全文获取类型
收费全文 | 22792篇 |
免费 | 1278篇 |
国内免费 | 2560篇 |
专业分类
林业 | 2064篇 |
农学 | 2347篇 |
基础科学 | 1697篇 |
3329篇 | |
综合类 | 8975篇 |
农作物 | 1354篇 |
水产渔业 | 1052篇 |
畜牧兽医 | 3334篇 |
园艺 | 1183篇 |
植物保护 | 1295篇 |
出版年
2024年 | 157篇 |
2023年 | 433篇 |
2022年 | 1087篇 |
2021年 | 1225篇 |
2020年 | 1175篇 |
2019年 | 1147篇 |
2018年 | 782篇 |
2017年 | 1070篇 |
2016年 | 920篇 |
2015年 | 1214篇 |
2014年 | 1245篇 |
2013年 | 1402篇 |
2012年 | 1767篇 |
2011年 | 1841篇 |
2010年 | 1737篇 |
2009年 | 1529篇 |
2008年 | 1423篇 |
2007年 | 1254篇 |
2006年 | 997篇 |
2005年 | 821篇 |
2004年 | 449篇 |
2003年 | 268篇 |
2002年 | 302篇 |
2001年 | 292篇 |
2000年 | 278篇 |
1999年 | 279篇 |
1998年 | 218篇 |
1997年 | 178篇 |
1996年 | 182篇 |
1995年 | 178篇 |
1994年 | 132篇 |
1993年 | 123篇 |
1992年 | 114篇 |
1991年 | 98篇 |
1990年 | 77篇 |
1989年 | 62篇 |
1988年 | 60篇 |
1987年 | 38篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1963年 | 4篇 |
1962年 | 2篇 |
1956年 | 8篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
ZHANG Zhan JIA Li-ting HOU Lei WANG Xue-mei CHANG Cai-hong YANG Ru-jing ZHANG Xi LIU Sheng-hong ZHENG Fang GONG Fei-li 《园艺学报》2005,21(12):2457-2461
AIM: To detect the effects of NK cells on the etiology of severe pre-eclampsia. METHODS: The peripheral blood and umbilical blood from severe pre-eclamptic patients and normal late pregnant women were collected. NK cells were seperated in percoll and counted by SAP. The proliferating ability of NK cells was measured by MTT and killing power of NK cells was determined by [51Cr] releasing test. The immunohistochemistry method was used to detect the quantity of NK cells and the expression of HLA-G in placenta of them. RESULTS: (1) Compared with that in normal late pregnant women, the counts of the NK cells in peripheral blood, umbilical blood and decidua of severe pre-eclamptic patients were significantly higher (all P<0.05). (2) Compared with that in normal late pregnant women, proliferating and killing ability of NK cells in peripheral blood and umbilical blood of severe pre-eclamptic patients were significantly higher. (3) The expression of HLA-G protein in placenta of severe pre-eclampsia group was lower than that in normal group (P<0.05). CONCLUSION: The quantity of NK cells in severe pre-eclamptic patients is increased with stronger biologic function. They may be related with the pathogenesis of severe pre-eclampsia. 相似文献
992.
993.
994.
995.
早熟和特早熟桃胚珠培养研究 总被引:14,自引:0,他引:14
本文以自然授粉的‘春蕾’、‘沪017’、‘布目早生’、‘1-4-8’、‘7-6-9’的胚珠为试材,研究了早熟和特早熟桃胚珠培养胚成苗的有关影响因素。本试验5个品种(品系)的结果表明,桃品种或品系的果实生育期愈短,胚珠培养胚的成苗率愈高,特早熟桃‘春蕾’花后48天的胚珠培养在改良S H培养基附加BA1.0mg/1 IAA1.0mg/1上30天,将长大的幼胚转移至TM培养基上,胚的成苗率达75%。此外,作者对胚珠培养技术在桃育种中的应用范围及其培养程序开展了讨论。 相似文献
996.
天水毛白杨种源试验的研究 总被引:2,自引:2,他引:0
本文介绍了毛白杨8个种源、220个无性系,在甘肃天水地区开展的种源选择试验及优良无性系筛选结果。经过7年的研究,摸清了毛白杨的变异规律及模式,筛选出3个种源,30个优良无性系,遗传增益达22%~28%,为造林区别提供了科学依据。试验证明无性系有种是一种投资少,见效快,经济效益高的良种选有方法,可降低成本5~6倍。 相似文献
997.
猴丰1号新菌株的选育及其酯酶同工酶分析 总被引:2,自引:0,他引:2
采用子实体组织分离与系统筛选法,从福建猴头的变异株中选育出了定名为“猴丰1号”的新菌株。该菌株菌丝体生长势强,发菌迅速;子实休菇形大,产量高。鲜菇产量比出发株福建猴头增加69.3%,比著名的常山99菌株增加16.8%。酯酶同工酶分析显示:猴丰1号的酯酶谱型与福建猴头相似,但有1条酶带发生了变异。由此说明,它确是源于福建猴头的自然变异株。 相似文献
998.
白翅叶蝉Erythroneura subrufa(Motschulsky)成虫与若虫均以刺吸口器刺进水稻叶片组织内吸取叶汁和叶绿素,被害初期,叶片上出现零星小白点,随后出现长短不一的点状白色斑条,受害严重的稻叶上满布白色斑纹,叶绿素丧失,叶片干萎。在稻叶蝉中除一点小叶蝉被害状出现小白点外,其他叶蝉为害水稻时,并不直接破坏叶绿素,亦不呈现白色斑纹,而是直接吸食叶液,使禾苗发黄而死。因而纠正了过去认为黑尾叶蝉、白翅叶蝉为害水稻后,都会造成叶片出现白色或褐色斑纹的报道。白翅叶蝉在湖南一年发生三代,在晚稻收割后以成虫迁向麦田、杂草等场所越冬,因其寿命很长,故长期不同世代交错。白翅叶蝉除为害水稻外,在初冬与早春还为害冬小麦。近年在湖南及我国南方部分稻区有回升趋势。 相似文献
999.
Chen L Auh C Chen F Cheng X Aljoe H Dixon RA Wang Z 《Journal of agricultural and food chemistry》2002,50(20):5558-5565
Stem tissues of tall fescue (Festuca arundinacea Schreb.) were sampled at three elongation stages and three reproductive stages. Anatomical analysis showed the deposition of guaiacyl (G) and syringyl (S) lignin during plant development and the formation of a lignified sclerenchyma ring. A dramatic increase in Klason lignin content was found from elongation stage to reproductive stage. Lignin composition analyzed by gas chromatography-mass spectrometry revealed that S lignin content and S/G ratio increased with stem development, but contents of p-hydroxyphenyl (H) and G lignins decreased during the same period. S lignin content and S/G ratio also increased from the younger upper internode down to the older basal internode of the stem, but G and H lignin decreased in parallel. Relative O-methyltransferase activities increased during stem development and in parallel with the lignification process of stem. The pattern of enzyme activity during development varied with the choice of substrate, with highest activities seen when substrates were caffeoylaldehyde and 5-hydroxyferulic acid, and lowest activities were seen when caffeic acid and 5-hydroxyconiferyl alcohol were used as substrates. The expression of caffeic acid O-methyltransferase and cinnamyl alcohol dehydrogenase genes increased during the stem elongation stage and remained at high levels during the reproductive stages. The changes at anatomical, metabolic, and molecular levels during plant development were closely associated with lignification and degradability. This study provides an integrated picture of the molecular and chemical events that accompany changes in lignin deposition and ruminal degradability. 相似文献
1000.
A new phytase expressed in yeast effectively improves the bioavailability of phytate phosphorus to weanling pigs 总被引:3,自引:0,他引:3
We have recently expressed a new phytase enzyme in a yeast system. Three experiments with a total of 140 weanling crossbred pigs were conducted to examine the efficacy of this enzyme in improving the bioavailability of phytate-P in corn-soybean meal diets to young pigs. Experiment 1 compared the efficacy of this new phytase with a commercially available phytase (Natuphos, BASF) for 4 wk at an inclusion level of 1,200 U/kg of diet. Experiment 2 compared the responses of pigs to four doses of the new phytase supplementation (300, 600, 900, and 1,200 U/kg of diet) for 4 wk. Experiment 3 compared the efficacy of this new phytase and Natuphos at a marginally optimal dose (700 U/kg of diet) for 5 wk. A group of pigs were fed the P-deficient basal diet as a negative control in Exp. 1, and a group of pigs were fed the basal diet plus .17 or .22% inorganic P as a positive control in all experiments. In Exp. 1, pigs fed the two sources of phytase had similar ADG (564 vs 567 g), gain/feed (.597 vs .589), plasma inorganic P concentrations (8.9 vs 8.4 mg/dL), and mobility scores (4.25 vs 4.46) that were higher (P < .05) than those of the negative control. In Exp. 2, plasma inorganic P concentration was a fairly linear response to the phytase dose (r > .83) at wk 1 and 2. Overall ADG of pigs also tended to increase with the phytase dose (P = .15). In Exp. 3, pigs fed the two sources of phytase had ADG (483 vs 506 g) similar to that of the positive control (508 g). These two groups also had similar plasma inorganic P concentrations (7.7 vs 7.4 mg/dL) that were lower (P < .05) than those of the positive control group (9.7 mg/dL). There was no significant effect of dietary treatments on ADFI in all three experiments. In conclusion, our new phytase was as effective as Natuphos, at the inclusion level of 700 or 1,200 U/kg of a P-deficient, corn-soybean meal diet, in improving phytate-P utilization by young pigs. 相似文献