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81.
Thermal-softening properties and cooling set of water-saturated bamboo were investigated using stressrelaxation measurements
in heating and cooling processes, followed by residual deflection measurement. In the heating process, an obvious decrease
in relative relaxation modulus due to thermal-softening of lignin was found at around 60°C. On the other hand, no clear change
in the relative relaxation modulus was recognized in the cooling process. After the cooling process, about 65% and 75% of
residual set was measured when the specimen was loaded on the epidermis and endodermis side, respectively. Also, residual
set depended on the maximum temperature reached in the heating process and the unloaded temperature in the cooling process.
From these results, it was deduced that the glass transition of lignin from the rubbery to glassy state is important to fix
the deformation. Comparing thermal-softening behavior between bamboo and wood, the relative relaxation modulus of wood decreased
steeply at higher temperatures than for bamboo. On the other hand, while about 75% of residual set was also found for wood,
almost the same as for bamboo, the recovery of deformation with time was larger for wood than for bamboo.
Part of this article was presented at the 53rd Annual Meeting of the Japan Zairyou Society, Okayama, May 2004 相似文献
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84.
介绍集体林林权制度改革的背景,经过调查,认为当前云南省各县(市)集体林权制度改革工作存在的问题主要有:督促、指导和检查不到位,宣传发动、技术培训工作不到位,存在不按工作程序开展工作情况,村民参与率低,对"三榜"公示制不按要求进行、林改工作急于求成等,提出加强林改队伍建设,加大宣传力度、扎实做好技术培训,严格按要求规范操作,不能将林改工作政治任务化等建议. 相似文献
85.
In the Loess Plateau, soil desiccation has become a serious problem for forest and grass vegetation. Soil desiccation leads to the formation of a dried soil layer (DSL). This paper presents the results of research carried out in the central part of the Loess Plateau. The objective of the research was to produce a statistically supported set of indicators for evaluating soil desiccation of forestlands, to present a heuristic idea for soil desiccation and to supply scientific support for replacing farmland with forest or grass in the Loess Plateau and other regions of China. Here, we suggest that more attention should be paid to soil desiccation and its effects on the ecosystem of the region in the future. The results showed that natural Quercus liaotungensis forestlands (NQF) retained more water content than regrown Robinnia pseudoscacia forestlands (RRF). Significant DSLs were formed in the RRF but not in the NQF. A possible reason for no formation of DSL in NQF could be due to the presence of an arbor–shrub–herb stand structure and large humus and litter accumulation, which increased the natural forest's (NF) adaptability to the environmental conditions. Soil water content in the north-facing slope was significantly larger than in the south-facing slope. DSLs formed in the 0–500 cm layer of the south-facing slope. When slope gradient was greater than 25°, soil water content deceased sharply and showed significant difference compared with 9°, 15° and 20° (P < 0.05). So, we conclude that plant species, aspect and slope angle could be the predicators for the formation of DSLs. The analysis on soil physical properties of 0–60 cm layer indicated that plant species, aspect and slope angle also have significant effects on bulk density, porosity, plant-available capacity, and hydraulic conductivity, especially in the 0–20 and 20–40 cm layers. In the NQF and RRF with north-facing slope, soil physical properties were improved. 相似文献
86.
论述我国集体林权制度改革的4个历史时期森林资源产权的基本情况及特点,对私有及公有的森林资源所有制分别进行了经济学分析,认为在森林资源集体所有的制度下无人真正关心森林资源经营管理的原因是,每个家庭对共有林的关心值以及全部家庭对共有林的总关心值均趋于零.藉此,提出了对林权制度改革的建议. 相似文献
87.
杨树微纤丝角的变异及其与木材性质的相关关系 总被引:6,自引:0,他引:6
微纤丝角为细胞次生壁S2层微纤丝排列方向与细胞主轴所形成的夹角,与木材的物理性质、力学性质和化学性质都有着直接的关系。应用x射线衍射法测定了7个杨树无性系(14株样木)胸径处各年轮的微纤丝角,并对应分析和测定了各年轮的木材基本密度、纤维长度、纤维宽度和纤维素含量。研究结果表明,杨树微纤丝角在年轮间存在显著差异,其径向变异规律为从髓心向外以微纤丝角逐渐降低,年轮间的平均微纤丝角在7.8旱?8褐洌荒静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾吭谀曷旨湟泊嬖谙灾钜臁O喙胤治霰砻鳎⑾怂拷怯肽静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾看嬖谙灾母合喙毓叵??0.01),相关系数分别为-0.450、-0.586、-0.516和-0.660。回归分析结果表明,多项式方程可较好地描述杨树微纤丝角与所测定的木材性质的关系,相关系数均在-0.45以上(n=125)。本文的研究结果认为,在今后针对杨树材性改良的育种计划中,微纤丝角是一个重要的选育和改良指标。图3表3参34。 相似文献
88.
中国林业产权制度的特点、问题和改革对策 总被引:33,自引:0,他引:33
概述了林业产权的概念和历史沿革,分析了现有产权制度的特点和存在的问题,提出了深化林业产权制度改革的对策,建议将林业产权纳入法治轨道,开展林业新“三定”,规范政府行政行为,强化产权保护,深化国有林改革,建立长期稳定的林业产权关系. 相似文献
89.
浙江集体林地使用权流转的调查研究 总被引:10,自引:2,他引:10
在社会主义市场经济条件下,林地使用权流转成为必然。本文在介绍了浙江集体林地使用权流转现状的基础上,分析了制约集体林地使用权流转的主要因素,并提出推进林地使用权流转的对策。 相似文献
90.
13种杨树木材物理力学性质的研究 总被引:14,自引:3,他引:14
采集1-69杨等10种黑杨的9年生试材,易县毛白杨等3种白杨的13年生试材,测试木材物理力学性能,分析心边材,不同树高位置,株间的变化规律,比较品种间木材性质的差异,试验结果表明,13种杨树全树木材心材率在14.6-34.1%,之间,生材含水率在86.2-148.5%之间,由生材干燥至含水率为12%所产生的干缩率在8.66%-11.96%这间,气干密度属低类或很低类,强度属弱类,硬度属软类或甚软类,冲击韧性中等;黑杨心材颜色深,心边材性质差异大,白杨心材颜色淡,心边材性质差异小,品种间木材物理力学性质差异较大,按其主要特点可将13个品种的木材分为4类。 相似文献