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   177582篇
  免费   9853篇
  国内免费   114篇
林业   7476篇
农学   5343篇
基础科学   1150篇
  20576篇
综合类   32683篇
农作物   6614篇
水产渔业   8687篇
畜牧兽医   90646篇
园艺   2150篇
植物保护   12224篇
  2018年   2216篇
  2017年   2456篇
  2016年   2297篇
  2015年   2030篇
  2014年   2454篇
  2013年   6489篇
  2012年   4704篇
  2011年   5745篇
  2010年   3635篇
  2009年   3727篇
  2008年   5653篇
  2007年   5446篇
  2006年   5232篇
  2005年   4895篇
  2004年   4762篇
  2003年   4765篇
  2002年   4600篇
  2001年   5510篇
  2000年   5340篇
  1999年   4335篇
  1998年   1732篇
  1997年   1755篇
  1996年   1677篇
  1995年   2037篇
  1994年   1847篇
  1993年   1790篇
  1992年   3672篇
  1991年   3790篇
  1990年   3827篇
  1989年   3809篇
  1988年   3517篇
  1987年   3613篇
  1986年   3705篇
  1985年   3577篇
  1984年   3028篇
  1983年   2715篇
  1982年   1842篇
  1981年   1727篇
  1979年   2736篇
  1978年   2254篇
  1977年   1930篇
  1976年   1784篇
  1975年   1884篇
  1974年   2572篇
  1973年   2483篇
  1972年   2489篇
  1971年   2263篇
  1970年   2098篇
  1969年   1998篇
  1967年   1676篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
Above ground production of a typical Cortaderia pilosa dominant sward in the Falkland Islands was estimated over one growing season by summing significant positive increments in DM production of various sward components and by sequential cutting to ground level. The standing crop was characterized by a high proportion of standing dead matter at all times of the year. Net herbage production was estimated as 2200 kg ha-1 and 1440 kg ha-1 by the 'difference' and "sequential culling" techniques, respectively. The pattern of leaf growth was determined on another site by regular linear measurements of a population of physiologically similar C. pilosa leaves. There was very little early season growth and most of the DM was produced in a short period in the middle part of the growing season. The poor early season growth was attributed to adverse climatic conditions. A significant increase in green matter digestibility in October and November was masked by the low digestibility and high contribution to the overall DM by the standing dead component of the herbage.
The implications of these findings are briefly discussed in relation to the increased utilization of C. pilosa by improved pasture management, including burning and possibly reseeding areas with improved species. Tissue turnover studies combined with more knowledge of sheep nutrition cycles would enable grazing systems to be developed on a sounder basis than previously.  相似文献   
192.
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   
193.
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   
194.
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   
195.
196.
197.
198.
199.
200.
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