全文获取类型
收费全文 | 235030篇 |
免费 | 13275篇 |
国内免费 | 157篇 |
专业分类
林业 | 9829篇 |
农学 | 8029篇 |
基础科学 | 1634篇 |
29738篇 | |
综合类 | 37655篇 |
农作物 | 8957篇 |
水产渔业 | 12060篇 |
畜牧兽医 | 122191篇 |
园艺 | 3156篇 |
植物保护 | 15213篇 |
出版年
2019年 | 2240篇 |
2018年 | 3500篇 |
2017年 | 3929篇 |
2016年 | 3673篇 |
2015年 | 3146篇 |
2014年 | 3879篇 |
2013年 | 9422篇 |
2012年 | 6852篇 |
2011年 | 8428篇 |
2010年 | 5658篇 |
2009年 | 5646篇 |
2008年 | 8188篇 |
2007年 | 7810篇 |
2006年 | 7523篇 |
2005年 | 6741篇 |
2004年 | 6528篇 |
2003年 | 6636篇 |
2002年 | 6102篇 |
2001年 | 7766篇 |
2000年 | 7627篇 |
1999年 | 6075篇 |
1998年 | 2507篇 |
1997年 | 2546篇 |
1996年 | 2332篇 |
1995年 | 2741篇 |
1994年 | 2428篇 |
1993年 | 2366篇 |
1992年 | 4908篇 |
1991年 | 5149篇 |
1990年 | 5020篇 |
1989年 | 5036篇 |
1988年 | 4667篇 |
1987年 | 4673篇 |
1986年 | 4707篇 |
1985年 | 4450篇 |
1984年 | 3641篇 |
1983年 | 3204篇 |
1982年 | 2164篇 |
1979年 | 3203篇 |
1978年 | 2609篇 |
1977年 | 2232篇 |
1976年 | 2161篇 |
1975年 | 2350篇 |
1974年 | 2798篇 |
1973年 | 2853篇 |
1972年 | 2705篇 |
1971年 | 2544篇 |
1970年 | 2527篇 |
1969年 | 2370篇 |
1967年 | 2079篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
Waldrop MM 《Science (New York, N.Y.)》1987,236(4801):522-523
As Supernova 1987A in the Large Magellanic Cloud continues on its inexorable course-it has currently reached magnitude 3.3, with perhaps another magnitude of brightening to go in the next few months before it begins its long, slow fade into oblivion-astronomers are following its every step with avid interest. Some recent developments: 相似文献
984.
985.
Thromboembolic meningoencephalitis (TEME) caused by Huemophilus somnus infection was diagnosed for the first time in New Zealand in an eight month old bull calf. Clinical signs included pyrexia, excessive salivation, recumbency, opisthotonus and rigidity of the front legs. Multiple red, malacic foci (1-10 mm in diameter) were visible grossly on the surface of the cerebrum and cerebellum, and were scattered throughout the brain parenchyma. Histologically these lesions consisted of focal haemorrhage, necrosis and neutrophilic infiltration. Fibrin thrombi and colonies of gram negative bacteria were present in many small blood vessels within necrotic foci. An organism with the morphological and biochemical characteristics of Haemophilus somnus was cultured from the brain. Although TEME is an important disease of feedlot cattle in North America and Europe it is relatively uncommon in cattle grazing pasture and is therefore unlikely to become a major problem in New Zealand. 相似文献
986.
A field strain of Cooperia oncophora resistant to oxfendazole was isolated from a commercial cattle rearing property in Waikato, New Zealand. Resistance to oxfendazole was assessed by means of a faecal egg count depression test and an in vitro egg hatch test. This is the first documented case of anthelmintic resistance in Cooperia spp. and the first report of anthelmintic resistance in cattle in New Zealand. 相似文献
987.
988.
Recovery of Mycoplasma spp. from the Reproductive Tract of the Mare during the Estrous Cycle 下载免费PDF全文
Bermudez V Miller R Johnson W Rosendal S Ruhnke L 《The Canadian veterinary journal. La revue veterinaire canadienne》1987,28(8):519-522
The sites in the genital tract from which mycoplasmas could be recovered at various stages of the estrous cycle were studied in five Standardbred mares naturally infected with Mycoplasma. Mycoplasma equigenitalium and Mycoplasma subdolum were most frequently isolated from the clitoral fossa as compared to the vagina, cervix, and uterus. The lowest isolation prevalence was observed in the uterus. The recovery of Mycoplasma spp. from the clitoral fossa did not differ at any stage of the estrous cycle; however, recovery from the vagina, cervix, and uterus was variable during the cycle and more organisms were recovered on the day of ovulation than at any other time. From these results it was concluded that the clitoral fossa is the most likely “ecological niche” for Mycoplasma spp. in the mare. Ureaplasmas were not isolated. 相似文献
989.
990.