全文获取类型
收费全文 | 36706篇 |
免费 | 2217篇 |
国内免费 | 3059篇 |
专业分类
林业 | 7648篇 |
农学 | 2431篇 |
基础科学 | 1383篇 |
6704篇 | |
综合类 | 12676篇 |
农作物 | 2692篇 |
水产渔业 | 1420篇 |
畜牧兽医 | 3724篇 |
园艺 | 1578篇 |
植物保护 | 1726篇 |
出版年
2024年 | 127篇 |
2023年 | 630篇 |
2022年 | 1063篇 |
2021年 | 1214篇 |
2020年 | 1224篇 |
2019年 | 1514篇 |
2018年 | 1165篇 |
2017年 | 1421篇 |
2016年 | 1986篇 |
2015年 | 2047篇 |
2014年 | 2298篇 |
2013年 | 2583篇 |
2012年 | 2920篇 |
2011年 | 2518篇 |
2010年 | 2032篇 |
2009年 | 2099篇 |
2008年 | 1783篇 |
2007年 | 1976篇 |
2006年 | 1843篇 |
2005年 | 1380篇 |
2004年 | 1083篇 |
2003年 | 815篇 |
2002年 | 707篇 |
2001年 | 696篇 |
2000年 | 646篇 |
1999年 | 543篇 |
1998年 | 475篇 |
1997年 | 407篇 |
1996年 | 409篇 |
1995年 | 411篇 |
1994年 | 340篇 |
1993年 | 304篇 |
1992年 | 268篇 |
1991年 | 233篇 |
1990年 | 212篇 |
1989年 | 197篇 |
1988年 | 151篇 |
1987年 | 83篇 |
1986年 | 38篇 |
1985年 | 43篇 |
1984年 | 22篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1963年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
51.
捕食线虫性真菌的分离培养及分布规律 总被引:6,自引:1,他引:5
对自然界中的捕食线虫性真菌进行了分离和种属区分,并对分布规律进行了研究。从土壤、粪便等材料中获得了2类活性较强的捕食线虫性菌株:即套捕型(hooping)捕食线虫性真菌和粘捕型(sticking)捕食线虫性真菌。主要的代表种类有3种。这些捕食线虫性真菌在捕食性结构分生孢子形态及某些生物学特性上有一定差异。套捕型捕食线虫性真菌代表种为少孢节丛孢菌(Arthrobotrys oligospara)和梨形指环菌(Dactylaria pyriformis),它们以菌环、菌网作为捕食性结构(器官),以套捕方式杀灭线虫幼虫。梨形指环菌可产生多量厚垣孢子(chlamyalospore)。粘捕型捕食线虫性真菌代表种为纺锤隔指孢菌(Dactylella ellipsospora)。可形成菌结捕食线虫性结构,以粘捕的方式杀灭线虫幼虫。结果表明:捕食线虫性真菌在土壤和家畜粪便中的分离率是40.41%;此类菌适合于生存在阴暗、潮湿、富含腐植质的环境中。在温暖季节时,采用0.4g/L玉米粉琼脂培养基(CMA)易于对其进行分离培养。 相似文献
52.
The effect of food deprivation on ova transport, hormonal profiles and metabolic changes was studied in 20 crossbred multiparous sows during their second oestrus after weaning. To determine the time of ovulation, transrectal ultrasonographic examination was performed. The sows were divided into 2 groups, one control group (C-group), which was fed according to Swedish standards, and one experimental group (E-group). The E-group sows were deprived of food from the first morning meal after ovulation until slaughter. Blood samples were collected every second hour from about 12 h before expected ovulation in the second oestrus after weaning until slaughter and were analysed for progesterone, prostaglandin F2 alpha-metabolite, insulin, glucose, free fatty acids and triglycerides. All sows were slaughtered approximately 48 h after ovulation and the genital tract was recovered. The isthmic part of the oviduct was divided into 3 equally long segments and flushed separately with phosphate buffered saline (PBS). Uterine horns were also flushed with PBS. A significantly greater number of ova were found in the first and second part of the isthmus in the E-group (p = 0.05) while in the C-group most of the ova were found in the third part of the isthmus or the uterus (p = 0.01). The level of prostaglandin F2 alpha-metabolite was significantly higher in the E-group compared with the C-group. The concentration of progesterone increased in both groups after ovulation but there were no significant differences between the groups. The other blood parameters showed that the food-deprived sows were in a catabolic state. The 48 h period of fasting results, directly or indirectly in an delayed ova transport, which may be due to a delayed relaxation in the smooth circular muscle layer of the isthmus. 相似文献
53.
54.
本文以黑龙江省三江平原耕地白浆土为主要研究对象,并以复区内存在的草甸土和暗棕壤作比较,研究了土壤各种理化性质与不同形态氮素之间的相关关系:白浆土中 HA 和 FA 的主要差别,在于前者含有较多的碱性氨基酸,而后者则含有较多的酸性氨基酸;各种不同形状 N素与土壤 pH 值,质地等相关性不显著,而与土壤有机质、全 N 和 C/N 比值等的相关性极为显著。 相似文献
55.
农机产业化是社会分工细化、生产专业化深化的必然产物,其实质是传统农业转变为现代产业的过程。日前,兵团农机产业化进程中存在着一些问题。为此,结合兵团实际,提出了推进农机产业化发展的基本思路。 相似文献
56.
57.
58.
Kunio Shirakihara Masahiko Yoshida Machiko Nishino Yoshimi Takao Kouichi Sawada 《Fisheries Science》2001,67(3):430-435
SUMMARY: The vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in the pelagic waters of Lake Biwa was evaluated from June to September in 1995–97 from eight acoustic surveys using a quantitative echosounder. In each survey, echoes from a depth range of 3 m to the sea bottom were collected at a station every 2.7 s for 24 h together with measurements of vertical profiles of water temperature and chlorophyll-a. The ayu's echoes were identified using an underwater video camera. The ayu were observed near the maximum chlorophyll-a depth and above the thermocline. Their density was highest at depths of 4–11 m with 2–4 individuals/m 3 and was almost zero below 20 m. Echo signs were recorded as having a frequent duration of more than 1 h at night, whereas were of a shorter duration in the day. The fish stay in the epilimnion during the day without any clear vertical migration, but are distributed more uniformly at night. The advantages of remaining in the epilimnion are discussed in terms of food availability and predator avoidance. 相似文献
59.
用红松每个家系结实株数、结塔数、塔重、种重、种子长宽厚之和5个因子进行红松结实特性综合性状评定,基本上反映出了红松家系结实数量及质量指标。 相似文献
60.
The root segments selected from dominant trees ofPopulus davidiana Dode were taken as reproductive material and were buried in different depths to carry out the reproduction of root turion
sprout. The affecting factors of gemination rate, survival rate, and height growth for cutting wood of root sprout were comparatively
analyzed. The results showed that the best suitable substrate for burying root is pearlite, with a germination rate of 15.16%.
3–4-cm root segments has the highest rate of germination (12.4%). The mixture of sand and soil (2∶1) is the best cutting substrate,
with a survival rate of 81.3%, while as to height growth of cutting wood, the mixture of turfy and soil (1∶1) is the best.
The cutting woods selected from different positions of stem show difference in height growth. The cutting wood from top stem
is higher obviously than those from middle or low stem.
Biography: XING Ya-juan (1969-), female, assistant researcher in Forest Research Institute of Heilongjiang Province, Harbin 150040,
P. R. China.
Responsible editor: Song Funan 相似文献