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81.
利用广义不确定关系计算量子态数目,进而计算Vaidya-Bonner黑洞的熵,此方法与brick-wall模型相比,优点为不必引入截断因子,就避免了发散问题。 相似文献
82.
旅游形象已成为旅游者选择目的地的主要依据之一,旅游形象测量是旅游形象策划的基础和依据。地质公园具有"自然"与"公园"双重属性,其形象测量方法应区别于一般的旅游形象测量方法。回顾了旅游目的地形象测量的相关研究基础,结合地质公园特点,认为在测量时必须遵循综合性、独特性及科学性三原则,构建了适合于地质公园形象测量的"天平"模型。 相似文献
83.
84.
针对汽车驱动桥总成生产中在线检测手段落后的现状,研制了QZS45型汽车驱动桥总成在线测试系统。该系统选用了隔离的静音检测室,采用计算机控制、变频调速电动机驱动;系统中的转矩转速、温度、噪声等测量信号通过板卡与计算机连接,通过编制控制软件,保证了在线检测工作的顺利进行,并实现了自动采样、自动判断、自动汇总的功能,满足了汽车驱动桥总成在线检测的各项要求。 相似文献
85.
Uncertainty in parameter estimates from sampling variation or expert judgment can introduce substantial uncertainty into ecological predictions based on those estimates. However, in standard population viability analyses, one of the most widely used tools for managing plant, fish and wildlife populations, parametric uncertainty is often ignored in or discarded from model projections. We present a method for explicitly incorporating this source of uncertainty into population models to fully account for risk in management and decision contexts. Our method involves a two-step simulation process where parametric uncertainty is incorporated into the replication loop of the model and temporal variance is incorporated into the loop for time steps in the model. Using the piping plover, a federally threatened shorebird in the USA and Canada, as an example, we compare abundance projections and extinction probabilities from simulations that exclude and include parametric uncertainty. Although final abundance was very low for all sets of simulations, estimated extinction risk was much greater for the simulation that incorporated parametric uncertainty in the replication loop. Decisions about species conservation (e.g., listing, delisting, and jeopardy) might differ greatly depending on the treatment of parametric uncertainty in population models. 相似文献
86.
BACKGROUND: For the registration of pesticides in the European Union, model simulations for worst‐case scenarios are used to demonstrate that leaching concentrations to groundwater do not exceed a critical threshold. A worst‐case scenario is a combination of soil and climate properties for which predicted leaching concentrations are higher than a certain percentile of the spatial concentration distribution within a region. The derivation of scenarios is complicated by uncertainty about soil and pesticide fate parameters. As the ranking of climate and soil property combinations according to predicted leaching concentrations is different for different pesticides, the worst‐case scenario for one pesticide may misrepresent the worst case for another pesticide, which leads to ‘scenario uncertainty’. RESULTS: Pesticide fate parameter uncertainty led to higher concentrations in the higher percentiles of spatial concentration distributions, especially for distributions in smaller and more homogeneous regions. The effect of pesticide fate parameter uncertainty on the spatial concentration distribution was small when compared with the uncertainty of local concentration predictions and with the scenario uncertainty. CONCLUSION: Uncertainty in pesticide fate parameters and scenario uncertainty can be accounted for using higher percentiles of spatial concentration distributions and considering a range of pesticides for the scenario selection. Copyright © 2010 Society of Chemical Industry 相似文献
87.
K.E. Anders Ohlsson Bhupinderpal Singh Anders Nordgren Peter Högberg 《Soil biology & biochemistry》2005,37(12):2273-2276
The δ13C of soil-respired CO2 (δr) is frequently determined using static closed chamber methods. δr is obtained as the intercept of the least squares linear regression of δ vs 1/C*, where measured δ13C-CO2 (δ) and volume fraction of CO2 (C*) values of chamber headspace samples are used. Theoretically, we show that the variance of the estimate of δr can be reduced by extending the 1/C* interval of the regression towards (i) higher or (ii) lower values, or (iii) distributing the 1/C* values optimally within the pre-selected headspace CO2 sampling time period. Experimental applications of these approaches indicated that: (1) lowering the initial CO2 level, thereby increasing 1/C*, yielded a positive bias to the δr result. (2) It was feasible to obtain lower variance in the δr estimate by lowering 1/C* values through extended CO2 sampling time. We also recommend that each chamber is sampled only once, mainly because this allows freedom to select the sampling times, in order to optimize the distribution of 1/C* values. 相似文献
88.
Abstract. The accuracy of a ThetaProbe (Delta-T Devices Ltd, UK) to obtain repeated measures of soil water content in pot plants was tested. This alternative to balance determinations led to a large underestimation of water content, varying from 12.2 to 21.8% of the total water content, depending on soil type. 相似文献
89.
90.
近10年黄河三角洲地区粮食产量及灰色预测 总被引:1,自引:0,他引:1
通过收集粮食产量的历史数据,分析了黄河三角洲地区近10年来粮食产量的变化趋势、19个县(市、区)的粮食贡献以及其空间分布格局。基于灰色理论和Matlab软件编程建立了现代黄河三角洲地区的粮食产量定量预测模型,并进行不确定性分析。结果表明,黄河三角洲地区未来几年内粮食产量呈上升趋势,GM(1,1)模型模拟预测值序列与实际值序列残差的关联度R、均方差比值C及小误差概率均判定该模型的精度为一级,误差较小,预测结果可靠。本研究所得结果可为粮农管理部门做相关决策提供依据。 相似文献