全文获取类型
收费全文 | 79366篇 |
免费 | 4274篇 |
国内免费 | 94篇 |
专业分类
林业 | 3256篇 |
农学 | 2059篇 |
基础科学 | 465篇 |
8649篇 | |
综合类 | 15491篇 |
农作物 | 3147篇 |
水产渔业 | 3464篇 |
畜牧兽医 | 41874篇 |
园艺 | 854篇 |
植物保护 | 4475篇 |
出版年
2019年 | 729篇 |
2018年 | 1104篇 |
2017年 | 1218篇 |
2016年 | 1061篇 |
2015年 | 911篇 |
2014年 | 1207篇 |
2013年 | 2642篇 |
2012年 | 2139篇 |
2011年 | 2612篇 |
2010年 | 1644篇 |
2009年 | 1748篇 |
2008年 | 2638篇 |
2007年 | 2439篇 |
2006年 | 2309篇 |
2005年 | 2174篇 |
2004年 | 2106篇 |
2003年 | 2171篇 |
2002年 | 1954篇 |
2001年 | 2394篇 |
2000年 | 2443篇 |
1999年 | 1876篇 |
1998年 | 721篇 |
1997年 | 718篇 |
1996年 | 712篇 |
1995年 | 813篇 |
1993年 | 743篇 |
1992年 | 1556篇 |
1991年 | 1753篇 |
1990年 | 1637篇 |
1989年 | 1647篇 |
1988年 | 1474篇 |
1987年 | 1535篇 |
1986年 | 1597篇 |
1985年 | 1549篇 |
1984年 | 1184篇 |
1983年 | 1057篇 |
1982年 | 704篇 |
1979年 | 1152篇 |
1978年 | 894篇 |
1977年 | 755篇 |
1975年 | 774篇 |
1974年 | 1024篇 |
1973年 | 1025篇 |
1972年 | 1043篇 |
1971年 | 994篇 |
1970年 | 988篇 |
1969年 | 905篇 |
1968年 | 811篇 |
1967年 | 800篇 |
1966年 | 732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Ohne Zusammenfassung 相似文献
112.
E. 《Forstwissenschaftliches Centralblatt》1909,31(3):182-184
Ohne Zusammenfassung 相似文献
113.
E. Knoche 《Forstwissenschaftliches Centralblatt》1904,26(7):371-393
Ohne Zusammenfassung 相似文献
114.
Three mature Quarter Horse geldings were used in 2 Latin square experiments to measure the effect of cutting and vacuum cleaning of oats on digestibility. The horses were fed at the maintenance level of digestible energy (DE) as recommended by the NRC.12The data were analyzed by Latin square analysis of variance, and Tukey's t test was used to determine any differences between specific means.No significant differences among treatments were observed during either experiment, indicating that the digestibility of nutrients from oats was not affected by cutting and vacuum cleaning. Differences in the digestibility of the ether extract (EE) fraction between periods of experiment 1 were noted. 相似文献
115.
116.
Sarah A. Slaughter Andrew D. Eitzer Sara E. Tolliver Sarah N. Holman Sara A. Colopy Seamus E. Hoey Samantha J. Loeber 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(5):515
A 14-week-old male unilaterally cryptorchid Clumber spaniel was presented for acute lethargy. Physical examination revealed abdominal pain, and a single testis was palpated in the scrotum. Abdominal ultrasound and computed tomography (CT) revealed a poorly vascularized, ovoid structure immediately caudal to the left kidney with scant regional peritoneal effusion. Left intra-abdominal testicular torsion was confirmed at surgery, and routine cryptorchidectomy was performed. The patient recovered uneventfully from anesthesia and surgery.Key clinical message:The most common CT characteristics of testicular torsion were present in this case and correlated well with sonographic findings to allow for rapid, accurate diagnosis and surgical planning of unilateral, non-neoplastic, intra-abdominal cryptorchid testicular torsion in a juvenile dog. Contrast enhanced CT facilitated accurate localization of the undescended testis and evaluation of testicular perfusion and may be a useful alternative to ultrasound for diagnosing testicular torsion, especially in indeterminate cases. 相似文献
117.
The conformation of the urethra, the position of the bladder neck and the distance between the external urethral orifice and the cranial pubic brim were compared in 30 continent and 30 incontinent bitches with incompetence of the urethral sphincter mechanism, using the measurements made from vagino-urethrograms. The bladder neck was significantly (P less than 0.001) further caudal in incontinent dogs than in continent dogs. Its position was not affected by neutering and could not be explained by the degree of urethral curvature. The distance from the external urethral orifice to the cranial pubic brim was correlated (P less than 0.001) with bodyweight but was not significantly different in the continent and incontinent bitches. In neutered animals, the distance between the cranial pubic brim and the external urethral orifice was significantly (P less than 0.05) shorter than in entire animals. 相似文献
118.
The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii. 相似文献
119.
120.
Effects of green pruning on growth and stem shape of Eucalyptus nitens (Deane and Maiden) Maiden 总被引:2,自引:0,他引:2
An experiment was established in two high quality Eucalyptus nitens Deane and Maiden (Maiden) plantations in Tasmania. At the start of the experiment the trees were three years old and the plantations were on the point of canopy closure. Selected trees were pruned to remove 0, 50% or 70% of the lower green crown length, and each was surrounded by eight unpruned trees. The 50% treatment had no impact on height or diameter increment in the two years following treatment, but removal of 70% of the lower crown length resulted in significant decreases in both height and diameter increment. There were no changes in the height of 50%-pruned trees relative to the height of surrounding unpruned trees (relative height), and it was concluded that dominance would not be affected by this treatment. The relative height of 70%-pruned trees was less at one site, and this treatment may result in loss of dominance. Stem taper was generally unaffected by either pruning treatment. Changes in stem form were restricted to trees in the 70% pruning treatment and were only transient. It was concluded that removal of 50% of the lower green crown length is an appropriate level of pruning for the species provided that growth rates are rapid and pruning is timed to coincide with canopy closure. Since dominance was unaffected by this level of pruning, thinning at the time of pruning is unnecessary. It may be possible to minimise the impact on growth of higher levels of pruning by thinning at the time of pruning. 相似文献