首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   83901篇
  免费   4643篇
  国内免费   94篇
林业   3615篇
农学   2237篇
基础科学   499篇
  9947篇
综合类   15547篇
农作物   3392篇
水产渔业   3954篇
畜牧兽医   43628篇
园艺   942篇
植物保护   4877篇
  2020年   717篇
  2019年   843篇
  2018年   1343篇
  2017年   1486篇
  2016年   1305篇
  2015年   1090篇
  2014年   1427篇
  2013年   2968篇
  2012年   2503篇
  2011年   2984篇
  2010年   1810篇
  2009年   1914篇
  2008年   2862篇
  2007年   2691篇
  2006年   2523篇
  2005年   2338篇
  2004年   2274篇
  2003年   2350篇
  2002年   2070篇
  2001年   2490篇
  2000年   2532篇
  1999年   1950篇
  1998年   744篇
  1997年   726篇
  1996年   729篇
  1995年   819篇
  1993年   751篇
  1992年   1571篇
  1991年   1773篇
  1990年   1654篇
  1989年   1678篇
  1988年   1483篇
  1987年   1556篇
  1986年   1607篇
  1985年   1562篇
  1984年   1192篇
  1983年   1066篇
  1979年   1160篇
  1978年   897篇
  1977年   763篇
  1975年   779篇
  1974年   1028篇
  1973年   1028篇
  1972年   1050篇
  1971年   997篇
  1970年   990篇
  1969年   907篇
  1968年   815篇
  1967年   806篇
  1966年   741篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Vitamin K-dependent multifactor coagulopathy in Devon Rex cats   总被引:1,自引:0,他引:1  
A coagulopathy attributable to a deficiency of vitamin K-dependent clotting factors (II, VII, IX, and X) was diagnosed in 3 Devon Rex cats. There was no evidence for exposure to vitamin-antagonist-related rodenticides. The cats did not have evidence of hepatic disease, gastrointestinal disease, or fat malassimilation. Oral treatment with vitamin K1 resulted in normalization of clotting factor concentrations. However, when treatment was discontinued in 2 cats, prothrombin and activated partial thromboplastin values became prolonged again, although the cats did not have clinical signs of a bleeding disorder.  相似文献   
992.
This laboratory investigated the anabolic effect of the synthetic steroid trienbolone acetate (TA) and found it effective in male and female meat turkeys without any apparent gross abnormalities (Poultry Sci., 61: 1386, 1982). The present study was undertaken to characterize the response of female turkeys, fed equicaloric diets varying in dietary protein density to anabolic agents implanted at 13 wks. TA and zeranol (Z) were tested singly and in combination (TAZ). Body weight gain and feed conversion at 16 wks of age were improved (P less than 0.01) with TA and TAZ. The response to TA was enhanced as dietary protein density increased. Carcass fat, protein, ash, energy, potassium, and calcium were not altered by implant treatment. A trend existed toward increased carcass fat with zeranol implantation. Carcass moisture (P less than 0.01) and sodium (P less than 0.05) were increased in the TA treatment. Blood plasma electrolytes were not affected by implant treatments but plasma calcium was decreased (P less than 0.05) by TAZ. No synergism was noted between TA and Z with respect to growth, feed conversion, carcass composition, plasma electrolytes with the exception of plasma calcium. No interaction was observed between dietary protein density and implant treatment. Performance variables increased and carcass fat decreased with increasing dietary protein density. These results confirm our earlier finding with respect to TA and provide additional evidence that dietary protein density influences the response of meat turkeys to TA. The data show that zeranol lacks an anabolic effect in turkeys.  相似文献   
993.
994.
995.
Midazolam HCl (1.0 or 2.0 mg/kg of body weight) was administered IM to 6 Canada geese to determine a sedative dose that would allow positioning for radiologic examination. The effects of both test doses on cardiopulmonary function were evaluated at 5, 10, 15, 20, 30, and 40 minutes after drug administration and were compared with 2 end-tidal isoflurane concentrations (1.5 and 2.5%). The 2.0 mg/kg dosage induced moderate sedation at 15 and 20 minutes; sedation was adequate for positioning the geese. Sedation induced by the 1.0 mg/kg dosage was inadequate. The effects of both test doses on blood pressure, heart rate, and temperature were not significantly different from each other and from baseline data. Respiratory rate increased significantly (P less than 0.05) at 10, 15, 20, and 30 minutes with the 2.0 mg/kg dosage, and at 15 and 20 minutes with the 1.0 mg/kg dosage. Blood pressure and respiratory rate were significantly (P less than 0.05) decreased with isoflurane when compared with baseline data and the midazolam test doses. The results of this study indicate that midazolam at a dosage of 2.0 mg/kg induces adequate sedation with minimal cardiopulmonary changes, and, as an alternative to general anesthesia with isoflurane, provides a satisfactory level of restraint for radiography.  相似文献   
996.
Encephalomyocarditis of swine in Greece   总被引:3,自引:0,他引:3  
  相似文献   
997.
A study was conducted on 40 buffalo-cows, assigned randomly, immediately after calving into three groups: group I (n = 10) injected with saline and taken as control; group II (n = 15) received 25 mg PGF2 alpha/animal (Lutalyse); group III (n = 15) received 25 mg PGF2 alpha + 25 i.u. oxytocin/animal (Syntocinon), single i.m. dose. Oxytocin and/or PGF2 alpha significantly (P less than 0.01) shortened the interval from calving to first service (38.33 and 31.53 days for groups II and III respectively, versus 91.60 days for controls). The treatment reduced the service period (38.29 and 35.87 days for groups II and III respectively, versus 45.40 days for controls). Concomitantly a significant (P less than 0.01) decrease in the open-days post partum was achieved (76.62 and 67.40 days for groups II and III respectively, versus 137.00 days for controls). In addition, the treated buffaloes needed significantly (P less than 0.01) fewer services per conception (1.67 and 1.20 S/C for groups II and III respectively) than the untreated ones (2.70 S/C), besides a substantial improvement (P less than 0.01) in their conception rate either at 60 or 85 days post partum. Significantly improved (P less than 0.05) results were obtained in the oxytocin and PGF2 alpha treated animals, than in those receiving PGF2 alpha alone for all the previous parameters, except for the service period. Buffaloes therefore seemed to respond better to such treatment than dairy cows.  相似文献   
998.
Formulation of rations to induce a compensated metabolic acidosis in the post-partum cow has proved a useful strategy for prevention of milk fever. Such acidification improves the ability of the animal to maintain calcium homeostasis by promoting the absorption of calcium from the intestine and mobilization of calcium from the bone. In humans, an acidogenic diet results in mild metabolic acidosis in association with a state of cortisol excess and this increase in plasma cortisol may increase bone catabolism. The objective of our experiment was to induce acidification by anionic salt supplementation and to study the effects of anionic supplementation on plasma cortisol and adrenocorticotropic hormone (ACTH) levels in sheep. Twenty-seven twin-bearing sheep were assigned to two experimental groups and a control group, depending on dietary cation-anion difference (DCAD) (+272.6, -88.9 and +164.5 mEq/kg DM respectively). Sheep assigned to each dietary treatment received their respective rations beginning 6 weeks pre-partum and continuing until 12 days post-partum. Anionic diet induced a non-respiratory systemic acidosis in association with a mild increase in plasma cortisol concentration without changes in plasma ACTH levels. Our data suggest that the mild hypercortisolism observed in sheep fed the anionic diet may not be an effector for bone resorption induced by anionic salts. A mild hypercortisolism of this magnitude may lead to osteoporosis but this might require many years of adrenal hypersecretion while anionic salts are only used during the last weeks of pregnancy.  相似文献   
999.
The protective capacity of an adult stage Ostertagia ostertagi globin antigen was tested in four vaccination experiments in cattle. In a preliminary experiment, calves were vaccinated three times intraperitoneally with 250 microg globin in Freund's adjuvant and challenged with a trickled infection of 25,000 infective larvae. In three subsequent field studies, calves were vaccinated twice or three times intramuscularly with 80-100 microg globin in Quil A and challenged with a natural gastrointestinal nematode infection on pasture. Higher globin-specific antibody levels were detected in the vaccinated calves than in the control animals in all vaccine trials. In the preliminary experiment, geometric mean cumulative egg counts in the globin group were reduced by 52% and total worm burdens were reduced by 28%, compared to the controls. In the first field trial cumulative faecal egg counts were reduced by 63% in the vaccinated calves. However, the reduction in faecal egg output in these two experiments was not statistically significant and no reduction in faecal egg counts was observed in the vaccinated animals in the two last field trials. In conclusion, vaccination of calves with O. ostertagi globin resulted in highly variable protection levels after challenge infection.  相似文献   
1000.
作者报道站立状态下用关节镜摘除马近端指(趾 )骨近背侧碎片骨折片的技术及应用效果。1 方法将马匹保定于柱栏内 ,通过静脉注射赛拉嗪 ,地托咪定 ,或 2种药联合进行镇静。动脉内注射2 %甲哌卡因进行镇痛 ,并于背侧至球节皮下弧形浸润麻醉。术部覆以无菌创巾 ,蹄部和蹄底应用不透水创巾。关节镜从掌指关节或跖趾关节的背侧关节囊进入 ,摘除碎骨折片。我们对所有纯种赛马的比赛记录均做了统计分析并与已发表的研究报道进行了比较。手术及术后住院治疗时间与全麻术马匹的相应时间进行比较 ,并对全身麻醉后潜在的危险性进行监测。2 结果术期或…  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号