全文获取类型
收费全文 | 13102篇 |
免费 | 682篇 |
国内免费 | 1042篇 |
专业分类
林业 | 1212篇 |
农学 | 1712篇 |
基础科学 | 303篇 |
877篇 | |
综合类 | 5437篇 |
农作物 | 1532篇 |
水产渔业 | 1019篇 |
畜牧兽医 | 1751篇 |
园艺 | 597篇 |
植物保护 | 386篇 |
出版年
2024年 | 72篇 |
2023年 | 264篇 |
2022年 | 344篇 |
2021年 | 472篇 |
2020年 | 442篇 |
2019年 | 468篇 |
2018年 | 253篇 |
2017年 | 399篇 |
2016年 | 547篇 |
2015年 | 428篇 |
2014年 | 592篇 |
2013年 | 616篇 |
2012年 | 876篇 |
2011年 | 886篇 |
2010年 | 783篇 |
2009年 | 718篇 |
2008年 | 660篇 |
2007年 | 788篇 |
2006年 | 737篇 |
2005年 | 621篇 |
2004年 | 509篇 |
2003年 | 453篇 |
2002年 | 325篇 |
2001年 | 339篇 |
2000年 | 270篇 |
1999年 | 254篇 |
1998年 | 233篇 |
1997年 | 186篇 |
1996年 | 165篇 |
1995年 | 170篇 |
1994年 | 130篇 |
1993年 | 132篇 |
1992年 | 115篇 |
1991年 | 100篇 |
1990年 | 94篇 |
1989年 | 88篇 |
1988年 | 69篇 |
1987年 | 50篇 |
1986年 | 44篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1956年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Kazuyoshi Nakata Tatsuo Hamano Ken-Ichi Hayashi Tadashi Kawai Seiji Goshima 《Fisheries Science》2001,67(3):449-455
SUMMARY: Preference for artificial burrows by the endangered Japanese crayfish species Cambaroides japonicus was studied to improve its cultivation. The occupation of artificial burrows, which were made from straight polyvinyl chloride pipes of different internal diameters ( Y , mm), by crayfishes of different total lengths ( X , mm) was significantly ( P < 0.001, n = 56) described by a linear regression: Y = 0.49 X + 3.42 (19.0 ≤ X ≤ 70.2). Among burrows of different lengths [crayfish total length (TL) × 1, × 2, × 3, and × 4], crayfishes significantly preferred burrows that were greater than TL × 3 ( P < 0.001, n = 588). 相似文献
2.
本文介绍了福建省林木种质资源的收集保存、研究利用,优良家系选育,树种内种源研究,高世代种子园研究,乡土树种栽培驯化,外来树种引种,提高种子园种子产量所采取的措施,无性繁殖技术等林木良种繁育概况;并就林木育种工作存在的问题及今后工作设想提出建设性意见。 相似文献
3.
G. J. Glova 《Ecology of Freshwater Fish》2003,12(4):247-253
Abstract – The interaction between brown trout ( Salmo trutta ; fork length (FL) range 255–390 mm) and inanga ( Galaxias maculatus ; FL range 55–115 mm) was tested during summer through autumn in an artificial stream consisting of a single run-riffle-pool sequence with a natural food supply. Each experimental trial lasted for 15 days, and consisted of two brown trout and 50 inanga collected fresh from a nearby stream, with each species given prior residence in four replicate tests, totalling eight trials in all. In addition, two control trials (each 10 days), with 50 inanga in each, were run. Brown trout almost exclusively occupied the pool, whereas inanga occupied all habitat types, although in different proportions, when tested with and without brown trout. The proportion of inanga in the pool was appreciably lower in the experimental trials with brown trout than in the control trials with no brown trout; prior residence had no significant effect on inanga habitat use. Mortality of inanga attributable to predation by brown trout ranged from 0 to 40% with a mean of 14.5 ± 4.7%. The results suggest that habitat use and survival of inanga populations in small streams can be adversely affected by brown trout. 相似文献
4.
本文详细报道了西瓜蔓枯病的症状和病原菌的形态特点,并鉴定其有性阶段为Mycosphaerellamelonis(Pass)Chiu et Walker,无性阶段为Ascochyta-cucumis Fautr et Roum.此外,还在其他瓜类作物上作了病原菌的致病性试验. 相似文献
5.
研究了陆地棉主要性状对混选—混交育种体系的响应。两轮群体提高了产量、早熟性和降低了麦克隆值的平均数;扩大了纤维品质的变幅;增加了高产株率,但对改进抗枯黄萎病性不明显。一轮群体的效果低于二轮。两次混交扩大了产量和纤维品质的变幅,增加了正末端的个体频率。一次混交的作用不及两次。早代混选相对缩小了群体变幅。一次混交后再经两代开放授粉和对一轮群体再混选,均表现出有益的反响。 相似文献
6.
Totally 13575 ewes of two different breeds, Dala and Spel, were inseminated with semen, frozen in straws and thawed at 70°C for 8 sec. An insemination dose of 0.2 ml containing approx. 150 × 106 spermatozoa with at least 45 to 50% progressive motility was imerted 5 to 12 mm into the cervix. The insemination was performed once between 12 and 30 h after the onset of heat. The NR rate of the Dala ewes increased significantly during the season. The NR rate of the ewes inseminated before 15. November was 44.3%, from 15. to 20. November 52.2%. from 20. to 25. November 55.3% and from 25. November and later 61.4%. The corresponding values for the ewes of the Spel breed were 57.3, 58.7, 61.5 and 71.0% respectively, and only the difference between the two last values was statistically significant. The difference between the fertility of the two breeds was significant within each of the periods . 相似文献
8.
9.
10.
研究目的在于探讨多巴胺受体激动剂(溴隐停)对地方良种肉鸡繁殖性能的影响。方法从628只28周龄健康的“惠州麻”黄羽肉种鸡群中随机选取1组鸡笼内的40鸡作为实验组,其余的作为对照组。实验组鸡群喂服溴隐停,每只鸡每天1.25mg,连用4d,停用4d后再用4d,对照组不使用。结果在4周的实验期内实验组和对照组的产蛋率分别为83.86%和69.96%;破蛋率分别为1.28%和1.69%,畸形蛋率分别为4.33%和1.19%;实验组平均每只鸡的产蛋总数比对照组多3.89个、合格种蛋数多3.26个;药物处理对平均蛋重无显著影响;使用溴隐停能够提高鸡血液中的雌激素水平。结论溴隐停能够通过抑制地方良种肉鸡体内促乳素的合成与分泌,减少抱窝现象的发生,提高其繁殖性能。 相似文献