全文获取类型
收费全文 | 858篇 |
免费 | 31篇 |
国内免费 | 143篇 |
专业分类
林业 | 70篇 |
农学 | 265篇 |
基础科学 | 63篇 |
171篇 | |
综合类 | 228篇 |
农作物 | 31篇 |
水产渔业 | 26篇 |
畜牧兽医 | 20篇 |
园艺 | 17篇 |
植物保护 | 141篇 |
出版年
2024年 | 10篇 |
2023年 | 22篇 |
2022年 | 28篇 |
2021年 | 23篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 25篇 |
2017年 | 34篇 |
2016年 | 46篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 49篇 |
2012年 | 65篇 |
2011年 | 54篇 |
2010年 | 50篇 |
2009年 | 50篇 |
2008年 | 41篇 |
2007年 | 47篇 |
2006年 | 47篇 |
2005年 | 34篇 |
2004年 | 51篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 33篇 |
2000年 | 21篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1983年 | 3篇 |
排序方式: 共有1032条查询结果,搜索用时 31 毫秒
81.
82.
沼液负压蒸发浓缩装置的设计与试验 总被引:2,自引:1,他引:2
为了解决沼液浓缩过程中有效成分流失的问题,采用低温负压蒸发浓缩的方法,结合沼液的理化性质,对沼液负压蒸发浓缩装置的主体部分(蒸发罐)和辅助设备(冷凝器、循环液槽、真空泵)分别进行了参数设计计算和设备选型,并在自制20 L负压蒸发浓缩装置上进行了系列试验。试验结果表明:当温度低于80℃时,沼液的有机质含量基本不变,蒸发温度高于80℃之后,有机质含量明显下降,80~100℃的变化率为9.4%;随着温度的升高,氮磷钾含量不断下降,氮含量流失最大,最大变化率为13%。蒸发浓缩后的沼液中有机质和氮磷钾含量随真空度的增大而升高;随着真空度的升高,沼液的蒸发温度逐渐降低,蒸发量不断增大,绝对真空度为0.025 MPa时,最低蒸发温度为67℃,蒸发量最高能达到8 324 m L/(m2·h),蒸发率为28.75%;绝对真空度维持在0.04 MPa到0.05 MPa之间,温度在75~80℃时,蒸发量能达到7 700 m L/(m2·h),蒸发率为26%左右。 相似文献
83.
84.
This study was designed to understand the impact of methyl bromide (MB) (CHaBr) and its alternatives on both free-living and root-knot nematodes in the soil. A randomized complete block experiment with six treatments and 4 replicates (each replicate in a separate greenhouse) was established in Qingzhou, Shandong Province, China. In addition to MB and untreated control (CK) treatments there were four alternative soil fumigation practices including MB virtually impermeable films (VIF), metam sodium (MS), MS VIF and soil solarization combined with selected biological control agents (SS BCA). Two tomato (Lycopersicum esculentum Mill.) cultivars, cv. Maofen-802 from the Xian Institute of Vegetable Science, China, and cv. AF179 Brillante from the Israeli Hazera Quality Seeds, were selected as test crops. The results indicated that Rhabditidae was the most dominant population with percentage abundance as high as 85% of the total number of identified free-living nematodes, followed by that of Cephalobidae. Methyl bromide and its alternatives except for the non-chemical SS BCA treatment controlled the target pest, root-knot nematodes. Also, the impact of the three chemical alternatives on free-living nematode number and functional group abundance was similar to the impact associated with a typical methyl bromide application. Chemical fumigation practices, especially that with MB, significantly reduced the number of nematodes in the soil and simultaneously significantly reduced the number of nematode genera thereby reducing nematode diversity. All the four soil chemical fumigation activities decreased soil microbial biomass and had an obvious initial impact on microorganism biomass. Furthermore, both plant-parasitic and fungivore nematodes were positively correlated with soil microbial biomass. 相似文献
85.
H. P. Collins A. Alva R. A. Boydston R. L. Cochran P. B. Hamm A. McGuire E. Riga 《Biology and Fertility of Soils》2006,42(3):247-257
Sodium N-methyldithiocarbamate (metam sodium) and 1,3 dichloropropene are widely used in potato production for the control of soil-borne
pathogens, weeds, and plant parasitic nematodes that reduce crop yield and quality. Soil fumigation with metam sodium has
been shown in microcosm studies to significantly reduce soil microbial populations and important soil processes such as C
and N mineralization. However, few published data report the impact of metam sodium on microbial populations and activities
in potato production systems under field conditions. Fall-planted white mustard (Brassica hirta) and sudangrass (Sorghum sudanense) cover crops may serve as an alternative to soil fumigation. The effect of metam sodium and cover crops was determined on
soil microbial populations, soil-borne pathogens (Verticillium dahliae, Pythium spp., and Fusarium spp.), free-living and plant-parasitic nematodes, and C and N mineralization potentials under potato production on five soil
types in the Columbia Basin of Eastern Washington. Microbial biomass C was 8–23% greater in cover crop treatments compared
to those fumigated with metam sodium among the soil types tested. Replacing fumigation with cover crops did not significantly
affect C or N mineralization potentials. Cumulative N mineralized over a 49-day laboratory incubation averaged 18 mg NO3-N kg−1 soil across all soil types and treatments. There was a general trend for N mineralized from fumigated treatments to be lower
than cover-cropped treatments. Soil fungal populations and free-living nematode levels were significantly lowered in fumigated
field trials compared to cover-cropped treatments. Fumigation among the five soil types significantly reduced Pythium spp. by 97%, Fusarium spp. by 84%, and V. dahliae by 56% compared to the mustard cover crop treatment. The percentage of bacteria and fungi surviving fumigation was greater
for fine- than coarse-textured soils, suggesting physical protection of organisms within the soil matrix or a reduced penetration
and distribution of the fumigants. This suggests the potential need for a higher rate of fumigant to be used in fine-textured
soils to obtain comparable reductions in soil-borne pathogens. 相似文献
86.
分析了长输管道真空干燥中真空泵组的有效抽速受管道流阻的影响,给出了有效抽速的计算方法,并用现场实验对其进行了验证.结果表明,处于管道出气口一端的压力小于管道另一端的压力.研究结果对进一步进行长输管道真空干燥抽气时间的预测研究提供了重要的依据. 相似文献
87.
在室内相对湿度50%-60%的恒温条件下,研究了不同剂量、温度、处理时间和有、无载物情况下环氧乙烷(ethylene oxide,EO)对小麦矮腥黑穗病菌(Tilletia controversa Kühn,TCK)的杀灭效果.结果表明,EO对TCK冬孢子有极强的杀灭作用.EO对TCK病菌的杀灭效果随处理温度升高、剂量的增加和熏蒸时间的延长而增强.无载物情况下,15、20、25℃处理120 h条件下达到100%杀菌效果的临界浓度值分别为10.5、7.3和6.8 g.m-3.EO对TCK的杀菌临界浓度随熏蒸时间延长和温度升高而降低.80%装载量条件下,EO对TCK病菌的LD50较无载物条件下的高. 相似文献
88.
木材真空-浮压干燥过程中自由水迁移特性 总被引:2,自引:4,他引:2
该文以马尾松为试验材料 ,通过对真空 浮压干燥中木材内部温度场、湿度场随压力浮动频率变化的试验研究 ,总结出木材在真空 浮压干燥过程中内部自由水迁移的基本规律 ,并对水分迁移的机制与驱动势进行了分析 .试验结果和理论分析显示 ,在真空 浮压干燥过程中自由水的输运由两部分完成 ,一部分为毛细管压力下液体的团块迁移 ;另一部分为在压力梯度下 ,由于压力波动而引起自由水的蒸发或沸腾后所产生的水蒸气的迁移 ,且后者在自由水的迁移过程中占主导地位 . 相似文献
89.
测试了有机硫熏蒸剂大扫灭(Dazomet)对三七(Panax notoginsengWall.)根围几种主要病原生物:线虫、细菌和真菌的最低灭生浓度(MBC值)分别为≥7.8、≥31.2和≥125μg/mL。4种主要病原真菌:立枯病丝核菌(Rhizoctoni solani)、根腐病菌毁坏柱孢霉(Cylindrocarpon destructant)、镰孢霉(Fusariumspp.)和黑斑病交链孢(Alternaria tenus)的MBC值分别为≥31.2、≥62.5、≥125和≥125μg/mL。钾-威百(K-Vapam)对线虫、细菌和病原真菌的灭生活性与Dazomet相当。连作三七田播种前和移苗前用98%大扫灭粉粒剂20~40 g/m2和35%钾-威百液剂30~50 mL/m2进行耕作层土壤熏蒸处理,对三七出苗和成苗率无显著影响;杂草和线虫发生量比对照分别减少90%~95%。播前处理比对照苗病发生率降低45.0%~82.5%,移苗前处理苗病发生率降低35.0%~50.0%。适当充足的土壤含水量、适时彻底的土壤毒气排除对提高药效和避免残毒对后茬药害至关重要。 相似文献
90.
王世尧 《大连水产学院学报》1995,10(1):67-71
本文介绍了真空解冻装置电气控制系统的设计思想与系统构成。该控制系统主要包括温度控制系统、真空度控制系统和定时控制系统。文中对系统主要电路的工作思路,性能和特点进行了分析,该系统经生产单位的试用,温度控制精度高,工作可靠。 相似文献