全文获取类型
收费全文 | 322539篇 |
免费 | 17557篇 |
国内免费 | 684篇 |
专业分类
林业 | 24547篇 |
农学 | 14242篇 |
基础科学 | 2997篇 |
46978篇 | |
综合类 | 45615篇 |
农作物 | 17478篇 |
水产渔业 | 18272篇 |
畜牧兽医 | 138002篇 |
园艺 | 6561篇 |
植物保护 | 26088篇 |
出版年
2019年 | 3757篇 |
2018年 | 4350篇 |
2017年 | 4778篇 |
2016年 | 5102篇 |
2015年 | 4504篇 |
2014年 | 5885篇 |
2013年 | 16596篇 |
2012年 | 8116篇 |
2011年 | 10458篇 |
2010年 | 8007篇 |
2009年 | 8425篇 |
2008年 | 9719篇 |
2007年 | 8933篇 |
2006年 | 9377篇 |
2005年 | 8574篇 |
2004年 | 8401篇 |
2003年 | 8144篇 |
2002年 | 7567篇 |
2001年 | 8690篇 |
2000年 | 8254篇 |
1999年 | 7236篇 |
1998年 | 4416篇 |
1997年 | 4454篇 |
1996年 | 4174篇 |
1995年 | 4846篇 |
1994年 | 4296篇 |
1993年 | 4023篇 |
1992年 | 5980篇 |
1991年 | 6202篇 |
1990年 | 5998篇 |
1989年 | 6049篇 |
1988年 | 5451篇 |
1987年 | 5567篇 |
1986年 | 5634篇 |
1985年 | 5667篇 |
1984年 | 5032篇 |
1983年 | 4641篇 |
1982年 | 3597篇 |
1981年 | 3410篇 |
1980年 | 3328篇 |
1979年 | 4394篇 |
1978年 | 3824篇 |
1977年 | 3464篇 |
1976年 | 3163篇 |
1975年 | 3112篇 |
1974年 | 3726篇 |
1973年 | 3769篇 |
1972年 | 3543篇 |
1971年 | 3349篇 |
1970年 | 3212篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Thurley DC 《New Zealand veterinary journal》1985,33(9):157-158
Major erosion of the labial or lingual surfaces was seen in histological sections of deciduous teeth from three of 208 sheep from two farms. In one, the erosion extended through both the enamel and the dentine and thus exposed the pulp cavity which had developed pulpitis. In the other cases the erosion affected the cementum and dentine of the tooth root, and did not penetrate as far as the pulp cavity. Dentine proliferation occurred on the adjacent pulpal surface, however, although pulpitis was not evident. 相似文献
993.
994.
Ackerman LJ 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(6):185-188,189
Pemphigus and pemphigoid are uncommon dermatological entities in domestic animals and of a presumed autoimmune nature. In one form or another, they have been reported in the dog, cat, horse and goat. Although these diseases are considered to be bullous dermatoses, the clinical presentation may vary from ulcerative to exfoliative to proliferative depending on the individual condition. Currently, four variants of pemphigus are recognized (vulgaris, vegetans, foliaceus, erythematosus) and two of pemphigoid (bullous, cicatricial) although cicatricial pemphigoid has not yet been conclusively demonstrated in animals. Diagnosis is based on history, clinical signs, histopathology and immunopathology. Therapy must be immunosuppressive to be effective and is palliative rather than curative. 相似文献
995.
Sources of variation and prospects for improvement of productive efficiency in the dairy cow: a review 总被引:4,自引:0,他引:4
D E Bauman S N McCutcheon W D Steinhour P J Eppard S J Sechen 《Journal of animal science》1985,60(2):583-592
In this review, "productive efficiency" in dairy cows is defined as the yield of milk obtained in ratio to the nutritional costs associated with maintenance, milk synthesis and loss of body condition during lactation. Improvements in efficiency could occur as a result of changes in digestion and nutrient absorption, maintenance requirement, utilization of metabolizable energy for production or nutrient partitioning. Digestibility can be greatly enhanced by appropriate dietary manipulation. Likewise, it may be possible to reduce maintenance requirements and improve the efficiency with which metabolizable energy is used for milk synthesis by manipulation of the pattern of nutrients presented to tissues. However, these factors apparently do not respond to selection for increased milk yield, and little variation is observed among cows. In contrast, individual cows differ substantially in feed intake and in the partitioning of nutrients among body tissues. Techniques associated with genetic engineering and the early prediction of genetic merit have the potential to improve productive efficiency by manipulation of these processes. However, changes in nutrient partitioning and feed intake during lactation are coordinated by a complex network of controls that accommodate the nutrient requirements of each tissue while maintaining homeostatic balance. Future improvements in productive efficiency will therefore depend on our ability to understand the manner in which these controls operate. 相似文献
996.
1. Automatic weighing equipment was tested on a flock of 752 roaster chickens reared on litter to 10 weeks of age.
2. Mean body weights obtained automatically were lower than those obtained manually, mainly because of birds perching on the automatic weighing perch with part of their body in contact with the floor.
3. Birds observed on the weighing perch on one day of the week were 3–5 times more likely to use the perch again on the following 2 d than expected on the basis of random perch use by flock members. These birds were also more likely to be seen in the area immediately surrounding the perch than in similar areas elsewhere in the pen. 相似文献
997.
Shapiro JL Rostkowski C Little PB Smith-Maxie L Julian RJ Van Dreumel AA 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(5):155-158
Caprine β-mannosidosis, a fatal inherited deficiency of the lysosomal enzyme β-mannosidase, was diagnosed in neonatal female Nubian crossbred twin kids from a small herd near Guelph, Ontario. The kids had been tetraplegic since birth, with whole body tremors, abnormal nystagmus and an intention tremor of the head. 相似文献
998.
999.
Advances in immunoparasitology 总被引:1,自引:0,他引:1
E J Soulsby 《Veterinary parasitology》1985,18(4):303-319
A selective review of the advances in immunoparasitology is presented. It is selective simply because it is not feasible to embrace the whole field of parasitology within the compass of a single review paper, for if it were attempted, it would suffer undue abbreviation. Emphasis is placed on the advances in helminthology and especially the gastro-intestinal parasites of ruminants, an obvious selection because of the interests of the author. Reviews are always somewhat retrospective in outlook; to write a review at the present time is especially foolhardy since developments in biology are such that totally new concepts can arise almost overnight, as it were. This is a particularly healthy state, and the discipline of parasitology is caught up in the application and interpretation of molecular biological considerations. "Parasitism" is a field of increasing importance and challenge. 相似文献
1000.
The lungs of 334 pigs were obtained from two slaughter plants in Minnesota and examined in detail. Macroscopic and microscopic evaluation, direct fluorescence for Mycoplasma hyopneumoniae and bacterial culture were done on all of them and a subsample of 50 were selected for virus culture. Mycoplasma hyopneumoniae, Pasteurella multocida and Haemophilus spp. were detected in 24.0%, 34.1% and 27.0% of the lungs, commonly in conjunction with each other. One isolate of Haemophilus pleuropneumoniae serotype 2 was detected and this represents the first report of its presence in the United States. No virus was detected in any of the lungs. Lungs with both M. hyopneumoniae and Pasteurella multocida had the greatest amount of macroscopic pneumonia (9.8% of the lung). Lungs with M. hyopneumoniae or P. multocida alone had 4.9% and 5.2% of the lung involved with pneumonia respectively. Lungs with Haemophilus sp. Taxon "minor group" had 3.8% of the lung involved which was not significantly different from lungs with none of these organisms being detected (1.6%). There was a positive correlation between the extent of M. hyopneumoniae infection, as scored by FAT and the amount of macroscopic pneumonia present (r = 0.46; P less than 0.001). Likewise, there was a positive correlation between the estimated concentration of P. multocida present, as scored by the relative number of colonies on blood agar and the amount of macroscopic pneumonia present (r = 0.60; P less than 0.001). Microscopically, the amount of lymphoreticular proliferation, polymorphonuclear cells and alveolar macrophages were evaluated.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献