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41.
沙漠水渠人工固沙区沙篙和沙拐枣灌丛的土壤水分特征对比 总被引:1,自引:0,他引:1
在古尔班通古特沙漠引水渠沿线建植5a的人工固沙区内,选择自然生长的沙蒿和沙拐枣灌丛,依据冠幅大小设置5个水平距离梯度和4个土层深度梯度.对比研究了二者的土壤水分特征.结果表明,随土层深度的增加,两种灌丛土壤含水量均呈增加趋.,中下部2层(20~40 cm和40~60 cm)土壤含水量显著(P<0.05)高于上部2层(0... 相似文献
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不同放牧率对冷蒿小禾草草原土壤微生物数量和生物量的影响 总被引:22,自引:6,他引:22
以围栏轮牧方式研究不同放牧率对退化草原土壤微生物的影响。结果表明,围栏及适度放牧四年后使土壤微生物的数量显著提高,有利于退化草原的逐步恢复。与对照区比较,放牧区微生物各类群的数量均呈减少趋势,并与土壤有机磷变化密切相关。九年后,在4羊/ha区的微生物量-C高于对照区,而在1.33和6.67只羊/ha-区则有所降低。 相似文献
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鄂尔多斯油蒿-本氏针茅群落生物量 总被引:6,自引:0,他引:6
在5年逐月观测基础上,利用多元分析方法,建立鄂尔多斯高原沙地油蒿--本氏针茅群落地上生物量对气候因子影响的逐月回归模型,结果表明,气候因子在不同时期对植物生长的作用差异显著,降水因子在各月都是影响生物量的显著因子,二者呈正相关,日照时数仅在6月对生物量产生显著影响,。平均气温在各月都不对生物量产生显著影响,7-10月各月生物量都受前月生物量的显著影响,说明植物生长的持续性对生物量的形成和积累是重要的,应用本文建立的模型对3种不同气候条件下,各月生物量的波动范围进行预测,建立累积回归模型,将逐月回归模型,累积回归模型的模拟值与实测值进行比较,结果在多数年份,逐月回归模型都比累积回归模型更接近实测值,与传统的累积回归模型相比,本模型具有三方面的优越性,即可揭示气候影响植物生长的重要细节,具有预测能力以及精度更高,因此是对传统累积气候模型进行的有益改进。 相似文献
45.
Landscape characteristics of disturbed shrubsteppe habitats in southwestern Idaho (U.S.A.) 总被引:4,自引:0,他引:4
We compared 5 zones in shrubsteppe habitats of southwestern Idaho to determine the effect of differing disturbance combinations on landscapes that once shared historically similar disturbance regimes. The primary consequence of agriculture, wildfires, and extensive fires ignited by the military during training activities was loss of native shrubs from the landscape. Agriculture created large square blocks on the landscape, and the landscape contained fewer small patches and more large shrub patches than non-agricultural areas. In contrast, fires left a more fragmented landscape. Repeated fires did not change the distribution of patch sizes, but decreased the total area of remaining shrublands and increased the distance between remaining shrub patches that provide seed sources. Military training with tracked vehicles was associated with a landscape characterized by small, closely spaced, shrub patches.Our results support the general model hypothesized for conversion of shrublands to annual grasslands by disturbance. Larger shrub patches in our region, historically resistant to fire spread and large-scale fires because of a perennial bunchgrass understory, were more fragmented than small patches. Presence of cheatgrass (Bromus tectorum), an exotic annual, was positively related to landscape patchiness and negatively related to number of shrub cells. Thus, cheatgrass dominance can contribute to further fragmentation and loss of the shrub patch by facilitating spread of subsequent fires, carried by continuous fuels, through the patch. The synergistic processes of fragmentation of shrub patches by disturbance, invasion and subsequent dominance by exotic annuals, and fire are converting shrubsteppe in southwestern Idaho to a new state dominated by exotic annual grasslands and high fire frequencies. 相似文献
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Ning Qing Liu Wolfgang SchuehlyMichaela von Freyhold Frank van der Kooy 《Industrial Crops and Products》2011,34(1):1084-1088
Treatment of uncomplicated malaria relies heavily on the sesquiterpene lactone artemisinin (ART), derived from the Chinese herb Artemisia annua. It is currently used as the first line treatment in the form of ART combination therapies in which different ART derivatives are combined with a non ART-like drug, which displays a different mechanism of action. This treatment regime is prescribed by the WHO in order to (1) effectively treat uncomplicated malaria and (2) to reduce the risk that drug resistance will develop. Considering the importance of ART in this treatment regime, various methods have been developed to increase the global production of ART. These methods include: large scale solvent extraction and purification from high yielding A. annua varieties, chemical/semi-chemical synthesis of artemisinin, and genetic engineering of unrelated organisms to produce ART in high quantities. Currently most of the commercial approaches to produce ART are based on solvent extraction and purification from the plant material. Classical extraction solvents include hexane or petroleum ether while ethanol, which is a more polar solvent, has recently been shown to be equally efficient. We developed a purification method from an ethanolic extract by using a diatomite-based purification protocol. Various volumes and ratios of solvents and diatomite were tested which resulted in ≥98% pure ART with a total recovery of around 60%. Our protocol for the isolation of ART may form a commercial scale alternative as it is both economically attractive due to the small amounts of purification materials needed and also environmentally friendlier than the methods previously described. 相似文献
49.
Luis MartínLuis F. Julio Jesus BurilloJesus Sanz Ana M. MainarAzucena González-Coloma 《Industrial Crops and Products》2011,34(3):1615-1621
A comparison between traditional extraction techniques (hydrodistillation and organic solvent extraction) and supercritical fluid extraction was made for two different populations and crops of Artemisia absinthium L., cultivated in the field and aeroponically. The composition of the extracts, volatile and non volatile oils, was analyzed by GC-MS and HPLC-DAD, respectively. The antifeedant and phytotoxic activity of the extracts was tested on insect pests (Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi) and plants (Lactuca sativa and Lolium perenne). The supercritical extracts exhibited stronger antifeedant effects than the traditional ones (up to 8 times more active) with moderate selective phytotoxic effects on L. perenne root growth (<50% inhibition). 相似文献
50.
采用菌丝生长速率法,研究南艾蒿(Artemisia verlotorum Lamotte)乙醇提取物及其萃取物、乙酸乙酯相活性富集片段对田七(Panax notoginseng)主要病害病原菌的抑制作用。结果表明,10 mg/m L的南艾蒿乙醇提取物对田七炭疽病原胶孢炭疽菌(Colletotriehum gloeosporioides)、田七根腐病原茄镰孢(Fusarium solani)、田七黑斑病原人参链格孢(Alternaria panax)的菌丝生长抑制作用明显,最大抑制率分别为89.66%、74.42%和75.93%;萃取物中乙酸乙酯萃取物对3种病原菌抑制率最大,分别为90.41%、82.68%、71.79%;富集片段F2在10 mg/m L浓度下对3种病原菌菌丝生长抑制率均达到100%。 相似文献