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1.
Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m−3, low-density with substrate LDS, high-density HD; 3000 PL/m−3), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m2 of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO2-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m−3) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account. 相似文献
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本试验以水蚯蚓作为饵料,研究了60日龄鳝苗不同密度下的增重、存活率及饵料转化率。试验分3个密度组,其对应的密度分别为2000尾/m2、3000尾/m2、4000尾/m2,每个密度组设4个平行;试验时间为30d。结果表明:在本试验条件下,3个密度组鳝苗的增重率、存活率随着密度的增大呈下降趋势,而其饵料系数随着密度增大而增大;其中在4000尾/m2的密度下,鳝苗的增重率最低,仅为1.12±0.13;饵料系数最高,为5.71±1.37。 相似文献
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选择不同林分类型和立地条件,按不同经营密度分别设立固定标准地,开展立地类型划分和最适密度选择。同时,在固定标准地内,对林分生长性状、形质指标、干物质积累量、枯枝落叶分解量及养分归还量进行连续定位观测。结果表明:经营密度对林分生长、干物质积累和枯枝落叶分解影响较大,且以中等经营密度(0.7)效果最理想。在立地类型划分、最适经营密度选择、密度效应分析、径级-株数分布规律研究的基础上,针对不同培育目标,分别提出不同立地条件下天然杨桦(胶合板材、普通建筑材、纸浆材)用材林高效经营技术,为科学经营存量种质资源,最大限度提高森林生产力奠定理论基础。 相似文献
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《Communications in Soil Science and Plant Analysis》2012,43(6):475-486
Abstract Samples of four soils having a wide range of volume weights (0.65, 1.02, 1.25, 1.62 g/cm3) were either weighed or measured by volume and extracted with: (a) the Bray P1 extractant, (b) the Mehlich double acid extractant for P, K, Ca, Mg, Mn, Zn and (c) neutral N NH4OAc for K, Ca, Mg all at a soil/extracting solution ratio of 1:10. The soil test results were recorded on a volume basis in mg/dm3 and on a weight basis in mg/kg. The test values for all macronutrients obtained with all extractants decreased, relative to a constant volume, with increasing VW of soil when analyzed and expressed on a weight basis. Results based on the use of a volume sample (scooped) but calculated on an assumed weight of soil changed the values in direct ratio of 1/assumed VW. The use of an assumed VW has no justification, since uniform soil test results can be obtained when expressed on a volume basis by either using a scooped sample of known volume or a weighed sample followed by multiplication with the VW of each soil. 相似文献
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不同种植密度下的棉田小气候特点 总被引:2,自引:0,他引:2
为研究种植密度对田间小气候的影响,2008年在南疆阿克苏试验点,通过大田试验对不同种植密度下(9.0、13.5、18、22.5、27.0万株/hm2)棉田群体冠层不同层次的温度、空气相对湿度、土壤水分等要素进行了测定。结果表明:在所设置的密度范围内,棉花的株高在55~75cm,并且随密度增加株高降低;而茎粗、株宽、叶宽、果枝数等也有类似趋势。花期和吐絮期,棉花宽窄行的冠层空气温度均较高,最高均超过了31℃,并随当日时间先升后降,窄行温度高于宽行,冠层40cm处高于20cm处。相对湿度符合开口向上抛物线模型,花期较高且变化较小,中午时段最低只有40%,比见絮期高10个百分点以上;各处理以中间密度的相对湿度最为稳定,变化最小。土壤水分方面,密度小的处理地表蒸发严重,密度大的叶片蒸腾较多,因此,密度适中的处理土壤水分保持较好,变化范围较小。土壤15cm处地温,前期密度大的处理地温较高,中期受叶片遮荫影响而下降,但后期高密度处理温度又会升高,不过处理间差异不大,最高相差不过1℃。 相似文献
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中美德系玉米品种的耐密性对深松耕作措施的响应分析 总被引:1,自引:0,他引:1
采取耕作方式×种植密度×品种三因素裂区试验,深松40 cm和旋耕15 cm耕作条件,在9.0万株/hm~2和10.5万株/hm~2种植密度下,对中系郑单958和登海618、美系先玉335和华美1号、德系KX3564和KWS2564不同血缘玉米品种的地上部形态、生理及产量构成指标进行对比分析。结果表明,深松可降低增密后玉米净光合速率、LAI、SPAD值和单株生产能力的下降幅度,缓解株型的变化,提高玉米的耐密性。我国玉米品种的耐密性对深松耕作响应与美系和德系玉米品种存在差异,深松耕作与旋耕相比,华美1号、KX3564、KWS2564、先玉335增加种植密度后,其穗位叶叶倾角、净光合速率、LAI、SPAD值下降缓慢,产量、耐密系数显著提高,其耐密适应性对深松耕作的响应度高于郑单958、登海618。 相似文献