全文获取类型
收费全文 | 3129篇 |
免费 | 74篇 |
国内免费 | 46篇 |
专业分类
电工技术 | 8篇 |
技术理论 | 2篇 |
综合类 | 94篇 |
化学工业 | 2537篇 |
金属工艺 | 2篇 |
机械仪表 | 21篇 |
建筑科学 | 20篇 |
矿业工程 | 40篇 |
能源动力 | 22篇 |
轻工业 | 256篇 |
水利工程 | 47篇 |
石油天然气 | 24篇 |
武器工业 | 1篇 |
无线电 | 3篇 |
一般工业技术 | 27篇 |
冶金工业 | 24篇 |
原子能技术 | 2篇 |
自动化技术 | 119篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 33篇 |
2019年 | 22篇 |
2018年 | 23篇 |
2017年 | 84篇 |
2016年 | 109篇 |
2015年 | 92篇 |
2014年 | 152篇 |
2013年 | 98篇 |
2012年 | 161篇 |
2011年 | 164篇 |
2010年 | 130篇 |
2009年 | 171篇 |
2008年 | 116篇 |
2007年 | 177篇 |
2006年 | 187篇 |
2005年 | 194篇 |
2004年 | 145篇 |
2003年 | 181篇 |
2002年 | 135篇 |
2001年 | 137篇 |
2000年 | 110篇 |
1999年 | 125篇 |
1998年 | 57篇 |
1997年 | 46篇 |
1996年 | 52篇 |
1995年 | 57篇 |
1994年 | 41篇 |
1993年 | 30篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 8篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
排序方式: 共有3249条查询结果,搜索用时 46 毫秒
91.
92.
由磷肥厂副产氟硅酸生产无水氟化氢 总被引:8,自引:0,他引:8
随着我国氟工业的高速发展,使得氟资源枯竭加快,磷矿中有丰富的氟资源,如何回收利用好氟资源,给企业创造较好的经济效益,是磷复肥企业共同关注的问题。介绍了国外用氟硅酸生产无水氟化氢的专利技术以及四川大学的科研成果,认为经过中试获得必要的设计参数,便可推广应用,市场前景看好。 相似文献
93.
94.
Slow release N fertilizers are receiving increasing attention for use on turf grass, but their fate in the plant-soil system is still poorly understood. We aimed to quantify the uptake and recovery of N by a mixture of grasses when applied as either urea or oxamide in different diameter granules using a tracer technique (15N). The effects of the N source on soil biomass, root density and amount of readily available organic C in soil were also evaluated.In a first experiment oxamide in 4–5 mm diameter granules was compared with urea. The initial N absorption, 40 days after fertilization (d.a.f.), was higher for urea (23.5%) than for oxamide (12.1%), but after 64 days absorption efficiencies were about the same (11%) for both fertilizers. Fertilizer-derived N lost by leaching was much greater from the urea-fertilized soil (1.57 g), compared with losses from oxamide-fertilized soil (0.05 g). The total residual fertilizer N remaining in the system at the end of the experiment was 26.7% of applied urea N and 39.6% of applied oxamide N. Cumulated absorption efficiencies, calculated after dismantling the lysimeters, were 43.1% for urea and 54.8% for oxamide (roots included). A priming effect caused by a larger uptake of soil N because of the better root development was found in the oxamide-treated lysimeter. Fertilization with oxamide also caused an increase in the amount of soil microbial biomass.In a second experiment, the efficiencies and fertilizer N uptake rates from oxamide applied at two different granule sizes (1–2 mm and 5–10 mm) were evaluated. The amount of soil N taken up by the grass was linearly related to root density (r = 0.92). 相似文献
95.
96.
包裹型缓释肥料生产技术实验研究 总被引:11,自引:0,他引:11
通过一系列的实验室研究和小型试验 ,选出了成本低、效果较好的包裹控释材料和粘结剂 ,提出了制造包裹型缓释肥料的生产工艺。对小试生产的包裹型缓释肥料进行缓释性评价 ,结果表明 :肥料的缓释性良好 ,工艺简便易行 ,生产成本低。 相似文献
97.
Gregory A. Gouveia Nazeer Ahmad Selwyn M. Griffith 《Nutrient Cycling in Agroecosystems》1995,42(1-3):205-214
Urea has become the most important N carrier in many parts of the world and its reaction when added to soil is unique in many ways. Two field experiments were therefore undertaken using15N to investigate the uptake efficiency of the added urea-15N which was banded in Experiment I and broadcast in Experiment II. In both experiments the uptake efficiencies were not affected by N-rate and cropping system (Exp. I) or crop residue management (Exp. II) and averaged 17.4 and 16.9% respectively. These low values were supported by evidences of high losses; high pH increases following urea application (volatilization), downward movement of N (leaching), and cycles of waterlogged and well drained conditions in the soil (de-nitrification). Evidence of leaching at least down to 30 cm in the profile was observed in the first experiment where urea was banded but not in experiment II where it was broadcast. The proportion of N in the crop that was derived from added urea (%Ndff) was 57.7% and 36.4% in experiments I and II respectively, suggesting that band application resulted in a higher proportion of the added N in the root zone compared to that for broadcast application. The results indicate the need to investigate other management strategies, such as higher application frequencies and placement closer to the root zone, in order to improve the uptake efficiency of added urea-N in upland rainfed dasheen. 相似文献
98.
99.
全国48家化肥催化剂制造厂总能力为57Kt/a,产量近30kt/a,设备利用率不到50%。平均万吨氨耗催化剂10.36t,高于国外5.60t水平。现生产31个品种203个型号的催化剂中有103种经部级鉴定,但经常使用的约50种。目前化肥催化剂工业水平与国外相比还存在四方面差距。 相似文献
100.
水稻全生育期应用腐植酸液肥的效果初报 总被引:1,自引:0,他引:1
腐植酸液肥——科力素(KLS)对水稻生长发育影响较大。试验表明,水稻苗床施用KLS明显刺激秧苗生长,处理区根长、根数、地上地下百株鲜重及带蘖率都好于对照区。不同生育时期喷施KLS,水稻发育加快,自返青期开始到成熟期都有不同程度提前,一般早熟3~5d。产量增加幅度为4.7%~21.1%,平均增产11.3%,亩增效37.44~204.48元,平均为99.2元,产投比约为12∶1。 相似文献