全文获取类型
收费全文 | 148012篇 |
免费 | 8217篇 |
国内免费 | 87篇 |
专业分类
林业 | 5541篇 |
农学 | 4431篇 |
基础科学 | 1043篇 |
17238篇 | |
综合类 | 25745篇 |
农作物 | 5543篇 |
水产渔业 | 7513篇 |
畜牧兽医 | 76945篇 |
园艺 | 1845篇 |
植物保护 | 10472篇 |
出版年
2018年 | 1834篇 |
2017年 | 2022篇 |
2016年 | 1922篇 |
2015年 | 1664篇 |
2014年 | 2051篇 |
2013年 | 5500篇 |
2012年 | 3909篇 |
2011年 | 4935篇 |
2010年 | 3026篇 |
2009年 | 3057篇 |
2008年 | 4817篇 |
2007年 | 4625篇 |
2006年 | 4503篇 |
2005年 | 4186篇 |
2004年 | 4078篇 |
2003年 | 4075篇 |
2002年 | 4007篇 |
2001年 | 4724篇 |
2000年 | 4571篇 |
1999年 | 3726篇 |
1998年 | 1499篇 |
1997年 | 1530篇 |
1996年 | 1425篇 |
1995年 | 1772篇 |
1994年 | 1601篇 |
1993年 | 1526篇 |
1992年 | 3176篇 |
1991年 | 3301篇 |
1990年 | 3349篇 |
1989年 | 3341篇 |
1988年 | 3065篇 |
1987年 | 3150篇 |
1986年 | 3236篇 |
1985年 | 3108篇 |
1984年 | 2622篇 |
1983年 | 2327篇 |
1982年 | 1590篇 |
1981年 | 1490篇 |
1980年 | 1443篇 |
1979年 | 2320篇 |
1978年 | 1920篇 |
1977年 | 1632篇 |
1976年 | 1445篇 |
1975年 | 1551篇 |
1974年 | 2088篇 |
1973年 | 2092篇 |
1972年 | 2056篇 |
1971年 | 1818篇 |
1970年 | 1713篇 |
1969年 | 1574篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Bovine-leukosis virus (BLV; also termed ‘bovine-leukemia virus’) is a retrovirus that primarily affects lymphoid tissue of dairy and beef cattle. Our objective was to investigate the association between BLV infection and annual value of production (AVP) on dairy herds within the United States, as part of the USDA National Animal Health Monitoring System’s 1996 dairy study. 1006 herds (in 20 states) with at least 30 dairy cows were interviewed during 1996. The agar-gel immunodiffusion test was used to detect serum antibodies to BLV. 10–40 cows from each herd were tested and each tested cow was classified as negative or positive based on results of a single test.
A multivariable regression model was used with the 976 herds with complete data for analysis. When compared to herds with no test-positive cows, herds with test-positive cows produced 218 kg per cow (i.e. 3%) less milk. The average reduction in AVP was $ 59 per cow for test-positive herds relative to test-negative herds. For the dairy industry as a whole, BLV seropositivity was associated with loss to producers of $ 285 million and $ 240 million for consumers. Most of this $ 525 million industry loss was due to reduced milk production in test-positive herds. 相似文献
993.
994.
The development of Veterinary Medicine in the Soviet Occupation Zone in Germany and the former German Democratic Republic (GDR) is sketched in highlights. After the collectivization of agriculture (1960) a centralistically controlled national veterinary system was established. It was suited to the requirements of the industrially organized animal production. The successive classification of socialistic veterinary administration was associated with the following matters: the extension of veterinary subject matters, a vertical division of work with the aid of newly created technical veterinary professions, and a penetration of the profession with political guidelines. As the professional level of the veterinary system in the GDR was relatively high the reflection in retrospective needs to be evaluated in a differentiated way considering the textual and social conditions. In spite of centralism and indoctrination the veterinary system remained professionally autonomous with islands of political independence, which sustained the identity of this profession. The latter formed the base for self renewal of the East German veterinary system at the end of the socialistic area 1989/1990. 相似文献
995.
Rijnen MM Verstegen MW Heetkamp MJ Haaksma J Schrama JW 《Journal of animal science》2003,81(1):182-190
The effects of dietary nonstarch polysaccharides (NSP) on behavior and heat production in group-housed sows were studied. Twelve groups of six nonpregnant sows were fed one of four experimental diets that were similar in composition except for starch and NSP contents. Exchanging sugar beet pulp silage (SBPS) for tapioca created the difference in dietary starch and NSP ratio. On a dry matter (DM) basis, diets contained 0, 10, 20, or 30% SBPS. Sows were group-housed. Intake of fermentable NSP (fNSP) for diets containing 0, 10, 20, or 30% SBPS averaged 7.06, 9.18, 11.61, and 13.73 g x kg(-0.75) d(-1), respectively. Sows were fed, once a day at 0800. Dry matter intake for diets containing 0, 10, 20, or 30% SBPS, averaged 38.05, 38.38, 38.53, and 38.35 g x kg(-075) x d(-1), respectively, and ME intake averaged 523, 518, 514, and 493 kJ x kg(-0.75) x d(-1), respectively. On average, sows spent 177 min/d on physical activity, of which 8.8% was spent on eating. Time spent in physical activity was affected by diet (P = 0.005). Sows fed 0 or 10% SBPS spent more time on physical activity than sows fed 20 or 30% SBPS (P = 0.002). Energy cost of physical activity averaged 464 kJ x kg(-0.75) x d(-1) (standard estimated mean of 31) and was similar for diets (P = 0.679). Total heat production (HP) and activity-related heat production (AHP) were affected by diet (P < 0.05). Sows tended to be quieter when fNSP intake increased (P = 0.063). The effect of fNSP intake on HP and AHP was not constant during the day. During the night period, fNSP intake did not affect HP and AHP (P > 0.10). During the day period, increased fNSP intake decreased HP (P = 0.006) and tended to decrease AHP (P = 0.062). During eating, increased fNSP intake increased HP (P = 0.012) and tended to increase AHP (P = 0.074). Despite similar DMI, sows fed 0 or 10% SBPS spent less time eating than sows fed 20 or 30% SBPS (P = 0.009). Feed consumption rate was higher (P = 0.003) in groups fed 0 or 10% SBPS than in groups fed 20 or 30% SBPS. Feed consumption rate decreased by 0.19 g DM x kg(-0.75). min(-1) (P = 0.003) for each gram of fNSP intake. The energy saving effect of physical activity on the NE value of fNSP from SBPS ranged between 2.3 and 3.7 kJ/g of fNSP intake. In conclusion, intake of fNSP from SBPS affected energy expenditure for physical activity (P = 0.063); however, this effect was not constant during the day. 相似文献
996.
Failure of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental Fasciola hepatica infection 总被引:2,自引:0,他引:2
De Bont J Claerebout E Riveau G Schacht AM Smets K Conder G Brake DA Capron A Vercruysse J 《Veterinary parasitology》2003,113(2):135-144
The potential of a recombinant Schistosoma bovis 28-kDa glutathione S-transferase (rSb28GST) to protect cattle against Fasciola hepatica was tested in a vaccination trial. Thirty two calves were randomly divided into four groups of eight animals. Calves of the three vaccine groups received two intramuscular injections at 3 weeks interval, of 0.250mg rSb28GST in either aluminium hydroxide (Al(OH)(3)), Quil A, or PBS emulsified in an equal volume of Freund's complete adjuvant (FCA).Animals of the control group received injections of Al(OH)(3)/PBS only. All animals were challenged orally with a total of 360 metacercariae of F. hepatica, spread over 6 weeks.All groups of vaccinated animals produced measurable IgG antibody titers to rSb28GST after vaccination. Animals immunised with FCA adjuvanted vaccine had the highest and more durable antibody titers and only sera from this group recognised an approximately 24kDa protein band from F. hepatica, that is thought to be a F. hepatica GST. Despite a good antibody response differences in cumulative faecal egg output between the groups were not statistically significant. In addition, no significant difference was found between groups in terms of total worm numbers or percentage of immature flukes recovered at necropsy. In conclusion, the recombinant S. bovis 28kDa GST was not found to adequately protect cattle against experimental F. hepatica challenge, using either aluminium hydroxide, Quil A or FCA as adjuvant. 相似文献
997.
Malignant lymphoma is a common malignancy in birds. Paraneoplastic syndromes, which are commonly observed in domestic animals, have not been reported in association with lymphoma in birds. Hypercalcemia and hyperglobulinemia were found on plasma chemistry in two Amazon parrots, which were presented with aspecific symptoms. In both cases radiography and ultrasound demonstrated signs of hepatomegaly, which proved to be due to malignant lymphoma on postmortem examination. The hypercalcemia was found to be most consistent with a paraneoplastic effect of the malignant lymphoma in these birds. The exact origin of the hyperglobulinemia remains unclear. 相似文献
998.
The objective of this experiment was to determine the effect of prerigor injection of several glycolytic inhibitors on pH, color, tenderness, and related traits of low-value beef cuts. The semimembranosus, triceps brachii, and supraspinatus muscles from each of 10 steer carcasses were removed 1 h postmortem. Control samples remained in the carcass at 2 degrees C for 24 h. Prerigor muscles were injected and tumbled with 10% (by weight) of one of four solutions: sodium citrate (NaC; 200 mM), sodium fluoride (NaF; 200 mM), sodium acetate (NaA; 200 mM), and calcium chloride (CaCl2; 300 mM). All muscles treated with NaC and NaF showed the highest pH and glycogen content (P < 0.05), indicating that glycolysis was inhibited. Injection of NaC in semimembranosus and supraspinatus produced the tenderest meat (P < 0.05), showing a greater increase in tenderization at 3 d than at 7 d postmortem. Treatment did not affect color or oxidation-reduction potential, but all treated muscles tended to be more oxidative (higher oxidation-reduction potential). Sodium citrate was identified as a potential compound to enhance tenderness of prerigor muscle without altering color. Further studies are required to investigate its effect on palatability traits and to provide a basis for commercial application of the process. 相似文献
999.
REASONS FOR PERFORMING STUDY: Mucosal ulcers and, occasionally, small granulomas on the axial surface of one or both arytenoid cartilages have been found in TB yearlings presented for post sale endoscopic examination. OBJECTIVES: To determine the incidence, endoscopic characteristics and outcome of a group of Thoroughbred yearlings affected with mucosal ulcers and granulomas of the arytenoid cartilage. HYPOTHESIS: The incidence of mucosal ulceration of the arytenoid cartilages of yearling Thoroughbreds is relatively high compared to other upper airway abnormalities; and that the majority of mucosal ulcers heal uneventfully, although a small percentage may progress to a granuloma and, less commonly, to arytenoid chondropathy. METHODS: The findings of post sale, upper airway endoscopic examinations of 3312 Thoroughbred yearlings, during a 5 year period, were reviewed, including those abnormalities listed in the conditions of sale and others not listed but considered likely to cause airway obstruction. Information obtained from the medical record of horses that had mucosal ulceration or granuloma of the arytenoid cartilage included the location and size of the lesion(s), sex of the affected horse and the presence and nature of other concurrent abnormalities of the upper portion of the respiratory tract. Additional information included treatment and results of follow-up, endoscopic examination by the authors or attending veterinarian. RESULTS: Mucosal lesions were seen in 0.63% of yearlings evaluated, which represented the most common, documented condition of the upper portion of the respiratory tract. The mucosal ulcers of 15 of 19 horses were considered to have healed without complication during follow-up examination; one of the 19 horses was lost to follow-up. Two horses affected with bilateral, arytenoid mucosal ulceration developed a granuloma at each site of ulceration. One horse developed a granuloma at a site of ulceration and, subsequently, arytenoid chondropathy. CONCLUSIONS: Arytenoid mucosal ulceration in sales yearlings was a relatively commonly encountered abnormality and a small percentage progressed to granuloma or chondropathy. POTENTIAL RELEVANCE: The mucosa of the arytenoid cartilage, particularly at the rostral margin of the vocal process, should be examined carefully during endoscopic examination of the upper portion of the respiratory tract of Thoroughbred yearlings presented for sale. Because a small percentage of mucosal ulcers may progress to granuloma or, less commonly, chondropathy, identification of mucosal ulcers of the arytenoid cartilage seen during post sale, endoscopic examination warrants notification to the purchaser and sales company. Medical therapy of affected horses should be considered and follow-up endoscopic examination performed to determine if the lesion has healed. 相似文献
1000.
Wilmink JM Veenman JN van den Boom R Rutten VP Niewold TA Broekhuisen-Davies JM Lees R Armstrong S van Weeren PR Barneveld A 《Equine veterinary journal》2003,35(6):561-569
REASONS FOR PERFORMING STUDY: Wound healing proceeds faster in ponies than in horses and complications during healing, such as wound infection, occur less frequently in ponies. Earlier studies suggested that this difference might be related to differences in the initial post traumatic inflammatory response. HYPOTHESIS: That polymorphonuclear leucocyte (PMN) function and profiles of humoral factors in local inflammatory processes are different in horses and ponies. METHODS: PMNs were isolated from venous blood of horses and ponies. Chemotaxis and reactive oxygen species (ROS) production was determined. Tissue cages were implanted in limbs and necks of horses and ponies and injected with carrageenan and, 3 weeks later, with LPS. In sequential samples of inflammatory exudate, the numbers of macrophages and PMNs and the production of PGE2, TNFalpha, IL-1, IL-6 and chemoattractants were determined. RESULTS: In vitro ROS production of PMNs was significantly higher in ponies than in horses, whereas in vitro PMN chemotaxis was significantly lower in ponies. In the tissue cages for both stimuli, the production of IL-1 and chemoattractants was significantly higher in ponies than in horses and remained so towards the end of the observation period in ponies. CONCLUSIONS: This study demonstrated a higher production of various inflammatory mediators by pony leucocytes. Despite the lower in vitro chemotaxis of pony PMNs, this higher in vivo production resulted in a stronger initial inflammatory response in ponies, as has been reported in studies on wound healing, through the attraction of leucocytes and triggering of the production of other cytokines. A stronger initial inflammation may promote healing by more rapid elemination of contaminants and earlier transition to repair. POTENTIAL RELEVANCE: Modulation of the initial inflammatory response might therefore be a valid option for therapeutic intervention in cases of problematic wound healing. Further, the intraspecies differences in leucocyte function may have an impact on many fields in equine medicine. 相似文献