全文获取类型
收费全文 | 8492篇 |
免费 | 525篇 |
国内免费 | 1183篇 |
专业分类
林业 | 341篇 |
农学 | 1533篇 |
基础科学 | 491篇 |
1834篇 | |
综合类 | 3051篇 |
农作物 | 934篇 |
水产渔业 | 511篇 |
畜牧兽医 | 898篇 |
园艺 | 162篇 |
植物保护 | 445篇 |
出版年
2024年 | 55篇 |
2023年 | 213篇 |
2022年 | 323篇 |
2021年 | 376篇 |
2020年 | 386篇 |
2019年 | 366篇 |
2018年 | 337篇 |
2017年 | 459篇 |
2016年 | 475篇 |
2015年 | 395篇 |
2014年 | 444篇 |
2013年 | 650篇 |
2012年 | 587篇 |
2011年 | 593篇 |
2010年 | 433篇 |
2009年 | 430篇 |
2008年 | 372篇 |
2007年 | 428篇 |
2006年 | 375篇 |
2005年 | 276篇 |
2004年 | 256篇 |
2003年 | 229篇 |
2002年 | 213篇 |
2001年 | 215篇 |
2000年 | 175篇 |
1999年 | 136篇 |
1998年 | 114篇 |
1997年 | 120篇 |
1996年 | 111篇 |
1995年 | 92篇 |
1994年 | 72篇 |
1993年 | 98篇 |
1992年 | 66篇 |
1991年 | 62篇 |
1990年 | 47篇 |
1989年 | 54篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 26篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1962年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
对没有隔热层的仓房,用聚苯乙烯泡沫塑料板吊顶及密封窗户,能在一定程度上降低粮温上升速度,保持粮食的新鲜度,延缓粮食的陈化,保持粮食的发芽率,节约熏蒸药剂,减轻保管员劳动强度。达到安全,经济,有效的目的。 相似文献
992.
孟繁诚 《金陵科技学院学报》1995,(3)
当前,南京郊县粮区蔬菜生产技术水平较低,存在一些问题,但发展蔬菜生产的有利条件很多,其生产潜力巨大,前景美好。粮区只要明确发展商品蔬菜生产的思路,注意搞好技术服务,处理好蔬菜栽培中的重大技术问题,粮区种菜是大有可为的。 相似文献
993.
The grain-filling characteristics of six rice varieties (combinations) and the relationships between their relative biochemistry composition during phytate synthesizing and grain plumpness were studied. Regarding results for ISHR1,ISHR2, R198 and JW21, with good grain plumpness, the two-step-filling in superior spikelets and inferior spikelets was not clear, while for ISHR3 and 559, with poor grain plumpness, it was very clear. From booting stage to flowering stage, the contents of phytate and inositol in varieties with good grain plumpness was obviously higher than those in varieties with poor grain plumpness. While at grain filling stage, the content of inorganic phosphorus in varieties with poor grain plumpness was obviously higher than that in varieties with good grain plumpness. The contents of phytate and inositol from booting stage to flowering stage was highly significantly correlated with the initial filling power (RO), the mean filling rate (RM) and grain filling percentage (PGF), and the content of inorganic phosphorus at grain filling stage was negatively significantly correlated with R0, FM and PGF. Furthermore, effective approach to improving grain filling was put forward. 相似文献
994.
995.
996.
Abstract – Body length, age, egg size, embryo salinity tolerance and length at hatching of the freshwater (salinity <0.1 ppt, Lake Peipsi) and brackish-water (salinity 2–6 ppt, Pärnu and Matsalu Bay) ruffe, Gymnocephalus cernuus (L.), were examined to reveal their reproductive success in moderate salinity. Eggs of females originating from brackish water were significantly larger than eggs of freshwater females. No correlation between egg size and female size and age was found in brackish-water populations. In the freshwater population there was a small negative correlation between egg size and female size, but no correlation with female age. Fertilisation by sperm of males of different origin (brackish water or freshwater) produced no significant differences at any critical developmental stage (fertilisation, gastrulation, hatching) in the development of eggs from brackish-water or freshwater females at 3.3, 5.5, 7.7 and 9.9 ppt salinity. Survival rates in different salinity depended only on female origin; embryonic salinity tolerance was higher in ruffe inhabiting brackish water. Obviously, embryo salinity tolerance in ruffe is determined by egg qualities. 相似文献
997.
Summary About 13,000 somaclones of 17 cultivars and clones of potato were obtained from in vitro callus cultures and individually
planted in a greenhouse, followed by tuber generations grown in the field. These plants were subjected to the multistage selection
procedure commonly used in potato breeding. Over a period of five years and three field generations the tuber number, size,
shape, eye depth, starch content, starch yield and tuber appearance of these somaclones were assessed and compared with that
of the controls. These characters varied depending on donor genotype and trait. The frequency of variants was assessed and
there were acceptable proportions of desirable abberrants and invariants among the somaclones. Depending on trait the average
gain rate for all donor genotypes ranged between 0.2 and 2.3% for-deviants, between 12.2 and 15.5% for invariants and between
0.1–1.4% for +deviants.
It is concluded that this technique should be used into potato breeding programmes to improve commercially important characteristics
of specific cultivars and breeding clones. 相似文献
998.
B. J. Clemens S. van de Wetering J. Kaufman R. A. Holt C. B. Schreck 《Ecology of Freshwater Fish》2009,18(3):418-426
Abstract – Pacific lamprey, Entosphenus tridentatus , return to streams and use somatic energy to fuel maturation. Body size decreases, the lamprey mature, spawn, and then die. We predicted that warm, summer temperatures (>20 °C) would accentuate shrinkage in body size, and expedite sexual maturation and subsequent death. We compared fish reared in the laboratory at diel fluctuating temperatures of 20–24 °C (mean = 21.8 °C) with fish reared at cooler temperatures (13.6 °C). The results confirmed our predictions. Lamprey from the warm water group showed significantly greater proportional decreases in body weight following the summer temperature treatments than fish from the cool water group. A greater proportion of warm water fish sexually matured (100%) and died (97%) the following spring than cool water fish (53% sexually mature, 61% died). Females tended to mature and die earlier than males, most obviously in the warm water group. 相似文献
999.
谈建立国家粮食安全体系的必要性 总被引:1,自引:0,他引:1
席晓东 《吉林粮食高等专科学校学报》2002,17(1):26-29
我国的粮食安全问题是一个值得高度重视的问题。建立国家粮食安全体系是从国情出发 ,保证粮食供求基本平衡的需要 ,是国家通过国际市场调节国内粮食市场供求关系的需要。 相似文献
1000.
吉林省粮食生产的结构变动与比较优势分析 总被引:2,自引:0,他引:2
在分析吉林省农业生产结构变动过程的基础上,采用显示性比较优势指标,分析了全省粮食生产的比较优势,为全省粮食生产结构调整提供了科学依据,并研究了全省粮食生产结构调整的对策。 相似文献