛋白和c-myc mRNA的相对表达量显著升高,而小脑和海马的p-p38蛋白和c-myc mRNA的相对表达量显著降低。综合试验结果,小型猪复合麻醉颉颃剂能够影响p-p38蛋白和c-myc mRNA的表达,这可能是其产生催醒作用的机制之一。  相似文献   
79.
ABSTRACT The mechanism of the effects of flumorph (a novel fungicide) was investigated by analyzing alterations of hyphal morphology, cell wall deposition patterns, F-actin organization, and other organelles in Phytophthora melonis. Calcofluor white staining suggested that flumorph did not inhibit the synthesis of cell wall materials, but disturbed the polar deposition of newly synthesized cell wall materials during cystospore germination and hyphal growth. After exposure to flumorph, zoospores were able to switch into cystospores accompanied with the formation of a cell wall, whereas cystospores failed to induce the isotropic-polar switch and did not produce germ tubes but continued the isotropic growth phase. In flumorph-treated hyphae, the most characteristic change was the development of periodic swelling ("beaded" morphology) and the disruption of tip growth. Newly synthesized cell wall materials were deposited uniformly throughout the diffuse expanded region of hyphae, in contrast to their normal polarized patterns of deposition. These alterations were the result of F-actin disruption, identified with the fluorescein isothiocynate (FITC)-phalloidin staining. The disruption of F-actin also was accompanied by disorganized organelles: each swelling of subapical hyphae was associated with a nucleus. Vesicles did not undergo polarized secretion to the apical hyphae, but diffused around nuclei for the subapical growth; thus, the cell wall was thickened with periodic expansion along the hyphae. Upon removing flumorph, normal tip growth and organized F-actin were observed again. These data, as well as data published earlier, suggest that flumorph may be involved in the impairment of cell polar growth through directly or indirectly disrupting the organization of F-actin. The primary site of action by flumorph in the disruption of the F-actin organization is under investigation.  相似文献   
80.
为了达到节水节能的目的,使用非离子型表面活性剂TX-100、正辛醇、异辛烷和酸性染料水溶液制备用于蚕丝纤维染色的非离子型反胶束体系。首先研究pH值和增溶水量对染料平衡吸附量的影响,接着使用酸性橙156、酸性黑234和酸性媒介黑9对蚕丝纤维进行吸附实验,并使用Langmuir和Freundlich等温吸附模型对实验数据进行拟合,考察染料结构与染料平衡吸附量之间的关系。结果表明,在反胶束体系中pH值的增加不利于蚕丝对酸性染料的吸附,在增溶水量W=10时染料的平衡吸附量达到极大值。此外,蚕丝纤维对酸性染料的吸附模型符合Langmuir吸附模型,该吸附过程为单分子吸附,并属于优惠吸附;蚕丝对酸性媒介黑9的平衡吸附量最大,这与染料的分子结构有关。  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