全文获取类型
收费全文 | 150138篇 |
免费 | 8304篇 |
国内免费 | 93篇 |
专业分类
林业 | 6819篇 |
农学 | 5195篇 |
基础科学 | 933篇 |
17625篇 | |
综合类 | 26472篇 |
农作物 | 5850篇 |
水产渔业 | 7426篇 |
畜牧兽医 | 77061篇 |
园艺 | 1900篇 |
植物保护 | 9254篇 |
出版年
2018年 | 2155篇 |
2017年 | 2418篇 |
2016年 | 2233篇 |
2015年 | 1910篇 |
2014年 | 2366篇 |
2013年 | 5689篇 |
2012年 | 4071篇 |
2011年 | 5012篇 |
2010年 | 3299篇 |
2009年 | 3237篇 |
2008年 | 4897篇 |
2007年 | 4707篇 |
2006年 | 4517篇 |
2005年 | 4020篇 |
2004年 | 3857篇 |
2003年 | 3930篇 |
2002年 | 3646篇 |
2001年 | 4860篇 |
2000年 | 4818篇 |
1999年 | 3841篇 |
1998年 | 1524篇 |
1997年 | 1582篇 |
1995年 | 1660篇 |
1994年 | 1401篇 |
1993年 | 1440篇 |
1992年 | 2978篇 |
1991年 | 3105篇 |
1990年 | 3147篇 |
1989年 | 3103篇 |
1988年 | 2832篇 |
1987年 | 2778篇 |
1986年 | 2855篇 |
1985年 | 2749篇 |
1984年 | 2254篇 |
1983年 | 1987篇 |
1982年 | 1366篇 |
1979年 | 2135篇 |
1978年 | 1674篇 |
1977年 | 1397篇 |
1976年 | 1398篇 |
1975年 | 1590篇 |
1974年 | 1933篇 |
1973年 | 1953篇 |
1972年 | 1908篇 |
1971年 | 1836篇 |
1970年 | 1755篇 |
1969年 | 1672篇 |
1968年 | 1479篇 |
1967年 | 1543篇 |
1966年 | 1385篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
J A Ellis H Russell J Cavender T R Haven 《Veterinary immunology and immunopathology》1992,34(1-2):35-45
Cattle were immunized with vaccines containing modified-live or inactivated bovine respiratory syncytial virus (BRSV) and serum antibody responses were analyzed. Compared with preinculation values, at Day 14 after two biweekly immunizations with modified-live or inactivated vaccines there were significant increases in BRSV-specific titers in the sera of cattle that received both types of vaccines, as determined by a whole cell ELISA. Using a blocking ELISA and radioimmune precipitation it was determined that there was recognition of the fusion (F) protein by antibodies from cattle that received both types of BRSV antigens: however, virus neutralization assays revealed that only cattle that received modified live virus, either in monovalent or polyvalent vaccines, developed neutralizing antibodies to BRSV after two immunizations. These results indicate that inactivation of BRSV can lead to a dissociation between serological recognition of the F protein and virus neutralization in vaccinated cattle. 相似文献
23.
24.
Methods of augmenting bovine mononuclear cell responsiveness during physiological transitions of the udder may enhance resistance of the mammary gland to intramammary infections. Interleukin-2 is required for proliferation of T-lymphocytes and may contribute to B-lymphocyte proliferation. Recombinant bovine interleukin-2 (rBoIL-2) was evaluated as a potential immunoenhancer of bovine mammary gland mononuclear cells. Bovine mononuclear cells were isolated from five primiparous Holstein cows at 14-18 and 28-32 days of involution and at 7-13 days prior to parturition. Bovine blood and mammary gland mononuclear cells were highly responsive to rBoIL-2. Response of mammary gland mononuclear cells to rBoIL-2 was comparable with response of blood mononuclear cells. These data suggest that rBoIL-2 may be an effective immunoenhancer of bovine mononuclear cells during the non-lactating and prepartum periods. 相似文献
25.
Intravenous frusemide (1.0 mg/kg bwt) or phentolamine (0.33 mg/kg bwt) was given to 7 horses 1 h before exercise and their effects on pulmonary artery and aortic pressure changes during strenuous exercise were examined. Short-term near-maximal treadmill exercise (10 m/sec, 3 degrees incline) produced increases in heart rate, mean pulmonary artery pressure (PAP), mean aortic pressure (AP), and packed cell volume (PCV). Frusemide did not affect heart rate, PAP or PCV during exercise. Frusemide significantly decreased mean AP by 10 to 15 mmHg during exercise. Phentolamine produced an increase in heart rate relative to control only early in exercise but not during later, more strenuous, exercise. Phentolamine had no statistically significant effect on AP, PAP, or PCV, but a significant reduction was observed between 180 and 230 sec of exercise when PAP and AP were standardised against heart rate. Frusemide did not prevent horses from haemorrhaging during exercise in this study. Treatment with phentolamine did not sufficiently reduce the PAP and AP to test our hypothesis that a reduction in PAP and AP would eliminate EIPH. 相似文献
26.
E. Conde A. M. Moreno I. Martin-Lacave A. Fernandez y H. Galera 《Anatomia, histologia, embryologia》1992,21(1):94-100
A systematic immunohistochemical study of the ultimobranchial tubule (UBT) has been carried out in 45 Wistar rats of different ages (0, 5, 10, 15, 20, 25, 30, 60 and 120 days). The existence of calcitonin immunoreactive cells in the UBT wall has been demonstrated in a 5-days old rat. In addition, immunohistochemical studies for thyroglobulin revealed positive staining in follicular cells connected to the UBT and, occasionally, in isolated cells lying within solid clusters from the UBT. These last results together with the continued and repeated existence of numerous mitosis and PAS (+) microfollicles, apparently rising from the UBT, support the hypothesis that the ultimobranchial body (UBB) may contribute partially to the formation of a part of the follicular component. 相似文献
27.
The effect of porcine somatotropin (pST) on the lipid profiles of adipose tissue and muscle was investigated. Sixteen crossbred barrows were injected daily with either 3 mg of pST or a placebo. After slaughter, total lipid and fatty acid composition of raw subcutaneous (SC) adipose and intermuscular (IM) adipose tissue and longissimus muscle were determined. The SC adipose tissue from pST-treated pigs had a 7.5% decrease in total lipid content; specific fatty acids 16:0, 18:0, and 18:1(n-9)c decreased most. The IM fat from pST-treated pigs had lower levels of 16:0 and 20:0. There was no effect of pST treatment on the lipid profile of the longissimus muscle. The data suggest that pST treatment produces small but significant changes in the saturated fatty acid content of adipose tissue in pigs. 相似文献
28.
S A Dee 《Veterinary Clinics of North America: Food Animal Practice》1992,8(3):641-660
Porcine urogenital disease is the result of an imbalance of the normal microflora of the urinary and reproductive tracts brought about by hormonal, environmental, and management-related stress factors. Production and economic losses can be substantial, and diagnosing and treating the problem can be frustrating. Through proper hygiene, facility design, and culling procedures, the severity of the problem can be minimized. 相似文献
29.
Losses due to mortality and rejection of carcases and viscera in a population of 2,959,607 pigs admitted for slaughter in Singapore abattoirs between 1984 and 1986 were studied. Mortality losses were 2822 pigs (9.5 per 10,000 admissions) while 3039 whole carcases (10.3 per 10,000 admissions) were condemned at post-mortem examination. The main reason for rejection of carcases was pyaemia (30.3%). Kidneys and livers were the two main organs of economic value rejected. Rejection of kidneys was primarily due to nephritis (54.8%) while liver condemnation was mainly due to cirrhosis (38.6%). The financial loss from abattoir rejection was S$5.27 millions or S$1.78 per pig admitted. The value of abattoir condemnation data as a tool in preventive medicine is discussed. 相似文献
30.
H Planton 《Revue d'élevage et de médecine vétérinaire des pays tropicaux》1989,42(2):245-252
A research program to study tropical pastures used by domestic livestock was implemented in Senegal. During field studies, numerous information was collected together with many samples with three main aims: pasture composition, diet composition and relationship between each other. The so-called method of epiderms, more often used in temperate areas, was chosen for analyzing and comparing the botanical composition of 105 samples, e.g., shepherd's hand-picking, alimentary bolus and faeces collected during a twelve-month period. In view of the results, some methodological problems are raised and discussed. 相似文献