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   89757篇
  免费   5530篇
  国内免费   46篇
林业   3738篇
农学   3466篇
基础科学   632篇
  11245篇
综合类   13526篇
农作物   3365篇
水产渔业   4936篇
畜牧兽医   47640篇
园艺   1165篇
植物保护   5620篇
  2020年   732篇
  2019年   955篇
  2018年   1582篇
  2017年   1846篇
  2016年   1661篇
  2015年   1404篇
  2014年   1718篇
  2013年   3716篇
  2012年   2934篇
  2011年   3588篇
  2010年   2342篇
  2009年   2330篇
  2008年   3472篇
  2007年   3210篇
  2006年   3138篇
  2005年   2668篇
  2004年   2576篇
  2003年   2591篇
  2002年   2372篇
  2001年   3390篇
  2000年   3304篇
  1999年   2553篇
  1998年   983篇
  1997年   1051篇
  1996年   883篇
  1995年   1022篇
  1994年   895篇
  1993年   896篇
  1992年   1845篇
  1991年   1919篇
  1990年   1856篇
  1989年   1859篇
  1988年   1608篇
  1987年   1594篇
  1986年   1627篇
  1985年   1526篇
  1984年   1225篇
  1983年   1033篇
  1982年   713篇
  1979年   1060篇
  1978年   816篇
  1975年   815篇
  1974年   897篇
  1973年   864篇
  1972年   805篇
  1971年   795篇
  1970年   800篇
  1969年   780篇
  1968年   708篇
  1967年   735篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A 17-year-old female blue and gold macaw ( Ara ararauna ) presented for evaluation of a discreet, conjunctival mass of the OD. No other abnormalities were found on ophthalmic or physical examination. A heterophilic leukocytosis was present on the complete blood count, and elevated aspartate aminotransferase activity, creatinine kinase activity and cholesterol were present on the plasma biochemistry panel. Surgical removal of the mass was complete and no recurrence has occurred by six months after excision. Reduction of dietary fats was recommended to reduce serum cholesterol levels and reduce the likelihood of future occurrence of xanthomas in this bird.  相似文献   
993.
994.
Control of heifer mastitis by nutrition   总被引:2,自引:0,他引:2  
Nutritional factors that are linked to mastitis in the mature dairy cow can be associated with mastitis in the first lactation cow as well. However, there may also be risk factors unique to the heifer due to differences in feeding management during rearing or pre-calving. Literature was reviewed to summarize current knowledge regarding links between heifer nutrition and mastitis with the potential to identify areas for future research. The preponderance of data relating nutrition and bovine mastitis involves selected micronutrients. Selenium and vitamin E enhance phagocytic activity and have been associated with decreased clinical mastitis risk. Copper has antioxidant functions and can reduce clinical mastitis in heifers. Zinc is implicated in maintaining the epithelial barriers to infection, but reports vary as to its role in udder health. Vitamin A and beta-carotene aid in maintaining the health of mucosal surfaces, and beta-carotene may also have antioxidant properties. Supplementation with vitamin A and beta-carotene has produced inconsistent results. Vitamin and mineral requirements of dairy heifers are generally influenced by growth rate and body weight relative to mature size, though little specific data is available. From a management standpoint, heifer rations should be supplemented where necessary, and a pre-fresh heifer diet is critical to assure that first lactation animals have adequate stores of minerals and vitamins. Adequate stores are necessary for transfer into colostrum by calving. Additional studies using field data and controlled studies are needed to further define the role of nutrition in animal health and in affecting specific mastitis-causing organisms.  相似文献   
995.
996.
A nonhealing wound associated with a laceration in a 12-year-old llama was evaluated. Initial attempts at closure were unsuccessful and biopsy revealed scar tissue. Subsequent biopsies, 18 mo later, revealed squamous cell carcinoma with regional metastasis. This report describes squamous cell carcinoma, secondary to a traumatic wound in a llama.  相似文献   
997.
We report a case of diphenhydramine intoxication in a dog. A five month old intact male Labrador Retriever was presented after ingesting approximately 36 diphenhydramine tablets (50 mg/tablet; approximate ingested dose of 1800 mg or 67 mg/kg). Physical examination findings included severe ataxia, profound disorientation, severe continuous spastic muscle tremors, hyperthermia, tachycardia, tachypnea, and hyperesthesia. The dog was unresponsive to intravenous diazepam and phenobarbital, but rapidly responded to an intravenous bolus and subsequent continuous infusion of guaifenesin and supportive fluid therapy. The serum diphenhydramine level on admission was 537 ng/ml. The toxic level is not reported for dogs, but is considered>60 ng/ml in people. The dog was discharged 24 hours after admission with no apparent residual effects.  相似文献   
998.
Summary

The intravenous and oral pharmacokinetics of an amoxicillin and clavulanic acid combination (20 mg/kg of sodium amoxicillin and 5 mg/kg of potassium clavulanate) were studied in six goats. After intravenous administration the pharmacokinetics of both drugs could be described by an open two‐compartment model. Amoxicillin had a greater distribution volume (0.19 ± 0.01 l/kg) than clavulanic acid (0.15 ± 0.01 l/kg), whereas the distribution and elimination constants were higher for the latter, which was eliminated more quickly than amoxicillin. After oral administration of both drugs their pharmacokinetic behaviour was best described by an open one‐compartment model with first‐order absorption. Elimination half‐lives were twice as long after oral (2.15 ± 0.20 h and 1.94 ± 0.16 h for amoxicillin and clavulanic acid respectively) than after intravenous administration (1.20 ± 0.16 h and 0.86 ± 0.09, respectively). An apparent ‘flip‐flop’ situation was evident in this study. Bioavailability was 27% for amoxicillin and 50% for clavulanic acid.  相似文献   
999.
Current methods for the quantification of plaque accumulation in cats and dogs are well-accepted adaptations of traditional human models, but have required substantial modifications in order to compensate for the inherent differences in compliance, cooperation, and temperament between animals and humans. While these modifications have sought to maintain or improve upon the accuracy and reproducibility of the original methods, they also have increased the complexity of the technique and have required additional scorer time and animal cooperation, which leads to increased cost of trials. Therefore, research was directed toward the development and validation of a new substrate scoring system that reduces resources while maintaining or increasing the reproducibility attributed to the more traditional methods. This new gingival contour plaque index was shown to be accurate and reproducible, but used fewer animals, required less time, and eliminated the need for many of the specialized procedures required by traditional methods.  相似文献   
1000.
Although conjugated linoleic acid (CLA) shows inhibitory effects on histamine release, eicosanoid production and pruritus in laboratory rodents, its use in canine atopic dermatitis (AD) has not been reported. The aims of this study were to assess the efficacy of CLA, black currant seed oil (BSO) or a combination of both, compared to placebo, in dogs with AD and to evaluate any changes in fatty acid metabolism with these treatments. Twenty-four dogs with AD were randomly allocated to four groups, and were treated orally each day for two months with either 1 mL/10 kg CLA (80% purity), 1 mL/10 kg pure BSO, 1 mL/10 kg CLA+1 mL/10 kg BSO, or 1 mL/10 kg sugar syrup (placebo). Serum was obtained on days 0, 30 and 60 for analysis of CLA metabolites, linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA). At the same time point, the owners were asked to assess pruritus and the veterinarians evaluated any skin lesions present. Although the best clinical results occurred with BSO treatment alone, improvement of clinical signs and pruritus was not significant with any of the treatments. Serum levels of GLA and DGLA significantly increased in BSO-treated dogs, but not in the CLA+BSO group. CLA at the dosage used in this study was not efficacious in treating canine AD, whereas BSO may help some dogs with AD, although further studies are necessary before this can be recommended as a treatment.  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