全文获取类型
收费全文 | 123364篇 |
免费 | 19172篇 |
国内免费 | 30869篇 |
专业分类
林业 | 14358篇 |
农学 | 16860篇 |
基础科学 | 12636篇 |
39256篇 | |
综合类 | 45859篇 |
农作物 | 8794篇 |
水产渔业 | 7516篇 |
畜牧兽医 | 14875篇 |
园艺 | 3929篇 |
植物保护 | 9322篇 |
出版年
2024年 | 1060篇 |
2023年 | 1559篇 |
2022年 | 2810篇 |
2021年 | 3432篇 |
2020年 | 4740篇 |
2019年 | 7802篇 |
2018年 | 7043篇 |
2017年 | 8322篇 |
2016年 | 8817篇 |
2015年 | 9273篇 |
2014年 | 8477篇 |
2013年 | 9496篇 |
2012年 | 9847篇 |
2011年 | 9196篇 |
2010年 | 8100篇 |
2009年 | 7269篇 |
2008年 | 6139篇 |
2007年 | 6709篇 |
2006年 | 6129篇 |
2005年 | 5573篇 |
2004年 | 3773篇 |
2003年 | 3252篇 |
2002年 | 2732篇 |
2001年 | 2526篇 |
2000年 | 2646篇 |
1999年 | 2869篇 |
1998年 | 2689篇 |
1997年 | 2421篇 |
1996年 | 2220篇 |
1995年 | 2199篇 |
1994年 | 2079篇 |
1993年 | 1771篇 |
1992年 | 1626篇 |
1991年 | 1348篇 |
1990年 | 1100篇 |
1989年 | 947篇 |
1988年 | 812篇 |
1987年 | 596篇 |
1986年 | 483篇 |
1985年 | 244篇 |
1984年 | 220篇 |
1983年 | 221篇 |
1982年 | 205篇 |
1981年 | 256篇 |
1980年 | 202篇 |
1979年 | 155篇 |
1978年 | 130篇 |
1975年 | 109篇 |
1965年 | 139篇 |
1964年 | 141篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
992.
993.
994.
995.
The effect of thiopental sodium, methoxyflurane and halothane on the acid-base status in sheep. 下载免费PDF全文
Experiments have been carried out on 20 adult fat-tailed ewes to determine the effects of thiopental sodium, methoxyflurane and halothane on acid-base status of the saliva loss during prolonged surgical anaesthesia. The rate of loss of base in saliva depends on the volume of saliva produced, which fell sharply at the onset of anesthesia with the volatile anaesthesia. Plasma pH and plasma pvCO2 excess were both increased by the volatile anaesthetics but fell sharply during thiopental anaesthesia. Plasma pH and plasma PvCO2 showed no consistent relationship. 相似文献
996.
997.
Peripartum events, rectal palpation findings, histological and bacteriological results of endometrial biopsy, and postpartum disease variables were included in a path analysis of reproductive performance for 55 Holstein-Friesian cows from one herd. Both logistic and least squares regression were used. Based on this model, dystocia had both direct and indirect sparing associations on poor reproductive performance. A larger corpus luteum on the ovary ipsilateral to the previously non-gravid horn at Day 26 postpartum indirectly was associated with a decreased likelihood of poor reproductive performance through reduced isolation of Actinomyces pyogenes from the uterus and reduced inflammation in the stratum compactum. In the model, A. pyogenes indirectly increased poor reproductive performance through reduced number of lymphocytic foci and increased inflammation in the stratum compactum at Day 26. Increased numbers of lymphocytic foci had a direct sparing effect on poor reproduction. Stratum compactum inflammation was associated with a direct and indirect increase in the likelihood that a cow would experience poor reproductive performance via increased occurrence of cystic ovarian disease. Presence of a larger follicle on the ovary ipsilateral to the previously gravid horn had a direct beneficial effect on reproductive performance. 相似文献
998.
Enzootic pneumonia: comparison of cough and lung lesions as predictors of weight gain in swine. 总被引:4,自引:0,他引:4 下载免费PDF全文
C R Morris I A Gardner S K Hietala T E Carpenter 《Canadian journal of veterinary research》1995,59(3):197-204
A prospective cohort study was undertaken in a commercial swine herd to determine the relationship between weight gain and the occurrence of enzootic pneumonia (EP). Estimates of the association between EP and weight gain were obtained from multiple linear regression models, using coughing episodes or slaughter checks as indicators of EP status. Models were estimated for pigs in 2 different age groups: roasters (n = 1084, sold at 32 to 50 kg) and market hogs (n = 1162, sold at 100 to 110 kg). The relationship between presence of lung lesions at slaughter and previous coughing episodes was also investigated. Throughout the study period, clinical evaluations were performed weekly, and coughing episodes recorded for each pig. Lungs were inspected at slaughter, and scores were expressed as the percentage of the lung with gross pneumonic lesions. Coughing and lung scores were significantly correlated, after adjusting for other covariates (R = 0.32 and 0.59, respectively, for market hogs and roasters). However, the agreement beyond chance between coughing history and lung lesions at slaughter was poor among both roasters and market hogs (kappa = 0.17 and 0.07, respectively). Although very specific, weekly assessment of coughing was not a sensitive indicator of lung lesions at slaughter. In multiple regression, lung score was a highly significant predictor of lower final weight in pigs of both age groups (P < 0.001 in the selected regression models).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
999.
Mitral valve prolapse in 3-year-old healthy Cavalier King Charles Spaniels. An echocardiographic study. 总被引:2,自引:0,他引:2 下载免费PDF全文
H D Pedersen B O Kristensen K A Lorentzen J Koch A L Jensen A Flagstad 《Canadian journal of veterinary research》1995,59(4):294-298
Clinical studies have shown that Cavalier King Charles Spaniels (CKCS) have a high prevalence of mitral valvular insufficiency (MVI). Echocardiography has the potential to disclose early valvular changes, and the present prospective study was designed to investigate the occurrence of mitral valve prolapse (MVP) in young CKCS without heart murmurs, and to correlate the degree of MVP with the clinical status of the dogs by including CKCS with MVI as well. The study was based on blinded evaluations of echocardiographic recordings of mitral valves from 34 CKCS and 30 control dogs. Thirteen (87%) of 15 three-year-old CKCS without heart murmurs had MVP (2 total and 11 partial), as compared with 1 (7%) of 15 three-year-old normal Beagle dogs (P < 0.0001), and none of 15 three-year-old normal Medium Size Poodles (P < 0.0001). Of 19 CKCS with MVI, MVP was found in 84% of the entire group and in 100% of dogs with pulmonary congestion or edema. The occurrence of total MVP tended to be higher in the group with MVI (47%, 9/19), when compared with the younger CKCS without heart murmurs (13%, 2/15, P = 0.06). MVP was positively associated with excessive heart rate variability (P = 0.003). The radius of curvature of the anterior mitral valve leaflet in systole was significantly reduced in dogs with MVP when compared with those without (P < 0.0001). In conclusion, this study shows that CKCS at an early age have a high occurrence of MVP. This suggests: 1) A genetic predisposition of CKCS to MVP; and 2) That MVP is a pathogenetic factor in the development of mitral valvular insufficiency. Follow up studies may add further support to these proposals, and clarify whether echocardiography may be an aid in selecting CKCS for future breeding. 相似文献
1000.