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   198430篇
  免费   10780篇
  国内免费   124篇
林业   8393篇
农学   6150篇
基础科学   1360篇
  23536篇
综合类   34192篇
农作物   7661篇
水产渔业   9871篇
畜牧兽医   101702篇
园艺   2533篇
植物保护   13936篇
  2018年   2491篇
  2017年   2817篇
  2016年   2652篇
  2015年   2386篇
  2014年   2835篇
  2013年   7335篇
  2012年   5332篇
  2011年   6411篇
  2010年   4046篇
  2009年   4060篇
  2008年   6179篇
  2007年   5858篇
  2006年   5636篇
  2005年   5920篇
  2004年   5657篇
  2003年   5558篇
  2002年   5001篇
  2001年   6001篇
  2000年   5789篇
  1999年   4751篇
  1998年   1930篇
  1997年   1969篇
  1995年   2289篇
  1994年   2037篇
  1993年   1951篇
  1992年   4044篇
  1991年   4273篇
  1990年   4384篇
  1989年   4329篇
  1988年   4039篇
  1987年   4090篇
  1986年   4164篇
  1985年   4029篇
  1984年   3466篇
  1983年   3046篇
  1982年   2095篇
  1981年   1897篇
  1980年   1861篇
  1979年   3144篇
  1978年   2550篇
  1977年   2269篇
  1976年   2063篇
  1975年   2235篇
  1974年   2879篇
  1973年   2902篇
  1972年   2824篇
  1971年   2555篇
  1970年   2398篇
  1969年   2285篇
  1967年   2061篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
211.
In a large pig breeding herd with high prevalence of post-parturient diseases of the sows, weaned sows of different parity groups with (n = 663) or without (n = 1125) recidiving mastitis metritis agalactia (MMA) in their previous history were subjected to ultrasonography. A total of 114 of 663 sows with recidiving MMA in their previous history and with ultrasonographic visible mammary gland changes, and 157 of sows without recidiving MMA in their previous history were culled and subjected to gross pathological and bacteriological examination of their mammary glands. The sows having suffered MMA had more (p < 0.001) hyperechogenic images in their mammary glands compared with the sow having suffered no recidiving MMA. Abdominal glands were more (p < 0.01) prone to pathological changes compared with the pectoral ones. Sows of high parity had more hyperechogenic images and gross pathological changes in their mammary glands compared with the sows of low parity.  相似文献   
212.
Canine distal renal tubular acidosis and urolithiasis   总被引:1,自引:0,他引:1  
Distal RTA is characterized by decreased distal renal tubular hydrogen ion secretion, decreased ability to acidify urine, hypercalciuria, hyperphosphaturia, hypocitraturia, and metabolic acidosis. Because of the resulting alterations in urine composition and pH, patients with distal RTA are predisposed to urolithiasis and renal calcification. Diagnosis of distal RTA is important because it is a potentially reversible disorder that, left untreated, may cause nephrocalcinosis, recurrent urolith formation, moderate to severe metabolic acidosis, and renal failure.  相似文献   
213.
Forty-one dairy cows were fed a low (LCa-13 g/d) and a high (HCa-83.5 g/d) calcium ration in the 8 weeks prior to parturition and the effect on the Ca mobilization rate around parturition was studied. Plasma Ca values were stable in the LCa group around parturition. In the older cows of the HCa group a very slight decrease in the mean plasma Ca was observed: 2.58 mmol/l at 12-36 h ante partum decreased to 2.38 mmol/l at parturition. Hypocalcaemia, which commonly occurs around parturition, did not occur in 40 of the cows. A subclinical hypocalcaemia (1.8 mmol/l) occurred in one cow (parity 10) from the HCa group. To assess the efficiency of Ca mobilization, a severe hypocalcaemia (1.0 mmol/l) with clinical signs was induced by means of Na2EDTA infusion (0.90 mmol/min), starting at 10 h post-partum. The older cows in the LCa group required more Na2EDTA than those in the HCa group. Higher urinary hydroxyproline excretion in the week before parturition in the LCa than in the HCa group suggested a higher bone turnover. Plasma PTH levels around parturition were not significantly different between the groups. The amount of colostrum milked out in the first 10 h post-partum did not influence Ca homeostasis around parturition. The results contradict those of many other experiments in which hypocalcaemia was observed in cows ingesting high levels of Ca. It is concluded that the restricted feed intake prepartum possibly had a favourable effect on Ca homeostasis.  相似文献   
214.
Success in veterinary dentistry lies in good home care and regular, thorough dental prophylaxis. The removal of supragingival and subgingival calculus must be accomplished before periodontal disease can be controlled. When gingival sulcus depths exceed 4 or 5 mm, the gingivae must be excised or reflected to allow proper treatment of the pocket area. Antibiotic therapy should be instituted in the extensively involved veterinary dental patient.  相似文献   
215.
216.
217.
218.
219.
220.
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