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排序方式: 共有3523条查询结果,搜索用时 218 毫秒
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273.
论述了"科技兴库"的意义和作用,并从五方面较详细地阐述了保证"科技兴库"的条件和措施,为培养和成为新时期合格的仓储工作者提供了借鉴条件。 相似文献
274.
根据松嫩平原西部水资源复合系统的特征和水资源条件,建立了区域水资源可持续利用评价指标体系。应用投影寻踪技术,采用实码遗传算法优化投影指标函数,将方案多维评价指标值综合为一维投影值,根据投影值的大小实现方案的优选。研究表明,投影寻踪技术可以有效地解决权重的人为干扰,通过优化排序实现对评价结果的定量化表征。 相似文献
275.
Recent research shows that most soils are more or less water repellent. Already subcritical water repellency may cause incomplete soil wetting and preferential flow. Both processes potentially reduce the residence time of water and solutes in the vadose zone, resulting in an enhanced risk of groundwater contamination. The objective of the present paper is, therefore, to evaluate the impact of reduced soil wettability on the soil water infiltration rate and to investigate the tendency towards preferential flow with the analysis of the immobile water content in the infiltration zone. In november 2002, a field experiment was done in a coniferous forest, 30 km N of Hannover, Germany. Soil hydrophobicity was quantified by measuring the contact angles. The hydraulic conductivity of the podsolic sandy soil was measured depth‐dependent with a double‐ring tension infiltrometer in three soil horizons. To quantify possible preferential‐flow effects, a LiBr‐Tracer was added to the infiltrating water to evaluate the mobile water‐content fraction after infiltration. Additionally, infiltration rates of water were compared with infiltration rates of ethanol which were determined after water infiltration at the same locations. Results show that the actual water repellency of field‐moist soil was mainly subcritical (contact angle <90°). Water infiltration rates were reduced due to subcritical repellency by a factor of 3–170 compared with ethanol infiltration rates (exclusion of wetting effects). This spatially variable infiltration behavior was not clearly reflected neither by the small‐scale contact‐angle measurements nor by the analysis of the average immobile soil water content in the infiltration zone. We conclude that this specific infiltration behavior of water caused by small‐scale wettability effects may temporarily reduce the local connectivity of water‐flow pathways. 相似文献
276.
This study aimed to compare predicted soil forces on a disk plow with measured forces within the tillage depth of clay (90 g kg−1 sand, 210 g kg−1 silt, 700 g kg−1 clay) and sandy loam (770 g kg−1 sand, 40 g kg−1 silt, 190 g kg−1 clay) soils. The model assumed the effects of both tilt angle and plowing speed. Two plowing speeds (4 and 10 km/h) at three tilt angles (15°, 20° and 25°) were compared and the draft, vertical, and side forces determined. A 3D nonlinear finite element model was used to predict the soil forces while a dynamometer was used to measure them on a disk plow in the field. An incremental method was used to deal with material nonlinearity and the Trapezoidal rule method was used to analyze the dynamic response of soil during tillage. Field tillage experiments were conducted to verify the results of the finite element model. It was found that increasing the tilt angle of the plow increased the draft and vertical forces and decreased the side force. Increasing plowing speed increased the draft and side forces and decreased the vertical force. Generally, the results from the finite element model were found to be compatible with the experimental results in clay soil, while in sandy loam the differences between predicted and measured data were probably due to problems of measuring soil mechanical characteristics in the triaxial test. 相似文献
277.
互联网上食品科技信息的开发与利用 总被引:1,自引:0,他引:1
朱玉强 《农业图书情报学刊》2004,16(12):132-134
互联网蕴藏着极其丰富的食品信息,本文介绍了利用浏览、分类、关键词等方式检索网上食品资料的方法,并提供了部分网址。 相似文献
278.
因特网上林业信息的获取 总被引:1,自引:0,他引:1
刘刚 《农业图书情报学刊》2004,16(12):129-131,188
因特网上有着丰富的林业信息资源,从因特网上检索资料方便快捷,省时省力。本文分类介绍了因特网一系列具有权威性和实用性的林业信息资源及其检索方法。 相似文献
279.
根据螺旋钻头升土理论,通过计算机处理,得出了升角和钻头其它参数的关系曲线,并对这些曲线的变化趋势进行分析,为设计钻头时合理选取升角值提供理论依据。 相似文献
280.
张国印 《金陵科技学院学报》2003,19(2):1-7
如果R是一个交换环且M是一个有限生成的拓扑模,则M是一个谱模的充分必要条件是对任意m1,m2∈M,存在一个有限生成子模F(∪)Im1Im2M,使得F ≡ Im1Im2M(那就是对每一个K∈Spec(M),K(∪)F当且反当K(∪)Im1 Im,M),其中ImM=miR,Imi(△)R,i=1,2. 相似文献