首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1357篇
  免费   51篇
  国内免费   266篇
林业   32篇
农学   132篇
基础科学   36篇
  677篇
综合类   536篇
农作物   87篇
水产渔业   23篇
畜牧兽医   84篇
园艺   38篇
植物保护   29篇
  2024年   10篇
  2023年   33篇
  2022年   34篇
  2021年   47篇
  2020年   54篇
  2019年   61篇
  2018年   49篇
  2017年   87篇
  2016年   76篇
  2015年   60篇
  2014年   89篇
  2013年   108篇
  2012年   150篇
  2011年   97篇
  2010年   73篇
  2009年   87篇
  2008年   68篇
  2007年   71篇
  2006年   50篇
  2005年   46篇
  2004年   39篇
  2003年   29篇
  2002年   32篇
  2001年   14篇
  2000年   21篇
  1999年   23篇
  1998年   36篇
  1997年   16篇
  1996年   25篇
  1995年   17篇
  1994年   14篇
  1993年   13篇
  1992年   12篇
  1991年   10篇
  1990年   8篇
  1989年   6篇
  1988年   5篇
  1987年   3篇
  1981年   1篇
排序方式: 共有1674条查询结果,搜索用时 15 毫秒
1.
Abstract. Nitrous oxide (N2O) is involved in both ozone destruction and global warming. In agricultural soils it is produced by nitrification and denitrification mainly after fertilization. Nitrification inhibitors have been proposed as one of the management tools for the reduction of the potential hazards of fertilizer-derived N2O. Addition of nitrification inhibitors to fertilizers maintains soil N in ammonium form, thereby gaseous N losses by nitrification and denitrification are less likely to occur and there is increased N utilization by the sward. We present a study aimed to evaluate the effectiveness of the nitrification inhibitor dicyandiamide (DCD) and of the slurry additive Actilith F2 on N2O emissions following application of calcium ammonium nitrate or cattle slurry to a mixed clover/ryegrass sward in the Basque Country. The results indicate that large differences in N2O emission occur depending on fertilizer type and the presence or absence of a nitrification inhibitor. There is considerable scope for immediate reduction of emissions by applying DCD with calcium ammonium nitrate or cattle slurry. DCD, applied at 25 kg ha–1, reduced the amount of N lost as N2O by 60% and 42% when applied with cattle slurry and calcium ammonium nitrate, respectively. Actilith F2 did not reduce N2O emissions and it produced a long lasting mineralization of previously immobilized added N.  相似文献   
2.
Storage proteins and glutathione in wheat play an important role in gluten network formation and can be modified by supplementation of nitrogen (N) and sulphur (S) in wheat plants. The glutathione thiol-disulfide status and its relationship to the molecular weight distribution wheat polymeric protein and dough rheological properties have been examined after different foliar S fertilizations (S derived from micronized elemental S and NS, a mixture of N urea and elemental S) applied at the post-anthesis stage. Changes in levels of reduced glutathione (GSH), glutathione disulfide (GSSG), polymeric protein-glutathione mixed disulfide (PPSSG) were analysed by reversed phase high performance liquid chromatography, during grain development using the wheat cultivars, Soissons and Trémie. During the grain desiccation phase, S supplementation (i) increased the GSSG/GSH ratio by 23–25% (ii) induced PPSSG accumulation, and (iii) decreased the formation of SDS-unextractable polymeric protein (UPP) and its molecular mass distribution. However, simultaneous N and S supplementation results in: (i) a decrease in PPSSG formation by 20–30% and (ii) an increase of UPP by 7–18% by enhancing both the branching of the aggregated proteins and their molecular weight. The mixograph parameters show that all forms of endogenous glutathione are linked to dough weakening and are negatively correlated with dough mixing tolerance, dough strength and consistency, while UPP is positively correlated with dough strength and consistency. These findings indicate that S nutrition influences dynamics of the glutathione forms in the grain and results in modification the degree of polymerization of storage protein. Thus both the changes in the form of glutathione and protein polymerization influence the rheological properties of dough.  相似文献   
3.
脱毒桐籽饼(粕)蛋白质及能量营养价值评价   总被引:2,自引:0,他引:2  
选用8头30kg的阉公猪和6只1.7kg的伊莎褐公鸡分别对3种脱毒桐籽饼(粕)Ⅰ、Ⅱ和Ⅲ的蛋白质、氨基酸消化率、代谢率进行了测定。结果表明 :3种脱毒桐饼(粕)Ⅰ、Ⅱ和Ⅲ的蛋白质含量分别为31.17 %、35.12 %和23.98 % ;总氨基酸含量为226.93mg/g、278.38mg/g和178.71mg/g,其中赖氨酸含量4.14mg/g、5.01mg/g和3.47mg/g ,蛋氨酸含量为1.24mg/g、1.33mg/g和0.92mg/g ;能量(GE)为17.72kJ/g、16.42kJ/g 和18.02kJ/g。脱毒桐粕Ⅰ的蛋白质消化率为75.15 % ,消化能为12.85MJ/kg;脱毒桐饼(粕)Ⅰ、Ⅱ的表观代谢能分别为4.88MJ/kg 和6.29MJ/kg,真代谢能为5.53MJ/kg 与6.94MJ/kg。3种脱毒桐饼(粕)的氨基酸之间存在不平衡状况 ,从限制性氨基酸的角度来看 ,脱毒桐饼(粕)的第一限制性氨基酸是蛋氨酸、第二限制性氨基酸为赖氨酸。  相似文献   
4.
[目的]建立一种分析微生物肥料菌种稳定性的T-RFLP指纹图谱技术。[方法]采用T-RFLP指纹图谱技术对进口细菌型微生物肥料菌种的稳定性进行分析。[结果]样品中优势菌的T-RFs片段主要是87、246、247、330 bp,其中330 bp为主要片段,Shannon多样性指数和均一性指数测定结果表明,不同批次产品间差异性较小,微生物群落结构较稳定。[结论]建立了微生物肥料菌种稳定性分析的T-RFLP指纹图谱技术,为进出口微生物肥料产品提供了一种快速分析方法。  相似文献   
5.
采用不同肥料种类和施肥剂量对秃杉人工林进行施肥对比试验。观测胸径、树高和蓄积生长量,分析不同肥料种类和施肥剂量对秃杉人工幼龄林高、粗和蓄积生长量的效应。试验结果表明,合理的施肥措施对秃杉人工林生长有明显促进作用,与对照相比,年高生长增加34%,粗生长增加26%,蓄积生长增加35%。  相似文献   
6.
以三年生狐臭柴为实验材料,设置自然光和遮光两种光照条件,用三种叶面肥进行喷施,分析不同肥料对狐臭柴叶片生物量和主要生化指标的影响。结果表明:喷施氮肥能显著提高狐臭柴叶片生物量,自然光及遮光下分别增加37.30%和15.02%,但果胶的积累减少,分别降低19.78%和17.35%;磷肥能显著提升叶片果胶的含量,分别增加158.08%和239.96%,但叶片生物量显著低于对照,分别降低55.83%和47.40%;复合肥对叶片生物量无明显影响,果胶含量轻微降低。各肥料均使可溶性糖含量降低,且在遮光条件下使叶片内可溶性蛋白含量增加,自然光下使可溶性蛋白含量降低。  相似文献   
7.
This study was conducted to determine the effects of dietary soybean curd residue (SCR) and soy sauce cake (SSC) on the growth performance, carcass traits and physiochemical and intramuscular fatty acid (FA) characteristics in Japanese Black steers. Ten steers (29.7 ± 0.3 months old, 856.6 ± 24.4 kg body weight) were assigned to either treatment C, fed a conventional concentrate or T, fed the test diet including dried SCR and SSC for 3 months. In growth performance, dry matter (DM) intake and average daily gain, and carcass traits did not differ significantly between the treatments. Color of beef was affected by the dietary treatments and meat samples from T showed higher a* value and chroma than those in C. On FA composition, there was no significant difference between the treatments in neutral lipids, whereas in polar lipids, meat samples from T had higher C16:1 (P < 0.05) and tended to have higher C16:0 (P = 0.05) and C18:1 (P = 0.08), but lower C17:0 (P = 0.098), C18:2 (P = 0.06) and C20:4 (P = 0.07) than those from C. The study suggested that SCR and SSC could be used as a substitute for conventional concentrate and would influence meat color and intramuscular FA composition of polar lipids.  相似文献   
8.
微肥Zn和Mn在苜蓿生产中的应用试验   总被引:2,自引:2,他引:0  
针对河南省气候土壤特点,Zn、Mn肥的生理功能以及牧草生产利用中存在的问题,对Zn、Mn微肥在优质牧草紫花苜蓿Medicago sativa生产中的配施技术进行了研究.结果表明:Zn肥对紫花苜蓿的有效范围为400~500 mg/kg,最佳浓度为430 mg/kg.430 mg/kg的Zn肥与380 mg/kg的Mn 肥结合使用,效果更好,可使牧草产量提高10.7%,种子产量提高13.7%.  相似文献   
9.
The field experiments conducted on the grey‐brown podzolic soil in the four growing seasons (1998–2001) at Krzeslice Farm, central‐western Poland comprised seven fertilization variants: 80NF + 80CAN; 80CAN + 80CAN; 80AN + 80AN; 80NF + 50CAN + 30CN; 80CAN + 50CAN +30CN; 80AN + 50AN + 30CN (where NF – nitrofos NPK; CAN – calcium‐ammonium nitrate; AN – ammonium nitrate; CN – calcium nitrate) and control (without N) applied in split rates at the beginning of spring regrowth (80 kg N ha?1), stem elongation (80 or 50) and flower buds visible stages (30). The yielding effect of tested fertilization variants was significant in comparison with the control (2.24 t ha?1). The highest mean seed yield (3.64 t ha?1) was collected from 80AN + 80AN and 80CAN + 80CAN variants. Mean values of 4 years indicate that the second N rate division (80 + 50 + 30) decreased yield, although not significantly in comparison with these two N treatments. Plants grown on these treatments have developed different patterns of growth to yield the seeds. These patterns were characterized by very high crop growth rate during flowering (above 21 g m?2 day?1) and negative at maturation (down to ?2.5 g m?2 day?1). Plants fertilized with ammonium nitrate (80AN + 80AN) reached maximum growth rate earlier (65 days), which lasted longer (20 days) than plants fertilized with calcium‐ammonium nitrate (71 days lasting 17.5 days). Plants grown on the control treatment reached the highest crop growth rate within 79 days (14.8 g m?2 day?1), which lasted 15 days.  相似文献   
10.
上流式厌氧污泥床处理豆制品废水启动研究   总被引:6,自引:2,他引:6  
用上流式厌氧污泥床(UASB)处理豆制品废水,以阐明这种消化器启动的效果。研究结果表明,产气率,COD去除率和甲烷含量分别为3.0L/(L.d),93%,58.4%。从第26天至46天的运转期间,UASB平均COD负荷率、产气率,COD去除率,甲烷含量分别为5.2gCOD/(L.d),3.5L/(L.d),90%,59.4%。出水乙酸,丙酸浓度分别为111mg/L,98mg/L,丁酸浓度不可测出。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号