全文获取类型
收费全文 | 75105篇 |
免费 | 2998篇 |
国内免费 | 262篇 |
专业分类
林业 | 6959篇 |
农学 | 3385篇 |
基础科学 | 548篇 |
10595篇 | |
综合类 | 12533篇 |
农作物 | 4385篇 |
水产渔业 | 4476篇 |
畜牧兽医 | 28187篇 |
园艺 | 1779篇 |
植物保护 | 5518篇 |
出版年
2019年 | 591篇 |
2018年 | 3887篇 |
2017年 | 3987篇 |
2016年 | 2141篇 |
2015年 | 857篇 |
2014年 | 961篇 |
2013年 | 1997篇 |
2012年 | 2688篇 |
2011年 | 4448篇 |
2010年 | 3880篇 |
2009年 | 3138篇 |
2008年 | 3536篇 |
2007年 | 4019篇 |
2006年 | 1739篇 |
2005年 | 1806篇 |
2004年 | 1634篇 |
2003年 | 1685篇 |
2002年 | 1522篇 |
2001年 | 1645篇 |
2000年 | 1640篇 |
1999年 | 1306篇 |
1998年 | 505篇 |
1997年 | 523篇 |
1996年 | 516篇 |
1995年 | 564篇 |
1994年 | 492篇 |
1993年 | 534篇 |
1992年 | 995篇 |
1991年 | 951篇 |
1990年 | 948篇 |
1989年 | 961篇 |
1988年 | 909篇 |
1987年 | 922篇 |
1986年 | 909篇 |
1985年 | 904篇 |
1984年 | 741篇 |
1983年 | 663篇 |
1979年 | 653篇 |
1978年 | 555篇 |
1977年 | 484篇 |
1976年 | 469篇 |
1975年 | 505篇 |
1974年 | 701篇 |
1973年 | 614篇 |
1972年 | 685篇 |
1971年 | 687篇 |
1970年 | 606篇 |
1969年 | 600篇 |
1968年 | 481篇 |
1967年 | 523篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
The use of phytotherapy to treat human diseases has its roots in pre-historical times. Despite the modern advances achieved in the field of synthetic chemistry, the most efficient drugs available have their genesis directly or indirectly related with the vegetal kingdom. Indigenous communities have long used plant extracts to treat illnesses. Many of these extracts have shown effective action, with new bioactive compounds being extracted and screened every year. These extracts have also proven to be good sources of therapeutic agents to the treatment of Leishmaniasis. This work highlights some of these agents, while trying to emphasize the importance of plants as a source of new and powerful drugs against this widespread disease. 相似文献
32.
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
33.
34.
35.
13~18周龄笼养蛋鸭适宜蛋白质和蛋氨酸水平的研究 总被引:4,自引:1,他引:3
用 32 4羽满 1 2周龄的金定鸭 ,通过饲养试验、代谢试验、屠宰试验和对试鸭产蛋期 (1 9~ 2 8周龄 )产蛋性能的观察 ,研究了在等能条件下(ME :1 1 51MJ/kg) ,不同蛋白质水平 (CP :1 3 %、 1 5 %、 1 7% )和蛋氨酸水平 (Met/CP :0 0 1 7、 0 0 2 2、 0 0 2 7)组成的 9种饲粮对 1 3~ 1 8周龄笼养蛋鸭的生长性能、养分利用、体成分沉积和产蛋期产蛋性能的影响。结果表明 :该阶段饲粮粗蛋白、蛋氨酸水平对体增重影响不显著 (P >0 0 5) ;体增重与蛋氨酸 (% )呈一定的正相关 (r=0 4574) ;CP为 1 3%、Met/CP为 0 0 2 7组采食量一直较稳定、较高 ,且饲料效率又好。代谢试验 :不同粗蛋白、蛋氨酸水平饲粮对试鸭氮存留率和能量的利用率影响显著(P <0 0 5或P<0 0 1 ) ,且它们随饲粮CP水平的升高而降低 ,随蛋氨酸水平升高而升高 ;磷的利用率也分别以CP为 1 3%的水平和Met/CP为 0 0 2 7的水平极显著地高于其他水平对磷利用率 (P <0 0 1 )。屠宰试验 :当Met/CP为 0 0 2 7时 ,体氮沉积量和体磷沉积量最佳。产蛋性能 :开产日龄和高峰日龄与 1 3~ 1 8周龄CP食入量呈弱的负相关 (r=- 0 1 83 3和r=- 0 0 984) ,与蛋氨酸食入量呈正相关 (r =0 5780和r =0 435 0 )。饲粮粗蛋白、蛋氨酸水平对 1 9~ 2 8周龄 相似文献
36.
37.
38.
1. The aim of this study was to determine the nitrogen balance and the performance of laying hens fed on diets with a protein content lower than the diets currently used in commercial practice but with adequate concentrations of lysine, sulphur amino acids, tryptophan and threonine. 2. Ninety-six Hy-Line Brown hens, 24 weeks old, were divided into 3 groups of 8 replicates and received, for 16 weeks, diets formulated to have 3 different protein concentrations: 170 (control), 150 and 130 g/kg CP and the same energy content. For each protein concentration, the contents of lysine, methionine, methionine+cystine, tryptophan and threonine were maintained at minimum requirement concentrations by supplying synthetic amino acids. 3. In the first half of the trial, egg production and egg weight were similar in all groups. From the 9th week onwards group 150 CP laid heavier eggs and had a slightly lower egg deposition and total mass. Food conversion ratio was best in the control group. 4. Nitrogen intake was related to the protein concentration of the diet, the food intake being almost the same in the 3 experimental groups. Faecal nitrogen content significantly and linearly decreased with reduction in dietary protein content and was about 50% of the intake. Considering the nitrogen faecal/intake ratio, the 150 CP group showed better nitrogen utilisation at each sampling time. 相似文献
39.
A 13-month-old Angus steer was examined with a 6-week history of lethargy, malaise and dribbling urine. Laboratory exam revealed crystalluria and poor renal function. Ultrasound revealed hydronephrosis and hydroureter. Euthanasia was chosen because of a poor prognosis for economic recovery. Necropsy demonstrated numerous calculi causing partial urethral obstruction approximately 25 cm from the end of the penis. Secondary renal changes were confirmed. Urolithiasis occurs commonly in ruminants. Secondary obstruction is usually complete with severe consequences. This is the first report of chronic partial obstructive urolithiasis resulting in endstage renal disease. 相似文献
40.