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   8662篇
  免费   550篇
  国内免费   50篇
林业   536篇
农学   441篇
基础科学   79篇
  1537篇
综合类   623篇
农作物   449篇
水产渔业   681篇
畜牧兽医   4002篇
园艺   122篇
植物保护   792篇
  2023年   84篇
  2022年   139篇
  2021年   260篇
  2020年   255篇
  2019年   316篇
  2018年   278篇
  2017年   313篇
  2016年   324篇
  2015年   224篇
  2014年   313篇
  2013年   488篇
  2012年   486篇
  2011年   530篇
  2010年   264篇
  2009年   300篇
  2008年   438篇
  2007年   428篇
  2006年   383篇
  2005年   357篇
  2004年   332篇
  2003年   298篇
  2002年   339篇
  2001年   243篇
  2000年   246篇
  1999年   211篇
  1998年   62篇
  1997年   60篇
  1996年   57篇
  1995年   51篇
  1994年   37篇
  1993年   38篇
  1992年   79篇
  1991年   52篇
  1990年   62篇
  1989年   69篇
  1988年   62篇
  1987年   51篇
  1986年   47篇
  1985年   59篇
  1984年   37篇
  1983年   42篇
  1982年   31篇
  1980年   24篇
  1979年   37篇
  1978年   21篇
  1977年   21篇
  1974年   23篇
  1973年   26篇
  1972年   24篇
  1970年   26篇
排序方式: 共有9262条查询结果,搜索用时 0 毫秒
81.
Journal of Plant Diseases and Protection - Tobacco (Nicotiana tabacum L.) is one of the major nonfood crops in the Southern of Brazil. During 2019/2020 and 2020/2021 crop seasons, Root Knot...  相似文献   
82.
The turbogenerator vibration faults have the character of variety. Many faults often occur synchronously. This paper introduces a diagnosing model based on parsimonious covering theory and probability. A model for turtogenerator's fault diagnosis is proposed. The availability of this method is proved by two fault diagnosis examples of turbogenerator. The results show that the model proposed can be used for multi_fault diagnosis together. It may make up shortage for some of expert systems and neural networks in some aspect. From the practice,this model has higher reliability and practicability.  相似文献   
83.
Summary The relative sensitivity of the cotton plant to water stress throughout the growing season was determined to identify when irrigation will have the greatest beneficial effect. Daily plant water stress for 72 different data sets of water applications was correlated to corresponding yield criteria. The magnitude of significant correlation was interpreted as the degree of sensitivity. Plant water stress during square formation and early flowering resulted in fewer bolls to reach maturity, but this detrimental effect was cancelled by the development of bigger bolls due to greater lint growth. This resulted in better seedcotton and lint yields. Flower and boll senescence which resulted from water stress during flowering peak, however, inhibited seedcotton and lint yields. The most pronounced inhibiting effect stress had on yields, was during boll development well after the end of effective flowering, when it inhibited boll development. Stress during ripening of the bolls increased lint and boll development and consequently enhanced yields. When limited quantities of water is available, preference should be given to irrigation during boll development, then by irrigation when the first flowers appear, followed by irrigation during peak flowering. Water should be withheld from opening of the first bolls.  相似文献   
84.
Summary A field experiment was conducted to determine the effect of overirrigation on the growth characteristics and production of cotton. Over-irrigation, resulting in saturated soil conditions, was achieved by flood irrigation at different levels of soil water depletion on a soil with a low percolation rate. The highest seedcotton and lint yields were obtained from plants that did not experience over-irrigation at any time during the growing season; similar yields were obtained from plants that only experienced moderate over-irrigation after the onset of flowering (Table 9). The yield response could be related to branch growth, flowering rate and length of growing season (Tables 3, 4, 5, 6, 7, and 8).  相似文献   
85.
在考虑特定水库的入流、库容特性及阻力、泄洪特性的基础上 ,按照水量平衡与输沙平衡原理 ,提出副坝逐渐溃决的流量过程线的 1种新的计算方法 ,该方法被用于某水库安全问题的研究 ,结果表明该方法是切实可行的。  相似文献   
86.
Whole-farm design models quantitatively analyze the effects of a variety of potential changes at the farm system level. Science-driven technical information is confronted with value-driven objectives of farmers or other social groupings under explicit assumptions with respect to exogenous variables that are important drivers of agricultural systems (e.g., market conditions). Hence, farm design is an outcome of objective specification and the potential of a system. In recent publications, whole-farm design modelling has been proposed to enhance (farm) innovation processes. A number of operational modelling tools now offers the opportunity to assess the true potential of whole-farm design modelling to enhance innovation. In this paper, we demonstrate that it is not trivial to find niches for the application of goal-based farm models. Model outcomes appeared not to match questions of farm managers monitoring and learning from their own and other farmers’ practices. However, our research indicates that whole-farm design modelling possesses the capabilities to make a valuable contribution to reframing. Reframing is the phenomenon that people feel an urge to discuss and reconsider current objectives and perspectives on a problem. Reframing might take place in a situation (i) of mutually felt dependency between stakeholders, (ii) in which there is sufficient pressure and urgency for stakeholders to explore new problem definitions and make progress. Furthermore, our research suggests that the way the researcher enters a likely niche to introduce a model and/or his or her position in this niche may have significant implications for the potential of models to enhance an innovation process. Therefore, we hypothesize that the chances of capitalizing on modelling expertise are likely to be higher when researchers with such expertise are a logical and more or less permanent component of ongoing trajectories than when these researchers come from outside to purposefully search for a niche.  相似文献   
87.
Among the most important Mediterranean annual crops, durum wheat is widely grown in drought-prone areas. Therefore, improving water-use efficiency (WUE) of durum wheat represents a major breeding goal. IDu-WUE (Improving Durum wheat for Water Use Efficiency and yield stability through physiological and molecular approaches) is a collaborative project among public and private research centres in Italy, Spain and WANA (West Asia and North Africa) countries (Morocco, Tunisia, Syria and Lebanon) funded by the European Union aimed at investigating the genetic variation for WUE and yield stability in durum wheat grown in Mediterranean droughtprone areas. During the first year of the project, a number of morpho-physiological traits (e.g. early vigour, flowering time, leaf rolling, number of fertile tillers, etc.), WUE, WUE-related traits (e.g. carbon isotope discrimination, canopy temperature, chlorophyll fluorescence, etc.), yield and its components have been investigated in a RIL population (249 lines) and a collection of ca. 190 durum wheat accessions characterized by a high level of linkage disequilibrium (Maccaferri et al., 2005),  相似文献   
88.
Here we report on the frequency of melanized fungal hyphae in 323 soils, covering different land use types. The proportion of total hyphae that was melanized averaged 61%. Arable fields with loamy sand, heathlands and city parks on sandy soils had the highest percentage of melanized hyphae. In addition to the frequency determinations, a microcosm study was performed on the role of melanized hyphae in two different ecosystems: an ex-arable field and a forest. Melanized hyphae appeared to be part of the active hyphae in the forest soil but not in the ex-arable soil. In conclusion, our results indicate that (1) melanized hyphae represent a large proportion of the total fungal biomass in soils and that (2) their function might differ between ecosystems.  相似文献   
89.
钾肥、覆膜对马铃薯硒素吸收分配及硒肥吸收率的影响   总被引:1,自引:0,他引:1  
采用田间试验方法研究了钾肥及覆膜对马铃薯硒素吸收分配的影响.结果表明:地膜覆盖及钾肥的施用提高了收获期马铃薯全株及块茎干物质产量;钾肥的施用显著提高马铃薯全株及块茎硒素含量与吸收累积量.钾肥与硒肥配合施用,使块茎硒素含量达0.148 mg·kg-1的富硒水平,对块茎硒素的富集有正交互效应,使收获期全株硒肥吸收率达17.8%,比单施硒肥提高1.5个百分点,块茎硒肥吸收率7.1%,提高2.7个百分点.覆膜对马铃薯全株、块茎硒含量及全株硒素吸收量无显著影响,但可显著提高块茎硒素累积量.覆膜硒肥配合,收获期全株硒肥吸收率20.0%,提高2.2个百分点,块茎硒肥吸收率10.1%,提高3.1个百分点.覆膜可显著促进硒素在体内由茎叶向块茎的转移.收获期,覆膜硒素运转率53%,提高10.1个百分点.  相似文献   
90.
Different sample preparation methods were evaluated for the simultaneous multielement analysis of wine samples by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Microwave-assisted digestion in closed vessel, thermal digestion in open reactor, and direct sample dilution were considered for the determination of Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Y, Mo, Cd, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Tl, Pb, and Bi in 12 samples of red wine from Valencia and Utiel-Requena protected designation of origin. ICP-MS allows the determination of 17 elements in most of the samples, and using ICP-OES, a maximum of 15 elements were determined. On comparing the sample pretreatment methodology, it can be concluded that the three assayed procedures provide comparable results for the concentration of Li, Na, Mg, Al, K, Ca, Mn, Fe, Zn, and Sr by ICP-OES. Furthermore, ICP-MS data found for Cu, Pb, and Ba were comparable. Digestion treatment provides comparable values using both total decomposition in open system and microwave-assisted treatment for Cu by ICP-OES and for Cr, Ni, and Zn by ICP-MS. Open vessel total digestion provides excess values for Cr, Mn, Fe, and Zn by ICP-OES and defect values for Se. However, direct measurement of diluted wine samples provided uncomparable results with the digestion treatment for Mn, Cu, Pb, Zn, Ba, and Bi by ICP-OES and for Mg, Cr, Fe, Ni, and Zn by ICP-MS. Therefore, it can be concluded that microwave-assisted digestion is the pretreatment procedure of choice for elemental analysis of wine by ICP-based techniques.  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