全文获取类型
收费全文 | 293270篇 |
免费 | 16876篇 |
国内免费 | 1423篇 |
专业分类
林业 | 24340篇 |
农学 | 14470篇 |
基础科学 | 3230篇 |
45809篇 | |
综合类 | 37153篇 |
农作物 | 17523篇 |
水产渔业 | 17502篇 |
畜牧兽医 | 119821篇 |
园艺 | 6663篇 |
植物保护 | 25058篇 |
出版年
2020年 | 3076篇 |
2019年 | 3855篇 |
2018年 | 4337篇 |
2017年 | 4816篇 |
2016年 | 5057篇 |
2015年 | 4631篇 |
2014年 | 5950篇 |
2013年 | 16584篇 |
2012年 | 7610篇 |
2011年 | 9909篇 |
2010年 | 8122篇 |
2009年 | 8517篇 |
2008年 | 8972篇 |
2007年 | 8076篇 |
2006年 | 8487篇 |
2005年 | 7769篇 |
2004年 | 7384篇 |
2003年 | 7230篇 |
2002年 | 6566篇 |
2001年 | 7347篇 |
2000年 | 7178篇 |
1999年 | 6336篇 |
1998年 | 4301篇 |
1997年 | 4343篇 |
1996年 | 4069篇 |
1995年 | 4654篇 |
1994年 | 4120篇 |
1993年 | 3789篇 |
1992年 | 5239篇 |
1991年 | 5550篇 |
1990年 | 5262篇 |
1989年 | 5149篇 |
1988年 | 4687篇 |
1987年 | 4829篇 |
1986年 | 4783篇 |
1985年 | 4855篇 |
1984年 | 4399篇 |
1983年 | 4032篇 |
1982年 | 3197篇 |
1981年 | 3019篇 |
1980年 | 2997篇 |
1979年 | 3868篇 |
1978年 | 3452篇 |
1977年 | 3096篇 |
1976年 | 2972篇 |
1975年 | 2837篇 |
1974年 | 3280篇 |
1973年 | 3234篇 |
1972年 | 2980篇 |
1971年 | 2882篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
271.
Verification by polymerase chain reaction of vertical transmission of Theileria sergenti in cows 总被引:2,自引:0,他引:2 下载免费PDF全文
Byeong K. Baek Kim B. Soo Jin H. Kim Jin Hur Bou O. Lee J. M. Jung Misao Onuma Anthony O. Oluoch Chang-Hyun Kim Ibulaimu Kakoma 《Canadian journal of veterinary research》2003,67(4):278-282
To evaluate the transplacental transfer of Theileria sergenti infection in cattle, we used DNA probes to detect T. sergenti in 6 pregnant cows and their calves. All the animals were monitored by parasitologic, serologic, and polymerase chain reaction (PCR) assays for a predicted 875-base-pair (bp) DNA product and a 684-bp amplicon detected by nested PCR in the blood and spleens of aborted fetuses. An open reading frame (ORF) starting at nucleotide 170 and terminating at position 1021 was shown to code for a polypeptide of 283 amino acid residues. All 6 dams and 5 calves were positive for T. sergenti in all tests. One calf was positive only with nested PCR. We conclude that transplacental transmission of T. sergenti is a significant problem. The relevance of the data in the programmed introduction of new (especially pregnant) animals into established clean herds needs serious consideration with regard to control of theileriosis and other tickborne diseases. 相似文献
272.
高温环境对甲状腺素值的影响还不清楚。在泌乳期间 ,饲养于 30℃的母猪与饲养于 2 0℃和 2 2℃的母猪相比 ,观察到甲状腺素的分泌不受影响(Prunier等 ,1997) ,降低不显著 (Barb等 ,1991)或显著降低 (MessiasdeBraganca等 ,1998)。刚断奶时 ,饲养于 30℃和饲养于 2 0℃的母猪 ,甲状腺素的浓度相近 ,而以后 (断奶后 8~ 12天 )则以饲养于30℃条件下者的甲状腺素浓度较低 (Prunier等 ,1997;MessiasdeBraganca等 ,1998)。高温对三碘甲状腺素浓度的影响比较明显 ,而在热应激期间 ,无论是泌乳母猪还是断奶后母猪 ,三碘甲状腺素的浓度都降低 (P… 相似文献
273.
M E Olson C J Hannigan P F Gaviller L A Fulton 《The Canadian veterinary journal. La revue veterinaire canadienne》2001,42(11):865-868
Dogs (n = 13), which had failed to be cured of giardiosis following chemotherapeutic measures, were treated with a Giardia vaccine (2-3 injections). Clinical signs resolved between 16 and 42 days postvaccination and cessation of fecal cyst shedding was between 21 and 70 days. Vaccination is a potential method of treating giardiosis in dogs. 相似文献
274.
275.
276.
Fireblight disease, caused by Erwinia amylovora was first detected in Bulgaria on quince in the region of Plovdiv in 1989. The disease was initially localized in that area but, during 1995/1997, due to favourable climate conditions, it became epidemic. Infected trees were grubbed out and destroyed. The main hosts are quince and pear (over 40% of affected trees), then apple, medlar and Cotoneaster. Containment measures undertaken by the Bulgarian NPPO are laid down in the Plant Protection Law, in Phytosanitary Regulation no. 1 for phytosanitary control, and in Phytosanitary Regulation no. 5 of 1996 (amended 1997) for containment of fireblight. Phytosanitary control is mainly focused on fruit‐tree nurseries and on the distribution of healthy plants for planting. In 2003, 41 protected zones and 29 protected sectors within infested areas have been established. 相似文献
277.
Abstract. The Pan‐European Soil Erosion Risk Assessment (pesera ) model was evaluated using existing soil erosion data collected under various types of climate, vegetation, landscape and soil conditions. The data used represent a variety of typical Mediterranean land uses such as winter wheat, vines, olives and bare, stony land prevailing in hilly areas. Using this data, the model was calibrated for sediment transport by overland flow and results compared to measured soil erosion values from runoff plots and a watershed on a monthly basis. The performance of the model was assessed statistically, showing that it can be satisfactorily used for predicting soil erosion rates under the conditions included in the study. The overall model estimate including all the available experimental data was 0.69 t ha?1 yr?1 with a maximum error of 1.49 t ha?1 yr?1. After validation, the model was applied to a small watershed (60 ha) of great ecological importance for the sea turtle Caretta caretta. For this purpose, soil and vegetation maps were compiled from all the necessary data for applying the model. The model was run for three years using daily data from an existing nearby meteorological station. The predicted and measured soil erosion rates for a 7‐month period were 0.31 t and 0.18 t, respectively. Application of the model to each mapping unit showed the over‐riding importance of land use for sediment generation under the given climatic conditions. Bare land, occupying 5.5% of the watershed area, generated up to 69% of the total sediments estimated for the watershed. It is concluded that the pesera model can be used as a regional diagnostic tool under a range of soil, topographic and climatic conditions for identifying the best land use type and vegetation cover to protect hilly areas from soil erosion. The calculated overall root mean square error for the model is 0.06 t ha?1 yr?1, compared to a soil erosion rate of 0.04 t ha?1 yr?1, which can be tolerated for protecting the area for the sea turtle. 相似文献
278.
279.
The French fisheries management regime is based on public and private ownership of fishing waters associated with a complex multilevel management system. A total of 730 operational commercial inland fisheries were examined by analysis of thematic interviews and questionnaires. Commercial fishermen are beginning to understand the nature of their own activity and its relationship to the concept of sustainable management. Nevertheless, fishermen have to face two major problems: first, they are poorly represented on decision making bodies where anglers are dominant, and secondly their activities are governed by two separate ministries. Opportunities for future development may lie in decision making at the catchment level. 相似文献
280.
L S Pelan-Mattocks B A Pesch M E Kehrli 《American journal of veterinary research》2001,62(11):1740-1744
OBJECTIVE: To develop an efficient and reliable method that accurately differentiates bovine lymphocytes from monocytes in leukograms. SAMPLE POPULATION: Blood samples from 30 healthy cows and 1 calf with bovine leukocyte adhesion deficiency. PROCEDURE: Flow cytometric analysis of intracellular complexity and CD45 expression on bovine leukocytes was compared with results for conventional light microscopy methods. Verification of leukocyte subpopulations determined by intracellular complexity and CD45 expression was conducted, using 2-color phenotypic analysis with selected monoclonal antibodies. RESULTS: The CD45 and side-scatter properties of bovine leukocytes clearly differentiated cell types, including neutrophils, eosinophils, monocytes, and lymphocytes. CONCLUSIONS AND CLINICAL RELEVANCE: This is a rapid assay that is simple to use. More importantly, it is more accurate than the conventional method that involves the use of blood slides and light microscopy, because of the ability of the assay to readily distinguish bovine monocytes and lymphocytes. Rapid preparation of samples and short analysis times allow for efficient and reliable examination of a large number of samples, and the task of viewing slides by light microscopy is eliminated. The labor-savings benefit of this procedure is most apparent in research environments that require frequent processing of batches of blood samples. 相似文献