全文获取类型
收费全文 | 183471篇 |
免费 | 10199篇 |
国内免费 | 118篇 |
专业分类
林业 | 7105篇 |
农学 | 5581篇 |
基础科学 | 1216篇 |
21261篇 | |
综合类 | 32056篇 |
农作物 | 6727篇 |
水产渔业 | 9120篇 |
畜牧兽医 | 95852篇 |
园艺 | 2262篇 |
植物保护 | 12608篇 |
出版年
2018年 | 2350篇 |
2017年 | 2528篇 |
2016年 | 2345篇 |
2015年 | 2090篇 |
2014年 | 2501篇 |
2013年 | 7084篇 |
2012年 | 4791篇 |
2011年 | 5956篇 |
2010年 | 3765篇 |
2009年 | 3742篇 |
2008年 | 5798篇 |
2007年 | 5586篇 |
2006年 | 5411篇 |
2005年 | 5000篇 |
2004年 | 4871篇 |
2003年 | 4909篇 |
2002年 | 4734篇 |
2001年 | 5698篇 |
2000年 | 5476篇 |
1999年 | 4500篇 |
1998年 | 1836篇 |
1997年 | 1863篇 |
1996年 | 1755篇 |
1995年 | 2131篇 |
1994年 | 1943篇 |
1993年 | 1876篇 |
1992年 | 3832篇 |
1991年 | 4099篇 |
1990年 | 4044篇 |
1989年 | 3990篇 |
1988年 | 3765篇 |
1987年 | 3798篇 |
1986年 | 3910篇 |
1985年 | 3803篇 |
1984年 | 3172篇 |
1983年 | 2835篇 |
1982年 | 1960篇 |
1981年 | 1811篇 |
1979年 | 2902篇 |
1978年 | 2377篇 |
1977年 | 2080篇 |
1976年 | 1916篇 |
1975年 | 1985篇 |
1974年 | 2609篇 |
1973年 | 2612篇 |
1972年 | 2518篇 |
1971年 | 2316篇 |
1970年 | 2258篇 |
1969年 | 2089篇 |
1967年 | 1805篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
J. H. McADAM 《Grass and Forage Science》1986,41(4):281-287
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
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
D J Polzin C A Osborne F W Bell 《Veterinary Clinics of North America: Small Animal Practice》1986,16(2):241-250
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.
A E van de Braak A T van 't Klooster A Malestein J A Faber 《The Veterinary quarterly》1986,8(1):12-23
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.
B J Hawkins 《Veterinary Clinics of North America: Small Animal Practice》1986,16(5):835-849
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.
Lockyer JN 《Science (New York, N.Y.)》1886,7(169):386-387
198.
199.
The vulvar labia of ewes naturally infected with ureaplasma were significantly more swollen and red than those of uninfected ewes. Similar changes were observed following experimental infection of previously uninfected ewes. These differences, although statistically significant, were not sufficiently marked to be useful in diagnosing infection by clinical examination. 相似文献
200.
Intrajugular injection of a purified E. coli lipopolysaccharide induced a biphasic fever in sheep after a latent period of 12 to 20 min. The changes in the blood flow from the liver and from the viscera drained by the portal vein were: (a) in the latent period, decreases in total hepatic blood flow (THF) due to decreased portal venous blood flow (PVF); (b) during the first febrile phase, increases in THF due to increased hepatic arterial blood flow and, (c) in the second febrile phase, increases in THF due to decreased PVF. Although there were large variations in the oxygen supply to the viscera drained by the portal vein and to the liver, there were relatively small or no changes in their oxygen consumption. 相似文献