全文获取类型
收费全文 | 118250篇 |
免费 | 6002篇 |
国内免费 | 82篇 |
专业分类
林业 | 5887篇 |
农学 | 3607篇 |
基础科学 | 566篇 |
12866篇 | |
综合类 | 23704篇 |
农作物 | 4652篇 |
水产渔业 | 5322篇 |
畜牧兽医 | 59197篇 |
园艺 | 1383篇 |
植物保护 | 7150篇 |
出版年
2018年 | 1438篇 |
2017年 | 1542篇 |
2016年 | 1421篇 |
2015年 | 1308篇 |
2014年 | 1565篇 |
2013年 | 4025篇 |
2012年 | 2920篇 |
2011年 | 3442篇 |
2010年 | 2270篇 |
2009年 | 2271篇 |
2008年 | 3392篇 |
2007年 | 3446篇 |
2006年 | 3179篇 |
2005年 | 3041篇 |
2004年 | 2893篇 |
2003年 | 2928篇 |
2002年 | 2783篇 |
2001年 | 3429篇 |
2000年 | 3414篇 |
1999年 | 2840篇 |
1998年 | 1071篇 |
1997年 | 1106篇 |
1995年 | 1247篇 |
1993年 | 1111篇 |
1992年 | 2245篇 |
1991年 | 2293篇 |
1990年 | 2386篇 |
1989年 | 2359篇 |
1988年 | 2236篇 |
1987年 | 2204篇 |
1986年 | 2241篇 |
1985年 | 2236篇 |
1984年 | 1843篇 |
1983年 | 1659篇 |
1982年 | 1136篇 |
1981年 | 1065篇 |
1979年 | 1744篇 |
1978年 | 1413篇 |
1977年 | 1222篇 |
1976年 | 1180篇 |
1975年 | 1339篇 |
1974年 | 1775篇 |
1973年 | 1744篇 |
1972年 | 1789篇 |
1971年 | 1712篇 |
1970年 | 1586篇 |
1969年 | 1494篇 |
1968年 | 1231篇 |
1967年 | 1325篇 |
1966年 | 1174篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
We compared the results of the ACTH stimulation tests with measurements of alkaline phosphatase and serum cholesterol during Lysodren therapy in 23 dogs with pituitary-dependent hyperadrenocorticism. The ACTH stimulation test proved to be a very sensitive parameter, by which the extent of Lysodren under- or overdosage could be reliably estimated. On the other hand, regulation of the individual Lysodren requirement was not possible by measuring AP and serum cholesterol only. However, it is highly probable that those two parameters can be used to evaluate the general state of metabolism, and they appear to be of prognostic value when greatly elevated. 相似文献
85.
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
86.
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
87.
X M Zhang W Herbst H Lange-Herbst T Schliesser 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(10):765-770
1,268 sera collected from slaughtered pigs in Hassia (FRG) from 1986 to 1988 were tested for antibodies against porcine and human influenza A virus strains using the single radial haemolysis test (SRHT). Antibodies against the porcine strains (subtype H1N1) A/Swine/Arnsberg/1/81, A/Swine/Iowa/15/30 and A/New Jersey/7/76 were detected in 411 (32.4%), 318 (25.1%) and 304 (24.0%) of sera, respectively. Up to 1988 a slight increase (10%) in the seroprevalence to A/Swine/Arnsberg/1/81 was noticed, whereas the results obtained with the other strains showed little variation. Antibodies against the human H1N1 strain A/Singapore/6/86 were only found in sera collected 1987 and 1988 in rates of 1.6% and 3.0%. Serological indication of infections with the human H3N2 strains A/Victoria/1/75, A/Hong Kong/1/68 and A/Philippines/2/82 could be shown in 286 (22.6%), 178 (14.4%) and 135 (10.6%) of the serum samples. Within the three year period the rate of sera positive for antibodies against A/Philippines/2/82 increased from 6.5% to 23.0%, whereas no variation in the rates were found using the other H3N2 strains. Antibodies simultaneously against porcine (H1N1) and human (H3N2) virus strains were detected in 9.9% of all sera tested. 相似文献
88.
89.
90.
Effect of dietary protein content on episodic growth hormone secretion and on heat production of male broiler chickens. 总被引:1,自引:0,他引:1
1. The effect of the crude protein content (200 and 150 g/kg) of isoenergetic diets on episodic growth hormone (GH) release and on heat production was investigated in male broiler chickens. 2. Decreasing the crude protein content of isoenergetic diets from 200 g/kg (HP diet) to 150 g/kg (LP diet) resulted in depressed body weight gain, impaired food conversion efficiency and increased abdominal fat deposition. 3. The pattern of growth hormone secretion was markedly affected by dietary treatment. Broiler chickens fed on the LP diet had higher overall mean, amplitude, baseline and peak frequency than the HP chickens. 4. The LP chickens produced more heat per unit of metabolic body weight than the HP chickens. 5. The hypothesis relating the pattern of GH secretion to protein conversion efficiency was corroborated. 相似文献