全文获取类型
收费全文 | 135732篇 |
免费 | 7789篇 |
国内免费 | 70篇 |
专业分类
林业 | 5578篇 |
农学 | 4647篇 |
基础科学 | 863篇 |
17509篇 | |
综合类 | 18999篇 |
农作物 | 5089篇 |
水产渔业 | 7092篇 |
畜牧兽医 | 72983篇 |
园艺 | 1802篇 |
植物保护 | 9029篇 |
出版年
2020年 | 1172篇 |
2019年 | 1410篇 |
2018年 | 2231篇 |
2017年 | 2492篇 |
2016年 | 2297篇 |
2015年 | 2000篇 |
2014年 | 2453篇 |
2013年 | 5733篇 |
2012年 | 4355篇 |
2011年 | 5168篇 |
2010年 | 3503篇 |
2009年 | 3548篇 |
2008年 | 5160篇 |
2007年 | 4974篇 |
2006年 | 4643篇 |
2005年 | 4264篇 |
2004年 | 4113篇 |
2003年 | 4180篇 |
2002年 | 3810篇 |
2001年 | 4776篇 |
2000年 | 4643篇 |
1999年 | 3750篇 |
1998年 | 1471篇 |
1997年 | 1452篇 |
1996年 | 1342篇 |
1995年 | 1600篇 |
1994年 | 1328篇 |
1993年 | 1359篇 |
1992年 | 2762篇 |
1991年 | 2902篇 |
1990年 | 2866篇 |
1989年 | 2898篇 |
1988年 | 2610篇 |
1987年 | 2595篇 |
1986年 | 2541篇 |
1985年 | 2400篇 |
1984年 | 1957篇 |
1983年 | 1717篇 |
1982年 | 1156篇 |
1979年 | 1653篇 |
1978年 | 1285篇 |
1977年 | 1135篇 |
1976年 | 1103篇 |
1975年 | 1164篇 |
1974年 | 1358篇 |
1973年 | 1448篇 |
1972年 | 1382篇 |
1971年 | 1198篇 |
1970年 | 1247篇 |
1969年 | 1147篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Parra MD Tuomola M Cabezas-Herrera J Cerón JJ 《Veterinary research communications》2006,30(2):113-126
A time-resolved immunofluorometric assay (TR-IFMA) was developed for the determination of C-reactive protein (CRP) in canine
serum. CRP was isolated from canine acute-phase serum by affinity chromatography on agarose coupled with phosphorylethanolamine.
This isolated dog CRP was used as standard to calibrate the assay. Intra-assay and inter-assay coefficients of variation were
in the ranges 5.3–7.1% and 4.8–13.3%, respectively. Accuracy, evaluated by adding 2 and 10 μg/ml of CRP to serum samples,
provided recoveries of 99.9% and 106.8%. High correlation was found between CRP measurements by TR-IFMA and a by commercial
enzyme-linked immunosorbent assay (R2 = 0.98). The limit of detection for the TR-IFMA method was 0.000067 μg/ml and the measurement of CRP in serial dilutions
of acute-phase dog sera generated curves with the same slope as the one constructed with purified CRP. The TR-IFMA provides
a precise, accurate and highly sensitive assay for CRP determination in dog samples. CRP levels in dogs with different diseases
ranged between 10.2 and 210.7 μg/ml and were significantly higher than those observed in healthy dogs (< 7.1 μmg/ml). 相似文献
922.
Analysis of the toxic potential of Palicourea corymbifera (Müll. Arg.) Standl. in laboratory animals
Ribeiro de Assis JC Suffredini IB Moreno PR Young MC Varella AD Younes RN Bernardi MM 《Research in veterinary science》2006,80(2):209-217
Palicourea species may produce bovine toxicity. Palicourea corymbifera grows in terra firme forests within the Amazon rain forest and in Tropical America, particularly in spots that gave place to gazing areas. The lyophilized extract done with the aerial organs of P. corymbifera were analyzed in male and female mice. Results revealed a significant toxicity: LD50 was 1.10 (1.04-1.15)g/kg for male mice, and 1.05 (1.00-1.10)g/kg for female mice. Locomotion was affected as well as there were reflexes linked to environmental stimuli in addition to changes in posture. Progressive central nervous system stimulus signs such as trembling and convulsions were detected, the latter followed by the animal's death. Macroscopic histopathological exams performed on the liver, kidneys and lungs of mice submitted to necropsy did not indicate the existence of lesions. General activity of animals, measured in an open field, was reduced as a result of the administration of the extract. Duration of locomotion and rearing frequency were reduced, in opposition to an increase in the duration of immobility. Thin layer chromatography analysis showed that monofluoroacetic acid is present in the lyophilized extract, but other qualitative techniques as gas chromatography/mass spectrometry and 19F nuclear magnetic resonance showed that the MFAA was not present in the extract, and that the toxicity is related to other compound, although the toxic profile is very similar to that of MFAA. P. corymbifera was shown to be significantly toxic to laboratory animals and investigation of the possible toxic substance shall be done. 相似文献
923.
Christopherson PW Insalaco TA van Santen VL Livesey L Bourne C Boudreaux MK 《Veterinary pathology》2006,43(1):78-82
Glanzmann thrombasthenia (GT) is an inherited, intrinsic platelet defect characterized by a quantitative or qualitative change in the platelet glycoprotein complex IIb-IIIa (integrin alpha(IIb)beta3). The subunits are encoded by separate genes and both subunits must be expressed for a stable complex to form on the platelet surface; therefore, a defect in either gene can result in GT. 相似文献
924.
Galán A Martín-Suárez EM Granados MM Gallardo JM Molleda JM 《Veterinary ophthalmology》2006,9(1):7-15
Fluorescein angiography without sedative or anesthetic agents was evaluated in 20 normal goats and 20 normal sheep. All of the angiographic phases were observed using 20 mg/kg fluorescein IV in both species. Fundus fluorescein angiography results revealed wide stars of Winslow in the tapetal fundus, central or marginal flow during the first part of the arterial phase, delayed filling of the focal areas in the choroid near the optic disc that often coincided with others in the disc, and lack of evidence of the 'striate area' in the tapetal fundi. In goats, the angiographic times were 6.54+/-1.25 s for the arterial phase (TA), 7.80+/-1.37 s for the arterio-venous phase (TAV), and 14.13+/-2.01 s for the venous phase (TV). I1: 1.30+/-0.30 s (time elapsing between TA and TAV), and I2: 6.20+/-1.60 s (time elapsing between TAV and TV). In sheep, times were 9.54+/-2.18 s TA, 11.73+/-2.10 s TAV, and 20.86+/-2.74 s TV. I1: 2.04+/-0.75 s and I2: 8.98+/-2.47 s, respectively. Due to the large size of the fundic vessels in sheep and goats, fluorescein angiography of the retinal vasculature can facilitate the study of the different vascular diseases in these species. 相似文献
925.
926.
Gardner RB Hart KA Stokol T Divers TJ Flaminio MJ 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2006,20(1):198-203
A 5-week-old Fell Pony colt was examined for fever, lethargy, and anemia. The colt had been lethargic for 1 week before examination, had continued to nurse, had a temperature of 104°F (40°C), and was treated with ceftiofur (5 mg/kg IM q12h). Approximately 36 hours before examination, the colt developed watery diarrhea. Blood work performed by the referring veterinarian on the day of admission revealed a PCV of 10%. 相似文献
927.
Shannon C. Thorum Sarah S. Comstock Shelly N. Hester Jill M. Shunk Marcia H. Monaco Sharon M. Donovan 《Veterinary immunology and immunopathology》2013,151(1-2):63-72
Bronchial-associated immune development is critically important to protect neonates from respiratory infections. Herein, bronchial-associated immune development in formula-fed and sow-reared pigs is described. Colostrum-fed newborn piglets were fed medicated sow milk replacer formula beginning at 48 h of life or remained with the sow. Blood and tissues were sampled at one-week (d7) and three-weeks (d21) of age. Lymphocyte subpopulations, including T helper 2, cytotoxic T, memory T, and NK cells, in peripheral blood, mediastinal lymph nodes, and thoracic lymph nodes were identified using flow cytometry. Additionally, IL-1β, IL-6, IL-12, TNFα, TGF-β1, TGF-β2, IFNα, IFNβ, and dectin gene expression were analyzed by quantitative RT-PCR. Total IgG, IgM, and IgA concentrations in serum were analyzed. Dietary and developmental effects were observed. This set of baseline measurements provides a framework for future respiratory challenge studies where the effects of diet on the neonate's ability to resist and/or recover from infection can be tested. 相似文献
928.
Terrie A. Becerra David M. Engle R. Dwayne Elmore Samuel D. Fuhlendorf 《Strength and Conditioning Journal》2013,66(5):529-538
Recent opposition to the rangeland management paradigm of achieving uniform, moderate grazing across entire landscapes has emerged because heterogeneity is recognized as the foundation of biodiversity, ecosystem resilience, and multifunctionality of agricultural landscapes. Agriculture production goals appear to drive the traditional rangeland management focus on homogeneity and uniformity. To determine if preference for homogeneity is a broadly applicable social construct or one limited to agricultural producers, we determined preferences for heterogeneous grassland landscapes expressed by three study populations—managers of working lands (ranchers), natural resource professionals (grassland/rangeland specialists), and the general population living in rangeland regions within the US Great Plains. We distributed surveys that included photographs of landscapes and patterned images to assess preference. Preference for heterogeneous landscapes among ranchers, natural resource professionals, and the general population in our study area were generally consistent with the central paradigm of managing rangeland for homogeneity. However, we discovered that people, across geographic location and population group, clearly prefer heterogeneous patterned images to homogeneous patterned images. This suggests that preference for homogeneity is acquired. 相似文献
929.
M.N. Lubell B.B. Cutts L.M. Roche M. Hamilton J.D. Derner E. Kachergis K.W. Tate 《Strength and Conditioning Journal》2013,66(6):609-620
This paper analyzes rancher participation in conservation programs in the context of a social-ecological framework for adaptive rangeland decision-making. We argue that conservation programs are best understood as one of many strategies of adaptively managing rangelands in ways that sustain livelihoods and ecosystem services. The framework hypothesizes four categories of variables affecting conservation program participation: operation/operator characteristics, time horizon, social network connections, and social values. Based on a mail survey of California ranchers, multinomial logit models are used to estimate the impact of these variables on different levels of rancher involvement in conservation programs. The findings suggest that ranchers with larger amounts of land, an orientation towards the future, and who are opinion leaders with access to conservation information, are more likely to participate in conservation programs. 相似文献
930.
Lenhardt L Cigankova V Zibrin M Kocisova J Tomkova I Sabo V Boda K Dadasheva OA Gurieva TS Mozes S 《Acta veterinaria》2001,70(2):127-131
The effect of microgravity on functional development of the small intestine of Japanese quails incubated for 2-3 d and hatched on the orbital station MIR was examined. After 5 d of space flight duodenal and jejunal alkaline phosphatase (AP) activity of the experimental group was compared with the AP activity in quails of the same age hatched on the Earth (laboratory controls). Short-term microgravity leading to decreased food intake resulted in significant increase of AP activity in both duodenal and jejunal enterocytes (P<0.001) of the experimental quails. The results suggest that increased AP activity probably reflects the delayed functional development of the small intestine as a consequence of inappropriate food intake during non-physiological conditions of space flight. 相似文献