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   23840篇
  免费   1516篇
  国内免费   2578篇
林业   2164篇
农学   2321篇
基础科学   1586篇
  3016篇
综合类   9749篇
农作物   1719篇
水产渔业   1386篇
畜牧兽医   3440篇
园艺   1402篇
植物保护   1151篇
  2024年   106篇
  2023年   367篇
  2022年   830篇
  2021年   937篇
  2020年   915篇
  2019年   897篇
  2018年   637篇
  2017年   1081篇
  2016年   871篇
  2015年   1196篇
  2014年   1215篇
  2013年   1468篇
  2012年   1922篇
  2011年   2044篇
  2010年   1849篇
  2009年   1702篇
  2008年   1601篇
  2007年   1532篇
  2006年   1318篇
  2005年   1039篇
  2004年   704篇
  2003年   595篇
  2002年   741篇
  2001年   658篇
  2000年   510篇
  1999年   276篇
  1998年   179篇
  1997年   151篇
  1996年   86篇
  1995年   92篇
  1994年   102篇
  1993年   67篇
  1992年   61篇
  1991年   59篇
  1990年   34篇
  1989年   22篇
  1988年   25篇
  1987年   15篇
  1986年   3篇
  1985年   4篇
  1984年   5篇
  1983年   2篇
  1981年   5篇
  1980年   2篇
  1979年   4篇
  1962年   2篇
  1956年   2篇
  1932年   1篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
981.
为探索芦笋种植对冷凉沙化区土壤的改良效果,在山西省朔州市右玉县,以未种植芦笋裸沙地为对照(CK),设置种植芦笋1、2、3和4年共4个处理,通过田间试验测定不同种植年限芦笋田土壤理化特性和芦笋生长发育情况。结果表明,与CK相比,随种植年限增加,土壤黏粒和粉砂粒含量递增,砂粒含量递减,土壤容重递减,土壤田间持水量递增;土壤pH和可溶性盐浓度(EC)递减;土壤有机质、全氮、有效磷和速效钾含量逐年递增。种植芦笋3年的土壤粒级、土壤容重、田间持水量、pH、EC值、土壤肥力发生显著变化;连续种植芦笋4年的土壤黏粒含量较CK增加到29.8%,粉砂粒含量增加到12.6%,砂粒含量降低到57.6%,田间土壤持水量显著提高,土壤容重显著降低,土壤由砂质壤土向砂质黏土转变;土壤pH降低0.75,EC值降低0.08mS/cm;土壤有机质含量增加28.89%,全氮、有效磷和速效钾含量分别增加95.12%、94.92%和45.40%;芦笋产量达6 037.5kg/hm 2。综合分析,连续种植芦笋4年可改善沙化土壤的物理结构,提高土壤养分,降低盐碱程度。芦笋是冷凉沙化区土壤改良的先锋作物之一,可实现生态效益与经济效益并举。  相似文献   
982.
983.
赵君  姚彤  李明  杨进 《北方园艺》2019,(14):93-99
以蓝盆花为试材,在土壤中分别施入浓度为0、10、20、30、40 g·kg^-1的玉米秸秆生物炭,研究了玉米秸秆生物炭施用对干旱胁迫下蓝盆花生长及根际土壤真菌丰度的影响,以期为利用生物炭缓解干旱胁迫对园林植物的生长提供科学依据。结果表明:干旱胁迫下,T2处理下蓝盆花的株高、茎粗、根数和根鲜质量均显著高于CK,其中在处理20 d后,分别比对照高26.23%、17.79%、26.67%和13.93%,T1和T3处理下蓝盆花的株高、茎粗、根数与对照差异不显著,T4处理下蓝盆花的各形态指标均显著低于对照。生物炭处理后还提高了干旱胁迫下土壤真菌丰度,随着生物炭含量的升高,土壤中子囊菌门、担子菌门、接合菌门、壶菌门和球囊菌门,以及子囊菌门未分类或未识别科、毛壳菌科、小子囊菌科、毛球壳科、丛赤壳科、小疱毛科、假球壳科以及担子菌门蘑菇科、接合菌门被孢霉科和半知菌亚门掷孢酵母科,所占群落比例均呈抛物线状变化,T2处理下,上述真菌在门和科分类水平所占群落的比例最大。在干旱胁迫下子囊菌门小子囊菌科、毛壳菌科、毛球壳科、接合菌门被孢霉科在促进蓝盆花生长方面的作用较为显著。土壤中施入浓度为20 g·kg^-1生物炭最能缓解干旱胁迫对蓝盆花生长产生的影响。  相似文献   
984.
采用超高效液相色谱(UPLC)法,对30个油菜品种薹和蕾中硫代葡萄糖苷(glucosinolate,简称硫苷)的组分及含量进行测定。结果表明:30个油菜品种的总硫苷含量变异范围较大,在21.67~119.29μmol·g-1之间;大多数油菜品种蕾中的硫苷含量高于薹,蕾中硫苷含量均值为37.26μmol·g-1,薹中为28.06μmol·g-1;薹和蕾中的硫苷组分相似,均以4-戊烯基硫苷和2-羟基-3-丁烯基硫苷为主要成分,两者在薹和蕾中的含量分别占总硫苷含量的46.24%、28.52%和45.19%、29.13%。进一步分析高、中、低硫苷含量油菜品种的硫苷组分及含量,结果表明油菜不同品种间硫苷含量的差异主要是由4-戊烯基硫苷引起的。  相似文献   
985.
鸡(土从)菌(Termitomyces spp.)是我国传统的典型野生食用菌,具有极高的科学研究价值。由于鸡(土从)菌无法人工栽培,年产量波动严重,市场价值较高,这导致了以假乱真的现象屡见不鲜,并造成了我国鸡(土从)菌市场和科研领域的混乱。通过综述鸡(土从)菌的分类地位、生物学特性、与白蚁的共生关系、食(药)用价值以及鸡地从菌栽培现状等,分析和展望了未来可能的研究方向。为推动鸡(土从)菌人工栽培研究以及传播正确的鸡(土从)菌知识提供参考,从而促进整个鸡(土从)菌产业的可持续发展。  相似文献   
986.
987.
Jun WU 《干旱区科学》2019,11(4):567-578
Soil tillage and straw retention in dryland areas may affect the soil aggregates and the distribution of total organic carbon. The aims of this study were to establish how different tillage and straw retention practices affect the soil aggregates and soil organic carbon (SOC) and total nitrogen (TN) contents in the aggregate fractions based on a long-term (approximately 15 years) field experimentin the semi-arid western Loess Plateau, northwestern China. The experiment included four soil treatments, i.e., conventional tillage with straw removed (T), conventional tillage with straw incorporated (TS), no tillage with straw removed (NT) and no tillage with straw retention (NTS), which were arranged in a complete randomized block design. The wet-sieving method was used to separate four size fractions of aggregates, namely, large macroaggregates (LA, >2000 μm), small macroaggregates (SA, 250-2000 μm), microaggregates (MA, 53-250 μm), and silt and clay (SC, <53 μm). Compared to the conventional tillage practices (including T and TS treatments), the percentages of the macroaggregate fractions (LA and SA) under the conservation tillage practices (including NT and NTS treatments) were increased by 41.2%-56.6%, with the NTS treatment having the greatest effect. For soil layers of 0-5, 5-10 and 10-30 cm, values of the mean weight diameter (MWD) under the TS and NTS treatments were 10.68%, 13.83% and 17.65%, respectively. They were 18.45%, 19.15% and 14.12% higher than those under the T treatment, respectively. The maximum contents of the aggregate-associated SOC and TN were detected in the SA fraction, with the greatest effect being observed for the NTS treatment. The SOC and TN contents were significantly higher under the NTS and TS treatments than under the T treatment. Also, the increases in SOC and TN levels were much higher in the straw-retention plots than in the straw-removed plots. The macroaggregates (including LA and SA fractions) were the major pools for SOC and TN, regardless of tillage practices, storing 3.25-6.81 g C/kg soil and 0.34-0.62 g N/kg soil. Based on the above results, we recommend the NTS treatment as the best option to boost soil aggregates and to reinforce carbon and nitrogen sequestration in soils in the semi-arid western Loess Plateau of northwestern China.  相似文献   
988.
Jun ZHANG 《干旱区科学》2019,11(3):419-430
Drip irrigation can produce high rice yields with significant water savings; therefore, it is widely used in arid area water-scarce northern China. However, high-frequency irrigation of drip irrigation with low temperature well water leads to low root zone temperature and significantly reduce the rice yield compared to normal temperature water irrigated rice, for example, reservoir water. The main purpose of this paper is to investigate the effects of low soil temperature on the yield reduction of drip irrigated rice in the spike differentiation stage. The experiment set the soil temperatures at 18°C, 24°C and 30°C under two irrigation methods(flood and drip irrigation), respectively. The results showed that, at the 30°C soil temperature, drip irrigation increased total root length by 53% but reduced root water conductivity by 9% compared with flood irrigation. Drip irrigation also increased leaf abscisic acid and proline concentrations by 13% and 5%, respectively. These results indicated that drip irrigated rice was under mild water stress. In the 18°C soil temperature, drip irrigation reduced hydraulic conductivity by 58%, leaf water potential by 40% and leaf net photosynthesis by 25% compared with flood irrigation. The starch concentration in male gametes was also 30% less in the drip irrigation treatment than in the flood irrigation treatment at soil temperature 18°C. Therefore, the main reason for the yield reduction of drip irrigated rice was that the low temperature aggravates the physiological drought of rice and leads to the decrease of starch content in male gametes and low pollination fertilization rate. Low temperature aggravates physiological water deficit in drip irrigated rice and leads to lower starch content in male gametes and low pollination fertilization rate, which is the main reason for the reduced yield of drip irrigated rice. Overall, the results indicated that the low soil temperatures aggravated the water stress that rice was under in the drip irrigated environment, causing declines both in the starch content of male gametes and in pollination rate. Low temperature will ultimately affect the rice yield under drip irrigation.  相似文献   
989.
采用孢子萌发法测定了烟草上米根霉Rhizopus oryzae对6种杀菌剂 (代森锰锌、多菌灵、嘧霉胺、嘧菌酯、啶酰菌胺及氟啶胺) 的敏感性,并就其适宜的保存条件进行了筛选,同时采用离体叶片法测定了上述6种杀菌剂对烟叶霉烂病的防治效果。结果表明:6种杀菌剂对米根霉孢子萌发和烟叶霉烂病均表现出了不同的抑制活性。其中,抑制孢子萌发活性最为明显的是氟啶胺和啶酰菌胺,其EC90值分别为0.67 和1.53 mg/L;其次为代森锰锌和嘧菌酯,15.16和17.66 mg/L;最弱为嘧霉胺和多菌灵,71.87和81.96 mg/L。对烟叶霉烂病防效最好的为嘧菌酯,50 mg/L处理的防效为85%;其次为啶酰菌胺,200 mg/L处理时防效为83%;氟啶胺的防效较差,1 000 mg/L处理时仅为48%;而代森锰锌、多菌灵和嘧霉胺在最高使用剂量 (分别为4 000、800和800 mg/L) 时防效均低于20%。病原菌保存方法筛选结果表明,保存后米根霉的孢子萌发率均发生了不同程度降低。其中,4 ℃保存于20%甘油组的孢子悬浮液萌发率为60%;4 ℃保存的孢子干样萌发率为36%;4 ℃保存的孢子悬浮液和 –20 ℃保存于20%甘油的孢子悬浮液萌发率均低于20%;20 ℃保存的孢子干样萌发率为11%;–20 ℃保存的孢子悬浮液萌发率为6%。研究结果可为烘烤期烟叶霉烂病防治和米根霉孢子的保存提供参考依据。  相似文献   
990.
This study aimed to identify the potential allelopathic indigenous rice (Oryza sativa L. ssp. indica) varieties from Bangladesh using a performance study in a weed‐infested field and to assess the extent of allelopathic interference relative to resource competition in a glasshouse experiment. Six varieties – namely, “Boterswar,” “Goria,” “Biron” and “Kartiksail” as the most allelopathic, “Hashikolmi” as weakly allelopathic and “Holoi” as nonallelopathic – were raised following a nonweed control method. The infestation levels of weed species were calculated using Simpson's Diversity Index (SDI), which ranged from 0.2 to 0.56. However, a significant correlation coefficient (0.87, P < 0.001) was obtained from these field data compared with the root inhibition percentage from the laboratory bioassay, and the “Boterswar” variety was the most allelopathic. The interactions between the allelopathic variety “Boterswar,” weakly allelopathic variety “Hashikolmi” and Echinochloa oryzicola via a target (rice)‐adjacent (E. oryzicola) cogrowth culture were determined in a hydroponic arrangement. The relative competitive intensity (RCI) and the relative neighbor effect (RNE) values showed that the crop–weed interaction was facilitation for “Boterswar” and competition for “Hashikolmi” and E. oryzicola in rice/E. oryzicola cogrowth cultures. The allelopathic effects of “Boterswar” were much higher than the resource competition in rice/E. oryzicola cogrowth cultures. The converse was observed for “Hashikolmi.” Moreover, the mineral content of E. oryzicola was severely affected by “Boterswar”/E. oryzicola cogrowth cultures’ exudate solution. Therefore, the allelopathic potential of “Boterswar” variety might be useful for developing the weed‐suppressing capacity of rice, which will likely have a significant influence on paddy weed control.  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