全文获取类型
收费全文 | 268375篇 |
免费 | 16152篇 |
国内免费 | 7743篇 |
专业分类
林业 | 30388篇 |
农学 | 24573篇 |
基础科学 | 8889篇 |
50612篇 | |
综合类 | 28065篇 |
农作物 | 19894篇 |
水产渔业 | 17417篇 |
畜牧兽医 | 77899篇 |
园艺 | 7985篇 |
植物保护 | 26548篇 |
出版年
2022年 | 2765篇 |
2021年 | 4752篇 |
2020年 | 4988篇 |
2019年 | 5593篇 |
2018年 | 5054篇 |
2017年 | 6044篇 |
2016年 | 6599篇 |
2015年 | 6836篇 |
2014年 | 8038篇 |
2013年 | 19216篇 |
2012年 | 8725篇 |
2011年 | 10517篇 |
2010年 | 10641篇 |
2009年 | 10986篇 |
2008年 | 9277篇 |
2007年 | 8662篇 |
2006年 | 9221篇 |
2005年 | 8182篇 |
2004年 | 6317篇 |
2003年 | 5887篇 |
2002年 | 4961篇 |
2001年 | 5518篇 |
2000年 | 5548篇 |
1999年 | 5893篇 |
1998年 | 5534篇 |
1997年 | 5377篇 |
1996年 | 5004篇 |
1995年 | 5434篇 |
1994年 | 4693篇 |
1993年 | 4339篇 |
1992年 | 4074篇 |
1991年 | 4060篇 |
1990年 | 3641篇 |
1989年 | 3431篇 |
1988年 | 3002篇 |
1987年 | 2992篇 |
1986年 | 2689篇 |
1985年 | 2994篇 |
1984年 | 2977篇 |
1983年 | 2887篇 |
1982年 | 2561篇 |
1981年 | 2519篇 |
1980年 | 2499篇 |
1979年 | 2437篇 |
1978年 | 2311篇 |
1977年 | 2203篇 |
1976年 | 2051篇 |
1975年 | 1804篇 |
1974年 | 1823篇 |
1973年 | 1734篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
971.
本文研究BCI一代数的极大理想、固执理想、弱正定关联理想之间的关系,得到的主要结果是:BCI一代数的固执理想是弱正定关联的极大理想 相似文献
972.
通过对13个制材车间车间环境噪声的测试分析,揭示了制材车间环境噪声的现状和特性,车间噪声严重超标,其声压级较高值出现在1 ̄16kHz频带范围内,根据测试分析结果,提出了降低制材车间环境噪声的途径。 相似文献
973.
974.
Experiments conducted m a phytotron on three rice varieties of different salinity tolerance revealed an increase in the content of endogenous abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi salt-tolerant), but in Pokkali (salt-tolerant) and IR28 (salt-sensitive) the increase in ABA content was marginal. Under sahnity stress, in general, 5 weekly sprayings of ABA (10-4 mol L-1 ) decreased Na and K concentrations in the shoot to the extent of 29.5 % and 3.3 %, respectively. However, ABA application significantly improved the K/Na ratio as well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and shoot dry weight. The results are discussed in relation to possible mechanism of salinity tolerance. 相似文献
975.
976.
1. Brown egg layers were fed diets differing in oil content, oil source and linoleic acid concentration and the effect on performance from 22 to 69 weeks of age was studied.
2. The birds responded with an increasing mean egg weight up to a linoleic acid intake of 2.75 g/bird d.
3. Increasing the intake of readily absorbable oil without increasing linoleic acid concentration did not increase mean egg weight. 相似文献
977.
Mastitis Caused by Haemophilus somnus in a Dairy Cow 总被引:2,自引:1,他引:1
978.
To assess respiratory function in dogs with tick paralysis, respiratory measurements were recorded on 14 dogs experimentally infested with Ixodes holocyclus. There was a progressive fall in respiratory rate with no change in tidal volume, which resulted in a significant fall in minute respiratory volume in the latter stages of the disease. The fall in respiratory rate was possibly central in origin and was accompanied by an increased alveolar-arterial oxygen tension difference, probably caused by pulmonary congestion and oedema. The "grunting" respiration seen in tick paralysis was due to closure of the vocal cords during expiration and could represent an attempt to re-expand collapsed parts of the lung. 相似文献
979.
Thirty eight newly weaned hinds were randomly allocated to one of two equal groups. One group received ivermectin, the other, oxfendazole at dose rates of 0.2 mg/kg and 4.5 mg/kg, respectively. All deer were drenched four times and were grazed on pasture. Both anthelmintics reduced D. viviparus faecal larval counts to low levels 20 days after dosing, but the mean larval output and the proportion of deer shedding D. viviparus larvae at 27 and 33 days after treatment, were significantly lower in the ivermectin treated group. There was no significant difference in weight gain between the two groups throughout the trial. This study suggests that ivermectin prevents reinfection with D. viviparus for approximately 14 days longer than oxfendazole. 相似文献
980.
MICHAEL M. PAVLETIC DVM DiplomateACVs MARILYN KOSTOLICH DVM PHILIP KOBLIK DVM PhD STEVE ENGLER VMD 《Veterinary surgery : VS》1987,16(4):283-293
Latissimus dorsi and cutaneous trunci myocutaneous flaps of equal dimension and location were randomly elevated on opposite sides of the thorax in 10 dogs (group 1) and resutured to their respective bed. The procedure was repeated in four additional dogs (group 2); however, the short perforating branches of the thoracodorsal artery and vein were divided at the base of each cutaneous trunci myocutaneous flap, whereas the cutaneous pedicle and underlying cutaneous trunci muscle were divided in the latissimus dorsi myocutaneous flaps to determine subsequent skin survivability and the major source of circulation of each myocutaneous flap. There was little difference in the percentage of skin survival between the latissimus dorsi and cutaneous trunci myocutaneous flaps in group 1 dogs. Circulation to the "skin island" of group 2 latissimus dorsi myocutaneous flaps originated from intramuscular anastomotic connections between the major branch of the thoracodorsal artery entering the latissimus dorsi muscle and the proximal lateral intercostal arteries perforating the muscle. Ligation of the short perforating branches of the thoracodorsal artery resulted in partial skin necrosis in all group 2 cutaneous trunci myocutaneous flaps. Results from this study indicate that it is unnecessary to elevate the latissimus dorsi muscle for major skin flap elevation and survival. The thicker latissimus dorsi myocutaneous flap is more difficult to develop surgically and appears to have no clinical major advantage over the more mobile cutaneous trunci myocutaneous flap or the adjacent thoracodorsal axial pattern flap for closure of large skin defects within the radius of flap rotation. 相似文献