全文获取类型
收费全文 | 150698篇 |
免费 | 8533篇 |
国内免费 | 912篇 |
专业分类
林业 | 6331篇 |
农学 | 4503篇 |
基础科学 | 1120篇 |
17913篇 | |
综合类 | 29554篇 |
农作物 | 5862篇 |
水产渔业 | 7048篇 |
畜牧兽医 | 76854篇 |
园艺 | 1936篇 |
植物保护 | 9022篇 |
出版年
2021年 | 1304篇 |
2020年 | 1433篇 |
2019年 | 1770篇 |
2018年 | 2362篇 |
2017年 | 2641篇 |
2016年 | 2377篇 |
2015年 | 2153篇 |
2014年 | 2575篇 |
2013年 | 5376篇 |
2012年 | 4771篇 |
2011年 | 5772篇 |
2010年 | 3716篇 |
2009年 | 3701篇 |
2008年 | 5342篇 |
2007年 | 5078篇 |
2006年 | 4670篇 |
2005年 | 4426篇 |
2004年 | 4102篇 |
2003年 | 4230篇 |
2002年 | 3905篇 |
2001年 | 4430篇 |
2000年 | 4508篇 |
1999年 | 3493篇 |
1998年 | 1388篇 |
1997年 | 1329篇 |
1995年 | 1435篇 |
1993年 | 1302篇 |
1992年 | 2766篇 |
1991年 | 3094篇 |
1990年 | 2979篇 |
1989年 | 2905篇 |
1988年 | 2651篇 |
1987年 | 2759篇 |
1986年 | 2833篇 |
1985年 | 2694篇 |
1984年 | 2193篇 |
1983年 | 1906篇 |
1979年 | 2033篇 |
1978年 | 1590篇 |
1977年 | 1328篇 |
1975年 | 1396篇 |
1974年 | 1855篇 |
1973年 | 1826篇 |
1972年 | 1827篇 |
1971年 | 1727篇 |
1970年 | 1679篇 |
1969年 | 1565篇 |
1968年 | 1321篇 |
1967年 | 1404篇 |
1966年 | 1300篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
K. Shiomitsu E. Sajo X. Xia D. W. Hunley G. E. Mauldin S. Li G. N. Mauldin 《Veterinary and comparative oncology》2008,6(3):193-200
The p53 gene is one of the important tumour suppressor genes that are involved with the cell survival signal pathway. One of the major functions of the p53 protein is to organize cell cycle regulation and induction of apoptosis for cellular genetic stability. It has been documented that more than 50% of all human cancers include a p53 mutation. We evaluated the difference in radiosensitivity between upregulating the expression of canine wild‐type p53 (cp53) in cultured osteosarcoma (D17) cells and naive D17 cells in vitro. We found that upregulating transfected cp53 D17 cells increased their radiation sensitivity in vitro, and there was a significant decrease (P < 0.009) in survival between cp53‐transfected D17 cells and naive D17 cells. In this experiment, a p53 enhancement ratio (p53ER) reached approximately 3.0 at high doses. The transfected cp53 D17 cells were significantly more radiosensitive at all doses evaluated than naive D17 cells, except at 1 Gy where too few data points were available. The p53ER increased rapidly at doses less than 4 Gy, achieving a maximum of about 3.0 for doses of 4 Gy and above. This study shows the enhanced radiosensitivity of the transfected p53 at clinically relevant doses. 相似文献
993.
SUSANNE A. E. B. BOROFFKA CHRISTIANE GÖRIG EDUARDO AURIEMMA MAARTJE H. A. C. PASSON‐VASTENBURG GEORGE VOORHOUT PAUL Y. BARTHEZ 《Veterinary radiology & ultrasound》2008,49(6):540-544
We describe the magnetic resonance (MR) imaging aspects of normal canine optic nerve, the diameter of the optic nerve as measured on MR images, and optimal MR sequences for the evaluation of the optic nerve using a 0.2 T MR unit. Three millimeter contiguous slides of the normal canine orbital region were acquired in transverse and dorsal oblique planes using a variety of tissue weighting sequences. It was apparent that detailed anatomic assessment of the optic nerve can be performed with low‐field MR imaging, but none of the sequences provided unequivocal superior image quality of the optic nerve. The mean diameter of the optic nerve sheath complex was 3.7 mm and of the optic nerve 1.7 mm. The intraorbital and intracanalicular parts of the optic nerve are consistently visible and differentiation between the optic nerve and optic nerve sheath complex is possible using low‐field MR systems. 相似文献
994.
995.
Amber L. Labelle Ralph E. Hamor Anne M. Barger Carol W. Maddox† Carrie B. Breaux 《Veterinary ophthalmology》2009,12(1):48-52
An 8-year-old male castrated Domestic Short-haired cat was examined for a 1-week history of blepharospasm and mucoid ocular discharge OS. Examination revealed ulcerative keratitis with stromal loss, stromal infiltrate, corneal edema, perilimbal vascularization and miosis. Cytology of the cornea revealed multiple dichotomously branching, septate fungal hyphae and severe, predominantly neutrophilic inflammation. PCR of the cytology samples confirmed the presence of Aspergillus flavus while fungal and bacterial cultures were negative. Treatment with topical 1% voriconazole solution was successful in resolving the keratomycosis. 相似文献
996.
A. de VRIES J. C. BREARLEY & P. M. TAYLOR 《Journal of veterinary pharmacology and therapeutics》2009,32(4):353-358
Volatile agent-induced hypotension may contribute to anaesthetic-related morbidity and mortality in horses. Dobutamine is commonly used to support arterial blood pressure (ABP) but little is known about its cardiovascular effects under clinical conditions. The aim of this clinical study was to elucidate the relationship between cardiovascular function and dobutamine infusion in isoflurane-anaesthetized horses. Forty-four horses anaesthetized for a variety of surgical procedures were studied. Premedication with acepromazine, methadone and detomidine was followed by induction of anaesthesia with ketamine and midazolam. Anaesthesia was maintained with isoflurane vaporized in oxygen. Routine anaesthetic monitoring was applied and cardiac output was measured by lithium dilution. Dobutamine was infused to maintain mean ABP above 70 mmHg. The relationship between dobutamine infusion rate, heart rate (HR), ABP and cardiac index was investigated immediately prior to ( T 0 ) and 15 min ( T 1 ) after dobutamine infusion started, followed at 30 min intervals ( T 2 , etc.). Arterial blood pressure increased significantly after dobutamine infusion started, HR and cardiac index increased significantly only with dobutamine infusion in combination with surgical stimulus. Although isoflurane decreases blood pressure mainly by vasodilation, dobutamine is an effective treatment for hypotension under clinical conditions in isoflurane-anaesthetized horses. The effect of dobutamine is not directly proportional to dose and surgical stimulus probably contributes to the cardiovascular improvement. 相似文献
997.
Among a vast number of forage trees, Vachellia karroo (Acacia karroo) remains one of the most widely distributed indigenous plant legumes in Southern Africa. The plant possesses some striking attributes, such as rapid growth rate, drought tolerance, adaptation to alkaline and acidic sterile soils, and resistance to a variety of edaphic and temperature changes. In past years V. karroo was recognised to be a major threat to rangeland productivity owing to its invasive nature. Research interest has shifted from its eradication as an unwanted plant to its utilisation as a feed resource for livestock. Extensive utilisation of V. karroo is mainly hindered by the presence of tannins and spines. Prospects to lessen the adverse effects of the anti-nutritional influences are now recognised. Vachellia karroo possesses desirable fatty acid profiles, and high protein and mineral contents that can improve animal performance. Presently, the use of V. karroo for goat production in communal areas is restricted owing to limited evidence for its nutritional value as animal feed. The present review, therefore, seeks to demonstrate the utility potential of V. karroo to improve growth performance, carcass characteristics, chevon quality, meat fatty acid profiles and as a natural anti-helminth for goats raised under an extensive system of production. 相似文献
998.
999.
Pharmacokinetics of gamithromycin after intravenous and subcutaneous administration in pigs 总被引:1,自引:0,他引:1
H. Wyns E. MeyerE. Plessers A. WatteynS. De Baere P. De BackerS. Croubels 《Research in veterinary science》2014
The aim of this study was to investigate the pharmacokinetic properties of gamithromycin in pigs after an intravenous (i.v.) or subcutaneous (s.c.) bolus injection of 6 mg/kg body weight. The plasma concentrations of gamithromycin were determined using a validated high-performance liquid chromatography–tandem mass spectrometry method, and the pharmacokinetics were noncompartmentally analysed. 相似文献
1000.
A.M.B. Veldhuis I.M.G.A. Santman-Berends J.M. Gethmann M.H. Mars L. van Wuyckhuise P. Vellema M. Holsteg D. Höreth-Böntgen F.J. Conraths G. van Schaik 《Preventive veterinary medicine》2014
Schmallenberg virus (SBV), a novel orthobunyavirus that rapidly spread throughout north-western Europe in 2011, caused congenital malformations in lambs and goat kids (Van den Brom et al., 2012) and newborn calves (Hoffmann et al., 2012). The impact of the SBV epidemic seemed limited however, in terms of the number of affected herds with malformed offspring (European Food Safety Authority, 2012b). Nevertheless, little is known with regard to the overall within-herd impact of SBV infection. The objective of the current study was to quantify the impact of the 2011 SBV epidemic on the productivity of dairy cattle in the Netherlands and the district of Kleve, Germany. 相似文献