全文获取类型
收费全文 | 153561篇 |
免费 | 9120篇 |
国内免费 | 812篇 |
专业分类
林业 | 6379篇 |
农学 | 5407篇 |
基础科学 | 1204篇 |
19024篇 | |
综合类 | 27303篇 |
农作物 | 5750篇 |
水产渔业 | 7743篇 |
畜牧兽医 | 79121篇 |
园艺 | 2128篇 |
植物保护 | 9434篇 |
出版年
2020年 | 1379篇 |
2019年 | 1728篇 |
2018年 | 2526篇 |
2017年 | 2908篇 |
2016年 | 2629篇 |
2015年 | 2375篇 |
2014年 | 2777篇 |
2013年 | 5958篇 |
2012年 | 5036篇 |
2011年 | 6159篇 |
2010年 | 4132篇 |
2009年 | 3981篇 |
2008年 | 5724篇 |
2007年 | 5405篇 |
2006年 | 5115篇 |
2005年 | 4609篇 |
2004年 | 4264篇 |
2003年 | 4359篇 |
2002年 | 4019篇 |
2001年 | 5076篇 |
2000年 | 4980篇 |
1999年 | 3885篇 |
1998年 | 1585篇 |
1997年 | 1584篇 |
1996年 | 1378篇 |
1995年 | 1573篇 |
1994年 | 1430篇 |
1993年 | 1411篇 |
1992年 | 2986篇 |
1991年 | 3249篇 |
1990年 | 3080篇 |
1989年 | 3065篇 |
1988年 | 2739篇 |
1987年 | 2794篇 |
1986年 | 2837篇 |
1985年 | 2605篇 |
1984年 | 2205篇 |
1983年 | 1873篇 |
1982年 | 1292篇 |
1979年 | 1923篇 |
1978年 | 1533篇 |
1976年 | 1296篇 |
1975年 | 1474篇 |
1974年 | 1770篇 |
1973年 | 1719篇 |
1972年 | 1626篇 |
1971年 | 1555篇 |
1970年 | 1543篇 |
1969年 | 1478篇 |
1967年 | 1330篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Twenty-five experimental and five control hysterectomy derived pigs were raised colostrum free under specific pathogen-free conditions. The experimental pigs were first inoculated with A. suum eggs at 8 weeks of age, and a second dose of infective eggs was given 15 days later. They were necropsied from 4 to 10 days post second infection.The ulcers found in the stomach of these pigs were confined to the esophagogastric area. A sequence of epithelial changes, erosions, and ulceration was seen in the stratified squamous epithelium. Edema and hemorrhage were noted in the lamina propria and submucosa. Vascular changes in the area were characterized by thickening of the wall and presence of thrombi in arteries as well as cellular degeneration and vacuolization of the media and intima of the veins.Changes in the muscularis were characterized by edema and degeneration of the muscle cells, which later were replaced by fibroblasts and heavy infiltration by eosinophils.Three of the control pigs received one dose of A. suum eggs, and were killed one on each of the 8th, 9th, and 10th days post infection. The remaining two pigs received no infective material and were killed when they were 11 weeks of age. Neither the uninoculated pigs nor the once-inoculated animals developed ulcerations in their stomachs.The possible mechanisms by which esophagogastric lesions are produced following A. suum larval migrations are discussed. 相似文献
992.
993.
Rhea V. Morgan DVM Gregory B. Daniel DVM MS Robert L. Donnell DVM 《Veterinary radiology & ultrasound》1994,35(2):102-108
Magnetic resonance (MR) images of the normal eye and orbit of the dog and cat were acquired. T1-weighted, proton-density, and T2-weighed images were obtained in the oblique dorsal, straight sagittal, and oblique sagittal planes. Signal intensity for the various orbital structures differed among the three resonance techniques. T1-weighted images provided the greatest contrast of the retrobulbar structures. T-1 weighted images also had the highest signal to noise ratio, thereby providing the best anatomic detail. Anatomic components of the globe, retrobulbar structures and ocular adnexa were easily seen in all MR sections. The oblique dorsal and oblique sagittal planes were superior for evaluating the optic nerve in its entirety. 相似文献
994.
Richard A. Rockar VMD Kenneth S. Drobatz DVM Frances S. Shofer PhD 《Journal of Veterinary Emergency and Critical Care》1994,4(2):77-83
An animal trauma triage (ATT) scoring system was devised to provide stratification of veterinary trauma patient populations based upon severity of injury. A retrospective population of 101 trauma patients and a prospective population of 88 patients were used to evaluate the predictive power of the ATT scoring system for survival seven days after initial presentation of the emergency service. In Both groups, the mean ATT score for survivors was significantly lower than the mean ATT score for non-survivors. In a logistic regression mode, the ATT score was found to be a significant predictor of the likelihood of survival seven days after initial presentation for both populartions. Each point increase in the ATT score resulted in a 2.3–2.6 times decreased likelihood of survival. The ATT scoring system is a useful objective classification scheme for predicting the likelihood to survive a traumatic incident and can serve as prototype for severity of injuroy scoring systems for the veterinary trauma patient. 相似文献
995.
996.
997.
998.
Angiography of normal and diseased feet in cattle was carried out. In osteomyelitis of distal phalanx there was a narrowing of the digital artery with diminished vascular supply to the affected digit. An area of bone necrosis was found to be avascular. With overgrown hooves, narrowing of both the medial and lateral digital arteries with ill-defined laminar vessels was seen. The vascular pattern in cattle with cork screw claws was characterized by a dilated tortuous digital artery and a crowded arterial network resulting in increased vascular supply in the affected claw. Abrupt stricture of common digital artery, a crowded vascular network in the area of the middle phalanx and filling defects of terminal arches were demonstrated in animals with exostosis 相似文献
999.
SUMMARY Serum samples from 272 horses, some III, were tested by the microscopic agglutination test for the presence of antibody to 12 serovars of Leptospira interrogans. Serums from 41.5% of horses reacted to one or more of the serovars tested; the most common reactions were to L. interrogans serovar ballum (15.1%), L. interrogans serovar autumnalis (11.8%), L. interrogans serovar icterohaemorrhagiae (9.9%), L. interrogans serovar pomona (8.1%) and L. interrogans serovar hardjo (7.7%). 相似文献
1000.
G.J. Benson D.V.M. M.S. S.K. Kneller D.V.M. M.S. M. Manohar B.V.Sc. Ph.D. J.C. Thurmon D.V.M. M.S. 《Journal of Equine Veterinary Science》1982,2(3):90-94
A radiographic technique was used to identify and characterize segmental diaphragmatic movement in anesthetized ponies breathing spontaneously and with controlled ventilation with and without muscle relaxant-induced paralysis. Paralyzed mechanically ventilated ponies were also studied at varying peak inspiratory pressures. Controlled ventilation induced a change in pattern of diaphragmatic displacement which was accentuated by paralysis and increased inspiratory pressure. In conclusion, these results indicate that uneven distribution of inspired gases is not corrected by mechanical ventilation. Furthermore, increased tidal volume during mechanical ventilation is largely wasted because this increased volume is distributed principally to the poorly perfused nondependent lung. Thus, while mechanical ventilation can alleviate hypoventilation, i.e., will decrease PaCO2, it will be of limited value in relieving arterial hypoxemia due to venous admixture in anesthetized patients. 相似文献