全文获取类型
收费全文 | 115858篇 |
免费 | 6488篇 |
国内免费 | 9620篇 |
专业分类
林业 | 10760篇 |
农学 | 9178篇 |
基础科学 | 4885篇 |
15244篇 | |
综合类 | 51909篇 |
农作物 | 6351篇 |
水产渔业 | 5325篇 |
畜牧兽医 | 17857篇 |
园艺 | 4177篇 |
植物保护 | 6280篇 |
出版年
2024年 | 609篇 |
2023年 | 1899篇 |
2022年 | 3195篇 |
2021年 | 3787篇 |
2020年 | 3807篇 |
2019年 | 4412篇 |
2018年 | 2527篇 |
2017年 | 4266篇 |
2016年 | 5451篇 |
2015年 | 4721篇 |
2014年 | 5692篇 |
2013年 | 6262篇 |
2012年 | 9060篇 |
2011年 | 8913篇 |
2010年 | 7073篇 |
2009年 | 6845篇 |
2008年 | 6551篇 |
2007年 | 7723篇 |
2006年 | 6655篇 |
2005年 | 5192篇 |
2004年 | 4234篇 |
2003年 | 3429篇 |
2002年 | 2608篇 |
2001年 | 2460篇 |
2000年 | 2245篇 |
1999年 | 1781篇 |
1998年 | 1411篇 |
1997年 | 1264篇 |
1996年 | 1133篇 |
1995年 | 1159篇 |
1994年 | 1029篇 |
1993年 | 861篇 |
1992年 | 786篇 |
1991年 | 671篇 |
1990年 | 568篇 |
1989年 | 447篇 |
1988年 | 351篇 |
1987年 | 245篇 |
1986年 | 185篇 |
1985年 | 90篇 |
1984年 | 62篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1956年 | 25篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
配料混合试验的设计和分析 总被引:2,自引:0,他引:2
莫惠栋 《扬州大学学报(农业与生命科学版)》2004,25(1):1-4
系统地介绍了配料混合试验的基本概念.指出了混合试验与常规因子试验的区别。提出配料混合试验的3种设计,即顶点和边界点设计、矩心设计和极顶设计。以2个实例演示了混合试验资料的统计方法,包括回归和方差分析.驻点分析和等值线分析。 相似文献
72.
通过群钻钻头直径D,进给量f和切削速度n对孔径扩张量,圆度,孔中心线垂直度和直线度影响的试验,得出它们的变化规律。 相似文献
73.
Indices of the tomato seedling quality maintenance level after production before field planting were studied through simulated experiments, small--scale operation, indoor analyses and measurements, and field observation. The results showed that under simulated shipping and storage conditions, seedling quality change following different durations (days) of shipping and storage was correlated significantly or even very significantly with certain physiological and morphological indices. With various measured indices following different periods of shipping and storage treatment subjected to multinomial successive regressive correlation analysis, the principal factors influencing seedling quality maintenance level are identified to be chlorophyll content→dry short weight→ leaf freshness index in order of their importance. Significance analysis with multinomial fitted equation indicated that correlations between any one of above three factors and the growth index after field planting reached very significant difference level. 相似文献
74.
石灰性土壤的电超滤(EUF)特性主要是浸提时因需控制电流而必须大大降低电压。在一定范围内,降压程度与土壤 CaCO_3%有密切关系。控流限额愈低,电压需成比例地下降,但土壤EUF-值减小不多。电流控制在一定值时,离子的解吸总量亦为定值。控流主要控制了各石灰性土壤解吸/溶解份额特大的 Ca+Mg 量近于定值,对于含量小的其他养分离子则并无多大影响,仍可区辨各土壤间的差别。通过冬小麦盆栽试验和有关化学测试法等方面的相关研究,表明采用国际通用的5g 土样和控电流方法测定 EUF-K 和-P 等有效养分,对于石灰性土壤也是可行的,但其EUF-(Ca+Mg)值则毫无植物营养有效性的意义。土壤 EUF 值只是一种指数,并非真正的解吸离子量。石灰性土壤 EUF-K 值因浸提时降压控流而略低,80℃时5min 内解吸的钾不一定是非交换性钾。由于 Ca-P 和 CaCO_3在高温高电压时浸出较多,故石灰性土壤 EUF-P 和-(Ca+Mg)的80℃值/20℃值之比,与酸性土壤或非石灰性土壤相比要大得多。 相似文献
75.
Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha–1 , respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha–1 , respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah. 相似文献
76.
77.
Abstract. Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plant-available phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (≶9mgPL−1 ) some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses. 相似文献
78.
79.
中密度纤维板砂光机的改进及降耗 总被引:2,自引:0,他引:2
笔者分析了中密度纤维板砂光机消耗较高、质量较差的原因,提出了改进措施。实施结果表明,砂光机运行正常,砂光产量和质量同步提高,消耗和成本下降,污染减轻。 相似文献
80.