全文获取类型
收费全文 | 164625篇 |
免费 | 8780篇 |
国内免费 | 105篇 |
专业分类
林业 | 6573篇 |
农学 | 4743篇 |
基础科学 | 1130篇 |
18577篇 | |
综合类 | 31673篇 |
农作物 | 6395篇 |
水产渔业 | 7512篇 |
畜牧兽医 | 85204篇 |
园艺 | 1892篇 |
植物保护 | 9811篇 |
出版年
2018年 | 1950篇 |
2017年 | 2167篇 |
2016年 | 2085篇 |
2015年 | 1776篇 |
2014年 | 2145篇 |
2013年 | 6107篇 |
2012年 | 4087篇 |
2011年 | 5053篇 |
2010年 | 3289篇 |
2009年 | 3328篇 |
2008年 | 5036篇 |
2007年 | 4638篇 |
2006年 | 4525篇 |
2005年 | 4162篇 |
2004年 | 4174篇 |
2003年 | 4139篇 |
2002年 | 3991篇 |
2001年 | 5119篇 |
2000年 | 5143篇 |
1999年 | 3894篇 |
1998年 | 1636篇 |
1997年 | 1664篇 |
1995年 | 1944篇 |
1994年 | 1801篇 |
1993年 | 1710篇 |
1992年 | 3603篇 |
1991年 | 3881篇 |
1990年 | 3708篇 |
1989年 | 3787篇 |
1988年 | 3498篇 |
1987年 | 3667篇 |
1986年 | 3808篇 |
1985年 | 3660篇 |
1984年 | 2927篇 |
1983年 | 2652篇 |
1982年 | 1798篇 |
1981年 | 1673篇 |
1979年 | 2699篇 |
1978年 | 2242篇 |
1977年 | 1845篇 |
1976年 | 1811篇 |
1975年 | 1852篇 |
1974年 | 2401篇 |
1973年 | 2509篇 |
1972年 | 2480篇 |
1971年 | 2332篇 |
1970年 | 2177篇 |
1969年 | 1999篇 |
1968年 | 1640篇 |
1967年 | 1744篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
The dietary lysine requirement of juvenile red drum Sciaenops ocellatus was reevaluated in two separate experiments. In the first experiment, lyophilized red drum muscle was combined with an L-form crystalline amino acid premix to yield diets containing approximately 35% protein on a dry-matter basis. Gradations (0.25%) of L-lysine HCl were added to the basal diet containing approximately 1.0% lysine. Each diet was fed to triplicate groups of juvenile red drum initially weighing 6–7 g for 8 weeks. Based on growth and feed efficiency data, the lysine requirement (±SE) was determined to be 1.55% (±0.079%) of dry diet or 4.430% of dietary protein. In a second experiment, the lysine requirement of red drum was investigated with diets containing 35% intact protein from zein and red drum muscle. Each of the zein-based diets containing incremental levels of lysine was fed to triplicate groups of juvenile red drum initially weighing 1–2 g for 8 weeks. A crystalline amino acid test diet serving as a control in this experiment significantly outperformed the zein-based diets, and palatability of those diets was questionable due to an obvious change in feeding behavior of the fish. Due to the inferior performance of the fish fed the zein-based diets, the authors were not successful in determining a requirement with these diets. Thus, a lysine requirement of 1.55% of dry diet (4.43% of dietary protein) as determined in the first experiment is recommended for juvenile red drum. 相似文献
72.
73.
Meat regulations also involve game inspection. This publication deals with the regulations concerning furred game intended for slaughter and furred game hunted for food. 相似文献
74.
Abstract. Experiments were conducted for one year on two different soil types. On a clay soil straw was either (a) burnt, (b) baled leaving the stubble, or (c) chopped and spread. The soil was tine cultivated to depths of 5, 10 or 15 cm or ploughed to 20 or 30 cm before winter wheat was sown conventionally. In addition, a direct-drilled crop was sown after each straw treatment. On a silt loam soil the direct-drilled, tine cultivated to 15 cm and ploughed to 30 cm treatments following burning or chopping and spreading straw were repeated.
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
75.
R D Park 《Veterinary Clinics of North America: Equine Practice》1989,5(1):47-66
A complete radiographic examination of the equine foot consists of properly exposed, processed, and positioned radiographs. For radiographic interpretation, in addition to knowing radiographic signs of disease, a knowledge of normal radiographic anatomy and possible insignificant anatomic variations is necessary. 相似文献
76.
Efficacy of ivermectin treatment (0.2 mg/kg) against 28-day experimental infections of Parascaris equorum was determined in 18 pony foals6–17.5 weeks old. There were 6 foals in each group: nontreated control, ivermectin injectable or oral paste. In comparison with larvae found in the nontreated controls, ivermectin injectable or paste was 96.0% and 99.9% efficacious. There was a distinct difference in drug effect against the larger (ca 26mm.) vs the smaller (13–19mm) larvae by the 2 formulations of ivermectin. There were no adverse signs related to treatment of the young foals. 相似文献
77.
T R Thedford L W Johnson 《Veterinary Clinics of North America: Food Animal Practice》1989,5(1):145-157
Although there are notable infectious conditions that are capable of producing clinical disease in the NWC, overall, these species are quite healthy. Of the bacterial diseases, enterotoxemia caused by Clostridium perfringens types C and D would be deemed the most significant in North America, while type A also would be regarded as important in South America. Other important bacterial infections of potential concern are tuberculosis, Johne's disease, anthrax, malignant edema, actinomycosis, tetanus, and the South American condition referred to as alpaca fever, which, to date, has not been observed in North America. Fungal infections include classical ringworm, principally caused by Trichophyton spp., and the cases of coccidioidomycosis that are associated with the arid desert lands of the southwestern United States. Most notable of naturally occurring viral infections in the NWC would be rabies, ecthyma, and a recently described blindness neuropathy that has been associated with the equine herpesvirus I. NWC can be infected experimentally with agents causing hoof-and-mouth disease and vesicular stomatitis, but naturally occurring cases do not seem to occur. Serological evidence of exposure to many viral agents, including blue tongue, parainfluenza 3, bovine respiratory syncytial virus, bovine herpesvirus I, bovine viral diarrhea, influenza A, and rotavirus, has been demonstrated; however, no clinical disease associated with these agents, as yet, is apparent. 相似文献
78.
W Ahne J R Winton T Kimura 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(8):561-567
Infectious diseases remain one of the most important limitations to the successful propagation of aquatic animals. Most of the losses caused by pathogens in aquaculture could be prevented by health inspection, adequate environment and sound management practices. Effective control measures, mainly based upon 1) avoidance of pathogens 2) modification of the environment 3) improvement of host resistance 4) vaccination and 5) chemoprophylaxis are described. 相似文献
79.
A survey of the potential use of synthetic oligopeptides in the field of virology is given. The potential value of synthetic peptides as vaccines and diagnostic antigens is discussed. The advantages compared to conventional vaccines as well as the limitations, e.g. the poor efficiency of immune response, are described. 相似文献
80.
Three strip test kits which measure calcium and/or magnesium in mares' mammary secretions were compared and assessed for their accuracy in:- 1) measuring these electrolytes compared to standard laboratory measurements, and 2) predicting the time of parturition. Daily samples of mammary secretions were obtained pre-partum from 35 Thoroughbred mares and allocated a score. Measurement of mammary secretion calcium and/or magnesium by the strip tests and laboratory methods correlated significantly (P less than 0.001). The results obtained for prediction of parturition were analysed by two methods. Method i) indicated that the majority of mares had a maximum score on the day of birth. However, the second method of analysis included all prepartum scores and this demonstrated that maximum scores occurred on more occasions prior to the day of birth than on the day of birth itself. The number of nights spent attending mares, and the percentage of occasions when foaling was missed, were also calculated for given strip test scores. The results indicate that the test kits are not particularly accurate in predicting time of parturition although they are a reliable means of measuring mammary secretion calcium and/or magnesium. It is suggested that the test kits may be more helpful by indicating when it is not necessary to attend mares at night. 相似文献