全文获取类型
收费全文 | 105521篇 |
免费 | 5475篇 |
国内免费 | 52篇 |
专业分类
林业 | 4309篇 |
农学 | 3039篇 |
基础科学 | 729篇 |
11684篇 | |
综合类 | 20720篇 |
农作物 | 4296篇 |
水产渔业 | 4631篇 |
畜牧兽医 | 54330篇 |
园艺 | 1195篇 |
植物保护 | 6115篇 |
出版年
2018年 | 1204篇 |
2017年 | 1332篇 |
2016年 | 1284篇 |
2015年 | 1093篇 |
2014年 | 1263篇 |
2013年 | 3933篇 |
2012年 | 2566篇 |
2011年 | 3186篇 |
2010年 | 2078篇 |
2009年 | 2055篇 |
2008年 | 3205篇 |
2007年 | 2937篇 |
2006年 | 2803篇 |
2005年 | 2638篇 |
2004年 | 2744篇 |
2003年 | 2678篇 |
2002年 | 2621篇 |
2001年 | 3272篇 |
2000年 | 3288篇 |
1999年 | 2440篇 |
1998年 | 1070篇 |
1997年 | 1081篇 |
1995年 | 1251篇 |
1994年 | 1164篇 |
1993年 | 1121篇 |
1992年 | 2362篇 |
1991年 | 2531篇 |
1990年 | 2438篇 |
1989年 | 2493篇 |
1988年 | 2272篇 |
1987年 | 2349篇 |
1986年 | 2484篇 |
1985年 | 2394篇 |
1984年 | 1918篇 |
1983年 | 1773篇 |
1982年 | 1165篇 |
1981年 | 1123篇 |
1980年 | 1025篇 |
1979年 | 1762篇 |
1978年 | 1424篇 |
1977年 | 1146篇 |
1976年 | 1130篇 |
1975年 | 1165篇 |
1974年 | 1524篇 |
1973年 | 1610篇 |
1972年 | 1584篇 |
1971年 | 1515篇 |
1970年 | 1408篇 |
1969年 | 1262篇 |
1967年 | 1094篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
A review on the biology, epidemiology, pathogenesis and diagnosis of Otodectes cynotis in dogs and cats is presented. Additionally, three cases of generalized otodectic mange in dogs are described. 相似文献
132.
Laurence O. Whiteley DVM PhD Samuel K. Maheswaran BVSc PhD Douglas J. Weiss DVM PhD Trevor R. Ames DVM MS Mathur S. Kannan BVSc PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(1):11-22
The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases. 相似文献
133.
S K Maheswaran D J Weiss M S Kannan E L Townsend K R Reddy L O Whiteley S Srikumaran 《Veterinary immunology and immunopathology》1992,33(1-2):51-68
To further define the role of Pasteurella haemolytica A1 leukotoxin in the pathogenesis of bovine pneumonic pasteurellosis, its in vitro effects on bovine neutrophils were investigated. Leukotoxin-containing culture supernatant, from P. haemolytica, stimulated a neutrophil respiratory burst as measured by the generation of oxygen-derived free radicals O2- and H2O2. This effect was immediate because preincubation of neutrophils with the culture supernatant for 5 min or longer substantially suppressed this respiratory burst. This suppression was due to cytolysis of the neutrophils. Prolonged incubation of neutrophils with the same culture supernatant caused further cytolysis and degranulation. Heat-inactivated P. haemolytica culture supernatant that had lost its cytotoxic properties failed to stimulate respiratory burst by neutrophils. Furthermore, the respiratory burst, cytolysis and degranulation were abrogated only by leukotoxin-neutralizing monoclonal and polyclonal antibodies, but not by antibodies against the lipopolysaccharide. These studies show that the leukotoxin component in the culture supernatant was responsible for the generation of oxygen-derived free radicals and proteolytic enzymes from neutrophils which may participate in direct lung injury. 相似文献
134.
R M Bednarski 《Veterinary Clinics of North America: Small Animal Practice》1992,22(2):273-275
Opioids produce unpredictable anesthesia that is associated with poor muscle relaxation, prolonged onset, and relatively difficult intubation. They often induce bradycardia, which must be countered with atropine or glycopyrrolate, and hypoventilation, which requires ventilatory support. Return to consciousness is often delayed, making postoperative assessment of the patient's condition difficult. Finally opioid induction is relatively expensive compared with other anesthetic induction regimens. 相似文献
135.
E Ogawa A Kawakami T Yagi T Amaya H Fujise R Takahashi 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(1):57-62
Oxidative damage to the membrane in canine erythrocytes with inherited high Na, K-ATPase activity (HK cells) was compared with that in normal canine cells (LK cells). When 30 mM beta-acetylphenylhydrazine (APH) was applied to HK and LK cells, lipid peroxidation and hemoglobin denaturation occurred. Lipid peroxidation determined from malondialdehyde (MDA) formation was significantly lower in HK than in LK cells so far as endogenous glutathione (GSH) concentration was maintained at appropriate levels. With the depletion of GSH, MDA formation was accelerated and difference between HK and LK cells was not significant. Denatured hemoglobin bound to the membrane protein was less in HK than in LK cells. During incubation with APH, osmotic fragility increased markedly in LK cells, while HK cells showed very little change. The amounts of total lipid, total and free cholesterol, glycolipid, phospholipid and fatty acids were essentially the same in both cell types. Fatty acid compositions showed very small differences. The membrane of HK cells thus appear to have greater protection against oxidative damage induced by APH, owing to the presence of excess GSH in HK cells. The capability of HK cells to withstand oxidative damage would not be due to differences in membrane lipid compositions. 相似文献
136.
I J Lean R L Baldwin H F Troutt M L Bruss J C Galland T B Farver J Rostami L D Weaver C A Holmberg 《American journal of veterinary research》1992,53(5):731-741
Metabolic and production responses are reported for 72 cows treated with bovine somatotropin (BST) for 30 days starting at day 70 of lactation. Of these 72 cows, 48 had been exposed in the preceding lactation to long-term treatment with BST at 3 dosages and 24 (controls) had not been given BST. Approximately half of the cows in each group were parity-2 cows, the rest were older. Comparisons between groups were made separately for parity-2, and older cows. Analyses, using pretreatment values of each variable as a covariate, indicated that older cows, but not parity-2 cows, significantly (P less than 0.05) increased milk production during treatment. Parity-2 cows, however, had a significantly higher milk fat percentage than controls following treatment. Cows treated with 51.6 or 86 mg BST/d in both parity groups had significantly higher serum-free fatty acids than controls. Estimated net energy balances were significantly lower for older treated cows, but did not significantly differ from controls for parity-2 treated cows. Older cows in the 86 mg of BST/d group tended to have higher concentrations of blood glucose than did older control-group cows. Treatment with BST did not significantly increase serum ketone concentrations in any group of animals, and none of the cows developed clinical ketosis during this period. Estimated net energy balance (ENEB) during treatment was a significant (P less than 0.05) covariate for free fatty acid concentrations in older cows and for milk fat percentage in parity-2 cows. Covariate adjusted analyses, using ENEB during treatment as a covariate, indicated that lipolytic stimuli already acting may be enhanced by treatment with BST, but a negative energy balance was not a necessary precondition for free fatty acid concentrations to increase following somatotropin treatment. Similarly, milk fat percentages for parity-2 treated cows were significantly (P less than 0.05) higher during treatment than controls when ENEB during treatment was used as a covariate. Increased milk fat concentrations in parity-2 treated cows were not associated with significant increases in the ratio of C18:C4-10 milk fatty acids, indicating that increased milk fat resulted from either an increase in incorporation of C18 fatty acids into milk fat coupled with an increase in de novo mammary synthesis of C4-10 milk fatty acids or an increase in C12-16 fatty acids that may arise either from increased tissue mobilization, from diet, or from de novo mammary synthesis. 相似文献
137.
T R Kasari T S Taylor A N Baird E L Morris 《Journal of the American Veterinary Medical Association》1992,201(7):1053-1057
Osteolytic defects were detected radiographically in the distal sesamoid bone of a 16-month-old Bralers heifer, in the middle phalanx of a 14-month-old American Gray Brahman bull, and in the distal phalanx of a 3-year-old American Gray Brahman bull. The articular cartilage was damaged in each animal because of osteolysis or pathologic fracture. After each animal was anesthetized and positioned in lateral recumbency, the lesions were curetted and packed with cancellous bone harvested from the same animal's tuber coxae. Basic postoperative management involved stall rest and immobilization of the graft site with a fiberglass cast (42 to 79 days), after which a support bandage was used for approximately 2 weeks. Recurrence of lameness has not been observed in these animals for 60 months, 58 months, and 21 months, respectively. These cases exemplify the benefit of using an autogenous cancellous bone graft for treatment of severe osteolysis of a digit in cattle. 相似文献
138.
M G O'Brien R J Boudrieau G N Clark 《Journal of the American Veterinary Medical Association》1992,201(11):1760-1765
The medical records from 44 dogs with traumatic luxation of the cubital joint were reviewed. Closed reduction was performed in 35 dogs, and open reduction in 9 dogs. Excellent or good results were achieved in 31 of 35 dogs (88.6%) treated by closed reduction and in 5 of 9 dogs (55.6%) treated by open reduction. Collateral ligament repair, performed in 5 dogs, did not appear to affect the prognosis. Factors such as body weight and type and duration of external coaptation also did not appear to influence the outcome. Increased dysfunction associated with open reduction most likely was caused by the chronic nature of the dislocation, iatrogenic damage to the articular cartilage during reduction, or both. A good prognosis for return to normal function with minimal gait abnormality can be expected in most cases of traumatic luxation of the cubital joint treated by early closed reduction. 相似文献
139.
Two mungbean varieties, Guj-1 and PIMS-1 differing in their productivity potential, were examined to investigate their photosynthetic system at various stages of growth in relation to yield with two different dates of sowing. Vertical leaves were found to be beneficial. On the other hand, excessive leaf area during the later stages of growth may be detrimental to yield. Lower LAD at seedling stage and overall high NAR values may be reflected in higher grain yield. NAR declined as season progressed and this, in turn, may be related with increase in LAI. The grain yield was considerably more at the first date of sowing as compared to second date of sowing, the effect was being more pronounced in var. PIMS-1 . Various environmental factors recorded at two different dates of sowing and at various stages of growth indicated that these factors may have influenced the yield potential at two different dates of sowing. 相似文献
140.
Response time of broiler chickens to cimaterol: meat tenderness, muscle composition fiber size, and carcass characteristics. 总被引:4,自引:0,他引:4
The response time to cimaterol (CIM), a beta-adrenergic agonist, by broiler chickens for carcass characteristics, muscle composition, muscle fiber size, catheptic enzyme activity, and tenderness was determined. Two trials were conducted in which chickens were fed a control diet (CON) containing 0 ppm of CIM or a diet containing 1 ppm of CIM. Trial 1 consisted of 55, 31-d-old broiler chickens individually fed for up to 48 h. At 0, 6, 12, 18, 24, and 48 h, five CON and five CIM-fed chickens were killed. Trial 2 consisted of 160, 33-d-old broiler chickens group-fed for up to 14 d. At 2, 4, 6, 8, 10, 12, and 14 d, 10 CON and 10 CIM-fed chickens were killed. The breast muscle (BM) and leg muscle (LM) weight, cathepsin B and L activities, DNA, RNA, and protein concentration, and BM shear force value (SFV) were measured in both trials. Thigh muscle (TM) SFV were measured in Trial 2 only. Fiber size of BM was measured (five birds per treatment) at d 2, 6, 10, and 14. In Trial 1, BM weight and SFV were lower in CIM-fed birds at 6 h (P less than .05). In Trial 2 BM SFV were higher at d 8 (P = .06) and d 10 (P less than .05) in CIM-fed chickens. The SFV of CIM-fed chickens were higher at d 4, 8, 10, 12, and 14 (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献